...
button = new JButton(leftAction)
...
menuItem = new JMenuItem(leftAction);

   To create an Action object, you generally create a subclass of
   AbstractAction and then instantiate it. In your subclass, you must
   implement the actionPerformed method to react appropriately when the
   action event occurs. Here's an example of creating and instantiating an
   AbstractAction subclass:
leftAction = new LeftAction("Go left", anIcon,
             "This is the left button.",
             new Integer(KeyEvent.VK_L));
--

                      A snapshot of ActionDemo when

                                                   A snapshot of ActionDemo when

   Here's the code that disables the "Go left" action:
boolean selected = ...//true if the action should be enabled;
                      //false, otherwise
leftAction.setEnabled(selected);

   After you create components using an Action, you might well need to
   customize them. For example, you might want to customize the appearance
   of one of the components by adding or deleting the icon or text. For
   example, ActionDemo.java has no icons in its menus, and no text in its
   buttons. Here's the code that accomplishes this:
menuItem = new JMenuItem();
menuItem.setAction(leftAction);