Java Desktop

As users of software applications, we commonly deal with the Graphical User Interface, which, in most of cases, contains the following main elements:

1. A menubar, which includes all the available commands and options (we'll call them functionalities)
2. A toolbar, which is a container for a subset of the most common and useful functionalities (typically a subset of "shortcuts" for the above mentioned commands and options)
3. A working space that is a kind of "container" panel, where the user can type, draw, or do any-thing related to the application

In this article I'll discuss the relationship between the menu and the toolbar from both sides: the application user and the application programmer.

In the role of developer of an application, I have to design a complete and efficient Graphical User Interface for the application function calls; a common choice is to provide the application with both a menubar and a toolbar.

First I'll start to design the menubar and then provide the GUI with a toolbar; however, I realize that part of the toolbar work was already done at the menubar design time. My question is: Can I save development time and work programming the GUI toolbar by using what it is already done for the menubar?

For example, suppose my text editor-like application supports clipboard operations. I have to insert the menu items "cut," "copy," and "paste" into the "Edit" menu, providing icon, accelerator key, and tooltips text for each of them. Then I have to associate what is commonly called "action," that is the code that implements the functionality (for "cut" it could be to delete the selected text and put it in the clipboard). Finally I have to manage the enabled or disabled status of each item (for example, disabling paste if clipboard is empty and enabling cut and copy if some text is selected). Of course, all these things are required for a complete and useful, user-friendly and good-looking menu.

Actually I would like to do something more, for instance, providing a toolbar for my application. First, I add three buttons with the same cut, copy, and paste icons (no text for them, according to the Look-and-Feel Design Guidelines), specifying the same tooltip text used for the menu items (note that I do exactly what I did before for the menubar). Then I link the buttons to the code that implements their functionalities (I repeat my actions again). At the end I write the code to disable and enable the buttons, following the same criteria used for the menu items. In conclusion, I do the same things twice! And everybody knows that doing something twice is not a matter of laziness; this may easily introduce unexpected errors and cause undesired effects (such as a menu item disabled and the corresponding button enabled), especially when the application grows up and new commands or options are added.

I concluded that my efforts could be better employed in designing and coding a good menubar, leaving the development of the corresponding toolbar to some automatic procedure.

This kind of utility can be very useful for applications that have many functionalities and require frequent maintenance. To my knowledge, even sophisticated GUI design editors (like form editors included in the most common IDEs such as Eclipse or NetBeans) don't offer enough support for this aspect and they don't provide anything that keeps linked menu items and buttons.

Solution
The idea for solving this problem comes from the Action class (which is included in the java.swing package); this class offers an interface that extends the ActionListener and can be used in cases where the same functionality could be accessed by several controls (just like menu items and buttons).

The Action interface allows you to define, in a single place:

• The actionPerformed method defined by the ActionListener interface. This method is called when the user activates the control (for example, when he or she selects a menu item or presses a button). This method contains the code to implement the functionality.
• The text describing each functionality; these strings can be used to set the text in a menu item or to display the flyover text for a button or a menu item (tooltip text).
• The icon that depicts the functionality.
• The enabled/disabled state of the functionality.
• The accelerator key used to quickly access the functionality.
• The mnemonic key used to "navigate" by keyboard through a set of Actions.

Certain containers, including menus and toolbars, know how to manage an Action object. In detail they can achieve information from the Action to:

• Create the component appropriate for the container (a button for the tool bar, a menu item for the menu)
• Get the suitable information to render the container (texts, icons, enabled/disabled state)
• Notify the change of state
• Activate the functionality

Implementation and Use
JToolBarMenu is an extension of the JToolBar from the javax.swing package (see sample use in Figures 1 and 2). It is initialized with a JMenuBar object, that is, the menubar the toolbar refers to.

There is no limitation on the way the menubar can be built: JToolBarMenu always shows a rational set of buttons derived from the menubar structure. Of course, if the menubar is built in a chaotic form, JToolBarMenu will be not so intuitive and tidy.

The set of buttons showed in the JToolBarMenu follows the same tree structure as the menubar. In fact, as root, there is a menubar, which has attached some menus (primary branches), and each of these branches contains next menu items (leaves) and/or some other submenu (other branches) and recursively going on.

It was developed as an algorithm to arrange, under all possible conditions and in the proper way, any input menubar. This algorithm consists of the following steps:

1.  It scans all menus present in the menubar. For each menu that is not empty, a separator is added to the toolbar.

2.  For each item present in the menu:

• If the item is a separator, a separator is obviously added.
• If the item is a submenu, the algorithm is recursively applied to the item again.
• if the item is a JRadioButtonMenuItem (a menu item with exclusive selection), it's collected in a vector until there is no more contiguous JRadioButtonMenuItems. When the collection is ready, a set of JToggleButton, each one corresponding to the item in the vector, is added and preceded by a new separator.
• If the item is a JCheckBox-MenuItem (menu item without an exclusive selection), a JToggleButton is added.
• Otherwise the item is simply a JMenuItem, thus a JButton is added.

This mechanism ensures consistency with the menubar structure and an attractive display because the role of the separators, which are always put in a right and rational position, result in a user-friendly layout.