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【正文】 alog contain a setJMenuBar( ) method— this means that you can add menu bars to both applets and dialogs. Either way, be sure not to confuse the setJMenuBar( ) method with the older setMenuBar( ) method of AWT when working with Swing menus, or the piler plains bitterly. If your application is running on a Macintosh, the Mac Lamp。F can be configured to place menu bars at the top of the screen, where Mac users expect to find them. Setting the system property to true activates thisbehavior. It39。s disabled by default because most Java programs do not expect this behavior, and they must be coded properly to deal with it. Notably, the Aqua Human Interface Guidelines require that the menu bar is always visible. If your application has any frames that lack menu bars, whenever one of these gains focus, it causes the menu bar to disappear, much to the user39。s consternation. The most mon way of dealing with this is to write a menu factory that generates an identical menu bar for each frame your application uses. Although this is a little extra work, the familiarity and fort it brings your Mac users is probably worth it. The second way to add a menu bar is much less mon. Recall that the JMenuBar class extendsJComponent. This means it can be positioned by a Swing layout manager like other Swing ponents. For example, we could replace the call 3 to setJMenuBar( ) with the following code: (new BevelBorder())。 ( ).add(menuBar, )。 Figure 145. JMenuBar positioned as a Swing ponent This places the menu bar at the bottom of the frame, as shown in Figure 145. (Note that we set a beveled border around the menu bar to help outline its location.) It would even be possible to add two or three menu bars in different locations. Swing does not require a single menu bar to be anchored to the top of a frame. Because they extend JComponent, multiple menu bars can be positioned anywhere inside a container. Of course, you39。d never actually want to do this without a very pelling reason. It robs the Lamp。F of its opportunity to place the menu bar in the appropriate location. Moving something as fundamental as a menu bar is alm
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