Learning Java

Chapter 16. Layout Managers

A layout manager arranges the child components of a container, as shown in Figure 16.1. It positions and sets the size of components within the container’s display area according to a particular layout scheme. The layout manager’s job is to fit the components into the available area while maintaining the proper spatial relationships among the components. Swing comes with a few standard layout managers that will collectively handle most situations; you can make your own layout managers if you have special requirements.

Figure 16-1. A layout manager at work

Every container has a default layout manager; therefore, when you make a new container, it comes with a LayoutManager object of the appropriate type. You can install a new layout manager at any time with the setLayout( ) method. For example, we can set the layout manager of a container to a BorderLayout:

setLayout (new BorderLayout( ));

Notice that we call the BorderLayout constructor, but we don’t even save a reference to the layout manager. This is typical; once you have installed a layout manager, it does its work behind the scenes, interacting with the container. You rarely call the layout manager’s methods directly, so you don’t usually need a reference (a notable exception is CardLayout). However, you do need to know what the layout manager is going to do with your components as you work with them. ...