Java Tip 129: SGLayout—a layout manager for the rest of us

SGLayout, a GridLayout rewrite, improves your layout control

By John Redmond, JavaWorld.com, 08/02/02

In "Java Tip 121: Flex Your Grid Layout" (JavaWorld, December 2001), Bogdan Dorohonceanu describes a GridLayout subclass that avoids the requirement that a grid's elements possess the same dimensions. In this Java Tip, I describe a layout manager, SGLayout, with similar flexibility and direct control over margins, gaps between rows and columns, and fine control over how to locate a component within the grids.

In one example, a simple password panel, Dorohonceanu incorporates a series of labeled text fields into a grid and shows how to improve the panel's appearance by decreasing the label column's width relative to that of the text field column.

Thinking I could improve upon GridLayout, I wrote SGLayout as a complete replacement. In so doing, I incorporated much of GridBagLayout's alignment power.

Note: You can download this article's complete source code from Resources.

SGLayout and its friends

I commence discussion with a rather silly GUI frame, seen in Figure 1, that illustrates SGLayout's possibilities. (I implemented this demo as SGDemo.java.) A JPanel instance, to which an SGLayout manager has been set, replaces the JFrame's contentPane:

  JPanel contentPanel = new JPanel();
  SGLayout contentLayout = new SGLayout(3, 2, , SGLayout.FILL,
     SGLayout.FILL, 15, 5);
  contentPanel.setLayout(contentLayout);

The layout manager in this case defines management of three rows and two columns. The component added to each grid position will fill the position in both the X- and Y-directions, and there will be a 15-pixel gap between the columns and 5-pixel gaps between the rows. It's complicated but straightforward. (Note that the conventional schizophrenia applies: rows before columns, but X-axis before Y-axis.)

A series of statements then destroys that arrangement's simple order:

  layout.setRowScale(1, 2.0);
  layout.setColumnScale(0, 0.65);

These statements make row 1 wider (by a factor of 2.0 relative to rows 0 and 2, which have a 1.0 default scale-value) and column 0 narrower than column 1 (by a factor of 0.65). The scale values are all relative and are maintained on resizing of the container:

    layout.setColumnAlignment(0, SGLayout.RIGHT, SGLayout.TOP);

This statement changes the alignment of all grid cells in the 0th column. Next, you change the individual cells' alignment (on a row, column basis):