SOLID principles provide guidance for writing maintainable, extensible code. Each principle addresses specific design challenges. Applied practically, they produce code that's easier to understand, test, and modify.
The Principles
Single Responsibility limits classes to one reason to change. Open/Closed enables extension without modification. Liskov Substitution ensures subtypes are substitutable. Interface Segregation prefers specific interfaces. Dependency Inversion inverts traditional dependencies.
- Single Responsibility: Split classes doing multiple things
- Open/Closed: Use abstraction for extension points
- Liskov Substitution: Ensure subtypes maintain contracts
- Interface Segregation: Create focused interfaces
- Dependency Inversion: Depend on abstractions not concretions
Practical Application
Apply principles when they solve real problems, not dogmatically. Simple code doesn't need over-engineering. Refactor toward SOLID when complexity demands it. Balance principles against pragmatic deadlines.