ما الخطأ فى هذا ال java كود؟

ما هو الخطأ فى هذا الكود ؟؟؟

What is the problem in this java source code

import java.awt.*;
import javax.swing.*;


public class GUI {


	public static void buildGUI(){
  
  


     JFrame frame = new JFrame();  
  JPanel panel1= new JPanel();
  JPanel panel2 = new JPanel();
  JPanel panel3 = new JPanel();
  

  
  JPanel mainpanel = new JPanel();
  mainpanel.setLayout(new BoxLayout(mainpanel,BoxLayout.PAGE_AXIS));
  mainpanel.setBorder(BorderFactory.createEmptyBorder(5,5,5,5));
  

  
  JButton button1 = new JButton("");
        panel1.add(button1);
        button1.addMouseListener(new java.awt.event.MouseAdapter() {
            public void mouseClicked(java.awt.event.MouseEvent evnt) {
                button1Clicked (evnt);
                button1.setText("X");
            }
        });
        
  
  
  
  JButton button2 = new JButton("");
  panel1.add(button2);
  
  
  JButton button3 = new JButton("");
  panel1.add(button3);
  
  
  JButton button4 = new JButton("");
  panel2.add(button4);
  
  JButton button5 = new JButton("");
  panel2.add(button5);
  
  
  JButton button6 = new JButton("");
  panel2.add(button6);
  
  
  JButton button7 = new JButton("");
  panel3.add(button7);
  
  
  JButton button8 = new JButton("");
  panel3.add(button8);
  
  JButton button9 = new JButton("");
  panel3.add(button9);
  
  
  
  mainpanel.add(panel1);
  mainpanel.add(panel2);
  mainpanel.add(panel3);
  
  
  
  frame.getContentPane().add(mainpanel);
  
  frame.pack();
  frame.setVisible(true);	

	}

	public static void main(String [] args){
  
  BuildGUI();
         

	}



}

و شكرا