What is Interface?

The interface is used to achieve abstraction in C#. It can only contain method declarations and properties. It is a contract between two entities. 

I am using the same example from the previous post on Abstraction, to know more about what is abstraction you can visit the same post.

interface IBird        //Interface keyword to declare it
{
    void Sound();    //Only method signature

}

Points to remember,

• Like abstract classes, no instance creation so no constructor is allowed.is allowed for Interfaces as well 
• Declaring interface with I comes out of practice to identify the same. 
• Interfaces can contain methods and properties but not fields
• All members of interface are abstract and public, you do not need to use public access modifiers
• Derived classes must have an implementation of Interface members, you do not require to use override keyword to implement the method like abstract classes
• The interface provides security and standard contract 
• 
  

class Dove: IBird                    //Inherited Interface
{
        public void Sound()        //interface method implementation
        {               
                Console.WriteLine("Coo Coo");
        }
 }

above is an implementation example of Interface IBird to Dove class.