An interface, like IHittable, can't possibly be made final since its whole purpose is to enable multiple different concrete subclasses that implement it. As yo

An interface, like IHittable, can't possibly be made final since its whole purpose is to enable multiple different concrete subclasses that implement it. As you say, that's the hot one -- and making the concrete subclasses themselves "final" enables no devirtualisations since there are no opportunities for it.