Interface in C#

interface is an another aspect of object oriented programming. An interface contains the declaration of properties,methods ,events. To implement these methods , a class must implement interface and define the methods in the interface. An interface is useful in a scenarios where there are multiple class that needs to have the same methods/functions. In this case , an interface can be defined containing only the method declaration and rest is the responsibility of the class to implement the interface and the methods according to class functionality.

A class can implement multiple interfaces. If a class implements an interface, It must implement all the methods declared in interface.

An Interface declaration is similar to class declaration. To declare an interface , interface keyword is used.

Syntax

public interface IAnimal {
void run();
void hunt();
}

Implementing Interface

Class c1:interface_name
{
}

Example

using System;
namespace InterfaceDemo
{
public interface Operations
{
void buyItems(string s1,string s2);
int showAmount();
}
}

Class Implementing interface.

using System;
namespace InterfaceDemo
{
public class ItemsList : Operations
{
private string item1;
private string item2;
private int amt;
public ItemsList(int a)
{
amt = a;
}
public void buyItems(string sI1,string sI2)
{
item1 = sI1;
item2 = sI2;
Console.WriteLine("Items to buy \" {0}\" , \"{1}\"", item1, item2);
}
public int showAmount()
{
return amt;
}
}
}

Main Class

using System;
namespace InterfaceDemo
{
class Program
{
static void Main(string[] args)
{
ItemsList i = new ItemsList(2000);
i.buyItems("Cooler", "Sofa");
int k=i.showAmount();
Console.WriteLine("Amount to be given is {0}", k);
Console.ReadKey();
}
}
}

Explanation

First we created an class file and declared an interface in it named operation

We declared two methods in this one with two parameters and other with return type.

Then we created as class called as ItemsList and implemented the interface operation.

We implemented both the methods defined in the interface in the class ItemsList

Finally in the main class , we created an object of ItemsList class and called the two methods.

Note- A class has to implement all the methods defined in the interface. Other wise program will throw an error.

Output