A simple program showing Java synchronization behavior.

output

Starting thread.
Starting thread.
Starting thread.
Starting thread.
Starting thread.
Starting thread.
Starting thread.
Starting thread.
Entered guarded block
Starting thread.
Starting thread.
Starting thread.
Starting thread.
Entered guarded block
Starting thread.
Entered guarded block
Starting thread.
Starting thread.
Entered guarded block
Starting thread.
Entered guarded block
Starting thread.
Starting thread.
Entered guarded block
Starting thread.
Starting thread.
Entered guarded block
Entered guarded block
Starting thread.
Starting thread.
Starting thread.
Entered guarded block
Starting thread.
Entered guarded block
Entered guarded block
Entered guarded block
Starting thread.
Entered guarded block
Starting thread.
Entered guarded block
Starting thread.
Entered guarded block
Starting thread.
Starting thread.
Starting thread.
Entered guarded block
Entered guarded block
Starting thread.
Entered guarded block
Starting thread.
Entered guarded block
Starting thread.
Starting thread.
Entered guarded block
Starting thread.
Entered guarded block
Starting thread.
Entered guarded block
Starting thread.
Starting thread.
Entered guarded block
Starting thread.
Entered guarded block
Entered guarded block
Starting thread.
Starting thread.
Entered guarded block
Starting thread.
Entered guarded block
Entered guarded block
Starting thread.
Entered guarded block
Starting thread.
Entered guarded block
Starting thread.
Entered guarded block
Starting thread.
Starting thread.
Entered guarded block
Entered guarded block
Starting thread.
Entered guarded block
Starting thread.
Entered guarded block
Entered guarded block
Starting thread.
Entered guarded block
Entered guarded block
Entered guarded block
Entered guarded block
Done!
Entered guarded block
Entered guarded block
Entered guarded block
Entered guarded block
Entered guarded block
Entered guarded block
Entered guarded block
Entered guarded block
Entered guarded block
Entered guarded block
Notifying everyone.
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Done!
Exit

SyncTest.java

public class SyncTest {
    public void test1(int x) throws InterruptedException {
        synchronized (this) {
            System.out.println("Entered guarded block");
            if (x != 42) {
                wait();
            }
            System.out.println("Done!");
        }
    }

    public void test2() {
        synchronized (this) {
            System.out.println("Notifying everyone.");
            notifyAll();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        final SyncTest sync = new SyncTest();

        for (int i = 0; i < 50 ; i++) {
            final int x = i;
            (new Thread(new Runnable() {
                @Override
                public void run() {
                    System.out.println("Starting thread.");
                    try {
                        sync.test1(x);
                    } catch (InterruptedException e) {
                        System.out.println("Interrupted!");
                    }
                }
            })).start();
        }

        Thread.sleep(2000);

        (new Thread(new Runnable() {
            @Override
            public void run() {
                sync.test2();
            }
        })).start();

        Thread.sleep(2000);

        System.out.println("Exit");
    }
}