jPanel问题

[yugijava]

高手看看~~谢了~~
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.table.*;
import com.person.main.ui.*;
import com.person.goods.ui.*;

public class Login extends JFrame{
//====================JMenu Start=================================================
private JMenuBar JBarFinance = new JMenuBar();
private JMenu JMenuGoods= new JMenu("商品");
private JMenuItem JMItemGoodsInto=new JMenuItem("商品信息操作");
private JMenu JMenuWage= new JMenu("工资");
private JMenuItem JMItemWageInto=new JMenuItem("工资录入");
private JMenuItem JMItemWageSearch=new JMenuItem("工资查询");
private JMenu JMenuEvent= new JMenu("备忘录");
private JMenuItem JMItemEventInto=new JMenuItem("工资录入");
private JMenuItem JMItemEventSearch=new JMenuItem("工资查询");
private JMenuItem JMItemExit= new JMenuItem("退出系统");
private GoodsMain goodsmain = new GoodsMain(this);
//====================JMenu end=================================================
ImageIcon icon=new ImageIcon("f:/A.jpg");
private JLabel ico = new JLabel(icon);
public Login(){
createUI();
addListener();
}
private void createUI(){
//=============================JMenuBar Add Start===============================
JMenuGoods.add(JMItemGoodsInto);
JBarFinance.add(JMenuGoods);
JBarFinance.add(JMenuWage);
JBarFinance.add(JMenuEvent);
JBarFinance.add(JMItemExit);
this.setJMenuBar(JBarFinance);
//=============================JMenuBar Add End=================================
back(ico);
// this.getContentPane().add("Center",ico) ;
this.setSize(900,600) ;
//=============================设置窗体在屏幕的中间 ============================
Dimension size = Toolkit.getDefaultToolkit().getScreenSize() ;
this.setLocation( (size.width-850)/2,(size.height-600)/2);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE) ;
}
public void back(Component aa){
this.getContentPane().add("Center",aa) ;

}

private void addListener(){
JMItemGoodsInto.addActionListener(new ActionListener(){public void actionPerformed(ActionEvent ae){
back(goodsmain);
//this.getContentPane().add("Center",goodsmain);
System.out.print("aaaaaaaa");
}
});
JMItemExit.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent ae){
int Exiting=1;
if(Exiting==0){
System.exit(0);
}
}
});
}
public static void main(String args[]){
new Login().setVisible(true);
}
}
小弟做一个程序把一个图片加到了label上，然后又把这个label加到JFrame上~~但是当我点击JFrame上的一个按钮来加载一个JPanel的时候JPanel显示不出来~请高手指点一下！！在线等~~谢谢了~~

[xtaotao]

private void addListener(){
JMItemGoodsInto.addActionListener(new ActionListener(){public void actionPerformed(ActionEvent ae){
back(goodsmain);
//this.getContentPane().add("Center",goodsmain);
this.paintComponents(this.getGraphics()); //加上这句应该可以了
System.out.print("aaaaaaaa");
}
});

还应该有别的方法吧，关注中。。。。。