17 Java Backend Developer Interview Questions and Answers

Java is one of the most popular programming languages in the world and backend developers who know Java can find work in a wide range of industries. If you’re a Java developer who’s looking for a new job, you need to be prepared to answer a variety of Java interview questions.

Your interviewer will want to know if you have the technical skills to do the job, but they will also be looking for evidence that you’re a good fit for the company culture. To help you prepare, we’ve put together a list of Java interview questions and answers that you can use to practice for your upcoming interview.

Are you familiar with the Spring framework?

The Spring framework is a popular Java application development framework that allows developers to create enterprise-level applications. Your answer should show the interviewer you have experience with this framework and can use it effectively in your work.

Example: “I’ve used the Spring framework for several years now, so I am very familiar with its features and functions. In my last role as a Java backend developer, I was responsible for creating new projects using the Spring framework and maintaining existing ones. This allowed me to become even more proficient at working with the framework and learn how to troubleshoot issues when they arose.”

What are some of the most important considerations when designing a RESTful API?

This question allows you to demonstrate your knowledge of the RESTful API design process. You can answer this question by providing a list of considerations and explaining what each one means in relation to designing an effective RESTful API.

Example: “There are several important considerations when designing a RESTful API, including URL structure, HTTP methods, media types, hypermedia links and data formats. The URL structure is very important because it determines how users access the API. I prefer using URLs that are easy for humans to read so they can understand the purpose of the resource. HTTP methods are also important because they determine which actions are available on the API. For example, if there’s no POST method, then users cannot create new resources. Media types are important because they define the format of the data being sent or received. Hypermedia links are important because they allow users to navigate between different resources without having to know all possible routes beforehand.”

How would you implement security in a Java backend application?

Security is an important aspect of any application, and the interviewer may ask you this question to assess your knowledge of how to implement security in Java applications. Use examples from previous experience or explain what steps you would take to ensure a secure environment for users.

Example: “In my last role as a Java backend developer, I was tasked with creating a new web portal that required high levels of security. To do so, I first created a user database where each user had their own username and password. Then, I used servlet filters to check if the user’s credentials were correct before allowing them access to certain pages. This ensured that only authorized users could enter the site.”

What is the difference between a HashMap and a TreeMap?

This question tests your knowledge of the Java API. You can answer this question by defining each type and explaining how they differ from one another.

Example: “A HashMap is a key-value pair that uses a hash function to store values in buckets, while TreeMap stores objects in sorted order according to their natural ordering. The main difference between these two types is that TreeMap preserves the original order of elements, while HashMap does not.”

Provide an example of when you would use a ThreadPool.

A ThreadPool is a group of threads that are used to execute tasks. This question allows the interviewer to assess your knowledge of Java’s ThreadPool and how you apply it in your work.

Example: “A ThreadPool is useful when I need to run many tasks at once, but each task takes a long time to complete. In this case, using a ThreadPool can help me save resources by allowing multiple tasks to be executed simultaneously. However, if one thread needs to wait for another thread to finish its task before continuing, then all other threads will also have to wait until the first thread finishes. To avoid this issue, I would use a Queue instead of a ThreadPool.”

If a client were to complain that their Java application was slow, what would be your first troubleshooting step?

This question is an opportunity to show your problem-solving skills and knowledge of Java. Your answer should include a step-by-step process for troubleshooting the issue, including what tools you would use to diagnose the problem.

Example: “My first step would be to determine whether the user’s computer was causing the slow performance or if it was due to the application itself. I would then check the server logs to see how long each request took to execute. If the requests were taking longer than expected, I would look at the CPU usage, memory consumption and garbage collection statistics to find out which component was slowing down the application.”

What would you do if you were working on a project and a lead developer asked you to rewrite all of your code?

This question is a good way to test your problem-solving skills and ability to work with others. Your answer should show that you can take constructive criticism, understand why the lead developer wants you to rewrite your code and are willing to do what’s necessary to complete the project successfully.

Example: “If I was asked to rewrite all of my code, I would first ask for more details about why this request was made. If it was because of performance issues or security concerns, I would be happy to rewrite my code as long as there was time left in the project to do so. However, if the request was made simply because the lead developer wanted me to change something about my coding style, I would politely decline and explain that I am always open to feedback and suggestions.”

How well do you understand the concept of threading in Java?

Threading is a key concept in Java, and the interviewer may ask this question to assess your knowledge of threading. Your answer should show that you understand how to use threads effectively in Java applications. You can describe how you would implement threading in Java projects.

