Java Swing, 2nd Edition

The JPopupMenu Class

Pop-up menus are an increasingly popular user-interface feature. These menus are not attached to a menu bar; instead, they are free-floating menus that associate themselves with an underlying component. This component is called the invoker . Linked to specific interface elements, pop-up menus are nicely context-sensitive. They are brought into existence by a platform-dependent pop-up trigger event that occurs while the mouse is over the invoking component. In AWT and Swing, this trigger is typically a mouse event. Once raised, the user can interact with the menu normally. Figure 14-9 is an example of a pop-up menu in Swing.

Figure 14-9. A pop-up menu in Swing

You can add or insert JMenuItem, Component, or Action objects to the pop-up menu with the add( ) and insert( ) methods. The JPopupMenu class assigns an integer index to each menu item and orders them based on the layout manager of the pop-up menu. In addition, you can add separators to the menu by using the addSeparator( ) method; these separators also count as an index. Figure 14-10 shows the class diagram for the JPopupMenu component. Starting with SDK 1.4, pop-up menus use the Popup class to actually draw themselves. This class is also used for other briefly displayed interface elements like tooltips.

Figure 14-10. JPopupMenu class diagram

Displaying the Pop-up Menu

Pop-up menus are usually raised by ...