📑 Table of Contents
1. [📋 Executive Summary](#-executive-summary)🎯 Main Topics Covered
- Executive Summary
📋 Executive Summary
Document: Object-Oriented Design Patterns
Type: Technical Documentation
Reading Time: ~20 min
Last Updated: December 2025
📊 Quick Stats
| Metric | Value |
|---|---|
| Total Patterns | 23 Gang of Four patterns |
| Categories | Creational (5), Structural (7), Behavioral (11) |
| Code Examples | 30+ implementations |
| UML Diagrams | 25+ visual representations |
| Languages | Java, Python, C++ examples |
🎯 Main Patterns Covered
Creational Patterns (5):
- Singleton — Ensure single instance
- Factory Method — Object creation interface
- Abstract Factory — Family of objects
- Builder — Complex object construction
- Prototype — Clone existing objects
Structural Patterns (7): 6. Adapter — Interface compatibility 7. Bridge — Separate abstraction from implementation 8. Composite — Tree structures 9. Decorator — Dynamic behavior addition 10. Facade — Simplified interface 11. Flyweight — Share common state 12. Proxy — Control access
Behavioral Patterns (11): 13. Chain of Responsibility — Request handling chain 14. Command — Encapsulate requests 15. Iterator — Sequential access 16. Mediator — Centralized communication 17. Memento — State snapshots 18. Observer — Event notification 19. State — Object state behavior 20. Strategy — Interchangeable algorithms 21. Template Method — Algorithm skeleton 22. Visitor — Operations on elements 23. Interpreter — Language grammar
💡 What You’ll Learn
- Recognize when and why to apply each design pattern
- Understand the problem each pattern solves
- Implement patterns in object-oriented languages
- Identify anti-patterns and code smells
- Refactor legacy code using design patterns
- Balance pattern usage (avoid over-engineering)
- Communicate design decisions using pattern vocabulary
- Apply patterns in real-world system architecture
📚 Prerequisites
- Solid OOP fundamentals (classes, inheritance, polymorphism, encapsulation)
- Experience with at least one OOP language (Java/C++/Python/C#)
- Understanding of interfaces and abstract classes
- Basic UML diagram reading skills
- Familiarity with software design principles (SOLID)
👥 Target Audience
✅ Software Engineers — Writing maintainable, scalable code
✅ Interview Candidates — Preparing for system design interviews
✅ Tech Leads — Establishing team coding standards
✅ Architects — Designing large-scale systems
✅ Code Reviewers — Identifying improvement opportunities
🎓 Learning Path
Beginner → Start with Singleton, Factory, Observer, Strategy (most common)
Intermediate → Add Decorator, Adapter, Template Method, Command
Advanced → Master Composite, Flyweight, Visitor, Interpreter
🔑 Key Principle
“Design patterns are solutions to recurring problems in software design.”
They provide a shared vocabulary and proven approaches, but should be applied judiciously—not forced into every situation.
Design Patterns
Concepts, examples, and anti-patterns.