AtomicLong compareAndSet() method in Java with examples

The Java.util.concurrent.atomic.AtomicLong.compareAndSet() is an inbuilt method in java that sets the value to the passed value in the parameter if the current value is equal to the expected value which is also passed in the parameter. The function returns a boolean value which gives us an idea if the update was done or not.

Syntax:

public final boolean compareAndSet(long expect,
                                       long val)

Parameters: The function accepts two mandatory parameters which are described below:

• expect: specifies the value that the atomic object should be.
• val: specifies the value to be updated if the atomic integer is equal to expect.

Return value: The function returns a boolean value, it returns true on success else false.

Below programs illustrate the above method:

Program 1:

// Java program that demonstrates
// the compareAndSet() function

import java.util.concurrent.atomic.AtomicLong;

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

        // Initially value as 0
        AtomicLong val = new AtomicLong(0);

        // Prints the updated value
        System.out.println("Previous value: "
                           + val);

        // Checks if previous value was 0
        // and then updates it
        boolean res = val.compareAndSet(0, 6);

        // Checks if the value was updated.
        if (res)
            System.out.println("The value was "
                               + "updated and it is "
                               + val);
        else
            System.out.println("The value was "
                               + "not updated");
    }
}

Output:

Previous value: 0
The value was updated and it is 6

Program 2:

// Java program that demonstrates
// the compareAndSet() function

import java.util.concurrent.atomic.AtomicLong;

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

        // Initially value as 0
        AtomicLong val = new AtomicLong(0);

        // Prints the updated value
        System.out.println("Previous value: "
                           + val);

        // Checks if previous value was 0
        // and then updates it
        boolean res = val.compareAndSet(10, 6);

        // Checks if the value was updated.
        if (res)
            System.out.println("The value was "
                               + "updated and it is "
                               + val);
        else
            System.out.println("The value was "
                               + "not updated");
    }
}

Output:

Previous value: 0
The value was not updated

Reference: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicLong.html#compareAndSet–