Which SOLID principle emphasizes depending on abstractions, not concrete implementations?

• A. Single Responsibility Principle
• B. Open/Closed Principle
• C. Dependency Inversion Principle
• D. Interface Segregation Principle

Answer: (C)

Dependency Inversion Principle focuses on depending on abstractions, not concrete implementations. It says high-level modules shouldn’t hard-code or depend on specific low-level classes; instead, both should depend on abstract contracts like interfaces or abstract classes. This creates loose coupling, making it easy to swap out implementations, mock them in tests, or evolve details without changing the core logic. In practice, you define a contract that expresses what the system needs (for example, an interface describing required methods), have the high-level code use that contract, and have the concrete details implement it. Dependency injection is a common way to provide those concrete implementations at runtime, wiring things together without the high-level code knowing the specifics.

Other principles address different concerns. Single Responsibility is about a module having one reason to change. Open/Closed is about extending behavior without modifying existing code. Interface Segregation is about keeping interfaces small and client-specific so a consumer isn’t forced to depend on methods it doesn’t use.