Interface

Basic Sample

private static void Main(string[] args)
{
var p = new Point(0, 0);
var q = new Point(10, 0);
Console.WriteLine(p.DistanceFrom(q));
}

public interface IPoint
{
double DistanceFrom(Point x);
}

public class Point : IPoint
{
private int x;
private int y;

public Point(int x, int y)
{
    this.x = x;
    this.y = y;
}

public double DistanceFrom(Point x)
{
    return Math.Sqrt((this.x - x.x) * (this.x - x.x) + (this.y - x.y) * (this.y - x.y));
}
}