11 — Creational Patterns

Driving question: When is object creation a design problem rather than a constructor call?

Learning objectives

• Compare Factory Method, Abstract Factory, Builder, Prototype, and Singleton by intent.
• Identify creation volatility and configuration coupling.
• Recognize overuse of factories and service locators.
• Refactor creation logic while preserving testability.

Creation as dependency management

Creation patterns become useful when clients should not know:

• concrete product classes;
• construction sequence;
• environment-specific configuration;
• product-family consistency rules;
• expensive cloning/initialization details.

Comparison

Pattern	Primary force	Typical liability
Factory Method	defer creation to subtype/extension point	inheritance coupling
Abstract Factory	create compatible product families	interface proliferation
Builder	separate complex construction sequence	extra indirection
Prototype	create by copying configured exemplar	clone semantics
Singleton	one globally accessible instance	hidden global dependency

Singleton

“Exactly one instance” and “globally reachable from anywhere” are different requirements. The latter often damages testability and dependency visibility.

Design / research exercise

Refactor a constructor-heavy object graph into two alternative designs: explicit composition root versus factory abstraction. Compare dependency visibility and test setup.

Suggested reading

• GoF, Creational Patterns chapters.