Understand the container, dependency injection, constructor injection, component scanning, and testable design.
Spring · fundamentals
Use the strong answer as your reference, explain it aloud in your own words, then choose how soon you want to review it again.
Interview prompt
Strong answer
Spring's container creates and wires objects according to configuration. Dependency injection makes collaborators explicit, keeps business logic independent from construction details, and allows tests to provide fakes. Constructor injection is usually the clearest default because required dependencies cannot be missing.
Key points
Interviewer looks for
Explain the difference between the object graph and the business logic that uses it.
Java example
1@Service
2final class OrderService {
3 private final OrderRepository orders;
4
5 OrderService(OrderRepository orders) {
6 this.orders = orders;
7 }
8}Topic interview questions
These questions are tied to this lesson. Read each question aloud, then compare your explanation with the strong answer.
Strong answer
Inversion of control means application object creation and wiring are managed by the container. Dependency injection supplies collaborators to an object instead of making the object construct them directly.
Strong answer
Required dependencies are explicit, can be final, and must be provided before the object is usable. Constructor injection also makes a class straightforward to unit test without starting Spring.
Strong answer
Component scanning finds classes annotated as components within configured packages and registers bean definitions for them. Package boundaries should be intentional so scanning does not create accidental dependencies.
Strong answer
A bean is any object managed by the application context. A component is a class discovered through component scanning, while @Bean methods and framework configuration can also create beans.
Strong answer
Instantiate the service directly with fake or mocked collaborators, then test business behavior independently of container startup. Use integration tests separately to verify wiring and framework behavior.
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