Introduced by Robert C. Martin, the SOLID principles are five design guidelines that help developers build software that is easy to maintain and extend over time.
1. Single Responsibility (SRP)
A class should have only one reason to change. This means each component should focus on a single piece of functionality.
2. Open/Closed (OCP)
Software entities should be open for extension but closed for modification. You should be able to add new functionality without changing existing code.
3. Liskov Substitution (LSP)
Objects of a superclass should be replaceable with objects of its subclasses without breaking the application.
4. Interface Segregation (ISP)
Clients should not be forced to depend on methods they do not use. Prefer many small, specific interfaces over one large, general one.
5. Dependency Inversion (DIP)
Depend upon abstractions, not concretions. High-level modules should not depend on low-level modules; both should depend on interfaces.