What is the concept of creating class instance using interface name?

Question

what is the concept of set variable or object or i don\'t know what it\'s called when i create instance of class and putting in left hand the name of interface,,, I Know tha

Answer 1

concept is simple:

public class Cat : IAnimal {
     public void Voice() {//implements IAnimal's method
         Console.WriteLine("Miyaoo");
     }
}

public class Dog: IAnimal {
     public void Voice() {  //implements IAnimal's method
         Console.WriteLine("Woof");
     }
}

public interface IAnimal {
      public void Voice();
}

after initialization

IAnimal animal1 = new Cat(); 
IAnimal animal2 = new Dog(); 

and somewhere in the code

public void MakeAnimalSound(IAnimal animal) {
   animal.Voice(); 
}

so you can do something like this:

MakeAnimalSound(animal1); //prints "Mew" even if type is IAnimal
MakeAnimalSound(animal2); //prints "Woof" even if type is IAnimal

This is polymorphism.