C# Language Interfaces Why we use interfaces
Example
An interface is a definition of a contract between the user of the interface and the class that implement it. One way to think of an interface is as a declaration that an object can perform certain functions.
Let's say that we define an interface IShape to represent different type of shapes, we expect a shape to have an area, so we will define a method to force the interface implementations to return their area :
public interface IShape
{
double ComputeArea();
}
Let's that we have the following two shapes : a Rectangle and a Circle
public class Rectangle : IShape
{
private double length;
private double width;
public Rectangle(double length, double width)
{
this.length = length;
this.width = width;
}
public double ComputeArea()
{
return length * width;
}
}
public class Circle : IShape
{
private double radius;
public Circle(double radius)
{
this.radius = radius;
}
public double ComputeArea()
{
return Math.Pow(radius, 2.0) * Math.PI;
}
}
Each one of them have its own definition of its area, but both of them are shapes. So it's only logical to see them as IShape in our program :
private static void Main(string[] args)
{
var shapes = new List<IShape>() { new Rectangle(5, 10), new Circle(5) };
ComputeArea(shapes);
Console.ReadKey();
}
private static void ComputeArea(IEnumerable<IShape> shapes)
{
foreach (shape in shapes)
{
Console.WriteLine("Area: {0:N}, shape.ComputeArea());
}
}
// Output:
// Area : 50.00
// Area : 78.54
