C# Interface

An interface is defined using the interface keyword, similar to a class. An Interface is a blueprint that outlines a group of methods, properties, events, or indexers that a class or struct must implement. Unlike classes, it contains only the declaration of the members. The implementation of the interface’s members will be given by a class that implements the interface implicitly or explicitly. There are some important points to remember, as mentioned below:

• Interfaces cannot have private members.
• By default, all the members of Interface are public and abstract.
• The interface will always be defined with the help of the keyword interface
• Interfaces cannot contain fields because they represent an implementation of data.
• We can achieve multiple inheritance with the interface but not with the classes.
• We can implement multiple interfaces in a single class separated by commas.

Example 1: Demonstrating the basic case for implementing the Interface.

// Demonstrate working of Interface 
using System;
 
interface inter1
{
	// method having only declaration 
	// with no definition
	void display();
}
// Implementing inteface in Geeks
class Geeks : inter1
{
	// providing the body part of function 
	public void display()
	{
		Console.WriteLine("Demonstration of interface");
	}
  	// Main Method
	public static void Main(String[] args)
	{
		Geeks t = new Geeks();
		t.display();
	}
}

Demonstration of interface

Example 2: Implementation of interfaces and the use of polymorphism in C#

// Using Interfaces and Polymorphism
using System;
// interface declaration 
interface Vehicle
{
	// abstract method. 
	void speedUp(int a);
}
// class implements interface 
class Bicycle : Vehicle
{
	int speed;
	// Method increase speed 
	public void speedUp(int increment)
	{
		speed = speed + increment;
	}
	// Method check speed
	public void CheckSpeed()
	{
		Console.WriteLine("speed: " + speed);
	}
}
// class implements interface 
class Bike : Vehicle
{
	int speed;
  
	// to increase speed 
	public void speedUp(int increment)
	{
		speed = speed + increment;
	}
	public void CheckSpeed()
	{
		Console.WriteLine("speed: " + speed);
	}
}
class Geeks
{
	public static void Main(String[] args)
	{
		// creating an instance of Bicycle 
		// doing some operations 
		Bicycle bicycle = new Bicycle();
		bicycle.speedUp(3);
		Console.WriteLine("Bicycle present state :");
		bicycle.CheckSpeed();
		// creating instance of bike. 
		Bike bike = new Bike();
		bike.speedUp(4);
		Console.WriteLine("Bike present state :");
		bike.CheckSpeed();
	}
}

Bicycle present state :
speed: 3
Bike present state :
speed: 4

Advantages of Interfaces

• Loose coupling: It is used to achieve loose coupling rather than concrete implementations, we can decouple classes and reduce interdependencies.
• Abstraction: Interface helps to achieve full abstraction.
• Maintainability: It helps to achieve component-based programming that can make code more maintainable.
• Multiple Inheritance: Interface used to achieve multiple inheritance and abstraction.
• Define architecture: Interfaces add a plug and play like architecture into applications.
• Modularity: Promote a cleaner and more modular design. By separating the definition of behavior from the implementation