Dependency Injection
Design pattern where components receive dependencies rather than creating them.
Definition
Dependency injection is a design pattern where components receive their dependencies from external sources rather than creating them internally. This inversion of control makes code more modular, testable, and flexible by decoupling components from specific implementations.
Dependency injection enables swapping implementations without changing consuming code—using test doubles in testing, different providers in different environments, or upgraded implementations transparently.
Why It Matters
Tightly coupled code is hard to test and change. Dependency injection creates the loose coupling needed for maintainable, testable, and flexible systems.
For developers, dependency injection skills enable building systems that can evolve without constant refactoring.
Examples in Practice
Injecting a mock payment processor during testing enables comprehensive order flow testing without real transactions.
Dependency injection allows swapping database implementations without changing application code.
A configuration change switches between cloud providers by injecting a different storage implementation.