DependencyInjection

Dependency Injection is a software design pattern and a form of inversion of control in which an object receives its dependencies from external sources rather than creating them itself. By decoupling the creation of dependencies from their use, DI promotes modular architecture, easier testing, and greater flexibility in swapping implementations.

DI typically relies on a container, framework, or assembler that manages object lifetimes, resolves dependencies, and wires objects together. Core concepts include the dependency graph, service registration, and automatic resolution. Common injection methods are constructor injection, setter injection, and interface injection. Constructor injection provides dependencies through an object’s constructor, while setter injection uses properties or methods to supply them, and interface injection uses a dedicated injector interface.

Lifetimes or scopes managed by a DI container include singletons, scoped instances, and transients. The container may reuse instances or recreate them as appropriate for the chosen lifetime. Benefits of DI include reduced coupling, improved testability through easy substitution of mocks or stubs, and greater maintainability by isolating implementation details behind abstractions. Drawbacks can include added architectural complexity, potential performance overhead, and the risk of overusing DI or creating opaque dependency graphs.

DI aligns with the dependency inversion principle: high-level modules should not depend on low-level modules; both depend on abstractions. It is widely supported across languages and frameworks, such as Spring in Java, .NET Core, and Angular, and can be implemented manually without a framework. A related pattern is the service locator, which is often discouraged in favor of explicit dependency provisioning.