Bean concept in Spring in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary purpose of a Spring Bean?

In Spring Framework, what is the main role of a Bean?

A It is a configuration file that defines application properties.

B It is a database connection object used for querying data.

C It is an object managed by the Spring container to provide application functionality.

D It is a user interface component for web pages.

💡 Hint

Think about what Spring manages to help build applications.

A Spring Bean is an object that the Spring container creates, manages, and wires together to build the application.

❓ component_behavior

intermediate

What happens when you annotate a class with @Component in Spring?

Consider a class annotated with @Component. What does Spring do with this class during application startup?

A Spring creates an instance of the class and registers it as a Bean in the application context.

B Spring ignores the class unless it is explicitly instantiated in code.

C Spring converts the class into a database entity automatically.

D Spring uses the class only for configuration properties.

💡 Hint

Think about how Spring detects and manages components automatically.

The @Component annotation tells Spring to create and manage an instance of the class as a Bean.

❓ state_output

advanced

What is the scope of a Bean annotated with @Scope("prototype")?

Given a Spring Bean annotated with @Scope("prototype"), what is the behavior when the Bean is requested multiple times?

A A new instance of the Bean is created each time it is requested.

B The same single instance of the Bean is shared across all requests.

C The Bean is created once per HTTP session and reused.

D The Bean is created once per web request and discarded afterward.

💡 Hint

Prototype scope means multiple instances instead of one.

Beans with prototype scope are created fresh each time they are requested from the container.

📝 Syntax

advanced

Which code snippet correctly defines a Bean using Java configuration in Spring?

Select the correct Java method to define a Bean in a @Configuration class.

Spring Boot

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class AppConfig {
    // Which method is correct?
}

A public MyService myService() { return new MyService(); }

B @Bean public MyService myService() { return new MyService(); }

C @Bean MyService myService { return new MyService(); }

D @Bean public void myService() { new MyService(); }

💡 Hint

Look for the correct method signature and annotation.

The method must be annotated with @Bean, have a return type, and return the Bean instance.

🔧 Debug

expert

What error occurs if two Beans have the same name in Spring context?

If two Beans are defined with the same name in Spring, what happens when the application starts?

A Spring merges both Beans into one automatically.

B Spring silently uses the first Bean and ignores the second one.

C Spring creates both Beans with different internal names without error.

D Spring throws a BeanDefinitionOverrideException or a similar error about duplicate Bean names.

💡 Hint

Spring does not allow two Beans with the same name by default.

Spring throws an error because Bean names must be unique to avoid confusion in dependency injection.

Practice

1. What is a Bean in the Spring framework?

easy

A. A type of Java exception

B. A database connection

C. An object managed by the Spring container

D. A user interface component

Solution

1. Step 1: Understand Spring's role

   Spring manages objects to help organize and connect parts of an application.

2. Step 2: Define what a Bean is

   A Bean is any object that Spring creates and manages in its container.

3. Final Answer:

   An object managed by the Spring container -> Option C

4. Quick Check:

   Bean = Managed object [OK]

Hint: Beans are Spring-managed objects, not UI or exceptions [OK]

Common Mistakes:

• Confusing beans with database connections
• Thinking beans are UI elements
• Assuming beans are exceptions

2. Which annotation is used to declare a class as a Spring Bean?

easy

A. @Qualifier

B. @Component

C. @Autowired

D. @RequestMapping

Solution

1. Step 1: Identify annotations for beans

   @Component marks a class as a Spring-managed bean.

2. Step 2: Differentiate from other annotations

   @Qualifier specifies which bean to inject, @Autowired injects beans, @RequestMapping maps web requests.

3. Final Answer:

   @Component -> Option B

4. Quick Check:

   @Component = Bean declaration [OK]

Hint: Use @Component to declare beans; others serve different roles [OK]

Common Mistakes:

• Confusing @Autowired with bean declaration
• Using @RequestMapping for beans
• Thinking @Qualifier declares beans

3. Given the code below, what will be printed (assuming the @Autowired field and System.out.println are inside a Spring-managed class)?

@Component
public class MyBean {
  public String greet() { return "Hello Spring"; }
}

@Autowired
MyBean myBean;

System.out.println(myBean.greet());

medium

A. Hello Spring

B. null

C. Compilation error

D. No output

Solution

1. Step 1: Understand @Component and @Autowired

   @Component creates the bean, @Autowired injects it into the field.

2. Step 2: Check method call output

   Calling greet() returns "Hello Spring", so it prints that string.

3. Final Answer:

   Hello Spring -> Option A

4. Quick Check:

   Injected bean method returns greeting [OK]

Hint: Autowired injects bean; method returns greeting string [OK]

Common Mistakes:

• Assuming null because of missing initialization
• Thinking it causes compile error
• Expecting no output without System.out.println

4. What is wrong with this Spring bean declaration?

@Component
public class MyService {
  @Autowired
  private MyRepository repo;

  public void doWork() {
    repo.save();
  }
}

Assuming MyRepository is not annotated as a bean.

medium

A. No @Autowired on MyService class

B. Missing @Service annotation on MyService

C. Method doWork() should return a value

D. MyRepository is not a Spring bean, so injection fails

Solution

1. Step 1: Check bean injection requirements

   Spring can only inject beans that are managed by the container.

2. Step 2: Identify missing bean annotation

   MyRepository lacks @Component or similar, so Spring cannot inject it.

3. Final Answer:

   MyRepository is not a Spring bean, so injection fails -> Option D

4. Quick Check:

   Injection requires bean annotation [OK]

Hint: Injected classes must be beans too [OK]

Common Mistakes:

• Thinking @Service is mandatory for injection
• Assuming method must return value
• Confusing @Autowired placement

5. You want to create a bean that returns a customized object. Which method correctly defines a bean using Java configuration?

hard

A. @Bean
public MyBean myBean() {
return new MyBean("custom");
}

B. @Component
public MyBean myBean() {
return new MyBean("custom");
}

C. public MyBean myBean() {
return new MyBean("custom");
}

D. @Autowired
public MyBean myBean() {
return new MyBean("custom");
}

Solution

1. Step 1: Understand @Bean usage

   @Bean annotation on a method inside a @Configuration class defines a bean returned by that method.

2. Step 2: Differentiate from other annotations

   @Component is for classes, not methods; @Autowired injects dependencies, not defines beans.

3. Final Answer:

   @Bean public MyBean myBean() { return new MyBean("custom"); } -> Option A

4. Quick Check:

   @Bean method returns custom bean [OK]

Hint: Use @Bean on methods inside @Configuration classes [OK]

Common Mistakes:

• Using @Component on methods instead of classes
• Omitting @Bean annotation
• Confusing @Autowired with bean creation