Dependency Inversion Principle Explained: Why High-Level Code Should Rely on Abstractions

The Dependency Inversion Principle (DIP), one of the five SOLID design principles, states that high-level modules should not depend on low-level modules — both should depend on abstractions. In practice, this means avoiding direct imports of concrete classes into core business logic layers, which reduces stability and increases complexity. A common violation occurs when a domain-layer class directly instantiates an infrastructure-layer class, tightly coupling the two. The fix involves creating an interface for the low-level module, implementing that interface in the infrastructure layer, and injecting the dependency into the high-level class via its constructor — a pattern known as Dependency Injection. This approach keeps the domain layer stable and flexible, since it relies on an abstraction rather than a specific implementation.