Which statement best describes dependency injection?

Which statement best describes dependency injection?

• A. Dependencies are resolved at compile time and fixed.
• B. Dependencies are provided from outside the object, reducing coupling and enabling mocks in tests.
• C. Dependencies are created inside the class with new; this improves encapsulation.
• D. The pattern only applies to singleton objects.

Answer: (B)

Dependency injection is a pattern where an object's collaborators are supplied from outside, rather than created by the object itself. This reduces coupling because the class depends on abstractions (interfaces) rather than concrete implementations, so the same class can work with different dependencies without changing its code. It also makes testing easier, since you can inject mock or fake dependencies during tests to verify behavior without relying on real services. This approach best describes why it’s useful: dependencies provided from outside let you swap implementations, configuration, or test doubles without touching the dependent class. In contrast, having dependencies resolved at compile time and fixed means the class hard-codes specific implementations, which tightens coupling and harms flexibility and testability. Creating dependencies inside the class with new further increases coupling because the class decides exactly which collaborators to instantiate, making it harder to substitute them in tests or in different environments. And dependency injection is a broad pattern that applies to regular objects, not only to singletons.

Dependency injection is a pattern where an object's collaborators are supplied from outside, rather than created by the object itself. This reduces coupling because the class depends on abstractions (interfaces) rather than concrete implementations, so the same class can work with different dependencies without changing its code. It also makes testing easier, since you can inject mock or fake dependencies during tests to verify behavior without relying on real services.

This approach best describes why it’s useful: dependencies provided from outside let you swap implementations, configuration, or test doubles without touching the dependent class. In contrast, having dependencies resolved at compile time and fixed means the class hard-codes specific implementations, which tightens coupling and harms flexibility and testability. Creating dependencies inside the class with new further increases coupling because the class decides exactly which collaborators to instantiate, making it harder to substitute them in tests or in different environments. And dependency injection is a broad pattern that applies to regular objects, not only to singletons.