#434 – Interfaces

An interface is a list of methods, properties, events and indexers that a class may implement.  The declaration of an interface looks similar to a class declaration, but doesn’t contain an implementation for any of its members.

        public interface ICowHerd
            // Properties
            string HerdName { get; set; }
            string HerdMotto { get; set; }
            List<CowInfo> Cows { get; set; }

            // Methods
            void DisplayHerdInfo();
            void DisplayCowInfo(int cowIndex);

            // Events
            event EventHandler<CowAddedEventArgs> CowAdded;

You can’t do anything with an interface by itself. You can’t instantiate it like a class.  Instead, a class can choose to implement an interface, which means that it will define an implementation for every member of the interface.  You can think of the interface as a contract that dictates the exact members that a class must implement if it decides to implement the interface.