Easier way to synchronize 2 threads in Java?

Question

I wan't to be sure that some piece of my code within the main thread will be executed after some piece of code executed withing the secondary thread. Here's what I got:

    final Object lock = new Object();
    final Thread t = new Thread(new Runnable() {
        public void run() {
            synchronized(lock) {
                System.out.println("qwerty");
                lock.notify();
            }
        }
    });

    synchronized(lock) {
        t.start();
        lock.wait();
    }

    System.out.println("absolutely sure, qwerty is above");

1. Is it correct solution?
2. Any shorter ways to do the same?

Answer 1

Things like notify() and wait() are really low-level synchronization primitives.

You should use higher-level abstractions whenever possible, like in this case, say, a CountDownLatch.

The following is just an example that should get you started (for example the timeout issues aren't taken into account here):

    final CountDownLatch latch = new CountDownLatch(1);
    final Thread t = new Thread(new Runnable() {
        public void run() {
            System.out.println("qwerty");
            latch.countDown();
        }
    });

    t.start();
    latch.await();

    System.out.println("absolutely sure, qwerty as been printed");

Low-level things like wait and notify are really just low-level Java idiosynchrasies that you shouldn't be concerned with (unless you're writing concurrency APIs).

Additionally, I'd suggest reading the amazing book: Java Concurrency In Practice.