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;
//			}
//		};
	}

}