Learning Java

Containers

A container is a kind of component that holds and manages other components. JComponent objects can be containers, because the JComponent class descends from the Container class.

Three of the most useful container types are JFrame , JPanel, and JApplet. A JFrame is a top-level window on your display. JFrame is derived from JWindow, which is pretty much the same but lacks a border. A JPanel is a generic container element used to group components inside of JFrames and other JPanels. The JApplet class is a kind of container that provides the foundation for applets that run inside web browsers. Like every other JComponent, a JApplet has the ability to contain other user interface components. You can also use the JComponent class directly, like a JPanel, to hold components inside of another container. With the exception of JFrame and JWindow, all the components and containers in Swing are lightweight.

A container maintains the list of “child” components that it manages, and has methods for dealing with those components. Note that this child relationship refers to a visual hierarchy, not a subclass/superclass hierarchy. By themselves, most components aren’t very useful until they are added to a container and displayed. The add( ) method of the Container class adds a component to the container. Thereafter, this component can be displayed in the container’s display area and positioned by its layout manager. You can remove a component from a container with the remove( ) method. ...