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
Action objects to the pop-up menu with the
add( ) and
insert( ) methods.
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
method; these separators also count as an index. Figure 14-10 shows the class
diagram for the
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
Figure 14-10. JPopupMenu class diagram
Pop-up menus are usually raised by ...