Java™ Application Development on Linux - Dator

384Chapter 17Other Ways: Alternatives to Swingdocumentation. 9 You might want to use that resource along with thislightweight tutorial to fill in the gaps and shortcuts.It should not be too surprising that there are similarities between SWT,AWT, and Swing. They all take different approaches to solving the sameproblem, namely how to control the complexity of a graphical event-drivenapplication. Because the problem is the same, there can’t help but be similaritiesbetween different solutions. By now you may have deduced that the Shellclass is an analog to the JFrame class, and that SWT uses a system of layoutmanagers not too different from Swing. If so, you are on the right track andwell on your way to using SWT.If we had to summarize the difference in approaches between SWT andSwing, it would be that SWT tries to provide a small number of complexclasses, and Swing tries to provide a large number of simpler classes. Obviously,this is a generalization, but everybody generalizes. Sorry.The Display is a class that provides the link to the underlying GUI system.Think of it as an abstraction of the interface to the windowing system. Inalmost all cases, an SWT application will have exactly one instance of Display.The Shell class represents a window. This class descends from a series ofabstract parent classes, so if you look at the Javadoc for Shell and think it issimple, be sure to drill down into those parent classes! We’ll discuss Shell quitea bit more as we go along.17.3PORTING BUDGETPRO TO SWTThe conversion of an existing application is a complex process. Always considerrewriting from scratch. Still, it is worthwhile to show an application convertedfrom Swing to SWT, because it will emphasize the relationship betweenthe two.We begin with the reobjecting. Starting with the BudgetPro class, weneed to add an instance of the Display class. Then the JFrame becomes aShell. Likewise, the JLabels become Labels. Then . . . Wait a minute. Youdon’t need a blow-by-blow account. Maybe it would be simpler to show youwhat SWT classes roughly correspond to the equivalent Swing classes(Table 17.1).9. http://download.eclipse.org/downloads/documentation/2.0/html/plugins/org.eclipse.platform.doc.isv/reference/api/