The document describes implementing a factory method design pattern to create different shape objects like circles, ellipses, rectangles and squares. It defines an interface IShape with methods to calculate area and perimeter. Classes are created for each shape inheriting the interface. A Creator class uses factory method to return the appropriate shape object based on user input character. Sample code demonstrates creating a circle object with radius 7 and computing its area and perimeter.

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Assignment for Factory Method Design Pattern in C# [ANSWERS]
Author: Kasun Ranga Wijeweera
Email: krw19870829@gmail.com
Date: 2020 April 11
1) Design a system to handle the shapes: circles, ellipses, rectangles and squares. Use the
Factory Method design pattern according to the instructions given below. Read all the steps
carefully before you begin answering the questions.
a) The interface should have two method prototypes for computing the area and
perimeter of the shapes.
interface IShape
{
double GetArea ();
double GetPerimeter ();
}
b) Create classes for each of the shapes. You should use inheritance appropriately.
class Circle : IShape
{
protected double a;
public Circle (double a)
{
this.a = a;
}
public virtual double GetArea ()
{
return Math.PI * Math.Pow(a, 2);
}
public virtual double GetPerimeter ()
{
return 2 * Math.PI * a;
}
}

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class Ellipse : Circle
{
double b;
public Ellipse (double a, double b) : base(a)
{
this.b = b;
}
public override double GetArea ()
{
return Math.PI * a * b;
}
public override double GetPerimeter ()
{
return 2 * Math.PI * Math.Sqrt ((Math.Pow (a, 2) + Math.Pow (b, 2)) / 2);
}
}
class Square : IShape
{
protected double a;
public Square (double a)
{
this.a = a;
}
public virtual double GetArea ()
{
return Math.Pow (a, 2);
}
public virtual double GetPerimeter ()
{
return 4 * a;
}
}

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class Rectangle : Square
{
double b;
public Rectangle(double a, double b) : base(a)
{
this.b = b;
}
public override double GetArea ()
{
return a * b;
}
public override double GetPerimeter ()
{
return 2 * a + 2 * b;
}
}
c) The object should be created based on the user inputs as shown in table below.
User input Object type
c Circle object
r Rectangle object
s Square object
e Ellipse object
class Creator
{
public IShape FactoryMethod (char ch, double a, double b)
{
if (ch == 'c')
{
return new Circle (a);
}
else if (ch == 's')
{
return new Square (a);
}
else if (ch == 'e')
{
return new Ellipse (a, b);

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}
else if (ch == 'r')
{
return new Rectangle (a, b);
}
}
}
d) Create a circle object with the radius = 7.
Creator c = new Creator ();
IShape shape;
shape = c.FactoryMethod (‘c’, 7, 0);
e) Compute the area and perimeter of the circle object created in (1) (d) above.
Console.WriteLine ("Circle area: {0}", shape.GetArea ());
Console.WriteLine ("Cirlce perimeter: {0}", shape.GetPerimeter ());
Note:
1. Circle of radius = r.
a. Area = πr2
b. Perimeter = 2πr
2. Ellipse of radii a and b.
a. Area = πab
b. Perimeter = 2π√{(a2
+b2
)/2}