Of this abstraction. The values for getRadius() or getCircumference() in the above mentioned illustration could possibly be stored directly, or they may be calculated, it won't issue for the caller; the setters may or won't have side effects; it won't make a difference to the caller. There's in fact a https://share.evernote.com/note/6febae8e-de70-cd79-37c3-61aabef647ef