@Autowired for dependency injection in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the @Autowired annotation do in Spring Boot?

@Autowired tells Spring to automatically provide the needed object (dependency) to a class. It helps connect parts of your app without manual setup.

beginner

Where can you use @Autowired in a Spring Boot class?

You can use @Autowired on fields, constructors, or setter methods to inject dependencies automatically.

intermediate

Why is constructor injection with @Autowired preferred over field injection?

Constructor injection makes dependencies clear and helps with testing. It also ensures the object is fully ready when created.

intermediate

What happens if Spring finds multiple beans of the same type when using @Autowired?

Spring throws an error because it doesn't know which bean to inject. You can fix this by using @Qualifier to specify the bean.

intermediate

How can you make a dependency optional with @Autowired?

You can set required = false in @Autowired(required = false) so Spring won't fail if the bean is missing.

What is the main purpose of @Autowired in Spring Boot?

A To create new beans manually

B To automatically inject dependencies

C To configure database connections

D To handle HTTP requests

@Autowired automatically injects dependencies into Spring-managed classes.

Which of these is NOT a valid place to use @Autowired?

A On a constructor

B On a setter method

C On a local variable inside a method

D On a field

@Autowired cannot be used on local variables inside methods.

If multiple beans of the same type exist, how can you specify which one to inject?

A Use <code>@Qualifier</code>

B Use <code>@Component</code>

C Use <code>@Service</code>

D Use <code>@Repository</code>

@Qualifier helps specify which bean to inject when multiple exist.

What does setting @Autowired(required = false) do?

A Disables dependency injection

B Forces Spring to always inject the bean

C Creates a new bean instance

D Makes the dependency optional

It makes the dependency optional, so Spring won't fail if the bean is missing.

Why is constructor injection recommended over field injection?

A It makes dependencies explicit and helps testing

B It requires less code

C It allows private fields to be injected

D It disables dependency injection

Constructor injection makes dependencies clear and improves testability.

Explain how @Autowired works for dependency injection in Spring Boot and where you can use it.

Think about how Spring connects parts of your app without manual setup.

Describe what happens if Spring finds multiple beans of the same type when using @Autowired and how to resolve it.

Imagine Spring is confused about which object to give you.