What components can we attach to the content pane in jframe?

Answer 1

The default implementation allows you to add any component that is a subclass of the Component class.

Every JFrame has one (and only one) Container object known as the root content pane. A Container object is itself a subclass of Component, so you may add other Container objects to the root content pane.

Currently, the root content pane is implemented as a JPanel but getContentPane() is only guaranteed to return a Container object. Although you can downcast the returned Container to a JPanel, this is not recommended as there's no guarantee that future versions will always use a JPanel (and downcasts are discouraged in any case). This creates a problem when you want to set a border on the root content pane because Container object's do not implement the setBorder method.

However, you can add a JPanel (with border) to the root content pane, effectively covering the entire root content pane, and then add any additional components to your JPanel, ignoring the root content pane altogether. Alternatively, you can construct a JPanel and replace the pre-defined root content pane with a call to JFrame.setContentPane(). In this way you guarantee the underlying root content pane is definitely a JPanel. Neither method is ideal, since both have a cost, but if you want a border in your root pane then it's a small price to pay.

For some examples on working with panels, see How To Use Panels in Oracle's The Java Tutorial.