.java

public class App {
public static void main(String[]args){
	//CountDownLatch, is a thread safe class
	//A synchronization aid that allows one or more threads
	//to wait until a set of operations being performed in other threads completes.
	//CountDownLatch(int count) 
	CountDownLatch latch=new CountDownLatch(1);
	//A CountDownLatch is initialized with a given count. 
	//The await methods block until the current count reaches zero
	ExecutorService exc=Executors.newFixedThreadPool(3);
	for(int i=0;i<3;i++){
		//creates three threads, each one gets a latch
		exc.submit(new Processor(latch));
	}
	try {
		// Causes the current thread to wait until the latch has counted down to zero,
		//unless the thread is interrupted, or the specified waiting time elapses.
		latch.await();
	} catch (InterruptedException e) {
		e.printStackTrace();
	}
	System.out.println("Completed");
}
}
class Processor implements Runnable{
	private CountDownLatch latch;
	public Processor(CountDownLatch latch){
		this.latch=latch;
	}
	@Override
	public void run() {
		System.out.println("Started...");
		try{
			//After three seconds each one will call countDown
		Thread.sleep(300);
		}catch(Exception e){
			
		}
		//countDown
		//Decrements the count of the latch, releasing all waiting threads if the count reaches zero.
		//every time countDown is called, the value specified, will be counted down by 1
		latch.countDown();
		
	}
	
}