Java Tutorial : CountDownLatch

import java.util.concurrent.CountDownLatch; 

public class countdown 
{ 
    public static void main(String args[])  
                   throws InterruptedException 
    { 

//       Creating CountDownLatch , there are 3 task being executed 
        CountDownLatch cdl = new CountDownLatch(3); 
  
//       Naming tasks and setting delay times 
//        1 second delay
        Task Task_One = new Task(1000, cdl,  "task 1"); 
//        5 second delay
        Task Task_Two = new Task(5000, cdl,  "task 2"); 
//        3 second delay 
        Task Task_Three = new Task(3000, cdl,   "task 3"); 

//       Starting tasks
        Task_One.start(); 
        Task_Two.start(); 
        Task_Three.start(); 
      
  
        // The main task waits here
        cdl.await(); 
  
        // Main thread running 
        System.out.println(Thread.currentThread().getName() + 
                           " You have hacked the main frame!"); 
        
    } 
} 
  
// What main thread does while waiting  
class Task extends Thread 
{ 
    private int dt; 
    private CountDownLatch cdl; 
  
    public Task(int dt, CountDownLatch cdl, 
                                    String name) 
    { 
        super(name); 
        this.dt = dt; 
        this.cdl = cdl; 
    } 
  
    @Override
    public void run() 
    { 
        try
        { 
//           task ran complete print finished 
            Thread.sleep(dt); 
            cdl.countDown(); 
            System.out.println(Thread.currentThread().getName() 
                            + " finished"); 
        } 
//        if not throw exception 
        catch (InterruptedException e) 
        { 
            e.printStackTrace(); 
        } 
    } 
} 

task 1 finished
task 3 finished
task 2 finished
main You have hacked the main frame!