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Using Layout Managers

Every container, by default, has a layout manager -- an object that implements the LayoutManager interface.* If a container's default layout manager doesn't suit your needs, you can easily replace it with another one. The Java platform supplies layout managers that range from the very simple (FlowLayout and GridLayout) to the special purpose (BorderLayout and CardLayout) to the very flexible (GridBagLayout and BoxLayout).

This section gives you an overview of some layout managers that the Java platform provides, gives you some general rules for using layout managers, and then tells you how to use each of the provided layout managers. It also points to examples of using each layout manager.

General Rules for Using Layout Managers

This section answers some common questions about layout managers:

• How do you choose a layout manager?
• How do you create a layout manager, associate it with a container, and tell it to start working?
• How does the layout manager know what components it manages?

How to Use BorderLayout

BorderLayout is the default layout manager for every content pane. (As described in Using Top-Level Containers, the content pane is the main container in all frames, applets, and dialogs.) A BorderLayout has five areas available to hold components: north, south, east, west, and center. All extra space is placed in the center area. Here's an applet that puts one button in each area:

This is a picture of the applet's GUI. To run the applet, click the picture. The applet will appear in a new browser window.

How to Use BoxLayout

The BoxLayout class puts components in a single row or column. It respects the components' requested maximum sizes, and also lets you align components. Here's an applet that uses a BoxLayout to put a bunch of buttons in a centered column:

This is a picture of the applet's GUI. To run the applet, click the picture. The applet will appear in a new browser window.

How to Use CardLayout

The CardLayout class lets you implement an area that contains different components at different times. Tabbed panes are intermediate Swing containers that provide similar functionality, but with a pre-defined GUI. A CardLayout is often controlled by a combo box , with the state of the combo box determining which panel (group of components) the CardLayout displays. Here's an applet that uses a combo box and CardLayout in this way:

This is a picture of the applet's GUI. To run the applet, click the picture. The applet will appear in a new browser window.

How to Use FlowLayout

FlowLayout is the default layout manager for every JPanel. It simply lays out components from left to right, starting new rows if necessary. Both panels in the CardLayout applet above use FlowLayout. Here's another example of an applet that uses a FlowLayout:

This is a picture of the applet's GUI. To run the applet, click the picture. The applet will appear in a new browser window.

How to Use GridLayout

GridLayout simply makes a bunch of components equal in size and displays them in the requested number of rows and columns. Here's an applet that uses a GridLayout to control the display of five buttons:

This is a picture of the applet's GUI. To run the applet, click the picture. The applet will appear in a new browser window.

How to Use GridBagLayout

GridBagLayout is the most sophisticated, flexible layout manager the Java platform provides. It aligns components by placing them within a grid of cells, allowing some components to span more than one cell. The rows in the grid aren't necessarily all the same height; similarly, grid columns can have different widths. Here's an applet that uses a GridBagLayout to manage five buttons:

This is a picture of the applet's GUI. To run the applet, click the picture. The applet will appear in a new browser window.

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