using System;

​

// an interface is defined as a syntactical contract that all dervied classes should follow, the interface defines the

// 'what' part of the contract and the deriving classes define the 'how', interfaces define properties, methods, and 

// events (members of the interface), interfaces contain only the declaration of the members. it's the responsibility 

// of the deriving class to define the members

// 

// abstract classes to some extent serve the same purpose, however they are mostly used when only few methods are to be 

// declared by the base class and the deriving class implements the functionalities

//

// a class can inherit from multiple interfaces (see below)

//

// why not just have method in Customer class w/o the interface (seem like an extra step) -- it's about structure and following rules

​

public class Program

{

    public static void Main()

    {

        Customer c = new Customer();

        c.Print();

        c.Print2();

    }

}

​

public interface ICustomer

{

    // interface members are public by default (don't need 'public' keyword)

    void Print();

    // this will throw an error (interfaces can only contain declarations - not implementation)

    //void Print() { Console.WriteLine("Hello"); }

}

​

public interface ICustomer2

{

    // interface members are public by default (don't need 'public' keyword)

    void Print2();  

}

​

// inherting from two interfaces

public class Customer : ICustomer, ICustomer2

{

    // override isn't needed when implementing method from an interface

    public void Print()

    {

        Console.WriteLine("interface print method");

    }

​

    public void Print2()

    {

        Console.WriteLine("interface print 2 method");

    }   

}