import java.util.concurrent.CountDownLatch;
 
class Aworker implements Runnable {
 private int num;
 private CountDownLatch begin;
 private CountDownLatch end;
 
 public Aworker(int num, final CountDownLatch begin, final CountDownLatch end) {
 this.num = num;
 this.begin = begin;
 this.end = end;
 }
 
 @Override
 public void run() {
 // TODO Auto-generated method stub
 try {
  System.out.println(num + "th people is ready");
  begin.await();  //準(zhǔn)備就緒
 } catch (InterruptedException e) {
  e.printStackTrace();
 } finally {
  end.countDown();  //計(jì)數(shù)器減一，到達(dá)終點(diǎn)
  System.out.println(num + "th people arrive");
 }
 }
}
 
public class Race {
 public static void main(String[] args) {
 int num = 10;
 CountDownLatch begin = new CountDownLatch(1);
 CountDownLatch end = new CountDownLatch(num);
 
 for (int i = 1; i <= num; i++) {
  new Thread(new Aworker(i, begin, end)).start();
 }
 
 try {
  Thread.sleep((long) (Math.random() * 5000));
 } catch (InterruptedException e1) {
  // TODO Auto-generated catch block
  e1.printStackTrace();
 } 
 System.out.println("judge say : run !");
 begin.countDown(); //裁判一聲令下開(kāi)始跑
 long startTime = System.nanoTime();
 try {
  end.await(); //等待結(jié)束
 } catch (InterruptedException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
 } finally {
  long endTime = System.nanoTime();
  System.out.println("judge say : all arrived !");
  System.out.println("spend time: " + (endTime - startTime));
 }
 }
}

1th people is ready
2th people is ready
4th people is ready
6th people is ready
3th people is ready
10th people is ready
8th people is ready
5th people is ready
7th people is ready
9th people is ready
judge say : run !
1th people arrive
4th people arrive
10th people arrive
5th people arrive
2th people arrive
judge say : all arrived !
9th people arrive
7th people arrive
8th people arrive
3th people arrive
6th people arrive
spend time: 970933