Questions
2 of 11
1Design a simple Logger class. Should it be Static, Singleton, or injected via Interface? Justify.
2How would you design a system for a Car that has different engine types (Petrol, Diesel, Electric)? Show the OOP model.
3How would you model a Bird class? What issues arise when you try to add a Penguin or Ostrich? (LSP violation)
4You have a class that validates user input. The validation rules change frequently. Which pattern would you use and why?
5How do you design an Undo/Redo functionality? (Command Pattern)
6How would you design a Plugin Architecture?
7How do you handle Cross-Cutting Concerns (Logging, Caching, Authentication) without polluting business logic? (AOP/Proxy/Decorator)
8You need to cache data. Some data expires in 1 minute, some in 1 hour. How do you design this using OOP?
9How would you design a Payment Gateway integration that supports multiple providers (PayPal, Stripe)?
10What is the Anemic Domain Model? Why is it considered an anti-pattern by many?
11What is Domain-Driven Design (DDD) in a nutshell? How does it relate to OOP?
OOPSOOPS
Basics
Inheritance and Composition
Polymorphism
Interfaces and Abstract Classes
Access Modifiers and Scope
Advanced Concepts and Design Principles
Trees
Real-World Design and Architecture Scenarios
02 / 11

How would you design a system for a Car that has different engine types (Petrol, Diesel, Electric)? Show the OOP model.

Difficulty: 3/10

Car and Engine Using Composition

I would model Car and Engine using composition rather than creating separate inheritance hierarchies such as PetrolCar, DieselCar, and ElectricCar. The Car depends on an IEngine abstraction, and concrete engines implement the behavior. This follows programming to an interface and makes adding another engine type possible without modifying Car.

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  1. 1

    Car has an Engine rather than inheriting from an engine.

  2. 2

    The engine abstraction isolates Car from concrete engine implementations.

  3. 3

    New engines can be introduced without modifying Car.

  4. 4

    Dependency injection can select the engine at runtime or configuration time.

  5. 5

    This design supports Open/Closed Principle and composition over inheritance.

Follow-up Questions

  • How would you add hybrid engines?
  • Would you use Factory or Strategy here?
  • How would you test Car without a real engine?
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