Most Common Java Interview Questions Asked in IT Companies

The most common Java interview questions asked in IT companies generally cover a wide range of topics including Java basics, object-oriented programming principles, core Java concepts, exception handling, multithreading, collections framework, and advanced features introduced in Java 8 and beyond. These questions are designed to evaluate candidates' understanding of Java fundamentals, coding skills, problem-solving abilities, and familiarity with Java APIs and design patterns.

Core Java Basics

These questions check familiarity with Java’s fundamental concepts, such as the difference between JDK, JRE, and JVM, the platform independence of Java, and memory management concepts. For instance:

What is the Java Virtual Machine (JVM) and what are its components?

Explain the difference between JDK, JRE, and JVM.

Why is Java considered platform independent?

What are access modifiers in Java and their purposes?

Object-Oriented Programming (OOP) Concepts

Java is an object-oriented language, and questions focus on OOP principles like inheritance, encapsulation, polymorphism, and abstraction:

What are the four pillars of OOP?

How does Java implement polymorphism?

What is the difference between method overloading and method overriding?

What are abstract classes and interfaces, and how do they differ?

Exception Handling

Handling errors gracefully is essential in Java, so interviews test knowledge of try-catch blocks, checked vs unchecked exceptions, and custom exceptions:

What is exception handling and why is it important?

What is the difference between checked and unchecked exceptions?

How can you create a custom exception?

Explain the use of finally block vs finalize() method.

Multithreading & Concurrency

Concurrency is a common topic, especially for mid-level to senior roles, covering thread lifecycle, synchronization, and thread safety:

What states can a thread go through in Java?

How can you create a thread? (Extending Thread vs implementing Runnable)

What is synchronization and why is it needed?

What are deadlocks, and how can they be prevented?

Java Collections Framework

Collections are fundamental for data manipulation, with questions focusing on List, Set, Map interfaces, and their implementations:

What are differences between ArrayList, LinkedList, and Vector?

What is the difference between HashSet and TreeSet?

How does HashMap work internally?

When to use ConcurrentHashMap over HashMap?

Java 8 and Later Features

Questions increasingly cover new concepts introduced in Java 8+, such as streams, lambda expressions, and functional interfaces:

What are lambda expressions and how are they used?

Explain the Stream API and its advantages.

What is a functional interface?

What are default and static methods in interfaces?

Coding and Scenario Questions

Candidates are often asked to solve coding problems or explain how to implement common algorithms and data structures in Java:

How to reverse a linked list in Java?

Write a program to count occurrences of a character in a string.

Explain how to implement a stack using an array or linked list.

Provide code examples demonstrating polymorphism or exception handling.

Additional Common Questions

What is the difference between final, finally, and finalize?

How does garbage collection work in Java?

What are volatile variables and when should they be used?

Can you overload the main() method?

Preparing for Java Interviews

Successful candidates prepare by mastering concepts mentioned above, practicing coding problems, reviewing Java API documentation, and understanding Java best practices and design patterns. Focusing on real-world scenarios that demonstrate practical problem-solving with Java will also increase confidence.

Summary Table of Common Questions

This comprehensive coverage ensures candidates are ready to face typical Java interviews at IT companies. Mastery of these topics reflects strong Java proficiency and practical coding capabilities.

If in-depth answers or sample code snippets for any of these questions are needed, that can be provided as well.

This knowledgebase is backed by extensive recent interview question collections from trusted sources and updated Java 8 and concurrency question trends in 2025.