package myball;
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
import java.net.*;
import java.util.*;
import java.math.*;

/** *//**
 * <p>Title: </p>
 *
 * <p>Description: </p>
 *
 * <p>Copyright: Copyright (c) 2007</p>
 *
 * <p>Company: </p>
 *
 * @author not attributable
 * @version 1.0
 */
public class Ball ...{
     int x_pos;
     int y_pos;
     int x_speed;
     int y_speed;
     int radius;
     Color c;
     Random rnd;
    public Ball(int x,int y,int mvx,int mvy,int mr,Color mcolor) ...{
        x_pos=x;
        y_pos=y;
        x_speed=mvx;
        y_speed=mvy;
        radius=mr;
        c=mcolor;

    }
    public Ball() ...{
    rnd=new Random();
    x_pos=((rnd.nextInt()))%(int)99+10;
    y_pos=(rnd.nextInt())%(int)99+10;
    x_speed=(rnd.nextInt())%(int)5+5;
    y_speed=(rnd.nextInt())%(int)5+5;
    radius=5+(rnd.nextInt())%(int)5;
    c=Color.red;
    }
    public  void move()...{
        x_pos=x_pos+x_speed;
        y_pos=y_pos+y_speed;
    }
   public void drawball(Graphics g)...{
    g.setColor(c);
    g.fillOval(x_pos-radius,y_pos-radius,2*radius,2*radius);

    }
  public void setVX(int mvx)...{
      x_speed=mvx;
  }
  public void setVY(int mvy)...{
      y_speed=mvy;
  }
  public void setXPos(int x)...{
      x_pos=x;
  }
  public void setYPos(int y)...{
      y_pos=y;
  }

}
package myball;

import java.awt.*;
import java.awt.event.*;
import java.applet.*;
import java.net.*;
import java.util.*;

public class BallApplet extends Applet implements Runnable ...{
    int x_pos=50;
    int y_pos=50;
    int x_speed=0;
    int y_speed=0;
    int radius=10;
    int maxspeed=5;
    int appletsize_x=300;
    int appletsize_y=300;
    Random rnd;
    private Image dbImage;
    private Graphics dbg;
    AudioClip bounce;
    AudioClip hit;
    Image backImage;
    ArrayList ball=new ArrayList();
    public void init()...{
    rnd=new Random();
    x_speed=(rnd.nextInt())%maxspeed;
    y_speed=(rnd.nextInt())%maxspeed;
    appletsize_x=this.getWidth();
    appletsize_y=this.getHeight();
    bounce=getAudioClip(getCodeBase(),"chimes.au");
    hit=getAudioClip(getCodeBase(),"gun.au");
    backImage=getImage(getCodeBase(),"ok.gif");
    //ballA=new Ball(200,200,-3,5,10,Color.cyan);
    //ballB=new Ball(x_pos,y_pos,x_speed,y_speed,radius,Color.yellow);
    //ballC=new Ball(90,90,4,3,10,Color.red);
   ball.add(new Ball(200,200,-3,5,10,Color.white));
   ball.add(new Ball(90,90,4,3,10,Color.white));
}
    public boolean ballHit(Ball a,Ball b)...{
        double  distance=0;
        double  x=0;
        double  y=0;
        double radius=0;
        int speed=0,space=0;
        radius=a.radius+b.radius;
        x=a.x_pos-b.x_pos;
        y=a.y_pos-b.y_pos;
        if(x<radius && y<radius)...{
           distance=Math.sqrt((x*x)+(y*y));
          if(distance>radius)...{
            return false;
            }
          else
          ...{
                speed=a.x_speed;
                a.setVX(b.x_speed);
                b.setVX(speed);
                if(x<0)...{
                    space=a.x_pos +(int) radius;
                    b.setXPos(space);
                }
                else
                ...{
                    space=b.x_pos+(int)radius;
                    a.setXPos((space));
                }

                speed=a.y_speed;
                a.setVY(b.y_speed);
                b.setVY(speed);
                if(y>0)...{
                    space=a.y_pos+(int)radius;
                    b.setYPos(space);
                }
                else
                ...{
                    space=b.y_pos+(int)radius;
                    a.setYPos(space);
                }
               return true;
          }
       }
        else
        ...{
             return false;
        }

