Picture of the Relations

Perhaps a picture is needed. Clouds represent class definitions, solid rectangles represent objects, and dotted rectangles represent the static part of a class. Look back at the example program as you study the diagram.

• ButtonFrame extends the class JFrame.
• main() is a static member of the ButtonDemo class, not part of any object.
• main() contains a reference variable frm, which refers to a ButtonFrame object.
• The ButtonFrame frame and its button are displayed on the screen.
• Events from the button are sent to the ButtonFrame object.
  • The ButtonFrame object is registered as a listener for Action Events.
  • The ButtonFrame class implements ActionListener.

Don't be discouraged if this is less than perfectly clear! It usually takes some time to get all of these relationships straight. A bit more practice would not hurt, either.