I get the error DelegatingMethodAccessor when i run this code from AlphaApp

[babs115]

atsun.reflect.D elegatingMethod AccessorImpl.in voke(Delegating MethodAccessorI mpl.java:43)
at java.lang.refle ct.Method.invok e(Method.java:4 97)
at bluej.runtime.E xecServer$3.run (ExecServer.jav a:730)

MainMenu

import java.awt.*;
import java.io.*;
import java.util.*;
import java.net.*;
import javax.swing.*;
import java.awt.event.*;
import java.awt.FlowLayout.*;

public class MainMenu extends JPanel
{
   static JLabel title, advert;
   static JButton addBooks, addSoftware, addProduct, viewCart, makeOrder;
   static JPanel manuPanel; 
   static CardLayout cardLayout; 
   static FlowLayout flowLayout;
   
   
   static public ArrayList<Order> orderHistory = new ArrayList<Order>();
   static public ArrayList<Book> bookList = new ArrayList<Book>();
   static public ArrayList<Cart> cart = new ArrayList<Cart>();
   static public ArrayList<Software> softwareList = new ArrayList<Software>();
   
   @SuppressWarnings("unchecked") //  gets rid of the unchecked or unsafe warning
   public MainMenu(){                    
       final String dir = System.getProperty("user.dir");
       Color Gray = new Color(1,1,1); 
       Color titleColor = new Color(1,1,1);
        
       setLayout(new FlowLayout());       
       manuPanel = new JPanel(new FlowLayout());
      
       addBooks = new JButton("ADD BOOKS");
       addBooks.setLocation (30,450);//(30,450);
       addBooks.setSize(80,40);
        add(addBooks);
        
       addSoftware = new JButton("ADD SOFTWARE");
       addSoftware.setLocation(30,451);
       addSoftware.setSize(80,40);
        add(addSoftware);       
       
       makeOrder = new JButton("MAKE ORDER");
       makeOrder.setLocation(30,452);
       makeOrder.setSize(80,40);
        add(makeOrder);
        
       viewCart = new JButton("VIEW CART");
       viewCart.setLocation(30,453);
       viewCart.setSize(80,40);
        add(viewCart);

         addBooks.addActionListener(new ActionListener()
         {
            public void actionPerformed(ActionEvent evt)
            {
                Product bookID = new Product();       //int productID = bookID.getproductID();          
               AlphaApp.cardLayout.show(AlphaApp.cards, "Add Books");
            }
        });
        
        addSoftware.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent evt)
            {
                                            
              AlphaApp.cardLayout.show(AlphaApp.cards, "Add Softwares");
            }
        });
        

        makeOrder.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent evt)
            {  
                AlphaApp.window.setSize(1200,800);
                AlphaApp.window.setResizable(false);
                AlphaApp.window.setLocationRelativeTo(null);  
                AlphaApp.makeOrderCard.book.setSelected(true);
                AlphaApp.makeOrderCard.updateBookTable();
                AlphaApp.cardLayout.show(AlphaApp.cards, "Make Order");              
            }
        });
        
        viewCart.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent evt)
            {
        boolean emptyRow = AlphaApp.viewCartCard.historyTable.getSelectedRowCount() > 0;
        if(!emptyRow){
           AlphaApp.viewCartCard.populateHistoryTable();               
        }else{
            JOptionPane.showMessageDialog(null, "MAKE AN ORDER!", "Information", JOptionPane.WARNING_MESSAGE);
        }
                AlphaApp.window.setSize(1000,600);
                AlphaApp.window.setLocationRelativeTo(null);     
                //AlphaApp.viewCartCard.updateCartTable();
                //AlphaApp.viewCartCard.updateOrderTable();       
                //AlphaApp.viewCartCard.populateHistoryTable(); 
                AlphaApp.cardLayout.show(AlphaApp.cards, "View Cart");              
            }
        });
        

      
        add(manuPanel);
        manuPanel.add(addBooks, "split 2, gapTop 130, gapRight 65"); 
        manuPanel.add(addSoftware, "gapTop 130, wrap");     
        manuPanel.add(makeOrder, "split 2, gapTop 50, gapRight 60");   
        manuPanel.add(viewCart, " sg a, wrap, gapTop 50");     
        
   
}

AlphaApp

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

public class AlphaApp extends JFrame
{
    static JFrame window;    
    static public CardLayout cardLayout;    
    static public JPanel cards;  
    
    MainMenu menu = new MainMenu();
    
    static public AddBooks addBooks = new AddBooks();
    static public AddSoftware addSoftwares = new AddSoftware();
    static public MakeOrder makeOrderCard = new MakeOrder();
    static public ViewCart viewCartCard = new ViewCart();
   
    
    public static void main(String [] args){
        try {  
                UIManager.setLookAndFeel("javax.swing.plaf.metal.MetalLookAndFeel");
                  
            }  
            catch (Exception ex1){}
            
       AlphaApp app = new AlphaApp();   
    }
    
    public AlphaApp(){        
        window = new JFrame("");
        window.setSize(800,600);
        window.setLocationRelativeTo(null);    // trying to center the window
        //window.setMinimumSize(new Dimension(400, 400)); // frame size
        window.setResizable(true);  
        
        
        cardLayout = new CardLayout();  // PANELS     
        cards = new JPanel(cardLayout);   //PANELS
        
             
       
                
        window.add(cards);
        cards.add(menu, "Main Menu");
        cards.add(addBooks, "Add Books");
        cards.add(addSoftwares, "Add Softwares");
        cards.add(makeOrderCard, "Make Order");
        cards.add(viewCartCard, "View Cart");
                       
        cardLayout.show(cards, "Main Menu");
        window.setVisible(true);
    }
    
   
}