Area Calculation based on Shape selected

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Hi All,

Recently I faced a question where I was asked to design an application. This application will have N number of buttons which have shapes mentioned on it(or buttons will be in particular shape e.g. Circle,Triangle). When any shape button is clicked user will be asked for information to calculate area(e.g. radius in case of circle) and then user will be presented with Area of the shape selected.

In order to answer the question I followed below approach.

1. Create abstract class Shape with abstract method Area()
2. All other shapes will implement this Shape class and will implement Area method for specialized calculation for area calculation

Now the interviewer asked me that how to use above structure.

I told that on the handler of button I will create object of particular shape's class and will invoke Area method with it.

But He told that if there are 1000 shapes then you will have to create 1000 handlers. even if you create single handler then inside it you will have to have 1000 if else conditions to create object of particular shape?

I could not answer after this and I'm still wondering how to achieve good design for this?

Please help me guys. Its bugging me since I gave this interview that what would be the ideal design for this?

Posted 6-Oct-15 1:45am

jahanpanahh

Updated 6-Oct-15 2:43am

Palash Mondal_

v5

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Tomas Takac 6-Oct-15 9:00am

You have these 1000 types of shapes and you only want to have a single handler. So you need to pass this type information into the handler somehow. Now what in C# is designed to pass type information around? Think about it! Programming is about solving problems.

jahanpanahh 7-Oct-15 0:43am

But I can pass the type information only when I know the type ryt? Here These shape buttons are normal buttons...then clicking on this button how would I know which type is it?

[no name] 10-Oct-15 9:21am

Dear jahanpanah
Do not bother too much about stupid interview questions. Especially in case the person tell you that there are 1000 shapes. There are some well known shapes (I assume our fingers are enough to count them, unless we are very theoretical) and all the others go to polygons...
Be proud not to work there ;)
Bruno

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Tomas Takac · Answer 1 · 2015-10-06T21:51:00

Solution 2

What I was getting at in my comment was you should use generics. Let's say we have following classes for shapes:

C#

public abstract class ShapeBase
{
    public abstract void Area();
}

public class Circle : ShapeBase
{
    public override void Area() { ... }
}

public class Triangle : ShapeBase
{
    public override void Area() { ... }
}

public class Square : ShapeBase
{
    public override void Area() { ... }
}

Then in your form you have one generic event handler:

C#

private void ButtonClick<TShape>() where TShape: ShapeBase, new()
{
    var shape = new TShape();
    shape.Area();
}

And you register this handler with the respective button clicks using different shape types:

C#

buttonCircle.Click += (sender, args) => ButtonClick<Circle>();
buttonTriangle.Click += (sender, args) => ButtonClick<Triangle>();
buttonSquare.Click += (sender, args) => ButtonClick<Square>();

Voila a single handler used with as many shapes as you want. You can argue you still need to register one thousand event handlers but that was not part of your question.

Posted 6-Oct-15 21:51pm

Tomas Takac

Comments

jahanpanahh 7-Oct-15 6:21am

Hey Tomas,

Thank you for your answer. I understand that multiple handler was not part of my question but you yourself can say whether it would be good design to write thousand lines to register handlers for different buttons?

We all know that in practice we dont see such situation but this was really a interview question and they wanted to test my design skills.

So If I would have given your answer to them I'm sure they would have told me that writing thousand lines for thousand buttons for registering handler is NOT A GOOD DESIGN!!

Tomas Takac 7-Oct-15 7:25am

I merely extending your design and I strongly believe I answered your question about how to do this using a single handler method without huge IF-ELSE inside. It's very important to know what the requirements are. When given a design assignment in an interview you should not hesitate to ask questions to clarify what needs to be done. It's not a school test.

You are right, this is not a good design. You are dealing with possibly many components not knowing the exact number. I would definitely use dynamic discovery. Read about MEF[^]. Long story short, your form would import all shapes, for each shape dynamically create a button and attach a handler. Each shape should also provide a designer to enter the data needed for area calculation. Try it yourself, if you hit a problem ask a question again.

I like this exercise, very much actually. I think I will use it in the next interview I do. Thank you for inspiration.

jahanpanahh 7-Oct-15 9:01am

THanks again Tomas for the response.

I wont be able to mark your response as Answer but yeah your links gives some information about how to go about it. I tried to read and understand but I as of now could not understand much.

THanks again!

CPallini 11-Oct-15 15:41pm

Wow, an OOP solution, eventually. My 5.

sreeyush sudhakaran · Answer 2 · 2015-10-07T22:51:00

Hi, Your question was breaking my heads , here I tried out to find a generic area calculator all you need is to pass co-ordinates and number of sides for your shape ( note in case of circle sides is 1)

I used polygon generic area calculation:

Refer here : http://www.mathopenref.com/coordpolygonarea.html[^]

Shape.cs
___________

C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace GenericAreaCalculator
{
    public class Shape
    {
        public Dictionary<int,int> x;
        public Dictionary<int,> y;

        public Shape()
        {
            x = new Dictionary<int,>();
            y = new Dictionary<int,>();
        }
    }
}

Area.cs
_______

C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace GenericAreaCalculator
{
    public class Area:Shape
    {
        public float CalculateArea(Shape Shapes,int sides)
        {
            float area = 0;
             int x1 = 0;
             int y2 = 0;
             int y1 = 0;
             int x2 = 0;

            if (sides > 1)
            {
                for (int index = 1; index < sides; index++)
                {
                     x1 = Shapes.x[index];
                     y2 = Shapes.y[index + 1];
                     y1 = Shapes.y[index];
                     x2 = Shapes.x[index + 1];
                    area = area + (((x1 * y2)) - ((y1 * x2)));

                }

                 int xn = Shapes.x[sides];              
                 y1 = Shapes.y[1];
                 int yn = Shapes.y[sides];
                 x1 = Shapes.x[1];
                 area = (area + (((xn * y1)) - ((yn * x1))))/2;
                
            }
            else if (sides == 1)
            {
                area = (float)(3.14 * Shapes.x[0] * Shapes.x[0]);
            }
            

            

            return Math.Abs(area);
        }
    }
}

Program.cs
___________

C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace GenericAreaCalculator
{
    class Program
    {
        static void Main(string[] args)
        {
            Shape shapeobj = new Shape();

            shapeobj.x.Add(1, 0);
            shapeobj.x.Add(2, 10);
            shapeobj.x.Add(3, 10);
            shapeobj.x.Add(4, 0);

            shapeobj.y.Add(1, 0);
            shapeobj.y.Add(2, 0);
            shapeobj.y.Add(3, 10);
            shapeobj.y.Add(4, 10);

            Area area = new Area();

            float ShapeArea = area.CalculateArea(shapeobj, 4);

        }
    }
}

Note : Here Index of Co-ordinates have much importance , Make it in sequence

sreeyush sudhakaran · Answer 3 · 2015-10-06T19:48:00

The below is a simple implemtation without using Design Patterns

I think the interviewer asked you about implementation of Observer Pattern

Please refer here about Observer Pattern :

http://www.dofactory.com/net/observer-design-pattern[^]

https://msdn.microsoft.com/en-us/library/ee850490(v=vs.110).aspx[^]

C#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace ScreenShotDesktop
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Button btn = (Button)sender;

            switch (btn.Text)
            {
                case "Circle" : //Calculate Area of Circle Here
                    break;
                case "Triangle": //Calculate Area of Triangle Here
                    break;
                    //And So on...
            }
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            foreach (Button btn in this.Controls)
            {
                btn.Click += new EventHandler(button1_Click);
            }
        }
    }
}

Area Calculation based on Shape selected

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