assignment of parameter is not allowed java

Avoid Check for Null Statement in Java

Last updated: January 8, 2024

Java Statements

Handling concurrency in an application can be a tricky process with many potential pitfalls . A solid grasp of the fundamentals will go a long way to help minimize these issues.

Get started with understanding multi-threaded applications with our Java Concurrency guide:

>> Download the eBook

Spring 5 added support for reactive programming with the Spring WebFlux module, which has been improved upon ever since. Get started with the Reactor project basics and reactive programming in Spring Boot:

>> Download the E-book

Baeldung Pro comes with both absolutely No-Ads as well as finally with Dark Mode , for a clean learning experience:

>> Explore a clean Baeldung

Once the early-adopter seats are all used, the price will go up and stay at $33/year.

Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page .

You can also ask questions and leave feedback on the Azure Container Apps GitHub page .

Java applications have a notoriously slow startup and a long warmup time. The CRaC (Coordinated Restore at Checkpoint) project from OpenJDK can help improve these issues by creating a checkpoint with an application's peak performance and restoring an instance of the JVM to that point.

To take full advantage of this feature, BellSoft provides containers that are highly optimized for Java applications. These package Alpaquita Linux (a full-featured OS optimized for Java and cloud environment) and Liberica JDK (an open-source Java runtime based on OpenJDK).

These ready-to-use images allow us to easily integrate CRaC in a Spring Boot application:

Improve Java application performance with CRaC support

Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

To learn more about Java features on Azure Container Apps, you can get started over on the documentation page .

And, you can also ask questions and leave feedback on the Azure Container Apps GitHub page .

Whether you're just starting out or have years of experience, Spring Boot is obviously a great choice for building a web application.

Jmix builds on this highly powerful and mature Boot stack, allowing devs to build and deliver full-stack web applications without having to code the frontend. Quite flexibly as well, from simple web GUI CRUD applications to complex enterprise solutions.

Concretely, The Jmix Platform includes a framework built on top of Spring Boot, JPA, and Vaadin , and comes with Jmix Studio, an IntelliJ IDEA plugin equipped with a suite of developer productivity tools.

The platform comes with interconnected out-of-the-box add-ons for report generation, BPM, maps, instant web app generation from a DB, and quite a bit more:

>> Become an efficient full-stack developer with Jmix

DbSchema is a super-flexible database designer, which can take you from designing the DB with your team all the way to safely deploying the schema .

The way it does all of that is by using a design model , a database-independent image of the schema, which can be shared in a team using GIT and compared or deployed on to any database.

And, of course, it can be heavily visual, allowing you to interact with the database using diagrams, visually compose queries, explore the data, generate random data, import data or build HTML5 database reports.

>> Take a look at DBSchema

Get non-trivial analysis (and trivial, too!) suggested right inside your IDE or Git platform so you can code smart, create more value, and stay confident when you push.

Get CodiumAI for free and become part of a community of over 280,000 developers who are already experiencing improved and quicker coding.

Write code that works the way you meant it to:

>> CodiumAI. Meaningful Code Tests for Busy Devs

The AI Assistant to boost Boost your productivity writing unit tests - Machinet AI .

AI is all the rage these days, but for very good reason. The highly practical coding companion, you'll get the power of AI-assisted coding and automated unit test generation . Machinet's Unit Test AI Agent utilizes your own project context to create meaningful unit tests that intelligently aligns with the behavior of the code. And, the AI Chat crafts code and fixes errors with ease, like a helpful sidekick.

Simplify Your Coding Journey with Machinet AI :

>> Install Machinet AI in your IntelliJ

Since its introduction in Java 8, the Stream API has become a staple of Java development. The basic operations like iterating, filtering, mapping sequences of elements are deceptively simple to use.

But these can also be overused and fall into some common pitfalls.

To get a better understanding on how Streams work and how to combine them with other language features, check out our guide to Java Streams:

Download the E-book

Do JSON right with Jackson

Get the most out of the Apache HTTP Client

Get Started with Apache Maven:

Working on getting your persistence layer right with Spring?

Explore the eBook

Building a REST API with Spring?

Get started with Spring and Spring Boot, through the Learn Spring course:

Explore Spring Boot 3 and Spring 6 in-depth through building a full REST API with the framework:

>> The New “REST With Spring Boot”

Get started with Spring and Spring Boot, through the reference Learn Spring course:

>> LEARN SPRING

Yes, Spring Security can be complex, from the more advanced functionality within the Core to the deep OAuth support in the framework.

I built the security material as two full courses - Core and OAuth , to get practical with these more complex scenarios. We explore when and how to use each feature and code through it on the backing project .

You can explore the course here:

>> Learn Spring Security

1. Overview

Generally, null variables, references and collections are tricky to handle in Java code. They are not only hard to identify but also complex to deal with.

As a matter of fact, any miss in dealing with null cannot be identified at compile time and results in a NullPointerException at runtime.

In this tutorial, we’ll take a look at the need to check for null in Java and various alternatives that help us to avoid null checks in our code.

3. Handling null Through the API Contract

As discussed in the last section, accessing methods or variables of null objects causes a NullPointerException . We also discussed that putting a null check on an object before accessing it eliminates the possibility of NullPointerException .

However, there are often APIs that can handle null values:

The print() method call would just print “null” but won’t throw an exception. Similarly, process() would never return null in its response. It rather throws an Exception .

So, for a client code accessing the above APIs, there is no need for a null check.

However, such APIs need to make it explicit in their contract. A common place for APIs to publish such a contract is the Javadoc.

But this gives no clear indication of the API contract and thus relies on the client code developers to ensure its compliance.

In the next section, we’ll see how a few IDEs and other development tools help developers with this.

4. Automating API Contracts

4.1. using static code analysis.

Static code analysis tools help improve the code quality a great deal. And a few such tools also allow the developers to maintain the null contract. One example is FindBugs .

FindBugs helps manage the null contract through the @Nullable and @NonNull annotations. We can use these annotations over any method, field, local variable, or parameter. This makes it explicit to the client code whether the annotated type can be null or not.

Let’s see an example:

Here, @NonNull makes it clear that the argument cannot be null . If the client code calls this method without checking the argument for null, FindBugs would generate a warning at compile time.

4.2. Using IDE Support

Developers generally rely on IDEs for writing Java code. And features such as smart code completion and useful warnings, for example when a variable may not have been assigned, certainly help a lot.

Some IDEs also allow developers to manage API contracts and thereby eliminate the need for a static code analysis tool. IntelliJ IDEA provides the @NonNull and @Nullable annotations.

To add the support for these annotations in IntelliJ, we need to add the following Maven dependency:

Now IntelliJ will generate a warning if the null check is missing, as in our last example.

IntelliJ also provides a Contract annotation for handling complex API contracts.

5. Assertions

Until now, we’ve only talked about removing the need for null checks from the client code. But that is rarely applicable in real-world applications.

Now let’s suppose that we’re working with an API that cannot accept null parameters or can return a null response that has to be handled by the client. This presents the need for us to check the parameters or the response for a null value.

Here, we can use Java Assertions instead of the traditional null check conditional statement:

In line 2, we check for a null parameter. If the assertions are enabled, this would result in an AssertionError .

Although it is a good way of asserting preconditions such as non- null parameters, this approach has two major problems :

Assertions are usually disabled in a JVM.
A false assertion results in an unchecked error that is irrecoverable.

Therefore, it is not recommended for programmers to use Assertions for checking runtime conditions. In the following sections, we’ll discuss other ways of handling null validations.

6. Avoiding Null Checks Through Coding Practices

6.1. preconditions.

It’s usually a good practice to write code that fails early. So, if an API accepts multiple parameters that aren’t allowed to be null , it’s better to check for every non- null parameter as a precondition of the API.

Let’s look at two methods — one that fails early and one that doesn’t:

Clearly, we should prefer goodAccept() over badAccept() .

As an alternative, we can also use Guava’s Preconditions for validating API parameters.

6.2. Using Primitives Instead of Wrapper Classes

Since null is not an acceptable value for primitives like int , we should prefer them over their wrapper counterparts like Integer wherever possible.

Consider two implementations of a method that sums two integers:

Now let’s call these APIs in our client code:

This would result in a compile-time error since null is not a valid value for an int .

And when using the API with wrapper classes, we get a NullPointerException :

There are also other factors for using primitives over wrappers, as we covered in another tutorial, Java Primitives Versus Objects .

6.3. Empty Collections

Occasionally, we need to return a collection as a response from a method. For such methods, we should always try to return an empty collection instead of null :

This way, we’ve avoided the need for our client to perform a null check when calling this method.

7. Using Objects

Java 7 introduced the new Objects API. This API has several static utility methods that take away a lot of redundant code.

Let’s look at one such method, requireNonNull() :

Now let’s test the accept() method:

So, if null is passed as an argument, accept() throws a NullPointerException .

This class also has isNull() and nonNull() methods that can be used as predicates to check an object for null .

8. Using Optional

8.1. using orelsethrow.

Java 8 introduced a new Optional API in the language. This offers a better contract for handling optional values compared to null .

Let’s see how Optional takes away the need for null checks:

By returning an Optional, as shown above, the process method makes it clear to the caller that the response can be empty and needs to be handled at compile time.

This notably takes away the need for any null checks in the client code. An empty response can be handled differently using the declarative style of the Optional API:

Furthermore, it also provides a better contract to API developers to signify to the clients that an API can return an empty response.

Although we eliminated the need for a null check on the caller of this API, we used it to return an empty response.

To avoid this, Optional provides an ofNullable method that returns an Optional with the specified value, or empty , if the value is null :

8.2. Using Optional With Collections

While dealing with empty collections, Optional comes in handy:

This function is supposed to return the first item of a list. The Stream API’s findFirst function will return an empty Optional when there is no data. Here, we have used orElse to provide a default value instead.

This allows us to handle either empty lists or lists that, after we have used the Stream library’s filter method, have no items to supply.

Alternatively, we can also allow the client to decide how to handle empty by returning Optional from this method:

Therefore, if the result of getList is empty, this method will return an empty Optional to the client.

Using Optional with collections allows us to design APIs that are sure to return non-null values, thus avoiding explicit null checks on the client.

It’s important to note here that this implementation relies on getList not returning null. However, as we discussed in the last section, it’s often better to return an empty list rather than a null .

8.3. Combining Optionals

When we start making our functions return Optional , we need a way to combine their results into a single value.

Let’s take our getList example from earlier. What if it were to return an Optional list, or were to be wrapped with a method that wrapped a null with Optional using ofNullable ?

Our findFirst method wants to return an Optional first element of an Optional list:

By using the flatMap function on the Optional returned from getOptional , we can unpack the result of an inner expression that returns Optional . Without flatMap , the result would be Optional<Optional<String>> . The flatMap operation is only performed when the Optional is not empty.

9. Libraries

9.1. using lombok.

Lombok is a great library that reduces the amount of boilerplate code in our projects. It comes with a set of annotations that take the place of common parts of code we often write ourselves in Java applications, such as getters, setters and toString() , to name a few.

Another of its annotations is @NonNull . So, if a project already uses Lombok to eliminate boilerplate code, @NonNull can replace the need for null checks.

Before we move on to some examples, let’s add a Maven dependency for Lombok:

Now we can use @NonNull wherever a null check is needed:

So, we simply annotated the object for which the null check would’ve been required, and Lombok generates the compiled class:

If param is null , this method throws a NullPointerException . The method must make this explicit in its contract, and the client code must handle the exception.

9.2. Using StringUtils

Generally, String validation includes a check for an empty value in addition to null value.

Therefore, this would be a common validation statement:

This quickly becomes redundant if we have to deal with a lot of String types. This is where StringUtils comes in handy.

Before we see this in action, let’s add a Maven dependency for commons-lang3 :

Let’s now refactor the above code with StringUtils :

So, we replaced our null or empty check with a static utility method isNotEmpty() . This API offers other powerful utility methods for handling common String functions.

10. Conclusion

In this article, we looked at the various reasons for NullPointerException and why it is hard to identify.

Then we saw various ways to avoid the redundancy in code around checking for null with parameters, return types and other variables.

All the examples are available over on GitHub .

Explore the secure, reliable, and high-performance Test Execution Cloud built for scale. Right in your IDE:

Basically, write code that works the way you meant it to.

Get started with Spring Boot and with core Spring, through the Learn Spring course:

>> CHECK OUT THE COURSE

Follow the Java Category

assignment of parameter is not allowed java

Java Course
Java Arrays
Java Strings
Java Collection
Java 8 Tutorial
Java Multithreading
Java Exception Handling
Java Programs
Java Project
Java Collections Interview
Java Interview Questions
Spring Boot

Parameter Passing Techniques in Java with Examples

There are different ways in which parameter data can be passed into and out of methods and functions . Let us assume that a function B() is called from another function A() . In this case A is called the “caller function” and B is called the “called function or callee function” . Also, the arguments which A sends to B are called actual arguments and the parameters of B are called formal arguments .

Types of parameters:

Formal Parameter: A variable and its type as they appear in the prototype of the function or method.

Syntax:

Actual Parameter: The variable or expression corresponding to a formal parameter that appears in the function or method call in the calling environment.

Syntax:

Important methods of Parameter Passing

1. Pass By Value: Changes made to formal parameter do not get transmitted back to the caller. Any modifications to the formal parameter variable inside the called function or method affect only the separate storage location and will not be reflected in the actual parameter in the calling environment. This method is also called as call by value . Java in fact is strictly call by value.

Example:

Time Complexity: O(1) Auxiliary Space: O(1)

Shortcomings:

Inefficiency in storage allocation
For objects and arrays, the copy semantics are costly

2. Call by reference(aliasing): Changes made to formal parameter do get transmitted back to the caller through parameter passing. Any changes to the formal parameter are reflected in the actual parameter in the calling environment as formal parameter receives a reference (or pointer) to the actual data. This method is also called as call by reference . This method is efficient in both time and space.

Please note that when we pass a reference, a new reference variable to the same object is created. So we can only change members of the object whose reference is passed. We cannot change the reference to refer to some other object as the received reference is a copy of the original reference.

Please see example 2 in Java is Strictly Pass by Value!

Please Login to comment...

Improve your Coding Skills with Practice

What kind of Experience do you want to share?

How to remove 'Assignment of Parameter 'variable' is not allowed'

I'm programming a Controller using Java and I'm checking the style using Sonar. In my Sonar I have an error that says:

'Assignment of Parameter 'variable' is not allowed.

The line that it's on is:

So I'm wondering how I could get that error off since I can't just create a setter when I'm using that annotation.

I'm using Eclipse . The rule being broke is Parameter Assignment .

apkisbossin

In your if condition block, you are setting variable to null and it happens to be your method parameter. Instead of assigning the value to the method parameter, create a local variable and use it and return the value of the local variable from the method if at all it is intended.

systemhalted

Donate For Us

If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!

Java Tutorial

What is Java
History of Java
Features of Java
C++ vs Java
Hello Java Program
Program Internal
How to set path?
JDK, JRE and JVM
JVM: Java Virtual Machine
Java Variables
Java Data Types
Unicode System

Control Statements

Java Control Statements
Java If-else
Java Switch
Java For Loop
Java While Loop
Java Do While Loop
Java Continue
Java Comments

Java Programs

Java object class.

Java OOPs Concepts
Naming Convention
Object and Class
Constructor
static keyword
this keyword

Java Inheritance

Inheritance(IS-A)
Aggregation(HAS-A)

Java Polymorphism

Method Overloading
Method Overriding
Covariant Return Type
super keyword
Instance Initializer block
final keyword
Runtime Polymorphism
Dynamic Binding
instanceof operator

Java Abstraction

Abstract class
Abstract vs Interface

Java Encapsulation

Access Modifiers
Encapsulation

Java OOPs Misc

Object class
Object Cloning
Wrapper Class
Java Recursion
Call By Value
strictfp keyword
javadoc tool
Command Line Arg
Object vs Class
Overloading vs Overriding

Java String

What is String
Immutable String
String Comparison
String Concatenation
Methods of String class
StringBuffer class
StringBuilder class
String vs StringBuffer
StringBuffer vs Builder
Creating Immutable class
toString method
StringTokenizer class
Java String FAQs

Java String Methods

String charAt()
String compareTo()
String concat()
String contains()
String endsWith()
String equals()
equalsIgnoreCase()
String format()
String getBytes()
String getChars()
String indexOf()
String intern()
String isEmpty()
String join()
String lastIndexOf()
String length()
String replace()
String replaceAll()
String split()
String startsWith()
String substring()
String toCharArray()
String toLowerCase()
String toUpperCase()
String trim()

Exception Handling

Java Exceptions
Java Try-catch block
Java Multiple Catch Block
Java Nested try
Java Finally Block
Java Throw Keyword
Java Exception Propagation
Java Throws Keyword
Java Throw vs Throws
Final vs Finally vs Finalize
Exception Handling with Method Overriding
Java Custom Exceptions

Java Inner Class

What is inner class
Member Inner class
Anonymous Inner class
Local Inner class
static nested class
Nested Interface

Java Multithreading

What is Multithreading
Life Cycle of a Thread
How to Create Thread
Thread Scheduler
Sleeping a thread
Start a thread twice
Calling run() method
Joining a thread
Naming a thread
Thread Priority
Daemon Thread
Thread Pool
Thread Group
ShutdownHook
Performing multiple task
Garbage Collection
Runtime class

Java Synchronization

Synchronization in java
synchronized block
static synchronization
Deadlock in Java
Inter-thread Comm
Interrupting Thread
Reentrant Monitor

Java Networking

Networking Concepts
Socket Programming
URLConnection class
HttpURLConnection
InetAddress class

Java Applet

Applet Basics
Graphics in Applet
Displaying image in Applet
Animation in Applet
EventHandling in Applet
JApplet class
Painting in Applet
Digital Clock in Applet
Analog Clock in Applet
Parameter in Applet
Applet Communication

Java Reflection

Reflection API
newInstance() method
creating javap tool
creating appletviewer
Call private method

Java Conversion

Java String to int
Java int to String
Java String to long
Java long to String
Java String to float
Java float to String
Java String to double
Java double to String
Java String to Date
Java Date to String
Java String to char
Java char to String
Java String to Object
Java Object to String
Java int to long
Java long to int
Java int to double
Java double to int
Java char to int
Java int to char
Java String to boolean
Java boolean to String
Date to Timestamp
Timestamp to Date
Binary to Decimal
Decimal to Binary
Hex to Decimal
Decimal to Hex
Octal to Decimal
Decimal to Octal
JDBC Introduction
JDBC Driver
DB Connectivity Steps
Connectivity with Oracle
Connectivity with MySQL
Access without DSN
DriverManager
PreparedStatement
ResultSetMetaData
DatabaseMetaData
Store image
Retrieve image
Retrieve file
CallableStatement
Transaction Management
Batch Processing
RowSet Interface
Internationalization
ResourceBundle class
I18N with Date
I18N with Time
I18N with Number
I18N with Currency
Java Array Class
getBoolean()
getDouble()
getLength()
newInstance()
setBoolean()
setDouble()
Java AtomicInteger Class
addAndGet(int delta)
compareAndSet(int expect, int update)
decrementAndGet()
doubleValue()
floatValue()
getAndAdd()
getAndDecrement()
getAndSet()
incrementAndGet()
getAndIncrement()
lazySet(int newValue)
longValue()
set(int newValue)
weakCompareAndSet(int expect,int newValue)
Java AtomicLong Methods
addAndGet()
compareAndSet()
weakCompareAndSet()
Java Authenticator
getPasswordAuthentication()
getRequestingHost()
getRequestingPort()
getRequestingPrompt()
getRequestingProtocol()
getRequestingScheme()
getRequestingSite()
getRequestingURL()
getRequestorType()
setDefault()
Java BigDecimal class
intValueExact()
movePointLeft()
movePointRight()
Big Integer Class
bitLength()
compareTo()
divideAndRemainder()
getLowestSetBit()
isProbablePrime()
modInverse()
nextProbablePrime()
probablePrime()
shiftLeft()
shiftRight()
toByteArray()
Java Boolean class
booleanValue()
logicalAnd()
logicalOr()
logicalXor()
parseBoolean()

Java Byte Class

byteValue()
compareUnsigned()
parseByte()
shortValue()
toUnsignedInt()
toUnsignedLong()
asSubclass()
desiredAssertionStatus()
getAnnotatedInterfaces()
getAnnotatedSuperclass()
getAnnotation()
getAnnotationsByType()
getAnnotations()
getCanonicalName()
getClasses()
getClassLoader()
getComponentType
getConstructor()
getConstructors()
getDeclaredAnnotation()
getDeclaredAnnotationsByType()
getDeclaredAnnotations()
getDeclaredConstructor()
getDeclaredConstructors()
getDeclaredField()
getDeclaredFields()
getDeclaredMethod()
getDeclaredMethods()
getDeclaringClass()
getFields()
getGenericInterfaces()
getGenericSuperClass()
getInterfaces()
getMethod()
getMethods()
getModifiers()
getPackage()
getPackageName()
getProtectionDomain()
getResource()
getSigners()
getSimpleName()
getSuperClass()
isAnnotation()
isAnnotationPresent()
isAnonymousClass()
isInstance()
isInterface()
isPrimitive()
isSynthetic()
Java Collections class
asLifoQueue()
binarySearch()
checkedCollection()
checkedList()
checkedMap()
checkedNavigableMap()
checkedNavigableSet()
checkedQueue()
checkedSet()
checkedSortedMap()
checkedSortedSet()
emptyEnumeration()
emptyIterator()
emptyList()
emptyListIterator()
emptyNavigableMap()
emptyNavigableSet()
emptySortedMap()
emptySortedSet()
enumeration()
frequency()
indexOfSubList()
lastIndexOfSubList()
newSetFromMap()
replaceAll()
reverseOrder()
singleton()
singletonList()
singletonMap()
synchronizedCollection()
synchronizedList()
synchronizedMap()
synchronizedNavigableMap()
synchronizedNavigableSet()
synchronizedSet()
synchronizedSortedMap()
synchronizedSortedSet()
unmodifiableCollection()
unmodifiableList()
unmodifiableMap()
unmodifiableNavigableMap()
unmodifiableNavigableSet()
unmodifiableSet()
unmodifiableSortedMap()
unmodifiableSortedSet()

Java Compiler Class

Java Compiler
compileClass()
compileClasses()

CopyOnWriteArrayList

Java CopyOnWriteArrayList
lastIndexOf()

Java Math Methods

Math.round()
Math.sqrt()
Math.cbrt()
Math.signum()
Math.ceil()
Math.copySign()
Math.nextAfter()
Math.nextUp()
Math.nextDown()
Math.floor()
Math.floorDiv()
Math.random()
Math.rint()
Math.hypot()
Math.getExponent()
Math.IEEEremainder()
Math.addExact()
Math.subtractExact()
Math.multiplyExact()
Math.incrementExact()
Math.decrementExact()
Math.negateExact()
Math.toIntExact()
Math.log10()
Math.log1p()
Math.expm1()
Math.asin()
Math.acos()
Math.atan()
Math.sinh()
Math.cosh()
Math.tanh()
Math.toDegrees
Math.toRadians

LinkedBlockingDeque

Java LinkedBlockingDeque
descendingIterator()
offerFirst()
offerLast()
peekFirst()
pollFirst()
Java Long class

LinkedTransferQueue

Java LinkedTransferQueue
spliterator()
Difference between Array and ArrayList
When to use ArrayList and LinkedList in Java
Difference between ArrayList and Vector
How to Compare Two ArrayList in Java
How to reverse ArrayList in Java
How to make ArrayList Read Only
Difference between length of array and size() of ArrayList in Java
How to Synchronize ArrayList in Java
How to convert ArrayList to Array and Array to ArrayList in java
Array vs ArrayList in Java
How to Sort Java ArrayList in Descending Order
How to remove duplicates from ArrayList in Java
Java MulticastSocket
getInterface()
getLoopbackMode()
getNetworkInterface()
getTimeToLive()
joinGroup()
leaveGroup()
setInterface()
setLoopbackMode()
setNetworkInterface()
setTimeToLive()
Java Number Class

Java Phaser Class

Java Phaser
arriveAndAwaitAdvance()
arriveAndDeregister()
getParent()
awaitAdvanceInterruptibly()
awaitAdvance()
bulkRegister()
forceTermination()
getArrivedParties()
getRegisteredParties()
getUnarrivedParties()
isTerminated()

ArrayList Methods

listIterator()
removeRange

Java Thread Methods

currentThread()
getPriority()
setPriority()
setDaemon()
interrupt()
isinterrupted()
interrupted()
activeCount()
checkAccess()
dumpStack()
getStackTrace()
enumerate()
getThreadGroup()
notifyAll()
setContextClassLoader()
getContextClassLoader()
getDefaultUncaughtExceptionHandler()
setDefaultUncaughtExceptionHandler()

