Design Patterns

Proven solutions to recurring design problems.

Context

You are selecting a design pattern for a problem. Understand the tradeoffs of each.

Domain Context

• Creational: How to create objects? (Singleton, Factory, Builder, Prototype)
• Structural: How to compose objects? (Adapter, Bridge, Facade, Proxy, Decorator)
• Behavioral: How do objects interact? (Observer, Strategy, State, Command, Iterator)

Instructions

1. Identify Problem: What design issue are you facing?
2. Map to Pattern: Which pattern solves this?
3. Understand Intent: Why does this pattern work?
4. Consider Tradeoffs: Complexity, flexibility, testability?
5. Implement: Code the pattern; don't memorize, understand
6. Refine: Adapt the pattern to your context

Anti-Patterns

• Applying patterns everywhere (pattern obsession); YAGNI
• Stacking patterns (Factory + Builder + Proxy); complexity without benefit
• Not understanding the pattern before using it; cargo cult programming
• Choosing pattern based on name not problem; same name, different intent
• Over-engineering simple problems with patterns; sometimes direct code is clearer

Further Reading

• Gang of Four, Design Patterns (the bible)
• Eric Freeman & Elisabeth Freeman, Head First Design Patterns
• Refactoring.Guru Design Patterns online