Onscreen Ruler is a simple, open source Java application which can be used to measure different components on screen, but it also can be used as an example of solving different problems in swing (like a draggable window or creating your own resize window component)

By viewing sources of JSlope Ruler you can learn how to rotate Java Graphics2D drawing, using LayeredPanes, designing custom Layout Managers and custom components.

 

 

 

 

 

Download Ruler now.

Requirements: it was compiled using JDK 1.5, but it can be recompiled for other JDK versions with swing support.