Java Projects

Free Java Projects
Payment Bill(JSP)
Transport (JSP)
Connect Globe (JSP)
Online Banking (JSP)
Online Quiz (JSP)
Classified (JSP)
Mailcasting (JSP)
Online Library (JSP)
Pharmacy (JSP)
Mailer (Servlet)
Baby Care (Servlet)
Chat Server (Core)
Library (Core)
Exam System (Core)
Java Apps (Core)
Fee Report (Core)
Fee (Servlet)
eLibrary (Servlet)
Fire Detection
Attendance System
Fibonacci Series in Java
Prime Number Program in Java
Palindrome Program in Java
Factorial Program in Java
Armstrong Number in Java
How to Generate Random Number in Java
How to Print Pattern in Java
How to Compare Two Objects in Java
How to Create Object in Java
How to Print ASCII Value in Java
How to Reverse a Number in Java
Java Program to convert Number to Word
Automorphic Number Program in Java
Peterson Number in Java
Sunny Number in Java
Tech Number in Java
Fascinating Number in Java
Keith Number in Java
Neon Number in Java
Spy Number in Java
ATM program Java
Autobiographical Number in Java
Emirp Number in Java
Sphenic Number in Java
Buzz Number Java
Duck Number Java
Evil Number Java
ISBN Number Java
Krishnamurthy Number Java
Bouncy Number in Java
Mystery Number in Java
Smith Number in Java
Strontio Number in Java
Xylem and Phloem Number in Java
nth Prime Number Java
Java Program to Display Alternate Prime Numbers
Java Program to Find Square Root of a Number Without sqrt Method
Java Program to Swap Two Numbers Using Bitwise Operator
Java Program to Find GCD of Two Numbers
Java Program to Find Largest of Three Numbers
Java Program to Find Smallest of Three Numbers Using Ternary Operator
Java Program to Check if a Number is Positive or Negative
Java Program to Check if a Given Number is Perfect Square
Java Program to Display Even Numbers From 1 to 100
Java Program to Display Odd Numbers From 1 to 100
Java Program to Find Sum of Natural Numbers
Java Program to copy all elements of one array into another array
Java Program to find the frequency of each element in the array
Java Program to left rotate the elements of an array
Java Program to print the duplicate elements of an array
Java Program to print the elements of an array
Java Program to print the elements of an array in reverse order
Java Program to print the elements of an array present on even position
Java Program to print the elements of an array present on odd position
Java Program to print the largest element in an array
Java Program to print the smallest element in an array
Java Program to print the number of elements present in an array
Java Program to print the sum of all the items of the array
Java Program to right rotate the elements of an array
Java Program to sort the elements of an array in ascending order
Java Program to sort the elements of an array in descending order
Java Program to Find 3rd Largest Number in an array
Java Program to Find 2nd Largest Number in an array
Java Program to Find Largest Number in an array
Java to Program Find 2nd Smallest Number in an array
Java Program to Find Smallest Number in an array
Java Program to Remove Duplicate Element in an array
Java Program to Print Odd and Even Numbers from an array
How to Sort an Array in Java
Java Matrix Programs
Java Program to Add Two Matrices
Java Program to Multiply Two Matrices
Java Program to subtract the two matrices
Java Program to determine whether two matrices are equal
Java Program to display the lower triangular matrix
Java Program to display the upper triangular matrix
Java Program to find the frequency of odd & even numbers in the given matrix
Java Program to find the product of two matrices
Java Program to find the sum of each row and each column of a matrix
Java Program to find the transpose of a given matrix
Java Program to determine whether a given matrix is an identity matrix
Java Program to determine whether a given matrix is a sparse matrix
Java Program to Transpose matrix
Java Program to count the total number of characters in a string
Java Program to count the total number of characters in a string 2
Java Program to count the total number of punctuation characters exists in a String
Java Program to count the total number of vowels and consonants in a string
Java Program to determine whether two strings are the anagram
Java Program to divide a string in 'N' equal parts.
Java Program to find all subsets of a string
Java Program to find the longest repeating sequence in a string
Java Program to find all the permutations of a string
Java Program to remove all the white spaces from a string
Java Program to replace lower-case characters with upper-case and vice-versa
Java Program to replace the spaces of a string with a specific character
Java Program to determine whether a given string is palindrome
Java Program to determine whether one string is a rotation of another
Java Program to find maximum and minimum occurring character in a string
Java Program to find Reverse of the string
Java program to find the duplicate characters in a string
Java program to find the duplicate words in a string
Java Program to find the frequency of characters
Java Program to find the largest and smallest word in a string
Java Program to find the most repeated word in a text file
Java Program to find the number of the words in the given text file
Java Program to separate the Individual Characters from a String
Java Program to swap two string variables without using third or temp variable.
Java Program to print smallest and biggest possible palindrome word in a given string
Reverse String in Java Word by Word
Reserve String without reverse() function
Linear Search in Java
Binary Search in Java
Bubble Sort in Java
Selection Sort in Java
Insertion Sort in Java
How to convert String to int in Java
How to convert int to String in Java
How to convert String to long in Java
How to convert long to String in Java
How to convert String to float in Java
How to convert float to String in Java
How to convert String to double in Java
How to convert double to String in Java
How to convert String to Date in Java
How to convert Date to String in Java
How to convert String to char in Java
How to convert char to String in Java
How to convert String to Object in Java
How to convert Object to String in Java
How to convert int to long in Java
How to convert long to int in Java
How to convert int to double in Java
How to convert double to int in Java
How to convert char to int in Java
How to convert int to char in Java
How to convert String to boolean in Java
How to convert boolean to String in Java
How to convert Date to Timestamp in Java
How to convert Timestamp to Date in Java
How to convert Binary to Decimal in Java
How to convert Decimal to Binary in Java
How to convert Hex to Decimal in Java
How to convert Decimal to Hex in Java
How to convert Octal to Decimal in Java
How to convert Decimal to Octal in Java
Java program to print the following spiral pattern on the console
Java program to print the following pattern
Java program to print the following pattern 2
Java program to print the following pattern 3
Java program to print the following pattern 4
Java program to print the following pattern 5
Java program to print the following pattern on the console
Java program to print the following pattern on the console 2
Java program to print the following pattern on the console 3
Java program to print the following pattern on the console 4
Java program to print the following pattern on the console 5
Java program to print the following pattern on the console 6
Java program to print the following pattern on the console 7
Java program to print the following pattern on the console 8
Java program to print the following pattern on the console 9
Java program to print the following pattern on the console 10
Java program to print the following pattern on the console 11
Java program to print the following pattern on the console 12
Singly linked list Examples in Java
Java Program to create and display a singly linked list
Java program to create a singly linked list of n nodes and count the number of nodes
Java program to create a singly linked list of n nodes and display it in reverse order
Java program to delete a node from the beginning of the singly linked list
Java program to delete a node from the middle of the singly linked list
Java program to delete a node from the end of the singly linked list
Java program to determine whether a singly linked list is the palindrome
Java program to find the maximum and minimum value node from a linked list
Java Program to insert a new node at the middle of the singly linked list
Java program to insert a new node at the beginning of the singly linked list
Java program to insert a new node at the end of the singly linked list
Java program to remove duplicate elements from a singly linked list
Java Program to search an element in a singly linked list
Java program to create and display a Circular Linked List
Java program to create a Circular Linked List of N nodes and count the number of nodes
Java program to create a Circular Linked List of n nodes and display it in reverse order
Java program to delete a node from the beginning of the Circular Linked List
Java program to delete a node from the end of the Circular Linked List
Java program to delete a node from the middle of the Circular Linked List
Java program to find the maximum and minimum value node from a circular linked list
Java program to insert a new node at the beginning of the Circular Linked List
Java program to insert a new node at the end of the Circular Linked List
Java program to insert a new node at the middle of the Circular Linked List
Java program to remove duplicate elements from a Circular Linked List
Java program to search an element in a Circular Linked List
Java program to sort the elements of the Circular Linked List
Java program to convert a given binary tree to doubly linked list
Java program to create a doubly linked list from a ternary tree
Java program to create a doubly linked list of n nodes and count the number of nodes
Java program to create a doubly linked list of n nodes and display it in reverse order
Java program to create and display a doubly linked list
Java program to delete a new node from the beginning of the doubly linked list
Java program to delete a new node from the end of the doubly linked list
Java program to delete a new node from the middle of the doubly linked list
Java program to find the maximum and minimum value node from a doubly linked list
Java program to insert a new node at the beginning of the Doubly Linked list
Java program to insert a new node at the end of the Doubly Linked List
Java program to insert a new node at the middle of the Doubly Linked List
Java program to remove duplicate elements from a Doubly Linked List
Java program to rotate doubly linked list by N nodes
Java program to search an element in a doubly linked list
Java program to sort the elements of the doubly linked list
Java Program to calculate the Difference between the Sum of the Odd Level and the Even Level Nodes of a Binary Tree
Java program to construct a Binary Search Tree and perform deletion and In-order traversal
Java program to convert Binary Tree to Binary Search Tree
Java program to determine whether all leaves are at same level
Java program to determine whether two trees are identical
Java program to find maximum width of a binary tree
Java program to find the largest element in a Binary Tree
Java program to find the maximum depth or height of a tree
Java program to find the nodes which are at the maximum distance in a Binary Tree
Java program to find the smallest element in a tree
Java program to find the sum of all the nodes of a binary tree
Java program to find the total number of possible Binary Search Trees with N keys
Java program to implement Binary Tree using the Linked List
Java program to search a node in a Binary Tree
Java Main Method
System.out.println()
Java Memory Management
Java ClassLoader
Java Decompiler
Java vs. JavaScript
Java vs. Kotlin
Java vs. Python
Java Absolute Value
How to Create File
Delete a File in Java
Open a File in Java
Sort a List in Java
Convert byte Array to String
Java Basics
How to Compile & Run Java Program
How to Run Java Program in Eclipse
How to Verify Java Version
Ways to Create an Object in Java
How to Run a Java program in Windows 10
Runnable Interface in Java
Java Keystore
Get input from user in Java
Read file line by line in Java
Take String input in Java
How to Read Excel File in Java
Read XML File in Java
CompletableFuture in Java
Java ExecutorService
How to iterate Map in Java
How to Return an Array in Java
How to Sort HashMap by Value
How to Sort HashMap in Java
Load Factor in HashMap
Array vs ArrayList
HashMap vs TreeMap
HashSet vs HashMap class
Compare Two ArrayList in Java
Merge Two Arrays in Java
Print Array in Java
Read CSV File in Java
Remove Special Characters from String
ArrayIndexOutOfBoundsException
ConcurrentModificationException
NoSuchElementException
NumberFormatException
How to Sort ArrayList in Java
How to Download Java
How to Call a Method in Java
How to Create Singleton Class in Java
How to Find Array Length in Java
How to Read Character in Java
Can We Overload main() Method in Java
How to Convert Char Array to String in Java
How to Run Java Program in CMD Using Notepad
How to Sort String Array in Java
How to Compare Dates in Java
How to Take Multiple String Input in Java Using Scanner
How to Remove Last Character from String in Java
How TreeMap Works Internally in Java
Java Program to Break Integer into Digits
Java Program to Calculate Area and Circumference of Circle
What is Diamond Problem in Java
Java Program to Read Number from Standard Input
How to Download Minecraft Java Edition
Can We Override Static Method in Java
How to Avoid Deadlock in Java
How to Achieve Abstraction in Java
How Garbage Collection Works in Java
How to Take Array Input in Java
How to Create Array of Objects in Java
How to Create Package in Java
How to Print in Java
What is Framework in Java
Why Java is Secure
How to Iterate List in Java
How to Use Eclipse for Java
Which Package is Imported by Default in Java
Could Not Find or Load Main Class in Java
How to Compare Two Arrays in Java
How to Convert String to JSON Object in Java
Which is Better Java or Python
How to Update Java
How to Get Value from JSON Object in Java Example
How to Split a String in Java with Delimiter
Structure of Java Program
Why We Use Constructor in Java
Java Create Excel File
Java Interpreter
javac is not Recognized
Dynamic Array in Java
Shunting yard algorithm
Java Destructor
Custom ArrayList in Java
ArrayList vs HashMap
Java Constant
Java Tokens
How to Enable Java in Chrome
Java Semaphore
Array to List in Java
JIT in Java
How to Clear Screen in Java
Java Logger
Reverse a String Using Recursion in Java
Java Path Vs File
Float Vs Double Java
Stack vs Heap Java
Abstraction vs Encapsulation
Top 10 Java Books
Public vs Private
What is Java Used For
Bitwise Operator in Java
SOLID Principles Java
Type Casting in Java
Conditional Operator in Java
Ternary Operator Java
Java Architecture
REPL in Java
Types of Exception in Java
Why String is Immutable or Final in Java
Java vs Kotlin
Set in Java
Why non-static variable cannot be referenced from a static context in Java
Java Developer Roles and Responsibilities
Types of Classes in Java
Marker Interface in Java
Static Function in Java
Unary Operators in Java
What is Advance Java
ArrayList Implementation
Convert ArrayList to String Array
Hashmap vs ConcurrentHashMap
List vs ArrayList
Map vs HashMap
HashSet vs LinkedHashSet
How TreeSet Works Internally
LinkedHashMap vs HashMap
Java Program to Solve Quadratic Equation
Scope Resolution Operator in Java
Composition in Java
File Operations in Java
NoClassDefFoundError in Java
Thread Concept in Java
Upcasting and Downcasting in Java
Dynamic Polymorphism in Java
String Pool in Java
What is constructor chaining in Java
Add elements to Array in Java
Advantages and disadvantages of Java
Advantages of JavaBeans
AWS SDK for Java with Apache Maven
AWT and Swing in Java
AWT Program in Java
Boolean values in Java
ByteStream Classes in Java
CharacterStream Classes in Java
Class and Interface in Java
ClassCast Exception in Java
Cloneable in Java
Constructor overloading in Java
Control Flow in Java
Convert Java Object to Json using GSON
Convert XML to JSON in Java
How to avoid null pointer exception in Java
Java constructor returns a value, but what
Singleton Class in Java
Doubly Linked List Program in Java
Association in Java
Big data Java vs Python
Branching Statements in Java
Collections Sort in Java 8
List vs Set in Java
How many days required to learn Java
Implicitly Typecasting in Java
Legacy Class in Java
Character Array in Java
Equals() and Hashcode() in Java
Externalization in Java
Identifiers in Java
InvocationTargetException
Java Pass by Value
Mutable and Immutable in Java
Power Function in Java
Primitive Data Types in Java
String Array in Java
Virtual Function in Java
C vs C++ vs Java
Java String Max Size
Convert Java object to JSON
How to Calculate Date Difference in Java
How to Improve Coding Skills in Java
Java Email Validation
Java Testing Tools
Permutation and Combination in Java
Unique Number in Java Program
Java Code for DES
Pig Latin Program in Java
Array Rotation in Java
Equilibrium Index of an Array in Java
Different Ways to Print Exception Message in Java
Java Copy Constructor Example
Why We Use Static Class in Java
What is Core Java
Set vs Map in Java
How to Create a New Folder in Java
Remove an Element from ArrayList in Java
How to Create Test Cases for Exceptions in Java
How to Convert JSON Array to ArrayList in Java
How to Create a Class File in Java
Java Spring Pros & Cons
Java Stack Trace
Array Slicing in Java
Flutter vs Java
Permutation of Numbers in Java
Magic Number in Java
Reference Data Types in Java
Counter variable in Java
How to take Character Input in Java using BufferedReader Class
Java employee details program
Java is case sensitive explain
Ramanujan Number or Taxicab Number in Java
Advanced Java Books in 2021
Fail Fast and Fail Safe Iterator in Java
How to build a Web Application Using Java
Is Java Interpreted or Compiled
Java Big Data Frameworks
Java Get Data From URL
No Main Manifest Attribute
Java missing return statement
Java program to remove duplicate characters from a string
JUnit test case example in Java
List of logical programs in Java
PermGen space Java
Unsigned Right Shift Operator in Java
Infix to Postfix Java
Memory Leak in Java
How To Write Test Cases In Java
Java 32-Bit Download For Windows 10
FizzBuzz Program in Java
A Java Runtime Environment JRE Or JDK Must Be Available
Java Does Not Open
No Java Virtual Machine was Found
Java Program Number to Word
Types of Garbage Collector in Java
No Suitable Driver Found For JDBC
AVL Tree program in Java
Fail-fast and Fail-safe in Java
Find unique elements in array Java
Highest precedence in Java
Java Closure
Java String Encoding
Prim's algorithm Java
Quartz scheduler java
Red Black Tree Java
GC Overhead Limit Exceeded
Generating QR Code in Java
Delegation Event Model in Java
Java Profilers
Java Flight Recorder
Bucket Sort in Java
Java Atomic
Wait vs Sleep in Java
Executor Framework Java
Gregorian calendar Java
int vs Integer Java
What is truncation in Java
Java HTTP Proxy Server
Java Static Constructor
How to prepare for Java Interview
Java callback function
Java 8 vs Java 11
Login Form Java
Vaadin Framework Java
EJB vs. Spring
Types of Applets in Java
Visitor Design Pattern Java
Advantages of Python over Java
Design Principles in Java
JSON Validator Java
Pseudocode Java
Windows Programming Using Java
Vert.x Java
Complex Java Programs
ORE Number Java
PalPrime Number Java
Twin Prime Numbers
Twisted Prime Number Java
Ugly number Java
Achilles Number in Java
Amicable Pair Number in Java
Playfair Cipher Program in Java
Java.lang.outofmemoryerror: java heap space
Banker's Algorithm Java
Kruskal Algorithm Java
Longest Common Subsequence
Travelling Salesman Problem
& vs && in Java
Jumping Number in Java
Lead Number in Java
Lucky Number in Java
Middle Digit Number in Java
Special Number in Java
Passing Array to Function In Java
Lexicographical Order Java
Adam Number in Java
Bell Number in Java
Reduce Java
LRU Cache Implementation
Goldbach Number in Java
How to Find Number of Objects Created in Java
Multiply Two Numbers Without Using Arithmetic Operator in Java
Sum of Digits of a Number in Java
Sum of Numbers in Java
Power of a Number in Java
Sum of Prime Numbers in Java
Cullen Number in Java
Mobile Number Validation in Java
Fermat Number in Java
Instantiation in Java
Exception Vs Error in Java
flatMap() Method in Java 8
How to Print Table in Java
Java Create PDF
Mersenne Number in Java
Pandigital Number in Java
Pell Number in Java
Java Get Post
Fork Join in Java
Java Callable Example
Blockchain Java
Design of JDBC
Java Anon Proxy
Knapsack Problem Java
Session Tracking in Java
What is Object-Oriented Programming
Literals in Java
Square Free Number in Java
What is an anagram in Java
What is programming
Iterate JSON Array Java
Java Date Add Days
Javac Command Not Found
Factorial Program in Java Using while Loop
Frugal Number in Java
Java Digital Signature
Catalan Number in Java
Partition Number in Java
Powerful Number in Java
Practical Number in Java
Chromatic Number in Java
Sublime Number in Java
Advanced Java Viva Questions
Getter and Setter Method in Java Example
How to convert String to String array in Java
How to Encrypt Password in Java
Instance Variable in Java
Java File Extension
Types of Inheritance in Java
Untouchable Number in Java
AES 256 Encryption in Java
Applications of Array in Java
Example of Static Import in Java
Hill Cipher Program in Java
Lazy Loading in Java
Rectangular Number in Java
How to Print Table in Java Using Formatter
IdentityHashMap Class in Java
Undulating Number in Java
Java Obfuscator
Java Switch String
Applet Life Cycle in Java
Banking Application in Java
Duodecimal in Java
Economical Number in Java
Figurate Number in Java
How to resolve IllegalStateException in Java
Java Coding Software
Java Create Jar Files
Java Framework List
Java Initialize array
java lang exception no runnable methods
Nonagonal Number in Java
SexagesimalFormatter in Java
Sierpinski Number in Java
Vigesimal in Java
Java Color Codes
JDoodle Java
Online Java Compiler
Pyramidal Number in Java
Relatively Prime in Java
Java Modulo
Repdigit Numbers in Java
Abstract Method in Java
Convert Text-to-Speech in Java
Java Editors
MVC Architecture in Java
Narcissistic Number in Java
Hashing Algorithm in Java
Java Escape Characters
Java Operator Precedence
Private Constructor in Java
Scope of Variables in Java
Groovy vs Java
Java File Upload to a Folder
Java Full Stack
Java Developer
Thread States in Java
Java EE vs Node.js
Loose Coupling in Java
Java Top 10 Libraries
Method Hiding in Java
Dijkstra Algorithm Java
Extravagant Number in Java
Java Unicode
New Line in Java
Return Statement in Java
Order of Execution of Constructors in Java Inheritance
Cardinal Number in Java
Hyperfactorial in Java
Identifier Expected Error in Java
Java Generate UUID
Labeled Loop in Java
Lombok Java
Ordinal Number in Java
Tetrahedral Number in Java
Cosmic Superclass in Java
Shallow Copy Java
BiFunction Java 8
Equidigital Number in Java
Fall Through in Java
Java Reserved Keywords
Parking Lot Design Java
Boyer Moore Java
Java Security Framework
Tetranacci Number in Java
BFS Algorithm in Java
CountDownLatch in Java
Counting sort in Java
CRC Program in Java
FileNotFoundException in Java
InputMismatchException in Java
Java ASCII Table
Lock in Java
Segment Tree in Java
Why main() method is always static in Java
Bellman-Ford Algorithm Java
BigDecimal toString() in Java
.NET vs Java
Java ZipFile
Lazy Propagation in Segment Tree in Java
Magnanimous Number in Java
Binary Tree Java
How to Create Zip File in Java
Java Dot Operator
Associativity of Operators in Java
Fenwick Tree in Java
How annotation works in Java
How to Find Length of Integer in Java
Java 8 filters
List All Files in a Directory in Java
How to Get Day Name from Date in Java
Zigzag Array in Java
Class Definition in Java
Find Saddle Point of a Matrix in Java
Non-primitive data types in Java
Pancake Number in Java
Pancake Sorting in Java
Print Matrix Diagonally in Java
Sort Dates in Java
Carmichael Numbers in Java
Contextual Keywords in Java
How to Open Java Control Panel
How to Reverse Linked List in Java
Interchange Diagonal Elements Java Program
Java Set to List
Level Order Traversal of a Binary Tree in Java
Bully algorithm in Java
Convert JSON File to String in Java
Convert Milliseconds to Date in Java
Copy Content/ Data From One File to Another in Java
Constructor vs Method in Java
Access Specifiers vs Modifiers
Java vs PHP
replace() vs replaceAll() in Java
this vs super in Java
Heap implementation in Java
How to Check null in Java
Java Arrays Fill
Rotate Matrix by 90 Degrees in Java
Exception Class in Java
Transient variable in Java
Web crawler Java
Zigzag Traversal of a Binary Tree in Java
Java Get File Size
Internal Working of ArrayList in Java
Java Program to Print Matrix in Z Form
Vertical Order Traversal of a Binary Tree in Java
Group By in Java 8
Hashing Techniques in Java
Implement Queue Using Array in Java
Java 13 Features
Package Program in Java
Canonical Name Java
Method Chaining in Java
Orphaned Case Java
Bottom View of a Binary Tree in Java
Coercion in Java
Dictionary Class in Java
Left View of a Binary Tree in Java
Pangram Program in Java
Top View of a Binary Tree in Java
Tribonacci Series in Java
Hollow Diamond Pattern in Java
Normal and Trace of a Matrix in Java
Right View of a Binary Tree in Java
Dining Philosophers Problem and Solution in Java
Shallow Copy vs Deep Copy in Java
Java Password Generator
Java Program for Shopping Bill
Lock Interface in Java
Convert JSON to Map in Java
Convert JSON to XML in Java
Middle Node of a Linked List in Java
Pernicious Number in Java
Cohesion in Java
How to get UTC time in Java
Jacobsthal Number in Java
Java Calculate Age
Tribonacci Number Java
Bernoulli number in Java
Cake Number in Java
Compare time in Java
Compare Two Sets in Java
Crown Pattern in Java
Convert List to Array in Java
Aggregation vs Composition
Morris Traversal for Inorder in Java
Morris Traversal for Preorder in Java
Package Naming Conversion in Java
India Map Pattern in Java
Ladder Pattern in Java
ORM Tools in Java
Odious Number in Java
Rat in a Maze Problem in Java
Sudoku in Java
Christmas Tree Pattern in Java
Double Hashing in Java
Magic Square in Java
Possible Paths from Top Left to Bottom Right of a Matrix in Java
Palindrome Partitioning Problem in Java
Rehashing in Java
Round Robin Scheduling Program in Java
Types of Statements in Java
Compound Assignment Operator in Java
Prime Points in Java
Butterfly Pattern in Java
Fish Pattern in Java
Flag Pattern in Java
Kite pattern in Java
Swastika Pattern in Java
Tug of War in Java
Clone HashMap in Java
Fibodiv Number in Java
Heart Pattern in Java
How to check data type in Java
Java Array Clone
Use of final Keyword in Java
Factorial of a Large Number in Java
Race Condition in Java
Static Array in Java
Water Jug Problem in Java
Electricity Bill Program in Java
Facts about null in Java
Maximizing Profit in Stock Buy Sell in Java
Permutation Coefficient in Java
Convert List to String in Java
List of Constants in Java
MOOD Factors to Assess a Java Program
Computing Digit Sum of All Numbers From 1 to n in Java
Read PDF File in Java
Finding Odd Occurrence of a Number in Java
Java Indentation
Zig Zag Star and Number Pattern in Java
Check Whether a Number is a Power of 4 or not in Java
Kth Smallest in an Unsorted Array in Java
BlockingQueue in Java
Next Greater Element in Java
Star Numbers in Java
3N+1 Problem in Java
Java Program to Find Local Minima in An Array
Processing Speech in Java
Java Output Formatting
House Numbers in Java
Java Program to Generate Binary Numbers
Longest Odd-Even Subsequence in Java
Java Subtract Days from Current Date
Java Future Example
Minimum Cost Path Problem in Java
Diffie-Hellman Algorithm in Java
Ganesha's Pattern in Java
Hamming Code in Java
Map of Map in Java
Print Pencil Shape Pattern in Java
Zebra Puzzle in Java
Display Unique Rows in a Binary Matrix in Java
Rotate A Matrix By 180 Degree in Java
Dangling Else Problem in Java
Java Application vs Java Applet
Dutch National Flag Problem in Java
Java Calculate Average of List
compareToIgnoreCase Java
Trimorphic Numbers in Java
Arithmetic Exception in Java
Java instanceof operator
Java Localization
Minimum XOR Value Pair in Java
Iccanobif Numbers in Java
Java Program to Count the Occurrences of Each Character
Java Technologies List
Java Program to Find the Minimum Number of Platforms Required for a Railway Station
Shift Operators in Java
Final Object in Java
Object Definition in Java
Shadowing in Java
Zipping and Unzipping Files in Java
Display the Odd Levels Nodes of a Binary Tree in Java
Java Variable Declaration
Nude Numbers in Java
Java Programming Challenges
Java URL Encoder
anyMatch() in Java 8
Sealed Class in Java
Camel case in Java
Career Options for Java Developers to Aim in 2022
Java Progress Bar
Maximum Rectangular Area in a Histogram in Java
Polygonal Number in Java
Two Sorted LinkedList Intersection in Java
Set Matrix Zeros in Java
Find Number of Island in Java
Balanced Prime Number in Java
Minecraft Bedrock vs Java Minecraft
arr.length vs arr[0].length vs arr[1].length in Java
Future in Java 8
How to Set Timer in Java
Construct the Largest Number from the Given Array in Java
Minimum Coins for Making a Given Value in Java
Eclipse Shortcuts Java
Empty Statement in Java
Java Program to Implement Two Stacks in an Array
Java Snippet
Longest Arithmetic Progression Sequence in Java
Types of Sockets in Java
Java Program to Add Digits Until the Number Becomes a Single Digit Number
Next Greater Number with Same Set of Digits in Java
Split the Number String into Primes in Java
Java Cron Expression
Huffman Coding Java
Java Snippet Class
Why Java is So Popular
Java Project idea
Java Web Development
Brilliant Numbers in Java
Sort Elements by Frequency in Java
Beautiful Array in Java
Moran Numbers in Java
Intersection Point of Two Linked List in Java
Sparse Number in Java
How to Check JRE Version
Java Programming Certification
Two Decimal Places Java
Eclipse Change Theme
Java how to Convert Bytes to Hex
Decagonal Numbers in Java
Java Binary to Hexadecimal Conversion
Java Hexadecimal to Binary Conversion
How to Capitalize the First Letter of a String in Java
Java &0XFF Example
Stream findFirst() Method in Java
Balanced Parentheses in Java
Caesar Cipher Program in Java
next() vs nextLine()
Java Split String by Comma
Spliterator in java 8
Tree Model Nodes in Jackson
Types of events in Java
Callable and Future in Java
How to Check Current JDK Version installed in Your System Using CMD
How to Round Double and Float up to Two Decimal Places in Java
Java 8 Multimap
Parallel Stream in Java
Java Convert Bytes to Unsigned Bytes
Display List of TimeZone with GMT and UTC in Java
Binary Strings Without Consecutive Ones in Java
Convert IP to Binary in Java
Returning Multiple Values in Java
Centered Square Numbers in Java
ProcessBuilder in Java
How to Clear Java Cache
IntSummaryStatistics Class in Java
Java ProcessBuilder Example
Java Program to Delete a Directory
Java Program to Print Even Odd Using Two Threads
Java Variant
MessageDigest in Java
Alphabet Pattern in Java
Java Linter
Java Mod Example
Stone Game in Java
TypeErasure in Java
How to Remove substring from String in Java
Program to print a string in vertical in Java
How to Split a String between Numbers and Letters
String Handling in Java
Isomorphic String in Java
Java ImageIO Class
Minimum Difference Subarrays in Java
Plus One to Array Problem in Java
Unequal Adjacent Elements in Java
Java Parallel Stream Example
SHA Hashing in Java
How to make Java projects
Java Fibers
Java MD5 Hashing Example
Hogben Numbers in Java
Self-Descriptive Numbers in Java
Hybrid Inheritance in Java
Java IP Address (IPv4) Regex Examples
