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Laying Out Components within a Container |
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 AWT supplies layout managers that range from the very simple (FlowLayout and GridLayout) to the special purpose (BorderLayout and CardLayout) to the ultra-flexible (GridBagLayout).This lesson gives you some general rules for using layout managers, gives you an overview of the layout managers the AWT provides, and then tells you how to use each of the AWT layout managers. In these pages are applets illustrating layout management. Each applet brings up a window that you can resize to see how resizing affects the layout.
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 layoout manager know what components it manages?
How to Use BorderLayout
BorderLayout is the default layout manager for all Windows, such as Frames and Dialogs. It 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.
How to Use CardLayout
Use the CardLayout class when you have an area that can contain different components at different times. CardLayouts are often controlled by Choices, with the state of the Choice determining which Panel (group of components) the CardLayout displays. Here's an applet that uses a Choice and CardLayout in this way.
How to Use FlowLayout
FlowLayout is the default layout manager for all Panels. It simply lays out components from left to right, starting new rows if necessary. Both Panels in the CardLayout figure above use FlowLayouts. Here's another example of an applet that uses a FlowLayout.
How to Use GridLayout
GridLayouts simply make a bunch of Components have equal size, displaying them in the requested number of rows and columns. Here's an applet that uses a GridLayout to control the display of five buttons.
How to Use GridBagLayout
GridBagLayout is the most sophisticated, flexible layout manager the AWT 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.
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Laying Out Components within a Container |