[Area] Interfaces [Syntax rule] A non-abstract base class that implements an interface cannot rely on a derived class for that implementation Now the compiler requires that every class that implements an interface must have or inherit a complete implementation of every method of the interface. For more information, see X++, C# Comparison: Object Oriented Programming.
When a base class implements an interface, it was possible for the class to not implement the methods of the interface if a derived class implemented the methods. The only limitation was that the new constructor method could not be called on the class.