clockapplet.java

这是一个用Java编写的图形时钟程序

//【例8.5】  图形时钟。

import java.awt.*;
import java.applet.Applet;
import java.util.Calendar;
import java.text.SimpleDateFormat;

public class ClockApplet extends Applet implements Runnable  //Applet支持线程
{
    private Thread athread;                                //线程
    private SimpleDateFormat sdateformat;                  //日期格式

    private int second_lastx=0, second_lasty=0;            //上次秒针值
    private int minute_lastx=0, minute_lasty=0;            //上次分针值
    private int hour_lastx=0, hour_lasty=0;                //上次时针值
    
    public void init() 
    {
        this.setBackground(Color.white);
        this.athread = null; 
        this.sdateformat = new SimpleDateFormat("yyyy年MM月dd日hh时mm分ss秒 a EEEEE");
    }
    
    public void paint(Graphics g)                          //显示数字和图形时钟
    {
        Calendar rightnow = Calendar.getInstance();        //获取当前日期和时间
        int second = rightnow.get(Calendar.SECOND);        //当前秒
        int minute = rightnow.get(Calendar.MINUTE);        //分
        int hour = rightnow.get(Calendar.HOUR);            //时

        int center_x = this.getWidth()/2;                  //图形时钟的原点
        int center_y = 60;
                                                           //以下计算秒针、分针、时针位置
        int second_x = (int)(Math.cos(second*Math.PI/30 - Math.PI/2)*45 + center_x);
        int second_y = (int)(Math.sin(second*Math.PI/30 - Math.PI/2)*45 + center_y);
        
        int minute_x = (int)(Math.cos(minute * Math.PI/30 - Math.PI/2)*40 + center_x);
        int minute_y = (int)(Math.sin(minute * Math.PI/30 - Math.PI/2)*40 + center_y);
        
        int hour_x = (int)(Math.cos((hour*30+minute/2)*Math.PI/180-Math.PI/2)*30 + center_x);
        int hour_y = (int)(Math.sin((hour*30+minute/2)*Math.PI/180-Math.PI/2)*30 + center_y);
        
        g.setFont(new Font("TimesRoman", Font.PLAIN, 14));
        g.setColor(Color.blue);
        g.drawOval(center_x-50, center_y-50, 100, 100);    //画圆和数字
        g.setColor(Color.darkGray);
        g.drawString("9", center_x-45, center_y+3); 
        g.drawString("3", center_x+40, center_y+3);
        g.drawString("12", center_x-5, center_y-37);
        g.drawString("6",  center_x-3, center_y+45);
        
        //时间变化时，需要重新画各个指针，即先消除原有指针，然后画新指针
        g.setColor(this.getBackground());                  //用背景色画线，可以消除原来画的线
        if (second_x != second_lastx || second_y != second_lasty)    //秒针变化
        {
            g.drawLine(center_x, center_y, second_lastx, second_lasty);
        }
        
        if (minute_x != minute_lastx || minute_y != minute_lasty)    //分针变化
        {
            g.drawLine(center_x, center_y-1, minute_lastx, minute_lasty);
            g.drawLine(center_x-1, center_y, minute_lastx, minute_lasty); 
        }
        
        if (hour_x != hour_lastx || hour_y != hour_lasty)            //时针变化
        {
            g.drawLine(center_x, center_y - 1, hour_lastx, hour_lasty);
            g.drawLine(center_x - 1, center_y, hour_lastx, hour_lasty); 
        }
        
        g.setColor(Color.darkGray);                        //显示数字时钟
        g.drawString(sdateformat.format(rightnow), 0, 150);  
        
        g.setColor(Color.blue);                            //画新指针
        g.drawLine(center_x, center_y, second_x, second_y);
        
        g.drawLine(center_x, center_y - 1, minute_x, minute_y);
        g.drawLine(center_x - 1, center_y, minute_x, minute_y);
        
        g.drawLine(center_x, center_y - 1, hour_x, hour_y);
        g.drawLine(center_x - 1, center_y, hour_x, hour_y);
        
        second_lastx = second_x;                           //保存指针位置
        second_lasty = second_y;
        minute_lastx = minute_x;
        minute_lasty = minute_y;
        hour_lastx = hour_x;
        hour_lasty = hour_y;
    }
    
    public void start()
    {
        if(athread == null)
        {
            athread = new Thread(this);
            athread.start();                     //启动线程
        }
    }
    
    public void stop()
    {
        if(athread != null)
        {
            athread.interrupt();                 //中断线程
            athread = null;
        }
    }
     
    public void run()                            //线程体，每隔一秒钟，刷新一次画面
    {
        while (athread != null) 
        {
             repaint();                          //调用paint()方法重画时钟
             try 
             {
                 athread.sleep(1000);
             }
             catch (InterruptedException e) {}
        }
    }
}