倒计时:CountDownLatch(火箭发射前的准备)读书笔记

public CountDownLatch(int count)

public class CountDownLatchDemo implements Runnable {
    static final CountDownLatch end = new CountDownLatch(10);
    static final CountDownLatchDemo demo = new CountDownLatchDemo();

    /**
     * When an object implementing interface <code>Runnable</code> is used
     * to create a thread, starting the thread causes the object‘s
     * <code>run</code> method to be called in that separately executing
     * thread.
     * <p>
     * The general contract of the method <code>run</code> is that it may
     * take any action whatsoever.
     *
     * @see Thread#run()
     */
    @Override
    public void run() {
        try {
            Thread.sleep(new Random().nextInt(10) * 1000);
            System.out.println("check complete");
            end.countDown();//完成 可以减1
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        ExecutorService exec = Executors.newFixedThreadPool(10);
        for (int i = 0; i < 10; i++) {
            exec.submit(demo);
        }
        end.await();//主线程等待所有10个线程完成任务 才能继续执行
        System.out.println("Fire!");
        exec.shutdown();
    }
}