Questions
23 of 24
1What are the SOLID principles? Explain each briefly.
2Explain the Single Responsibility Principle (SRP) with an example.
3Explain the Open/Closed Principle (OCP). How do you achieve it without modifying existing code?
4Explain the Liskov Substitution Principle (LSP). What happens if it's violated? (Square/Rectangle problem)
5Explain the Interface Segregation Principle (ISP). Why are fat interfaces bad?
6Explain the Dependency Inversion Principle (DIP). How does it relate to Dependency Injection?
7What is the difference between Aggregation and Composition?
8What is the Factory Pattern? How does it help in achieving OCP?
9What is the Abstract Factory Pattern? How does it differ from Factory Method?
10What is the Strategy Pattern? How does it replace complex conditional logic?
11What is the Observer Pattern? Where is it used in real life? (Event handling, Pub/Sub)
12What is the Decorator Pattern? How does it add functionality dynamically?
13What is a Singleton Pattern? What are the thread-safety concerns and how to handle them?
14What is an Anti-Pattern? Can you name a few? (God Object, Spaghetti Code, Golden Hammer)
15What is "Coupling" and "Cohesion"? Explain the relationship between them.
16What are Generics/Templates? How do they improve type safety and performance compared to casting?
17What is Type Erasure (Java) vs Reified Generics (C#)?
18What is Variance in Generics? (Covariance and Contravariance)
19What are Extension Methods (C#) or Default Methods (Java)? When should you use them?
20What is Reflection? How can it be used to break Encapsulation? What are the performance costs?
21What is the "Law of Demeter"? (Don't talk to strangers)
22Explain "Tell, Don't Ask" principle.
23What is the DRY principle? How does OOP help achieve it?
24What is the YAGNI principle?
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
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What is the DRY principle? How does OOP help achieve it?

Difficulty: 2/10

DRY - Don't Repeat Yourself

DRY means avoiding duplicated knowledge and logic so that a business rule has a single authoritative representation. OOP can help through encapsulation, reusable abstractions, composition, inheritance where appropriate, polymorphism and shared services. However, DRY does not mean eliminating every similar-looking line of code. Premature abstraction can create stronger coupling than the duplication it removes, so I optimize for eliminating duplicated knowledge rather than merely duplicated syntax.

javascript
  1. 1

    DRY targets duplicated knowledge and business rules.

  2. 2

    Encapsulation centralizes responsibilities.

  3. 3

    Composition is often safer than inheritance for reuse.

  4. 4

    Polymorphism can remove duplicated conditional behavior.

  5. 5

    Avoid abstracting code merely because it looks similar if the concepts may evolve independently.

Follow-up Questions

  • When can DRY become harmful?
  • DRY vs WET?
  • How does composition support DRY?
  • Does inheritance always improve code reuse?
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