Top Technical QuestionsAs it’s always the case, companies typically give you a chance to wow them with your programming skills and then your soft skills. So let’s first get into the most popular technical questions and possible answers to them, as well as the main topics you need to brush up on to ace the Java interview.
What are your favorite features of Java?Your interviewer may ask you this simple question to make sure you have a solid understanding of each Java feature, especially those that differ Java from other programming languages. In this case, you should show your familiarity with Java, answering something like, "I like the high performance of Java, and I appreciate that it’s an object-oriented, cross-platform language, which you can run any platform.”
What are abstract classes, and why should you use them?Basically, an abstract class is a class that includes abstract methods. These methods, in their turn, have declarations. And rather than implementations, they’re backed by sub-classes of the abstract class. That’s why they are flexible and easy to customize.
Explain inheritance as you understand it.Inheritance is when one object (or a class) is based on another object and uses the same implementation. For instance, it’s like having an automobile and a motorcycle class (they both inherit from a Vehicle class).
Is there a difference between method overriding and overloading? If yes, explain.They are both examples of polymorphism. But they are different – the method overloading intends that you have the same method but change its parameters, signature, or return type. Method overriding means that you have a method that belongs to an extended class, and you modify its behavior.
How to ensure high quality and fix the majority of errors in code?Performing a quality control process is essential for any project's success. In your answer, you should be ready to clearly describe the process of testing/fixing the software for bugs you use. It’s also preferable to show that you understand the importance of delivering error-free results to the clients. You may say, "Ensuring high quality is my main responsibility as a developer. I use the unit testing frameworks (like JUnit) to test the quality of my code. I always check system errors in IDE. I can write tests, wrap the code to “trap” exceptions, and utilize try/catch statements. I can also perform code-based testing to find potential errors.”
Why is it more secure to store sensitive data in a character array rather than a String?Since character arrays are mutable objects, it’s possible to set a character array to ‘blank’ as soon as someone is finished with it. That’s why nothing will be stored in memory. But the situation is entirely different with Strings. They are immutable and stored in the String pool. Anyone with access to a related memory dump can easily find the sensitive data.
What is JDK?This question can also evaluate your core Java knowledge. JDK is a Java Development Kit that consists of the Java Virtual Machine and Java Runtime Environment. Simply put, JDK provides the Java application programming interface.
How do you understand the Java virtual machine?This question can help your interviewer determine whether you are familiar with the relationship between Java and hardware. Try to clearly explain your understanding of a virtual machine, say, "if you use a computer that does not support Java, you can use a virtual machine to run any Java program on any platform. This specification compiles Java code to Bytecode.”
Does Java support multiple inheritances for classes?No, the Java programming language doesn’t support multiple inheritances for classes. It was created for simplicity of use, so multiple inheritances for classes are avoided in Java.
What is a default constructor?The compiler typically generates a nullary constructor if no constructors are defined for a class. And this constructor is known as the default constructor.
What is the difference between StringBuilder and StringBuffer?StringBuffer is synchronized and can be called by one thread at a time. StringBuilder, on the other hand, is not synchronized, meaning it can be called by multiple threads simultaneously.
Give us a definition of inheritanceInheritance is a mechanism that allows the class to acquire the fields and methods of its parent class. Inheritance is possible only when an “is-a” relationship exists between classes. Yet, all the abovementioned questions just scratch the surface of the technical part of the interview. Besides them, you should be prepared for such questions:
- If you were reviewing somebody else’s code, where would you place most of your focus?
- What features, if any, would you like to add to Java? Why?
- We want to install a new software system. What steps would you take to meet our needs before software deployment? (e.g. research methods)
- When do you use polymorphism?
- What are the most effective techniques to prioritize program requirements?
- What are the differences between String, StringBuilder, and StringBuffer in Java?
- Are you familiar with cloud systems? What are their pros and cons?
- Describe the programming processes at work from the time you type in a website’s URL to when it finishes loading on your screen.
- What is your field of expertise, and what would you like to learn more about? Why?
- Describe a time when a program you developed didn’t run. How did you troubleshoot your code?
- What’s a project that you’ve worked on recently? What was your role in it?
- Describe a time when you managed to reduce the user’s perception of waiting. What features did you use?
- What’s your most successful project so far? What was your role? Describe the challenges you faced during this project.
- Explain any of your previous projects and the process by which you opted to complete them.
- Did you experience any hindrances during your project, and how you managed it?
- What is known as MVC?
- Do you use an agile software development process?
- How good are you with OOP analysis?
- Tell me something about multi-threading.
- What do you know about unit testing?
- Name the procedure for detecting a bug in an application.
General Questions During an InterviewBesides technical skills, be prepared that interviewers will evaluate your soft skills. That’s why they may ask you:
How can you explain technical information to clients or co-workers with non-technical backgrounds?The answer to this question may show how you can communicate with others. And while answering it, try to highlight your active listening and good communication skills. Example: "I always use simple language while communicating with clients or people from other departments. I also make sure they understand the information completely prior to getting down to work”.
Do you feel comfortable working in a team?This question is often asked to evaluate your teamwork skills, as most projects require collaboration. Yet, if you are comfortable working both in-team and independently, don’t forget to highlight it in your answer. Example: "Working in a team and independently have advantages for me. I like communicating with the team to set goals and achieve them together. I am also eager to learn from more experienced team members. Not to mention, regular meetings can speed up the project's progress”.
Why are you the best fit for this position?To answer this question right, you’ll need to check information about the company beforehand. Don’t respond with common answers like, “Because I’m skilled and motivated.” Instead, try to highlight how you can contribute to their specific needs. Gathering info beforehand can help you craft your responses that will align with the goals and values of the company you’re applying to.
Bonus TipsLast but not least, here are the additional hints for passing an interview successfully:
Be honest. Be honest when answering questions, and avoid making any blurry guesses. If you’re unfamiliar with some term or topic, then it’s better to explain how you can learn about it rather than trying to nick it. This will show your honesty and commitment to learning during the interview.
Practice possible answers. Create an approximate list of questions that you can encounter during the interview. Then, answer and practice them. By doing so, you can improve your confidence during the “real” interview.
Highlight your skills. Don’t forget to put an emphasis on your most-valued skills (both soft and hard). If you already have some previous work experience, you can mention your previous job duties.
Don’t be shy to ask questions. We also recommend you ask your own questions to find out more about the position and show the interviewer that you’re genuinely interested in the company. You may ask, "What are the biggest challenges facing the team right now?” or “Do you offer an opportunity to grow?”.
Develop a portfolio. For entry-level Java specialists, creating a portfolio is a fantastic way to show your passion for the field. You can add the projects you've completed during the CodeGym University India course (included in the curriculum) to impress a potential employer and show the application of your practical skills, which is particularly relevant for those with zero coding experience.