Understanding the Factory Method Design Pattern

Introduction to the Factory Method Design Pattern

The Factory Method Design Pattern is a creational design pattern that provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created. This pattern is particularly useful when there is a need to delegate the instantiation process to child classes.

Key Concepts

• Creator: An abstract class or interface that declares the factory method, which returns an object of a Product class.
• Concrete Creator: A class that implements or extends the Creator class and overrides the factory method to return an instance of a Concrete Product.
• Product: An interface or abstract class that defines the objects the factory method creates.
• Concrete Product: A subclass of Product that implements the product interface.

Benefits

• Flexibility: Subclasses can alter the class of objects that will be created independently from the client.
• Encapsulation: Clients are decoupled from the actual concrete classes needed to create instances, relying solely on interfaces.

Example in Code

Here’s how you might implement the Factory Method Pattern in C# within a logistics management system where different types of transportation are needed:

// Product interface
public interface ITransport
{
    void Deliver();
}

// Concrete Products
public class Truck : ITransport
{
    public void Deliver()
    {
        Console.WriteLine("Deliver by land in a box");
    }
}

public class Ship : ITransport
{
    public void Deliver()
    {
        Console.WriteLine("Deliver by sea in a container");
    }
}

// Creator class
public abstract class Logistics
{
    public abstract ITransport CreateTransport();

    public void PlanDelivery()
    {
        ITransport transport = CreateTransport();
        transport.Deliver();
    }
}

// Concrete Creator
public class RoadLogistics : Logistics
{
    public override ITransport CreateTransport()
    {
        return new Truck();
    }
}

public class SeaLogistics : Logistics
{
    public override ITransport CreateTransport()
    {
        return new Ship();
    }
}

// Example usage
class Program
{
    static void Main(string[] args)
    {
        Logistics logistics = new RoadLogistics();
        logistics.PlanDelivery();

        logistics = new SeaLogistics();
        logistics.PlanDelivery();
    }
}