i have hit a brick wall whilst attempting to create a two class java calculator but have been unsuccessful so far in getting it working. i have the code for an interface which works and displays ok but creating a seperate class 'CalcEngine' to do the actual calculations has proven to be beyond me. I'd appreciate it if someone could kick start things for me and create a class calcEngine which works with the interface class and allows input when from single button i.e. if one is pressed on the calc then 1 displays onscreen. please note i'm not asking someone to do the whole thing for me as i want to learn and i'm confident i can do the rest including addition subtraction etc. once i get over the obstacle of getting the two classes to communicate. any and all assistance would be very much appreciated. Please see the calcInterface class code below -

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


/**
*A Class that operates as the framework for a calculator. 
*No calculations are performed in this section
*/
public class CalcFrame
implements ActionListener
{
    private CalcEngine calc;

    private JFrame frame;
    private JTextField display;
    private JLabel status;

    /**
     * Constructor for objects of class GridLayoutExample
     */
    public CalcFrame()
    {
        makeFrame();
        //calc = engine;
    }



    /**
     * This allows you to quit the calculator.
     */

    // Alows the class to quit.
    private void quit()
    {
        System.exit(0);


    }

    // Calls the dialog frame with the information about the project.
    private void showAbout()
    {
        JOptionPane.showMessageDialog(frame, 
                    "Group Project",
                    "About Calculator Group Project", 
                    JOptionPane.INFORMATION_MESSAGE);
    }





    private void makeFrame()
    {
        frame = new JFrame("Group Project Calculator");
        makeMenuBar(frame);

        JPanel contentPane = (JPanel)frame.getContentPane();
        contentPane.setLayout(new BorderLayout(8, 8));
        contentPane.setBorder(new EmptyBorder( 10, 10, 10, 10));



        /**
     * Insert a text field
     */
        display = new JTextField();
        contentPane.add(display, BorderLayout.NORTH);

        //Container contentPane = frame.getContentPane();
        contentPane.setLayout(new GridLayout(4, 4));
        JPanel buttonPanel = new JPanel(new GridLayout(4, 4));
        contentPane.add(new JButton("1"));
        contentPane.add(new JButton("2"));
        contentPane.add(new JButton("3"));
        contentPane.add(new JButton("4"));
        contentPane.add(new JButton("5"));
        contentPane.add(new JButton("6"));
        contentPane.add(new JButton("7"));
        contentPane.add(new JButton("8"));
        contentPane.add(new JButton("9"));
        contentPane.add(new JButton("0"));
        contentPane.add(new JButton("+"));
        contentPane.add(new JButton("-"));
        contentPane.add(new JButton("/"));
        contentPane.add(new JButton("*"));
        contentPane.add(new JButton("="));
        contentPane.add(new JButton("C"));

        contentPane.add(buttonPanel, BorderLayout.CENTER);

        //status = new JLabel(calc.getAuthor());
        //contentPane.add(status, BorderLayout.SOUTH);

        frame.pack();
        frame.setVisible(true);
    }

    /**
     * Create the main frame's menu bar.
     * The frame that the menu bar should be added to.
     */
    private void makeMenuBar(JFrame frame)
    {
        final int SHORTCUT_MASK =
            Toolkit.getDefaultToolkit().getMenuShortcutKeyMask();


        JMenuBar menubar = new JMenuBar();
        frame.setJMenuBar(menubar);

        JMenu menu;
        JMenuItem item;

        // create the File menu
        menu = new JMenu("File");
        menubar.add(menu);

        // create the Quit menu with a shortcut "Q" key.
         item = new JMenuItem("Quit");
            item.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_Q, SHORTCUT_MASK));
            item.addActionListener(new ActionListener() {
                               public void actionPerformed(ActionEvent e) { quit(); }
                           });
        menu.add(item);

        // Adds an about menu.
        menu = new JMenu("About");
        menubar.add(menu);

        // Displays 
        item = new JMenuItem("Calculator Project");
            item.addActionListener(new ActionListener() {
                               public void actionPerformed(ActionEvent e) { showAbout(); }
                           });
        menu.add(item);

    }


 /**
     * An interface action has been performed.
     * Find out what it was and handle it.
     * @param event The event that has occured.
     */
    public void actionPerformed(ActionEvent event)
    {
        String command = event.getActionCommand();

        if(command.equals("0") ||
           command.equals("1") ||
           command.equals("2") ||
           command.equals("3") ||
           command.equals("4") ||
           command.equals("5") ||
           command.equals("6") ||
           command.equals("7") ||
           command.equals("8") ||
           command.equals("9")) {
            int number = Integer.parseInt(command);
            calc.numberPressed(number);
        }
        else if(command.equals("+")) {
            calc.plus();
        }
        else if(command.equals("-")) {
            calc.minus();
        }
        else if(command.equals("=")) {
            calc.equals();
        }
        else if(command.equals("C")) {
            calc.clear();
        }
        else if(command.equals("?")) {

        }
        // else unknown command.

        redisplay();
    }

    /**
     * Update the interface display to show the current value of the 
     * calculator.
     */
    private void redisplay()
    {
        display.setText("" + calc.getDisplayValue());
    }

    /**
     * Toggle the info display in the calculator's status area between the
     * author and version information.
     */

}