TestThread.java

package test.another;

import java.util.concurrent.CountDownLatch;

public class TestThread extends Thread{
	
	public static void main(String[] args) {
		CountDownLatch latch = new CountDownLatch(2);
		new Thread(new TestRunnable(latch, "1")).start();
		new Thread(new TestRunnable(latch, "2")).start();
		
		new Thread(new TestRunnable("3")).start();
		new Thread(new TestRunnable("4")).start();
	}
		

}

class TestRunnable implements Runnable{
	private final CountDownLatch latch ;
	private final String name;
	public TestRunnable(CountDownLatch latch, String name){
		this.latch=latch;
		this.name=name;
	}
	public TestRunnable(String name){
		this(null,name);
	}
	@Override
	public void run() {
		if (latch != null) {
			latch.countDown();
			try {
				latch.await();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		System.out.println(name+" thread starts at "+System.currentTimeMillis());
	}
	
}