Difference between getAndSet and compareAndSet in AtomicBoolean

Question

The thread title should be self-explnatory... I\'m a bit confused between the specification of below methos from AtomicBoolean class:

• java.u

Answer 1

You can look at the code for better understanding :

public final boolean getAndSet(boolean newValue) {
    for (;;) {
        boolean current = get();
        if (compareAndSet(current, newValue))
            return current;
    }
}

In getAndSet, if the value of the boolean has changed between the time you get() the old value and the time you try to change its value, compareAndSet won't change its value. Therefore, getAndSet calls compareAndSet in a loop until the boolean is set to the new value.

As to your code example :

flag.getAndSet(false) returns the old value of the AtomicBoolean. On the other hand, flag.compareAndSet(x,false) (note there are two arguments) returns whether the AtomicBoolean was modified, or in other words, it returns whether the old value of the AtomicBoolean was x.