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The compareAndSet() method of a AtomicReferenceArray class is used to atomically sets the value of index i of AtomicReferenceArray to newValue, if the current value at index i of AtomicReferenceArray object is equal to the expectedValue.This method will return true if update is successful. Syntax:

public final boolean
       compareAndSet(
           int i, E expectedValue, E newValue)

Parameters: This method accepts:

i which is an index of AtomicReferenceArray to perform the operation,
expectedValue which is the expected value and
newValue which is the new value to set.

Return value: This method returns true if successful and false return indicates that the actual value was not equal to the expected value. Below programs illustrate the compareAndSet() method: Program 1:

Java

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

import java.util.concurrent.atomic.*;

public class GFG {
    public static void main(String[] args)
    {
        // create an atomic reference object.
        AtomicReferenceArray<Integer> ref
            = new AtomicReferenceArray<Integer>(3);

        // set some value
        ref.set(0, 1234);
        ref.set(1, 4322);

        // apply compareAndSet()
        boolean op1
            = ref.compareAndSet(0, 5434, 8913);
        boolean op2
            = ref.compareAndSet(1, 3236, 6543);

        // print
        System.out.println("Operation at index 0: "
                           + op1);
        System.out.println("Operation at index 0: "
                           + op2);
    }
}

Output:

Operation at index 0: false
Operation at index 0: false

Program 2:

Java

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

import java.util.concurrent.atomic.*;

public class GFG {
    public static void main(String[] args)
    {
        // create an atomic reference object.
        AtomicReferenceArray<String> ref
            = new AtomicReferenceArray<String>(3);

        // set some value
        ref.set(0, "GFG");
        ref.set(1, "JS");

        // apply compareAndSet()
        boolean op1
            = ref.compareAndSet(
                0, "GFG",
                "GEEKS FOR GEEKS");
        boolean op2
            = ref.compareAndSet(
                1, "JS",
                "JAVA SCRIPT");

        // print
        System.out.println("Operation at index 0: "
                           + op1);
        System.out.println("New value at index 0: "
                           + ref.get(0));
        System.out.println("Operation at index 1: "
                           + op2);
        System.out.println("New value at index 1: "
                           + ref.get(1));
    }
}

Output:

Operation at index 0: true
New value at index 0: GEEKS FOR GEEKS
Operation at index 1: true
New value at index 1: JAVA SCRIPT

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

AtomicReferenceArray compareAndSet() method in Java with Examples

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