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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 the layout managers 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 to Use BorderLayout

BorderLayout is the default layout manager for every content pane (an important container found in all frames, applets, and dialogs). A BorderLayout uses five areas 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:

Click this figure to run the applet.
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:

Click this figure to run the applet.
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(in the Creating a User Interface trail) 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:

Click this figure to run the applet.
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:

Click this figure to run the applet.
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:

Click this figure to run the applet.
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 ten buttons in a panel:

Click this figure to run the applet.
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.

* In JDK 1.1 a second interface, LayoutManager2, was introduced. LayoutManager2 extends LayoutManager, providing support for maximum size and alignment. Currently, only BoxLayout implements LayoutManager2. All the other layout managers in the Java platform implement only LayoutManager.


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