SOLID Principles

The SOLID principles are five high-level guidelines for object-oriented design: Single Responsibility (one concern per class), Open/Closed (open for extension, closed for modification), Liskov Substitution (subclasses must be substitutable for their parent), Interface Segregation (no forced dependency on unused interfaces), and Dependency Inversion (depend on abstractions, not concretions).

When applied together, these principles produce systems that are modular, extensible, and robust under change. Code becomes easier to test, refactor, and extend without breaking existing functionality.

• Following SOLID leads to software that is easier to extend, test, and refactor without breaking existing functionality. Each principle addresses a different aspect of good OO design.
• A class with a single responsibility (SRP) that depends on well-defined interfaces (ISP, DIP) and uses inheritance appropriately (LSP) and polymorphism for extensions (OCP) will likely be easy to maintain.
• Changes to one part of the system won't cascade into breakages elsewhere, because the code is loosely coupled and well-encapsulated.
• SOLID does not guarantee a perfect design, but it provides proven guidelines for object-oriented programming.