PUBLIC MARKS with tags oop & dev

That way you have to go out of your way to override something that wasn't designed. If you don't explicitly open the seal, then the compiler only allows normal inheritance, but if you use the seal-opening mechanism then the compiler will hand over the trust to you - and you are responsible for the consequences. So I'd prefer to replace Josh Bloch's 'prohibit' with a 'discourage'.

Refactoring is a disciplined technique for restructuring an existing body of code, altering its internal structure without changing its external behavior.

We are enthousiastic software developers trying to put agile principles in practice.