What is Dependency Injection and why is it useful?

Short answer: Dependency Injection (DI) is a design pattern that allows an object to receive its dependencies from an external source rather than creating them itself. This promotes loose coupling, enhances testability, and simplifies code maintenance. Benefits: Improves modularity Enables easier unit testing (via mock dependencies) Promotes adherence to SOLID principles (especially the Dependency Inversion Principle)

Real-world example (ShopNest)

Patterns in ShopNest should solve a real pain (swappable payments, test seams)—not be added for decoration.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.