Have you applied the SOLID principles when designing your code?

Yes, the SOLID principles are often applied in code design to improve its quality, maintainability, and extensibility. Briefly about each principle with an example:

• S (Single Responsibility Principle) — a class should have one responsibility.

  class UserRepository {
      void save(User user) { /* save user */ }
  }
  class UserValidator {
      boolean isValid(User user) { /* validate data */ }
  }
  

• O (Open/Closed Principle) — software entities should be open for extension but closed for modification.

  interface Shape {
      double area();
  }
  class Circle implements Shape { /* implementation */ }
  class Rectangle implements Shape { /* implementation */ }
  

• L (Liskov Substitution Principle) — objects of subclasses should replace objects of base classes without altering the correctness of the program.

• I (Interface Segregation Principle) — it's better to have several specific interfaces than one general-purpose interface.

• D (Dependency Inversion Principle) — dependencies should be based on abstractions, not on concrete classes.

Applying SOLID helps create flexible and maintainable code, especially in large projects.