Converting Long to Date in JAVA
Java 17 new features
GCD of Different SubSequences in Java
Sylvester Sequence in Java
Console in Java
Asynchronous Call in Java
Minimum Window Substring in Java
Nth Term of Geometric Progression in Java
Coding Guidelines in Java
Couple Holding Hands Problem in Java
Count Ones in a Sorted binary array in Java
Ordered Pair in Java
Tetris Game in Java
Factorial Trailing Zeroes in Java
Java Assert Examples
Minimum Insertion To Form A Palindrome in Java
Wiggle Sort in Java
Java Exit Code 13
Java JFileChooser
What is LINQ
NZEC in Java
Box Stacking Problem
K Most Frequent Elements in Java
Parallel Programming in Java
How to Generate JVM Heap Memory Dump
Java Program to use Finally Block for Catching Exceptions
Count Login Attempts Java
Largest Independent Set in Java
Longest Subarray With All Even or Odd Elements in Java
Open and Closed Hashing in Java
DAO Class in Java
Kynea Numbers in Java
UTF in Java
Zygodromes in Java
ElasticSearch Java API
Form Feed in Java
Java Clone Examples
Payment Gateway Integration in Java
What is PMD
RegionMatches() Method in Java
Repaint() Method in Java
Serial Communication in Java
Count Double Increasing Series in A Range in Java
Longest Consecutive Subsequence in Java
Smallest Subarray With K Distinct Numbers in Java
String Sort Custom in Java
Count Number of Distinct Substrings in a String in Java
Display All Subsets of An Integer Array in Java
Digit Count in a Factorial Of a Number in Java
Valid Parentheses Problem in Java
Median Of Stream Of Running Integers in Java
Arrow Operator in Java
Java Learning app
Create Preorder Using Postorder and Leaf Nodes Array
Display Leaf nodes from Preorder of a BST in Java
Unicodes for Operators in Java
XOR and XNOR operators in Java
AWS Lambda in Java
AWS Polly in Java
SAML in Java
SonarQube in Java
UniRest in Java
Override equals method in Java
Undo and Redo Operations in Java
Size of longest Divisible Subset in an Array in Java
Sort An Array According To The Set Bits Count in Java
Two constructors in one class in Java
Union in Java
What is New in Java 15
ART in Java
Definite Assignment in Java
Cast Operator in Java
Diamond operator in Java
Java Singleton Enum
Three-way operator | Ternary operator in Java
GoF Design Pattern Java
Shorthand Operator in Java
What is new in Java 17
How to Find the Java Version in Linux
What is New in Java 12
Exception in Thread Main java.util.NoSuchElementException no line Found
How to reverse a string using recursion in Java
Java Program to Reverse a String Using Stack
Java Program to Reverse a String Using the Stack Data Structure
Reverse Middle Words of a String in Java
Sastry Numbers in Java
Sum of LCM in Java
Tilde Operator in Java
8 Puzzle problems in Java
Maximum Sum Such That No Two Elements Are Adjacent in Java
Reverse a String in Place in Java
Reverse a string Using a Byte array in Java
Reverse a String Using Java Collections
Reverse String with Special Characters in Java
get timestamp in java
How to convert file to hex in java
AbstractSet in java
List vs Set vs Map in Java
Birthday Problem in Java
How to Calculate the Time Difference Between Two Dates in Java
Number of Mismatching Bits in Java
Palindrome Permutation of a String in Java
Grepcode java.util.Date
How to add 24 hrs to date in Java
How to Change the Day in The Date Using Java
Java ByteBuffer Size
java.lang.NoSuchMethodError
Maximum XOR Value in Java
How to Add Hours to The Date Object in Java
How to Increment and Decrement Date Using Java
Multithreading Scenarios in Java
Switch case with enum in Java
Longest Harmonious Subsequence in Java
Count OR Pairs in Java
Merge Two Sorted Arrays Without Extra Space in Java
How to call a concrete method of abstract class in Java
How to create an instance of abstract class in Java
Java Console Error
503 error handling retry code snippets Java
Implementation Of Abstraction In Java
How to avoid thread deadlock in Java
Number of Squareful Arrays in Java
One-Time Password Generator Code In Java
Real-Time Face Recognition In Java
Converting Integer Data Type to Byte Data Type Using Typecasting in Java
How to Generate File checksum Value
Index Mapping (or Trivial Hashing) With Negatives allowed in Java
Shortest Path in a Binary Maze in Java
customized exception in Java
Difference between error and exception in Java
How to solve deprecated error in Java
Jagged Array in Java
CloneNotSupportedException in Java with Examples
Difference Between Function and Method in Java
Immutable List in Java
Nesting Of Methods in Java
How to Convert Date into Character Month and Year Java
How to Mock Lambda Expression in Java
How to Return Value from Lambda Expression Java
if Condition in Lambda Expression Java
Chained Exceptions in Java
Final static variable in Java
Java File Watcher
Various Operations on HashSet in Java
Word Ladder Problem in Java
Various Operations on Queue in Java
Various Operations on Queue Using Linked List in Java
Various Operations on Queue Using Stack in Java
Get Yesterday's Date from Localdate Java
Get Yesterday's Date by No of Days in Java
Advantages of Lambda Expression in Java 8
Cast Generic Type to Specific type Java
ConcurrentSkipListSet in Java
Fail Fast Vs. Fail-Safe in Java
Get Yesterday's Date in Milliseconds Java
Get Yesterday's Date Using Date Class Java
Getting First Date of Month in Java
Gregorian Calendar Java Current Date
How to Calculate Time Difference Between Two Dates in Java
How to Calculate Week Number from Current Date in Java
Keystore vs Truststore
Leap Year Program in Java
Online Java Compiler GDB
Operators in Java MCQ
Separators In Java
StringIndexOutOfBoundsException in Java
Anonymous Function in Java
Default Parameter in Java
Group by Date Code in Java
How to add 6 months to Current Date in Java
How to Reverse A String in Java Letter by Letter
Java 8 Object Null Check
Java Synchronized
Types of Arithmetic Operators in Java
Types of JDBC Drivers in Java
Unmarshalling in Java
Write a Program to Print Reverse of a Vowels String in Java
ClassNotFound Exception in Java
Null Pointer Exception in Java
Why Does BufferedReader Throw IOException in Java
Java Program to Add two Complex Numbers
Read and Print All Files From a Zip File in Java
Reverse an Array in Java
Right Shift Zero Fill Operator in Java
Static Block in Java
Accessor and Mutator in Java
Array of Class Objects in Java
Benefits of Generics in Java
Can Abstract Classes Have Static Methods in Java
ClassNotFoundException Java
Creating a Custom Generic Class in Java
Generic Queue Java
Getting Total Hours From 2 Dates in Java
How to add 2 dates in Java
How to Break a Date and Time in Java
How to Call Generic Method in Java
How to Increment and Decrement Date using Java
Java Class Methods List
Java Full Stack Developer
Java.lang.NullPointerException
Least Operator to Express Number in Java
Shunting Yard Algorithm in Java
Switch Case Java
Treeset Java Operations
Types of Logical Operators in Java
What is Cast Operator in Java
What is Jersey in Java
Alternative to Java Serialization
API Development in Java
Disadvantage of Multithreading in Java
Find the row with the maximum number of 1s
Generic Comparator in Java
Generic LinkedList in Java
Generic Programming in Java Example
How Can I Give the Default Date in The Array Java
How to Accept Date in Java
How to add 4 years to Date in Java
How to Check Date Equality in Java
How to Modify HTML File Using Java
Java 8 Multithreading Features
Java Abstract Class and Methods
Java Thread Dump Analyser
Process vs. Thread in Java
Reverse String Using Array in Java
Types of Assignment Operators in Java
Types of Bitwise Operators in Java
Union and Intersection Of Two Sorted Arrays In Java
Vector Operations Java
Java Books Multithreading
Advantages of Generics in Java
Arrow Operator Java
Generic Code in Java
Generic Method in Java Example
Getting a Range of Dates in Java
Getting the Day from a Date in Java
How Counter Work with Date Using Java
How to Add Date in Arraylist Java
How to Create a Generic List in Java
Java Extend Multiple Classes
Java Function
Java Generics Design Patterns
Why Are Generics Used in Java
XOR Binary Operator in Java
Check if the given string contains all the digits in Java
Constructor in Abstract Class in Java
Count number of a class objects created in Java
Difference Between Byte Code and Machine Code in Java
Java Program to Append a String in an Existing File
Main thread in Java
Store Two Numbers in One Byte Using Bit Manipulation in Java
The Knight's Tour Problem in Java
Business Board Problem in Java
Business Consumer Problem in Java
Buy as Much Candles as Possible Java Problem
Get Year from Date in Java
How to Assign Static Value to Date in Java
Java List Node
Java List Sort Lambda
Java Program to Get the Size of a Directory
Misc Operators in Java
Reverse A String and Reverse Every Alternative String in Java
Reverse a String in Java Using StringBuilder
Reverse Alternate Words in A String Java
Size of Empty Class in Java
Titniry Operation in Java
Triple Shift Operator in Java
Types of Conditional Operators in Java
View Operation in Java
What is Linked list Operation in Java
What is Short Circuit && And or Operator in Java
What is the & Operator in Java
Why to use enum in Java
XOR Bitwise Operator in Java
XOR Logical Operator Java
Compile-Time Polymorphism in Java
Convert JSON to Java Object Online
Difference between comparing String using == and .equals() method in Java
Difference Between Singleton Pattern and Static Class in Java
Difference Between Static and Non-Static Nested Class in Java
Getting Date from Calendar in Java
How to Swap or Exchange Objects in Java
Java Get Class of Generic Parameter
Java Interface Generic Parameter
Java Map Generic
Java Program for Maximum Product Subarray
Java Program To Print Even Length Words in a String
Logger Class in Java
Manacher's Algorithm in Java
Mutable Class in Java
Online Java IDE
Package getImplementationVersion() method in Java with Examples
Set Default Close Operation in Java
Sorting a Java Vector in Descending Order Using Comparator
Types of Interfaces in Java
Understanding String Comparison Operator in Java
User-Defined Packages in Java
Valid variants of main() in Java
What is a Reference Variable in Java
What is an Instance in Java
What is Retrieval Operation in ArrayList Java
When to Use the Static Method in Java
XOR Operations in Java
7th Sep - Array Declaration in Java
7th Sep - Bad Operand Types Error in Java
7th Sep - Data Structures in Java
7th Sep - Generic Type Casting In Java
7th Sep - Multiple Inheritance in Java
7th Sep - Nested Initialization for Singleton Class in Java
7th Sep - Object in Java
7th Sep - Recursive Constructor Invocation in Java
7th Sep - Java Language / What is Java
7th Sep - Why is Java Platform Independent
7th Sep - Card Flipping Game in Java
7th Sep - Create Generic Method in Java
7th Sep - Difference between super and super() in Java with Examples
7th Sep - for loop enum Java
7th Sep - How to Convert a String to Enum in Java
7th Sep - Illustrate Class Loading and Static Blocks in Java Inheritance
7th Sep - Introduction To Java
7th Sep - Java Lambda foreach
7th Sep - Java Latest Version
7th Sep - Java Method Signature
7th Sep - Java Practice Programs
7th Sep - Java SwingWorker Class
7th Sep - java.util.concurrent.RecursiveAction class in Java With Examples
7th Sep - Largest Palindrome by Changing at Most K-digits in Java
7th Sep - Parameter Passing Techniques in Java with Examples
7th Sep - Reverse a String in Java Using a While Loop
7th Sep - Reverse a String Using a For Loop in Java
7th Sep - Short Circuit Operator in Java
7th Sep - Java 8 Stream API
7th Sep - XOR Operation on Integers in Java
7th Sep - XOR Operation on Long in Java
Array Programs in Java
Concrete Class in Java
Difference between Character Stream and Byte Stream in Java
Difference Between Static and non-static in Java
Different Ways to Convert java.util.Date to java.time.LocalDate in Java
Find the Good Matrix Problem in Java
How Streams Work in Java
How to Accept Different Formats of Date in Java
How to Add Date in MySQL from Java
How to Find the Size of int in Java
How to Make a Field Serializable in Java
How to Pass an Array to Function in Java
How to Pass an ArrayList to a Method in Java
Implementing the Java Queue Interface
Initialization of local variable in a conditional block in Java
isnull() Method in Java
Java Array Generic
Java Program to Demonstrate the Lazy Initialization Non-Thread-Safe
Java Program to Demonstrate the Non-Lazy Initialization Thread-Safe
Java Static Field Initialization
Machine Learning Using Java
Mars Rover Problem in Java
Model Class in Java
Nested Exception Handling in Java
Program to Convert List to Stream in Java
Static Polymorphism in Java
Static Reference Variables in Java
Sum of Two Arrays in Java
What is Is-A-Relationship in Java
When to Use Vector in Java
Which Class cannot be subclassed in Java
Word Search Problem in Java
XOR Operation Between Sets in Java
Burger Problem in Java Game
Convert Set to List in Java
Floyd Triangle in Java
How to Call Static Blocks in Java
Interface Attributes in Java
Java Applications in the Real World
Java Concurrent Array
Java Detect Date Format
Java Interface Without Methods
Java Iterator Performance
Java Packet
Java Static Instance of Class
Java TreeMap Sort by Value
Length of List in Java
List of Checked Exceptions in Java
Message Passing in Java
Product Maximization Problem in Java
Terminal Operations in Java 8
Understanding Base Class in Java
Difference between Early Binding and Late Binding in Java
Collectors toCollection() in Java
Difference between ExecutorService execute() and submit() method in Java
Difference between Java and Core Java
Different Types of Recursions in Java
Initialize a static map in Java with Examples
Merge Sort Using Multithreading in Java
Why Thread.stop(), Thread.suspend(), and Thread.resume() Methods are Deprecated After JDK 1.1 Version
Circular Primes in Java
Difference Between poll() and remove() Method of a Queue
EvalEx Java: Expression Evaluation in Java
Exeter Caption Contest Java Program
FileInputStream finalize() Method in Java
Find the Losers of the Circular Game problem in Java
Finding the Differences Between Two Lists in Java
Finding the Maximum Points on a Line in Java
Get Local IP Address in Java
Handling "Handler dispatch failed" Nested Exception: java.lang.StackOverflowError in Java
Harmonic Number in Java
How to Find the Percentage of Uppercase Letters, Lowercase Letters, Digits, and Special Characters in a String Using Java
Interface Variables in Java
Java 8 Interface Features
Java Class Notation
Java Exception Messages Examples and Explanations
Java Package Annotation
Java Program to Find First Non-Repeating Character in String
Java Static Type Vs. Dynamic Type
Kaprekar Number in Java
Multitasking in Java
Niven Number in Java
Rhombus Pattern in Java
Shuffle an Array in Java
Static Object in Java
The Scope of Variables in Java
Toggle String in Java
Use of Singleton Class in Java
What is the Difference Between Future and Callable Interfaces in Java
Aggregate Operation in Java 8
Bounded Types in Java
Calculating Batting Average in Java
Compare Two LinkedList in Java
Comparison of Autoboxed Integer objects in Java
Count Tokens in Java
Cyclomatic Complexity in Java
Deprecated Meaning in Java
Double Brace Initialization in Java
Functional Interface in Java
How to prevent objects of a class from Garbage Collection in Java
Java Cast Object to Class
Java isAlive() Method
Java Line Feed Character
java.net.MulticastSocket class in Java
Keytool Error java.io.FileNotFoundException
Matrix Diagonal Sum in Java
Number of Boomerangs Problem in Java
Sieve of Eratosthenes Algorithm in Java
Similarities Between Bastar and Java
Spring vs. Struts in Java
Switch Case in Java 12
The Pig Game in Java
Unreachable Code Error in Java
Who Were the Kalangs of Java
2048 Game in Java
Abundant Number in Java
Advantages of Applet in Java
Alpha-Beta Pruning Java
ArgoUML Reverse Engineering Java
Can Constructor be Static in Java
Can we create object of interface in Java
Chatbot Application in Java
Difference Between Component and Container in Java
Difference Between Java.sql and Javax.sql
Find A Pair with Maximum Product in Array of Integers
Goal Stack Planning Program in Java
Half Diamond Pattern in Java
How to find trigonometric values of an angle in Java
How to Override tostring() method in Java
Inserting a Node in a Doubly Linked List in Java
Java 9 Immutable Collections
Java 9 Interface Private Methods
Java Convert Array to Collection
Java Transaction API
Methods to Take Input in Java
Parallelogram Pattern in Java
Reminder Program in Java
Sliding Window Protocol in Java
Static Method in Java
String Reverse in Java 8 Using Lambdas
Types of Threads in Java
What is thread safety in Java? How do you achieve it?
xxwxx.dll Virus Java 9
Java 8 Merge Two Maps with Same Keys
Java 8 StringJoiner, String.join(), and Collectors.joining()
Java 9 @SafeVarargs Annotation Changes
Java 9 Stream API Improvements
Java 11 var in Lambda Expressions
Sequential Search Java
Thread Group in Java
User Thread Vs. Daemon Thread in Java
Collections Vs. Streams in Java
Import statement in Java
init() Method in Java
Java Generics Jenkov
Ambiguity in Java
Benefits of Learning Java
Designing a Vending Machine in Java
Monolithic Applications in Java
Name Two Types of Java Program
Random Access Interface in Java
Rust Vs. Java
Types of Constants in Java
Execute the Main Method Multiple Times in Java
Find the element at specified index in a Spiral Matrix in Java
Find The Index of An Array Element in Java
Mark-and-Sweep Garbage Collection Algorithm in Java
Shadowing of Static Functions in Java
Straight Line Numbers in Java
Zumkeller Numbers in Java
Types of Layout Manager in Java
Virtual Threads in Java 21
Add Two Numbers Without Using Operator in Java
Automatic Type Promotion in Java
ContentPane Java
Difference Between findElement() and findElements() in Java
Difference Between Inheritance and Interfaces in Java
Difference Between Jdeps and Jdeprscan tools in Java
Find Length of String in Java Without Using Function
InvocationTargetException in Java
Java Maps to JSON
Key Encapsulation Mechanism API in Java 21
Placeholder Java
String Templates in Java 21
Why Java is Robust Language
Collecting in Java 8
containsIgnoreCase() Method in Java
Convert String to Biginteger In Java
Convert String to Map in Java
Define Macro in Java
Difference Between Lock and Monitor in Java Concurrency
Difference Between the start() and run() Methods in Java
Generalization and Specialization in Java
getChannel() Method in Java
How to Check Whether an Integer Exists in a Range with Java
HttpEntity in Java
Lock Framework Vs. Thread Synchronization in Java
Niven Number Program in Java
Passing Object to Method in Java
Pattern Matching for Switch in Java 21
Swap First and Last Digit of a Number in Java
Adapter Design Pattern in Java
Best Automation Frameworks for Java
Building a Search Engine in Java
Bytecode Verifier in Java
Caching Mechanism in Java
Comparing Two HashMap in Java
Cryptosystem Project in Java
Farthest from Zero Program in Java
How to Clear Linked List in Java
Primitive Data Type Vs. Object Data Type in Java
setBounds() Method in Java
Unreachable Code or Statement in Java
What is Architecture Neutral in Java
Difference between wait and notify in Java
Dyck Path in Java
Find the last two digits of the Factorial of a given Number in Java
How to Get an Environment Variable in Java
Java Program to open the command prompt and insert commands
JVM Shutdown Hook in Java
Semiprimes Numbers in Java
12 Tips to Improve Java Code Performance
Ad-hoc Polymorphism in Java
Array to String Conversion in Java
CloudWatch API in Java
Essentials of Java Programming Language
Extends Vs. Implements in Java
2d Array Sorting in Java
Aliquot Sequence in Java
Authentication and Authorization in Java
Cannot Find Symbol Error in Java
Compare Two Excel Files in Java
Consecutive Prime Sum Program in Java
Count distinct XOR values among pairs using numbers in range 1 to N
Difference Between Two Tier and Three Tier Architecture in Java
Different Ways of Reading a Text File in Java
Empty Array in Java
FCFS Program in Java with Arrival Time
Immutable Map in Java
K-4 City Program in Java
Kahn's algorithm for Topological Sorting in Java
Most Popular Java Backend Tools
Recursive Binary Search in Java
Set Intersection in Java
String Reverse Preserving White Spaces in Java
The Deprecated Annotation in Java
What is JNDI in Java
Backtracking in Java
Comparing Doubles in Java
Consecutive Prime Sum in Java
Finding Missing Numbers in an Array Using Java
Good Number Program in Java
How to Compress Image in Java Source Code
How to Download a File from a URL in Java
Passing an Object to The Method in Java
Permutation program in Java
Profile Annotation in Java
Scenario Based Questions in Java
Understanding Static Synchronization in Java
Types of Errors in Java
Abstract Factory Design Pattern in Java
Advantages of Kotlin Over Java
Advantages of Methods in Java
Applet Program in Java to Draw House with Output
Atomic Boolean in Java
Bitset Class in Java
Bouncy Castle Java
Chained Exception in Java
Colossal Numbers in Java
Compact Profiles Java 8
Convert Byte to Image in Java
Convert Set to Array in Java
Copy ArrayList to another ArrayList Java
Copy Data from One File to Another in Java
Dead Code in Java
Driver Class Java
EnumMap in Java
Farthest Distance of a 0 From the Centre of a 2-D Matrix in Java
How to Terminate a Program in Java
Instance Block in Java
Iterative Constructs in Java
Java 10 var Keyword
Nested ArrayList in Java
Square Pattern in Java
String Interpolation in Java
Unnamed Classes and Instance Main Method in Java 21
What is difference between cacerts and Keystore in Java
Agile Principles Patterns and Practices in Java
Color Method in Java
Concurrent Collections in Java
Create JSON Node in Java
Difference Between Checkbox and Radio Button in Java
Difference Between Jdeps and Jdeprscan Tools in Java
Difference Between Static and Dynamic Dispatch in Java
Difference Between Static and Non-Static Members in Java
Error Java Invalid Target Release 9
Filedialog Java
String Permutation in Java
Structured Concurrency in Java
Uncaught Exception in Java
ValueOf() Method in Java
Virtual Thread in Java
Difference Between Constructor Overloading and Method Overloading in Java
Difference Between for loop and for-each Loop in Java
Difference Between Fork/Join Framework and ExecutorService in Java
Difference Between Local, Instance, and Static Variables in Java
Difference Between Multithreading and Multiprocessing in Java
Difference Between Serialization and Deserialization in Java
Difference Between Socket and Server Socket in Java
Advantages of Immutable Classes in Java
BMI Calculator Java
Code Coverage Tools in Java
How to Declare an Empty Array in Java
How To Resolve Java.lang.ExceptionInInitializerError in Java
Java 18 Snippet Tag with Example
Object Life Cycle in Java
print() Vs. println() in Java
@SuppressWarnings Annotation in Java
Types of Cloning in Java
What is portable in Java
What is the use of an interpreter in Java
Abstract Syntax Tree (AST) in Java
Aliasing in Java
CRUD Operations in Java
Euclid-Mullin Sequence in Java
Frame Class in Java
Initializing a List in Java
Number Guessing Game in Java
Number of digits in N factorial to the power N in Java
Rencontres Number in Java
Skewed Binary Tree in Java
Vertical zig-zag traversal of a tree in Java
Wap to Reverse a String in Java using Lambda Expression
Concept of Stream in Java
Constraints in Java
Context Switching in Java
Dart Vs. Java
Dependency Inversion Principle in Java
Difference Between Containers and Components in Java
Difference Between CyclicBarrier and CountDownLatch in Java
Difference Between Shallow and Deep Cloning in Java
Dots and Boxes Game Java Source code
DRY Principle Java
How to get File type in Java
IllegalArgumentException in Java example
Is the main() method compulsory in Java
Java Paradigm
Lower Bound in Java
Method Binding in Java
Overflow and Underflow in Java
Padding in Java
Passing and Returning Objects in Java
Single Responsibility Principle in Java
ClosedChannelException in Java with Examples
How to Fix java.net.ConnectException Connection refused connect in Java
java.io.UnsupportedEncodingException in java with Examples
Selection Statement in Java
Difference Between Java 8 and Java 9
Difference Between Nested Class and Inner Class in Java
Difference Between OOP and POP in Java
Difference Between Static and Dynamic in Java
Difference Between Static Binding and Dynamic Binding in Java
Difference Between Variable and Constant in Java
Alternate Pattern Program in Java
Architecture Neutral in Java
AutoCloseable Interface in Java
BitSet Class in Java
Border Layout Manager in Java
Digit Extraction in Java
Dynamic Method Dispatch Java
Dynamic Variable in Java
How to Convert Double to string in Java
How to Convert Meter to Kilometre in Java
How to Install SSL Certificate in Java
How to Protect Java Source Code
How to Use Random Object in Java
Java Backward Compatibility
Java New String Class Methods from Java 8 to Java 17
Mono in Java
Object to int in Java
Predefined Streams in Java
Prime Factor Program in Java
Transfer Statements in Java
What is Interceptor in Java
Java Array Methods
java.lang.Class class in Java
Reverse Level Order Traversal in Java
Working with JAR and Manifest files In Java
Alphabet Board Path Problem in Java
Composite Design Pattern Java
Default and Static Methods in Interface Java 8
Difference Between Constraints and Annotations in Java
Difference Between fromJson() and toJson() Methods of GSON in Java
Difference Between Java 8 and Java 11
Difference Between map() and flatmap() Method in Java 8
Difference Between next() and nextLine() Methods in Java
Difference Between orTimeout() and completeOnTimeOut() Methods in Java 9
Disadvantages of Array in Java
How Synchronized works in Java
How to Create a Table in Java
ID Card Generator Using Java
Introspection in JavaBeans
Java 15 Features
Java Object Model
Java Tools and Command-List
Next Permutation Java
Object as Parameter in Java
Optimizing Java Code Performance
Pervasive Shallowness in Java
Sequenced Collections in Java 21
Stdin and Stdout in Java
Stream count() Function in Java
String.strip() Method in Java
Vertical Flip Matrix Problem in Java
Calling Object in Java
Characteristics of Constructor in Java
Counting Problem in Multithreading in Java
Creating Multiple Pools of Objects of Variable Size in Java
Default Exception in Java
How to Install Multiple JDK's in Windows
Differences Between Vectors and Arrays in Java
Duplicate Class Errors in Java
Example of Data Hiding in Java
Foreign Function and Memory APIs in Java 21
Generic Tree Implementation in Java
getSource() Method in Java
Giuga numbers in Java
Hessian Java
How to Connect Login Page to Database in Java
Difference between BlueJ and JDK 1.3
How to Solve Incompatible Types Error in Java
Java 8 Method References
Java 9 Try with Resources Improvements
Menu-Driven Program in Java
Mono Class in Java
Multithreading Vs. Asynchronous in Java
Nested HashMap in Java
Number Series Program in Java
Object Slicing in Java
Oracle Java
Print 1 to 100 Without Loop in Java
Remove elements from a List that satisfy given predicate in Java
Replace Element in Arraylist Java
Sliding Puzzle Game in Java
Strobogrammatic Number in Java
Web Methods in Java
Web Scraping Java
Window Event in Java
@Builder Annotation in Java
Advantages of Abstraction in Java
Advantages of Packages in Java
Bounce Tales Java Game Download
Breaking Singleton Class Pattern in Java
Building a Brick Breaker Game in Java
Building a Scientific Calculator in Java
Circle Program in Java
Class Memory in Java
Convert Byte to an Image in Java
Count Paths in Given Matrix in Java
Difference Between Iterator and ListIterator in Java with Example
Distinct Character Count Java Stream
EOFException in Java
ExecutionException Java 8
Generic Object in Java
How to Create an Unmodifiable List in Java
How to Create Dynamic SQL Query in Java
How to Return a 2D Array in Java
Java 8 Stream.distinct() Method
Java setPriority() Method
Mutator Methods in Java
Predicate Consumer Supplier Java 8
Program to Generate CAPTCHA and Verify User Using Java
Random Flip Matrix in Java
System Class in Java
Vigenere Cipher Program in Java
Behavior-Driven Development (BDD) in Java
CI/ CD Tools for Java
cint in Java
Command Pattern in Java
CSV to List Java
Difference Between Java Servlets and CGI
Difference Between Multithreading Multitasking, and Multiprocessing in Java
Encoding Three Strings in Java
How to Import Jar File in Eclipse
Meta Class Vs. Class in Java
Meta Class Vs. Super Class in Java
Print Odd and Even Numbers by Two Threads in Java
Scoped value in Java
Upper-Bounded Wildcards in Java
Wildcards in Java
Zero Matrix Problem in Java
All Possible Combinations of a String in Java
Atomic Reference in Java
Final Method Overloading in Java| Can We Overload Final Methods
Constructor in Inheritance in Java
Design Your Custom Connection Pool in Java
How Microservices Communicate with Each Other in Java
How to Convert String to Timestamp in Java
Java 10 Collectors Methods
Java and Apache OpenNLP
Java Deep Learning
Java Iterator Vs. Listiterator Vs. Spliterator
Pure Functions in Java
Use of Constructor in Java | Purpose of Constructor in Java
Implement Quintet Class with Quartet Class in Java using JavaTuples
Java Best Practices
Efficiently Reading Input For Competitive Programming using Java 8
Length of the longest substring without repeating characters in Java
Advantages of Inner Class in Java
AES GCM Encryption Java
Array Default Values in Java
Copy File in Java from one Location to Another
Creating Templates in Java
Different Packages in Java
How to Add Elements to an Arraylist in Java Dynamically
How to Add Splash Screen in Java
How to Calculate Average Star Rating in Java
Immutable Class with Mutable Object in Java
Java instanceOf() Generics
Set Precision in Java
Snake Game in Java
Tower of Hanoi Program in Java
Two Types of Streams Offered by Java
Uses of Collections in Java
Additive Numbers in Java
Association Vs. Aggregation Vs. Composition in Java
Covariant and Contravariant Java
Creating Immutable Custom Classes in Java
mapToInt() in Java
Methods of Gson in Java
Server Socket in Java
Check String Are Permutation of Each Other in Java
Containerization in Java
Difference Between Multithreading and Multiprogramming in Java
Flyweight Design Pattern
HMAC Encryption in Java
How to Clear Error in Java Program
5 Types of Java
Design a Job Scheduler in Java
Elements of Java Programming
Generational ZCG in Java 21
How to Print Arraylist Without Brackets Java
Interface Vs. Abstract Class After Java 8
Java 9 Optional Class Improvements
Number of GP sequence Problem in Java
Pattern Matching for Switch
Range Addition Problem in Java
Swap Corner Words and Reverse Middle Characters in Java
Kadane's Algorithm in Java
Capture the Pawns Problem in Java
Find Pair With Smallest Difference in Java
How to pad a String in Java
When to use Serialization and Externalizable Interface
Which Component is responsible to run Java Program
Difference Between Java and Bastar
Difference Between Static and Instance Methods in Java
Difference Between While and Do While loop in Java
Future Interface in Java
Invert a Binary tree in Java
Java Template Engine
KeyValue Class in JavaTuples
Quantifiers in Java
Swapping Pairs of Characters in a String in Java
Version Enhancements in Exception Handling introduced in Java SE 7
Find all Palindromic Sub-Strings of a given String in Java
Find if String is K-Palindrome or not in Java
Count Pairs from an Array with Even Product of Count of Distinct Prime Factor in Java
Find if an Array of Strings can be Chained to form a Circle in Java
Find largest factor of N such that NF is less than K in Java
Lexicographically First Palindromic String in Java
LinkedTransferQueue removeAll() method in Java with Examples
Next Smallest Palindrome problem in Java

