You are correct the way you are handling the return values. A Shape has location and colour. I am not convinced that a circle has radius and diameter; I would remove the diameter field and change the getDiameter method, if I need it at all:-The paintComponent method ought not to be part of the Shape class. It is part of the Component class, and should not be in other classes. It should also have protected access. How do you paint the shapes then? Start with this thread, which will probably answer that question.