Hey SteveO, Well, you generally use an interface to define a common behavior among unrelated classes. For example if you had a Person class and a Car class with no common ancestors, they could both implement an interface Wash since both occasionally need to knock off the trail dust. Inheritance or extending a class on the other hand involves classes with similar state and behavior, for example, Vehicle, Automobile, Car, etc. Each inherited level usually adds either more state or behavior.
Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius - and a lot of courage - to move in the opposite direction. - Ernst F. Schumacher