Learning Java

Menus

A JMenu is a standard pull-down menu with a fixed name. Menus can hold other menus as submenu items, enabling you to implement complex menu structures. In Swing, menus are first-class components, just like everything else. You can place them wherever a component would go. Another class, JMenuBar , holds menus in a horizontal bar. Menu bars are real components, too, so you can place them wherever you want in a container: top, bottom, or middle. But in the middle of a container, it usually makes more sense to use a JComboBox rather than some kind of menu.

Menu items may have associated images and shortcut keys; there are even menu items that look like checkboxes and radio buttons. Menu items are really a kind of button. Like buttons, menu items fire action events when they are selected. You can respond to menu items by registering action listeners with them.

There are two ways to use the keyboard with menus. The first is called mnemonics . A mnemonic is one character in the menu name. If you hold down the Alt key and type a menu’s mnemonic, the menu will drop down, just as if you had clicked on it with the mouse. Menu items may also have mnemonics. Once a menu is dropped down, you can select individual items in the same way.

Menu items may also have accelerators . An accelerator is a key combination that selects the menu item, whether or not the menu that contains it is showing. A common example is the accelerator Ctrl-C, which is frequently used as a shortcut for the