import java.util.concurrent.CountDownLatch;
public class TestThread extends Thread{
CountDownLatch cd;
String threadName;
public TestThread(CountDownLatch cd,String threadName){
 this.cd=cd;
 this.threadName=threadName;

}
@Override
public void run() {
 System.out.println(threadName+" start working...");
 dowork();
 System.out.println(threadName+" end working and exit...");
 cd.countDown();//告訴同步類完成一個線程操作完成

}
private void dowork(){
 try {
 Thread.sleep(2000);
 System.out.println(threadName+" is working...");
 } catch (InterruptedException e) {
 // TODO Auto-generated catch block
 e.printStackTrace();
 }

}

}

import java.util.concurrent.CountDownLatch;
public class TsetCountDownLatch {

 public static void main(String[] args) {
 try {
  CountDownLatch cd = new CountDownLatch(3);// 表示一共有三個線程
  TestThread thread1 = new TestThread(cd, "thread1");
  TestThread thread2 = new TestThread(cd, "thread2");
  TestThread thread3 = new TestThread(cd, "thread3");
  thread1.start();
  thread2.start();
  thread3.start();
  cd.await();//等待所有線程完成
  System.out.println("All Thread finishd");
 } catch (InterruptedException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
 }
 }
}

 thread1 start working...
 thread2 start working...
 thread3 start working...
 thread2 is working...
 thread2 end working and exit...
 thread1 is working...
 thread3 is working...
 thread3 end working and exit...
 thread1 end working and exit...
 All Thread finishd