AtomicReferenceArray compareAndExchangeAcquire() method in Java with Examples

The compareAndExchangeAcquire() 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 which is referred to as the witness value is equal to the expectedValue.This method will return the witness value, which will be the same as the expected value. This method exchanges the value with memory ordering effects compatible with memory_order_acquire ordering.

Syntax:

public final boolean
       compareAndExchangeAcquire(
           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 the witness value, which will be the same as the expected value if successful.

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

// Java program to demonstrate
// compareAndExchangeAcquire() 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 compareAndExchangeAcquire()
        int oldV1
            = ref.compareAndExchangeAcquire(
                0, 1234, 8913);
        int oldV2
            = ref.compareAndExchangeAcquire(
                1, 4322, 6543);

        // print
        System.out.println(
            "Old value at index 0: "
            + oldV1);
        System.out.println(
            "Old value at index 1: "
            + oldV2);
    }
}

Output:

Program 2:

// Java program to demonstrate
// compareAndExchangeAcquire() 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 compareAndExchangeAcquire()
        String oldV1
            = ref.compareAndExchangeAcquire(
                0, "GFG",
                "GEEKS FOR GEEKS");
        String oldV2
            = ref.compareAndExchangeAcquire(
                1, "JS",
                "JAVA SCRIPT");

        // print
        System.out.println(
            "Old value at index 0: "
            + oldV1);
        System.out.println(
            "New value at index 0: "
            + ref.get(0));
        System.out.println(
            "Old value at index 1: "
            + oldV2);
        System.out.println(
            "New value at index 1: "
            + ref.get(1));
    }
}

Output:

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