Summary

Pattern Comparison

Pattern	When to Apply	Strengths	Caveats	Common Use Cases
Observer	When notification targets may change	Loosely coupled, extensible	Hard to manage order and dependencies	Events, UI updates, webhook notifications
Mediator	When multiple components interact	Centralized coordination	Mediator may become overly responsible	UI components, complex business workflows
DI	When testability or replaceability is key	Flexible, test-friendly	Requires lifecycle/configuration management	Service layer, external dependency injection

Choosing the Right Pattern

• Want extensible notifications? → Use Observer
• Need centralized control over many services? → Use Mediator
• Need testability and loose coupling? → Use Dependency Injection (DI)

Team Discussion Snippets

• “OrderService is calling too many services directly—let’s decouple with Observer.”
• “There are too many services interacting—Mediator could help centralize the control.”
• “We might want to swap this service for a mock—DI would make testing much easier.”