Layouts
Posted on: July 26, 2006 at 12:00 AM
Posted on: July 26, 2006 at 12:00 AM
Create a new layout object and use the container's setLayout method to set the layout.
Java Notes
Layouts
Layouts tell Java where to put components in
containers (JPanel, content pane, etc).
Every panel (and other container) has a default layout,
but it's better to set the layout explicitly for clarity.
Create a new layout object (using one of its
constructors) and use the container's setLayout method to
set the layout. Each layout has its own way to resize components
to fit the layout, and you must become familiar with these.
Tools. Creating your layouts by hand is simple for the simple layouts, but for really good layouts using the difficult GridBagLayout, you might want to use a program to help you. A good review of some of these programs is at Java GUI Builders (www.fullspan.com/articles/java-gui-builders.html) by Mitch Stuart.
General advice
.- Initial Iterations. To quickly get the first iterations
of a program running, use
FlowLayout. The result is often ugly, but if there are only a few components, it's quick.FlowLayoutis rarely the correct layout to use in a finished program. - Simple programs.
BorderLayoutis often a good layout for simple programs. More complicated layouts can often be nestingBorderLayouts within otherBorderLayouts. This andFlowLayoutare the most important layouts for beginners. - Grids of equal sized elements (eg, a calculator keypad), can be created with
with
GridLayout. - Single Rows or colums of components are sometimes best done with
BoxLayout. - More complicated layouts may require
GridBagLayout. Getting aGridBagLayoutto work correctly can be time-consuming, but it produces excellent results.
More notes
- FlowLayout - left to right, top to bottom. Good for initial testing. FlowLayout does not respect preferred size information, so it may make variable size elements (eg, a graphics panel) extremely small.
- BorderLayout - north, east, south, west, and center areas. Has various rules for how components are stretched to fit these areas. Both common and useful.
- GridLayout - equal sized grid elements.
- BoxLayout and Boxes - horizontal or vertical sequence of components.
- GridBagLayout - unequal sized grid. Can produce excellent results, but can be difficult to use.
SpringLayoutwas added in Java 1.4, but is difficult for humans. It is rumored to be intended for authomatic layout programs..CardLayoutis good for something like a wizard interface which shows one of several possible layouts (think about a stack of index cards). Tabbed panes are something like a card layout with tabs.- The Null layout (absolute positioning) is possible, but is a bad idea.
- Tabbed panes are something like a card layout with tabs. They are not implemented as a layout, but as a type of panel.
- Non-standard layout managers. Because of deficiencies in the standard Java layout managers, several good, free, alternatives exist.
- You can even define your own layout manager, but this isn't a trivial amount of work. Sun's How to Build a Layout Manager article, java.sun.com/developer/technicalArticles/Interviews/LayoutMgr/, gives a description of the process, altho it is rather unclearly written.
Webliography
- Karsten Lentzsch has good articles at www.jgoodies.com/articles/
- Sun has a nice overview of the layout idea at java.sun.com/docs/books/tutorial/uiswing/layout/using.html
- Effective Layout Management: Short Course at java.sun.com/developer/onlineTraining/GUI/AWTLayoutMgr/shortcourse.html
- mindprod.com/jgloss/layout.html