Stage 2 · Lesson 6 of 7
Dependency injection in practice
is the everyday technique behind dependency inversion: instead of an object creating the things it needs, you pass them in, usually through the . One place near program start, called the , creates the real objects and wires them together.
Frameworks can do the wiring for you: Spring in Java and the built-in container in ASP.NET Core are the best-known examples. In Python and TypeScript, passing arguments by hand is often enough. The payoff is testing: a passes a payment gateway, and nothing real gets charged.
Common trapblaming dependency injection when a constructor needs eight services; that class simply has too many responsibilities, and injection has made the problem visible.
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Resources for this stage
Start with· follow one of these
- CoursePaidGrokking SOLID Design Principles
Design Gurus · Beginner · $50 one-time
One chapter per principle, each with the violation and the refactoring that fixes it
- CourseFreeMIT 6.102: Software Construction
MIT · Intermediate
Free: the Specifications and Interfaces and Subtyping readings explain substitution as contracts