Java Interview Questions & Answers 2026 | Freshers & Experienced

Java is one of the most widely used programming languages in the world, making it a core subject in technical interviews for roles such as Software Developer, Backend Engineer, Full-Stack Developer, and Android Developer. Java interviews usually test a candidate's conceptual understanding, coding skills, object-oriented principles, memory management, multithreading, and practical problem-solving ability.

This guide provides a brief overview and detailed explanations of important Java interview questions, helping candidates prepare systematically.

Basic Java Interview Questions

1. What is Java?

Java is a high-level, object-oriented, platform-independent programming language developed by Sun Microsystems. It follows the principle of "Write Once, Run Anywhere", meaning compiled Java code can run on any system with a Java Virtual Machine (JVM).

2. What are the main features of Java?

Key features include:

Object-Oriented
Platform Independent
Secure
Robust
Multithreaded
High Performance
Portable

These features make Java suitable for enterprise-level applications.

3. What is JVM, JRE, and JDK?

JVM (Java Virtual Machine): Executes Java bytecode
JRE (Java Runtime Environment): Provides libraries and JVM to run Java programs
JDK (Java Development Kit): Includes JRE plus development tools like compiler and debugger
Object-Oriented Programming (OOP) Questions

4. What are the four pillars of OOP in Java?

Encapsulation: Wrapping data and methods into a single unit
Inheritance: Acquiring properties of another class
Polymorphism: Ability to perform multiple actions
Abstraction: Hiding implementation details

5. Difference between Abstract Class and Interface

Abstract class can have both abstract and non-abstract methods
Interface supports multiple inheritance
Abstract class uses extends, interface uses implements

Core Java Interview Questions

6. What is the difference between == and .equals()?

== compares reference addresses
.equals() compares content or values

7. What is String immutability in Java?

Strings are immutable, meaning once created, their values cannot be changed. This improves security, thread safety, and performance.

8. What is the difference between Array and ArrayList?

Arrays have fixed size
ArrayList has dynamic size
Arrays can store primitives and objects
ArrayList stores only objects

Exception Handling Questions

9. What is Exception Handling in Java?

Exception handling allows a program to handle runtime errors gracefully using:

try
catch
finally
throw
throws

10. Difference between Checked and Unchecked Exceptions

Checked exceptions are checked at compile time
Unchecked exceptions occur at runtime
Multithreading Interview Questions

11. What is Multithreading?

Multithreading enables a program to execute multiple threads simultaneously, improving performance and CPU utilization.

12. How can you create a thread in Java?

By extending Thread class
By implementing Runnable interface
Memory Management & Collections

13. What is Garbage Collection?

Garbage Collection automatically removes unused objects from memory, improving efficiency.

14. What is the Java Collections Framework?

It provides classes like:

List
Set
Map
Queue

These help in efficient data storage and manipulation.

Advanced Java Interview Questions

15. What is the difference between HashMap and Hashtable?

HashMap is non-synchronized
Hashtable is synchronized
HashMap allows one null key

16. What is Serialization?

Serialization converts an object into a byte stream for storage or transmission.

Conclusion

Java interview questions range from basic concepts to advanced topics like multithreading, memory management, and collections. A strong grasp of core Java fundamentals, OOP principles, and practical coding scenarios is essential to succeed in interviews. Regular practice, mock interviews, and revising concepts will significantly improve confidence and performance.