Example: “Threading is an important concept in Java because it allows developers to create multiple tasks within one application. I have used threading in my past two roles as a Java backend developer, where I implemented threading into my code by using the Thread class. This allowed me to run different functions at once, which helped me complete projects more quickly.”

Do you have experience working with the Hibernate framework?

Hibernate is a framework that allows developers to create and manage data objects. Your answer should show the interviewer you have experience with this framework, but also highlight your ability to adapt to new frameworks if necessary.

Example: “I have worked with Hibernate in previous positions where I was responsible for creating and managing database tables. However, I am open to working with other frameworks as well. In my current role, we use Spring Boot, which is similar to Hibernate because it’s an ORM framework. I find that both of these frameworks are easy to learn and implement when needed.”

When working on a team of developers, how do you handle constructive criticism?

This question can help the interviewer understand how you handle working with others and your ability to accept feedback. Your answer should show that you are open to receiving constructive criticism from your team members, as well as giving it when necessary.

Example: “I believe in being honest with my team members about any issues I have with their work or ideas. In my last role, I had a teammate who was new to the company and didn’t know all of our processes yet. When he presented an idea for a project, I gave him some advice on how we typically do things at the company and helped him develop his idea into something more feasible. He appreciated the feedback and used it to create a better proposal.”

We want to increase the speed of our application. What strategies would you use to do this?

This question allows you to show your knowledge of how to optimize the performance of an application. You can answer this by describing a situation where you increased the speed of an application and the steps you took to do so.

Example: “I would first look at the database, which is usually the slowest part of any Java application. I would then use caching to store frequently used data in memory for faster access. Next, I would reduce network latency by using local servers instead of remote ones. Finally, I would remove unnecessary code from my application.”

Describe your experience with the JUnit framework.

The JUnit framework is a testing framework that allows developers to test their code. This question helps the interviewer understand your experience with this framework and how you use it in your daily work.

Example: “I’ve used the JUnit framework for all of my projects because it’s an essential tool for Java development. I find it helpful when creating unit tests, as well as integration tests. It also makes it easier to write better code by identifying errors before they occur. In my last role, I was responsible for writing new code using the JUnit framework.”

What makes Java an ideal programming language for backend development?

This question allows you to show your knowledge of Java and how it can be used in a professional setting. You should explain why you chose Java as your primary programming language, what makes it unique or how it has helped you develop backend applications.

Example: “Java is an ideal programming language for backend development because it’s object-oriented, which means that I can create reusable code that can be applied to different projects. It also uses the ‘write once, run anywhere’ principle, so my programs are compatible with many operating systems. This saves time when testing new software on multiple platforms.”

Which programming languages do you feel are most similar to Java?

This question is a great way to test your knowledge of Java and how it compares to other programming languages. Your answer should include the name of the language, what you feel are its similarities to Java and why you think they’re similar.

Example: “I would say that C++ and Java are the most similar in terms of syntax. They both use curly braces for blocks, have semicolons at the end of each statement and support pointers. However, I find that C++ is more complex than Java because it supports multiple inheritance while Java only supports single inheritance.”

What do you think are the biggest challenges facing Java backend developers today?

This question helps the interviewer get a sense of your knowledge and experience with Java backend development. Your answer should include an example of how you overcame one of these challenges in the past.

Example: “The biggest challenge facing Java backend developers today is that it’s not as popular as other programming languages, which means there are fewer resources available to help us learn new things. I’ve overcome this challenge by using online forums and communities to ask questions when I need help. Another challenge is that Java is a complex language, so it can be difficult to know where to start when learning it. To overcome this challenge, I started out by learning the basics of Java before moving on to more advanced concepts.”

How often do you update your knowledge of Java and programming languages in general?

This question can help the interviewer determine how committed you are to your career and whether you’re likely to stay with their company for a long time. Your answer should show that you have an interest in learning new things, but it’s also important to mention any certifications or training you’ve completed recently.

Example: “I try to learn something new every day about Java or programming languages in general. I’m currently enrolled in a course on Spring Boot development, which is helping me understand more advanced concepts of Java. I am also working toward my certification as a Certified Professional Developer.”

There is a bug in the code you’ve written for a project. How do you handle this?

This question is an opportunity to show your problem-solving skills and ability to work with a team. Your answer should include the steps you take to identify the bug, how you fix it and what you do if there are any issues in implementing the solution.

Example: “I first try to find out whether the bug is due to my coding or something else. If I’m sure that it’s due to my coding, then I will go through the code line by line to see where the issue may be. Once I have identified the error, I will write a new piece of code to replace the existing one. However, if I am not sure about the cause of the bug, I will discuss it with my manager and other members of the development team to decide on the best course of action.”