Questions
5 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
05 / 24

Explain the Interface Segregation Principle (ISP). Why are fat interfaces bad?

Difficulty: 3/10

Interface Segregation Principle

ISP says clients should not be forced to depend on methods they do not use. A fat interface combines unrelated capabilities and forces implementations to provide meaningless methods, often resulting in empty implementations or UnsupportedOperationException. I prefer small, cohesive interfaces organized around client needs rather than one large interface representing an entire subsystem.

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  1. 1

    Keep interfaces cohesive and client-focused.

  2. 2

    Avoid forcing implementations to support irrelevant operations.

  3. 3

    Smaller interfaces improve mocking and testing.

  4. 4

    ISP reduces accidental coupling between unrelated capabilities.

  5. 5

    Do not split interfaces so aggressively that the design becomes fragmented and difficult to understand.

Follow-up Questions

  • What makes an interface fat?
  • How does ISP improve unit testing?
  • How does ISP relate to SRP?
  • Can too many small interfaces be harmful?
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