Java Interview Questions — Complete Campus Preparation Guide

Java remains the most widely tested language in Indian campus hiring. Service companies (TCS, Infosys, Wipro, Cognizant) assess OOP, collections, and exception handling in online tests and technical interviews. Product companies add JVM internals, concurrency, and Spring Boot architecture questions.

What interviewers expect

Freshers should explain JDK vs JRE vs JVM, demonstrate equals/hashCode contracts, and compare ArrayList vs LinkedList with time complexity. Mid-level campus questions cover HashMap internals, synchronized vs concurrent collections, and garbage collection generations.

4-week study plan

Week 1: Core Java — classes, inheritance, interfaces, static/final, exception hierarchy.
Week 2: Collections framework — List, Set, Map implementations and when to use each.
Week 3: Multithreading — Runnable, ExecutorService, volatile, deadlocks.
Week 4: Spring Boot basics — REST controllers, dependency injection, JPA entities.

Common mistakes

• Using == for String comparison
• Ignoring hashCode() when overriding equals()
• Calling run() instead of start() on threads
• Unable to explain project Java stack confidently

Practice resources

Solve 30 curated Java Q&A on CampusJobsHub, build one REST API with Spring Boot, and revise two mini-projects before your drive.

Browse all Java interview questions with easy, medium, and hard difficulty filters.