public CountDownLatch(int count) {
        if (count < 0) throw new IllegalArgumentException("count < 0");
        this.sync = new Sync(count);
 }

public class DownLoadWorker implements Runnable{
    private String url;
    private  CountDownLatch countDownLatch;

    public DownLoadWorker(String url, CountDownLatch countDownLatch) {
        this.url = url;
        this.countDownLatch = countDownLatch;
    }

    @Override
    public void run() {
        //省略無數(shù)業(yè)務(wù)代碼
        System.out.println("線程" + Thread.currentThread().getName() + "開始下載完成");
        countDownLatch.countDown();
    }
}

public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch=new CountDownLatch(5);
        //使用Stream 生成5個線程
        List<Thread> workers = Stream
                .generate(() -> new Thread(new DownLoadWorker("https://image.baidu.com/", countDownLatch)))
                .limit(5)
                .collect(toList());
        //運行線程
        workers.forEach(Thread::start);
        //等待線程完成
        countDownLatch.await();
        System.out.println("圖片已下載完~~~");
}

ExecutorService service = Executors.newFixedThreadPool(5);
final CountDownLatch latch = new CountDownLatch(5);
for(int x = 0; x < 5; x++) {
    service.submit(new Runnable() {
        public void run() {
            // do something
            latch.countDown();
        }
    });
}
latch.await();