10 Essential Java Interview Questions and Answers

Updated: June 27, 2023

If you want to go where the demand is, you can’t go wrong with a career in Java. Java is consistently rated as one of the most popular programming languages. In fact, it’s used by over 12 million developers around the world. Once you get an interview, you should be prepared to answer both general and technical questions as employers gauge your Java know-how. Before the big day, review our interview preparation resources. Then, read on for a list of the top 10 Java interview questions and answers.

1. Tell me about yourself.

This is a classic interview question for a reason, and many interviewers kick off the interview by asking it. You can read more about how to craft the perfect answer in our “Tell me about yourself” interview guide. Basically, the interviewer wants to get to know you—but they also want to know how you’ll create value for the business. Focus on relevant skills and accomplishments (but throw in a memorable detail or two), and keep your response to a minute or less. Here’s a sample response to get you started:

“I graduated six months ago, with a dual degree in computer science and biology. For the past year, I’ve been working on back-end development as an intern at a financial institution. I spend most of my time developing applications to better manage transactions. I love problem-solving, so I take an evaluative approach to solving issues, and I work through each process by trying out different solutions. Having majored in biology, I bring a unique skill set to my programming work, as well as a lot of knowledge about scientific software and research. I’m used to working in fast-paced environments, with a diversity of people, so I’m excited to hit the ground running.”

2. How would other people describe you?

This is another popular interview question that provides a perfect opportunity to differentiate yourself from the competition and show why you’d be an asset to the company. Additionally, the interviewer wants to get a better sense of your personality and work style based on others’ opinions. You’ll get bonus points for specific examples and for citing feedback you’ve received from past supervisors or colleagues. Answer honestly, with examples that show how you would address the organization’s specific needs.

“I think people would say that I’m a skilled communicator, in terms of speaking, writing, and listening. I pride myself on knowing my audience, so that I can tailor my tone and content accordingly. As a programmer, a lot of people prefer to sit behind a screen all day, but my previous coworkers were all impressed by my interpersonal skills and outgoing nature. I pay attention to what clients and colleagues are saying, and I notice what they aren’t saying. I pick up on things quickly, and I can figure out what people need through their body language and other subtle hints. It allows me to better solve people’s problems—and I’ll do that here, too.”

3. What is your most significant accomplishment?

Interviewers ask this question get insight into your work patterns, your actual performance, as well what matters most to you. Set up the situation, then go into detail about your actions and the impressive results they yielded. This question calls for specific stories, so you’ll benefit from using the STAR method. And remember: This is an excellent opportunity to brag about yourself, so don’t hold back!

“When I started at my current company, the onboarding process consisted of a PowerPoint presentation and a 20-page packet of HR policies. It wasn’t thorough, and most of it didn’t feel relevant. So, I approached HR to see if I could update the training to be more engaging and valuable for new hires. I wrote up several highly relevant scenarios that new hires might come across, based on my own experience, and then described how to best address them. I also wrote up a proposal for a mentorship program. Both HR and my manager loved my ideas, and the program has been receiving rave reviews since. Ever since, my higher-ups have been reaching out with problems that need creative solutions.”

4. What is your greatest strength? What is your greatest weakness?

These two questions are so common you can almost bet money on them. When answering the greatest strength question, it’s important to frame your answer in the context of the company’s unique needs and how your strength can help to meet them. Ensure your chosen strength is work-related and relevant to the position. Then, support it with evidence. For the greatest weakness, choose a weakness that isn’t a true deficiency and isn’t vital to the job at hand. You’re in Java, so don’t say that you’re bad with numbers. Be honest, and focus the majority of your response on what you’re doing to address your shortcomings and improve. You can read more about the greatness strength and weakness questions here.

“My greatest strength is that I have an extremely strong work ethic. I’m known for completing projects ahead of schedule, which is an important attribute in this industry. Technology is always changing, and sometimes things don’t work out as expected. I can change direction quickly, and I take the initiative to come up with different ways to solve a problem. My greatest weakness is my lack of experience. I’m a recent graduate, and I don’t have a lot of work experience. But I’m a fast learner, and I’m highly adaptable, so I’m confident that I’ll build my skill set quickly once I start working full-time. Additionally, I stay up-to-date on the latest programming trends, and I pride myself on bringing a fresh perspective.”

5. Tell me what you like about Java.

There are a lot of programming languages out there, but you chose Java—and the interviewer wants to know why. This is your chance to show that you’re passionate about what you do. And be sure to assure the interviewer that you’re in this for the long haul. They want to know that you won’t get bored a few months from now and jump ship.

