well, considering you know only the slight basics, I suggest you do the following.
learn how to create an applet (provides an easy window to paint on)
move 'em around
try to hit them with your mouse
this task requires no widget-creating (Applet is a window already and can be viewed by the appletviewer). You do some eventhandling and mousepolling and a little painting.
Ressources to perform this task can be found on the web. Start here, e.g.: http://java.sun.com/learning/tutorial/index.html
Just a starter, of course. Worked for me a few years ago.