Why IoC matters in Spring Boot - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a Spring component using IoC.

Spring Boot

@[1]
public class MyService {
    // service logic
}

Drag options to blanks, or click blank then click option'

AService

BComponent

CAutowired

DRepository

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Autowired instead of a component annotation

Using @Repository for a service class

The @Service annotation marks the class as a Spring service component managed by IoC.

2fill in blank

medium

Complete the code to inject a dependency using IoC in Spring.

Spring Boot

public class MyController {
    @[1]
    private MyService myService;
}

Drag options to blanks, or click blank then click option'

AComponent

BAutowired

CService

DInject

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Component instead of @Autowired

Using @Service on fields

The @Autowired annotation tells Spring to inject the dependency automatically.

3fill in blank

hard

Fix the error in the code to properly use IoC for dependency injection.

Spring Boot

public class MyController {
    private MyService myService;

    public MyController([1] MyService myService) {
        this.myService = myService;
    }
}

Drag options to blanks, or click blank then click option'

A@Autowired

BAutowired

C@Inject

DInject

Attempts:

3 left

💡 Hint

Common Mistakes

Missing @ symbol

Using plain 'Autowired' without @

Using @Inject without proper setup

The constructor parameter needs the @Autowired annotation for Spring to inject the dependency via constructor.

4fill in blank

hard

Fill both blanks to create a Spring bean and inject it using IoC.

Spring Boot

@[1]
public class NotificationService {
}

public class UserController {
    @[2]
    private NotificationService notificationService;
}

Drag options to blanks, or click blank then click option'

AComponent

BAutowired

CService

DInject

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Service instead of @Component here

Forgetting @Autowired on the field

@Component marks the class as a Spring bean, and @Autowired injects it where needed.

5fill in blank

hard

Fill all three blanks to define a Spring service, inject it, and use it in a method.

Spring Boot

@[1]
public class EmailService {
    public void sendEmail() {
        System.out.println("Email sent");
    }
}

public class NotificationController {
    @[2]
    private EmailService emailService;

    public void notifyUser() {
        emailService.[3]();
    }
}

Drag options to blanks, or click blank then click option'

AService

BAutowired

CsendEmail

DComponent

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Component instead of @Service for service class

Forgetting to call the method

Missing @Autowired annotation

@Service marks the class as a service bean, @Autowired injects it, and sendEmail() calls the method.

Practice

1. What is the main benefit of Inversion of Control (IoC) in Spring Boot?

easy

A. It requires developers to manually create and connect all objects.

B. It makes the application run faster by skipping object creation.

C. It lets the framework manage object creation and dependencies automatically.

D. It disables dependency injection to improve security.

Solution

1. Step 1: Understand IoC concept

   IoC means the framework controls how objects are created and connected instead of the developer doing it manually.

2. Step 2: Identify benefit in Spring Boot

   This automatic management helps keep code clean, flexible, and easier to test.

3. Final Answer:

   It lets the framework manage object creation and dependencies automatically. -> Option C

4. Quick Check:

   IoC = framework manages objects [OK]

Hint: IoC means framework controls object creation, not you [OK]

Common Mistakes:

• Thinking IoC means manual object creation
• Confusing IoC with performance optimization
• Believing IoC disables dependency injection

2. Which annotation in Spring Boot is used to automatically inject dependencies managed by IoC?

easy

A. @Component

B. @Autowired

C. @Service

D. @RequestMapping

Solution

1. Step 1: Identify dependency injection annotation

   @Autowired tells Spring Boot to inject the required dependency automatically.

2. Step 2: Differentiate from other annotations

   @Component and @Service mark classes as beans, but @Autowired injects them. @RequestMapping is for web routes.

3. Final Answer:

   @Autowired -> Option B

4. Quick Check:

   Dependency injection uses @Autowired [OK]

Hint: Use @Autowired to inject dependencies automatically [OK]

Common Mistakes:

• Confusing @Component with injection annotation
• Using @RequestMapping for dependency injection
• Mixing @Service with injection instead of bean declaration

3. Given the code below, what will be printed when the application runs?

@Component
public class Printer {
  public void print() { System.out.println("Hello IoC"); }
}

@Component
public class User {
  @Autowired
  private Printer printer;

  public void show() { printer.print(); }
}

// In main method:
User user = context.getBean(User.class);
user.show();

medium

A. Hello IoC

B. NullPointerException

C. No output

D. Compilation error

Solution

1. Step 1: Understand IoC bean creation

   Both Printer and User are marked @Component, so Spring creates and manages them.

2. Step 2: Check dependency injection and method call

   @Autowired injects Printer into User, so user.show() calls printer.print(), printing "Hello IoC".

3. Final Answer:

   Hello IoC -> Option A

4. Quick Check:

   IoC injects Printer, prints message [OK]

Hint: IoC injects dependencies, so method prints expected output [OK]

Common Mistakes:

• Assuming printer is null causing NullPointerException
• Thinking no output because print() is not called
• Confusing compilation error due to annotations

4. What is wrong with this Spring Boot code snippet that uses IoC?

@Component
public class Service {
  private Repository repo;

  public Service() {
    repo = new Repository();
  }
}

medium

A. No error, this is correct IoC usage.

B. Service class must not have a constructor.

C. @Component annotation is missing on Repository class.

D. Repository should be injected by Spring, not created with new.

Solution

1. Step 1: Identify manual object creation

   The Service class creates Repository with new, bypassing Spring IoC container.

2. Step 2: Explain correct IoC practice

   Spring should inject Repository using @Autowired to manage dependencies and lifecycle.

3. Final Answer:

   Repository should be injected by Spring, not created with new. -> Option D

4. Quick Check:

   Manual new breaks IoC, use injection [OK]

Hint: Avoid new; let Spring inject dependencies with @Autowired [OK]

Common Mistakes:

• Thinking constructor is not allowed in @Component
• Assuming missing annotation on Repository is the main issue
• Believing manual new is correct IoC usage

5. You want to replace a service implementation without changing the code that uses it. How does IoC in Spring Boot help achieve this?

hard

A. By letting you swap the implementation bean, Spring injects the new one automatically.

B. By forcing you to rewrite all code that uses the service.

C. By disabling dependency injection to avoid conflicts.

D. By requiring manual object creation everywhere.

Solution

1. Step 1: Understand IoC flexibility

   IoC allows you to define multiple implementations as beans and swap them easily.

2. Step 2: Explain automatic injection of new implementation

   Spring injects the chosen implementation wherever the service is used without code changes.

3. Final Answer:

   By letting you swap the implementation bean, Spring injects the new one automatically. -> Option A

4. Quick Check:

   IoC enables easy swapping of implementations [OK]

Hint: Swap beans; Spring injects new implementation automatically [OK]

Common Mistakes:

• Thinking code must be rewritten for new implementations
• Believing IoC disables injection for flexibility
• Assuming manual creation is required for changes