Question

I have a multithreaded program where I want the one of the thread to print the statement after all the thread finished.How can I do that? and How do I know that all the threads finished?

ExecutorService pool = Executors.newCachedThreadPool();
    for(int i = 0; i < myList.size(); ++i) {
            pool.execute (new ThreadProcessRunnable (args));
    }


    public class ThreadProcessRunnable implements Runnable {
           public void run() {


           System.out.println("last thread should execute this");
    }
    }

Answer 1

This is a REALLY basic example/concept of using a CountDownLatch

public class TestCountDownLatch {

  private static CountDownLatch latch;

  public static void main(String[] args) {

    latch = new CountDownLatch(10);
    ExecutorService pool = Executors.newCachedThreadPool();
    for (int i = 0; i < 10; ++i) {
      pool.execute(new Worker(i));
    }
  }

  public static class Worker implements Runnable {

    private int number;

    public Worker(int number) {
      this.number = number;
    }

    @Override
    public void run() {

      try {
        System.out.println(number + " is sleeping...");
        Thread.sleep((long) (Math.round(Math.random() * 1000)));
      } catch (InterruptedException ex) {
      }

      System.out.println(number + " is Completed...");
      latch.countDown();

      if (latch.getCount() == 0) {

        System.out.println(number + " was last...");

      }

    }
  }
}

Simple Single Thread Test Case

public class TestCountDownLatch {

  private static CountDownLatch latch;

  public static void main(String[] args) {

    latch = new CountDownLatch(1);
    ExecutorService pool = Executors.newCachedThreadPool();
    for (int i = 0; i < 1; ++i) {
      pool.execute(new Worker(i));
    }
  }

  public static class Worker implements Runnable {

    private int number;

    public Worker(int number) {
      this.number = number;
    }

    @Override
    public void run() {

      try {
        System.out.println(number + " is sleeping...");
        Thread.sleep((long) (Math.round(Math.random() * 1000)));
      } catch (InterruptedException ex) {
      }

      System.out.println(number + " is Completed...");
      latch.countDown();

      if (latch.getCount() == 0) {

        System.out.println(number + " was last...");

      }

    }
  }
}