What is an interface in C#?

An Interface is a named collection of semantically similar abstract members or functions. A class or a structure may follow a behaviour that is prescribed by an interface. The keyword interface is used to create an interface. Note that while defining members inside an interface, there is no need to specify the access specifier, as they are public by default.

See syntax below:

public interface IBooks

{

  long int ISDN_No;

}

As a convention, interfaces in .NET are prefixed with an "I" in uppercase, as a good programming practice.

Methods inside an interface do not have a body. They only signify that such a method should exist in the implementing class or structure.

Classes that display a common set of features, such as having similar types of member variables or member functions, are designed in such a way that they implement a common interface.

How to implement an interface in C#?

An interface may be implemented using the keyword "implements" in VB.NET, and using a colon in C#. See code C# example below:

//In C#

interface IBooks
{
    long int Cost { get; } //Interface property  
}

//ComputerBooks is a class that implements an Interface IBooks

public class ComputerBooks : IBooks

{

  // Implementation of the property

  public long int Cost 
  {
        get { return 100; } //Read only value
    }

}