Using Objects through Interfaces

Once a developer defines an interface and implements the interface in a concrete class, a developer using the class can use the class through the interface.

To use a class through an interface:

1. Define a variable of the type of interface. Type ICar var , for example.

2. Set the interface variable equal to an instance of a class that implements the interface. Type = new Escort(); for example ( Figure 8.21 ).

   Figure 8.21 Although the variable's type is ICar you can't say new ICar. You have to create an instance of a class that implements the interface. Interfaces are not creatable types.

    interface ICar {    string Run();    string Stop();    string PlayMusic(); } class Escort : ICar {    public string Run()    {      return "I'm running as fast as I can!";    }   public string Stop()    {      return "Oh good, I finally get to stop";    }    public string PlayMusic()    {      return "We are the pirates who don't do anything...";    } } class Driver {    public string GoToWork()    {  ICar car = new Escort();  string msg = "";      msg+= car.Run();      msg+= car.PlayMusic();      msg+= car.Stop();      return msg;    } } 

Tip

• You can't create instances of an interface. An interface is an abstract type, which means that it is not a creatable class. Instead you create instances of a class that implements the interface.