You should not extend the JFrame
class unnecessarily (only if you are adding extra functionality to the JFrame
class)
JFrame:
JFrame
extends Component
and Container
.
It is a top level container used to represent the minimum requirements for a window. This includes Border
s, resizability (is the JFrame
resizeable?), title bar, controls (minimize/maximize allowed?), and event handlers for various Event
s like windowClose
, windowOpened
etc.
JPanel:
JPanel
extends Component
, Container
and JComponent
It is a generic class used to group other Component
s together.
It is useful when working with LayoutManager
s e.g. GridLayout
f.i adding components to different JPanel
s which will then be added to the JFrame
to create the gui. It will be more manageable in terms of Layout
and re-usability.
It is also useful for when painting/drawing in Swing, you would override paintComponent(..)
and of course have the full joys of double buffering.
A Swing GUI cannot exist without a top level container like (JWindow
, Window
, JFrame
Frame
or Applet
), while it may exist without JPanel
s.