“Java is an object-oriented language, and I love working with those because they make my job easier. Java makes it easy for me to organize objects quickly and in a way that makes sense. Additionally, Java automatically manages memory, which gives me one less thing to worry about. Finally, I was initially drawn to Java because so many others use it! It’s inspiring to know that 9 million other developers are using Java, just like me. And if I run into a problem, there’s almost always someone else who ran into it—and solved it—first.”

6. Why is Java considered platform independent?

Java’s slogan is WORA, which stands for “write once, run anywhere.” Aspiring Java professionals need to know what this means and why it’s so important. Java is well-known for being platform independent, so have an articulate answer ready to go for this question.

“Java is considered platform-independent because, thanks to bytecode, it can run on any and all operating systems—whether they’re Mac, Linux, or Windows. Java’s cross-platform benefits are super beneficial in a networked environment, since companies typically use many different kinds of computers and devices.”

7. What are JVM, JRE, and JDK?

As with any technical role, you should know your jargon and acronyms before the interview. JVM (Java Virtual Machine), JRE (Java Runtime Environment), and JDK (Java Development Kit) are core concepts in Java programming. In asking this question, your interviewer is checking that you know the basics of the language before they begin checking your knowledge of more complex topics.

“JVM stands for Java Virtual Machine, which is an abstract machine that provides a runtime environment for the Java bytecode. JRE stands for Java Runtime Environment, which refers to the specific runtime environment in which the Java bytecode can be executed. JRE implements the JVM and provides all support files that the JVM uses during runtime. JDK is the Java Development Kit, which is the tool that allows you to gather, document, and package Java programs. It includes the JRE as well as development tools.”

8. What is the difference between ArrayList and vector?

This is another basic question, asked in the beginning of an interview before ramping to more advanced topics. Prospective employers will expect you to know the difference between these two classes, so it’s best to be prepared.

“An ArrayList is not synchronized, which makes it much faster. While a vector is synchronized, which slows it down, it’s thread safe and limited to one thread at a time. Other than Hashtable, Vector is the only other class that uses both Enumeration and Iterator, while ArrayList can only use Iterator for traversing an ArrayList.”

9. How do equals() and == differ?

Again, this is a question that allows you to demonstrate your depth of understanding when it comes to specific characteristics of Java. Prospective employers want a guarantee that you are well versed in all things Java.

“Both are used to compare objects to check equality. However, equals() is a method used to compare the values of two objects, while the ‘==’ equality is an operator used to compare both primitives and objects.”

10. Java does not support multiple inheritance. How did this prevent the “diamond problem” in the past, and why is this no longer true?

While this question may be highly technical, it is extremely relevant with Java, and answering it correctly shows that you understand common problems. In your response, stress your ability to stay up-to-date on the newest versions and issues.

“Java does not allow multiple inheritance for classes, only for interfaces. In the past, this prevented the ‘diamond problem,’ more typically seen in C++, as it is only possible to inherit an implementation from the single parent class. With Java 8, a class can now inherit a method implementation from either its parent class or any of its interfaces, increasing the chance for the compiler to reject the compilation.”

Understanding the Interviewer’s Perspective

As an interviewee, it’s important to consider what the interviewer is looking for. They’re not only assessing technical skills, but also problem-solving abilities, passion for the field, and how well a candidate might fit within their team. Here are a few things they’re likely considering:

Technical Competency

The interviewer is checking whether the candidate has a solid understanding of Java and its applications. The questions asked aim to test knowledge of core concepts and the ability to apply these concepts to real-world scenarios. It’s not just about memorizing facts–the interviewer wants to see how the candidate thinks and solves problems.

Problem-Solving Skills

Interviewers often ask questions that require candidates to demonstrate their problem-solving abilities. This could be a coding challenge or a hypothetical scenario. They’re observing how the candidate approaches the problem, breaks it down into manageable parts, and works towards a solution.

Passion and Curiosity

Interviewers look for signs of genuine interest and curiosity in the field. This can often be a good indicator of a candidate’s willingness to keep learning and growing as a professional. Questions about why the candidate chose Java or what they like about it can give the interviewer insight into their passion and motivation.

Communication Skills 

Being able to explain complex concepts in a clear and understandable way is a critical skill in software development. The interviewer is paying attention to how the candidate explains their thought process and their solutions – this can give them a good idea of the candidate’s communication skills.

Cultural Fit

Lastly, the interviewer is trying to gauge whether the candidate would be a good fit for the team and the company culture. This doesn’t mean the candidate has to be just like everyone else on the team – diversity in thought and experience can be a great asset. But the interviewer wants to feel confident that the candidate can collaborate effectively with others, handle feedback, and align with the company’s values and goals.

Remember, the interview is not just about proving ability to do the job, but demonstrating potential to grow with the job and contribute to the success of the team and the company. Java is popular for a reason. Practice your coding, build your portfolio, and craft your own unique answers to these 10 questions. You’ll be programming a successful career in no time.