AtomicReference compareAndSet() method in Java with Examples

The compareAndSet() method of a AtomicReference class is used to Atomically sets the value to newValue to AtomicReference object, if the current value of AtomicReference object equal to the expectedValue and returns the true if operation is successful else return false. This method updates the value with memory semantics of setting as if the variable was declared volatile.

Syntax:

public final V compareAndSet(V expectedValue,
                             V newValue)

Parameters: This method accepts expectedValue which is the expected value and newValue which is the new value to set.

Return value: This method returns the witness value, which will be the same as the expected value if successful.

Below programs illustrate the compareAndSet() method:
Program 1:

// Java program to demonstrate
// AtomicReference.compareAndSet() method

import java.util.concurrent.atomic.AtomicReference;

public class GFG {
    public static void main(String[] args)
    {

        // create an atomic reference object.
        AtomicReference<Long> ref
            = new AtomicReference<Long>();

        // set some value
        ref.set(987654321L);

        // apply compareAndSet()
        boolean response
            = ref.compareAndSet(1234L,
                                999999L);

        // print value
        System.out.println(" Value is set = "
                           + response);
    }
}

Output:

Value is set = false

Program 2:

// Java program to demonstrate
// AtomicReference.compareAndSet() method

import java.util.concurrent.atomic.AtomicReference;

public class GFG {
    public static void main(String[] args)
    {

        // create an atomic reference object.
        AtomicReference<String> ref
            = new AtomicReference<String>();

        // set some value
        ref.set("Geeks For Geeks");

        // apply compareAndSet()
        boolean response
            = ref.compareAndSet(
                "Geeks For Geeks",
                "GFG");

        // print value
        System.out.println(" Value is set = "
                           + response);
    }
}

Output:

Value is set = true

References: https://docs.oracle.com/javase/10/docs/api/java/util/concurrent/atomic/AtomicReference.html#compareAndSet(V, V)