在java程序中利用线程

package 第十一章;

import java.awt.Button;
import java.awt.Color;
import java.awt.Font;
import java.awt.Frame;
import java.awt.Label;
import java.awt.Panel;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.*;

public class shijian extends Frame {

Panel pan=new Panel();
Label lbl=new Label();
Button btn1=new Button("开始");
Button btn2=new Button("停止");
boolean p=true;

public shijian(String str) {
super(str);
}
public shijian(){
buju();
}
public static void main(String agrs[]){
shijian sj=new shijian();
}
public void buju(){
shijian f=new shijian("显示时间");
f.setSize(500,500);
f.setBackground(Color.gray);
f.setLayout(null);
f.setVisible(true);

pan.setSize(500, 500);
pan.setLocation(0, 0);
pan.setBackground(Color.darkGray);
pan.setLayout(null);

lbl.setSize(300,100);
lbl.setLocation(100, 100);
lbl.setBackground(Color.yellow);
//		lbl.setFont();
Font kl=new Font("宋体",0,25);
lbl.setFont(kl);

btn1.setSize(100,50);
btn1.setLocation(100, 250);
btn2.setSize(100,50);
btn2.setLocation(300, 250);

pan.add(btn2);
pan.add(btn1);
pan.add(lbl);
f.add(pan);

//		监听开始事件
btn1.addActionListener(new ActionListener(){

@Override
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
kaishi(e);
}});
//		监听停止事件
btn2.addActionListener(new ActionListener(){

@Override
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
tingzhi(e);
}});

}
//	点击开始时调用
public void kaishi(ActionEvent e){
p=true;
Thread t=new Thread(){
public void run() {
// TODO Auto-generated method stub
while(p){
Date d=new Date();
lbl.setText(d.toLocaleString());
try {
Thread.sleep(1000);
} catch (InterruptedException e1) {
e1.printStackTrace();
}
}
}
};
t.start();
}

public void tingzhi(ActionEvent e){
//		Thread t=new Thread(){
//			public void run() {
// TODO Auto-generated method stub
p=false;
//			}
//		};
}

}