Java Linked Lists and Iterators Part 1 Design and implement a class Menu which u

Question

Java Linked Lists and Iterators

Part 1

Design and implement a class Menu which uses doubly linked lists as main data structures. A menu consists of main menu items, organized as a doubly linked list, each main menu item having associated a submenu, organized as a doubly linked list of submenu items (see an example of a Menu object in the file MenuExample.pdf posted below).

The class Menu should define a default constructor which builds an empty menu and the following methods:

- addMainMenuItem, for adding a new main menu item with empty submenu. The method should have the following signature:

     public boolean addMainMenuItem(String newItem, String existingItem,
                                                           int position)

This method works in the following way:
(i) if parameter existingItem is null, the newItem will be added at the end of the list;
(ii) if the parameter existingItem is not null, the newItem will be added before existingItem if parameter position is -1 and after the existinItem if parameter position is 1;

- deleteMainMenuItem, deletes the main menu item specified by name;

- addSubMenuItem, adds a submenu item specified by name to a main menu item specified by name;

- toString, traverses the linked lists data structures and generates the string representation of a menu object, organized on lines. Each line should include the main menu item followed by its submenu items. The items should be separated by a semicolon character. The toString method will be invoked from other programs (such as the driver of Part 2) to display the menu.

Note. If necessary, additionally (housekeeping) methods may be defined for the class Menu. Give reasons for the new added methods. The class Menu.java should compile without errors.

Part 2

Write a driver program MenuTest.java to test the Menu class. In the driver program, do the following tasks:

a) Read menu items from the input file Menu.txt and build a menu object which includes the specified items. Each file line contains a main menu item followed by its submenu items, all items being separated by the semicolon character. After reading the file and building the menu, display the menu.

Example of the content of the input file Menu.txt:

File;New;Open;Save;SaveAs;Close;
View;Color;Gray;Zoom;Ruler;Grid;
Process;Select;Move;Rotate;Scale;Delete;Group;
About;Release;Version;Contact;Description;

In the example above, File, View, Process and About are the main menu items. The main menu item File has New, Open, Save, SaveAs and Close as its submenu items.

b) Add a new main menu item and its associated submenu before a main menu item specified by the user. Read the data from the input file MenuAdd.txt. Using the toString method, display the menu after adding the new item.

c) Delete the previously added menu item. Using the toString method, display the menu after deleting the menu item.

d) Add a new main menu item and its associated submenu after a main menu item of an existing menu. Read the data from the input file MenuAdd.txt. Using the toString method, display the menu after adding the new item.

The input file MenuAdd.txt contains one line specifying the new main menu item and its submenu items.

Example of the content of the input file MenuAdd.txt for adding a new menu item

Layout;Margins;Orientation;Size;

The example above indicates that the main menu item Layout has the submenu items Margins, Orientation and Size.

Note. The input files Menu.txt and MenuAdd.txt will be created by the students using a simple text editor (such as Notepad).

Explanation / Answer

public class PopupMenuDemo implements ActionListener, ItemListener {
  JTextArea output;

  JScrollPane scrollPane;

  String newline = " ";

  public JMenuBar createMenuBar() {
    JMenuBar menuBar;
    JMenu menu, submenu;
    JMenuItem menuItem;
    JRadioButtonMenuItem rbMenuItem;
    JCheckBoxMenuItem cbMenuItem;

    //Create the menu bar.
    menuBar = new JMenuBar();

    //Build the first menu.
    menu = new JMenu("A Menu");
    menu.setMnemonic(KeyEvent.VK_A);
    menu.getAccessibleContext().setAccessibleDescription(
        "The only menu in this program that has menu items");
    menuBar.add(menu);

    //a group of JMenuItems
    menuItem = new JMenuItem("A text-only menu item", KeyEvent.VK_T);
    //menuItem.setMnemonic(KeyEvent.VK_T); //used constructor instead
    menuItem.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_1,
        ActionEvent.ALT_MASK));
    menuItem.getAccessibleContext().setAccessibleDescription(
        "This doesn't really do anything");
    menuItem.addActionListener(this);
    menu.add(menuItem);

    ImageIcon icon = createImageIcon("images/1.gif");
    menuItem = new JMenuItem("Both text and icon", icon);
    menuItem.setMnemonic(KeyEvent.VK_B);
    menuItem.addActionListener(this);
    menu.add(menuItem);

    menuItem = new JMenuItem(icon);
    menuItem.setMnemonic(KeyEvent.VK_D);
    menuItem.addActionListener(this);
    menu.add(menuItem);

    //a group of radio button menu items
    menu.addSeparator();
    ButtonGroup group = new ButtonGroup();

    rbMenuItem = new JRadioButtonMenuItem("A radio button menu item");
    rbMenuItem.setSelected(true);
    rbMenuItem.setMnemonic(KeyEvent.VK_R);
    group.add(rbMenuItem);
    rbMenuItem.addActionListener(this);
    menu.add(rbMenuItem);

    rbMenuItem = new JRadioButtonMenuItem("Another one");
    rbMenuItem.setMnemonic(KeyEvent.VK_O);
    group.add(rbMenuItem);
    rbMenuItem.addActionListener(this);
    menu.add(rbMenuItem);

