请看看我的程序为何不能重绘呢？

[ximenwushuang2000]

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
public class Gobang extends Frame
{
Image oimg = null;
Graphics og = null;
Image img = this.getToolkit().getImage("C:\\bmw.JPG");
public static void main(String[] args)
{
new Gobang().init();
}
public void init()
{
setSize(300,300);
setVisible(true);
this.addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
System.exit(0);
}
});
Graphics g = this.getGraphics();
g.setColor(Color.GRAY);
for(int i=1;i<=9;i++)
{
g.drawLine(0,i*30,300,i*30);
g.drawLine(i*30,0,i*30,300);
}
this.addMouseListener(new MouseAdapter(){
public void mouseReleased(MouseEvent e)
{
Graphics g = e.getComponent().getGraphics();
g.drawImage(img,e.getX(),e.getY(),null);
og.drawImage(img,e.getX(),e.getY(),null);
}
});
Dimension d = this.getSize();
oimg = createImage(d.width,d.height);
og = oimg.getGraphics();
}
public void paint(Graphics g)
{
if(oimg != null)
og.drawImage(oimg,0,0,this);
}
}