keyto8_2.java

Java程序设计第八章的课后练习题目的答案 欢迎大家来参考

import java.awt.*;
import java.applet.*;
import javax.swing.*;

public class KeyTo8_2 extends JApplet implements Runnable
{
	int x1=0,y1=0,w1=230,h1=70;
	int x2=10,y2=10,w2=210,h2=50;
	int dx=1;
	int xFlag;
	int Ball_x=10;
	float ColorRed=1.0f;
	float ColorGreen=0.0f;
	boolean st=true;
	Thread Ball_thread;
	Image OffScreen;
	Graphics drawOffScreen;
	public void init()
	{
		
	    OffScreen=createImage(w1,h1);
	    drawOffScreen=OffScreen.getGraphics();
	}
	
	public void start()
	{
		if(Ball_thread==null)
		{
			Ball_thread=new Thread(this);
			Ball_thread.start();
		}
	}
	public void stop()
	{
		if(Ball_thread!=null)
		{
			Ball_thread.stop();
			Ball_thread=null;
		}
	}
	public void run()
	{

		while(true)
		{
			if(Ball_x>=170)
			{
				xFlag=-1;;
				
			}
		
			else if(Ball_x<=10)
			{
				xFlag=1;
			}
			Ball_x+=dx*xFlag;
			
			
			
			repaint();
			try
			{
				Thread.sleep(20);
			}catch(InterruptedException e){}
		}
	}

	public void paint(Graphics g) 
	{
		if(st==true)
		{
		  drawOffScreen.setColor(Color.blue);
		  drawOffScreen.fillRect(0,0,w1,h1);
		}
        
    	drawOffScreen.setColor(Color.white);
		drawOffScreen.fillRect(x2,y2,w2,h2);
		
		drawOffScreen.setColor(new Color(ColorRed,ColorGreen,0.0f));
		drawOffScreen.fillOval(Ball_x,y2,h2,h2);
		g.drawImage(OffScreen,0,0,this);
		ColorRed-=xFlag*1.0/w2;
		ColorGreen+=xFlag*1.0/w2;
		st=false;
	}
	public void update(Graphics g)
	{
		paint(g);
	}
}