clock.java

一款由Ｊａｖａ实现的电子时钟程序

import java.awt.Graphics;
import java.awt.Color;
import java.util.Calendar;
/*类Clock继承了java.applet.Applet，由于要用到线程，因而实现了Runnable接口*/
public class Clock extends java.applet.Applet implements Runnable {
	/*声明一个Thread对象threadObj*/
	Thread threadObj; 
    /*下面的6个变量分别代表前一个位置秒针、分针、时针末端的横纵坐标*/
    int lastxs, lastys, lastxm,lastym, lastxh, lastyh;
    /*lastdate为前一个指针位置对应的日期*/    
    String lastdate;
    /*handColor用于设置时针、分针和钟框的颜色*/
    Color handColor;             
    /*numberColor设置秒针和钟面上数字的颜色*/
    Color numberColor;
    /*声明一个Calendar对象，用于取得当前时间*/
	Calendar rightnow = Calendar.getInstance();		
	/*获得当前日期的年份并赋给yearInt*/
	int yearInt  = rightnow.get(rightnow.YEAR); 
	/*获得当前日期的月份并赋给monthInt*/
	int monthInt = rightnow.get(rightnow.MONTH);
	/*值得注意的是：月份以0为基准开始计数，一月对应的month值为0，依次类推*/
	/*获得当前的日期，赋给dayInt*/
	int dayInt   = rightnow.get(rightnow.DATE);  
	/*获得当前时间时钟对应的整数并赋给hoursInt*/
	int hoursInt = rightnow.get(rightnow.HOUR_OF_DAY);  
	/*获得当前时间分针对应的整数并赋给minutesInt*/
	int minutesInt = rightnow.get(rightnow.MINUTE);     
	/*获得当前时间秒针对应的整数并赋给secondsInt*/
	int secondsInt = rightnow.get(rightnow.SECOND);     
	/*获得当前时间对应的星期并赋给dayofweekInt*/
	int dayofweekInt = rightnow.get(rightnow.DAY_OF_WEEK); 
	/*值得注意的是通过DAY_OF_WEEK获得的星期值中，星期天对应的值为1，星期一对应的为2，依次类推，为此，将利用getweekday方法转换（参考getweekday方法）。*/
	/*init()方法用来初始化指针的位置和颜色，以及日期*/
    public void init() {
    	/*将秒针、分针和时钟初始位置的横纵坐标设置为0*/
        lastxs = lastys = lastxm = lastym = lastxh = lastyh = 0;
		/*将上面获得的信息用字符串表示出来*/
		lastdate = yearInt + "年" + (monthInt + 1) + "月" + dayInt + "日" + hoursInt + ":" + minutesInt + ":" + secondsInt + " 星期" + getweekday(dayofweekInt);
        /*设置时钟上时、分、秒针的颜色*/
        handColor = Color.red;
        /*设置时钟上数据的颜色*/
        numberColor = Color.darkGray;
    }
	/*下面的方法变换星期的表示，将1,2,3,4,5,7匹配为7,1,2,3,4,5,6*/
	public int getweekday(int dayInt) {
		int weekdayInt;
		switch(dayInt) {
			case 1:	weekdayInt = 7;
			break;
			default: weekdayInt = dayInt - 1;
		}
		return weekdayInt;
	}
	/*start()方法用来启动Clock线程*/	
	public void start() {
			/*初始化线程对象，名称为“Clock”*/
			threadObj = new Thread(this, "Clock");
			threadObj.start();
	}
    /*update()方法用来刷新图象*/
    public void update(Graphics g) {
        paint(g);
    }
	/*run()方法用来实现刷新时钟图象*/
	public void run() {
        while (threadObj != null) {
			try {
				threadObj.sleep(10);
			} catch(InterruptedException e) {}
			/*repaint方法用于时间的刷新显示*/
			repaint();
		}
	}
	/*paint()绘制指针位置并进行可能的刷新操作，同时显示当前日期和时间*/
	public void paint(Graphics g) {
        /*下面的前6个int变量分别代表时针、分钟和秒钟外边缘端点的横纵坐标，xcenter和ycenter代表时钟的中心位置*/
        int xh, yh, xm, ym, xs, ys, xcenter = 100, ycenter = 70;
 		/*下面的语句用于获得当前时间*/
 		Calendar rightnow = Calendar.getInstance();
		yearInt  = rightnow.get(rightnow.YEAR);
		monthInt = rightnow.get(rightnow.MONTH);
		dayInt   = rightnow.get(rightnow.DATE);
		hoursInt = rightnow.get(rightnow.HOUR_OF_DAY);
		minutesInt   = rightnow.get(rightnow.MINUTE);
