Steinar, you missed my point. I explicitly said not to get bogged down in my example. The point is that changing the internal details of your class shouldn't result in your users being forced to change their code. As I said, exposing your implementation tightly couples your code and your users. As Matthew pointed out, you shouldn't have sets and gets for every item in your class. You should have a clearly thought out api that isn't tied to the internal detail. Exposing internal, either through making data public or blindly creating gets and sets for private data members is just bad OO design.

An addition to my example that makes things little cleared would be a subclass that validated the words you could use. With a public variable I couldn't enforce that, but I could override my setter to add validation.