501f3c83476a001c1e36e6e62da4b12f

这是我自己照着书上敲的

/*
 * Created on 2007-9-24
 *
 * TODO To change the template for this generated file go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
import java.awt.*;
import java.applet.*;
import java.awt.event.*;
/**
 * @author Administrator
 *
 * TODO To change the template for this generated type comment go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
public class BounceApplet extends Applet 
{
	public BounceApplet()
	{
		BounceExpress bounce=new BounceExpress();
		bounce.setSize(300,200);
		bounce.show();
	}
}
class BounceExpress extends Frame
{
	Canvas canvas;
	Button blackButton,redButton,closeButton;
	public BounceExpress()
	{
		canvas=new Canvas();
		Panel p=new Panel();
		blackButton=new Button("添加黑色小球");
		redButton=new Button("添加红色小球");
		closeButton=new Button("关闭窗口");
		Listener listener=new Listener();
		setTitle("BounceExpress");
		canvas.setBackground(Color.lightGray);
		add("Center",canvas);
		add("South",p);
		p.add(blackButton);
		p.add(redButton);
		p.add(closeButton);
		blackButton.addActionListener(listener);
		redButton.addActionListener(listener);
		closeButton.addActionListener(listener);
		this.addWindowListener(new WListener());
	}
	class WListener extends WindowAdapter
	{
		public void windowClosing(WindowEvent e)
		{
			dispose();
		}
	}
	class Listener implements ActionListener
	{
		public void actionPerformed(ActionEvent e)
		{
			if(e.getSource()==blackButton)
			{
				Ball b=new Ball(canvas,Color.black);
				b.setPriority(Thread.NORM_PRIORITY);
				b.start();
			}
			else
				if(e.getSource()==redButton)
				{
					Ball b=new Ball(canvas,Color.red);
					b.setPriority(Thread.NORM_PRIORITY+2);
					b.start();
				}
				else
					if(e.getSource()==closeButton)
					{
						dispose();
					}
		}
	}
}
class Ball extends Thread
{
	private Canvas box;
	private static final int XSIZE=10;
	private static final int YSIZE=10;
	private int x=0,y=0;
	private int dx=2,dy=2;
	private Color color;
	public Ball(Canvas _canvas,Color _color)
	{
		box=_canvas;
		color=_color;
		this.setDaemon(true);
	}
	public void draw()
	{
		Graphics g=box.getGraphics();
		g.setColor(color);
		g.fillOval(x,y,XSIZE,YSIZE);
	}
	public void move()
	{
		Graphics g=box.getGraphics();
		if(g==null)
			return;
		g.setColor(color);
		g.setXORMode(box.getBackground());
		g.fillOval(x,y,XSIZE,YSIZE);
		x+=dx;
		y+=dy;
		Dimension d=box.getSize();
		if(x<0)
		{
			x=0;
			dx=-dx;
		}
		if(x+XSIZE>=d.width)
		{
			x=d.width-XSIZE;
			dx=-dx;
		}
		if(y<0)
		{
			y=0;
			dy=-dy;
		}
		if(y+YSIZE>=d.height)
		{
			y=d.height-YSIZE;
			dy=-dy;
		}
		g.fillOval(x,y,XSIZE,YSIZE);
	}
	public void run()
	{
		draw();
		for( ; ; )
		{
			move();
			try
			{
				Thread.sleep(50);
			}
			catch(InterruptedException e)
			{
				e.printStackTrace();
			}
		}
	}
}