public class VideoConference implements Runnable{ 
  private final CountDownLatch countDownLatch; 
  private int number; 
  public VideoConference(int number) { 
    this.number = number; 
    this.countDownLatch = new CountDownLatch(number);//使用Number初始化其内部的计数器，当初始化完成后，不能再次初始化 
  } 
  public void arrive(String name){ 
    //每个需要同步的任务，在任务完成时，需要调用该方法 
    countDownLatch.countDown();//countDownLatch内部的计数器减1 
    System.out.print("arrive:"+name+"\n"); 
    try{ 
      countDownLatch.await();//await方法是线程进入休眠，当countDownLatch计数器为0时，将被唤醒 
      //线程被唤醒，在这里可以执行一系列任务 
      System.out.print("name:"+name + " say:let's start..." +"\n"); 
    }catch (InterruptedException e){ 
      e.printStackTrace(); 
    } 
  } 
  public void run(){ 
    System.out.print("has arrive:"+(number-countDownLatch.getCount())+"\n"); 
    try{ 
      countDownLatch.await();//await方法是线程进入休眠，当countDownLatch计数器为0时，将被唤醒 
      //线程被唤醒，在这里可以执行一系列任务 
      System.out.print("all arrived:"+(number-countDownLatch.getCount())+"\n"); 
    }catch (InterruptedException e){ 
      e.printStackTrace(); 
    } 
  } 
} 

public class Participant implements Runnable{ 
  private VideoConference videoConference; 
  private String name; 
 
  public Participant(String name, VideoConference videoConference) { 
    this.name = name; 
    this.videoConference = videoConference; 
  } 
  public void run(){ 
    try { 
      //do something 
      Thread.sleep(50); 
      // 
      videoConference.arrive(name); 
    }catch (InterruptedException e){ 
      e.printStackTrace(); 
    } 
  } 
 
  public static void main(String[] args){ 
    VideoConference videoConference = new VideoConference(10); 
    Thread videoThread = new Thread(videoConference); 
    videoThread.start(); 
    for(int i=0; i<10; i++){ 
      Thread thread = new Thread(new Participant("participant:"+i,videoConference)); 
      thread.start(); 
    } 
  } 
}