帮忙看看代码哪错了.
import java.awt.BorderLayout;

import javax.swing.JButton;
import javax.swing.JPanel;

public class ddd extends JPanel{

private JPanel ctrlPanel = new JPanel();

public ddd()
{
this.add(ctrlPanel,BorderLayout.SOUTH);
}
public void setCtrlPanel(JPanel ctrlPanel) {
this.ctrlPanel = ctrlPanel;
}

public JPanel getCtrlPanel()
{
return ctrlPanel;
}

}

class CommonPanel extends JPanel
{
private JButton addBtn = new JButton( "添加 ");
private JButton updateBtn = new JButton( "修改 ");
private JButton delBtn = new JButton( "删除 ");
private JButton cancelBtn = new JButton( "取消 ");

public CommonPanel()
{
add(addBtn);
add(updateBtn);
add(delBtn);
add(cancelBtn);
}
}

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class ee extends ddd{
private JButton addBtn = new JButton( "添加 ");
private JButton updateBtn = new JButton( "修改 ");
private JButton delBtn = new JButton( "删除 ");
private JButton cancelBtn = new JButton( "取消 ");

ee()
{
//JPanel p3 = this.getCtrlPanel();
//p3.add(addBtn);
//p3.add(updateBtn);
//p3.add(delBtn);
//p3.add(cancelBtn);

JPanel p3 = new CommonPanel();

this.setCtrlPanel(p3);


}

/**
* @param args
*/
public static void main(String[] args) {
// TODO 自动生成方法存根
JFrame ff = new JFrame();
ff.setSize(500,400);

ee e1 = new ee();
ff.add(e1);
ff.setVisible(true);
}

}




我用setCtrlPanel方法改变了this.ctrlPanel 的引用，为什么界面不会出现那4 个按钮。


[解决办法]
class ddd1 extends JPanel {

private JPanel ctrlPanel = new JPanel();

public ddd1() {
this.add(ctrlPanel, BorderLayout.SOUTH);
}

public void setCtrlPanel(JPanel ctrlPanel) {
this.remove(this.ctrlPanel);
this.add(ctrlPanel);
this.ctrlPanel = ctrlPanel;
}

public JPanel getCtrlPanel() {
return ctrlPanel;
}

}
这样改就可以了
[解决办法]
试试吧，调整好了．
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.BorderLayout;

/**
* <p> Title: </p>
*
* <p> Description: </p>
*
* <p> Copyright: Copyright (c) 2007 </p>
*
* <p> Company: </p>
*
* @author not attributable
* @version 1.0

*/
public class ddd extends JPanel {

private JPanel ctrlPanel = new JPanel();

public ddd() {
this.add(ctrlPanel, BorderLayout.SOUTH);
}

public void setCtrlPanel(JPanel ctrlPanel) {
this.ctrlPanel = ctrlPanel;
}

public JPanel getCtrlPanel() {
return ctrlPanel;
}

}


class CommonPanel extends JPanel {
private JButton addBtn = new JButton( "添加 ");
private JButton updateBtn = new JButton( "修改 ");
private JButton delBtn = new JButton( "删除 ");
private JButton cancelBtn = new JButton( "取消 ");

public CommonPanel() {
add(addBtn);
add(updateBtn);
add(delBtn);
add(cancelBtn);
}
}


class ee extends ddd {
private JButton addBtn = new JButton( "添加 ");
private JButton updateBtn = new JButton( "修改 ");
private JButton delBtn = new JButton( "删除 ");
private JButton cancelBtn = new JButton( "取消 ");

ee() {
JPanel p3 = this.getCtrlPanel();
p3.add(addBtn);
p3.add(updateBtn);
p3.add(delBtn);
p3.add(cancelBtn);

this.setCtrlPanel(p3);

}

/**
* @param args
*/
public static void main(String[] args) {
// TODO 自动生成方法存根
JFrame ff = new JFrame();

ff.setSize(500, 400);

ee e1 = new ee();
ff.getContentPane().add(e1);
ff.setVisible(true);
}

}


[解决办法]
class ddd1 extends JPanel {

private JPanel ctrlPanel = new JPanel();

public ddd1() {
this.add(ctrlPanel, BorderLayout.SOUTH);
}

public void setCtrlPanel(JPanel ctrlPanel) {
this.add(ctrlPanel);
}

public JPanel getCtrlPanel() {
return ctrlPanel;
}

}

[解决办法]
ee e1 = new ee();→ee继承bbb→this.add(ctrlPanel,BorderLayout.SOUTH);
这个时候的ctrlPanel内并没用东西→ee构造函数内JPanel p3 = new CommonPanel();
→这个时候，才给ctrlPanel负值，所以要从新加值
也就是说bbb构造内的东西没什么用。