class Timer{

    private static int num;

    void add(String name){

      //synchronized (this){

        num++;

        try{  Thread.sleep(1);  }

        catch(InterruptedException e){};

        System.out.println(name+"  you are the  "+num+"  user to use timer!");

      //}

    }

 }

 public class TestSync implements Runnable{

     Timer timer = new Timer();

     public static void main(String[] args) {

        TestSync t = new TestSync();

        Thread t1 = new Thread(t,"t1");

        Thread t2 = new Thread(t,"t2");

        t1.start();

        t2.start();

     }

     public void run(){

        timer.add(Thread.currentThread().getName());

     }

 }