java : CountDownLatch

package com.example.app;

import java.util.concurrent.CountDownLatch;
import java.util.stream.IntStream;

public class CountDownLatchTest {
    private static CountDownLatch countDownLatch=new CountDownLatch(5);
    public static void main(String[] args) throws InterruptedException {

        IntStream.range(0,5).forEach(i -> new Thread(
                new Runnable() {
                    @Override
                    public void run() {
                        try {
                            Thread.sleep(500);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        System.out.println(Thread.currentThread().getName()+ " will count down......");
                        countDownLatch.countDown();
                    }
                }
        ).start());

        countDownLatch.await();
        System.out.println("program will exit......");

    }
}