CountDownLatch小Demo

public class TestDemo {

    @Test
    public void testCountDownLatch() throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(5);

        for (int i = 0; i < 5; i++) {
            int k = i;
            new Thread(() -> {
                try {
                    Thread.sleep(100);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                } finally {
                    System.out.printf("%s同学作业写完了%n",k);
                    countDownLatch.countDown();//有一位同学写完作业就减一
                }
            }).start(); //开启子线程
        }

        System.out.println("班长等同学写完作业");
        countDownLatch.await(); //countDownLatch为0时await释放，主线程继续往下走
        System.out.println("所有同学作业写完，班长关教室");
    }
}

结果