Java Swing, 2nd Edition

The JMenuBar Class

Swing’s JMenuBar class supersedes the AWT MenuBar class. This class creates a horizontal menu bar component with zero or more menus attached to it. JMenuBar uses the DefaultSingleSelectionModel as its data model because the user can raise, or activate , only one of its menus at a given time. Once the mouse pointer leaves that menu, the class removes the menu from the screen (or cancels it, in Swing lingo), and all menus again become eligible to be raised. Figure 14-4 shows the class hierarchy for the JMenuBar component.

Figure 14-4. JMenuBar class diagram

You can add JMenu objects to the menu bar with the add( ) method of the JMenuBar class. JMenuBar then assigns an integer index based on the order in which the menus were added. The menu bar displays the menus from left to right on the bar according to their assigned index. In theory, there is one exception: the help menu. You are supposed to be allowed to mark one menu as the help menu; the location of the help menu is up to the L&F. In practice, trying to do this results in JMenuBar throwing an Error.

Menu Bar Placement

You can attach menu bars to Swing frames or applets in one of two ways. First, you can use the setJMenuBar( ) method of JFrame, JDialog, JApplet, or JInternalFrame:

JFrame frame = new JFrame("Menu"); JMenuBar menuBar = new JMenuBar( ); // Attach the menu bar to the frame. frame.setJMenuBar(menuBar); ...