Parameter passing in Java refers to the mechanism of transferring data between methods or functions. Java supports two types of parameters passing techniques

Understanding these techniques is essential for effectively utilizing method parameters in Java.

A variable and its corresponding data type are referred to as formal parameters when they exist in the definition or prototype of a function or method. As soon as the function or method is called and it serves as a placeholder for an argument that will be supplied. The function or method performs calculations or actions using the formal parameter.

In the above syntax:

The value or expression that corresponds to a formal parameter and is supplied to a function or method during a function or method call is referred to as an actual parameter is also known as an argument. It offers the real information or value that the method or function will work with.

functionName(argument)

In the above syntax:

In Call-by-value the copy of the value of the actual parameter is passed to the formal parameter of the method. Any of the modifications made to the formal parameter within the method do not affect the actual parameter.

Create a class named CallByValueExample.

Inside the main method:

Declare an integer variable num and assign it the value 10.

Print the value of num before calling the method.

Call the modifyValue method, passing num as the actual parameter.

Print the value of num after calling the method.

Define the modifyValue method that takes an integer parameter value:

Modify the formal parameter value by assigning it the value 20.

Print the value of value inside the method.

The implementation of the above steps given below

CallByValueExample.java

Time Complexity is O(1).

Space Complexity is O(1).

call by reference" is a method of passing arguments to functions or methods where the memory address (or reference) of the variable is passed rather than the value itself. This means that changes made to the formal parameter within the function affect the actual parameter in the calling environment.

In "call by reference," when a reference to a variable is passed, any modifications made to the parameter inside the function are transmitted back to the caller. This is because the formal parameter receives a reference (or pointer) to the actual data.

Start

Define the class "CallByReference"

Declare instance variables: a (int) and b (int)

Define a constructor to assign values to a and b

Define the method "changeValue" inside the "CallByReference" class:

Accept a parameter of type "CallByReference" called "obj"

Add 10 to the value of "obj.a"

Add 20 to the value of "obj.b"

Define the class "Main"

Define the main method

Create an instance of "CallByReference" called "object" with values 10 and 20

Print the values of "object.a" and "object.b"

Call the "changeValue" method on "object" and pass "object" as an argument

Print the updated values of "object.a" and "object.b"

End

The implementation of the above steps given below

CallByReferenceExample.java

Time Complexity is O(1).

Space Complexity is O(1).

Latest Courses

We provides tutorials and interview questions of all technology like java tutorial, android, java frameworks

Contact info

G-13, 2nd Floor, Sec-3, Noida, UP, 201301, India

[email protected] .

Interview Questions

Online compiler.

Inspectopedia Help

Unchecked warning.

Reports code on which an unchecked warning will be issued by the javac compiler. Every unchecked warning may potentially trigger ClassCastException at runtime.

Locating this inspection

Can be used to locate inspection in e.g. Qodana configuration files , where you can quickly enable or disable it, or adjust its settings.

Path to the inspection settings via IntelliJ Platform IDE Settings dialog, when you need to adjust inspection settings directly from your IDE.

Settings or Preferences | Editor | Inspections | Java | Compiler issues

Inspection options

Here you can find the description of settings available for the Unchecked warning inspection, and the reference of their default values.

Not selected

Inspection Details
By default bundled with:	, ,
Can be installed with plugin:	Java, 242.22892

Assignment to property of function parameter no-param-reassign

Last updated: Mar 7, 2024 Reading time · 3 min

# Table of Contents

Disabling the no-param-reassign ESLint rule for a single line
Disabling the no-param-reassign ESLint rule for an entire file
Disabling the no-param-reassign ESLint rule globally

# Assignment to property of function parameter no-param-reassign

The ESLint error "Assignment to property of function parameter 'X' eslint no-param-reassign" occurs when you try to assign a property to a function parameter.

To solve the error, disable the ESLint rule or create a new object based on the parameter to which you can assign properties.

assignment to property of function parameter eslint no param reassign

Here is an example of how the error occurs.

The ESLint rule forbids assignment to function parameters because modifying a function's parameters also mutates the arguments object and can lead to confusing behavior.

One way to resolve the issue is to create a new object to which you can assign properties.

We used the spread syntax (...) to unpack the properties of the function parameter into a new object to which we can assign properties.

If you need to unpack an array, use the following syntax instead.

The same approach can be used if you simply need to assign the function parameter to a variable so you can mutate it.

We declared the bar variable using the let keyword and set it to the value of the foo parameter.

We are then able to reassign the bar variable without any issues.

# Disabling the no-param-reassign ESLint rule for a single line

You can use a comment if you want to disable the no-param-reassign ESLint rule for a single line.

Make sure to add the comment directly above the assignment that causes the error.

# Disabling the no-param-reassign ESLint rule for an entire file

You can also use a comment to disable the no-param-reassign ESLint rule for an entire file.

Make sure to add the comment at the top of the file or at least above the function in which you reassign parameters.

The same approach can be used to disable the rule only for a single function.

The first comment disables the no-param-reassign rule and the second comment enables it.

If you try to reassign a parameter after the second comment, you will get an ESLint error.

# Disabling the no-param-reassign ESLint rule globally

If you need to disable the no-param-reassign rule globally, you have to edit your .eslintrc.js file.

If you only want to be able to assign properties to an object parameter, set props to false instead of disabling the rule completely.

The following code is valid after making the change.

If you use a .eslintrc or .eslintrc.json file, make sure to double-quote the properties and values.

If you want to only allow assignment to object parameters, use the following line instead.

Make sure all properties are double-quoted and there are no trailing commas if your config is written in JSON.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

eslint is not recognized as an internal or external command
Plugin "react" was conflicted between package.json » eslint-config-react-app
React: Unexpected use of 'X' no-restricted-globals in ESLint
TypeScript ESLint: Unsafe assignment of an any value [Fix]
ESLint error Unary operator '++' used no-plusplus [Solved]
ESLint Prefer default export import/prefer-default-export
Arrow function should not return assignment. eslint no-return-assign
TypeError: Cannot redefine property: X in JavaScript [Fixed]
ESLint: disable multiple rules or a rule for multiple lines
Expected linebreaks to be 'LF' but found 'CRLF' linebreak-style
Missing return type on function TypeScript ESLint error

Borislav Hadzhiev

Web Developer

Stack Exchange Network

Stack Exchange network consists of 183 Q&A communities including Stack Overflow , the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

Java: Why not allow nulls in methods to represent optional parameters?

I wanted to follow up on this previous question I asked related to @Laive comment , but I couldn't think of an excellent way to do so without asking another question, so here we go.

With the previous question in context, many users suggested the approach of creating a parameter. The object for a method that has many parameters, others pointed out that plans probably should not have many settings.

I am assuming that the technique has been engineered correctly, and it's been decided that the method should have a reasonable number of parameters, but not only 1 or 2).

Creating a parameter object, if you have optional parameters, needs to have some way in your object parameters. Declaring that a certain as the optional parameter is "not there", and then in your code, you would have to handle that case.

I researched blogs and stuff on the topic, and it seems like it is not preferred to have a method signature that accepts nulls as a flag for "optional value not present".

What is the difference between a param object with an optional field which has a "field not set" value, and a method with explicit parameters for which null is a valid value to represent "optional parameter not set", and why is one acceptable and the other not?

2 As you're dealing with a number of issues in this area, it seems to me like maybe your parameters are really an entity/concept that should be formally made manifest, rather than say, making your clients deal with some loosely/informally associated variables. You might then also consider a builder pattern , to construct such a parameter object/entity. – Erik Eidt Commented Nov 8, 2019 at 17:03
I don't think one is worse than the other, they are basically equivalent. But with method arguments you have an alternative: overloads. This is better. You can use a private method for the generic implementation which is called by the public methods. This way you have more control, you can just throw if the client passes null for any argument. – Martin Maat Commented Jul 6, 2021 at 17:25

5 Answers 5

In general it is a bad idea to use null to indicate an optional value. It is a bad idea whether it is for a return value, an object property, a local variable or any other context. So parameters is just one case of a general rule.

So why is it a bad idea? Two reasons:

It is not possible in Java to indicate in the type system if null is allowed or not.
The default value for an uninitialized reference is null .

This means a reference can be null for two reasons:

There is a bug and the value was not properly initialized
It is intentionally null to indicate the lack of an optional value

Since the code can't distinguish between the two cases, a bug may go unnoticed because the code cannot distinguish a bug from the legitimate value. Therefore other approaches to indicate optional values are preferred.

Using a parameter-object with nullable properties is not really better though since you have the same issue: You don't know if the property is null due to a bug or intentionally. So I disagree with your premise that this is better.

That is a good point, I never thought of it that way; I've used null to represent "optional value not present" in my code a lot without thinking that, in a black box, "null" could be indication of a bug in code flow. – Ertai87 Commented Nov 8, 2019 at 22:11

The problem with using nulls is that you need to document that null is a valid value, then remember that an object could be null. Also, the person using your method will constantly have to refer to the documentation to see if that parameter could be null.

Instead, if you had a Parameters object, those optional fields could be stored as Optional<Foo> fooParam which forces the user of that parameters class to explicitly check for and deal with missing values:

So no explicit checks for null and users of the code don't have to wonder what the params should be for myMethod

2 But according to the creator of the Optional class, Optional is intended to be used only in the return value for methods, and is explicitly not intended to be used as a parameter. How does this approach not violate that constraint (or at the very least, not obfuscate the code to make it look like the constraint isn't being violated when it actually is)? – Ertai87 Commented Nov 8, 2019 at 15:35
Furthermore, in your business logic (myMethod in your case), it is true you don't have an explicit null check, but you do have an implicit one (inside Optional::orElse); you're not saving anything except obfuscating away your null check to make it look like you're not doing it when you actually are; I don't understand how this solves the problem. – Ertai87 Commented Nov 8, 2019 at 15:37
1 It's not a parameter, it's a field in a class. I guess if you really wanted, you could have the fooParam be just a Foo that may or may not be null and in getFooParam() return Optional.ofNullable(fooParam) . in my opinion, the code isn't obfuscating anything, it's making things more clear by yelling to the world, THIS COULD BE NULL AND HERE'S WHAT TO DO IF IT IS. – Matthew Commented Nov 8, 2019 at 15:38
2 Also, it solves the problem because the implementer of myMethod doesn't have to remember to check for null, the implementer MUST do something about the Optional and it's clearer to the caller of myMethod that the foo param is optional. – Matthew Commented Nov 8, 2019 at 15:45

I think the main problem with nulls as optional parameters is that it makes code harder to read. For example, let's say I have a method with 6 parameters where the last 5 are optional:

Looking at that, it's not terribly easy to tell which parameter I am providing and which ones I am not. I have to count and look at the definition of the method to understand what's going on. Really there are two problems, though. Too many parameters is probably the bigger one. Anytime you have a function that takes multiple distinct parameters of the same type (i.e. not varargs), it's more difficult to mentally parse:

Since nulls are a valid value for any Object reference, they turn distinguishable parameters into indistinguishable ones. A simple example can demonstrate this last point:

Assume a function with lots of parameters like so:

An example of all the parameters filled in might look like this:

This is ugly, for sure. Too much going on but if I can remember that x parameters come before y and that fill comes before stroke, you can pretty quickly scan to see what the width parameter is. I know that something of type Point is the center, the dimensions are Floats, etc.

Now let's assume all of the parameters are optional where null represents a default. This is a little far-fetched for something like this but bear with me for demonstrative purposes:

Now, when I look at this, it takes more time to make sense of what is being specified. The type information is gone because null is a valid value for any object type. I see a float in there, but which dimension is it? I need to slow down and probably pull up the definition.

1 I'm not sure I see how null in this case is any worse than having a method that takes a whole bunch of parameters of the same data type in the first place; you still have to cross-reference the method signature with the argument list to make sense of what's going on. Not to say the latter isn't also a problem, but given that you are prepared to do the latter, I don't see how null really exacerbates that issue. – Ertai87 Commented Nov 8, 2019 at 22:13
I've added a more detailed example to help illustrate the problem. – JimmyJames Commented Nov 11, 2019 at 15:19

Let me start by describing two problems with Java:

No distinction between nullable and non-nullable types.
No support for parameters defaults

Non-Nullable Types

Many languages (including Java) make no distinction between types/variables that can accept a null value and ones that can't (except for primitive types like int - which can't have a value of null).

A common technique in other languages is to assume a bare type such as: String cannot accept a null value, however the type String? can be either a String or null

This system allows the compiler to provider two protections:

Firstly it's not possible to leave a non-nullable variable uninitialized (and/or null ).
Secondly it's not possible to assign a nullable variable ( String? ) to a non-nullable variable ( String )

You can achieve the same protection that other languages provide in Java by:

Using the Optional type, i.e: Optional<String>
and Not intentionally using nulls in your code base.

If you follow this pattern strictly you can avoid NPE's introduced by your code. However since you will likely have to use other libraries and the JDK itself, it is still possible for nulls to creep in from other locations.

Parameter Defaults

Other languages also allow defaults values to be set for parameters. These can typically be used in one of two ways:

Avoid the need to specify all parameters (assuming the remaining parameters are defaulted)
Use "named" parameters to only specify the values you want to pass.

Back to Your question

The primary advantage to a parameter object is that it can be passed through many levels of methods.

Perhaps you have a class that has a few public methods and a bunch of private ones, most parameters are not needed by the top level object, so you can just pass the parameter object through to the lower level methods. When you need to refactor the parameter list you can simply add a new parameter to the object and use it where it needs to be used, without having to go through a long call chain updating all the signatures.

The downside of this solution is parameter bloat - it is too easy to just keep adding additional parameters to the object and passing it around more and more places. When this happens it is no longer clear which of the parameters is actually used by a given method. Note: Some will point out that in this case your main class is two complex and should be broken into smaller classes each with their own dedicated parameter objects.

Parameter default (in other languages) help greatly with your public API - so that your callers don't have to send long lists of parameters, but they don't help you inside your class as you still have to pass a bunch of parameters around.

Another (Java specific) problem is the "double null check" in that you have to check that you have a valid pointer to the parameter object (not null) and that the actual parameter itself is not null, this is where other languages can help by not allowing particular parameters to have a null value.

Java is not inherently "less safe" than other languages - by using good standards for example leveraging the Optional class you can achieve similar levels of compiler type checking, but Java lacks the syntactic sugar of other languages, as a result you may end up with more complex method signatures to achieve the same result.

"Another (Java specific) problem is the "double null check" in that you have to check that you have a valid pointer to the parameter object (not null) and that the actual parameter itself is not null, this is where other languages can help by not allowing particular parameters to have a null value." I have no idea what you are referring to here. All parameters in Java are pass-by-value. There's no way to have a 'non-null pointer' that points to null in Java. A reference in Java either points to an object, or it's null. – JimmyJames Commented Jul 6, 2021 at 14:25

The problem

What is the difference between a param object with an optional field which has a "field not set" value, and a method with explicit parameters for which null is a valid value to represent "optional parameter not set", and why is one acceptable and the other not?

Let's say you have an UpdatePerson use case. Person has many properties, some of which are Address and Employment (for the example code below, I'm going to only list these two properties for brevity's sake). You want to be able to call UpdatePerson , but only provide partial information about the person (i.e. only the fields that need actual updating). Any missing parameters should be ignored and thus remain unchanged.

Therefore, you create your method:

This example touches on the spirit of your approach with many optional parameters.

So how do you call this method when you want to update the person's address, but not their employment? Well, as you said:

a method with explicit parameters for which null is a valid value to represent "optional parameter not set"

Therefore, you want to do something like:

Okay, that works.

Second question, what if this person gets a new job, but does not move house? Well, similarly:

So far, so good.

Third question. How do you call this method when the person loses their job? Therefore, their employment should be nullified (hint hint). Which leads to:

But by applying your approach from above, how do we distinguish between not updating the address because it is null, and nullifying the employment because it is null?

When null is a meaningful value in and of itself, null cannot at the same time be used to indicate the absence of a value.

JacquesB's answer is also correct that you may want to reserve null specifically to indicate a bug, therefore also giving you a reason to not give null an intended meaning. It's the same as what I described in principle, just a different concrete example.

The problem here stems from you using the employment method parameter in two ways: as the value holder for the person's Employment property, and as an indicator for whether the UpdatePerson method should update the person's employment or not. Your meanings for null clash, and it becomes impossible to figure out which of the two meanings you're conveying.

Tangentially:

When IndexOf cannot find an occurrence, it returns -1 . The reason it is able to do so is because -1 is a meaningless index value , and therefore it can be given a special meaning unrelated to the "normal" meaning of the returned integer value. If -1 were a meaningful index value, which in some languages it is (negative index = counting from the back), then IndexOf wouldn't be able to use it as a special "nothing found" value.

The solution?

You might think to yourself that you can therefore use null as a way to indicate optional parameters if null is not a valid value to be used (for Person.Employment ). Technically, you could implement that. But it's a bad idea, for several reasons:

This requires a reader to have perfect knowledge of all accepted values for all properties at all times, before the reader can understand exactly what is happening when you call UpdatePerson(123, null, null) . Which of these is being updated? Which isn't?
You may change the implementation in the future, suddenly (dis)allowing null to be used as a valid value in the entity. This would then force you to have to re-evaluate all usages of this method, in order to now start/stop using null to indicate the absence of an optional parameter
You have to use two different systems: one for properties that can be null and one for properties that can't be null .

It is much easier to steer away from using null , and instead using a different marker for presence/absence of a parameter. For example, you could wrap your values in a wrapper class that explicitly indicates absence/presence.

Forgive the C# syntax, I'm no Java dev. As far as I'm aware, I'm only using language features that also exist in Java.

Now you have a way to see the difference:

Which means your method can meaningfully understand what needs to be done:

This is just a basic solution, but it covers the biggest issue. Note that while I didn't particularly wrap your updatable properties in a single DTO, it's definitely worth considering doing so. I just kept it simpler for my example's purpose.

Clean coding advice

You've been given this feedback before, both in this question and the previous one, but the problem here is bigger than just what your question focuses on.

Using a silly example, if you ask "should I hold my breath when jumping in a pool of lava?", while technically not an answer to the literal question you're asking, the most sensical answer is "don't jump in a pool of lava to begin with".

Similarly, having too many method parameters is sign of a bad method design. Rather than finding ways to accommodate this design, it should be re-evaluated in its entirety so you never get to this problem area to begin with.

However, you asked your question with a very narrow scope, and it would require a broader view on the situation to find out how you should restructure your classes/methods in order to not end up with such a vast collection of optional parameters.

Your Answer

Reminder: Answers generated by artificial intelligence tools are not allowed on Software Engineering Stack Exchange. Learn more

Sign up or log in

Post as a guest.

Required, but never shown

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy .

Not the answer you're looking for? Browse other questions tagged java methods parameters null or ask your own question .

The Overflow Blog
One of the best ways to get value for AI coding tools: generating tests
The world’s largest open-source business has plans for enhancing LLMs
Featured on Meta
User activation: Learnings and opportunities
Site maintenance - Mon, Sept 16 2024, 21:00 UTC to Tue, Sept 17 2024, 2:00...

Hot Network Questions

Rocky Mountains Elevation Cutout
On the history of algae classification
How to NDSolve stiff ODE?
In Photoshop, when saving as PNG, why is the size of my output file bigger when I have more invisible layers in the original file?
Convert base-10 to base-0.1
security concerns of executing mariadb-dump with password over ssh
how to smooth a road while holding max and min z points constant?
Function with memories of its past life
Browse a web page through SSH? (Need to access router web interface remotely, but only have SSH access to a different device on LAN)
Is a thing just a class with only one member?
If Act A repeals another Act B, and Act A is repealed, what happens to the Act B?
The meaning of an implication in an existential quantifier
Multi-producer, multi-consumer blocking queue
Custom PCB with Esp32-S3 isn't recognised by Device Manager for every board ordered
What properties of the fundamental group functor are needed to uniquely determine it upto natural isomorphism?
How frequently is random number generated when plotting function containing RandomReal?
What's the difference between "Erase All Content and Settings" and using the Disk Utility to erase a Mac with Apple silicon
Who pays the cost of Star Alliance lounge usage for cross-airline access?
Why is resonance such a widespread phenomenon?
Movie where a young director's student film gets made (badly) by a major studio
Why do I often see bunches of medical helicopters hovering in clusters in various locations
History of the migration of ERA from AMS to AIMS in 2007
Fast leap year check
Ubuntu 22.04.5 - Final Point Release

Saved searches

Use saved searches to filter your results more quickly.

