大家帮我看看这个多线程计时器哪里出错了？

[halw002]

要求是：要用多线程做一个计时器，有开始和停止(清空)功能。。完全没有头绪

package csteaching;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;


public class C2 extends JFrame implements ActionListener,Runnable{
	Thread t;
	String threadName;
	JTextField t1;
	JButton b1;
	JButton b2;
	boolean flag = false;
	int h=0,m=0,s=0;
	
	public C2(){
		super("TIME");
		setSize(600,400);
		setLayout(new GridLayout(3,1));
		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		t1=new JTextField();
		b1=new JButton("Start");
		b2=new JButton("Stop");
		add(t1);
		add(b1);
		add(b2);
		b1.addActionListener(this);
		b2.addActionListener(this);
	}
	
	public void actionPerformed(ActionEvent e){
		if(e.getActionCommand().equals("Start")){
	        flag=true;
		}
		else{
			flag=false;
			h=0;
			m=0;
			s=0;
		}
	}
	
	public void run(){
		if(Thread.currentThread().getName().equals("timer")){
			while(flag){
				Timer();
			}
		}
		if(Thread.currentThread().getName().equals("show_time")){
			show_time();
		}
	}
	
	public void Timer(){
		try{
		Thread.currentThread().sleep(1000);
		}catch (InterruptedException e) {}
		s++;
		if(s==61){m++;s=0;}
		if(m==61){h++;m=0;}
	}
	
	public void show_time(){
		t1.setText(h+":"+m+":"+s);
	}
	
	public static void main(String[] args) throws InterruptedException {
		C2 tt = new C2();
		tt.setVisible(true);
		Thread t1=new Thread(tt);
		Thread t2=new Thread(tt);
		t1.setName("timer");
		t2.setName("show_time");
		t1.start();
		t2.start();
	}
}