On the final day in a short introductory Java class at the Dalian University of Technology, the students modified a very simple Thing class to give it more interesting behavior.

The source code and lab are available here.

And here is an example, using this modified Thing code and also using ThingsApplet.java to work as an applet as opposed to a Swing application. Click in the gray area and on the Things and the button, and stuff will happen: