Java Developer interview questions & mock practice
A Java Developer interview in 2026 runs across 4 rounds — core java round, multithreading & memory, spring / framework round, coding + design. Below are the most-asked Java Developer interview questions and a focused prep plan. Rehearse every answer with OnJob's free AI mock interview and get instant, specific feedback before the real one.
The Java Developer interview process
Core Java, OOP, collections, multithreading and Spring Boot — the Java interview that dominates services companies and enterprise backends in India.
Core Java round
OOP, collections, exceptions and the JVM.
Multithreading & memory
Threads, synchronisation, garbage collection.
Spring / framework round
Spring Boot, dependency injection, REST and JPA.
Coding + design
DSA in Java plus basic low-level design.
Most-asked Java Developer interview questions
12 of the questions Java Developer candidates are asked most often in India. Practise answering each one out loud in your AI mock interview.
- 1. What is the difference between an abstract class and an interface in Java?
- 2. Explain the four pillars of OOP with Java examples.
- 3. What is the difference between ArrayList and LinkedList?
- 4. Explain how HashMap works internally in Java.
- 5. What is the difference between == and .equals() in Java?
- 6. What is the difference between String, StringBuilder and StringBuffer?
- 7. Explain the Java memory model and how garbage collection works.
- 8. What is the difference between checked and unchecked exceptions?
- 9. How do you create a thread, and what is the difference between Runnable and Thread?
- 10. What is the difference between synchronized and volatile?
- 11. What is dependency injection in Spring, and why is it useful?
- 12. Explain the difference between @Component, @Service and @Repository in Spring.
How to prepare for your Java Developer interview
Master collections cold: HashMap internals, ArrayList vs LinkedList, and when to use which.
Know OOP and the 'why' behind interfaces vs abstract classes — these come up in almost every Java interview.
Be solid on multithreading: synchronization, volatile, the ExecutorService, and common concurrency pitfalls.
Learn Spring Boot fundamentals: DI, annotations, REST controllers, JPA/Hibernate and exception handling.
Understand the JVM basics: heap vs stack, garbage collection, and what causes OutOfMemoryError.
Practise other roles
- Software Engineer
- Frontend Developer
- Backend Developer
- Full Stack Developer
- Data Analyst
- Data Scientist
- Product Manager
- DevOps Engineer
- Python Developer
- UI/UX Designer
- Sales / Business Development
- Digital Marketing
- HR / Recruiter
- Accountant
- Customer Support
- Data Engineer
- Machine Learning Engineer
- QA / Test Engineer
- Android Developer
- iOS Developer
- Business Analyst
- Project Manager
- Scrum Master
- SQL Developer
- React Developer
- Node.js Developer
- Cloud Engineer (AWS)
- Cybersecurity Analyst
- Network Engineer
- Database Administrator
- SEO Specialist
- Content Writer
- Graphic Designer
- Sales Executive
- Business Development Manager
- Operations Manager
- Financial Analyst
- Chartered Accountant
- Customer Success Manager
- Technical Support Engineer
- Civil Engineer
Java Developer interview — FAQs
What questions are asked in a Java Developer interview?
Common Java Developer interview questions include: What is the difference between an abstract class and an interface in Java? Explain the four pillars of OOP with Java examples. What is the difference between ArrayList and LinkedList? Explain how HashMap works internally in Java. Interviews usually run across 4 rounds — Core Java round, Multithreading & memory, Spring / framework round, Coding + design. Practice all of them with instant AI feedback using OnJob's free mock interview.
How many rounds are in a Java Developer interview?
A typical Java Developer interview has 4 rounds: Core Java round (OOP, collections, exceptions and the JVM.); Multithreading & memory (Threads, synchronisation, garbage collection.); Spring / framework round (Spring Boot, dependency injection, REST and JPA.); Coding + design (DSA in Java plus basic low-level design.).
How do I prepare for a Java Developer interview?
To prepare for a Java Developer interview: Master collections cold: HashMap internals, ArrayList vs LinkedList, and when to use which. Know OOP and the 'why' behind interfaces vs abstract classes — these come up in almost every Java interview. Be solid on multithreading: synchronization, volatile, the ExecutorService, and common concurrency pitfalls. Then run a full AI mock interview on OnJob to rehearse out loud and get instant, specific feedback before the real thing.
What skills do I need for a Java Developer role?
Core Java Developer skills tested in interviews include Core Java, OOP, Collections, Multithreading, Spring Boot, JPA / Hibernate, JVM. OnJob shows you exactly which of these skills stand between you and a 100% match on every live Java Developer job.
Is OnJob's Java Developer mock interview free?
Yes. OnJob's AI mock interview is free to start (₹0) and gives you instant feedback on your answers. Pro (₹99/month) adds unlimited interview-prep AI alongside recruiter tracking and unlimited applications.
Ace your Java Developer interview
Rehearse every Java Developer question out loud with OnJob's AI mock interview and get instant, specific feedback. Then apply to AI-matched jobs in one click — free to start.
Everything about Java Developer on OnJob
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