Thank you so much!Ramesh!
Would you mind doing me a favour again?
There are two Demos using different way to creat a thread,one is by
inheriting class Thread while another is by implementing interface
Runnable,but the results of these two examples are quite different.

Demo1:
class MultiThread4 implements Runnable{
    private int ticket = 100;
    public void run(){
        while(ticket>0)
            System.out.println(ticket-- +"is saled by " +
Thread.currentThread().getName());
            }
    }
class MultiThreadDemo4{
    public static void main(String[] name){
        MultiThread4 m =new MultiThread4();
        Thread t1 = new Thread(m,"Window 1");
        Thread t2 = new Thread(m,"Window 2");
        Thread t3 = new Thread(m,"Window 3");
        t1.start();
        t2.start();
        t3.start();
        }
    }

Demo2:
class NMultiThread4 extends Thread{
    NMultiThread4(String name){
        super(name);
            }
    private int ticket = 100;
    public void run(){
        while(ticket>0)
            System.out.println(ticket-- +"is saled by " +
Thread.currentThread().getName());
            }
    }
class NMultiThreadDemo4{
    public static void main(String[] name){
        NMultiThread4 t1 = new NMultiThread4("Window 1");
        NMultiThread4 t2 = new NMultiThread4("Window 1");
        NMultiThread4 t3 = new NMultiThread4("Window 1");
        t1.start();
        t2.start();
        t3.start();
        }
    }

Why?
Thanks in advance!