|No such thing as a small change
The point I'm trying to make is that certain properties are derived from others, and while you can go in both directions, there's often a good point not to do so. I agree that there are without any doubt some circumstances in which you'd determine the radius from the area, but this is irrelevant to the discussion.
My point is that getters and setters very often don't come in pairs.
I hope this clarifies things a bit, -gjb-