class PingPong extends Thread {
  String message;
  
  public PingPong(String ms){
    message = ms;
  }

  public void run(){
    while (true){
      System.out.println(message);
      try {
	sleep(10);
      }
      catch (InterruptedException e){}
    }
  }

  public static void main(String[] args){
    PingPong ping = new PingPong("Ping");
    PingPong pong = new PingPong("Pong");
    ping.start();
    pong.start();
  }
}