    //a group of check box menu items
    menu.addSeparator();
    cbMenuItem = new JCheckBoxMenuItem("A check box menu item");
    cbMenuItem.setMnemonic(KeyEvent.VK_C);
    cbMenuItem.addItemListener(this);
    menu.add(cbMenuItem);

    cbMenuItem = new JCheckBoxMenuItem("Another one");
    cbMenuItem.setMnemonic(KeyEvent.VK_H);
    cbMenuItem.addItemListener(this);
    menu.add(cbMenuItem);

    //a submenu
    menu.addSeparator();
    submenu = new JMenu("A submenu");
    submenu.setMnemonic(KeyEvent.VK_S);

    menuItem = new JMenuItem("An item in the submenu");
    menuItem.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_2,
        ActionEvent.ALT_MASK));
    menuItem.addActionListener(this);
    submenu.add(menuItem);

    menuItem = new JMenuItem("Another item");
    menuItem.addActionListener(this);
    submenu.add(menuItem);
    menu.add(submenu);

    //Build second menu in the menu bar.
    menu = new JMenu("Another Menu");
    menu.setMnemonic(KeyEvent.VK_N);
    menu.getAccessibleContext().setAccessibleDescription(
        "This menu does nothing");
    menuBar.add(menu);

    return menuBar;
  }

  public Container createContentPane() {
    //Create the content-pane-to-be.
    JPanel contentPane = new JPanel(new BorderLayout());
    contentPane.setOpaque(true);

    //Create a scrolled text area.
    output = new JTextArea(5, 30);
    output.setEditable(false);
    scrollPane = new JScrollPane(output);

    //Add the text area to the content pane.
    contentPane.add(scrollPane, BorderLayout.CENTER);

    return contentPane;
  }

  public void createPopupMenu() {
    JMenuItem menuItem;

    //Create the popup menu.
    JPopupMenu popup = new JPopupMenu();
    menuItem = new JMenuItem("A popup menu item");
    menuItem.addActionListener(this);
    popup.add(menuItem);
    menuItem = new JMenuItem("Another popup menu item");
    menuItem.addActionListener(this);
    popup.add(menuItem);

    //Add listener to the text area so the popup menu can come up.
    MouseListener popupListener = new PopupListener(popup);
    output.addMouseListener(popupListener);
  }

  public void actionPerformed(ActionEvent e) {
    JMenuItem source = (JMenuItem) (e.getSource());
    String s = "Action event detected." + newline + "    Event source: "
        + source.getText() + " (an instance of " + getClassName(source)
        + ")";
    output.append(s + newline);
    output.setCaretPosition(output.getDocument().getLength());
  }

  public void itemStateChanged(ItemEvent e) {
    JMenuItem source = (JMenuItem) (e.getSource());
    String s = "Item event detected."
        + newline
        + "    Event source: "
        + source.getText()
        + " (an instance of "
        + getClassName(source)
        + ")"
        + newline
        + "    New state: "
        + ((e.getStateChange() == ItemEvent.SELECTED) ? "selected"
            : "unselected");
    output.append(s + newline);
    output.setCaretPosition(output.getDocument().getLength());
  }

  // Returns just the class name -- no package info.
  protected String getClassName(Object o) {
    String classString = o.getClass().getName();
    int dotIndex = classString.lastIndexOf(".");
    return classString.substring(dotIndex + 1);
  }

  /** Returns an ImageIcon, or null if the path was invalid. */
  protected static ImageIcon createImageIcon(String path) {
    java.net.URL imgURL = PopupMenuDemo.class.getResource(path);
    if (imgURL != null) {
      return new ImageIcon(imgURL);
    } else {
      System.err.println("Couldn't find file: " + path);
      return null;
    }
  }

  /**
   * Create the GUI and show it. For thread safety, this method should be
   * invoked from the event-dispatching thread.
   */
  private static void createAndShowGUI() {
    //Make sure we have nice window decorations.
    JFrame.setDefaultLookAndFeelDecorated(true);

    //Create and set up the window.
    JFrame frame = new JFrame("PopupMenuDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //Create/set menu bar and content pane.
    PopupMenuDemo demo = new PopupMenuDemo();
    frame.setJMenuBar(demo.createMenuBar());
    frame.setContentPane(demo.createContentPane());

    //Create and set up the popup menu.
    demo.createPopupMenu();

    //Display the window.
    frame.setSize(450, 260);
    frame.setVisible(true);
  }

  public static void main(String[] args) {
    //Schedule a job for the event-dispatching thread:
    //creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        createAndShowGUI();
      }
    });
  }

  class PopupListener extends MouseAdapter {
    JPopupMenu popup;

    PopupListener(JPopupMenu popupMenu) {
      popup = popupMenu;
    }

    public void mousePressed(MouseEvent e) {
      maybeShowPopup(e);
    }

    public void mouseReleased(MouseEvent e) {
      maybeShowPopup(e);
    }

    private void maybeShowPopup(MouseEvent e) {
      if (e.isPopupTrigger()) {
        popup.show(e.getComponent(), e.getX(), e.getY());
      }
    }
  }
}
           
         

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