When designing... Think about... Android Example Backend Example
Data Models Encapsulation + Validation ViewModel with StateFlow rules Entity with JPA annotations
Architecture Layers Abstraction boundaries Use Cases between ViewModel and Repository Service interfaces between Controller and Repository
Testing Polymorphism for test doubles Mock repositories for unit tests Mock services in integration tests
Extensibility Open/Closed principle New repository implementations New strategy implementations
State Management Unidirectional data flow Redux/MVI with immutable state Event sourcing with snapshots
Error Handling Graceful degradation Try-catch with Result type Exception handling with logging