To see all available qualifiers, see our documentation .

Notifications You must be signed in to change notification settings

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement . We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Static Analysis#6 - Assignment of parameter 'X' is not allowed #11

minjyo commented Jun 17, 2020 • edited by dasd412 Loading

Resolution Method - parameter를 넘겨줄 때, 미리 할당해서 넘겨주기

dasd412 commented Jun 19, 2020

1.calculateTime()호출 하기 전 미리 calendar.getInstance() 호출하는 걸로 수정
2.return time에서 return (hour 60+sec);으로 수정하고 time 삭제

Sorry, something went wrong.

No branches or pull requests

Java SE > Java SE Specifications > Java Language Specification

Chapter 5. Conversions and Contexts

Chapter 5. Conversions and Contexts

Table of Contents

Every expression written in the Java programming language either produces no result ( §15.1 ) or has a type that can be deduced at compile time ( §15.3 ). When an expression appears in most contexts, it must be compatible with a type expected in that context; this type is called the target type . For convenience, compatibility of an expression with its surrounding context is facilitated in two ways:

First, for some expressions, termed poly expressions ( §15.2 ), the deduced type can be influenced by the target type. The same expression can have different types in different contexts.

Second, after the type of the expression has been deduced, an implicit conversion from the type of the expression to the target type can sometimes be performed.

If neither strategy is able to produce the appropriate type, a compile-time error occurs.

The rules determining whether an expression is a poly expression, and if so, its type and compatibility in a particular context, vary depending on the kind of context and the form of the expression. In addition to influencing the type of the expression, the target type may in some cases influence the run time behavior of the expression in order to produce a value of the appropriate type.

Similarly, the rules determining whether a target type allows an implicit conversion vary depending on the kind of context, the type of the expression, and, in one special case, the value of a constant expression ( §15.28 ). A conversion from type S to type T allows an expression of type S to be treated at compile time as if it had type T instead. In some cases this will require a corresponding action at run time to check the validity of the conversion or to translate the run-time value of the expression into a form appropriate for the new type T .

Example 5.0-1. Conversions at Compile Time and Run Time

A conversion from type Object to type Thread requires a run-time check to make sure that the run-time value is actually an instance of class Thread or one of its subclasses; if it is not, an exception is thrown.

A conversion from type Thread to type Object requires no run-time action; Thread is a subclass of Object , so any reference produced by an expression of type Thread is a valid reference value of type Object .

A conversion from type int to type long requires run-time sign-extension of a 32-bit integer value to the 64-bit long representation. No information is lost.

A conversion from type double to type long requires a non-trivial translation from a 64-bit floating-point value to the 64-bit integer representation. Depending on the actual run-time value, information may be lost.

The conversions possible in the Java programming language are grouped into several broad categories:

Identity conversions

Widening primitive conversions

Narrowing primitive conversions

Widening reference conversions

Narrowing reference conversions

Boxing conversions

Unboxing conversions

Unchecked conversions

Capture conversions

String conversions

Value set conversions

There are six kinds of conversion contexts in which poly expressions may be influenced by context or implicit conversions may occur. Each kind of context has different rules for poly expression typing and allows conversions in some of the categories above but not others. The contexts are:

Assignment contexts ( §5.2 , §15.26 ), in which an expression's value is bound to a named variable. Primitive and reference types are subject to widening, values may be boxed or unboxed, and some primitive constant expressions may be subject to narrowing. An unchecked conversion may also occur.

Strict invocation contexts ( §5.3 , §15.9 , §15.12 ), in which an argument is bound to a formal parameter of a constructor or method. Widening primitive, widening reference, and unchecked conversions may occur.

Loose invocation contexts ( §5.3 , §15.9 , §15.12 ), in which, like strict invocation contexts, an argument is bound to a formal parameter. Method or constructor invocations may provide this context if no applicable declaration can be found using only strict invocation contexts. In addition to widening and unchecked conversions, this context allows boxing and unboxing conversions to occur.

String contexts ( §5.4 , §15.18.1 ), in which a value of any type is converted to an object of type String .

Casting contexts ( §5.5 ), in which an expression's value is converted to a type explicitly specified by a cast operator ( §15.16 ). Casting contexts are more inclusive than assignment or loose invocation contexts, allowing any specific conversion other than a string conversion, but certain casts to a reference type are checked for correctness at run time.

Numeric contexts ( §5.6 ), in which the operands of a numeric operator may be widened to a common type so that an operation can be performed.

The term "conversion" is also used to describe, without being specific, any conversions allowed in a particular context. For example, we say that an expression that is the initializer of a local variable is subject to "assignment conversion", meaning that a specific conversion will be implicitly chosen for that expression according to the rules for the assignment context.

Example 5.0-2. Conversions In Various Contexts

This program produces the output:

5.1. Kinds of Conversion

Specific type conversions in the Java programming language are divided into 13 categories.

5.1.1. Identity Conversion

A conversion from a type to that same type is permitted for any type.

This may seem trivial, but it has two practical consequences. First, it is always permitted for an expression to have the desired type to begin with, thus allowing the simply stated rule that every expression is subject to conversion, if only a trivial identity conversion. Second, it implies that it is permitted for a program to include redundant cast operators for the sake of clarity.

5.1.2. Widening Primitive Conversion

19 specific conversions on primitive types are called the widening primitive conversions :

byte to short , int , long , float , or double

short to int , long , float , or double

char to int , long , float , or double

int to long , float , or double

long to float or double

float to double

A widening primitive conversion does not lose information about the overall magnitude of a numeric value in the following cases, where the numeric value is preserved exactly:

from an integral type to another integral type

from byte , short , or char to a floating point type

from int to double

from float to double in a strictfp expression ( §15.4 )

A widening primitive conversion from float to double that is not strictfp may lose information about the overall magnitude of the converted value.

A widening primitive conversion from int to float , or from long to float , or from long to double , may result in loss of precision - that is, the result may lose some of the least significant bits of the value. In this case, the resulting floating-point value will be a correctly rounded version of the integer value, using IEEE 754 round-to-nearest mode ( §4.2.4 ).

A widening conversion of a signed integer value to an integral type T simply sign-extends the two's-complement representation of the integer value to fill the wider format.

A widening conversion of a char to an integral type T zero-extends the representation of the char value to fill the wider format.

Despite the fact that loss of precision may occur, a widening primitive conversion never results in a run-time exception ( §11.1.1 ).

Example 5.1.2-1. Widening Primitive Conversion

This program prints:

thus indicating that information was lost during the conversion from type int to type float because values of type float are not precise to nine significant digits.

5.1.3. Narrowing Primitive Conversion

22 specific conversions on primitive types are called the narrowing primitive conversions :

short to byte or char

char to byte or short

int to byte , short , or char

long to byte , short , char , or int

float to byte , short , char , int , or long

double to byte , short , char , int , long , or float

A narrowing primitive conversion may lose information about the overall magnitude of a numeric value and may also lose precision and range.

A narrowing primitive conversion from double to float is governed by the IEEE 754 rounding rules ( §4.2.4 ). This conversion can lose precision, but also lose range, resulting in a float zero from a nonzero double and a float infinity from a finite double . A double NaN is converted to a float NaN and a double infinity is converted to the same-signed float infinity.

A narrowing conversion of a signed integer to an integral type T simply discards all but the n lowest order bits, where n is the number of bits used to represent type T . In addition to a possible loss of information about the magnitude of the numeric value, this may cause the sign of the resulting value to differ from the sign of the input value.

A narrowing conversion of a char to an integral type T likewise simply discards all but the n lowest order bits, where n is the number of bits used to represent type T . In addition to a possible loss of information about the magnitude of the numeric value, this may cause the resulting value to be a negative number, even though chars represent 16-bit unsigned integer values.

A narrowing conversion of a floating-point number to an integral type T takes two steps:

In the first step, the floating-point number is converted either to a long , if T is long , or to an int , if T is byte , short , char , or int , as follows:

If the floating-point number is NaN ( §4.2.3 ), the result of the first step of the conversion is an int or long 0 .

Otherwise, if the floating-point number is not an infinity, the floating-point value is rounded to an integer value V , rounding toward zero using IEEE 754 round-toward-zero mode ( §4.2.3 ). Then there are two cases:

If T is long , and this integer value can be represented as a long , then the result of the first step is the long value V .

Otherwise, if this integer value can be represented as an int , then the result of the first step is the int value V .

Otherwise, one of the following two cases must be true:

The value must be too small (a negative value of large magnitude or negative infinity), and the result of the first step is the smallest representable value of type int or long .

The value must be too large (a positive value of large magnitude or positive infinity), and the result of the first step is the largest representable value of type int or long .

In the second step:

If T is int or long , the result of the conversion is the result of the first step.

If T is byte , char , or short , the result of the conversion is the result of a narrowing conversion to type T ( §5.1.3 ) of the result of the first step.

Despite the fact that overflow, underflow, or other loss of information may occur, a narrowing primitive conversion never results in a run-time exception ( §11.1.1 ).

Example 5.1.3-1. Narrowing Primitive Conversion

The results for char , int , and long are unsurprising, producing the minimum and maximum representable values of the type.

The results for byte and short lose information about the sign and magnitude of the numeric values and also lose precision. The results can be understood by examining the low order bits of the minimum and maximum int . The minimum int is, in hexadecimal, 0x80000000 , and the maximum int is 0x7fffffff . This explains the short results, which are the low 16 bits of these values, namely, 0x0000 and 0xffff ; it explains the char results, which also are the low 16 bits of these values, namely, '\u0000' and '\uffff' ; and it explains the byte results, which are the low 8 bits of these values, namely, 0x00 and 0xff .

Example 5.1.3-2. Narrowing Primitive Conversions that lose information

5.1.4. Widening and Narrowing Primitive Conversion

The following conversion combines both widening and narrowing primitive conversions:

byte to char

First, the byte is converted to an int via widening primitive conversion ( §5.1.2 ), and then the resulting int is converted to a char by narrowing primitive conversion ( §5.1.3 ).

5.1.5. Widening Reference Conversion

A widening reference conversion exists from any reference type S to any reference type T , provided S is a subtype ( §4.10 ) of T .

Widening reference conversions never require a special action at run time and therefore never throw an exception at run time. They consist simply in regarding a reference as having some other type in a manner that can be proved correct at compile time.

5.1.6. Narrowing Reference Conversion

Six kinds of conversions are called the narrowing reference conversions :

From any reference type S to any reference type T , provided that S is a proper supertype of T ( §4.10 ).

An important special case is that there is a narrowing reference conversion from the class type Object to any other reference type ( §4.12.4 ).

From any class type C to any non-parameterized interface type K , provided that C is not final and does not implement K .

From any interface type J to any non-parameterized class type C that is not final .

From any interface type J to any non-parameterized interface type K , provided that J is not a subinterface of K .

From the interface types Cloneable and java.io.Serializable to any array type T [] .

From any array type SC [] to any array type TC [] , provided that SC and TC are reference types and there is a narrowing reference conversion from SC to TC .

Such conversions require a test at run time to find out whether the actual reference value is a legitimate value of the new type. If not, then a ClassCastException is thrown.

5.1.7. Boxing Conversion

Boxing conversion converts expressions of primitive type to corresponding expressions of reference type. Specifically, the following nine conversions are called the boxing conversions :

From type boolean to type Boolean

From type byte to type Byte

From type short to type Short

From type char to type Character

From type int to type Integer

From type long to type Long

From type float to type Float

From type double to type Double

From the null type to the null type

This rule is necessary because the conditional operator ( §15.25 ) applies boxing conversion to the types of its operands, and uses the result in further calculations.

At run time, boxing conversion proceeds as follows:

If p is a value of type boolean , then boxing conversion converts p into a reference r of class and type Boolean , such that r .booleanValue() == p

If p is a value of type byte , then boxing conversion converts p into a reference r of class and type Byte , such that r .byteValue() == p

If p is a value of type char , then boxing conversion converts p into a reference r of class and type Character , such that r .charValue() == p

If p is a value of type short , then boxing conversion converts p into a reference r of class and type Short , such that r .shortValue() == p

If p is a value of type int , then boxing conversion converts p into a reference r of class and type Integer , such that r .intValue() == p

If p is a value of type long , then boxing conversion converts p into a reference r of class and type Long , such that r .longValue() == p

If p is a value of type float then:

If p is not NaN, then boxing conversion converts p into a reference r of class and type Float , such that r .floatValue() evaluates to p

Otherwise, boxing conversion converts p into a reference r of class and type Float such that r .isNaN() evaluates to true

If p is a value of type double , then:

If p is not NaN, boxing conversion converts p into a reference r of class and type Double , such that r .doubleValue() evaluates to p

Otherwise, boxing conversion converts p into a reference r of class and type Double such that r .isNaN() evaluates to true

If p is a value of any other type, boxing conversion is equivalent to an identity conversion ( §5.1.1 ).

If the value p being boxed is an integer literal of type int between -128 and 127 inclusive ( §3.10.1 ), or the boolean literal true or false ( §3.10.3 ), or a character literal between '\u0000' and '\u007f' inclusive ( §3.10.4 ), then let a and b be the results of any two boxing conversions of p . It is always the case that a == b .

Ideally, boxing a primitive value would always yield an identical reference. In practice, this may not be feasible using existing implementation techniques. The rule above is a pragmatic compromise, requiring that certain common values always be boxed into indistinguishable objects. The implementation may cache these, lazily or eagerly. For other values, the rule disallows any assumptions about the identity of the boxed values on the programmer's part. This allows (but does not require) sharing of some or all of these references. Notice that integer literals of type long are allowed, but not required, to be shared.

This ensures that in most common cases, the behavior will be the desired one, without imposing an undue performance penalty, especially on small devices. Less memory-limited implementations might, for example, cache all char and short values, as well as int and long values in the range of -32K to +32K.

A boxing conversion may result in an OutOfMemoryError if a new instance of one of the wrapper classes ( Boolean , Byte , Character , Short , Integer , Long , Float , or Double ) needs to be allocated and insufficient storage is available.

5.1.8. Unboxing Conversion

Unboxing conversion converts expressions of reference type to corresponding expressions of primitive type. Specifically, the following eight conversions are called the unboxing conversions :

From type Boolean to type boolean

From type Byte to type byte

From type Short to type short

From type Character to type char

From type Integer to type int

From type Long to type long

From type Float to type float

From type Double to type double

At run time, unboxing conversion proceeds as follows:

If r is a reference of type Boolean , then unboxing conversion converts r into r .booleanValue()

If r is a reference of type Byte , then unboxing conversion converts r into r .byteValue()

If r is a reference of type Character , then unboxing conversion converts r into r .charValue()

If r is a reference of type Short , then unboxing conversion converts r into r .shortValue()

If r is a reference of type Integer , then unboxing conversion converts r into r .intValue()

If r is a reference of type Long , then unboxing conversion converts r into r .longValue()

If r is a reference of type Float , unboxing conversion converts r into r .floatValue()

If r is a reference of type Double , then unboxing conversion converts r into r .doubleValue()

If r is null , unboxing conversion throws a NullPointerException

A type is said to be convertible to a numeric type if it is a numeric type ( §4.2 ), or it is a reference type that may be converted to a numeric type by unboxing conversion.

A type is said to be convertible to an integral type if it is an integral type, or it is a reference type that may be converted to an integral type by unboxing conversion.

5.1.9. Unchecked Conversion

Let G name a generic type declaration with n type parameters.

There is an unchecked conversion from the raw class or interface type ( §4.8 ) G to any parameterized type of the form G < T 1 ,..., T n > .

There is an unchecked conversion from the raw array type G [] k to any array type of the form G < T 1 ,..., T n > [] k . (The notation [] k indicates an array type of k dimensions.)

Use of an unchecked conversion causes a compile-time unchecked warning unless all type arguments T i (1 ≤ i ≤ n ) are unbounded wildcards ( §4.5.1 ), or the unchecked warning is suppressed by the SuppressWarnings annotation ( §9.6.4.5 ).

Unchecked conversion is used to enable a smooth interoperation of legacy code, written before the introduction of generic types, with libraries that have undergone a conversion to use genericity (a process we call generification). In such circumstances (most notably, clients of the Collections Framework in java.util ), legacy code uses raw types (e.g. Collection instead of Collection<String> ). Expressions of raw types are passed as arguments to library methods that use parameterized versions of those same types as the types of their corresponding formal parameters.

Such calls cannot be shown to be statically safe under the type system using generics. Rejecting such calls would invalidate large bodies of existing code, and prevent them from using newer versions of the libraries. This in turn, would discourage library vendors from taking advantage of genericity. To prevent such an unwelcome turn of events, a raw type may be converted to an arbitrary invocation of the generic type declaration to which the raw type refers. While the conversion is unsound, it is tolerated as a concession to practicality. An unchecked warning is issued in such cases.

5.1.10. Capture Conversion

Let G name a generic type declaration ( §8.1.2 , §9.1.2 ) with n type parameters A 1 ,..., A n with corresponding bounds U 1 ,..., U n .

There exists a capture conversion from a parameterized type G < T 1 ,..., T n > ( §4.5 ) to a parameterized type G < S 1 ,..., S n > , where, for 1 ≤ i ≤ n :

If T i is a wildcard type argument ( §4.5.1 ) of the form ? , then S i is a fresh type variable whose upper bound is U i [ A 1 := S 1 ,..., A n := S n ] and whose lower bound is the null type ( §4.1 ).

If T i is a wildcard type argument of the form ? extends B i , then S i is a fresh type variable whose upper bound is glb( B i , U i [ A 1 := S 1 ,..., A n := S n ] ) and whose lower bound is the null type.

glb( V 1 ,..., V m ) is defined as V 1 & ... & V m .

It is a compile-time error if, for any two classes (not interfaces) V i and V j , V i is not a subclass of V j or vice versa.

If T i is a wildcard type argument of the form ? super B i , then S i is a fresh type variable whose upper bound is U i [ A 1 := S 1 ,..., A n := S n ] and whose lower bound is B i .

Otherwise, S i = T i .

Capture conversion on any type other than a parameterized type ( §4.5 ) acts as an identity conversion ( §5.1.1 ).

Capture conversion is not applied recursively.

Capture conversion never requires a special action at run time and therefore never throws an exception at run time.

Capture conversion is designed to make wildcards more useful. To understand the motivation, let's begin by looking at the method java.util.Collections.reverse() :

The method reverses the list provided as a parameter. It works for any type of list, and so the use of the wildcard type List<?> as the type of the formal parameter is entirely appropriate.

Now consider how one would implement reverse() :

The implementation needs to copy the list, extract elements from the copy, and insert them into the original. To do this in a type-safe manner, we need to give a name, T , to the element type of the incoming list. We do this in the private service method rev() . This requires us to pass the incoming argument list, of type List<?> , as an argument to rev() . In general, List<?> is a list of unknown type. It is not a subtype of List<T> , for any type T . Allowing such a subtype relation would be unsound. Given the method:

the following code would undermine the type system:

So, without some special dispensation, we can see that the call from reverse() to rev() would be disallowed. If this were the case, the author of reverse() would be forced to write its signature as:

This is undesirable, as it exposes implementation information to the caller. Worse, the designer of an API might reason that the signature using a wildcard is what the callers of the API require, and only later realize that a type safe implementation was precluded.

The call from reverse() to rev() is in fact harmless, but it cannot be justified on the basis of a general subtyping relation between List<?> and List<T> . The call is harmless, because the incoming argument is doubtless a list of some type (albeit an unknown one). If we can capture this unknown type in a type variable X , we can infer T to be X . That is the essence of capture conversion. The specification of course must cope with complications, like non-trivial (and possibly recursively defined) upper or lower bounds, the presence of multiple arguments etc.

Mathematically sophisticated readers will want to relate capture conversion to established type theory. Readers unfamiliar with type theory can skip this discussion - or else study a suitable text, such as Types and Programming Languages by Benjamin Pierce, and then revisit this section.

Here then is a brief summary of the relationship of capture conversion to established type theoretical notions. Wildcard types are a restricted form of existential types. Capture conversion corresponds loosely to an opening of a value of existential type. A capture conversion of an expression e can be thought of as an open of e in a scope that comprises the top level expression that encloses e .

The classical open operation on existentials requires that the captured type variable must not escape the opened expression. The open that corresponds to capture conversion is always on a scope sufficiently large that the captured type variable can never be visible outside that scope. The advantage of this scheme is that there is no need for a close operation, as defined in the paper On Variance-Based Subtyping for Parametric Types by Atsushi Igarashi and Mirko Viroli, in the proceedings of the 16th European Conference on Object Oriented Programming (ECOOP 2002). For a formal account of wildcards, see Wild FJ by Mads Torgersen, Erik Ernst and Christian Plesner Hansen, in the 12th workshop on Foundations of Object Oriented Programming (FOOL 2005).

5.1.11. String Conversion

Any type may be converted to type String by string conversion .

A value x of primitive type T is first converted to a reference value as if by giving it as an argument to an appropriate class instance creation expression ( §15.9 ):

If T is boolean , then use new Boolean( x ) .

If T is char , then use new Character( x ) .

If T is byte , short , or int , then use new Integer( x ) .

If T is long , then use new Long( x ) .

If T is float , then use new Float( x ) .

If T is double , then use new Double( x ) .

This reference value is then converted to type String by string conversion.

Now only reference values need to be considered:

If the reference is null , it is converted to the string " null " (four ASCII characters n , u , l , l ).

Otherwise, the conversion is performed as if by an invocation of the toString method of the referenced object with no arguments; but if the result of invoking the toString method is null , then the string " null " is used instead.

The toString method is defined by the primordial class Object ( §4.3.2 ). Many classes override it, notably Boolean , Character , Integer , Long , Float , Double , and String .

See §5.4 for details of the string context.

5.1.12. Forbidden Conversions

Any conversion that is not explicitly allowed is forbidden.

5.1.13. Value Set Conversion

Value set conversion is the process of mapping a floating-point value from one value set to another without changing its type.

Within an expression that is not FP-strict ( §15.4 ), value set conversion provides choices to an implementation of the Java programming language:

If the value is an element of the float-extended-exponent value set, then the implementation may, at its option, map the value to the nearest element of the float value set. This conversion may result in overflow (in which case the value is replaced by an infinity of the same sign) or underflow (in which case the value may lose precision because it is replaced by a denormalized number or zero of the same sign).

If the value is an element of the double-extended-exponent value set, then the implementation may, at its option, map the value to the nearest element of the double value set. This conversion may result in overflow (in which case the value is replaced by an infinity of the same sign) or underflow (in which case the value may lose precision because it is replaced by a denormalized number or zero of the same sign).

Within an FP-strict expression ( §15.4 ), value set conversion does not provide any choices; every implementation must behave in the same way:

If the value is of type float and is not an element of the float value set, then the implementation must map the value to the nearest element of the float value set. This conversion may result in overflow or underflow.

If the value is of type double and is not an element of the double value set, then the implementation must map the value to the nearest element of the double value set. This conversion may result in overflow or underflow.

Within an FP-strict expression, mapping values from the float-extended-exponent value set or double-extended-exponent value set is necessary only when a method is invoked whose declaration is not FP-strict and the implementation has chosen to represent the result of the method invocation as an element of an extended-exponent value set.

Whether in FP-strict code or code that is not FP-strict, value set conversion always leaves unchanged any value whose type is neither float nor double .

5.2. Assignment Contexts

Assignment contexts allow the value of an expression to be assigned ( §15.26 ) to a variable; the type of the expression must be converted to the type of the variable.

Assignment contexts allow the use of one of the following:

an identity conversion ( §5.1.1 )

a widening primitive conversion ( §5.1.2 )

a widening reference conversion ( §5.1.5 )

a boxing conversion ( §5.1.7 ) optionally followed by a widening reference conversion

an unboxing conversion ( §5.1.8 ) optionally followed by a widening primitive conversion.

If, after the conversions listed above have been applied, the resulting type is a raw type ( §4.8 ), an unchecked conversion ( §5.1.9 ) may then be applied.

In addition, if the expression is a constant expression ( §15.28 ) of type byte , short , char , or int :

A narrowing primitive conversion may be used if the type of the variable is byte , short , or char , and the value of the constant expression is representable in the type of the variable.

A narrowing primitive conversion followed by a boxing conversion may be used if the type of the variable is:

Byte and the value of the constant expression is representable in the type byte .

Short and the value of the constant expression is representable in the type short .

Character and the value of the constant expression is representable in the type char .

The compile-time narrowing of constant expressions means that code such as:

is allowed. Without the narrowing, the fact that the integer literal 42 has type int would mean that a cast to byte would be required:

Finally, a value of the null type (the null reference is the only such value) may be assigned to any reference type, resulting in a null reference of that type.

It is a compile-time error if the chain of conversions contains two parameterized types that are not in the subtype relation ( §4.10 ).

An example of such an illegal chain would be:

The first three elements of the chain are related by widening reference conversion, while the last entry is derived from its predecessor by unchecked conversion. However, this is not a valid assignment conversion, because the chain contains two parameterized types, Comparable<Integer> and Comparable<String> , that are not subtypes.

If the type of the expression cannot be converted to the type of the variable by a conversion permitted in an assignment context, then a compile-time error occurs.

If the type of an expression can be converted to the type of a variable by assignment conversion, we say the expression (or its value) is assignable to the variable or, equivalently, that the type of the expression is assignment compatible with the type of the variable.

If the type of the variable is float or double , then value set conversion ( §5.1.13 ) is applied to the value v that is the result of the conversion(s):

If v is of type float and is an element of the float-extended-exponent value set, then the implementation must map v to the nearest element of the float value set. This conversion may result in overflow or underflow.

If v is of type double and is an element of the double-extended-exponent value set, then the implementation must map v to the nearest element of the double value set. This conversion may result in overflow or underflow.

The only exceptions that may arise from conversions in an assignment context are:

A ClassCastException if, after the conversions above have been applied, the resulting value is an object which is not an instance of a subclass or subinterface of the erasure ( §4.6 ) of the type of the variable.

