import java.awt.*; 
import java.applet.*; 
public class carton extends Applet implements Runnable{ 
    Thread thd; 
    int i,j,k; 
    Image bimg; 
    Graphics bg;
    String namestr[] = new String[5] ; 
    Image img[]=new Image[5]; 
    MediaTracker mt;
    boolean error;
    public void init(){
        i=-20;j=20;k=-1;
        thd=null;
        error=false;
       try{
           //创建媒体跟踪器
           mt=new MediaTracker(this);       
           for (int j1=0; j1<5; j1++) { 
               namestr[j1] ="./image/"+String.valueOf(j1+1)+".gif" ; 
               img[j1]=getImage(getCodeBase(),namestr[j1]); 
               mt.addImage(img[j1],j1);
             } 
           mt.waitForAll();
          }
       catch(Exception e){
           System.out.println("init:"+e.toString());
           System.exit(0);
           }

      //创建脱屏图像
    bimg=createImage(this.getWidth(),this.getHeight());
    bg=bimg.getGraphics();
     }
  
    public void paint(Graphics g){
             g.drawImage(img[k],i,j,this);
             }

    public synchronized void update(Graphics g){
             paint(bg);
             g.drawImage(bimg,0,0,this);
             }


    public void run(){ 
       try {
            //设置优先级
           Thread.currentThread().setPriority(Thread.NORM_PRIORITY);
           while (true){ 
                 i=i+20;k=k+1;
                 if(k>=5)k=0;
                 if(i>=500){i=0;j=j+20;}
                 if(j>=500){i=0;j=20;k=0;}
                 repaint();   
                 Thread.sleep(1000);
                }
          } 
       catch (Exception e){System.out.println("Thead:"+e.toString());
                } 
       } 

    public void start() { 
          if (thd == null) { 
              thd = new Thread(this); 
              thd.start(); 
             } 
          } 

   public void stop() { 
         bg.dispose();
         thd = null; 
         }
}

问题出在：
如果最小化窗口，再最大化
Thead:java.lang.InterruptedException: sleep interrupted
Thead:java.lang.InterruptedException: sleep interrupted

以后sleep(1000)就根本不起作用了