For an example of lots of cool stuff in Java GUI building all put together: Copy all files (*.class + MC.gui) from ~jalewis/451/java/madcat to your own directory then use:
java -mx64M MadcatGUI tigger MC.gui
It is advisable to do this on machines with large screen real estate. If you wish to try it on a laptop or other smaller-screened machine, try substituting "twister" for "tigger" in the execution line above.