This circumstance can only arise as a result of heap pollution ( §4.12.2 ). In practice, implementations need only perform casts when accessing a field or method of an object of parameterized type when the erased type of the field, or the erased return type of the method, differ from its unerased type.

An OutOfMemoryError as a result of a boxing conversion.

A NullPointerException as a result of an unboxing conversion on a null reference.

An ArrayStoreException in special cases involving array elements or field access ( §10.5 , §15.26.1 ).

Example 5.2-1. Assignment Conversion for Primitive Types

The following program, however, produces compile-time errors:

because not all short values are char values, and neither are all char values short values.

Example 5.2-2. Assignment Conversion for Reference Types

The following test program illustrates assignment conversions on reference values, but fails to compile, as described in its comments. This example should be compared to the preceding one.

Example 5.2-3. Assignment Conversion for Array Types

In this example:

The value of veclong cannot be assigned to a Long variable, because Long is a class type other than Object . An array can be assigned only to a variable of a compatible array type, or to a variable of type Object , Cloneable or java.io.Serializable .

The value of veclong cannot be assigned to vecshort , because they are arrays of primitive type, and short and long are not the same primitive type.

The value of cpvec can be assigned to pvec , because any reference that could be the value of an expression of type ColoredPoint can be the value of a variable of type Point . The subsequent assignment of the new Point to a component of pvec then would throw an ArrayStoreException (if the program were otherwise corrected so that it could be compiled), because a ColoredPoint array cannot have an instance of Point as the value of a component.

The value of pvec cannot be assigned to cpvec , because not every reference that could be the value of an expression of type ColoredPoint can correctly be the value of a variable of type Point . If the value of pvec at run time were a reference to an instance of Point[] , and the assignment to cpvec were allowed, a simple reference to a component of cpvec , say, cpvec[0] , could return a Point , and a Point is not a ColoredPoint . Thus to allow such an assignment would allow a violation of the type system. A cast may be used ( §5.5 , §15.16 ) to ensure that pvec references a ColoredPoint[] :

5.3. Invocation Contexts

Invocation contexts allow an argument value in a method or constructor invocation ( §8.8.7.1 , §15.9 , §15.12 ) to be assigned to a corresponding formal parameter.

Strict invocation contexts allow the use of one of the following:

Loose invocation contexts allow a more permissive set of conversions, because they are only used for a particular invocation if no applicable declaration can be found using strict invocation contexts. Loose invocation contexts allow the use of one of the following:

a boxing conversion ( §5.1.7 ) optionally followed by widening reference conversion

an unboxing conversion ( §5.1.8 ) optionally followed by a widening primitive conversion

If, after the conversions listed for an invocation context have been applied, the resulting type is a raw type ( §4.8 ), an unchecked conversion ( §5.1.9 ) may then be applied.

A value of the null type (the null reference is the only such value) may be assigned to any reference type.

If the type of the expression cannot be converted to the type of the parameter by a conversion permitted in a loose invocation context, then a compile-time error occurs.

If the type of an argument expression is either float or double , then value set conversion ( §5.1.13 ) is applied after the conversion(s):

If an argument value of type float is an element of the float-extended-exponent value set, then the implementation must map the value to the nearest element of the float value set. This conversion may result in overflow or underflow.

If an argument value of type double is an element of the double-extended-exponent value set, then the implementation must map the value to the nearest element of the double value set. This conversion may result in overflow or underflow.

The only exceptions that may arise in an invocation context are:

A ClassCastException if, after the type conversions above have been applied, the resulting value is an object which is not an instance of a subclass or subinterface of the erasure ( §4.6 ) of the corresponding formal parameter type.

Neither strict nor loose invocation contexts include the implicit narrowing of integer constant expressions which is allowed in assignment contexts. The designers of the Java programming language felt that including these implicit narrowing conversions would add additional complexity to the rules of overload resolution ( §15.12.2 ).

Thus, the program:

causes a compile-time error because the integer literals 12 and 2 have type int , so neither method m matches under the rules of overload resolution. A language that included implicit narrowing of integer constant expressions would need additional rules to resolve cases like this example.

5.4. String Contexts

String contexts apply only to an operand of the binary + operator which is not a String when the other operand is a String .

The target type in these contexts is always String , and a string conversion ( §5.1.11 ) of the non- String operand always occurs. Evaluation of the + operator then proceeds as specified in §15.18.1 .

5.5. Casting Contexts

Casting contexts allow the operand of a cast operator ( §15.16 ) to be converted to the type explicitly named by the cast operator.

Casting contexts allow the use of one of:

a narrowing primitive conversion ( §5.1.3 )

a widening and narrowing primitive conversion ( §5.1.4 )

a widening reference conversion ( §5.1.5 ) optionally followed by either an unboxing conversion ( §5.1.8 ) or an unchecked conversion ( §5.1.9 )

a narrowing reference conversion ( §5.1.6 ) optionally followed by either an unboxing conversion ( §5.1.8 ) or an unchecked conversion ( §5.1.9 )

a boxing conversion ( §5.1.7 ) optionally followed by a widening reference conversion ( §5.1.5 )

an unboxing conversion ( §5.1.8 ) optionally followed by a widening primitive conversion ( §5.1.2 ).

Value set conversion ( §5.1.13 ) is applied after the type conversion.

The compile-time legality of a casting conversion is as follows:

An expression of a primitive type may undergo casting conversion to another primitive type, by an identity conversion (if the types are the same), or by a widening primitive conversion, or by a narrowing primitive conversion, or by a widening and narrowing primitive conversion.

An expression of a primitive type may undergo casting conversion to a reference type without error, by boxing conversion.

An expression of a reference type may undergo casting conversion to a primitive type without error, by unboxing conversion.

An expression of a reference type may undergo casting conversion to another reference type if no compile-time error occurs given the rules in §5.5.1 .

The following tables enumerate which conversions are used in certain casting conversions. Each conversion is signified by a symbol:

- signifies no casting conversion allowed

≈ signifies identity conversion ( §5.1.1 )

ω signifies widening primitive conversion ( §5.1.2 )

η signifies narrowing primitive conversion ( §5.1.3 )

ω η signifies widening and narrowing primitive conversion ( §5.1.4 )

⇑ signifies widening reference conversion ( §5.1.5 )

⇓ signifies narrowing reference conversion ( §5.1.6 )

⊕ signifies boxing conversion ( §5.1.7 )

⊗ signifies unboxing conversion ( §5.1.8 )

In the tables, a comma between symbols indicates that a casting conversion uses one conversion followed by another. The type Object means any reference type other than the eight wrapper classes Boolean , Byte , Short , Character , Integer , Long , Float , Double .

Table 5.5-A. Casting conversions to primitive types

To →
From ↓
	≈	ω	ωη	ω	ω	ω	ω	-
	η	≈	η	ω	ω	ω	ω	-
	η	η	≈	ω	ω	ω	ω	-
	η	η	η	≈	ω	ω	ω	-
	η	η	η	η	≈	ω	ω	-
	η	η	η	η	η	≈	ω	-
	η	η	η	η	η	η	≈	-
	-	-	-	-	-	-	-	≈
	⊗	⊗,ω	-	⊗,ω	⊗,ω	⊗,ω	⊗,ω	-
	-	⊗	-	⊗,ω	⊗,ω	⊗,ω	⊗,ω	-
	-	-	⊗	⊗,ω	⊗,ω	⊗,ω	⊗,ω	-
	-	-	-	⊗	⊗,ω	⊗,ω	⊗,ω	-
	-	-	-	-	⊗	⊗,ω	⊗,ω	-
	-	-	-	-	-	⊗	⊗,ω	-
	-	-	-	-	-	-	⊗	-
	-	-	-	-	-	-	-	⊗
	⇓,⊗	⇓,⊗	⇓,⊗	⇓,⊗	⇓,⊗	⇓,⊗	⇓,⊗	⇓,⊗

Table 5.5-B. Casting conversions to reference types

To →
From ↓
	⊕	-	-	-	-	-	-	-	⊕,⇑
	-	⊕	-	-	-	-	-	-	⊕,⇑
	-	-	⊕	-	-	-	-	-	⊕,⇑
	-	-	-	⊕	-	-	-	-	⊕,⇑
	-	-	-	-	⊕	-	-	-	⊕,⇑
	-	-	-	-	-	⊕	-	-	⊕,⇑
	-	-	-	-	-	-	⊕	-	⊕,⇑
	-	-	-	-	-	-	-	⊕	⊕,⇑
	≈	-	-	-	-	-	-	-	⇑
	-	≈	-	-	-	-	-	-	⇑
	-	-	≈	-	-	-	-	-	⇑
	-	-	-	≈	-	-	-	-	⇑
	-	-	-	-	≈	-	-	-	⇑
	-	-	-	-	-	≈	-	-	⇑
	-	-	-	-	-	-	≈	-	⇑
	-	-	-	-	-	-	-	≈	⇑
	⇓	⇓	⇓	⇓	⇓	⇓	⇓	⇓	≈

5.5.1. Reference Type Casting

Given a compile-time reference type S (source) and a compile-time reference type T (target), a casting conversion exists from S to T if no compile-time errors occur due to the following rules.

If S is a class type:

If T is a class type, then either | S | <: | T |, or | T | <: | S |. Otherwise, a compile-time error occurs.

Furthermore, if there exists a supertype X of T , and a supertype Y of S , such that both X and Y are provably distinct parameterized types ( §4.5 ), and that the erasures of X and Y are the same, a compile-time error occurs.

If T is an interface type:

If S is not a final class ( §8.1.1 ), then, if there exists a supertype X of T , and a supertype Y of S , such that both X and Y are provably distinct parameterized types, and that the erasures of X and Y are the same, a compile-time error occurs.

Otherwise, the cast is always legal at compile time (because even if S does not implement T , a subclass of S might).

If S is a final class ( §8.1.1 ), then S must implement T , or a compile-time error occurs.

If T is a type variable, then this algorithm is applied recursively, using the upper bound of T in place of T .

If T is an array type, then S must be the class Object , or a compile-time error occurs.

If T is an intersection type, T 1 & ... & T n , then it is a compile-time error if there exists a T i (1 ≤ i ≤ n ) such that S cannot be cast to T i by this algorithm. That is, the success of the cast is determined by the most restrictive component of the intersection type.

If S is an interface type:

If T is an array type, then S must be the type java.io.Serializable or Cloneable (the only interfaces implemented by arrays), or a compile-time error occurs.

If T is a class or interface type that is not final ( §8.1.1 ), then if there exists a supertype X of T , and a supertype Y of S , such that both X and Y are provably distinct parameterized types, and that the erasures of X and Y are the same, a compile-time error occurs.

Otherwise, the cast is always legal at compile time (because even if T does not implement S , a subclass of T might).

If T is a class type that is final , then:

If S is not a parameterized type or a raw type, then T must implement S , or a compile-time error occurs.

Otherwise, S is either a parameterized type that is an invocation of some generic type declaration G , or a raw type corresponding to a generic type declaration G . Then there must exist a supertype X of T , such that X is an invocation of G , or a compile-time error occurs.

Furthermore, if S and X are provably distinct parameterized types then a compile-time error occurs.

If T is an intersection type, T 1 & ... & T n , then it is a compile-time error if there exists a T i (1 ≤ i ≤ n ) such that S cannot be cast to T i by this algorithm.

If S is a type variable, then this algorithm is applied recursively, using the upper bound of S in place of S .

If S is an intersection type A 1 & ... & A n , then it is a compile-time error if there exists an A i (1 ≤ i ≤ n ) such that A i cannot be cast to T by this algorithm. That is, the success of the cast is determined by the most restrictive component of the intersection type.

If S is an array type SC [] , that is, an array of components of type SC :

If T is a class type, then if T is not Object , then a compile-time error occurs (because Object is the only class type to which arrays can be assigned).

If T is an interface type, then a compile-time error occurs unless T is the type java.io.Serializable or the type Cloneable (the only interfaces implemented by arrays).

If T is an array type TC [] , that is, an array of components of type TC , then a compile-time error occurs unless one of the following is true:

TC and SC are the same primitive type.

TC and SC are reference types and type SC can undergo casting conversion to TC .

Example 5.5.1-1. Casting Conversion for Reference Types

Here, the first compile-time error occurs because the class types Long and Point are unrelated (that is, they are not the same, and neither is a subclass of the other), so a cast between them will always fail.

The second compile-time error occurs because a variable of type EndPoint can never reference a value that implements the interface Colorable . This is because EndPoint is a final type, and a variable of a final type always holds a value of the same run-time type as its compile-time type. Therefore, the run-time type of variable e must be exactly the type EndPoint , and type EndPoint does not implement Colorable .

Example 5.5.1-2. Casting Conversion for Array Types

This program compiles without errors and produces the output:

5.5.2. Checked Casts and Unchecked Casts

A cast from a type S to a type T is statically known to be correct if and only if S <: T ( §4.10 ).

A cast from a type S to a parameterized type ( §4.5 ) T is unchecked unless at least one of the following is true:

All of the type arguments ( §4.5.1 ) of T are unbounded wildcards

T <: S and S has no subtype X other than T where the type arguments of X are not contained in the type arguments of T .

A cast from a type S to a type variable T is unchecked unless S <: T .

A cast from a type S to an intersection type T 1 & ... & T n is unchecked if there exists a T i (1 ≤ i ≤ n ) such that a cast from S to T i is unchecked.

An unchecked cast from S to a non-intersection type T is completely unchecked if the cast from | S | to | T | is statically known to be correct. Otherwise, it is partially unchecked .

An unchecked cast from S to an intersection type T 1 & ... & T n is completely unchecked if, for all i (1 ≤ i ≤ n ), a cast from S to T i is either statically known to be correct or completely unchecked. Otherwise, it is partially unchecked .

An unchecked cast causes a compile-time unchecked warning, unless suppressed by the SuppressWarnings annotation ( §9.6.4.5 ).

A cast is checked if it is not statically known to be correct and it is not unchecked.

If a cast to a reference type is not a compile-time error, there are several cases:

The cast is statically known to be correct.

No run-time action is performed for such a cast.

The cast is a completely unchecked cast.

The cast is a partially unchecked or checked cast to an intersection type.

Where the intersection type is T 1 & ... & T n , then for all i (1 ≤ i ≤ n ), any run-time check required for a cast from S to T i is also required for the cast to the intersection type.

The cast is a partially unchecked cast to a non-intersection type.

Such a cast requires a run-time validity check. The check is performed as if the cast had been a checked cast between | S | and | T |, as described below.

The cast is a checked cast to a non-intersection type.

Such a cast requires a run-time validity check. If the value at run time is null , then the cast is allowed. Otherwise, let R be the class of the object referred to by the run-time reference value, and let T be the erasure ( §4.6 ) of the type named in the cast operator. A cast conversion must check, at run time, that the class R is assignment compatible with the type T , via the algorithm in §5.5.3 .

Note that R cannot be an interface when these rules are first applied for any given cast, but R may be an interface if the rules are applied recursively because the run-time reference value may refer to an array whose element type is an interface type.

5.5.3. Checked Casts at Run Time

Here is the algorithm to check whether the run-time type R of an object is assignment compatible with the type T which is the erasure ( §4.6 ) of the type named in the cast operator. If a run-time exception is thrown, it is a ClassCastException .

If R is an ordinary class (not an array class):

If T is a class type, then R must be either the same class ( §4.3.4 ) as T or a subclass of T , or a run-time exception is thrown.

If T is an interface type, then R must implement ( §8.1.5 ) interface T , or a run-time exception is thrown.

If T is an array type, then a run-time exception is thrown.

If R is an interface:

If T is a class type, then T must be Object ( §4.3.2 ), or a run-time exception is thrown.

If T is an interface type, then R must be either the same interface as T or a subinterface of T , or a run-time exception is thrown.

If R is a class representing an array type RC [] , that is, an array of components of type RC :

If T is an interface type, then a run-time exception is thrown unless T is the type java.io.Serializable or the type Cloneable (the only interfaces implemented by arrays).

This case could slip past the compile-time checking if, for example, a reference to an array were stored in a variable of type Object .

If T is an array type TC [] , that is, an array of components of type TC , then a run-time exception is thrown unless one of the following is true:

TC and RC are the same primitive type.

TC and RC are reference types and type RC can be cast to TC by a recursive application of these run-time rules for casting.

Example 5.5.3-1. Incompatible Types at Run Time

This program uses casts to compile, but it throws exceptions at run time, because the types are incompatible.

5.6. Numeric Contexts

Numeric contexts apply to the operands of an arithmetic operator.

Numeric contexts allow the use of:

A numeric promotion is a process by which, given an arithmetic operator and its argument expressions, the arguments are converted to an inferred target type T . T is chosen during promotion such that each argument expression can be converted to T and the arithmetic operation is defined for values of type T .

The two kinds of numeric promotion are unary numeric promotion ( §5.6.1 ) and binary numeric promotion ( §5.6.2 ).

5.6.1. Unary Numeric Promotion

Some operators apply unary numeric promotion to a single operand, which must produce a value of a numeric type:

If the operand is of compile-time type Byte , Short , Character , or Integer , it is subjected to unboxing conversion ( §5.1.8 ). The result is then promoted to a value of type int by a widening primitive conversion ( §5.1.2 ) or an identity conversion ( §5.1.1 ).

Otherwise, if the operand is of compile-time type Long , Float , or Double , it is subjected to unboxing conversion ( §5.1.8 ).

Otherwise, if the operand is of compile-time type byte , short , or char , it is promoted to a value of type int by a widening primitive conversion ( §5.1.2 ).

Otherwise, a unary numeric operand remains as is and is not converted.

After the conversion(s), if any, value set conversion ( §5.1.13 ) is then applied.

Unary numeric promotion is performed on expressions in the following situations:

Each dimension expression in an array creation expression ( §15.10.1 )

The index expression in an array access expression ( §15.10.3 )

The operand of a unary plus operator + ( §15.15.3 )

The operand of a unary minus operator - ( §15.15.4 )

The operand of a bitwise complement operator ~ ( §15.15.5 )

Each operand, separately, of a shift operator << , >> , or >>> ( §15.19 ).

A long shift distance (right operand) does not promote the value being shifted (left operand) to long .

Example 5.6.1-1. Unary Numeric Promotion

5.6.2. Binary Numeric Promotion

When an operator applies binary numeric promotion to a pair of operands, each of which must denote a value that is convertible to a numeric type, the following rules apply, in order:

If any operand is of a reference type, it is subjected to unboxing conversion ( §5.1.8 ).

Widening primitive conversion ( §5.1.2 ) is applied to convert either or both operands as specified by the following rules:

If either operand is of type double , the other is converted to double .

Otherwise, if either operand is of type float , the other is converted to float .

Otherwise, if either operand is of type long , the other is converted to long .

Otherwise, both operands are converted to type int .

After the conversion(s), if any, value set conversion ( §5.1.13 ) is then applied to each operand.

Binary numeric promotion is performed on the operands of certain operators:

The multiplicative operators * , / , and % ( §15.17 )

The addition and subtraction operators for numeric types + and - ( §15.18.2 )

The numerical comparison operators < , <= , > , and >= ( §15.20.1 )

The numerical equality operators == and != ( §15.21.1 )

The integer bitwise operators & , ^ , and | ( §15.22.1 )

In certain cases, the conditional operator ? : ( §15.25 )

Example 5.6.2-1. Binary Numeric Promotion

The example converts the ASCII character G to the ASCII control-G (BEL), by masking off all but the low 5 bits of the character. The 7 is the numeric value of this control character.


Chapter 4. Types, Values, and Variables		Chapter 6. Names

Disallow Reassignment of Function Parameters (no-param-reassign)

Assignment to variables declared as function parameters can be misleading and lead to confusing behavior, as modifying function parameters will also mutate the arguments object. Often, assignment to function parameters is unintended and indicative of a mistake or programmer error.

This rule can be also configured to fail when function parameters are modified. Side effects on parameters can cause counter-intuitive execution flow and make errors difficult to track down.

Rule Details

This rule aims to prevent unintended behavior caused by modification or reassignment of function parameters.

Examples of incorrect code for this rule:

Examples of correct code for this rule:

This rule takes one option, an object, with a boolean property "props" , and arrays "ignorePropertyModificationsFor" and "ignorePropertyModificationsForRegex" . "props" is false by default. If "props" is set to true , this rule warns against the modification of parameter properties unless they're included in "ignorePropertyModificationsFor" or "ignorePropertyModificationsForRegex" , which is an empty array by default.

Examples of correct code for the default { "props": false } option:

Examples of incorrect code for the { "props": true } option:

Examples of correct code for the { "props": true } option with "ignorePropertyModificationsFor" set:

Examples of correct code for the { "props": true } option with "ignorePropertyModificationsForRegex" set:

When Not To Use It

If you want to allow assignment to function parameters, then you can safely disable this rule.

Class ParameterAssignmentCheck

java.lang.Object
com.puppycrawl.tools.checkstyle.AbstractAutomaticBean
com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter
com.puppycrawl.tools.checkstyle.api.AbstractCheck
com.puppycrawl.tools.checkstyle.checks.coding.ParameterAssignmentCheck

Disallows assignment of parameters.

Rationale: Parameter assignment is often considered poor programming practice. Forcing developers to declare parameters as final is often onerous. Having a check ensure that parameters are never assigned would give the best of both worlds.

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

parameter.assignment

Nested Class Summary

Nested classes/interfaces inherited from class com.puppycrawl.tools.checkstyle. abstractautomaticbean, field summary.

Fields
Modifier and Type	Field	Description

< >
< < >>

Constructor Summary

Constructors
Constructor	Description
()

Method Summary

All Methods
Modifier and Type	Method	Description
	( rootAST)
	( ast)
	()
	()
	()
	( ast)
	( lambdaAst)
	( ast)
	( ast)
	( ast)
	( parametersAst)
	( ast)

Methods inherited from class com.puppycrawl.tools.checkstyle.api. AbstractCheck

Methods inherited from class com.puppycrawl.tools.checkstyle.api. abstractviolationreporter, methods inherited from class com.puppycrawl.tools.checkstyle. abstractautomaticbean, methods inherited from class java.lang. object, field detail, parameternamesstack, parameternames, constructor detail, parameterassignmentcheck, method detail, getdefaulttokens, getrequiredtokens, getacceptabletokens, checknestedident, visitmethoddef, visitlambda, visitmethodparameters, visitlambdaparameters, visitparameters.

Why is assignment to 'this' not allowed in java?

The error I get from the compiler is "The left hand side of an assignment must be a variable". My use case is deep copying, but is not really relevant.

In C++, one can assign to *this . *this 。-->

The question is not how to circumvent assignment to this . this 分配。--> It's very simple, but rather what rationale is there behind the decision not to make this a variable. this 一个变量。-->

Are the reasons technical or conceptual?

My guess so far - the possibility of rebuilding an Object in a random method is error-prone (conceptual), but technically possible.

EDIT Please restrain from variations of "because java specs say so". 编辑请避免使用“因为Java规范这么说”的变体。--> I would like to know the reason for the decision 这个决定的原因 -->

solution1 13 ACCPTED 2011-11-02 11:46:52

In C++, one can assign to *this 在C ++中，可以分配给 *this -->

Yes, but you can't do this = something in C++, which I actually believe is a closer match for what you're asking about on the Java side here. this = something C ++中的 this = something 功能，我实际上认为这与您在Java方面提出的要求更接近。-->

[...] what rationale is there behind the decision not to make this a variable. [...]决定不 this 进行可变的依据是什么？ -->

I would say clarity / readability.

this was chosen to be a reserved word, probably since it's not passed as an explicit argument to a method. this 选择是一个保留字，大概是因为它没有作为一个明确的参数的方法传递。--> Using it as an ordinary parameter and being able to reassign a new value to it, would mess up readability severely.

In fact, many people argue that you shouldn't change argument-variables at all, for this very reason.

Are the reasons technical or conceptual? 原因是技术上的还是概念上的？ -->

Mostly conceptual I would presume. A few technical quirks would arise though. If you could reassign a value to this , you could completely hide instance variables behind local variables for example. this 分配一个值，则可以将实例变量完全隐藏在局部变量后面。-->

My guess so far - the possibility of rebuilding an Object in a random method is error-prone (conceptual), but technically possible. 到目前为止，我的猜测-用随机方法重建对象的可能性容易出错（概念上），但在技术上是可行的。 -->

I'm not sure I understand this statement fully, but yes, error prone is probably the primary reason behind the decision to make it a keyword and not a variable.

solution2 5 2011-11-02 11:50:28

IMO, conceptual.

The this keyword is a short hand for "the reference to the object whose method you are currently executing". this 关键字是“对当前正在执行其方法的对象的引用”的简写。--> You can't change what that object is. It simply makes no sense in the Java execution model.

Since it makes no sense for this to change, there is no sense in making it a variable. this 更改没有任何意义，因此将其设置为变量是没有意义的。-->

(Note that in C++ you are assigning to *this , not this . And in Java there is no * operator and no real equivalent to it.) *this ，而不是 this 。在Java中，没有 * 运算符，也没有与之等效的实数。）-->

If you take the view that you could change the target object for a method in mid flight, then here are some counter questions. 可以在飞行中更改方法的目标对象，那么这里有一些反问。-->

What is the use of doing this? What problems would this (hypothetical) linguistic feature help you solve ... that can't be solved in a more easy-to-understand way?

How would you deal with mutexes? For instance, what would happen if you assign to this in the middle of a synchronized method ... and does the proposed semantic make sense? this 在一个synchronized方法的中间......并执行提出语义有意义吗？--> (The problem is that you either end up executing in synchronized method on an object that you don't have a lock on ... or you have to unlock the old this and lock the new this with the complications that that entails. And besides, how does this make sense in terms of what mutexes are designed to achieve?) this 并锁定新的 this ，这会带来复杂性。此外，这对于设计要实现的互斥锁有何意义？）-->

How would you make sense of something like this:

Sure you can ascribe a semantic to this but:

you've broken encapsulation of the subclass in a way that is hard to understand, and
you've not actually achieved anything particularly useful.

If you try seriously to answer these questions, I expect you'll come to the conclusion that it would have been a bad idea to implement this. (But if you do have satisfactory answers, I'd encourage you to write them up and post them as your own Answer to your Question!) 确实有满意的答案，我建议您将它们写下并发布为您对问题的自己的答案！）-->

But in reality, I doubt that the Java designers even gave this idea more than a moment's consideration. (And rightly so, IMO)

The *this = ... form of C++ is really just a shorthand for a sequence of assignments of the the attributes of the current object. *this = ... 形式实际上只是当前对象属性的一系列分配的简写形式。--> We can already do that in Java ... with a sequence of normal assignments. There is certainly no need for new syntax to support this. (How often does a class reinitialize itself from the state of another class?)

