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Practice

What are SOLID principles?

This question assesses your understanding of core object-oriented programming (OOP) design principles. Instead of memorizing definitions, it's better to explain why each principle matters and how you apply them in practice.


Answer 1: Full explanation of each principle​

English​

The SOLID principles are five guidelines that help developers write clean, scalable, and maintainable code in object-oriented systems.

  1. Single Responsibility Principle (SRP)
    A class should only have one reason to change. This means handling one specific responsibility to keep the code easier to test and modify.

  2. Open/Closed Principle (OCP)
    Code should stay open to adding new behavior, but closed to changing existing logic. I follow this by using abstractions and extension patterns rather than modifying stable components.

  3. Liskov Substitution Principle (LSP)
    Subclasses should work anywhere their parent class is expected, without breaking the program. I try to design subclasses that behave consistently with their base types.

  4. Interface Segregation Principle (ISP)
    I avoid forcing classes to implement large interfaces they don't need. Instead, I split them into smaller, focused ones based on actual usage.

  5. Dependency Inversion Principle (DIP)
    I avoid directly depending on concrete classes. Instead, I rely on abstractions such as interfaces, which helps decouple logic and makes testing easier.

Together, these principles reduce coupling and make the system easier to maintain as it grows.

Key Phrases​

  • single responsibility: One reason to change
  • open for extension: Add features without changing existing code
  • substitution safety: Replace parent class without breaking functionality
  • interface segregation: Use small, relevant interfaces
  • dependency inversion: Rely on abstractions, not concrete classes

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