Handling Events - Beginning Java - page 911

@Override
public void windowClosing(WindowEvent e) {
window.dispose(); // Release the

window resources
System.exit(0); // End the

application
}

}

private SketcherFrame window; // The
application window
private static Sketcher theApp; // The
application object
}

Directory "Sketcher 3 using an Adapter class"

This example displays the same application window as the previous example.
How It Works
As the Sketcher class is no longer the listener for window , it doesn't need to implement the Win-
dowListener interface. The WindowHandler class is the listener class for window events. Because the
WindowHandler class is an inner class to the Sketcher class, it has access to all the members of the class,
so calling the dispose() method for the window object is still quite straightforward — you just access
the window field of the top-level class.
The WindowAdapter object that is the listener for the window object is created in the argument to the
addWindowListener() method for window . You don't need an explicit variable to contain it because it
is stored in a data member of the SketcherFrame class that is inherited from the Window class.

WARNING It is very important to use the @Override annotation when you are us-
ing adapter classes. An easy mistake to make when you ' re using adapter classes is
to misspell the name of the method that you are using to implement the event — typ-
ically by using the wrong case for a letter. If you have not specified the @Override
annotationforyourmethod,youwon ' tgetanyindicationofthis.Youaren ' toverrid-
ing the adapter class method at all; you ' re adding a new method. Your code should
compile perfectly well but your program does not handle any events. They are all
passed to the method in the adapter class with the name your method should have
had — which does nothing, of course.

You haven't finished with low-level events yet by any means, and you return to handling more low-level
events in the next chapter when you begin to add drawing code to the Sketcher program. In the mean-
time, let's start looking at how you can manage semantic events.

Semantic Events