26 Best Java Topics for Interviews in 2024 (with Resources)

Hello folks Java Interviews are a little bit different than traditional programming interviews on tech giants and product-based companies like Google, Amazon, Microsoft, or Facebook. 

First, even though it has questions from Data Structures and Algorithms like String or Array, you can still manage to clear Java interviews if you are not an expert on them. 

The questions are a little bit easier and more practical than those companies. Another essential thing about Java interviews are questions based upon Java programming language and JDK API. 

Since Java is also an Object-oriented programming language, you will find lots of OOP questions there.

Since Java is primarily used as an application programming language, the focus is aligned accordingly with questions mostly focusing on API, Java concepts, and design patterns.

Also, Java interviews change a lot depending upon the candidate's experience. For example, junior developers with 1 to 2 or 3 to 4 years of experience will see more questions on topics like Java fundamentals, API, data structure, and algorithms.

More senior developers like Java programmers with 5 to 6 years of experience will find more questions on concurrent programming, Java concurrency API, JVM internals, GC tuning, and Java Performance.

So your preparation should be aligned with your experience and not just focused on common programming questions.

Also, Java EE interviews are totally different than core Java interviews because core Java interviews are mostly focused on core Java concepts like Concurrency, Collections, and JVM internals, while Java EE interviews are based upon a framework like JSF, Spring, Hibernate, and others.

The best way to prepare for Java interviews is to read a book like Grokking the Java Interview or  join a course like Java Interview Guide: 200+ Interview Questions and Answers, though there is no substitute for the experience you can still manage to sail through by carefully preparing for your Java interviews.

26 Best Topics for Java Interviews in 2024?

As I told you, the importance of topics depends upon the candidate's experience. I would ask more questions from Java fundamentals like String, Collections, equals() and hashcode and OOP concept to a fresher or Junior Java developers of 2 years experience, but those topics will be too trivial for Java developer of 4 to 5 years experience.

 For those, I prefer to ask Concurrency, JVM internals, Garbage Collection, testing, and design patterns. Another thing that decides which topic you should prepare for your interview is the Job description.

Also, there is no better guide than the Job description to prepare for relevant topics.

For example, if you are going to work for a core Java multi-threading based application, then you should prepare well for core Java topics like multithreading and concurrency, Java Collections, Generics, Enum, GC Algorithms, and JVM internals.

Similarly, if you are going to work for a Java Web Service application then preparing about REST and SOAP, XML, JSON, and other relevant topics.

For Java, web application developers, JSP, Servlet, Spring, and Hibernate are more critical than multi-threading and JVM internals. Similarly, for an Android developer, apart from knowledge of Java fundamentals, knowing Android API is more important.

Nevertheless, here is the list of topics I suggest to any Java developer who is serious about interviews.

1. Java Fundamentals (core java questions)
2. Object-Oriented Concepts (questions)
3. Data Structure and Algorithms (questions)
4. Multithreading, concurrency, and thread basics (questions)
5. Date type conversion and fundamentals (questions)
6. Garbage Collection (questions)
7. Java Collections Framework (questions)
8. Array (questions)
9. String (questions)
10. GOF Design Patterns (questions)
11. SOLID design principles (questions)
12. Abstract class and interface (questions)
13. Java basics e.g. equal and hashcode (questions)
14. Generics and Enum (questions)
15. Java IO and NIO (questions)
16. Common Networking protocols like TCP, UDP, HTTP
17. Data structure and algorithm in Java (questions)
18. Regular expressions (questions)
19. JVM internals (questions)
20. Java Best Practices
21. JDBC  (questions)
22. Date, Time, and Calendar (questions)
23. XML Processing in Java (questions)
24. JUnit  (interview questions)
25. Programming questions (questions)
26. New Java Features from Java 8 to Java 22 (questions)

Apart from these topics, you could also take help from books like Java interview exposed and the Cracking the coding interview. These are great books written, especially from the interview perspective, and it will give you a good idea of what to expect in Java programming job interviews.

You will also find questions asked from various tech companies like Facebook, Google, and Investment banks like Barclays, Citi, Deutsche Bank, Morgan Stanley, and others.

For a more serious developer who wants to become an expert and not just focus on clearing an interview, I suggest you take a look at my 12 advanced Java books for experienced programmers article. It contains books for every important topic in Java.

And if you lack on some topic, you can always go back to the book you read or the course you followed to learn the Java-like The Complete Java Masterclass course on Udemy is a very comprehensive course and best for learning from scratch.

5 Best Courses and Books For Java Interviews in 2024

Recently I come across some excellent books to prepare for core Java and web developer interviews, these books focus more on core Java concepts like multi-threading, collections, Java fundamentals, etc., but also touch on web development concepts like Web service, Spring, Hibernate, JSP, Servlet, etc.

These books and courses are both cheap, will cost you less than $15 but gives you enough practice and ideas to do well on your Java interviews.

Though nothing can beat the true experience and constant learning, if you are short of experience and not in touch with Java for more than a year, then you can use these books to prepare better for your Java interviews.

1. Java Interview Guide: 200+ Interview Questions and Answers

This is an excellent course to get an idea about Java interviews. It is very well organized and covers almost all the topics we have discussed here and probably more, e.g., web services, spring, hibernate, JDBC, etc. It is equally useful for both entry-level Java programmer and experienced Java developer interviews.

