Junior Java Developer Interview Questions - IT Hiring

Introduction

Hiring the right Junior Java Developer in the IT industry is critical to building reliable, maintainable applications and sustaining team velocity. Entry-level developers often set the foundation for code quality, testing practices, and collaboration.

This guide contains structured Junior Java Developer interview questions across basic, intermediate, and advanced levels, plus five pre-screening one-way video interview questions ideal for asynchronous screening. Use these to improve candidate selection and standardise evaluations.

Junior Java Developer Interview Questions

Basic Junior Java Developer Interview Questions

• What are the core features of the Java programming language that make it suitable for enterprise development?
• Explain the four main principles of object-oriented programming (encapsulation, abstraction, inheritance, polymorphism).
• What is the difference between the JDK, JRE, and JVM?
• When should you use == versus .equals() when comparing objects in Java?
• Explain how try-catch-finally works and when to use checked vs unchecked exceptions.
• Describe the main Java Collection interfaces (List, Set, Map) and give one use case for each.
• What is a thread in Java and what are two ways to create a new thread?
• How does Java garbage collection work at a high level, and what can cause memory leaks?

Intermediate Junior Java Developer Interview Questions

• You override equals() but not hashCode(); what problems could this cause when objects are stored in HashSet or HashMap?
• A production log shows frequent NullPointerExceptions. Describe your approach to reproduce and fix the issue.
• Given a slow database query called from a Java service, what steps would you take to diagnose and improve response time?
• You have a shared counter updated by multiple threads; describe how you would make updates thread-safe and why synchronization is needed.
• Explain how you would design a simple REST endpoint to create and return a resource using a Java framework (describe controllers, DTOs, validation).
• Show how you would use Java Streams and lambda expressions to transform a list of objects into a filtered, sorted list.
• How would you process a very large file in Java without running out of memory?
• Describe dependency injection and the benefits of using an IoC container versus manual object creation.
• What should you cover when writing unit tests for a service method? Which mocking approach or framework would you choose?
• Explain the basics of how you would include automated builds and tests for a Java project in a CI pipeline.

Advanced Junior Java Developer Interview Questions

• When tuning JVM performance, what factors influence your choice of garbage collector (for example G1 vs. other collectors)?
• Describe a scalable microservice design for a Java-based system. How should services communicate and handle failures?
• Which tools and metrics would you use to profile a Java application experiencing high CPU usage?
• Explain concurrency patterns you might use beyond synchronized blocks (thread pools, Executors, CompletableFuture).
• How would you approach diagnosing a memory leak using heap dumps and what signs would you look for?
• What practices do you follow to prevent common security issues in Java applications (e.g., SQL injection, insecure deserialization)?
• Explain how class loaders work in Java and why class loading issues can cause linkage or compatibility problems.
• Discuss transaction isolation levels and how you would choose one to balance consistency and performance.
• How would you design a Java application for high availability and graceful degradation under load?
• As a junior developer, how would you contribute to code reviews and mentor peers to improve team quality?

Pre-Screening Video Interview Questions for Junior Java Developer

These five pre-screening one-way video interview questions are ideal for ScreeningHive. They assess communication, hands-on experience, problem solving, and cultural fit while enabling efficient, standardised candidate comparisons during early screening.

1. Describe a Java project you worked on. What was your role and what technologies did you use?

   This evaluates practical experience, clarity in describing contributions, and familiarity with core Java tools and frameworks.

2. Explain a challenging bug you fixed. What steps did you take from discovery to resolution?

   This checks debugging methodology, ability to reproduce issues, and learning from incidents.

3. Walk through how you would find and resolve a NullPointerException in a service method called by multiple clients.

   This assesses problem solving, use of logging/stack traces, and understanding of null-safety and defensive coding.

4. How would you implement a simple POST endpoint to create a user (describe validation, error handling, and testing)?

   This evaluates API design thinking, familiarity with common Java web frameworks, and attention to validation and tests.

5. How do you keep your Java skills up to date and what recent learning resource or practice helped you improve?

   This judges continuous learning, initiative, and cultural fit for teams that value ongoing development.

Conclusion / CTA

These Junior Java Developer interview questions help hiring managers, recruiters, and HR teams evaluate technical ability, problem solving, and team fit at each stage of recruitment. Structuring interviews by basic, intermediate, and advanced topics ensures consistent and fair assessment.

ScreeningHive simplifies early-stage selection through one-way video interviews, enabling faster screening and standardised evaluations across candidates. Try ScreeningHive for a FREE sign-up and accelerate your hiring workflow with consistent, asynchronous pre-screening.