Java Tutorial (original) (raw)

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.

Basic Code Example

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

Java `

public class HelloWorld { public static void main(String[] args) { System.out.println("Hello World!"); } }

`

To understand working of this code, refer Java Introduction.

Why Learn 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 the java.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.

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.

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 the java.io and java.nio packages for efficient file operations.

Networking

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

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.

Practice

Introduction to Java

Writing First Program in Java

Variables and Primitive DataTypes

Non Primitive DataTypes

Type Conversion in Java

Input in Java