Questions
1 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?
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Advanced Concepts and Design Principles
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01 / 24

What are the SOLID principles? Explain each briefly.

Difficulty: 3/10

SOLID Principles

SOLID is a set of five object-oriented design principles that help produce maintainable, extensible and loosely coupled software. In a large codebase, I use SOLID as a set of design heuristics rather than rigid rules. The goal is to make responsibilities clear, minimize unnecessary dependencies and make change safer.

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  1. 1

    SRP: A class should have one primary responsibility and one reason to change.

  2. 2

    OCP: Software entities should be open for extension but closed for unnecessary modification.

  3. 3

    LSP: Subtypes must remain substitutable for their base types without breaking expected behavior.

  4. 4

    ISP: Clients should not be forced to depend on methods they do not need.

  5. 5

    DIP: High-level policy should depend on abstractions rather than concrete low-level details.

Follow-up Questions

  • Which SOLID principle is most commonly violated in legacy systems?
  • Can SOLID principles conflict with each other?
  • How does dependency injection support DIP?
  • Can applying SOLID lead to over-engineering?
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