What is meant by implementing an interface?

Perhaps it’s best if we start with what an interface is, and then work towards what implementing one means.

Example #1:

Every single McDonald’s in the world has certain commonalities. In fact, if you want to run a McDonald’s franchise, you must follow their franchisee rules:

1. Must sell Big Macs.
2. Restaurants must have a Big M
3. Must pay franchisee fees.
4. Restaurants must be clean (sic!?) at all times.

These are their rules. It’s in the contract. Every restaurant is bound to follow that contract. Each restaurant is slightly different, but they are the same when it comes to the above rules. This is also a very good thing for a customer. If you walk into any McDonald’s restaurant in the world, you know for certain that you can purchase a Big Mac.

What does McDonald’s have to do with interfaces?

An “interface” is nothing more than a contract. Any restaurant that “implements” or signs the contract, is bound to follow it. Or in other words, any restaurant that implements the McDonald’s franchisee interface, is bound to follow it.

Why is it called IMcDonald’s interface instead of McDonald’s interface?

When ever you name an interface, it is common practice for the name to begin with an “I”.

Example #2

All planes in the world have certain commonalities, no matter what type. In other words, they all implement the Iplane interface. The IPlane interface stipulates that any plane which implements it must have:

1. Two wings
2. an engine
3. and it must fly

Therefore, if a Boeing 737 follows these rules, as a customer, you a guaranteed that your purchase will have wings and will fly. Here is an example of a Boeing 737 implementing the above interface:

 public interface IPlane
{
    void Fly();
    void HasTWoWings();
    void Engine();
}

class Boeing737 : IPlane //  <-------------- the Boeing 737 implements the interface
{
    // this means that the Boeing737 MUST have a fly, hastwowings and an engine method.
    // the interface doesn't specify HOW the plane must fly. So long as it does fly
    // the compiler doesn't care.


    public void Fly()
    {
        Console.WriteLine("Come fly with me, let's fly, let's fly awaaaaaaaay");
    }

    public void HasTWoWings()
    {
        Console.WriteLine("I've got two wings");

    }

    public void Engine()
    {
        Console.WriteLine("BRrrrrrrrooooooooooooooooooooooooooooooooom!");
    }
}

I hope that helps you folks.