如何在jframe中导入两张图片（gif），让一个押在另一个上边……

Question

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;public class applet3  extends JFrame implements Runnable {
Image img1;
Image img2;
MediaTracker mt;
JPanel contentPanel=(JPanel)this.getContentPane();
int myLeft=0;
Thread thread=new Thread(this);
public applet3() {
super("myJFrame");
this.setSize(400,300);
this.setResizable(false);
this.setLocation(this.getToolkit().getScreenSize().width/2-this.getWidth()/2,this.getToolkit().getScreenSize().height/2-this.getHeight()/2);
img1=this.getToolkit().getImage("1.jpg");
img2=this.getToolkit().getImage("2.jpg");
mt=new MediaTracker(this);
mt.addImage(img1,0);
mt.addImage(img2,0);
try {
      mt.waitForAll(0);
    }catch(Exception e) {
      System.out.println(e.toString());
      return;
    }
this.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
contentPanel.addMouseListener(new MouseAdapter() {
      public void mouseClicked(MouseEvent e) {
        try{thread.start();}catch(Exception ex){System.out.println(ex.toString());}
      }
});
this.setVisible(true);
}public void run() {
try{
while((myLeft+=5)<=this.getWidth()) {
      this.repaint();
      Thread.sleep(100);
}}catch(Exception e){}
}public void update(Graphics g) {
  g.clearRect(0,0,this.getWidth(),this.getHeight());
  g.drawImage(img2,0,0,this.getWidth(),this.getHeight(),this);
  g.drawImage(img1,myLeft,0,this.getWidth(),this.getHeight(),this);
}public void paint(Graphics g) {
    g.drawImage(img1,0,0,this.getWidth(),this.getHeight(),this);
}public static void main(String args[]) {
    new applet3();
}
}