What is the AtomicBoolean.compareAndSet() method in Java?

AtomicBoolean represents a boolean value that can be updated atomicallyAn atomic operation performs a single unit of work on a resource. No other operations are allowed on the same resource until the performing operation is finished.. AtomicBoolean is present in the java.util.concurrent.atomic package.

The compareAndSet method of AtomicBoolean will atomically set the given value as the current value if the already present value is equal to the expected value.

Syntax

public final boolean compareAndSet(boolean expect, boolean newValue)

Argument

This method takes two arguments:

  1. The expected value.
  2. The new updated value if the current value matches the expected value.

Return value

This method returns true if the current value is equal to the expected value and the new value is updated. Otherwise, false will be returned.

Code

The below code demonstrates how to use the compareAndSet method.

import java.util.concurrent.atomic.AtomicBoolean;
class compareSet
{
  public static void main(String[] args) {
    AtomicBoolean atomicBoolean = new AtomicBoolean(false);
    System.out.println("atomicBoolean value : " + atomicBoolean.get());
    boolean expectedValue = true, newValue = true;
    boolean isUpdated = atomicBoolean.compareAndSet(expectedValue, newValue);
    System.out.println("compareAndSet(true, true) is updated : " + isUpdated);
    
    System.out.println("\natomicBoolean value: " + atomicBoolean);
    expectedValue = false;
    isUpdated = atomicBoolean.compareAndSet(expectedValue, newValue);
    System.out.println("compareAndSet(false, true) is updated : " + isUpdated);
    
    System.out.println("atomicBoolean value: " + atomicBoolean);
    
  }
}

Explanation

  • Line 1: We import the AtomicBoolean class.

  • Line 6: We create a new object for the AtomicBoolean class with the name atomicBoolean and the value false.

  • Line 9: We create two boolean variables expectedVal and newVal, with values true and true, respectively.

  • Line 11: We call the compareAndGet method with expectedVal and newVal as arguments. This method will check if the expectedVal matches the actual value. In our case, the actual value is false, and expectedVal is true. Both values are not equal, so false will be returned.

  • Line 16: We change the value of the expectedVal variable to false.

  • Line 17: We call the compareAndGet method with expectedVal and newVal as arguments. This method will check if the expectedVal matches the actual value. In our case, the actual value is false, and expectedVal is false. Both values are equal, so the newVal (true) will be updated as the actual value, and true will be returned.

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