The document discusses the factory design pattern, highlighting its utility in decoupling systems and minimizing client exposure to instantiation logic. It provides code examples demonstrating how to implement a factory pattern to create objects like cars and bikes based on user input. Additionally, it introduces the concept of replacing 'if' statements with polymorphism to improve design flexibility.

1. Simple Factory Design Pattern With
RIP
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Arifur Rahman
Software Engineer
Brain Station-23

2. What is factory pattern ?
The factory pattern is a popularly used design pattern and it is very useful to restrict clients
from knowing the actual business logic methods, it is useful to create a decoupled system,
and it is useful to eliminate object creation in a client environment.
Intent :
1. Creates objects without exposing the instantiation logic to the client.
2. Refers to the newly created object through a common interface.
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3. Problem :
For example we have a scenario where based on user input we need to call particular class methods.
//
// customer enters their choice
//
If (choice == "Car")
{
// call car class and it’s methods
Car c = new Car();
c.buy();
}
If (choice == "bike")
{
// call bike class and it’s methods
Bike b = new Bike();
b.buy();
}
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4. Factory pattern
public enum ChoiceType : int
{
Bike = 1,
Car
}
// Interface
public interface IChoice
{
string Buy();
}
public class clsBike : IChoice
{
public string Buy(){
return ("You choose Bike");
}
}
public class clsCar : IChoice
{
public string Buy(){
return ("You choose Car");
}
}
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5. Factory pattern contd.
// Factory Class
public class FactoryChoice
{
static public IChoice getChoiceObj(ChoiceType choice)
{
IChoice objChoice = null;
if (choice == ChoiceType.Car)
{
objChoice = new clsCar();
}
else if (choice == ChoiceType.Bike)
{
objChoice = new clsBike();
}
return objChoice;
}
}
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6. RIP (Replace IF with Polymorphism)
public class FactoryChoice
{
private IDictionary<ChoiceType, IChoice> _choices;
public FactoryChoice()
{
_choices = new Dictionary<ChoiceType, IChoice>
{
{ChoiceType.Bike, new clsBike() },
{ChoiceType.Car, new clsCar()}
};
}
static public IChoice getChoiceObj(ChoiceType choice)
{
var factory = new FactoryChoice();
return factory._choices[choice];
}
}
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7. Factory pattern contd.
class Program
{
static void Main(string[] args)
{
//Client class
IChoice objInvoice;
objInvoice = FactoryChoice.getChoiceObj(ChoiceType.Bike);
Console.Write(objInvoice.Buy());
Console.ReadKey();
}
}
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