计算二维形状的表面积

Question

A friend recently had a telephone interview and he was asked a technical question:

Q) If I wanted to calculate the surface area of some 2D shapes then what "Bucket" would I use. He had 20 minutes to write some code and the interviewer called him back. He sent the code via email and the code was not discussed for the remainder of the interview (there were no other technical questions). He sent me the code:

Windows Forms app

namespace ShapesApp
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            this.Load += form_load;
        }

        public void form_load (Object o, EventArgs e)
        {
            List<Shape> listShape = new List<Shape>();
            Shapes.Circle circle = new Shapes.Circle();
            Shapes.Rectangle rectangle = new Shapes.Rectangle();
            Shapes.Square square = new Shapes.Square();
            Shapes.Triangle triangle = new Shapes.Triangle();
            listShape.Add(rectangle);
            listShape.Add(square);
            listShape.Add(triangle);

            foreach (Shape shape in listShape)
            {
                double a = 10;
                double b = 10;
                double surfaceArea = shape.CalculateSurfaceArea(a,b);
                Console.WriteLine("The surface area of a " + shape.GetType() + " is: " + surfaceArea);
            }
        }

    }
}

Shapes - Class Library

namespace Shapes
{
    public abstract class Shape
    {
        abstract public double CalculateSurfaceArea(double Double1, double Double2);
    }

    public class Circle : Shape
    {
        public override double CalculateSurfaceArea(double pi, double radius)
        {
            return (pi * radius) * (pi * radius);
        }
    }

    public class Triangle : Shape
    {
        public override double CalculateSurfaceArea(double Base, double Height)
        {
            return (Base*Height)/2;
        }
    }

    public class Rectangle : Shape
    {
        public override double CalculateSurfaceArea(double Length, double Width)
        {
            return Length * Width;
        }
    }

}

The interviewer has said that he "struggled" with the test. What is wrong with the code?

Answer 1

Calculating area is the behavior and every shape has his own formula for calculating it. Because calculating area can involve different amount of variables and constants method will not take any parameter and variables will be concern of class which implement interface .

So I think method of calculating area can be abstracted as interface:

public interface ICalculatingArea
{
    double CalculateArea();
}

Then every shape will implement it on its own manner.

public class Rectangle:ICalculatingArea
{

    public double Width {get; set;}
    public double Length {get; set;}

    public double CalculateArea()
    {
        return Length * Width;
    }
}

In the main program it is enough to cast shape classes to the interface type and use CalculateArea method