Abstract base classes that implement an interface

Question

Let\'s say that I have an abstract base class something simple like

abstract class Item : IDisplayable
    {
        public int Id { get; set; }
        pub         


        

Answer 1

Since Item inherits from IDisplayable, anything that derives from Item must also implement IDisplayable. So explicitly adding IDisplayable to those classes is redundant.

EDIT: @EricLippert makes an excellent point below about the effect of re-implementing interfaces. I'm leaving this answer to preserve the discussion in the comments.