Copyright (c) SEMM NL All rights reserved.
Author : Paul Hamaker. Part of JavaLessons.com
This class extends javax.swing.JPanel , so it cannot function on its own.
To run it standalone, we subclass a javax.swing.JFrame.
This is created in the stand-alone entry point, the main method ...
and our panel is added to it as its contentpane.
We must make the frame visible, because by default it's not !
To make the frame closable, we use an adapter without a name, an anonymous one.
Notice the syntax.
It's the argument to addWindowListener.