Dependency Injection
A design pattern where objects receive their dependencies from external sources rather than creating them.
Also: DI · IoC
Definition
Dependency injection (DI) is a software design pattern where a class receives its dependencies (services or objects it needs) from external sources rather than instantiating them itself. This inversion of control decouples components, making code more testable (dependencies can be mocked), flexible (implementations can be swapped), and maintainable. DI frameworks like Spring (Java), Angular, and .NET's built-in DI container automate the wiring of dependencies throughout application code.
Example
“Instead of a UserService creating its own DatabaseConnection, it declares the connection as a constructor parameter; the DI framework injects the appropriate connection at runtime, enabling easy substitution with a mock during unit tests.”
Synonyms
- inversion of control
- DI
- constructor injection
- IoC
Antonyms / Opposites
- hard-coded dependencies
- tightly coupled code
Images
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Related Terms
- solid-principles
- unit-testing
- design-pattern
- object-oriented-programming