Declarations, Initialization, and Scoping - SCJP Sun Certified Programmer for Java Platform SE6 - page 157

Inner Classes as Event Handlers
A common use of inner classes is for event handlers. An event handler is the type of
object that often needs access to the members of its outer class but likely won't be
reused by another class, making it a good candidate for an inner class. The ColorChanger
class discussed in Listing 2.1 earlier in this chapter declared a member inner class named
MyButtonListener :
7. public class ColorChanger extends Frame {
8. private Button redBtn, whiteBtn, blueBtn;
23. private class MyButtonListener implements ActionListener {
24. public void actionPerformed(ActionEvent e) {
25. String label = e.getActionCommand();
26. if(label.equals(redBtn.getLabel())) {
27. ColorChanger.this.setBackground(RED);
28. } else if(label.equals(whiteBtn.getLabel())) {
29. ColorChanger.this.setBackground(WHITE);
30. } else if(label.equals(blueBtn.getLabel())) {
31. ColorChanger.this.setBackground(BLUE);
32. }
33. }
34. }
54. private void initializeEvents() {
55. MyButtonListener m = new MyButtonListener();
56. redBtn.addActionListener(m);
57. whiteBtn.addActionListener(m);
58. blueBtn.addActionListener(m);
59. }
60. //Remainder of class definition...
71. }
Notice the MyButtonListener class uses the special this syntax for accessing the
setBackground method that ColorChanger inherits from Frame . The inner class also
references the three private Button fi elds of the outer class.