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Factory Method Design Pattern

Design pattern is such an important part of the software design that most of the companies expect the knowledge of design patterns. If you are not aware of it then it may possible that while designing software system you may end up baffling up.

So I decided to work on a design patterns. In this article I will discuss about factory creational design pattern. Before moving ahead it is important to give the logical model of this pattern.

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Consider an analogy. A person wants to eat the bread for that he will go the bakery. Bakery will create bread and give it to customer. In the whole process the person who wants to eat the bread is client, bakery is the factory and bread is the product. In the whole analogy the bakery hides the process of making the bread from the person. In other words the person is abstracted from the process of creating bread, all he wants is the product i.e. bread.

The basic steps for implementing this pattern is

Create the interfaces of product.
Create concrete product classes which will inherit the product interface. In the above analogy if the user asks for simple bread and a garlic bread then 2 classes SimpleBread and GarlicBread will be created which will be inherited from IBread interface.
Create a class for factory that contains the method that will return the product interface.
Finally use the factory class to get the product.

To use this analogy let us work on a real time application in which a task is given to you to create a calculation system that facilitates the user to do addition, subtraction, multiplication and division or in simple terms a calculator. In this scenario a person who is using this calculator is a client, calculator is a factory and result of the calculation is the product. The person who is using the system is not aware of how the calculation is done all he concerns about is the result of the calculation.

Step I - Create The Interfaces Of Product.

// A Simple Interface
public interface iCalc {
	int ReturnResult(int arg1, int arg2);
}

In this case Result is the end product so I have created an interface called iCalc. This interface has a method called ReturnResult(We will implement method later).

Step II - Create Concrete Product Classes Which Will Inherit The Product Interface.

public class Sum: iCalc {
	public int ReturnResult(int arg1, int arg2) {
		return (arg1 + arg2);
	}
}

public class Difference: iCalc {
	public int ReturnResult(int arg1, int arg2) {
		return (arg1 - arg2);
	}
}

public class Multiplication: iCalc {
	public int ReturnResult(int arg1, int arg2) {
		return (arg1 * arg2);
	}
}

public class Division: iCalc {
	public int ReturnResult(int arg1, int arg2) {
		return Convert.ToInt32(arg1 / arg2);
	}
}

In the system we have to do four operations i.e. addition,subtraction, multiplication and division. So we have created 4 classes one for each operation and implement the method ReturnResult according to the operation.

Step III - Create A Class For Factory That Contains The Method That Will Return The Product Interface

public enum CalculationType {
	Sum,
	Difference,
	Multiplication,
	Division
}
public class Calculator {
	public static iCalc CreateOperation(CalculationType oCalculationType) {
		if (oCalculationType == CalculationType.Sum) {
			return new Sum();
		}
		else if (oCalculationType == CalculationType.Difference) {
			return new Difference();
		}
		else if (oCalculationType == CalculationType.Multiplication) {
			return new Multiplication();

		}
		else if (oCalculationType == CalculationType.Division) {
			return new Division();
		}
		else {
			throw new ApplicationException("Problem Occurs");
		}
	}
}

As you can see from the above code a method getResult which will create a product called result i.e. product according to the requirement.

Step IV - Finally Use The Factory Class To Get The Product

iCalc x = Calculator. CreateOperation(CalculationType.Sum);
int abc = x.ReturnResult(1, 2)

Posted By -	Karan Gupta

Posted On -	Tuesday, June 1, 2010

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