CountDownLatch，一个同步辅助类，在完成一组正在其他线程中执行的操作之前，它允许一个或多个线程一直等待。

主要方法

public CountDownLatch(int count);

public void countDown();

public void await() throws InterruptedException

构造方法参数指定了计数的次数

countDown方法，当前线程调用此方法，则计数减一

awaint方法，调用此方法会一直阻塞当前线程，直到计时器的值为0

package multiThread;import java.util.concurrent.CountDownLatch;public class Demon3 {    public static void main(String[] args) {        CountDownLatch countDownLatch = new CountDownLatch(3);        new MyThread(countDownLatch, "thread1").start();        new MyThread(countDownLatch, "thread2").start();        new MyThread(countDownLatch, "thread3").start();                  try {            //等待所有进程执行完            countDownLatch.await();            System.out.println("All thread stopped");        } catch (InterruptedException e) {            e.printStackTrace();        }    }}class MyThread extends Thread {          private CountDownLatch countDownLatch;    private String threadName;    public MyThread(CountDownLatch countDownLatch, String threadName) {        this.countDownLatch = countDownLatch;        this.threadName = threadName;    }    @Override    public void run() {                  System.out.println(threadName + "RUN!!");                  try {            Thread.sleep(10000);        } catch (InterruptedException e) {            e.printStackTrace();        }                  System.out.println(threadName + "Stopped!!");        countDownLatch.countDown(); //执行完减1    }      }