Pick one of the following problems to do for your interclass problem. Ideal solutions to all of these include the use of an image. You would paint to the image and then draw that image when the paint method is called. They can all be done without that, but that would make them more functional.
1. Color Paint (keys) - For this I want you to write an applet that "paints" when the mouse is clicked (if you want you can make it happen for dragging to). It can just draw a small rectangle or circle each time at the location of the mouse. The color it paints with will vary based on keys the user hits. You can decide what keys give what colors. For example, if the user hits the R key then it should start drawing in red.
2. Shape Painting (keys) - This is just like the first problem except that instead of varying what color is painted, the user can change what shape is painted. At the very least you should have a square and a circle as options. So if the user hits S then the clicks draw squares. If they hit C it draws circles. Rectangles and ovals would be simple to implement as well, but aren't required.
3. Color Paint (mouse) - This is very much like the first problem only now the color selection is made by clicking the mouse on colored squares on either the left or right side. So this one is more like what you are used to with Paint where there is a little palette that you can select from.
4. Shape Paint (mouse) - This is a combination of 2 and 3 where you select the shape you draw using the mouse.