import java.awt.Graphics;
import java.util.Calendar;
import java.awt.Color;
/*類Clock繼承了java.applet.Applet，并實(shí)現(xiàn)了Runnable接口,由于類Clock中需要使用Thread對(duì)象*/
public class Clock extends java.applet.Applet implements Runnable {
	/*聲明一個(gè)Thread對(duì)象*/
	Thread threadObj;
	/*下面的三個(gè)int變量表示時(shí)鐘上一次顯示時(shí)間的時(shí)、分和秒*/
	int oldhours,oldminutes,oldseconds;
	/*布爾變量boolVar用于控制時(shí)間的第一次顯示*/
	boolean boolVar = true;
	/*在start()方法中對(duì)線程對(duì)象進(jìn)行初始化，并啟動(dòng)線程*/
	public void start() {
		if(threadObj == null) {
			/*實(shí)例化一個(gè)線程對(duì)象，線程的名稱為Clock，線程的運(yùn)行目標(biāo)對(duì)象為當(dāng)前類的對(duì)象*/
			threadObj = new Thread(this, "Clock");
			threadObj.start();
		}
	}
	/*下面的run()方法每過一秒對(duì)當(dāng)前的時(shí)間進(jìn)行刷新*/
	public void run() {
		while(threadObj != null) {
			try {
				threadObj.sleep(1000);
			} catch(InterruptedException e) {}
			/*repaint方法用于時(shí)間的刷新顯示*/
			repaint();
		}
	}
	/*paint方法獲得當(dāng)前的時(shí)間并將它顯示出來*/
	public void paint(Graphics g) {
		Calendar now = Calendar.getInstance();
		/*下面的三個(gè)語句用于獲得當(dāng)前時(shí)間的時(shí)、分和秒*/
		int hours = now.get(now.HOUR_OF_DAY);
		int minutes = now.get(now.MINUTE);
		int seconds = now.get(now.SECOND);
		//顯示當(dāng)前時(shí)間
        g.setColor(Color.black);
		g.drawString(hours + ":" + minutes + ":" + seconds, 60, 60);
		
		/*
		//下面的if和else語句分別控制時(shí)間的第一次顯示和后續(xù)顯示。
        if(boolVar == true){
        	//第一次顯示時(shí)間時(shí)，不必進(jìn)行刷新，直接顯示時(shí)間就可以了
			g.setColor(Color.black);
			g.drawString(hours + ":" + minutes + ":" + seconds, 60, 60);
			boolVar = false;
		}
		else{
			//除了第一次以外，都需要在顯示當(dāng)前時(shí)間之前將上一次時(shí)間顯示去掉
			g.setColor(getBackground());
			g.drawString(oldhours + ":" + oldminutes + ":" + oldseconds, 60, 60);
			g.setColor(Color.black);
			g.drawString(hours + ":" + minutes + ":" + seconds, 60, 60);
		}
		*/
		
		oldhours = hours;
		oldminutes = minutes;
		oldseconds = seconds;
	}
	/*update()方法用來刷新圖象*/
    public void update(Graphics g) {
        paint(g);
    }
	/*停止線程的運(yùn)行*/
	public void stop() {
		threadObj = null;
	}
}