Three Types of Design Patterns

Creational Patterns

Problem they solve: How to create families of related objects without coupling code to concrete classes.

Why they matter: Centralize construction logic, delay decisions about concrete types, enable configurability and testing.

• Typical forces: You want to swap implementations at runtime, hide construction complexity, or enforce creation constraints (e.g., a single instance).
• Representative patterns: Factory Method, Abstract Factory, Builder, Prototype, Singleton.
• Consequences: Reduced coupling to concrete classes; possible increase in indirection and number of types.

Analogy: A restaurant kitchen (factory) prepares meals for customers without requiring them to know how each dish is made.

Structural Patterns

Problem they solve: How to compose classes and objects to form larger structures while keeping those structures flexible.

Why they matter: Promote reuse by composing behavior from simpler parts; provide uniform interfaces over disparate components.

• Typical forces: You need to adapt incompatible interfaces, add responsibilities dynamically, or represent part–whole hierarchies.
• Representative patterns: Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy.
• Consequences: Greater flexibility via composition; may add layers that obscure control flow if overused.

Analogy: An electrical adapter lets a U.S. plug fit into a European socket, enabling compatibility without changing either device.

Behavioral Patterns

Problem they solve: How objects communicate, distribute responsibilities, and vary algorithms without tight coupling.

Why they matter: Clarify control flow, encapsulate algorithms, and decouple senders from receivers.

• Typical forces: You want to replace an algorithm at runtime, notify many dependents of a change, or route requests without hard-coding receivers.
• Representative patterns: Strategy, Template Method, Observer, Mediator, Command, Iterator, State, Chain of Responsibility, Memento, Visitor, Interpreter.
• Consequences: Increased flexibility in collaboration; potential proliferation of small types and indirection.

Analogy: A theater director (mediator) coordinates actors, ensuring smooth interaction without requiring the actors to manage all communications themselves.

How to Choose

• Creation pain? If object construction is leaking into business logic or varies by environment → consider Creational.
• Integration pain? If components don’t fit together or you need to add behavior without modifying types → consider Structural.
• Collaboration pain? If algorithms or workflows must vary independently of clients or many objects must coordinate → consider Behavioral.

Quick Reference

• Creational → Factory Method, Abstract Factory, Builder, Prototype, Singleton
• Structural → Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy
• Behavioral → Strategy, Template Method, Observer, Mediator, Command, Iterator, State, Chain of Responsibility, Memento, Visitor, Interpreter

Next Steps

Use this page as a map. When facing a design problem, first identify whether you are struggling with creation, composition, or collaboration, then select candidate patterns from the corresponding group for deeper study.