I note that you commented thus:

I wonder what the semantics of this = xy; this = xy; 的语义是什么 this = xy; --> should be. What do you think it should do? – JimmyB Nov 2 '11 at 12:18 Provided xy is of the right type, the reference of this would be set to xy , making the "original" object gc-eligible - kostja Nov 2 '11 at 12:24 xy 是正确的类型，则将 xy 的引用设置为 xy ，从而使“原始”对象具有gc资格 -kostja 2011年11月2日在12:24-->

That won't work.

The value of this is (effectively) passed by value to the method when the method is invoked. this 值（有效）按值传递给方法。--> The callee doesn't know where the this reference came from. this 引用来自何处。-->

Even if it did, that's only one place where the reference is held. Unless null is assigned in all places, the object cannot be eligible of garbage collection. null 否则该对象将不符合垃圾回收的条件。-->

Ignoring the fact that this is technically impossible, I do not think that your idea would be useful OR conducive to writing readable / maintainable code. Consider this:

Why would you want to do that? Supposing that the method name was something innocuous rather than kill , would you expect the method to be able to zap the value of mine ? kill ，您是否希望该方法能够改变 mine 的值？-->

I don't. In fact, I think that this would be a misfeature: useless and dangerous.

Even without these nasty "make it unreachable" semantics, I don't actually see any good use-cases for modifying this . this 好的用例。-->

solution3 4 2011-11-02 11:34:04

because this is final , 因为 this 是 final ， -->

this is keyword, not a variable. this 是关键字，不是变量。--> and you can't assign something to keyword. now for a min consider if it were a reference variable in design spec..and see the example below 一下它是否是设计规范中的参考变量。请参阅下面的示例-->

and it holds implicit reference to the object calling method. and it is used for reference purpose only, now consider you assign something to this so won't it break everything ? this 所以不会打破它的一切吗？-->

Example 例 -->

consider the following code from String class (Note: below code contains compilation error it is just to demonstrate OP the situation) String 类中的以下代码（注意：以下代码包含编译错误，仅用于演示OP的情况）-->

solution4 3 2011-11-02 11:42:20

this isn't even a variable. this 甚至都不是变量。--> It's a keyword, as defined in the Java Language Specification : Java语言规范中所定义，这是一个关键字：-->

When used as a primary expression, the keyword this denotes a value that is a reference to the object for which the instance method was invoked (§15.12), or to the object being constructed

So, it's not possible as it's not possible to assign a value to while . while 赋值。-->

solution5 1 2018-05-23 17:24:36

Assigning to (*this) in C++ performs a copy operation -- treating the object as a value-type . (*this) 会执行复制操作-将对象视为值类型。-->

Java does not use the concept of a value-type for classes. Object assignment is always by-reference . 是按引用进行的。-->

To copy an object as if it were a value-type: How do I copy an object in Java? 如何在Java中复制对象？ -->

The terminology used for Java is confusing though: Is Java “pass-by-reference” or “pass-by-value” Java是“按引用传递”还是“按值传递” -->

Answer: Java passes references by value. Java按值传递引用。 --> (from here ) 这里开始）-->

In other words, because Java never treats non-primitives as value-types, every class-type variable is a reference (effectively a pointer).

So when I say, "object assignment is always by-reference", it might be more technically accurate to phrase that as "object assignment is always by the value of the reference". 的值 ”。-->

The practical implication of the distinction drawn by Java always being pass-by-value is embodied in the question " How do I make my swap function in java? ", and its answer: You can't . 始终是按值传递的区分的实际含义体现在“ 如何在Java中创建交换函数？ ”问题中，其答案是：您不能。--> Languages such as C and C++ are able to provide swap functions because they, unlike Java, allow you to assign from any variable by using a reference to that variable -- thus allowing you to change its value (if non-const) without changing the contents of the object that it previously referenced. 任何变量进行赋值-从而允许您更改其值（如果为非常量）而无需更改先前引用的对象的内容。-->

It could make your head spin to try to think this all the way through, but here goes nothing...

Java class-type variables are always "references" which are effectively pointers. Java pointers are primitive types. Java assignment is always by the value of the underlying primitive (the pointer in this case). 总是通过基础原语（在这种情况下为指针）的值进行的。--> Java simply has no mechanism equivalent to C/C++ pass-by-reference that would allow you to indirectly modify a free-standing primitive type, which may be a "pointer" such as this . this 。-->

Additionally, it is interesting to note that C++ actually has two different syntaxes for pass-by-reference. 两种不同的语法用于传递引用。--> One is based on explicit pointers, and was inherited from the C language. The other is based on the C++ reference-type operator & . 引用类型的运算符 & 。--> [There is also the C++ smart pointer form of reference management, but that is more akin to Java-like semantics -- where the references themselves are passed by value.] 智能指针形式，但这更类似于Java的语义-引用本身通过值传递。]-->

Note: In the above discussion assign-by and pass-by are generally interchangeable terminology. 分配” 和“ 传递” 通常是可互换的术语。--> Underlying any assignment, is a conceptual operator function that performs the assignment based on the right-hand-side object being passed in. 运算符函数，该函数根据传入的右侧对象执行分配。-->

So coming back to the original question : If you could assign to this in Java, that would imply changing the value of the reference held by this . 回到原始问题：如果可以用Java分配给 this ，则意味着更改 this 所持有的引用的值。--> That is actually equivalent to assigning directly to this in C++, which is not legal in that language either. this 分配，这在该语言中也不合法。-->

In both Java and C++, this is effectively a pointer that cannot be modified. this 实际上都是无法修改的指针。--> Java seems different because it uses the . 似乎有所不同，因为它使用 . --> operator to dereference the pointer -- which, if you're used to C++ syntax, gives you the impression that it isn't one.

You can , of course, write something in Java that is similar to a C++ copy constructor , but unlike with C++, there is no way of getting around the fact that the implementation will need to be supplied in terms of an explicit member-wise initialization. 可以用Java编写类似于C ++ 复制构造函数的内容，但是与C ++不同，没有办法避免这样的事实，即需要以显式的成员初始化方式提供实现。。--> [In C++ you can avoid this, ultimately, only because the compiler will provide a member-wise implementation of the assignment operator for you.] 赋值运算符的成员实现。-->

The Java limitation that you can't copy to this as a whole is sort-of artificial though. this 作为一个整体排序的人造虽然。--> You can achieve exactly the same result by writing it out member-wise, but the language just doesn't have a natural way of specifying such an operation to be performed on a this -- the C++ syntax, (*this) doesn't have an analogue in Java. 可以通过以成员方式将其写入来获得完全相同的结果，但是该语言只是没有一种自然的方式来指定要在 this 上执行的此类操作-C ++语法， (*this) 却没有在Java中有一个类似物。--> And, in fact, there is no built-in operation in Java that reassigns the contents of any existing object -- even if it's not referred to as this . 而且，实际上，Java中没有内置的操作可以重新分配任何现有对象的内容-即使未将其称为 this 。 --> [Such an operation is probably more important for stack-based objects such as are common in C++.]

Regarding the use-case of performing a deep copy : It's complicated in Java . 深层复制的用例：在Java中这很复杂。-->

For C++, a value-type-oriented language. The semantic intention of assignment is generally obvious. If I say a=b , I typically want a to become and independent clone of b , containing an equal value . a=b ，我通常希望 a 成为 b 独立克隆，包含相等的值。--> C++ does this automatically for assignment , and there are plans to automate the process, also, for the comparison. C ++会自动执行此任务以进行赋值，并计划自动进行该过程以及进行比较。-->

For Java, and other reference-oriented languages, copying an object, in a generic sense, has ambiguous meaning. Primitives aside, Java doesn't differentiate between value-types and reference-types , so copying an object has to consider every nested class-type member (including those of the parent) and decide, on a case-by-case basis, if that member object should be copied or just referenced. Java不会区分值类型和引用类型，因此复制对象必须考虑每个嵌套的类类型成员（包括父类的成员），并根据具体情况确定是否该成员对象应该被复制或被引用。--> If left to default implementations, there is a very good chance that result would not be what you want. 如果留给默认实现，则很有可能结果不是您想要的。 --> Comparing objects for equality in Java suffers from the same ambiguities . 比较对象是否相等存在相同的歧义。-->

Based on all of this, the answer to the underlying question : why can't I copy an object by some simple, automatically generated, operation on this , is that fundamentally, Java doesn't have a clear notion of what it means to copy an object . ，回答下面的问题：为什么我不能用一些简单的，自动生成，运行复制对象 this 是从根本上，Java没有什么意思复制一个清晰的概念，一个对象。-->

One last point, to answer the literal question:

What rationale is there behind the decision not to make this a variable? this 变量作为变量的背后是什么原因？-->

It would simply be pointless to do so. The value of this is just a pointer that has been passed to a function, and if you were able to change the value of this , it could not directly affect whatever object, or reference, was used to invoke that method. this 的值只是传递给函数的指针，如果您能够更改 this 的值，则它不会直接影响用来调用该方法的任何对象或引用。--> After all, Java is pass-by-value.

solution6 1 2011-11-02 11:38:12

The this in Java is a part of the language, a key word, not a simple variable. this 是语言的一部分，是关键字，而不是简单的变量。--> It was made for accessing an object from one of its methods, not another object. Assigning another object to it would cause a mess. If you want to save another objects reference in your object, just create a new variable.

The reason is just conceptual. this was made for accessing an Object itself, for example to return it in a method. this 做是为了访问对象本身，例如通过方法返回它。--> Like I said, it would cause a mess if you would assign another reference to it. Tell me a reason why altering this would make sense. this 才有意义。-->

solution7 0 2011-11-03 01:09:59

Assigning to *this in C++ isn't equivalent to assigning this in Java. *this 在C ++中并不等同于分配 this 在Java中。--> Assigning this is, and it isn't legal in either language. this 是正确的，而且两种语言都不合法。-->

Related Question
Related Blog
Related Tutorials

The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:[email protected].

boolean-expression
assignment-operator
inheritance
polymorphism
concurrency
type-conversion
variable-assignment
type-parameter

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

View all journals
Explore content
About the journal
Publish with us
Sign up for alerts
Published: 14 September 2024

Datopotamab–deruxtecan plus durvalumab in early-stage breast cancer: the sequential multiple assignment randomized I-SPY2.2 phase 2 trial

Rebecca A. Shatsky 1 na1 ,
Meghna S. Trivedi 2 na1 ,
Christina Yau 3 ,
Rita Nanda ORCID: orcid.org/0000-0001-5248-0876 4 ,
Hope S. Rugo ORCID: orcid.org/0000-0001-6710-4814 3 ,
Marie Davidian 5 ,
Butch Tsiatis 5 ,
Anne M. Wallace 1 ,
A. Jo Chien 3 ,
Erica Stringer-Reasor 6 ,
Judy C. Boughey ORCID: orcid.org/0000-0003-3820-3228 7 ,
Coral Omene 8 , 9 ,
Mariya Rozenblit 10 ,
Kevin Kalinsky ORCID: orcid.org/0000-0002-3113-7902 11 ,
Anthony D. Elias 12 ,
Christos Vaklavas ORCID: orcid.org/0000-0002-9919-2748 13 ,
Heather Beckwith 14 ,
Nicole Williams 15 ,
Mili Arora 16 ,
Chaitali Nangia 17 ,
Evanthia T. Roussos Torres ORCID: orcid.org/0000-0002-0740-5102 18 ,
Brittani Thomas 19 ,
Kathy S. Albain 20 ,
Amy S. Clark 21 ,
Carla Falkson 22 ,
Dawn L. Hershman 2 ,
Claudine Isaacs ORCID: orcid.org/0000-0002-9646-1260 23 ,
Alexandra Thomas ORCID: orcid.org/0000-0001-9022-2229 24 ,
Jennifer Tseng 25 ,
Amy Sanford 26 ,
Kay Yeung 1 ,
Sarah Boles 1 ,
Yunni Yi Chen 3 ,
Laura Huppert 3 ,
Nusrat Jahan 6 ,
Catherine Parker 6 ,
Karthik Giridhar 7 ,
Frederick M. Howard 4 ,
M. Michele Blackwood 8 ,
Tara Sanft 10 ,
Natsuko Onishi ORCID: orcid.org/0000-0003-4495-9187 3 ,
Adam L. Asare 3 , 27 ,
Philip Beineke 27 ,
Peter Norwood 27 ,
Lamorna Brown-Swigart ORCID: orcid.org/0000-0003-2076-5177 3 ,
Gillian L. Hirst ORCID: orcid.org/0000-0002-4502-0035 3 ,
Jeffrey B. Matthews 3 ,
Brian Moore 24 ,
W. Fraser Symmans ORCID: orcid.org/0000-0002-1526-184X 28 ,
Elissa Price 3 ,
Diane Heditsian 3 ,
Barbara LeStage 3 ,
Jane Perlmutter 29 ,
Paula Pohlmann ORCID: orcid.org/0000-0001-7914-5162 28 ,
Angela DeMichele ORCID: orcid.org/0000-0003-1297-4251 21 ,
Douglas Yee ORCID: orcid.org/0000-0002-3387-4009 14 ,
Laura J. van ’t Veer ORCID: orcid.org/0000-0002-9838-8298 3 ,
Nola M. Hylton 3 &
Laura J. Esserman ORCID: orcid.org/0000-0001-9202-4568 3

Nature Medicine ( 2024 ) Cite this article

Metrics details

Breast cancer
Clinical trial design

Sequential adaptive trial designs can help accomplish the goals of personalized medicine, optimizing outcomes and avoiding unnecessary toxicity. Here we describe the results of incorporating a promising antibody–drug conjugate, datopotamab–deruxtecan (Dato-DXd) in combination with programmed cell death-ligand 1 inhibitor, durvalumab, as the first sequence of therapy in the I-SPY2.2 phase 2 neoadjuvant sequential multiple assignment randomization trial for high-risk stage 2/3 breast cancer. The trial includes three blocks of treatment, with initial randomization to different experimental agent(s) (block A), followed by a taxane-based regimen tailored to tumor subtype (block B), followed by doxorubicin–cyclophosphamide (block C). Subtype-specific algorithms based on magnetic resonance imaging volume change and core biopsy guide treatment redirection after each block, including the option of early surgical resection in patients predicted to have a high likelihood of pathologic complete response, which is the primary endpoint assessed when resection occurs. There are two primary efficacy analyses: after block A and across all blocks for six prespecified HER2-negative subtypes (defined by hormone receptor status and/or response-predictive subtypes). In total, 106 patients were treated with Dato-DXd/durvalumab in block A. In the immune-positive subtype, Dato-DXd/durvalumab exceeded the prespecified threshold for success (graduated) after block A; and across all blocks, pathologic complete response rates were equivalent to the rate expected for the standard of care (79%), but 54% achieved that result after Dato-DXd/durvalumab alone (block A) and 92% without doxorubicin–cyclophosphamide (after blocks A + B). The treatment strategy across all blocks graduated in the hormone-negative/immune-negative subtype. No new toxicities were observed. Stomatitis was the most common side effect in block A. No patients receiving block A treatment alone had adrenal insufficiency. Dato-DXd/durvalumab is a promising therapy combination that can eliminate standard chemotherapy in many patients, particularly the immune-positive subtype.

ClinicalTrials.gov registration: NCT01042379 .

This is a preview of subscription content, access via your institution

Access options

Access Nature and 54 other Nature Portfolio journals

Get Nature+, our best-value online-access subscription

24,99 € / 30 days

cancel any time

Subscribe to this journal

Receive 12 print issues and online access

195,33 € per year

only 16,28 € per issue

Buy this article

Purchase on SpringerLink
Instant access to full article PDF

Prices may be subject to local taxes which are calculated during checkout

Data availability

De-identified participant-level data and/or clinical specimens are made available to members of the research community upon approval of the I-SPY Data Access and Publications Committee. Details of the application and review process are available at https://www.quantumleaphealth.org/for-investigators/clinicians-proposal-submissions/ . I-SPY aims to make complete patient-level clinical datasets available for public access within 6 months of publication, as the data are complex and require significant annotation to ensure their usability.

Code availability

The statistical code used in this clinical trial is available to other investigators upon approval of the I-SPY Data Access and Publications Committee. Investigators interested in accessing the code may complete an application at https://www.quantumleaphealth.org/for-investigators/clinicians-proposal-submissions/ and include a brief description of the intended use. Access to the code may be granted upon approval of the request, subject to compliance with ethical guidelines and applicable institutional and regulatory requirements.

Siegel, R. L., Giaquinto, A. N. & Jemal, A. Cancer statistics, 2024. CA Cancer J. Clin. 74 , 12–49 (2024).

Article PubMed Google Scholar

Giaquinto, A. N. et al. Breast cancer Statistics, 2022. CA Cancer J. Clin. 72 , 524–541 (2022).

Swain, S. M., Whaley, F. S. & Ewer, M. S. Congestive heart failure in patients treated with doxorubicin. Cancer 97 , 2869–2879 (2003).

Article CAS PubMed Google Scholar

Harrington, D. & Parmigiani, G. I-SPY 2—a glimpse of the future of phase 2 drug development? N. Engl. J. Med. 375 , 7–9 (2016).

Das, S. & Lo, A. W. Re-inventing drug development: a case study of the I-SPY 2 breast cancer clinical trials program. Contemp. Clin. Trials 62 , 168–174 (2017).

Cortazar, P. et al. Pathological complete response and long-term clinical benefit in breast cancer: the CTNeoBC pooled analysis. Lancet 384 , 164–172 (2014).

I-SPY2 Trial Consortium et al. Association of event-free and distant recurrence–free survival with individual-level pathologic complete response in neoadjuvant treatment of stages 2 and 3 breast cancer. JAMA Oncol. 6 , 1355–1362 (2020).

Lavori, P. W. & Dawson, R. Introduction to dynamic treatment strategies and sequential multiple assignment randomization. Clin. Trials 11 , 393–399 (2014).

Article PubMed PubMed Central Google Scholar

Kidwell, K. M. SMART designs in cancer research: past, present, and future. Clin. Trials 11 , 445–456 (2014).

Li, W. et al. Predicting breast cancer response to neoadjuvant treatment using multi-feature MRI: results from the I-SPY 2 TRIAL. NPJ Breast Cancer 6 , 63 (2020).

Article CAS PubMed PubMed Central Google Scholar

Li, W. et al. Abstract P4-02-10: MRI models by response predictive subtype for predicting pathologic complete response. Cancer Res. 83 , abstr. P4-02-10 (2023).

Onishi, N. et al. Abstract P3-03-01: functional tumor volume at 3 and 6-week MRI as an indicator of patients with inferior outcome after neoadjuvant chemotherapy. Cancer Res. 82 , abstr. P3-03-01 (2022).

Wolf, D. M. et al. Redefining breast cancer subtypes to guide treatment prioritization and maximize response: predictive biomarkers across 10 cancer therapies. Cancer Cell 40 , 609–623.e6 (2022).

Piccart, M. et al. 70-gene signature as an aid for treatment decisions in early breast cancer: updated results of the phase 3 randomised MINDACT trial with an exploratory analysis by age. Lancet Oncol. 22 , 476–488 (2021).

Cardoso, F. et al. 70-gene signature as an aid to treatment decisions in early-stage breast cancer. N. Engl. J. Med. 375 , 717–729 (2016).

Göker, E. et al. Treatment response and 5-year distant metastasis-free survival outcome in breast cancer patients after the use of MammaPrint and BluePrint to guide preoperative systemic treatment decisions. Eur. J. Cancer 167 , 92–102 (2022).

Loibl, S. et al. A randomised phase II study investigating durvalumab in addition to an anthracycline taxane-based neoadjuvant therapy in early triple-negative breast cancer: clinical results and biomarker analysis of GeparNuevo study. Ann. Oncol. 30 , 1279–1288 (2019).

Foldi, J. et al. Neoadjuvant durvalumab plus weekly nab-paclitaxel and dose-dense doxorubicin/cyclophosphamide in triple-negative breast cancer. NPJ Breast Cancer 7 , 9 (2021).

Pusztai, L. et al. Durvalumab with olaparib and paclitaxel for high-risk HER2-negative stage II/III breast cancer: results from the adaptively randomized I-SPY2 trial. Cancer Cell 39 , 989–998.e5 (2021).

Okajima, D. et al. Datopotamab deruxtecan (Dato-DXd), a novel TROP2-directed antibody-drug conjugate, demonstrates potent antitumor activity by efficient drug delivery to tumor cells. Mol. Cancer Ther. 20 , 2329–2340 (2021).

Bardia, A. et al. Datopotamab deruxtecan in advanced or metastatic HR + /HER2 - and triple-negative breast cancer: results from the phase I TROPION-PanTumor01 Study. J. Clin. Oncol. 42 , 2281–2294 (2024).

McKenzie, J. A. et al. The effect of topoisomerase I inhibitors on the efficacy of T-cell-based cancer immunotherapy. J. Natl Cancer Inst. 110 , 777–786 (2018).

Iwai, T. et al. Topoisomerase I inhibitor, irinotecan, depletes regulatory T cells and up-regulates MHC class I and PD-L1 expression, resulting in a supra-additive antitumor effect when combined with anti-PD-L1 antibodies. Oncotarget 9 , 31411–31421 (2018).

Schmid, P. Datopotamab derutecan (Dato-DXd) + durvalumab (D) as first-line (1L) treatment for unresectable locally advanced/metastatic triple-negative breast cancer (a/mTNBC): updated results from BEGONIA, a phase Ib/II study. Ann. Oncol. 34 , S337 (2023).

Bardia, A. et al. TROPION-Breast03: a randomized phase III global trial of datopotamab deruxtecan ± durvalumab in patients with triple-negative breast cancer and residual invasive disease at surgical resection after neoadjuvant therapy. Ther. Adv. Med. Oncol. 16 , 17588359241248336 (2024).

Rugo, H. S. et al. Adaptive randomization of veliparib–carboplatin treatment in breast cancer. N. Engl. J. Med. 375 , 23–34 (2016).

Nanda, R. et al. Effect of pembrolizumab plus neoadjuvant chemotherapy on pathologic complete response in women with early-stage breast cancer. JAMA Oncol. 6 , 676–684 (2020).

Yau, C. et al. Residual cancer burden after neoadjuvant chemotherapy and long-term survival outcomes in breast cancer: a multicentre pooled analysis of 5161 patients. Lancet Oncol. 23 , 149–160 (2022).

Schmid, P. et al. Pembrolizumab for early triple-negative breast cancer. N. Engl. J. Med. 382 , 810–821 (2020).

Cardoso, F. et al. LBA21 KEYNOTE-756: phase III study of neoadjuvant pembrolizumab (pembro) or placebo (pbo) + chemotherapy (chemo), followed by adjuvant pembro or pbo + endocrine therapy (ET) for early-stage high-risk ER+/HER2– breast cancer. Ann. Oncol. 34 , S1260–S1261 (2023).

Article Google Scholar

Schneider, B. J. et al. Management of immune-related adverse events in patients treated with immune checkpoint inhibitor therapy: ASCO guideline update. J. Clin. Oncol. 39 , 4073–4126 (2021).

Symmans, W. F. et al. Measurement of residual breast cancer burden to predict survival after neoadjuvant chemotherapy. J. Clin. Oncol. 25 , 4414–4422 (2007).

National Cancer Institute. Common Terminology Criteria for Adverse Events (CTCAE) | Protocol Development | CTEP. https://ctep.cancer.gov/protocolDevelopment/electronic_applications/ctc.htm (2021).

Basch, E. et al. Development of the National Cancer Institute’s patient-reported outcomes version of the common terminology criteria for adverse events (PRO-CTCAE). J. Natl Cancer Inst. 106 , dju244 (2014).

Jacob, S. et al. Use of PROMIS to capture patient reported outcomes over time for patients on I-SPY2. J. Clin. Oncol. 41 , 611–611 (2023).

Pearman, T. P., Beaumont, J. L., Mroczek, D., O’Connor, M. & Cella, D. Validity and usefulness of a single‐item measure of patient‐reported bother from side effects of cancer therapy. Cancer 124 , 991–997 (2018).

Oken, M. M. et al. Toxicity and response criteria of the Eastern Cooperative Oncology Group. Am. J. Clin. Oncol. 5 , 649–655 (1982).

Beltran, P. J. et al. Ganitumab (AMG 479) inhibits IGF-II–dependent ovarian cancer growth and potentiates platinum-based chemotherapy. Clin. Cancer Res. 20 , 2947–2958 (2014).

Brahmer, J. R. et al. Society for Immunotherapy of Cancer (SITC) clinical practice guideline on immune checkpoint inhibitor-related adverse events. J. Immunother. Cancer 9 , e002435 (2021).

Haanen, J. et al. Management of toxicities from immunotherapy: ESMO Clinical Practice Guideline for diagnosis, treatment and follow-up. Ann. Oncol. 33 , 1217–1238 (2022).

Download references

Acknowledgements

Research reported in this paper was supported by the NCI of the National Institutes of Health (NIH) under award numbers P01CA210961 and U01CA225427 (to L.J.E. and N.M.H.). We acknowledge the generous support of the study sponsors and operations management, QLHC (2013 to present) and the Foundation for the NIH (2010 to 2012; to L.J.E.). We sincerely appreciate the ongoing support for the I-SPY2.2 trial from the Safeway Foundation, the William K. Bowes, Jr. Foundation, Give Breast Cancer the Boot and QLHC (all to L.J.E.) and the Breast Cancer Research Foundation (to L.J.E. and L.J.v.V.). We thank all the patients who volunteered to participate in I-SPY2. AstraZeneca provided funds and study drugs (datopotamab–deruxtecan and durvalumab). With the exception of QLHC, the funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript. We thank D. Wolf and J. Gibbs and the I-SPY patient advocates for all their important contributions to this work.

Author information

These authors contributed equally: Rebecca A. Shatsky, Meghna S. Trivedi.

