Create A semaphore based coordination in Java

//w  w  w  .jav  a2  s .  co m
import java.util.concurrent.Semaphore;

public class Main {
  public static void main(String args[]) throws Exception {
    Semaphore sem = new Semaphore(1, true);
    Thread thrdA = new Thread(new MyThread(sem, "Message 1"));
    Thread thrdB = new Thread(new MyThread(sem, "Message 2"));

    thrdA.start();
    thrdB.start();

    thrdA.join();
    thrdB.join();

  }
}

class MyThread implements Runnable {
  Semaphore sem;
  String msg;
  MyThread(Semaphore s, String m) {
    sem = s;
    msg = m;
  }

  public void run() {
    try {
      sem.acquire();
      System.out.println(msg);
      Thread.sleep(10);
      sem.release();
    } catch (Exception exc) {
      System.out.println("Error Writing File");
    }
  }
}