How to Use SOLID Principles in Daily Programming

As experience grows, developers recognize that maintainable and readable code becomes essential. SOLID principles provide the foundation for writing code that stands the test of time.

Single Responsibility Principle

Classes should have one reason to change. Instead of a monolithic UserService that handles authentication, email notifications, and data validation, split responsibilities into focused classes.

Open/Closed Principle

Code should be open for extension but closed for modification. For example, a payment processing system should allow adding new payment providers (PayPal, Stripe, Crypto) without modifying existing processor code.

Liskov Substitution Principle

Subclasses must behave as their parent class promises. The classic violation: a Penguin class extending Bird breaks if Bird has a fly() method. Design your hierarchies around actual capabilities.

Interface Segregation Principle

Prefer smaller, focused interfaces over massive ones. A Worker interface with work(), eat(), and sleep() methods doesn’t make sense for a Robot worker. Split into Workable, Eatable, and Sleepable interfaces.

Dependency Inversion Principle

Depend on abstractions, not concrete implementations. Instead of directly depending on MySQLDatabase, depend on a Database interface. This makes swapping implementations trivial.

Conclusion

SOLID principles aren’t academic exercises — they’re practical tools for writing better code. Apply them thoughtfully, and your codebase will be easier to maintain, extend, and understand.