		secondsInt   = rightnow.get(rightnow.SECOND);
		dayofweekInt = rightnow.get(rightnow.DAY_OF_WEEK);
		/*字符串today包含当前日期和时间信息*/
		String today = yearInt + "年" + (monthInt + 1) + "月" + dayInt + "日" + hoursInt + ":" + minutesInt + ":" + secondsInt + " 星期" + getweekday(dayofweekInt);
		/*计算秒针、分针、时针外边缘端点的横纵坐标（设定三针长度分别为45，40，30）*/
        xs = (int)(Math.cos(secondsInt * 3.14f / 30 - 3.14f / 2) * 45 + xcenter);
        ys = (int)(Math.sin(secondsInt * 3.14f / 30 - 3.14f / 2) * 45 + ycenter);
        /*值得注意的是，计算分针外边缘端点的横纵坐标时，需要考虑秒针对它的影响*/
        xm = (int)(Math.cos((minutesInt + secondsInt/60f) * 3.14f / 30 - 3.14f / 2) * 40 + xcenter);
        ym = (int)(Math.sin((minutesInt + secondsInt/60f) * 3.14f / 30 - 3.14f / 2) * 40 + ycenter);
        /*计算时针外边缘端点的横纵坐标时，需要考虑分针对它的影响，将秒针的影响忽略了*/
        xh = (int)(Math.cos((hoursInt * 30 + minutesInt / 2) * 3.14f / 180 - 3.14f/2) * 30 + xcenter);
        yh = (int)(Math.sin((hoursInt * 30 + minutesInt / 2) * 3.14f / 180 - 3.14f/2) * 30 + ycenter);
	    /*绘制矩形和数字（9, 12, 3, 6）*/ 
	    handColor = Color.red;
        g.setColor(handColor);
        /*下面的语句绘制红色的矩形外框*/
        g.drawRect(xcenter - 50, ycenter - 50, 100, 100);
        g.setColor(numberColor);
        g.drawString("9",xcenter-45,ycenter+3); 
        g.drawString("3",xcenter+40,ycenter+3);
        g.drawString("12",xcenter-5,ycenter-37);
        g.drawString("6",xcenter-3,ycenter+45);
    	/*下面的语句根据当前时间和上一次显示的时间时、分、秒针是否相同来擦除相应的指针，绘制新指针*/
        g.setColor(getBackground());
        if (xs != lastxs || ys != lastys) {
            /*擦除秒针的显示*/
            g.drawLine(xcenter, ycenter, lastxs, lastys);
            /*擦除界面中日期和时间的字符串*/
            g.drawString(lastdate, 30, 150);
        }       
        if (xm != lastxm || ym != lastym) {
        	/*擦除分针的显示，分针是由两条线组成的*/
            g.drawLine(xcenter, ycenter-1, lastxm, lastym);
            g.drawLine(xcenter-1, ycenter, lastxm, lastym); }
        if (xh != lastxh || yh != lastyh) {
        	/*擦除时针的显示，也是由两条线组成的*/
            g.drawLine(xcenter, ycenter-1, lastxh, lastyh);
            g.drawLine(xcenter-1, ycenter, lastxh, lastyh); 
        }
        /*重新显示秒针和时间字符串*/
        g.setColor(numberColor);
    	g.drawString("", 30, 150);
		g.drawString(today, 30, 150);
        g.drawLine(xcenter, ycenter, xs, ys);
        /*将分针和时针的颜色设置为蓝色*/
        handColor = Color.blue;
        g.setColor(handColor);
        /*绘制分针和时针，都分别由两条线组成*/
        g.drawLine(xcenter, ycenter - 1, xm, ym);
        g.drawLine(xcenter - 1, ycenter, xm, ym);       
        g.drawLine(xcenter, ycenter - 1, xh, yh);
        g.drawLine(xcenter - 1, ycenter, xh, yh);
        g.drawLine(xcenter, ycenter - 2, xh, yh);
        g.drawLine(xcenter - 2, ycenter, xh, yh);              
        /*将当前时间的时、分、秒针的横纵坐标赋给前一次时间对应的变量*/
        lastxs=xs; 
        lastys=ys;
        lastxm=xm; 
        lastym=ym;
        lastxh=xh; 
        lastyh=yh;
        /*将当前日期赋给上一次日期*/
        lastdate = today;
	}
}