What is the difference between synchronized and volatile in Java?

Point	synchronized	volatile
Applies to	Methods and blocks	Variables
Mutual exclusion	Yes (one thread at a time)	No
Visibility of changes	Yes	Yes
Atomic count++	Yes, inside a synchronized block	No
Cost	Higher (locking)	Low

Use volatile for a simple flag which one thread writes and others read. Use synchronized, a Lock or AtomicInteger when several steps must be done together.

public class Main {
    static volatile boolean running = true;

    public static void main(String[] args) throws InterruptedException {
        Thread worker = new Thread(() -> {
            long loops = 0;
            while (running) {
                loops++;
            }
            System.out.println("Worker stopped");
        });
        worker.start();
        Thread.sleep(200);
        running = false;                // the worker sees this change because of volatile
        worker.join();
    }
}

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