Question

I am learning Java gui. The way I learnt to create a window is to inherit or Extend JFrame class and it is good to use it, as JFrame contains all the properties of a Window. Now If I want to add something to this window, I need to use add() method. But Today I came across JPanel which also creates a windows and we can add stuff by jpanelObjec.add().

What is the difference between the two methods? Are they somehow related?

Answer 1

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 Borders, resizability (is the JFrame resizeable?), title bar, controls (minimize/maximize allowed?), and event handlers for various Events like windowClose, windowOpened etc.

JPanel:

JPanel extends Component, Container and JComponent

It is a generic class used to group other Components together.

• It is useful when working with LayoutManagers e.g. GridLayout f.i adding components to different JPanels 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 JPanels.