这个程序怎么不对！

Question

class  AllPanels  extends  JPanel  implements  ActionListener  
{  
           AllSwings  frame;  
           JButton  b1=new  JButton("White");  
           JButton  b2=new  JButton("Black");  
           JButton  b3=new  JButton("Green");  
           JButton  b4=new  JButton("Blue");  
           AllPanels()  
           {  
                       setLayout(new  GridLayout(2,2,5,5));  
                       add(b1);  b1.addActionListener(this);
                       add(b2);  b2.addActionListener(this);
                       add(b3);  b3.addActionListener(this);
                       add(b4);  b4.addActionListener(this);           }  
           public  void  actionPerformed(ActionEvent  evt)  
           {  
                       AllSwings  als=new  AllSwings();  
                       Object  source=evt.getSource();  
                       if(source==b1)  
                       {  
                                   als.swatch.setBackground(Color.white);  
                       }  
                       else  if(source==b2)  
                       {  
                                   als.swatch.setBackground(Color.black);  
                       }  
                       else  if(source==b3)  
                       {  
                                   als.swatch.setBackground(Color.green);  
                       }  
                       else  if(source==b4)  
                       {  
                                   als.swatch.setBackground(Color.blue);  
                       }  
                       repaint();  
           }  
}

Answer 1

import  java.awt.*;  
import  java.awt.event.*;  
import  javax.swing.*;  
 
public  class  AllSwings  extends  JFrame  
{   class  AllPanels  extends  JPanel  implements  ActionListener  
{  
           //AllSwings  frame;  
           JButton  b1=new  JButton("White");  
           JButton  b2=new  JButton("Black");  
           JButton  b3=new  JButton("Green");  
           JButton  b4=new  JButton("Blue");  
           AllPanels()  
           {  
                       setLayout(new  GridLayout(2,2,5,5));  
                       add(b1);  b1.addActionListener(this);
                       add(b2);  b2.addActionListener(this);
                       add(b3);  b3.addActionListener(this);
                       add(b4);  b4.addActionListener(this);

           }  
           public  void  actionPerformed(ActionEvent  evt)  
           {  
                       //AllSwings  als=new  AllSwings();  
                       Object  source=evt.getSource();
                       if(source==b1)  
                       {  
                           
                                   swatch.setBackground(Color.white);  
                       }  
                       else  if(source==b2)  
                       {  
                                   swatch.setBackground(Color.black);  
                       }  
                       else  if(source==b3)  
                       {  
                                   swatch.setBackground(Color.green);  
                       }  
                       else  if(source==b4)  
                       {  
                                   swatch.setBackground(Color.blue);  
                       }  
                       repaint();  
           }  
}           AllPanels  pls;  
           JPanel  swatch;  
           AllSwings()  
           {  
                       setTitle("AllSwings");  
                       setSize(300,100);  
                         
                       JPanel  pane=new  JPanel();  
                       pane.setLayout(new  GridLayout(1,2,5,10));  
                         
                       swatch=new  JPanel();  
                       swatch.setBackground(Color.black);  
                         
                       pls=new  AllPanels();  
                       pane.add(swatch);  
                       pane.add(pls);  
                         
                       setContentPane(pane);                          
           }  
           public  static  void  main(String[]  args)  
           {  
                       AllSwings  as=new  AllSwings();  
                       as.setResizable(false);  
                       as.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
                       as.show();  
           }  
}  
把AllPanels变成内部类倒是挺简单的，但是方法不太好，呵呵!