判断已知数是否为质数 + 显示时间 ，要求判断完毕同时停止时间输出
         但未能如愿 ，望高手指点 ， 小弟感激不敬~~~~~~~~~~~~~~

import java.util.*;

class TestThread208_4
{
    public static void main(String[] args)
    {
        ShowTime time = new ShowTime();
        DoCount count = new DoCount();
        Thread thread1 = new Thread(time);
        Thread thread2 = new Thread(count);
        thread1.start();
        thread2.start();
    }
}


class ShowTime implements Runnable
{
    boolean flg = true;
    public void run()
    {
        while(flg)
        {
            System.out.println(new Date());
            try{
                Thread.sleep(600);
            }catch(InterruptedException e){
                System.err.println(e);
            }
        }
    }
    public void stopRun()
    {
        flg = false;
    }
}


class DoCount implements Runnable
{
    public void run()
    {
        int num = 34243;
        int j = 0;
        for(int i=2;i<num;i++)
        {
            if(num%i==0)       j=1;
            else               j=2;
        }
        switch(j)
        {
            case 1:
                   System.out.println(num+"不是质数");
                   break;
            case 2:
                   System.out.println(num+"是质数");
                   break;      
        }
        new ShowTime().stopRun();[size=2]
    }
}[/size]

这个有必要用线程吗?如果是因为数字大,那么你就应该使用线程,但是也不是这个样子啊.