Authors and Affiliations

University of California San Diego, San Diego, CA, USA

Rebecca A. Shatsky, Anne M. Wallace, Kay Yeung & Sarah Boles

Columbia University, New York, NY, USA

Meghna S. Trivedi & Dawn L. Hershman

University of California San Francisco, San Francisco, CA, USA

Christina Yau, Hope S. Rugo, A. Jo Chien, Yunni Yi Chen, Laura Huppert, Wen Li, Natsuko Onishi, Adam L. Asare, Lamorna Brown-Swigart, Gillian L. Hirst, Jeffrey B. Matthews, Elissa Price, Diane Heditsian, Barbara LeStage, Laura J. van ’t Veer, Nola M. Hylton & Laura J. Esserman

University of Chicago, Chicago, IL, USA

Rita Nanda & Frederick M. Howard

North Carolina State University, Raleigh, NC, USA

Marie Davidian & Butch Tsiatis

University of Alabama at Birmingham, Birmingham, AL, USA

Erica Stringer-Reasor, Nusrat Jahan & Catherine Parker

The Mayo Clinic, Rochester, MN, USA

Judy C. Boughey & Karthik Giridhar

Cooperman Barnabas Medical Center, New Brunswick, NJ, USA

Coral Omene & M. Michele Blackwood

Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, USA

Coral Omene

Yale University, New Haven, CT, USA

Mariya Rozenblit & Tara Sanft

Emory University, Atlanta, GA, USA

Kevin Kalinsky

University of Colorado, Denver, CO, USA

Anthony D. Elias

University of Utah Huntsman Cancer Institute, Salt Lake City, UT, USA

Christos Vaklavas

University of Minnesota, Minneapolis, MN, USA

Heather Beckwith & Douglas Yee

The Ohio State University, Columbus, OH, USA

Nicole Williams

University of California Davis, Davis, CA, USA

HOAG Family Cancer Institute, Newport Beach, CA, USA

Chaitali Nangia

University of Southern California, Los Angeles, CA, USA

Evanthia T. Roussos Torres

Sparrow Health System, Lansing, MI, USA

Brittani Thomas

Loyola University Chicago Stritch School of Medicine, Chicago, IL, USA

Kathy S. Albain

University of Pennsylvania, Philadelphia, PA, USA

Amy S. Clark & Angela DeMichele

University of Rochester Medical Center, Rochester, NY, USA

Carla Falkson

Lombardi Comprehensive Cancer Center Georgetown University, Washington, DC, USA

Claudine Isaacs

Wake Forest University, Winston-Salem, NC, USA

Alexandra Thomas & Brian Moore

City of Hope Orange County Lennar Foundation Cancer Center, Irvine, CA, USA

Jennifer Tseng

Sanford Health, Sioux Falls, SD, USA

Amy Sanford

Quantum Leap Healthcare Collaborative, San Francisco, CA, USA

Adam L. Asare, Philip Beineke & Peter Norwood

University of Texas MD Anderson Cancer Center, Houston, TX, USA

W. Fraser Symmans & Paula Pohlmann

The Gemini Group, Ann Arbor, MI, USA

Jane Perlmutter

You can also search for this author in PubMed Google Scholar

Contributions

Arm chaperone: R.A.S. and M.S.T. contributed equally to this work. Leadership: C.Y., H.S.R., R.N., B.M., J.P., P.P., A.D.M., D.Y., L.J.v.V., N.M.H. and L.J.E. Study design: C.Y., M.D., B. Tsiatis, A.D.M., D.Y., L.J.v.V., N.M.H. and L.J.E. Formal analysis: C.Y. and P.N. Enrolled patients: R.A.S., M.S.T., H.S.R., R.N., A.M.W., A.J.C., E.S.-R., J.C.B., C.O., M.R., K.K., A.D.E., C.V., H.B., N.W., M.A., C.N., E.T.R.T., B. Thomas, K.S.A., A.S.C., C.F., D.L.H., C.I., A.T., J.T., A.S., K.Y., S.B., Y.Y.C., L.H., N.J., C.P., K.G., F.M.H., M.M.B., T.S., A.D.M., D.Y. and L.J.E. Lab studies: L.B.-S., G.L.H. and L.J.v.V. Imaging/pathology: W.L., N.O., W.F.S. and N.M.H. Data management: A.L.A. and P.B. Administrative: G.L.H. and J.B.M. First draft: R.A.S., M.S.T., C.Y., P.N., J.B.M. and L.J.E. Editing and review: R.A.S., M.S.T., C.Y., H.S.R., R.N., M.D., B. Tsiatis, A.M.W., A.J.C., E.S.-R., J.C.B., C.O., M.R., K.K., A.D.E., C.V., H.B., N.W., M.A., C.N., E.T.R.T., B. Thomas, K.S.A., A.S.C., C.F., D.L.H., C.I., A.T., J.T., A.S., K.Y., S.B., Y.Y.C., L.H., N.J., C.P., K.G., F.M.H., M.M.B., T.S., W.L., N.O., A.L.A., P.B., P.N., L.B.-S., G.L.H., J.B.M., B.M., W.F.S., E.P., D.H., B.L.S., J.P., P.P., A.D.M., D.Y., L.J.v.V., N.M.H. and L.J.E.

Corresponding author

Correspondence to Laura J. Esserman .

Ethics declarations

Competing interests.

R.A.S. reports institutional research funding from OBI Pharma, QLHC, AstraZeneca and Gilead; serves on AstraZeneca and Stemline Advisory Boards and Gilead Speaker’s Bureau; and has a consultancy role with QLHC. M.S.T. reports institutional research funding from Lilly, Gilead Sciences, Phoenix Molecular Designs, AstraZeneca, Regeneron, Merck and Novartis. C.Y. reports institutional research grant from NCI/NIH; salary support and travel reimbursement from QLHC; US patent titled, ‘Breast cancer response prediction subtypes’ (no. 18/174,491); and University of California Inventor Share. R.N. reports research funding from Arvinas, AstraZeneca, BMS, Corcept Therapeutics, Genentech/Roche, Gilead, GSK, Merck, Novartis, OBI Pharma, OncoSec, Pfizer, Relay, Seattle Genetics, Sun Pharma and Taiho Oncology and advisory roles with AstraZeneca, BeyondSpring, Daiichi Sankyo, Exact Sciences, Fujifilm, GE, Gilead, Guardant Health, Infinity, iTeos, Merck, Moderna, Novartis, OBI, OncoSec, Pfizer, Sanofi, Seagen and Stemline. H.S.R. reports institutional research support from AstraZeneca, Daiichi Sankyo, F. Hoffmann-La Roche AG/Genentech, Gilead Sciences, Lilly, Merck & Co., Novartis Pharmaceuticals Corporation, Pfizer, Stemline Therapeutics, OBI Pharma, Ambrx and Greenwich Pharma and has advisory and consulting roles with Chugai, Puma, Sanofi, Napo and Mylan. M.D. reports research grants from NIH/NCI and NIH/NIA, and contracts from PCORI. A.J.C. reports institutional research funding from Merck, Amgen, Puma, Seagen, Pfizer and Olema and has advisory roles with AstraZeneca and Genentech. E.S.-R. reports grants from V Foundation, NIH and Susan G. Komen; institutional research funding from GSK, Seagen, Pfizer and Lilly; and consulting and honoraria from Novartis, Merck, Seagen, AstraZeneca and Lilly; is a Cancer Awareness Network Board member and receives support from ASCO and NCCN. J.C.B. reports institutional research funding from Eli Lilly and SymBioSis, participation on the Data Safety Monitoring Committee of Cairn Surgical and honoraria from PER, PeerView, OncLive, EndoMag and UpToDate. C.O. reports consulting fees from AstraZeneca, Guardant Health and Jazz Pharmaceuticals. K.K. reports advisory and consultant roles for Eli Lilly, Pfizer, Novartis, AstraZeneca, Daiichi Sankyo, Puma, 4D Pharma, OncoSec, Immunomedics, Merck, Seagen, Mersana, Menarini Silicon Biosystems, Myovant, Takeda, Biotheranostics, Regor, Gilead, Prelude Therapeutics, RayzeBio, eFFECTOR Therapeutics and Cullinan Oncology and reports institutional research funding from Genentech/Roche, Novartis, Eli Lilly, AstraZeneca, Daiichi Sankyo and Ascentage. A.D.E. reports support from Scorpion, Infinity and Deciphera. C.V. reports institutional research funding from Pfizer, Seagen, H3 Biomedicine/Eisai, AstraZeneca and CytomX; research funding to their previous institution from Genentech, Roche, Pfizer, Incyte, Pharmacyclics, Novartis, TRACON Pharmaceuticals, Innocrin Pharmaceuticals, Zymeworks and H3 Biomedicine; advisory and consulting roles with Guidepoint, Novartis, Seagen, Daiichi Sankyo, AstraZeneca and Cardinal Health; unpaid consulting with Genentech; and participation in non-CME activity with Gilead and AstraZeneca. N.W. reports participation on Gilead’s Advisory Board and honoraria from OncLive, NCCN and Total Health Conferencing. K.S.A. reports institutional research funding from AstraZeneca, Daiichi Sankyo, Seattle Genetics, QLHC and the IDSM committee at Seattle Genetics. A.S.C. reports institutional research funding from Novartis and Lilly. C.F. reports honoraria from Curio Science and OncLive and institutional research funding from Eli Lily. C.I. reports institutional research funding from Tesaro/GSK, Seattle Genetics, Pfizer, AstraZeneca, BMS, Genentech, Novartis and Regeneron; consultancy roles with AstraZeneca, Genentech, Gilead, ION, Merck, Medscape, MJH Holdings, Novartis, Pfizer, Puma and Seagen; and royalties from Wolters Kluwer (UpToDate) and McGraw Hill (Goodman and Gilman). A.T. owns stock at Johnson & Johnson, Gilead, Bristol Myers Squibb; reports participation on Pfizer’s Advisory Board: AstraZeneca; reports institutional research funding from Merck and Sanofi; and has royalties from UpToDate. J.T. serves as institutional principal investigator for clinical trial with Intuitive Surgical and is the Editor Lead for ABS, CGSO, SCORE, Breast Education Committee Track Leader, ASCO SESAP 19 and Breast Co-Chair, ACS. K.Y. received research support unrelated to this work and paid to the institution from Pfizer, Gilead, Seagen, Dantari Pharmaceuticals, Treadwell Therapeutics and Relay Therapeutics and support from American Cancer Society IRG grant (no. IRG-19-230-48-IRG), UC San Diego Moores Cancer Center, Specialized Cancer Center support grant NIH/NCI (P30CA023100) and Curebound Discovery Award (2023, 2024). L.H. reports advisory and consultancy roles with Pfizer, and AstraZeneca. K.G. reports participation in advisory boards with honoraria to the institution from AstraZeneca, Novartis, Puma Biotechnologies, Eli Lilly, Gilead, Exact Sciences, NeoGenomics and TerSera Therapeutics. F.M.H. reports consultancy for Novartis. T.S. reports honoraria from Hologic. A.L.A., P.B. and P.N. are employees of QLHC. G.L.H. reports an institutional research grant from NIH (1R01CA255442). W.F.S. reports shares in IONIS Pharmaceuticals and Eiger Biopharmaceuticals; received consulting fees from AstraZeneca; is a cofounder with equity in Delphi Diagnostics; and issued patents for: (1) a method to calculate residual cancer burden, and (2) genomic signature to measure sensitivity to endocrine therapy. J.P. reports honoraria from Methods in Clinical Research (Faculty SCION Workshop) and support from ASCO and Advocate Scholarship; AACR (SSP Program); and VIVLI, U Wisc SPORE (EAB), QuantumLEAD (COVID DSMB), PCORI; is a reviewer; and is an I-SPY advocate lead. P.P. reports institutional research funding from Genentech/Roche, Fabre-Kramer, Advanced Cancer Therapeutics, Caris Centers of Excellence, Pfizer, Pieris Pharmaceuticals, Cascadian Therapeutics, Bolt, Byondis, Seagen, Orum Therapeutics and Carisma Therapeutics; consulting fees from Personalized Cancer Therapy, OncoPlex Diagnostics, Immunonet BioSciences, Pfizer, HERON, Puma Biotechnology, Sirtex, Caris Life Sciences, Juniper, Bolt Biotherapeutics and AbbVie; honoraria from Dava Oncology, OncLive/MJH Life Sciences, Frontiers (Publisher), SABCS and ASCO; Speakers’ Bureau: Genentech/Roche (past); and US patent no. 8,486,413, US patent no. 8,501,417, US patent no. 9,023,362 and US patent no. 9,745,377; and uncompensated roles with Pfizer, Seagen and Jazz. A.D.M. reports institutional research funding from Novartis, Pfizer, Genentech and NeoGenomics and is a program chair of the Scientific Advisory Committee, ASCO. D.Y. reports research funding from NIH/NCI: P30CA 077598, P01CA234228-01 and R01CA251600; consulting fees from Martell Diagnostics; and honoraria and travel for speaking at the ‘International Breast Cancer Conference’. L.J.v.V. is a founding advisor and shareholder of Exai Bio and is a part-time employee and owns stock in Agendia. N.M.H. reports institutional research funding from NIH. L.J.E. reports funding from Merck & Co., participation on an advisory board for Blue Cross Blue Shield, and personal fees from UpToDate and is an unpaid board member of QLHC. All other authors declare no competing interests.

Peer review

Peer review information.

Nature Medicine thanks Barbara Pistilli and Sze-Huey Tan for their contribution to the peer review of this work. Primary Handling Editor: Ulrike Harjes, in collaboration with the Nature Medicine team.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary information.

Supplementary Figs. 1 and 2 and Tables 1–7.

Reporting Summary

Rights and permissions.

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and permissions

About this article

Cite this article.

Shatsky, R.A., Trivedi, M.S., Yau, C. et al. Datopotamab–deruxtecan plus durvalumab in early-stage breast cancer: the sequential multiple assignment randomized I-SPY2.2 phase 2 trial. Nat Med (2024). https://doi.org/10.1038/s41591-024-03267-1

Download citation

Received : 07 August 2024

Accepted : 23 August 2024

Published : 14 September 2024

DOI : https://doi.org/10.1038/s41591-024-03267-1

Share this article

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative

Quick links

Explore articles by subject
Guide to authors
Editorial policies

Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers
Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand
OverflowAI GenAI features for Teams
OverflowAPI Train & fine-tune LLMs
Labs The future of collective knowledge sharing
About the company Visit the blog

Collectives™ on Stack Overflow

Find centralized, trusted content and collaborate around the technologies you use most.

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

Get early access and see previews of new features.

Space is not allowed after parameter prefix ':'

My problem is i try to insert text that contain char : in my query

I have tried to put double backslash // before char : but still not working.

enclosing the query in single-quotes seems wrong. what context is this appearing in? – Nathan Hughes Commented Feb 10, 2015 at 3:50
Similar question was answered here stackoverflow.com/a/9461939/4454454 – MaxZoom Commented Feb 10, 2015 at 3:51
@NathanHughes i just update the info. there is no single quote for enclosing the query. this is when i put the query in log.info() – ggDeGreat Commented Feb 10, 2015 at 4:00
@MaxZoom using interceptor in one way, but i really dont know how to code it. i prefer other faster way, which something like put additional double backslash to make it worked. – ggDeGreat Commented Feb 10, 2015 at 4:05
4 wouldn't it be easier to add the values as parameters instead of hard-coding them? that way they would be out of the way at the time that hibernate parses this looking for named parameters. – Nathan Hughes Commented Feb 10, 2015 at 4:08

4 Answers 4

From my experience I will tell you. There are two scenarios 1) You want to specify a parameter in the query whose value set dynamically.

Here you wont get any problem if you are setting parameter with same name as "userId"; 2) You are typecasting the value

when you are doing this you have to use escape character otherwise hibernate will think that it is a parameter. And it will give an error "All parameters are not set " you can overcome this with writing code using escape character

So this will solve your problem. And if you are wrongly used forward slash instead of backward slash you will get the error "space is not allowed after prefix"

But I highly recommended you to use the CAST function instead of using "::" this operator ie select CAST(count(id) as integer) It is the better way of type casting and it will lead to minimal errors

1 i had the problem with assignment in mysql: @current_client_user_id := client_user_id – tibi Commented Apr 11, 2019 at 11:57

Here Hibernate is parsing an insert that contains a hard-coded value that has a colon in it. If you rewrite the insert to use parameters then Hibernate won't see the value as part of the statement.

I didn't solve this problem via Spring Boot and I have created a function (actually a procedure) and used it as a query and the problem has been solved.

The problem is that your RECORD column contains ":", so, Hibernate waits for a parameter after it. I hade the same problem of you

2 so help this person with a solution – tibi Commented Apr 11, 2019 at 11:56

Your Answer

Reminder: Answers generated by artificial intelligence tools are not allowed on Stack Overflow. Learn more

Sign up or log in

Post as a guest.

Required, but never shown

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy .

Not the answer you're looking for? Browse other questions tagged java oracle hibernate or ask your own question .

The Overflow Blog
One of the best ways to get value for AI coding tools: generating tests
The world’s largest open-source business has plans for enhancing LLMs
Featured on Meta
User activation: Learnings and opportunities
Site maintenance - Mon, Sept 16 2024, 21:00 UTC to Tue, Sept 17 2024, 2:00...
What does a new user need in a homepage experience on Stack Overflow?
Announcing the new Staging Ground Reviewer Stats Widget

Hot Network Questions

Concerns with newly installed floor tile
Why do I often see bunches of medical helicopters hovering in clusters in various locations
Why is the \[ThickSpace] character defined as 5/18 em instead of 1/4 em as in Unicode?
Custom PCB with Esp32-S3 isn't recognised by Device Manager for every board ordered
siunitx dollar per hour broken going from SI to qty
Why was Panama Railroad in poor condition when US decided to build Panama Canal in 1904?
Stuck as a solo dev
How can I analyze the anatomy of a humanoid species to create sounds for their language?
Browse a web page through SSH? (Need to access router web interface remotely, but only have SSH access to a different device on LAN)
Will "universal" SMPS work at any voltage in the range, even DC?
Is it defamatory to publish nonsense under somebody else's name?
Subject verb agreement - I as well as he is/am the culprit
Does SpaceX Starship have significant methane emissions?
Understanding symmetry in a double integral
If Act A repeals another Act B, and Act A is repealed, what happens to the Act B?
Copyright Fair Use: Is using the phrase "Courtesy of" legally acceptable when no permission has been given?
Do I have to use a new background that's been republished under the 2024 rules?
When I use \llap to overlap words, the space between the overlapped words and the rest of the text is too much: how do I fix it?
Is a thing just a class with only one member?
Unwanted text replacement of two hyphens with an em-dash
Is it safe to use the dnd 3.5 skill system in pathfinder 1e?
Drill perpendicular hole through thick lumber using handheld drill
Equation of Time (derivation Analemma)
How can I switch from MAG to TRU heading in a 737?

IMAGES

java
[Solved] JAVA Variable declaration not allowed here
What are Parameters in Java
What are Parameters in Java
How to call method with Parameters in Java?
Using an array as the parameter for a method in Java

VIDEO

Fix Exception occurred while executing 'put'
ICSE CLASS IX
#20. Assignment Operators in Java
Why is Multiple inheritance not allowed in C# or Java
Assignment operator in Java
Java for Testers

COMMENTS

java
In your if condition block, you are setting variable to null and it happens to be your method parameter. Instead of assigning the value to the method parameter, create a local variable and use it and return the value of the local variable from the method if at all it is intended.
Sonar violation on "disallowed assignment of parameters"
I suspect one of 2 things are happening here: 1 - There is a bug in the checkstyle plugin. 2 - The code sonar analysed is not quite the code you posted here. I believe that violation should apply in the following case: /**. * @param lastAccessTime the lastAccessTime to set. */. public void setLastAccessTime(Date lastAccessTime) lastAccessTime ...
Remove Assignments to Parameters
First, if a parameter is passed via reference, then after the parameter value is changed inside the method, this value is passed to the argument that requested calling this method. Very often, this occurs accidentally and leads to unfortunate effects. Even if parameters are usually passed by value (and not by reference) in your programming ...
Avoid Check for Null Statement in Java
It's usually a good practice to write code that fails early. So, if an API accepts multiple parameters that aren't allowed to be null, it's better to check for every non-null parameter as a precondition of the API. Let's look at two methods — one that fails early and one that doesn't:
Rules For Variable Declaration in Java
The first character must not be a digit. Blank spaces cannot be used in variable names. Java keywords cannot be used as variable names. Variable names are case-sensitive. There is no limit on the length of a variable name but by convention, it should be between 4 to 15 chars. Variable names always should exist on the left-hand side of ...
Parameter Passing Techniques in Java with Examples
Syntax: function_name(datatype variable_name) Actual Parameter: The variable or expression corresponding to a formal parameter that appears in the function or method call in the calling environment. Syntax: func_name(variable name(s)); Important methods of Parameter Passing. 1. Pass By Value: Changes made to formal parameter do not get transmitted back to the caller.
How to remove 'Assignment of Parameter 'variable' is not allowed'
How to remove 'Assignment of Parameter 'variable' is not allowed'I'm programming a Controller using Java and I'm checking the style. ... 'Assignment of Parameter 'variable' is not allowed. The line that it's on is: @RequestParam(value="variable", required=false) String variable ...
Parameter Passing Techniques in Java with Examples
Step 2: Inside the main method: Step 2.1: Declare an integer variable num and assign it the value 10. Step 2.2: Print the value of num before calling the method. Step 2.3: Call the modifyValue method, passing num as the actual parameter. Step 2.4: Print the value of num after calling the method.
Unchecked warning
Settings or Preferences | Editor | Inspections | Java | Compiler issues. Inspection options. Here you can find the description of settings available for the Unchecked warning inspection, and the reference of their default values. Ignore unchecked assignment. Not selected. Ignore unchecked generics array creation for vararg parameter. Not selected
Assignment to property of function parameter no-param-reassign
function createEmployee(emp) { // ⛔️ Assignment to property of function parameter 'emp'. eslint no-param-reassign. emp.name = 'bobby hadz'; emp.salary = 500; return emp; } The ESLint rule forbids assignment to function parameters because modifying a function's parameters also mutates the arguments object and can lead to confusing behavior.
Restrictions on Generics (The Java™ Tutorials > Learning the Java
To use Java generics effectively, you must consider the following restrictions: Cannot Instantiate Generic Types with Primitive Types. Cannot Create Instances of Type Parameters. Cannot Declare Static Fields Whose Types are Type Parameters. Cannot Use Casts or instanceof With Parameterized Types. Cannot Create Arrays of Parameterized Types.
Do Not Reassign Parameters · Java for small teams
Reassigning to parameters makes code harder to understand and provides no meaningful advantage over creating a new variable. If the method is large, it can be difficult to track the lifecycle of a parameter. Even within short methods, re-using parameters will cause problem. As the variable is being used to represent two separate concepts, it is ...
Java: Why not allow nulls in methods to represent optional parameters
It is not possible in Java to indicate in the type system if null is allowed or not. The default value for an uninitialized reference is null. This means a reference can be null for two reasons: There is a bug and the value was not properly initialized; It is intentionally null to indicate the lack of an optional value
Static Analysis#6
Resolution Method - parameter를 넘겨줄 때, 미리 할당해서 넘겨주기 Mode/Stopwatch.java - line 132 Mode/Stopwatch.java - line 137
Chapter 5. Conversions and Contexts
The contexts are: Assignment contexts (§5.2, §15.26), in which an expression's value is bound to a named variable. Primitive and reference types are subject to widening, values may be boxed or unboxed, and some primitive constant expressions may be subject to narrowing. An unchecked conversion may also occur.
no-param-reassign
Rule Details. This rule aims to prevent unintended behavior caused by modification or reassignment of function parameters. Examples of incorrect code for this rule: /*eslint no-param-reassign: "error"*/ function foo (bar) {. bar = 13; } function foo (bar) {. bar++;
ParameterAssignmentCheck (checkstyle 10.17.0 API)
Disallows assignment of parameters. Rationale: Parameter assignment is often considered poor programming practice. Forcing developers to declare parameters as final is often onerous. Having a check ensure that parameters are never assigned would give the best of both worlds. Parent is com.puppycrawl.tools.checkstyle.TreeWalker.
Why is assignment to 'this' not allowed in java?
It's a keyword, as defined in the Java Language Specification : When used as a primary expression, the keyword this denotes a value that is a reference to the object for which the instance method was invoked (§15.12), or to the object being constructed. So, it's not possible as it's not possible to assign a value to while .
Assignment to "in" mode parameter not allowed
The in mode in joueurActuel : in T_Joueur; is a guarantee you have given to the compiler that you will not update or modify joueurActuel in any way within the procedure where you declared this formal parameter. The fact that it's a record is nothing to do with the problem. joueurActuel.c1 := predColonne(joueurActuel.c1); is an attempt to modify joueurActuel, despite the guarantee.
Datopotamab-deruxtecan plus durvalumab in early-stage breast cancer
Here we describe the results of incorporating a promising antibody-drug conjugate, datopotamab-deruxtecan (Dato-DXd) in combination with programmed cell death-ligand 1 inhibitor, durvalumab ...
java
My problem is i try to insert text that contain char : in my query I have tried to put double backslash // before char : but still not working. ABNORMALLY.java.lang.IllegalArgumentException: org.

Avoid Check for Null Statement in Java

1. Overview

Further reading:

3. Handling null Through the API Contract

4. Automating API Contracts

4.2. Using IDE Support

5. Assertions

6. Avoiding Null Checks Through Coding Practices

6.2. Using Primitives Instead of Wrapper Classes

6.3. Empty Collections

7. Using Objects

8. Using Optional

8.2. Using Optional With Collections

8.3. Combining Optionals

9. Libraries

9.2. Using StringUtils

10. Conclusion

Parameter Passing Techniques in Java with Examples

Types of parameters:

Please Login to comment...

Improve your Coding Skills with Practice

What kind of Experience do you want to share?

How to remove 'Assignment of Parameter 'variable' is not allowed'

apkisbossin

systemhalted

Donate For Us

Java Tutorial

Control Statements

Java Programs

Java Inheritance

Java Polymorphism

Java Abstraction

Java Encapsulation

Java OOPs Misc

Java String

Java String Methods

Exception Handling

Java Inner Class

Java Multithreading

Java Synchronization

Java Networking

Java Applet

Java Reflection

Java Conversion

Java Byte Class

Java Compiler Class

CopyOnWriteArrayList

Java Math Methods

LinkedBlockingDeque

LinkedTransferQueue

Java Phaser Class

ArrayList Methods

Java Thread Methods

Java Projects

Latest Courses

Contact info

Interview Questions

Inspectopedia Help

Locating this inspection

Inspection options

# Table of Contents

# Assignment to property of function parameter no-param-reassign

# Disabling the no-param-reassign ESLint rule for a single line

# Disabling the no-param-reassign ESLint rule for an entire file

# Disabling the no-param-reassign ESLint rule globally

# Additional Resources

Borislav Hadzhiev

Stack Exchange Network

Java: Why not allow nulls in methods to represent optional parameters?

5 Answers 5

Non-Nullable Types

Parameter Defaults

Back to Your question

The problem

The solution?

Clean coding advice

Your Answer

Sign up or log in

Not the answer you're looking for? Browse other questions tagged java methods parameters null or ask your own question .

Hot Network Questions