🔍 Adapter vs Bridge

✅ Purpose of Comparison

Both Adapter and Bridge are classified as structural patterns, but they serve different purposes. While their diagrams may appear similar at first glance, their design intent and usage scenarios diverge significantly. Understanding these distinctions helps engineers choose the most appropriate abstraction technique depending on the context—whether for retrofitting compatibility or promoting future extensibility.

✅ Comparison Overview

Aspect	Adapter	Bridge
Primary Purpose	Ensure compatibility with an existing interface	Separate abstraction and implementation
Change Direction	Applied to existing classes (bottom-up)	Designed from the start (top-down)
Flexibility	Low (wraps fixed interface)	High (independent extension of both sides)
Use Case Timing	When integrating external or legacy components	When designing extensible frameworks
Reusability	Limited to specific context	Broad across various implementations

✅ Similarities

• Both decouple classes to promote modularity and reduce tight coupling.
• Both introduce an intermediary layer between interface and implementation.
• Both are effective in managing changing requirements without modifying core logic.

✅ Key Differences

Viewpoint	Adapter	Bridge
Direction of Use	Wraps existing code	Designed proactively for extension
Client Awareness	Client uses Target interface	Client uses Abstraction
Flexibility	Adapts one class at a time	Enables N×M abstraction-implementation
Change Frequency	Used when target can't be changed	Used when both sides evolve independently
Design Strategy	Compatibility wrapper	Layered extension architecture

✅ When to Use Which?

• ✅ Need to connect to an existing, incompatible API → Use Adapter
• ✅ Want to separate concerns cleanly for future growth → Use Bridge
• ✅ Working with legacy systems or third-party code → Adapter
• ✅ Building a scalable, pluggable architecture → Bridge

✅ UML Class Diagrams

Adapter Pattern

Bridge Pattern

✅ Practical Design Notes

• ✅ Adapter is useful for ad-hoc integration, but overuse can lead to structural complexity.
• ✅ Bridge offers high extensibility, but may require more upfront design effort.
• ▶️ Example:
  Use Adapter when integrating with a legacy notification API.
  Use Bridge when you want to separate notification types (e.g., error/warning) from delivery methods (e.g., email/Slack).

✅ Summary

• Adapter acts as a retrofitted wrapper to provide compatibility.
• Bridge is a structural separation of abstraction and implementation for extensibility.
• While the structures may look similar, they differ significantly in intended usage and expansion direction.
• Choosing the right pattern depends on the architectural goals at the time of design.