Java™ Application Development on Linux - Dator

380Chapter 17Other Ways: Alternatives to Swing17.2.3 Portability: Better and WorseHow about portability? Well, it depends on what “portability” means to you.If portability means “looks and runs the same on all platforms,” then Swingoffers better portability. If portability means “runs on all platforms for whichthere is a Java runtime,” then Swing offers better portability. If portabilitymeans “looks like a native application on all supported platforms,” then SWTis your choice. Make your selection accordingly.TIPThe bottom line: If you only learn one Java GUI, make it Swing.17.2.4 The Rest of the ChapterThe rest of this chapter will be devoted to describing the basic classes of SWTby converting one of the application classes from the previous chapter fromSwing to SWT. We will not attempt to explain the operating principles ofGUIs. For an introduction to GUI programming, see the previous chapter onSwing. It introduces the concepts and programming principles for GUIprogramming in Java. SWT is functionally similar, although quite spartan,providing only basic windows, controls, and events.Eclipse also contains a family of higher level user interface classes, knowncollectively as JFace, that provide UI features such as dialogs, wizards, fonthandlers, and images. We will not cover JFace in this book.17.2.5 SWT: Close to the MetalSWT breaks some of the Java contract. For example, you cannot rely on garbagecollection to clean up SWT objects. Any SWT object you create with new mustbe explicitly destroyed with a call to the dispose() method. Why? Since SWTis implemented with native methods, the low-level implementation allocatesnative OS data structures and objects that must be explicitly freed. Since theJava garbage collector cannot be relied upon to collect objects at a certain time(or ever, for that matter), these allocations can result in memory leaks andaddress space conflicts. As we shall see, however, SWT is well designed tominimize the amount of this that you need to worry about.SWT is also close to the metal in the sense that it does not abstract theunderlying message-based event system that drives both X Window and