Interface in c# with example

As everyone aware with Diamond Problem (Multiple inheritance) in C#. For the deeper look, the "diamond problem" (sometimes referred to as the "deadly diamond of death) is an ambiguity that arises when two classes B and C inherit from A, and class D inherits from both B and C. If there is a method in A that B and C have overridden, and D does not override it, then which version of the method does D inherit: that of B, or that of C. So achieving this multiple inheritance we try to use interface in our Project/Solution. Mean to say, we cannot inherit from multiple classes, but you can implement multiple interfaces.

                                                                        Diamond Problem in C#

An interface looks like an abstract class. Why, Interface it look like an abstract class because It has only declaration similar to Abstract class (Abstract methods), there is no implementation for them within the interface. The class who implements that interface is responsible for defining those methods. An interface only contains the signatures of declarations of events, indexers, methods and properties. All of these are public in Interface, There is no need to write a public for methods of the interface. Because the interface assumes everything in the interface is public.

In this article, I try to explain two important uses of the interface.

1. For Multiple inheritance.

2. Expose useful information to others.

Here I am giving an example to explain uses of the interfaces.

Suppose there is an Organization have no of task, roles and team, every team have own task and responsibility. But we need to stop that one team can interfere or access at task of another team. To achieve this situation we need to use Interface.

namespace OrgModel
{
    interface IUiTeam
    {
        void Desiging();
        void Testing();
    }
    interface IDevlopmentTeam
    {
        void Coding();
        void Testing();
    }
    interface IMarktingTeam
    {
         void Sales();
        void Marketing();
    }

    class Organization : IUiTeam, IDevlopmentTeam, IMarktingTeam   //Multiple inheritance
    {
        public void Desiging()
        {
            Console.WriteLine("Design UI");
        }
        public void Coding()
        {
            Console.WriteLine("Doing Code");
        }
        public void Testing()
        {
            Console.WriteLine("Test Project Bug");
        }
        public void Sales()
        {
            Console.WriteLine("Sale work");
        }
        public void Marketing()
        {
            Console.WriteLine("Marking tasks");
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            IUiTeam UiTeam = new Organization(); // Team Ui & responsibility
            UiTeam.Desiging();
            UiTeam.Testing();

            IDevlopmentTeam DevTeam = new Organization(); //Team Development & responsibility
            DevTeam.Coding();
            DevTeam.Testing();

            IMarktingTeam MarketingTeam = new Organization(); //Team Marketing & responsibility
            MarketingTeam.Marketing();
            MarketingTeam.Sales();
            Console.ReadKey();

        }
    }
}

As per code above Organization (Class Organization), Have few operations to i.e. Designing (), Coding (), Testing (), Sales (), Marketing (). Here we create three interface (IUiTeam, IDevlopmentTeam, IMarktingTeam) as team assign them their responsibility, like IUiTeam have only method Designing () and Testing (). Now while we create object of Organization using IUiTeam interface, It expose only method which are assign. Have a look at image below.

Here we just restrict this IUiTeam team to use only these two methods. It unable to access other method of Organization (Class Organization). So we do the same with other interface (IDevlopmentTeam, IMarktingTeam) assign them their own responsibility.