极简版秒表（java GUI）

package javaPractice;

import javax.swing.*;
import java.text.*;
import java.util.*;
import java.awt.*;
import java.awt.event.*;

public class Stopwatch {
	public static void main(String[] args) {
		new Timer();
	}
}

class Timer extends JFrame{
	JLabel jl;
	JTextField jt1,jt2;
	JButton jb;
	SimpleDateFormat df;
	private static TimeNow thread;

	Timer(){
		this.setSize(400,300);//初始化窗口
		this.setTitle("Stopwatch");
		this.setLayout(null);

		df = new SimpleDateFormat("hh:mm:ss");//设置时间格式

		jt1 = new JTextField();//实例化组件
		jt2 = new JTextField();
		jb = new JButton("Current time");

		jt1.setText(df.format(new Date()));
		jt1.setBounds(105,50,120,35);//定义各组件的显示位置和大小
		jb.setBounds(90,110,150,30);
		jt2.setBounds(105,170,120,35);

		this.add(jt1);//把现有组件添加到窗体窗口
		this.add(jb);
		this.add(jt2); 

		this.setLocationRelativeTo(null);//窗口居中显示
		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		this.setVisible(true);	

		thread = new TimeNow();

		jb.addActionListener(new ButtonListener());
	}

	class TimeNow implements Runnable{
		public void run() {
			while(true) {
				jt1.setText(df.format(new Date()));
				try {
					Thread.sleep(1);
				}catch(InterruptedException e) {
					e.printStackTrace();
					System.exit(1);
				}
			}
		}

		public void start() {
			jt2.setText(df.format(new Date()));
		}
	}

	class ButtonListener implements ActionListener{
		JPanel jp = new JPanel();

	    public void actionPerformed(ActionEvent e) {
			thread.start();
		}
	}
}