How to make sure all the subclass threads exited ?

Question

Having -

for (int i = 0; i<10 ; i++) {
            Runnable r = new Runnable(){...}
            new Thread(r).start();
        } 
// I want to continue here only after all the subclass threads before exited . 
...

How could I make sure all the subclass threads exited before I continue on after the for section ?

Does exist any solution besides keep all the Runnable's in a List<Runnable> and finally check its isAlive() for each element ?

Answer 1

How could I make sure all the subclass threads exited before I continue on after the for section ?

I'd use the ExecutorService classes. See the Java tutorial on them. Something like:

// create a thread pool with 10 workers
ExecutorService threadPool = Executors.newFixedThreadPool(10);
// or you can create an open-ended thread pool
// ExecutorService threadPool = Executors.newCachedThreadPool();
for (int i = 0; i < 10; i++) {
   threadPool.submit(new Runnable(){...});
}
// once we have submitted all jobs to the thread pool, it should be shutdown
threadPool.shutdown();

Then you can wait for them to finish with:

threadPool.awaitTermination(Long.MAX_VALUE, TimeUnit.MILLISECONDS);

If you still want to do your own threads then typically you keep them around in a List and call join() on each one of them:

List<Thread> threadList = new ArrayList<Thread>();
for (int i = 0; i < 10; i++) {
   Thread thread = new Thread(new Runnable(){...});
   thread.start();
   threadList.add(thread);
}
// this waits for all of the threads to finish before continuing
for (Thread thread : threadList) {
   thread.join();
}