    }
    public boolean ballOut(Ball b)...{
        if(b.x_pos>appletsize_x-b.radius)...{
          x_speed=-(b.x_speed);
          b.setVX(x_speed);
          b.setXPos(appletsize_x-b.radius);
          return true;
          }
      else if(b.x_pos<b.radius)
      ...{
          x_speed=-(b.x_speed);
          b.setXPos(b.radius);
          b.setVX(x_speed);
          return true;
      }
      if(b.y_pos>appletsize_y-b.radius)...{
          b.setYPos(appletsize_y-b.radius);
          b.setVY(-(b.y_speed));
          return true;
      }
      else if(b.y_pos<b.radius)...{
         b.setYPos(b.radius);
         y_speed=-(y_speed);
         b.setVY(-(b.y_speed));
         return true;
      }
        return false;
    }
    public boolean mouseDown(Event e,int x,int y) ...{

        return true;
    }
    public boolean keyDown(Event e,int key)...{

        return true;
    }
    void newBall()...{
        ball.add(new Ball());
    }
    void eatBall(Ball b)...{
        ball.remove(b);
    }
    public void start()...{
    Thread th=new Thread(this);
    th.start();
    }
    public void stop()...{}
    public void destory()...{}
    public void run()...{
    Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
    while(true)...{

       /**//* if(ballHit(ballA,ballB)){
            hit.play();
        }
        if(ballHit(ballA,ballC )){
            hit.play();
        }
        if(ballHit(ballB,ballC)){
            hit.play();
        }
        if(ballOut(ballA)){
           bounce.play();
       }
       ballA.move();
       if(ballOut(ballB)){
           bounce.play();
       }
       ballB.move();
       if(ballOut(ballC)){
           bounce.play();
       }
       ballC.move(); */
       int i=0,j=0;
       int size=0;
       Ball ballA,ballB,ballEat;
       ballEat=null;
       size=ball.size();
       for(i=0;i<size;i++)
       ...{  ballA=(Ball)(ball.get(i));
           for(j=i+1;j<size;j++)
           ...{  ballB=(Ball)(ball.get(j));
               if(ballHit(ballA,ballB))...{
                   hit.play();
                   //add a new ball
                   if (ballA.radius == ballB.radius) ...{
                       newBall();
                   }
                   else if(ballA.radius > ballB.radius)...{
                       ballEat=ballB;
                   }
                   else ...{
                       ballEat=ballA;
                   }
               }
       }
       }
       if(ballEat!=null)...{
           eatBall(ballEat);
       }
       for(i=0;i<ball.size();i++)...{
           ballA=(Ball)ball.get(i);
           if(ballOut(ballA))...{
               bounce.play();
           }
           ballA.move();
       }
       repaint();
        try ...{
            Thread.sleep(20);
        }
        catch(InterruptedException ex)...{

        }
        Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
    }
    }
    public void paint(Graphics g)...{
    g.drawImage(backImage,0,0,this);
   /**//* ballA.drawball(g);
    ballB.drawball(g);
    ballC.drawball(g); */
   Ball ballA;
   for(int i=0;i<ball.size();i++)
   ...{
       ballA=(Ball)ball.get(i);
       ballA.drawball(g);
   }

    }
    public void update(Graphics g)...{
        if(dbImage==null)
        ...{
            dbImage=createImage(this.getSize().width,this.getSize().height);
            dbg=dbImage.getGraphics();
        }
        dbg.setColor(getBackground());
        dbg.fillRect(0,0,this.getWidth(),this.getHeight());
        dbg.setColor(getForeground());
        paint(dbg);
        g.drawImage(dbImage,0,0,this);
    }
}
文章出處：http://www.diybl.com/course/3_program/game/2007124/90041.html