FileDocCategorySizeDatePackage
MenuScribble.javaAPI DocExample7167Mon Sep 22 13:30:30 BST 1997None

MenuScribble

public class MenuScribble extends Applet implements ActionListener
An applet with a popup menu or an application with pulldown menus

Fields Summary
protected int
lastx
protected int
lasty
protected Color
color
protected PopupMenu
popup
Constructors Summary
Methods Summary
public voidactionPerformed(java.awt.event.ActionEvent e)
This is the method defined by the ActionListener interface. All the menu item commands are handled here because the applet was specified as the listener for all menu items. Note the use of getActionCommand() to determine the command string registered with the individual items.

    String cmd = e.getActionCommand();
    if (cmd.equals("quit")) System.exit(0);   // Don't do this in an applet
    else if (cmd.equals("clear")) clear();    // defined below
    else if (cmd.equals("about")) /* not yet implemented */ ;
    else if (cmd.equals("red")) color = Color.red;
    else if (cmd.equals("green")) color = Color.green;
    else if (cmd.equals("blue")) color = Color.blue;
    else if (cmd.equals("black")) color = color.black;
protected voidclear()
Clear the applet area. Used by actionPerformed() above

    Graphics g = this.getGraphics();
    g.setColor(this.getBackground());
    g.fillRect(0, 0, this.getSize().width, this.getSize().height);
protected static voidcreateMenuItems(java.awt.Menu pane, java.awt.event.ActionListener listener, java.lang.String[] labels, java.lang.String[] commands, int[] shortcuts)
This is the convenience routine for adding menu items to a menu pane. It works for pulldown or popup menu panes, since PopupMenu extends Menu.

    for(int i = 0; i < labels.length; i++) {
      MenuItem mi = new MenuItem(labels[i]);
      mi.addActionListener(listener);
      if ((commands != null) && (commands[i] != null))
        mi.setActionCommand(commands[i]);
      if ((shortcuts != null) && (shortcuts[i] != 0))
        mi.setShortcut(new MenuShortcut(shortcuts[i]));
      pane.add(mi);
    }
public voidinit()
The init() method. If the program is invoked as an applet, the browser allocates screen space for it and calls this method to set things up. If running as an applet, this method creates a popup menu and adds it to the applet.

    // If we are not in a frame (i.e. we are an applet), create a popup menu
    if (!(this.getParent() instanceof Frame)) {
      // Create the popup menu
      popup = new PopupMenu("File");
      // Add items to it using the convenience routine below
      createMenuItems(popup, this,
                      new String[] {"Clear", "Red", "Green", "Blue", "Black"},
                      new String[] {"clear", "red", "green", "blue", "black"},
                      new int[] { KeyEvent.VK_C, KeyEvent.VK_R, KeyEvent.VK_G,
                                    KeyEvent.VK_B, KeyEvent.VK_L });
      // Add the popup menu to the component it will appear over.
      this.add(popup);
    }

    // Define, instantiate and register the Listener objects for scribbling
    this.addMouseListener(new MouseAdapter() {
      public void mousePressed(MouseEvent e) {
        lastx = e.getX(); lasty = e.getY();
      }
    });
    this.addMouseMotionListener(new MouseMotionAdapter() {
      public void mouseDragged(MouseEvent e) {
        Graphics g = getGraphics();
        int x = e.getX(), y = e.getY();
        g.setColor(color);               // draw with the specified color
        g.drawLine(lastx, lasty, x, y);
        lastx = x; lasty = y;
      }
    });
public static voidmain(java.lang.String[] args)
The main() method. If this program is invoked as an application, this method will create a window and pulldown menu system for it.

    Frame f = new Frame();                     // Create a window
    MenuScribble applet = new MenuScribble();  // Create the applet panel
    f.add(applet, "Center");                   // Add applet to window
    applet.init();                             // Initialize the applet

    // Create a menubar and tell the frame about it
    MenuBar menubar = new MenuBar();
    f.setMenuBar(menubar);

    // Create three pulldown menus for the menubar
    Menu file = new Menu("File");
    Menu colors = new Menu("Colors");
    Menu help = new Menu("Help");

    // Add the menus to the bar, and treat Help menu specially.
    menubar.add(file);
    menubar.add(colors);
    menubar.add(help);
    menubar.setHelpMenu(help);

    // Add two items, with a keyboard shortcuts to the File menu
    MenuItem clear = new MenuItem("Clear", new MenuShortcut(KeyEvent.VK_C));
    clear.addActionListener(applet);   // Say who's listening for the events
    clear.setActionCommand("clear");   // A detail to go along with the events
    file.add(clear);                   // Add item to menu pane
    MenuItem quit = new MenuItem("Quit", new MenuShortcut(KeyEvent.VK_Q));
    quit.addActionListener(applet);
    quit.setActionCommand("quit");
    file.add(quit);

    // Add items to the other two menus, this time using a  convenience
    // method defined below.  Note use of new anonymous array syntax.
    createMenuItems(colors, applet,
                    new String[] { "Red", "Green", "Blue", "Black" },
                    new String[] { "red", "green", "blue", "black" },
                    new int[] { KeyEvent.VK_R, KeyEvent.VK_G,
                                KeyEvent.VK_B, KeyEvent.VK_L });
    createMenuItems(help, applet,
                    new String[] { "About" }, new String[] {"about"},
                    new int[] { KeyEvent.VK_A });

    // Handle window close requests
    f.addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) { System.exit(0); }
    });

    f.setSize(400, 400);     // Set the size of the window
    f.show();                // Finally, pop the window up.
public voidprocessMouseEvent(java.awt.event.MouseEvent e)
This method is required to make the popup menu, if any, pop up. It uses the low-level Java 1.1 event handling mechanism to test all mouse events (except mouse motion events) to see if they are the platform- dependent popup menu trigger. If so, it calls show() to pop the popup up. If not, it passes the event to the superclass version of this method so that it is dispatched as usual and can be passed to the listener object registered by the init method for scribbling.

    if ((popup != null) && e.isPopupTrigger())
      popup.show(this, e.getX(), e.getY());
    else super.processMouseEvent(e);