2. Grokking the Java and Spring Boot Interview

These two are my books which I prepared after a lot of people ask me to write about a book on Java Interview. This book book contains frequently asked Java questions from essential topics like

• 1. Object-Oriented Programming
• 2. Java Fundamentals
• 3. Java Collections
• 4. Java Multithreading
• 5. Garbage Collection
• 6. JDBC
• 7. Generics
• 8. Design PAtterns
• 9. Telephonic Interview Questions 

You can also combine this book with my Grokking the Spring Boot Interview to prepare well as Spring related questions are commonly asked in Java Interviews. This book coves spring framework, spring boot, Microservices, and spring cloud. You can also use code friends20 to get 20% discount on buying the Java Interview bundle which covers Java, Spring Boot, and SQL. 

3. Java Interview Bootcamp: The Complete Guide To Finding And Landing Your Next Java Developer Role 

This is a nice, small books, around 50 pages of interview questions, ideal if you have Java interviews in a couple of days or hours. Even though the book is short, it touches on many essential areas of Java-like concurrency, collection, performance tuning, garbage collection, and standard programming concepts, like big O notation, data structure, and algorithms, etc.

In short, if you are running out of time for your next Java interviews, this book will help you.

4. Java Multithreading for Senior Engineering Interviews

If you have an interview coming up, then I highly suggest you double down on concurrency and this is an excellent course to prepare for Multithreading and Concurrency Interview questions in Java.

Concurrency and Multithreading can be one of the most challenging topics brought up during most interviews, even for experienced developers. However, gaining mastery in concurrency will put you at a considerable advantage over other interviewees.

In this course, you’ll get a sneak peek at the most common types of concurrency interview questions like Producer-Consumer, Dining Philosopher, Reader-Writer, bounded buffer, and more, but you’ll also build a solid foundation of the basics as well as advanced concurrency concepts that will stick with you in your career and help you to perform at the highest level in interviews.

5. Java Multithreading & Concurrency - Interview Practice Exams

Michael Pogrebinsky also have a nice practice question course called Java Multithreading & Concurrency - Interview Practice Exams on Udemy where he has shared 100+ questions on Java Concurrency and Multithreading concepts like OS fundamentals, race conditions, thread-safety, concurrency utilis, inter thread communication, lock free algorithms and data structures, synchronization and locking and much, along with take home exercises to prepare for Java Software Engineering Job Interview.

The course includes five practice tests covering various aspects of Java Multithreading and Concurrency, with a total of 101 questions. These exams are designed to challenge and prepare individuals for interviews involving Java Multithreading, Concurrency, Parallel Programming, and Java Performance. 

The self-assessment structure of the course comprises multiple-choice questions organized into self-contained exams. Each exam is timed, automatically checked, and scored, providing a comprehensive evaluation of the individual's proficiency in Java Multithreading.

Overall, this Java Multithreading & Concurrency course provides a valuable opportunity for candidates and developers to assess and strengthen their skills, gain confidence in tackling interview questions, and enhance their overall proficiency in Java Multithreading and Concurrency. 

That's all about how to prepare for Java interviews guys.  The Java ecosystem is vast and but depending upon Job description, you can further narrow down your preparation areas, e.g., if you are going for core Java interviews, then you should focus more on core java concepts, like, multi-threading, collections, and JVM internals.

Similarly, if you are going for a Java web developer interview, then you should focus more on the web development aspect, like security, MVC frameworks like Spring, Struts, and ORM frameworks like Hibernate and iBatis.

Further Learning
The Complete Java MasterClass
Data Structures and Algorithms: Deep Dive Using Java
Algorithms and Data Structures - Part 1 and 2


Other Java Interview resources for you

• 133 Java Interview Questions from the last 5 years (list)
• 15 Data Structure and Algorithm Interview Questions (list)
• 10 Spring Framework Interview Questions (list)
• 20 Spring Boot Interview Questions with answer (spring boot)
• 20 Hibernate Framework Interview Questions with Answers (list)
• 25 Spring Security Interview Questions Answers (spring security questions)
• 50 Java Concurrency Interview Questions (list)
• 25 Java Collection Interview Questions (list)
• 15 Advanced Microservice questions for 5 years experienced (microservices)
• 10 RESTful Web Service Interview Questions for Java developers (list)
• 10 Data Structure and Algorithms Courses for Interviews (courses)
• 50+ Data Structure and Algorithm Questions (questions)
• 20 Spring MVC Interview Questions for Java Developers  (questions)
• 20 Spring and REST Interview Questions for Java Programmers  (questions)
• 50+ Java Collections Interview Questions with Answers (questions)
• 10 Courses to prepare for Coding Interviews (courses)

Thanks for reading this article, if you have found this article useful and worth sharing, then please share it with your friends and colleagues. If you have any suggestions or feedback or if you want to share any of your personal tips which helped you to do well in the Java interview, then please drop a comment.

P. S. - I have also written two books on Java and Spring Boot Interviews. If you like my work and prepare well for the Java developer interview, you can also check out my books on Gumroad. More than 1000 people have already bought Grokking the Java Interview book last year.