Java interview questions

If you’re applying for a Java programming job, then it’s important that you come to the interview prepared. You will need to be ready to demonstrate that you’ll fit within the corporate culture and that you have the skills and experience to make a positive impact on the company.

Every job you apply for will have different questions and the complexity of each question will vary, depending on the seniority of your role, or the person interviewing you. However, you can still be prepared by considering some of the questions that you may get asked.

Examples of Java interview questions:

Take a look at these five possible Java interview questions and answers to help you ace your next interview. Write down your own answers which you can then read through, or get a friend or family member to role-play with you.

1. In your own words, explain what Java is and how it is used in the technology industry today

Your interviewer may start off by asking you some basic Java interview questions. This helps them to ensure you understand the fundamentals. Whilst you can explain that Java is a versatile programming language, created in 1995 by Sun Microsystems and later acquired by Oracle in 2010, the interviewer will be looking for more. Explain how Java is one of the most popular programming languages in the world and is used by millions of products every day. Java is concurrent, class-based and object-oriented, which are just some of the key principles that make it so popular. Giving facts, figures and examples of how Java is used can really help to grab the interviewer’s attention. For example, according to Oracle, there are more than nine million Java developers around the world. This quick fact can demonstrate that you also have an understanding of the industry and you go beyond just the basics.

Don’t forget that your interviewer may not work in technology themselves. So, whilst you want to show your range of knowledge, ensure you explain everything in a clear and simple way that your interviewer will understand.

2. Why would a character array be preferred over a String for passwords?

Expect your interviewer to ask you specific questions about Java to test your theoretical knowledge. The above question is just one example. The answer to this specific Java interview question would be that a character array is more secure than a String. However, that’s not going to impress your interviewer. Instead, show your depth of knowledge by expanding on this point. For example, in Java, Strings cannot be changed and will therefore be stored in a String Pool until it is “garbage collected”. This means that a password will still be available in memory and could potentially be exploited. A character array, on the other hand, can be set to blank or zero, which gives you control over what is stored in memory, making it a more secure option to use for sensitive information.

3. Look at this code and tell me what is wrong with it and why

As well as your theoretical knowledge, Java interview questions can also test your practical Java skills. They may show you some code and ask questions about it, either during the interview itself or as a separate timed exam afterwards.

Remember to take your time when answering these questions. If you’re unsure, ask them to repeat the question. If you don’t know the answer, be honest and say so. You can write down the question and answer it after the interview. This allows you to go away and look up the answer for yourself. This approach shows that whilst you may not know everything, you’re willing to learn.

4. What Java IDEs do you prefer using?

Java IDEs, or Integrated Development Environments, typically provide programmers with a code editor, compiler and a debugger, all within a graphical user interface (GUI). There are lots of different IDEs to choose from though, with Eclipse and NetBeans being some of the most popular ones. For this question, simply share some of the IDEs you have used, explain the IDE that you prefer using and discuss its benefits against other alternatives.

5. Tell me about a Java project you have worked on that you have been proud of

An interviewer will want to see your breath and depth of experience so this is an opportunity to really shine. Don’t just discuss the last project you've worked on. Consider all the projects you have been involved in and pick out a couple that may impress your interviewer. Are there any projects that were unique, allowed you to take charge, or required you to develop your skills perhaps?

By familiarising yourself with these Java interview questions, you’ll feel more confident when entering your interview. Of course, this isn’t an exhaustive list, but they will help you consider some of the questions that you may get asked.

Want more examples of common job interview questions and answers? Take a look at our "job interview tips" hub or search for current jobs.