Interfaces

Inside Interfaces only methods can be defined.

The methods don't have body and must be declared in the classes that implement the interface.

Syntax

Defining interfaces:

interface InterfaceName { // code }

Implementing interface:

class ClassName : InterfaceName

Example

using System; namespace ConsoleApp1 { interface Vehicle { // Function that must be defined in // each class that extends the interface double getInsuranceCost(int months); } class Car : Vehicle { // Implementation of interface. public double getInsuranceCost(int months) { return 25 * months; } } class Bicycle : Vehicle { // Implementation of interface. public double getInsuranceCost(int months) { return 0; } } class Program { static void Main(string[] args) { Car car = new Car(); Console.WriteLine("Car's Year Insurance: " + car.getInsuranceCost(12) + " $"); Bicycle bicycle = new Bicycle(); Console.WriteLine("Bike's Year Insurance: " + bicycle.getInsuranceCost(12) + " $"); } } }

Output:

Car's Year Insurance: 300 $ Bike's Year Insurance: 0 $

Explanation:

• An interface is defined at lines 5 - 10.
• At line 9 a method is declared. This method must be declared in each class that implements the interface.
• At line 12 and 21 the classes Car and Bicycle implement the interface. For this reason they must define the function getInsuranceCost. If this is not done then the code won't compile.