Practical Design Pattern Guide
✅ Purpose and Intent
This chapter focuses on the practical application of design patterns to real-world development challenges.
Rather than discussing patterns in the abstract, it starts from common issues encountered in implementation
— such as "difficult to test," "state management is messy," or "authorization is hard to maintain" —
and shows how combinations of design patterns can be used to solve them effectively.
By leveraging pattern synergy, this chapter addresses key software design concerns such as:
- Separation of concerns
- Flexibility and extensibility
- Testability
- Clear boundaries between state and operations
The aim is to strengthen the reader's ability to apply patterns strategically by emphasizing reproducible structures and judgment criteria relevant to actual development.
✅ Structure and How to Read
Each section follows a consistent structure:
- Problem Overview – Describes practical problems encountered in real projects
- Solution Overview – Maps design patterns to specific solution strategies
- Pattern Synergy – Explains how the selected patterns work together
- UML Class Diagram – Visual representation of structure and responsibilities
- Explanation – Describes roles, interactions, and structural benefits
- Practical Notes – Use cases and implementation benefits
- Summary – Key takeaways and value of the proposed structure
This chapter focuses on thought process and architectural clarity, rather than source code.
✅ Use Case Coverage (8 Examples)
| Situation / Problem | Pattern Combination |
|---|---|
| Difficult to test | DI + Strategy |
| Complex UI state updates | Observer + State |
| Need to implement Undo/Redo | Command + Memento |
| API calls are heavy and slow | Proxy + Flyweight |
| Coordinating multiple UI components | Composite + Mediator |
| Need to authorize certain operations | Proxy + Command |
| Messy configuration and dependency setup | Factory + Singleton |
| Need to generate authenticated resources | Factory + Proxy |