20 Autowired Interview Questions and Answers

Autowired is a popular annotation used in Spring-based applications. It allows developers to inject dependencies into their beans without having to configure them in the XML file. While the Autowired annotation is relatively simple, there are a few key things that interviewers will want to know about how you use it. In this article, we discuss the most common Autowired questions and how you should answer them.

Autowired Interview Questions and Answers

Here are 20 commonly asked Autowired interview questions and answers to prepare you for your interview:

1. What is Spring Autowiring?

Autowiring is a feature of Spring that allows beans to be automatically wired together. This means that you don’t have to explicitly specify dependencies between beans in your configuration file. Instead, the Spring container will look at the types of beans that are required and wire them together automatically.

2. Can you explain the different types of autowiring in Spring?

Spring offers several different types of autowiring, each with its own advantages and disadvantages. The most common type of autowiring is byName, which simply looks for a bean with the same name as the property that is being autowired. Another option is byType, which looks for a bean with the same type as the property that is being autowired. There is also constructor autowiring, which looks for a constructor with the same type as the property that is being autowired. Finally, there is autowiring by annotation, which looks for an annotation on the property that is being autowired.

3. How can we enable autowiring in spring?

We can enable autowiring in spring by using the @Autowired annotation on fields, setters, and constructors. This annotation tells spring to automatically inject the dependencies into the annotated fields.

4. What are some advantages of using autowiring?

Autowiring can save a lot of time and effort when configuring dependencies in an application. It can also help to make code more readable and maintainable by eliminating the need to explicitly specify dependencies. Additionally, autowiring can help to ensure that dependencies are always valid and up-to-date.

5. What are some disadvantages of using autowiring?

One potential disadvantage of using autowiring is that it can make your code more difficult to read and understand. If you are not familiar with how autowiring works, then it can be difficult to follow the flow of control through your code. Additionally, autowiring can sometimes lead to unexpected results if you are not careful in how you configure it.

6. Why do you think it’s important to use constructor injection over setter injection?

Constructor injection is generally seen as the better option because it ensures that all required dependencies are present before the object is used. With setter injection, it’s possible to forget to set a required dependency, which can lead to errors. Additionally, constructor injection can help make code more readable and maintainable.

7. Can you give me an example of how to inject beans into other beans with Spring Boot?

You can inject beans into other beans with Spring Boot by using the @Autowired annotation. For example, if you have a bean called Foo and a bean called Bar, you can inject Foo into Bar by adding the @Autowired annotation to the Bar class.

8. Can you explain what circular dependency is and how does Spring handle it?

Circular dependency is when two classes each depend on the other. Spring will not be able to create an instance of either of these classes if they have a circular dependency.

9. In which scenarios will Spring fail to create a bean for autowiring?

There are a few scenarios in which Spring will fail to create a bean for autowiring. One is if the class is not annotated with @Component or a similar annotation. Another is if the class is not registered in the application context. Finally, if there is more than one bean of the same type in the application context, autowiring will fail.

10. What is the difference between @Autowired and @Resource annotations in Spring? Which one would you recommend when injecting dependencies?

The @Autowired annotation is used for auto-wiring dependencies in Spring. This means that the Spring container will automatically resolve and inject dependencies into your bean. The @Resource annotation is used to inject resources into your bean, such as a JDBC DataSource. When it comes to injecting dependencies, I would recommend using @Autowired.

11. Is it possible to autowire a list of beans into another bean? If yes, then how?

Yes, it is possible to autowire a list of beans into another bean. You can do this by using the @Autowired annotation on a field in the bean that you want to autowire the list into.

12. When should you avoid using autowiring in your projects?

There are a few reasons why you might want to avoid using autowiring in your projects. The first is that it can make your code more difficult to read and understand. If you are using autowiring, it can be hard to tell at a glance what dependencies a particular class has. This can make it difficult to refactor code or add new features. Additionally, autowiring can make your code more difficult to test, as it can be hard to mock dependencies. Finally, autowiring can lead to unexpected behavior if you are not careful. If you are not careful about specifying the exact types of dependencies that you want to inject, you may end up with unexpected results.

13. What do you understand about the term “bean” used in Spring boot?

A bean is simply an object that is managed by the Spring framework. These beans can be created and destroyed as needed, and they can be injected into other beans as dependencies.

14. What is the purpose of using the Autowired annotation?

The Autowired annotation is used in Spring to automatically inject beans into your code. This means that you do not need to explicitly define a setter method for each bean, and it also means that the Spring container will take care of injecting the dependencies for you. This can save a lot of time and boilerplate code when working with Spring.

15. How does Spring resolve conflicts during autowiring?

Spring will attempt to resolve conflicts during autowiring by looking at the type of the bean being injected and the type of the property into which it is being injected. If there is a match, then Spring will autowire the bean. If there is more than one match, then Spring will attempt to resolve the conflict by looking at the bean’s id.

16. What is auto-detection in Spring?

Auto-detection is a feature in Spring that allows beans to be automatically created and injected into your application. This can be done either through scanning your classpath for annotated classes, or by explicitly declaring the beans in your configuration file.

17. What is the importance of the Qualifier annotation?

The Qualifier annotation is used to resolve ambiguities when multiple beans of the same type are present in the Spring container. It is also used to specify a custom bean name for the annotated component.

18. Can you give me an example of how to use the @Qualifier annotation to choose which implementation of an interface needs to be injected at runtime?

@Qualifier is used to specify which implementation of an interface should be injected at runtime. For example, if you have two implementations of the same interface, you can use @Qualifier to specify which one should be used.

19. What is the right way to find out if two objects have the same value in Java?

The right way to find out if two objects have the same value in Java is to use the equals() method. This method is inherited from the Object class, and it compares the values of two objects to see if they are equal. If you are comparing two objects that are not of the same type, then you will need to use the instanceof operator to make sure that you are comparing apples to apples.

20. What is the best way to sort a Map by its values?

There are a few ways to sort a Map by its values, but the most common way is to use the Collections.sort() method. This method takes a map and a comparator, and then sorts the map according to the comparator.