20 Dependency Injection Interview Questions and Answers

Dependency Injection is a software design pattern that allows for the removal of hard-coded dependencies and makes it possible to change them, if needed. This design pattern is used in many programming languages, including PHP. If you are interviewing for a position that involves PHP programming, you may be asked questions about Dependency Injection. In this article, we will review some of the most common questions about Dependency Injection and how you can answer them.

Dependency Injection Interview Questions and Answers

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

1. What is Dependency Injection?

Dependency Injection is a technique for decoupling software components. This decoupling allows for more flexibility and easier testing of software components.

2. How does dependency injection help with unit testing code?

Dependency injection is a technique that helps to decouple code dependencies from each other. This can be helpful in unit testing code, because it allows you to mock out dependencies and test the code in isolation. This can make it easier to identify bugs and test edge cases.

3. What are the main types of dependency injection?

The main types of dependency injection are constructor injection, setter injection, and interface injection.

4. Can you explain what constructor injection is? When should it be used?

Constructor injection is a type of dependency injection where dependencies are injected into an object via its constructor. This is generally used when the dependencies are required for the object to function properly, as opposed to being injected later on.

5. What are some pros and cons of using constructor injection over other approaches?

Some pros of using constructor injection are that it can help make code more testable and modular, and it can also make it easier to manage dependencies. However, some cons include the potential for code bloat and the need to create a new instance of the class for each dependency.

6. Does Spring support method injection? If yes, then how?

Yes, Spring does support method injection. This is done by annotating a method with the @Autowired annotation. Spring will then call that method and inject the dependencies that are needed.

7. Is there a way to create dependencies without injecting them into dependent objects?

There is no way to create dependencies without injecting them into dependent objects. Dependency injection is the only way to create dependencies.

8. What’s the difference between @Autowired and @Inject annotations in Spring?

@Autowired is used for autowiring byType in Spring framework. @Inject is a standard annotation for dependency injection, which is supported by many frameworks like Spring, CDI, etc.

9. What do you understand about XML-based config files for dependency injection in Spring?

XML-based config files are used to configure dependency injection in Spring. This allows you to specify which beans are to be injected into which other beans, as well as to specify other properties such as the scope of the beans.

10. Can you give me an example of how you would implement multiple constructors in spring?

In Spring, you can use the @Autowired annotation on a constructor with multiple arguments to have Spring automatically resolve the dependencies for you.

11. What is Setter Injection? Why is it preferred over constructor injection?

Setter injection is a type of dependency injection where dependencies are injected into an object through setter methods. This is preferred over constructor injection because it allows for dependencies to be optional, and it also allows for dependencies to be injected after the object has been constructed.

12. Do all setter methods require annotations in Spring?

No, not all setter methods require annotations in Spring. However, if you want your setter methods to be dependency injected, then they must be annotated with @Autowired.

13. Are there any disadvantages associated with using Spring for dependency management?

While there are many advantages to using Spring for dependency management, there are a few potential disadvantages to keep in mind. First, Spring can add a lot of complexity to a project, which can make it more difficult to understand and maintain. Additionally, Spring can be slow to start up, which can impact the performance of an application.

14. What’s your opinion on Guice?

I believe that Guice is a great tool for dependency injection, and it has helped me in a number of projects. I particularly like the way that it allows you to bind interfaces to implementations, which can be very helpful in large projects.

15. What do you understand about lazy initialization? How can it be done in Spring?

Lazy initialization is the process of deferring the creation of an object until it is needed. This can be useful in situations where an object is not required immediately, which can help to improve performance. In Spring, lazy initialization can be done by using the @Lazy annotation.

16. Can you give me an example of how you would use autowiring based on name?

Autowiring by name is a process of automatically injecting a bean into another bean by matching the bean’s name to the name of the property that is being injected. For example, if you have a bean with the name “foo” and you want to inject it into a property with the name “bar”, you can use autowiring by name to have the bean automatically injected.

17. How do you make sure that only one bean is registered in Spring?

You can use the @Scope annotation to specify that a bean is a singleton.

18. Is it possible to inject values from property files into beans in Spring? If yes, then how?

Yes, it is possible to inject values from property files into beans in Spring. This can be done using the PropertyPlaceholderConfigurer class. This class will take values from a property file and inject them into beans as they are created.

19. What is the difference between direct field access and property-setter injection?

Direct field access is when you simply set the value of a field directly, without going through a property setter. Property-setter injection is when you set the value of a field by calling the property setter method. The main difference between the two is that direct field access bypasses any logic that might be in the property setter, while property-setter injection executes that logic.

20. Can constructors have arguments with different roles (such as required vs optional)?

Yes, constructors can have arguments with different roles. For example, a constructor might have an argument that is required in order for the object to be created, and another argument that is optional.