fix missing override keyword

[roidanton]

Did not use final b/c being not sure if these classes are ought to be subclassed by consumers.

[AntonioNoack]

Didn't you just move the override keyword from the front of a function farther towards the end of its head?

[roidanton]

No.
Having the override (or final) keyword in place enables a compile time check if the derived function signature exists in the base class. Using virtual on an already virtual function is meaningless and doesn't provide any compile time protection -> in case the function signature between a derived and the base class changes. the compiler wouldn't recognize and just add an additional function then.