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.

1. Simple Factory Design Pattern With
RIP
1
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.
2

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();
}
3

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");
}
}
4

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;
}
}
5

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];
}
}
6

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();
}
}
7

8. 8