import java.awt.*; 

import java.util.*; 

import javax.swing.*; 

//数字时钟 

public class ClockDemo extends JFrame implements Runnable{ 

Thread clock; 

public ClockDemo(){ 

super("数字时钟"); //调用父类构造函数 

setFont(new Font("Times New Roman",Font.BOLD,60)); //设置时钟的显示字体 

start(); //开始进程 

setSize(280,100); //设置窗口尺寸 

setVisible(true); //窗口可视 

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //关闭窗口时退出程序 

} 

public void start(){ //开始进程 

if (clock==null){ //如果进程为空值 

clock=new Thread(this); //实例化进程 

clock.start(); //开始进程 

} 

} 

public void run(){ //运行进程 

while (clock!=null){ 

repaint(); //调用paint方法重绘界面 

try{ 

Thread.sleep(1000); //线程暂停一秒(1000毫秒) 

} 

catch (InterruptedException ex){ 

ex.printStackTrace(); //输出出错信息 

} 

} 

} 

public void stop(){ //停止进程 

clock=null; 

} 

public void paint(Graphics g){ //重载组件的paint方法 

Graphics2D g2=(Graphics2D)g; //得到Graphics2D对象 

Calendar now=new GregorianCalendar(); //实例化日历对象 

String timeInfo=""; //输出信息 

int hour=now.get(Calendar.HOUR_OF_DAY); //得到小时数 

int minute=now.get(Calendar.MINUTE); //得到分数 

int second=now.get(Calendar.SECOND); //得到秒数 

if (hour<=9) 

timeInfo+="0"+hour+":"; //格式化输出 

else 

timeInfo+=hour+":"; 

if (minute<=9) 

timeInfo+="0"+minute+":"; 

else 

timeInfo+=minute+":"; 

if (second<=9) 

timeInfo+="0"+second; 

else 

timeInfo+=second; 

g.setColor(Color.white); //设置当前颜色为白色 

Dimension dim=getSize(); //得到窗口尺寸 

g.fillRect(0,0,dim.width,dim.height); //填充背景色为白色 

g.setColor(Color.orange); //设置当前颜色为橙色 

g.drawString(timeInfo,20,80); //显示时间字符串 

} 

public static void main(String[] args){ 

new ClockDemo(); 

} 

}