Hjælp med GUI'en

Hej folkens!! skal op til java eksamen snart.
Har fået udleveret følgende spørgsmål, som jeg ik har styr på. Nogen der kan hjælpe??

1)Kort beskrivelse af, hvad der sker i GUI'en.

2)Beskriv udfra implementationen den metode, som opbygger GUI- framen.

2)Beskriv udfra implementationen af klassen, hvordan metoden actionPerformed()virker, f.eks. når clear-knappen aktiveres.

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

/**
* A graphical user interface for the calculator. No calculation is being
* done here. This class is responsible just for putting up the display on
* screen.
*/
public class CalculatorGUI implements ActionListener
{
    private CalculatorUI ui;
    private JFrame frame;
    private JTextField display;
    private JLabel status;
    private static String version = "version 1.0";
    private String displaystring;
    private State state;
    private CalculatorEngine engine = new CalculatorEngine(true);

    /**
    * Creates a user interface for a given calculator.
    */
    public CalculatorGUI()
    {
        makeFrame();
        frame.setVisible(true);
        displaystring = "";
    }

    /**
    * Make this interface visible again. (Has no effect if it is already
    * visible.)
    */
    public void setVisible(boolean visible)
    {
        frame.setVisible(visible);
    }

    /**
    * Makes the frame for the user interface.
    */
    private void makeFrame()
    {
        //Create a Frame window with a title
        frame = new JFrame("The ITD12 Calculator");
        //Make a menu bar
        makeMenuBar(frame);
       
        //Get the content pane for this frame to hold GUI-components
        Container contentPane = frame.getContentPane();

        //Set a border layout for the content pane
        contentPane.setLayout(new BorderLayout());

        //Create a text field window
        display = new JTextField();

        //Create a label
        status = new JLabel("Morten og Jesper");
       
        //Place the text field in the content panes northern border
        contentPane.add(display, BorderLayout.NORTH);
        //Place the label in the content panes southern border
        contentPane.add(status, BorderLayout.SOUTH);

        //Now create a button panel with a grid layout holding all the buttons
        //The grid has 5 rows and 4 columns
        JPanel buttonPanel = new JPanel(new GridLayout(5,4));
            //Row 1
            buttonPanel.add(new JLabel(" ")); //Column 1
            buttonPanel.add(new JLabel(" ")); //Column 2
            buttonPanel.add(new JLabel(" ")); //Column 3
            addButton(buttonPanel, "C");      //Column 4
            //Row 2
            addButton(buttonPanel, "7");
            addButton(buttonPanel, "8");
            addButton(buttonPanel, "9");
            addButton(buttonPanel, "/");
            //Row 3
            addButton(buttonPanel, "4");
            addButton(buttonPanel, "5");
            addButton(buttonPanel, "6");
            addButton(buttonPanel, "*");
            //Row 4
            addButton(buttonPanel, "1");
            addButton(buttonPanel, "2");
            addButton(buttonPanel, "3");
            addButton(buttonPanel, "-");
            //Row 5           
            addButton(buttonPanel, "0");
            addButton(buttonPanel, ".");
            addButton(buttonPanel, "=");
            addButton(buttonPanel, "+");
       
        //Place the button panel in the content panes center border
        contentPane.add(buttonPanel, BorderLayout.CENTER);
       
       
        //Make the window fit the layouts set up
        frame.pack();   
    }

    /**
    * Sets up a menubar with menus and menu items
    */
    private void makeMenuBar(JFrame frame)
    {
        //Create a menu bar
        JMenuBar menuBar = new JMenuBar();
        //Add it to the frame
        frame.setJMenuBar(menuBar);

        //Create a menu
        JMenu helpMenu = new JMenu("Help");
        //Push the menu to the right
        menuBar.add(Box.createHorizontalGlue());
        //Add it to the menu bar
        menuBar.add(helpMenu);

        //Create a menu item
        JMenuItem aboutItem = new JMenuItem("About");
        //add it to the help menu
        helpMenu.add(aboutItem);
        //add this object to the action listener
        aboutItem.addActionListener(this);

    }

    /**
    * Add a button to the button panel.
    */
    private void addButton(JPanel buttonPanel, String buttonText)
    {
        JButton button = new JButton(buttonText);
        button.addActionListener(this);
        buttonPanel.add(button);
    }


    private void onAbout()
    {
        JOptionPane.showMessageDialog(frame, "Simple calculator " + version + "\n" + "Created by Kaleb & Fatih");
    }


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

        if (command.equals("About"))
        {
            onAbout();
            return;
        }

        char chr = command.charAt(0);
       
        displaystring += command;
       
        display.setText(displaystring);
       
        state.ui.parseInput(chr);
       
        System.out.println("Test result from CalculatorGUI : " + state.engine.getResult());
       
        String convertstring = "";
       
            if (chr == '=')
            {
       
            display.setText(convertstring + state.engine.getResult());
            displaystring = "";
            }
           
                else if (chr == 'C')
                {
                    displaystring = "";
                    display.setText(displaystring);
                }
               
           
            System.out.println("Button pressed: " + chr);

    }

}