This class is protected so that it can be subclassed by other look and feels to implement their own mouse handling behavior. All overridden methods should call the parent methods so that the menu selection is correct. 

 protected ChangeListener createChangeListener(JComponent c) 
{
        return null;
}

 protected MenuDragMouseListener createMenuDragMouseListener(JComponent c) 
{
        return getHandler();
}

 protected MenuKeyListener createMenuKeyListener(JComponent c) 
{
        return (MenuKeyListener)getHandler();
}

 protected MenuListener createMenuListener(JComponent c) 
{
        return null;
}

 protected MouseInputListener createMouseInputListener(JComponent c) 
{
        return getHandler();
}

 protected PropertyChangeListener createPropertyChangeListener(JComponent c) 
{
        return getHandler();
}

 public static ComponentUI createUI(JComponent x) 
{
         
        return new BasicMenuUI();
}

 BasicMenuItemUI.Handler getHandler() 
{
        if (handler == null) {
            handler = new Handler();
        }
        return handler;
}

 public Dimension getMaximumSize(JComponent c) 
{
        if (((JMenu)menuItem).isTopLevelMenu() == true) {
            Dimension d = c.getPreferredSize();
            return new Dimension(d.width, Short.MAX_VALUE);
        }
        return null;
}

 protected String getPropertyPrefix() 
{
        return "Menu";
}

 protected  void installDefaults() 
{
        super.installDefaults();
        updateDefaultBackgroundColor();
        ((JMenu)menuItem).setDelay(200);
        crossMenuMnemonic = UIManager.getBoolean("Menu.crossMenuMnemonic");
}

 protected  void installKeyboardActions() 
{
        super.installKeyboardActions();
        updateMnemonicBinding();
}

  void installLazyActionMap() 
{
        LazyActionMap.installLazyActionMap(menuItem, BasicMenuUI.class,
                                           getPropertyPrefix() + ".actionMap");
}

 protected  void installListeners() 
{
        super.installListeners();
        if (changeListener == null)
            changeListener = createChangeListener(menuItem);
        if (changeListener != null)
            menuItem.addChangeListener(changeListener);
        if (menuListener == null)
            menuListener = createMenuListener(menuItem);
        if (menuListener != null)
            ((JMenu)menuItem).addMenuListener(menuListener);
}

 static  void loadActionMap(LazyActionMap map) 
{
        BasicMenuItemUI.loadActionMap(map);
        map.put(new Actions(Actions.SELECT, null, true));
}

 protected  void setupPostTimer(JMenu menu) 
{
        Timer timer = new Timer(menu.getDelay(), new Actions(
                                    Actions.SELECT, menu,false));
        timer.setRepeats(false);
        timer.start();
}

 protected  void uninstallDefaults() 
{
        menuItem.setArmed(false);
        menuItem.setSelected(false);
        menuItem.resetKeyboardActions();
        super.uninstallDefaults();
}

 protected  void uninstallKeyboardActions() 
{
        super.uninstallKeyboardActions();
        lastMnemonic = 0;
}

 protected  void uninstallListeners() 
{
        super.uninstallListeners();
        if (changeListener != null)
            menuItem.removeChangeListener(changeListener);
        if (menuListener != null)
            ((JMenu)menuItem).removeMenuListener(menuListener);
        changeListener = null;
        menuListener = null;
        handler = null;
}

  void updateMnemonicBinding() 
{
        int mnemonic = menuItem.getModel().getMnemonic();
        int[] shortcutKeys = (int[])DefaultLookup.get(menuItem, this,
                                                   "Menu.shortcutKeys");
        if (shortcutKeys == null) {
            shortcutKeys = new int[] {KeyEvent.ALT_MASK};
        }
        if (mnemonic == lastMnemonic) {
            return;
        }
        InputMap windowInputMap = SwingUtilities.getUIInputMap(
                       menuItem, JComponent.WHEN_IN_FOCUSED_WINDOW);
        if (lastMnemonic != 0 && windowInputMap != null) {
            for (int i=0; i< shortcutKeys.length; i++) {
                windowInputMap.remove(KeyStroke.getKeyStroke
                                      (lastMnemonic, shortcutKeys[i], false));
            }
        }
        if (mnemonic != 0) {
            if (windowInputMap == null) {
                windowInputMap = createInputMap(JComponent.
                                              WHEN_IN_FOCUSED_WINDOW);
                SwingUtilities.replaceUIInputMap(menuItem, JComponent.
                                       WHEN_IN_FOCUSED_WINDOW, windowInputMap);
            }
            for (int i=0; i< shortcutKeys.length; i++) {
                windowInputMap.put(KeyStroke.getKeyStroke(mnemonic,
                                         shortcutKeys[i], false),
                                   "selectMenu");
            }
        }
        lastMnemonic = mnemonic;
}