coin.java

一个applet程序

import java.applet.*;
import java.awt.*;
public class Coin extends Applet
{int numCoins=3;
 Rectangle[] coins=new Rectangle[numCoins];
 Rectangle[] slots=new Rectangle[numCoins];
 Color[] colors={Color.red,Color.green,Color.blue};
 Image bbuf;
 Graphics bbufG;
 int dragging=-1;
 Point offset;
 
 public void init()
 {for(int i=0;i<numCoins;i++)
  {coins[i]=new Rectangle(rand(50),rand(50),50, 50);
   slots[i]=new Rectangle();
  }
 }
 
 
 public int rand(int r)
 {return (int)Math.floor(Math.random()*r);
 }
 
 
 public void paint(Graphics g)
 {update(g);
 }
 
 public void update(Graphics g)
 {int w=size().width;
  int h=size().height;
  if(bbuf==null||w>bbuf.getWidth(null)||h>bbuf.getHeight(null))
  {bbuf=createImage(w,h);
   bbufG=bbuf.getGraphics();
  }
  bbufG.setColor(Color.gray);
  bbufG.fillRect(0, 0,size().width, size().height);
  for(int i=0;i<numCoins;i++)
  {slots[i].reshape(i*w/3,h-30,w/3, 30);
   slots[i].grow(-5, -2);
   bbufG.setColor(colors[i]);
   bbufG.fillRect(slots[i].x,slots[i].y,slots[i].width,slots[i].height);
  }
  for(int i=0;i<numCoins;i++)
  {if(!coins[i].isEmpty())
   {if(dragging==i&&coins[i].intersects(slots[i]))
    {bbufG.setColor(Color.black);
    }
    else
    {bbufG.setColor(colors[i]);
    }
    bbufG.fillOval(coins[i].x,coins[i].y,coins[i].width, coins[i].height);
   }
  }
  g.drawImage(bbuf,0,0,this);
 }
  
  
  public synchronized boolean mouseDown(Event evt, int x, int y)
  {for(int i=coins.length-1;i>=0;i--)
   {if(!coins[i].isEmpty()&&coins[i].inside(x, y))
    {dragging=i;
     offset=new Point(coins[i].x-x,coins[i].y-y);
     return true;
    }
   }
   return false;
  }
  
  
  public synchronized boolean mouseDrag(Event evt,int x, int y)
  {if(dragging>=0)
   {coins[dragging].move(x, y);
    coins[dragging].translate(offset.x,offset.y);
    repaint();
    return true;
   }
   return false;
  }
  
  public synchronized boolean mouseUp(Event evt,int x,int y)
  {if(dragging>=0)
   {if(coins[dragging].intersects(slots[dragging]))
    { coins[dragging].width=0;
    dragging=-1;
    }
   repaint();
   return true;
  }
  return false;
  }
 }