class example {
   public static void main(String[] a) {

     // alternative 1
      ExtnOfThread t1 = new ExtnOfThread();
      t1.start();

     // alternative 2
      Thread t2 = new Thread (new ImplOfRunnable());
      t2.start();
   }
}

class ExtnOfThread extends Thread {
   public void run() {
         System.out.println("Extension of Thread running");
// next line compiles and runs just fine
         try {sleep(1000);}
         catch (InterruptedException ie) {return;}
   }
}

class ImplOfRunnable implements Runnable {
   public void run() {
         System.out.println("Implementation of Runnable running");

// next line will not compile - thread method sleep() not known
//         try {sleep(1000);}
//         catch (InterruptedException ie) {return;}

         // do it like this
         Thread t = Thread.currentThread(); 
         try { t.sleep(1000); } 
         catch  (InterruptedException ie) { return; }
   }
}