Factory Method Pattern – Design Patterns (ep 4)

TL;DR

The Factory Method Pattern encapsulates object instantiation so creation can be handled uniformly and changed through polymorphism. Episode 4 distinguishes three factory variants discussed in Head First Design Patterns, Simple Factory, Factory Method, and Abstract Factory, while focusing on Factory Method. It explains why wrapping construction is valuable when choosing a class or its parameters requires business logic, so read on for the pattern’s motivation and object-oriented structure.

Transcript

it's finally time for the factory pattern if you're not already familiar with this playlist what we're doing is that we're walking through all of the patterns in this book head first design patterns one by one by one so if you're not already subscribed now is a good time to subscribe so that you won't... Read More

Key Insights

• The Factory Method Pattern is a design pattern used to define an interface for creating objects, allowing subclasses to alter the type of objects that will be created.
• The pattern is useful for encapsulating object creation logic, making the code more flexible and easier to maintain.
• The Factory Method Pattern supports polymorphism, allowing different factories to produce objects of the same type but with different characteristics or behaviors.
• It helps in reducing class explosion by parameterizing object creation, avoiding the need for numerous subclasses.
• The pattern separates the creation of objects from their usage, promoting the principle of composition over inheritance.
• It is particularly useful in scenarios where the exact type of object to be created cannot be determined until runtime.
• The pattern aids in creating dynamic applications where object creation logic can change based on different conditions or inputs.
• Simple Factory, often confused with the Factory Method, lacks the polymorphic capabilities and flexibility offered by the Factory Method Pattern.

Questions & Answers

Q: What is the Factory Method Pattern?

The Factory Method Pattern encapsulates object instantiation instead of constructing objects directly wherever they are used. A factory becomes responsible for creating the appropriate object, providing a uniform approach across the program.

Q: Why is a factory needed in object-oriented programming?

Object-oriented programs eventually need to instantiate classes with the new keyword. A factory addresses where that construction should happen by moving it behind a dedicated creation operation.

Q: Why not instantiate objects directly with new?

Direct construction can become complex when computation or business logic determines which class to instantiate or which parameters to pass. Encapsulating that work in a factory keeps the construction logic away from the code that uses the resulting object.

Q: How does the Factory Method Pattern support polymorphism?

When a factory is an instance, it can be swapped at runtime for an instance of another factory. This lets the program vary object construction through polymorphism instead of fixing creation logic at each usage point.

Q: How is Factory Method related to dependency injection?

Dependency injection lets code act as though it already has the object it needs, supplied through a constructor or method. Factory Method addresses the other side of that arrangement: the required object still has to be instantiated somewhere before it can be passed around.

Q: What factory variants are discussed in Head First Design Patterns?

The book discusses three versions: Simple Factory, Factory Method, and Abstract Factory. This episode focuses on Factory Method, while the next episode is designated for Abstract Factory.

Q: Is Simple Factory considered a design pattern in this episode?

No. The presenter agrees with the book’s position that Simple Factory is not actually a design pattern, although it may arise while explaining the increased abstraction from Simple Factory to Factory Method.

Q: What class structure can a factory use to create different objects?

The example describes classes A, B, and C that inherit from one superclass or implement one interface called I. Because they follow the same contract, instances of those classes can be treated as the same type while the factory determines which one to create.

Summary & Key Takeaways

• The Factory Method Pattern is a crucial design pattern in object-oriented programming that defines an interface for creating an object but allows subclasses to decide which class to instantiate. It provides a way to encapsulate object creation, making the codebase more flexible and maintainable.

• By using the Factory Method Pattern, developers can introduce polymorphism in object creation, allowing different factories to produce objects of the same type but with varying characteristics. This pattern helps reduce class explosion by parameterizing object creation, thus avoiding numerous subclasses.

• The pattern is especially beneficial when the exact type of object to be created is not known until runtime. It promotes composition over inheritance by separating the creation of objects from their usage, making applications more dynamic and adaptable to change.