Swing Components and the Containment Hierarchy

Some of the top-level containers offered by swing are - JApplet, JDialog, and JFrame.  Because of the intricacies involved in making lightweight and heavyweight components work together in Swing, you can't just add() anything you like to a JFrame, JApplet, or JDialog object; first, you must get something called a "content pane," and then you can add Swing components to that. 

            The different types of panes that are part of container are as follows -

The Root Pane

In general, you don't directly create a JRootPane object. Instead, you get a JRootPane (whether you want it or not!) when you instantiate JInternalFrame or one of the top-level Swing containers, such as JApplet, JDialog, and JFrame.  Its a lightweight container used behind the scenes by these top-level containers. As the preceding figure shows, a root pane has four parts:

i)          The layered pane

Serves to position its contents, which consist of the content pane and the optional menu bar. Can also hold other components in a specified Z order.  JLayeredPane adds depth to a JFC/Swing container, allowing components to overlap each other when needed. An Integer object specifies each component's depth in the container, where higher-numbered components sit "on top" of other components.  It allows for the definition of a several layers within itself for the child components.

JLayeredPane manages its list of children like Container, but allows for the definition of a several layers within itself. Children in the same layer are managed exactly like the normal Container object, with the added feature that when children components overlap, children in higher layers display above the children in lower layers.

ii)         The content pane

The container of the root pane's visible components, excluding the menu bar.

iii)        The optional menu bar

The home for the root pane's container's menus. If the container has a menu bar, you generally use the container's setJMenuBar method to put the menu bar in the appropriate place.

iv)        The glass pane

Hidden, by default. If you make the glass pane visible, then it's like a sheet of glass over all the other parts of the root pane. It's completely transparent unless you implement the glass pane's paint method so that it does something, and it intercepts input events for the root pane. The glass pane is useful when you want to be able to catch events or paint over an area that already contains one or more components. For example, you can deactivate mouse events for a multi-component region by having the glass pane intercept the events. Or you can display an image over multiple components using the glass pane.