Java Tutorial

Last Updated :08 Dec, 2025

Java is a high-level, object-oriented programming language used to build web apps, mobile applications, and enterprise software systems.

Known for its Write Once, Run Anywhere capability, which means code written in Java can run on any device that supports the Java Virtual Machine (JVM).
Syntax and structure is similar to C-based languages like C++ and C#.

Basic Code Example

The following is a simple program that displays the message “Hello, World!” on the screen.

Java

publicclassHelloWorld{publicstaticvoidmain(String[]args){System.out.println("Hello World!");}}

To understand working of this code, refer Java Introduction.

Why Learn Java?

Used to build Android apps, desktop and web apps, enterprise backend systems, and cloud-based software.
In high demand with many job opportunities in software development.
Has popular frameworks like Spring and Hibernate which makes it powerful for enterprise applications.
Supports object-oriented programming for clean, maintainable and reusable code.
Top companies like Amazon, Netflix, and LinkedIn use Java.

Basics

Java basics form the foundation of your programming journey, covering essential concepts like syntax, data types, variables, loops, and conditionals.

Methods

Java methods are reusable blocks of code that perform specific tasks and help organize your program. They improve code readability, reduce repetition, and make debugging easier.

Arrays

Java arrays are containers that store multiple values of the same data type in a single variable. They provide an efficient way to manage and access collections of data using index-based positions.

Strings

Java Strings represent sequences of characters and are widely used in text processing. They are immutable, meaning once created, their values cannot be changed.

Regex

Java Regex (Regular Expressions) allows pattern matching and text manipulation using thejava.util.regex package. It is powerful for validating, searching, and replacing strings based on specific patterns.

OOP Concepts

Java follows the Object-Oriented Programming (OOP) paradigm, which organizes code into classes and objects. Core OOP principles like inheritance, encapsulation, polymorphism, and abstraction make Java modular and scalable.

Interfaces

Java interfaces define a contract that classes must follow, specifying method signatures without implementations. They enable abstraction and support multiple inheritance in Java through a clean, structured approach.

Exception Handling

Java Exception Handling is a mechanism to handle runtime errors, ensuring the program runs smoothly without crashing. It uses keywords like try, catch, throw, throws, and finally to manage exceptions.

Memory Allocation

Java Memory Allocation refers to how memory is assigned to variables, objects, and classes during program execution. It involves stack and heap memory, with the JVM managing allocation and garbage collection automatically.

Collections

Java Collections provide a framework for storing and manipulating groups of objects efficiently. It includes interfaces like List, Set, and Map, along with classes like ArrayList, HashSet, and HashMap.

Collections Class
Collection Interface
Quiz:Collection
List Interface
ArrayList
LinkedList
Quiz:List,ArrayList,LinkedList
Set Interface
HashSet
TreeSet
Quiz:Set and HashSet
Queue Interface
Priority Queue
Deque Interface
Map Interface
HashMap
Quiz:Queue and Map Interface
Iterator
Comparator Interface
Comparable Interface
Quiz:Iterators,Comparator vs Comparable
Project:Face Detection System

Lambda Expressions and Streams

Java Streams and Lambda Expressions simplify data processing by enabling functional-style operations on collections. Lambdas provide concise syntax for anonymous functions, while Streams allow efficient filtering, mapping, and reduction of data.

Lambda Expressions
Method References
Java Streams
Quiz:Lambda Expressions and Streams
To know Java 8 in detail, refer to -Java 8 Features

Multithreading and Synchronization

Java Multithreading allows concurrent execution of two or more threads, enabling efficient CPU utilization and faster program performance. It is commonly used for tasks that required parallel processing and responsiveness from multiple ends.

File Handling

Java File Handling enables programs to create, read, write, and manipulate files stored on the system. It uses classes from thejava.io andjava.nio packages for efficient file operations.

Networking

Java Networking enables communication between devices over a network using classes from thejava.net package. It supports protocols like TCP and UDP for building client-server applications and data exchange.

Introduction to Java Networking
Quiz:Networking Basics and Protocols
Socket Programming
Server Socket Class
Quiz:Sockets and Server Communication
URL Class and Methods
Project:Chat Application

Java Database Connectivity(JDBC)

Interview Questions

Prepare for Java interviews with these commonly asked questions, covering core concepts, OOP, collections, multithreading, exception handling, and frameworks like Spring and Hibernate.