Java™ Application Development on Linux - Dator

17.3 Porting BudgetPro to SWT389Key SWT AbstractionsComposite is one of the key abstractions in SWT. Any control that maycontain other controls is a Composite.Here’s a quick rundown of the key abstract classes and interfaces inSWT, along with the basics of the functionality they embody:•A Widget is the abstract superclass of all user interface objects inSWT. At this level the methods exist that create, dispose, and dispatchevents to listeners. Every single class we use in this chapter,with the exception of event handlers and layout managers, is aWidget.•A Control is the abstract superclass of all windowed user interfaceclasses. This is almost all of the UI classes, either by direct descentor through classes such as Sash or Scrollable. All constructorsfor Control classes require a Composite parent class as a constructorargument.•A Composite is a Control which is capable of containing otherControls. One direct descendant of Control which is very similarto the Swing JPanel is Group.The relationships and the power of these abstractions will becomeclear as you work with real-life examples.(well, maybe not really skyrocket, since the import changes have alreadyproduced a lot of errors right off the bat).Finally, we remove the AbstractTableModel member. SWT has asimpler (and more limited) table functionality that we will discuss later.17.3.2 Step 2: Converting the main() MethodThe main (pun unintended) changes that need to be made here include allocatingthe SWT Display, changing from instantiating a JFrame to a Shell,doing away with the Swing “look and feel” stuff (an SWT application alwayslooks like a platform-native application, that’s SWT’s main selling point), andreworking the construction of the GUI. We’ll explain that a little bit later.For now, we take care of the simple changes. Remember that main() is astatic method, so we do not have any nonstatic class members available right