HANDLING EXCEPTIONS AND EVENTS - Java Programming: From Problem Analysis to Program Design - page 763

If you use the inner class mechanism to handle a window event, you can create the class
by extending the definition of the class WindowAdapter and provide the definition of
only the methods that the program needs. Similarly, to handle window events, if the class
containing the application program does not extend the definition of another class, you
can make that class extend the definition of the class WindowAdapter .
Chapter 6 discussed in detail how to use the inner class mechanism. The GUI part of the
programming example in Chapter 10, which can be found in the Additional Student Files
folder at www.cengagebrain.com, explained how to make the class containing the application
program implement more than one interface. As stated in Chapter 10, there is one more
way to handle events in a program—using the mechanism of anonymous classes. This
mechanism is quite useful to handle events such as window and mouse events because the
corresponding interfaces contain more than one method, and the program might want to
use only one method.
Recall from Chapter 6 that to register an action listener object to a GUI component, you
use the method addActionListener . To register a WindowListener object to a GUI
component, you use the method addWindowListener . The WindowListener object
being registered is passed as a parameter to the method addWindowListener .
Consider the following code:
this .addWindowListener( new WindowAdapter()
{

public void windowClosing(WindowEvent e)
{

System.exit(0);

}

}

);

The preceding statements create an object of the anonymous class, which extends the
class WindowAdapter and overrides the method windowClosing . The object created
is passed as an argument to the method addWindowListener . The method
addWindowListener is invoked by explicitly using the reference this .
Similarly, you can handle mouse events by using the interface MouseListener . The
definition of the interface MouseListener and the class MouseAdapter is:
public interface MouseListener
{

1
1

void mouseClicked(MouseEvent e);
//This method executes when a mouse button is clicked
//on a component.
void mouseEntered(MouseEvent e);
//This method executes when the mouse enters a component.
void mouseExited(MouseEvent e);
//This method executes when the mouse exits a component.
void mousePressed(MouseEvent e);
//This method executes when a mouse button is
//is pressed on a component.