import java.awt.Graphics;
import java.awt.Color;
import java.util.Calendar;
/*類Clock繼承了java.applet.Applet，由于要用到線程，因而實現了Runnable接口*/
public class Clock extends java.applet.Applet implements Runnable {
	/*聲明一個Thread對象threadObj*/
	Thread threadObj; 
    /*下面的6個變量分別代表前一個位置秒針、分針、時針末端的橫縱坐標*/
    int lastxs, lastys, lastxm,lastym, lastxh, lastyh;
    /*lastdate為前一個指針位置對應的日期*/    
    String lastdate;
    /*handColor用于設置時針、分針和鐘框的顏色*/
    Color handColor;             
    /*numberColor設置秒針和鐘面上數字的顏色*/
    Color numberColor;
    /*聲明一個Calendar對象，用于取得當前時間*/
	Calendar rightnow = Calendar.getInstance();		
	/*獲得當前日期的年份并賦給yearInt*/
	int yearInt  = rightnow.get(rightnow.YEAR); 
	/*獲得當前日期的月份并賦給monthInt*/
	int monthInt = rightnow.get(rightnow.MONTH);
	/*值得注意的是：月份以0為基準開始計數，一月對應的month值為0，依次類推*/
	/*獲得當前的日期，賦給dayInt*/
	int dayInt   = rightnow.get(rightnow.DATE);  
	/*獲得當前時間時鐘對應的整數并賦給hoursInt*/
	int hoursInt = rightnow.get(rightnow.HOUR_OF_DAY);  
	/*獲得當前時間分針對應的整數并賦給minutesInt*/
	int minutesInt = rightnow.get(rightnow.MINUTE);     
	/*獲得當前時間秒針對應的整數并賦給secondsInt*/
	int secondsInt = rightnow.get(rightnow.SECOND);     
	/*獲得當前時間對應的星期并賦給dayofweekInt*/
	int dayofweekInt = rightnow.get(rightnow.DAY_OF_WEEK); 
	/*值得注意的是通過DAY_OF_WEEK獲得的星期值中，星期天對應的值為1，星期一對應的為2，依次類推，為此，將利用getweekday方法轉換（參考getweekday方法）。*/
	/*init()方法用來初始化指針的位置和顏色，以及日期*/
    public void init() {
    	/*將秒針、分針和時鐘初始位置的橫縱坐標設置為0*/
        lastxs = lastys = lastxm = lastym = lastxh = lastyh = 0;

		/*將上面獲得的信息用字符串表示出來*/
		lastdate = yearInt + "年" + (monthInt + 1) + "月" + dayInt + "日" + hoursInt + ":" + minutesInt + ":" + secondsInt + " 星期" + getweekday(dayofweekInt);
        /*設置時鐘上時、分、秒針的顏色*/
        handColor = Color.red;
        /*設置時鐘上數據的顏色*/
        numberColor = Color.darkGray;
    }
	/*下面的方法變換星期的表示，將1,2,3,4,5,7匹配為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()方法用來啟動Clock線程*/	
	public void start() {
			/*初始化線程對象，名稱為“Clock”*/
			threadObj = new Thread(this, "Clock");
			threadObj.start();
	}
    /*update()方法用來刷新圖象*/
    public void update(Graphics g) {
        paint(g);
    }
	/*run()方法用來實現刷新時鐘圖象*/
	public void run() {
        while (threadObj != null) {
			try {
				threadObj.sleep(10);
			} catch(InterruptedException e) {}
			/*repaint方法用于時間的刷新顯示*/
			repaint();
		}
	}
	/*paint()繪制指針位置并進行可能的刷新操作，同時顯示當前日期和時間*/
	public void paint(Graphics g) {
        /*下面的前6個int變量分別代表時針、分鐘和秒鐘外邊緣端點的橫縱坐標，xcenter和ycenter代表時鐘的中心位置*/
        int xh, yh, xm, ym, xs, ys, xcenter = 100, ycenter = 70;
 		/*下面的語句用于獲得當前時間*/
 		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包含當前日期和時間信息*/
		String today = yearInt + "年" + (monthInt + 1) + "月" + dayInt + "日" + hoursInt + ":" + minutesInt + ":" + secondsInt + " 星期" + getweekday(dayofweekInt);
		/*計算秒針、分針、時針外邊緣端點的橫縱坐標（設定三針長度分別為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，計算分針外邊緣端點的橫縱坐標時，需要考慮秒針對它的影響*/
        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);
        /*計算時針外邊緣端點的橫縱坐標時，需要考慮分針對它的影響，將秒針的影響忽略了*/
        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);
	    /*繪制矩形和數字（9, 12, 3, 6）*/ 
	    handColor = Color.red;
        g.setColor(handColor);
        /*下面的語句繪制紅色的矩形外框*/
        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);
    	/*下面的語句根據當前時間和上一次顯示的時間時、分、秒針是否相同來擦除相應的指針，繪制新指針*/
        g.setColor(getBackground());
        if (xs != lastxs || ys != lastys) {
            /*擦除秒針的顯示*/
            g.drawLine(xcenter, ycenter, lastxs, lastys);
            /*擦除界面中日期和時間的字符串*/
            g.drawString(lastdate, 30, 150);
        }       
        if (xm != lastxm || ym != lastym) {
        	/*擦除分針的顯示，分針是由兩條線組成的*/
            g.drawLine(xcenter, ycenter-1, lastxm, lastym);
            g.drawLine(xcenter-1, ycenter, lastxm, lastym); }
        if (xh != lastxh || yh != lastyh) {
        	/*擦除時針的顯示，也是由兩條線組成的*/
            g.drawLine(xcenter, ycenter-1, lastxh, lastyh);
            g.drawLine(xcenter-1, ycenter, lastxh, lastyh); 
        }
        /*重新顯示秒針和時間字符串*/
        g.setColor(numberColor);
    	g.drawString("", 30, 150);
		g.drawString(today, 30, 150);
        g.drawLine(xcenter, ycenter, xs, ys);
        /*將分針和時針的顏色設置為藍色*/
        handColor = Color.blue;
        g.setColor(handColor);
        /*繪制分針和時針，都分別由兩條線組成*/
        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);              
        /*將當前時間的時、分、秒針的橫縱坐標賦給前一次時間對應的變量*/
        lastxs=xs; 
        lastys=ys;
        lastxm=xm; 
        lastym=ym;
        lastxh=xh; 
        lastyh=yh;
        /*將當前日期賦給上一次日期*/
        lastdate = today;
	}
}