Wait until all threads done

public void testThreadSync() {
    Thread[] threads = new Thread[TEST_THREAD_COUNT];
    final CountDownLatch latch = new CountDownLatch(TEST_THREAD_COUNT);
    for (int i = 0; i < TEST_THREAD_COUNT; i++) {
        threads[i] = new Thread(new Runnable() {    
            public void run() {
                try {
                    Thread.sleep(random.nextInt(100));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                latch.countDown();
            }
        });
        threads[i].start();
    }
    try {
        latch.await();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

import java.util.concurrent.CountDownLatch;

import java.lang.Thread;

CountDownLatch mDoneSignal = new CountDownLatch(TOTAL_THREADS);
-----------------------------------------------------------------

 Thread thread = new Thread(new Runnable() { //anonymous function
    @Override
public void run() {
        //code
        mDoneSignal.countDown();
}
});

Thread thread = new Thread(() -> {    //or lambda
    //code
    mDoneSignal.countDown();
});
-----------------------------------------------------------------

try {
    mDoneSignal.await();     //await block, until CountDownLatch countDown from TOTAL_THREADS to 0, then all thread ending and go to next
}catch(InterruptedException e){
    e.printStackTrace();
}

Reference 
https://www.cnblogs.com/zl1991/p/6930160.html