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Trail: Creating a GUI with JFC/Swing
Lesson: Laying Out Components Within a Container

How to Use GridBagLayout

Here's an applet that shows a GridBagLayout (in the API reference documentation) in action.

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.

GridBagLayout is the most flexible -- and complex -- layout manager the Java platform provides. A GridBagLayout places components in a grid of rows and columns, allowing specified components to span multiple rows or columns. Not all rows necessarily have the same height. Similarly, not all columns necessarily have the same width. Essentially, GridBagLayout places components in rectangles (cells) in a grid, and then uses the components' preferred sizes to determine how big the cells should be.

The following figure shows the grid for the preceding applet. As you can see, the grid has three rows and three columns. The button in the second row spans all the columns; the button in the third row spans the two right columns.

If you enlarge the window as shown in the following figure, you'll notice that the bottom row, which contains Button 5, gets all the new vertical space. The new horizontal space is split evenly among all the columns. This resizing behavior is based on weights the program assigns to individual components in the GridBagLayout. You'll also notice that each component takes up all the available horizontal space -- but not (as you can see with button 5) all the available vertical space. This behavior is also specified by the program.

GridBagLayout shown after the user enlarged it.

The way the program specifies the size and position characteristics of its components is by specifying constraints for each component, To specify constraints, you set instance variables in a GridBagConstraints object and tell the GridBagLayout (with the setConstraints method) to associate the constraints with the component.

The following sections explain the constraints you can set and provide examples.

Specifying Constraints

This page tells you what instance variables GridBagConstraints has, what values you can set them to, and how to associate the resulting GridBagConstraints with a component.

The Example Explained

This page puts it all together, explaining the code for the program on this page.

The GridBagLayout API

The GridBagLayout and GridBagConstraints classes each have only one constructor, with no arguments. Instead of invoking methods on a GridBagConstraints object, you manipulate its instance variables, as described in Specifying Constraints. Generally, the only method you invoke on a GridBagLayout object is setConstraints, as demonstrated in The Example Explained.

Examples that Use GridBagLayout

You can find examples of using GridBagLayout throughout this tutorial. The follwing table lists a few.

Example Where Described Notes
GridBagWindow This section Uses many features -- weights, insets, internal padding, horizontal fill, exact cell positioning, multi-column cells, and anchoring (component positioning within a cell).
TextSamplerDemo Using Text Components (in the Creating a GUI with JFC/Swing trail) Aligns two pairs of labels and text fields, plus adds a label across the full width of the container.
ContainerEventDemo How to Write a Container Listener (in the Creating a GUI with JFC/Swing trail) Positions five components within a container, using weights, fill, and relative positioning.

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