Java™ Application Development on Linux - Dator

390Chapter 17Other Ways: Alternatives to Swingnow. The original BudgetPro constructor took a JFrame argument, now itwill have to get a Display and a Shell. So we have to allocate a local Displayand a local Shell. We also need to add the Display argument to theBudgetPro constructor.After this is done, we modify the call to the constructor to pass the localDisplay and Shell to our class instance.Next, we have to set a layout manager. The original application used theSwing BorderLayout layout manager. SWT doesn’t have such a critter.Fortunately, the original used only the north, center, and south positionsof the BorderLayout. SWT has a simple layout manager called aFillLayout that puts its contained controls in a single row or column, equallysized. Putting the three controls in a column will end up looking much likeusing the north, center, and south of a BorderLayout. So we change the callto the frame.setLayout() to pass in a new FillLayout and add theSWT.VERTICAL attribute.The SWT ClassThe SWT class is pretty bare-bones. Its primary use is a library of namedconstants used for attributes to Widget (and other) constructors. You’llsee such SWT.xxxx constants all over your typical SWT application.There are a handful of methods that the SWT class provides, all ofthem static, including error(), which throws an SWTException,getPlatform(), which returns a string with the name of the platformon which SWT is running, and getVersion(), which returns an intversion number.It also has a subclass, called OLE, which is a Windows-only class thatprovides ActiveX support for SWT. Obviously, such use is nonportableand non-Linux, so we won’t talk any more about it.The next block of code in main() sets the Swing look and feel. SWT hasnothing like this. All SWT applications look like native applications (we seemto be saying that a lot), so all of this code may be removed.The next block of code calls methods on the application object (app) that,in the original, construct the three “chunks” of UI and add them to the frameusing the BorderLayout attributes. Since, as we explained earlier, all SWTcontrols must be explicitly joined to a parent control when they are constructed,