Inverting dependencies so `UserService` depends on an `INotifier` interface rather than hardcoding `EmailSender`. This allows adding `SMSNotifier` without touching user logic (Open/Closed Principle).
Visual representation of control loops, memory layout, and execution flow for SOLID Design Principles.
A class should have one, and only one, reason to change.
Software entities should be open for extension, but closed for modification.
Derived classes must be substitutable for their base classes without breaking the app.
Clients should not be forced to depend on interfaces they do not use.
Depend upon abstractions (interfaces), not concrete implementations.
Detailed answers, interviewer pro tips, key takeaway summaries, and code examples formulated for technical rounds.
✅ Correction: Single Responsibility means a class has only 1 business actor/domain responsibility to serve.
5 principles for writing clean, scalable software.