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OOP

1. Core OOP Principles (Deep Understanding)​

  • Encapsulation (information hiding, invariants)
  • Abstraction (interfaces, contracts, boundaries)
  • Inheritance (when to use vs. composition)
  • Polymorphism (subtyping vs. parametric vs. ad-hoc)
  • SOLID principles (with real-world tradeoffs)

2. Object Design & Modeling​

  • Domain-driven design (entities, value objects, aggregates)
  • Rich vs. anemic domain models
  • Modeling real-world systems with objects
  • Object lifecycle & state transitions
  • Avoiding “god objects” and tight coupling

3. Design Patterns (Not Just Names — Usage & Tradeoffs)​

Creational

  • Factory, Abstract Factory, Builder, Singleton (and why to avoid it)

Structural

  • Adapter, Decorator, Composite, Facade, Proxy

Behavioral

  • Strategy, Observer, Command, State, Template Method, Visitor, Mediator

Know:

  • When not to use a pattern
  • How patterns emerge naturally from good design

4. Composition Over Inheritance​

  • Favoring composition
  • Role-based composition
  • Delegation vs. inheritance
  • Mixins / traits (language-specific)

5. Interfaces, APIs & Contracts​

  • Interface segregation
  • Liskov Substitution Principle (LSP) in practice
  • Designing stable public APIs
  • Backward compatibility strategies
  • Versioning object models

6. Dependency Management​

  • Dependency inversion principle (DIP)
  • Constructor vs. setter vs. method injection
  • Dependency injection frameworks (Spring, Guice, .NET DI, etc.)
  • Avoiding service locator anti-pattern

7. Object-Oriented Architecture​

  • Layered architecture
  • Hexagonal (Ports & Adapters)
  • Clean Architecture
  • Onion architecture
  • How OOP fits into microservices & modular monoliths

8. Error Handling & Robustness​

  • Exception hierarchies
  • Checked vs. unchecked exceptions (language-specific)
  • Fail-fast vs. graceful degradation
  • Designing recoverable vs. unrecoverable errors

9. Testing Object-Oriented Systems​

  • Unit testing objects in isolation
  • Mocking vs. fakes vs. stubs
  • Test-driven development (TDD)
  • Designing testable objects
  • Testing polymorphic behavior

10. Performance & Memory Considerations​

  • Object allocation costs
  • Garbage collection impact
  • Object pooling (when justified)
  • Immutability vs. mutability
  • Value objects vs. reference objects

11. Concurrency & OOP​

  • Thread safety in object design
  • Immutable objects
  • Synchronization strategies
  • Actor model vs. shared state
  • Designing concurrent-safe APIs

12. Refactoring & Legacy Code​

  • Refactoring object hierarchies
  • Breaking large classes safely
  • Replacing inheritance with delegation
  • Eliminating code smells (e.g., feature envy, shotgun surgery)

13. Language-Specific Mastery (Pick Your Stack)​

  • Java: JVM memory model, equals/hashCode, serialization, streams
  • C#: value vs. reference types, async/await, immutability
  • Python: duck typing, multiple inheritance, dataclasses
  • C++: RAII, rule of 5, smart pointers
  • Kotlin/Swift: data classes, sealed classes, value types

14. Anti-Patterns to Avoid​

  • God object
  • Anemic domain model
  • Tight coupling
  • Inheritance abuse
  • Over-engineering
  • Premature abstraction

15. Communication & Leadership in OOP​

  • Explaining design decisions
  • Mentoring juniors on design
  • Leading design reviews
  • Balancing purity vs. pragmatism