The code from page 371 makes a JFrame, inside of which is a button and a custom widget. The custom widget fills the background black, and also draws an oval whose colour changes randomly when the button is pressed.
What I don't understand is how the custom widgets' width and height attributes are being updated with the JFrames size - even as I resize the frame, becuase I haven't assigned anything to the attributes in code.
posted 6 years ago
Because you added your panel to the CENTER of a BorderLayout. The panel is automatically resized to occupy all the spaces available to the panel.