Top 20 Java Interview Questions & Answers for Freshers in 2025

Are you preparing for a Java-related job interview? You are at the right place. We hope it will help you find your dream job or dream candidate.

1.What is Java?

Java is a high-level, object-oriented programming language originally developed by Sun Microsystems and now maintained by Oracle. It is platform-independent, meaning applications written in Java can run on any system that supports the Java Virtual Machine (JVM), ensuring cross-platform compatibility.

2.Explain OOPS ?

Object-Oriented Programming (OOPs) is a programming paradigm based on the concept of objects and classes. It helps in designing modular, reusable, and scalable software by organizing code into real-world entities.

3.Key Features of OOPS in Java

Java follows four main principles of OOPs:

• Polymorphism
• Encapsulation
• Abstraction
• Inheritance

4.Explain Array with example?

Arrays in Java are a data structure that holds a fixed-size sequential collection of elements of the same type. Once created, the array’s size cannot be changed. Arrays allow you to store multiple values in a single variable and access them via an index.

int[] numbers = new int[5];

• Declaration: int[] numbers = new int[5]; creates an array named numbers that can hold 5 integers.
• Assignment: Values are assigned to each element of the array using their respective indices.
• Access: The for-loop iterates through the array using numbers.length to determine the number of elements, and prints each element with its index.

Arrays are useful for managing collections of data where the size is known in advance. However, if you need a resizable data structure, consider using classes like ArrayList from the Java Collections Framework.

5. What are constructors in Java?

• A constructor is a special method used to initialize an object.
• Types: Default constructor, Parameterized constructor, Copy constructor.

class Car {
    String model;
    Car(String model) { this.model = model; } // Constructor
}

6.What is a Lambda Expression in Java?

A lambda expression provides a concise way to write anonymous methods.

Syntax: (parameters) -> { body }

(a, b) -> a + b; // Adds two numbers

7. Why Use OOPs in Java?

• Code Reusability – Write once, use multiple times.
• Modularity – Organized and manageable code.
• Security – Encapsulation prevents unauthorized data access.
• Flexibility – Easy modification and extension of code.
• Scalability – Helps in developing large applications efficiently.

8. What is the difference between JVM and JRE?

JRE has class libraries and other JVM files however, it does not have any tools for Java development such as a debugger and compiler. While JVM has a Just In Time(JIT) tool to convert all the Java codes into compatible machine language.

9.What is JIT Complier?

A JIT (Just-In-Time) Compiler is a part of the runtime environment that improves the performance of programs by compiling bytecode into native machine code at runtime.

10.Explain the difference between Array and ArrayList in Java.

Feature	Array	ArrayList
Size	Fixed	Dynamic
Performance	Faster	Slower
Data Type	Can be primitive or objects	Only objects

11. Explain Out Of Memory Error in Java.

An OutOfMemoryError in Java occurs when the Java Virtual Machine (JVM) runs out of memory and is unable to allocate more objects. This usually happens due to inefficient memory management, excessive object creation, or memory leaks.

12. What are the Java IDE?

There are several popular Integrated Development Environments (IDEs) for Java development. Here are some of the top options:

IntelliJ IDEA

Eclipse

NetBeans

BlueJ

JDeveloper

DrJava

MyEclipse

13. What are lambda expressions in Java?

A lambda expression is a concise way to represent anonymous functions, introduced in Java 8.

Example: List names = Arrays.asList(“John”, “Jane”, “Jack”);
names.forEach(name -> System.out.println(name));

14. Different types of Garbage Collectors in Java

• Serial Garbage Collector
• Parallel Garbage Collector
• CMS (Concurrent Mark-Sweep) Garbage Collector
• G1 (Garbage First) Garbage Collector
• Z Garbage Collector
• Shenandoah Garbage Collector

15.Advantages of OOP?

• Enhances code modularity and reusability
• Supports real-world modeling
• Reduces code duplication and maintenance effort
• Improves scalability and extensibility

16. What is Method?

A method in Java is a block of code that performs a specific task. It is used to improve code reusability, modularity, and organization. Methods allow us to define behavior that can be executed multiple times without rewriting the code.

returnType methodName(parameters) {
    // method body
    return value;  // (if returnType is not void)
}

17. Explain operators and its types.

Operators in Java are symbols that perform operations on variables and values. Java provides various types of operators to perform arithmetic, logical, relational, bitwise, and other operations.

• Arithmetic Operators
• Relational (Comparison) Operators
• Logical Operators
• Bitwise Operators
• Assignment Operators
• Ternary Operator (?:)
• Increment and Decrement Operators

18. Explain Token in Java

A token in Java is the smallest unit of a program that holds meaning. The Java compiler breaks the source code into tokens for processing.

There are five types of tokens in Java:

1. Keywords
2. Identifiers
3. Literals
4. Operators
5. Special Symbols

19. Define Architectural neutral

Architectural Neutral means that Java code can run on any platform without modification. This is achieved using Java Bytecode and the Java Virtual Machine (JVM).

20.What is Bytecode in Java?

Bytecode is an intermediate representation of a Java program that is generated after compilation. It is not machine-specific but is understood by the Java Virtual Machine (JVM).

Conclusion:-

Mastering these Java interview questions will give you an edge in your next job interview. Keep practicing and refining your understanding to excel in Java programming roles. Best of luck !!