# Dependency Injection
Confidence: high
Last verified: 2026-05-22
Generation: human_only


## TL;DR

Dependency Injection (DI) is a technique where objects receive their dependencies from outside rather than creating them internally. It enables loose coupling, testability (mock dependencies), and centralized configuration.

## Core Explanation

Types: constructor injection (preferred — immutable dependencies), setter injection (optional dependencies), interface injection. DI containers: Spring (Java), Angular, NestJS. Inversion of Control (IoC): the framework calls your code, not vice versa. DI is an implementation of IoC.

## Further Reading

- [Inversion of Control Containers and the Dependency Injection pattern (Martin Fowler)](undefined)