进入瞧瞧这是怎么回事呀

Question

以下这个小程序的目的是:点击一下鼠标,换一幅图片.
但是没有达到预期的效果呀.请高手帮助给改一下呀
import   java.applet.*;
import   java.awt.*;
import   java.awt.event.*;
public class gun   extends   Applet   implements   MouseListener{
Image   image,shot1,shot2;
Graphics     draw;
boolean  b;
int  appletwidth,appletheight;
public   void  init(){
setBackground(Color.darkGray);
appletwidth=getSize().width;
appletheight=getSize().height;
addMouseListener(this);
shot1=getImage(getDocumentBase(),"image/java1.gif");
shot2=getImage(getDocumentBase(),"image/java2.gif");
image=createImage(appletwidth,appletheight);
draw=image.getGraphics();
setSize(700,700);
}
public  void  update(Graphics   g){paint(g);}
public  void   paint(Graphics  g){
g.drawImage(image,0,0,this);
  draw.drawImage(shot2,20,20,this);b=false;



}

public  void  mouseClicked(MouseEvent  e){
b=true;
if(b)  {  draw.clearRect(0,0,appletwidth,appletheight);
        draw.drawImage(shot2,20,20,this);b=false;
}if(!b){ draw.clearRect(0,0,appletwidth,appletheight);
   draw.drawImage(shot1,20,20,this);
   b=true;
} 
repaint();
} public  void   mousePressed(MouseEvent  e){}
public  void   mouseReleased(MouseEvent  e){}
public  void  mouseEntered(MouseEvent  e){}
public  void  mouseExited(MouseEvent  e){}

}

Answer 1

package com.test;import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.io.File;import javax.imageio.ImageIO;public class gun extends Applet implements MouseListener {
Image image, shot1, shot2; Graphics draw; boolean b; int appletwidth, appletheight; public void init() {
setBackground(Color.darkGray);
appletwidth = getSize().width;
appletheight = getSize().height;
addMouseListener(this);shot1=getImage(getDocumentBase(), "image/java1.gif "); 
shot2=getImage(getDocumentBase(), "image/java2.gif ");  image = createImage(appletwidth, appletheight);
draw = image.getGraphics();
setSize(700, 700);
} public void update(Graphics g) {
paint(g);
} public void paint(Graphics g) {
g.drawImage(image, 0, 0, this);
// draw.drawImage(shot2, 20, 20, this);
// b = false;
} public void mouseClicked(MouseEvent e) {
System.out.println(b);
// b = true;
if (b) {
image = shot2;
// draw.clearRect(0, 0, appletwidth, appletheight);
// draw.drawImage(shot2, 20, 20, this);
b = false;
} else if (!b) {
image = shot1;
// draw.clearRect(0, 0, appletwidth, appletheight);
// draw.drawImage(shot1, 20, 20, this);
b = true;
}
repaint();
} public void mousePressed(MouseEvent e) {
} public void mouseReleased(MouseEvent e) {
} public void mouseEntered(MouseEvent e) {
} public void mouseExited(MouseEvent e) {
}}