Java remains one of the most in-demand programming languages, especially in enterprise software, fintech, banking and iGaming. Whether you’re applying for a Mid, Senior or Lead Java Developer role, these are some of the most common questions you should expect.
Core Java
- What are the main features of Java?
- What is the difference between JDK, JRE and JVM?
- Explain the principles of Object-Oriented Programming.
- What is the difference between an abstract class and an interface?
- What is polymorphism?
- What are immutable objects?
- What is the difference between
==and.equals()? - What is the difference between
ArrayListandLinkedList? - What is the Java Collections Framework?
- Explain HashMap and how it works.
Java Concurrency
- What is multithreading?
- What is the difference between synchronized and Lock?
- What is a deadlock?
- What is the Executor Framework?
- What is CompletableFuture?
Spring & Backend Development
- What is Spring Boot?
- Explain Dependency Injection.
- What is Spring Security?
- What are REST APIs?
- How do you secure REST APIs?
Databases
- Explain transactions.
- What is database indexing?
- What is the difference between SQL and NoSQL?
- What are optimistic and pessimistic locking?
Architecture
- What are Microservices?
- What is Event-Driven Architecture?
- What is Apache Kafka?
- What is Docker and why is it used?
- What is Kubernetes?
- How would you design a scalable backend system?
Final Tip
For senior Java positions, interviewers are interested not only in your coding ability but also in your understanding of architecture, scalability, cloud technologies and system design. Be prepared to explain your decisions using real examples from previous projects.