FactoryMethod

Factory Method Pattern

Intent

Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.

Problem

You need to create objects, but the exact type of object needed isn't known until runtime. Hard-coding the object creation makes the code inflexible and difficult to extend.

Solution

The Factory Method pattern provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created.

Structure

Creator (abstract)
├── FactoryMethod() (abstract)
└── AnOperation()
    
ConcreteCreator
└── FactoryMethod() (returns ConcreteProduct)

Product (interface)
└── ConcreteProduct (implements Product)

When to Use

• A class can't anticipate the type of objects it needs to create
• A class wants its subclasses to specify the objects it creates
• Classes delegate responsibility to one of several helper subclasses

C# Implementation

See the Program.cs file for an implementation example.

Pros

• Avoids tight coupling between creator and concrete products
• Single Responsibility Principle - product creation in one place
• Open/Closed Principle - can introduce new product types without breaking existing code

Cons

• Code can become more complicated with many new subclasses
• Requires subclassing just to create objects