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Java Tutorial

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Java Roadmap Java Introduction What is Java?History & Features JDK vs JRE vs JVM How Java Works Install Java & Setup First Java Program Java vs Other Languages

Syntax & Structure Java Keywords & Reserved Words Naming Conventions Data Types Variables Type Casting Operators Increment & Decrement Operators Escape Sequences Math Class User Input (Scanner)Wrapper Classes Autoboxing & Unboxing final Keyword Comments

if Statement if-else Statement else-if Ladder Nested if Statements switch Statement for Loop for-each Loop while Loop do-while Loop break Statement continue Statement Nested Loops

Arrays Basics Multi-dimensional Arrays Array Methods (Arrays class)Passing Arrays to Methods Practice Questions

String Basics String Methods String Comparison equals() vs ==String Pool Immutable Strings StringBuilder String Formatting Practice Questions

Defining Methods Parameters & Return Types Method Overloading Recursion Variable Arguments (varargs)Pass by Value vs Pass by Reference Practice Questions

Classes & Objects Constructors this Keyword static Keyword Encapsulation Inheritance super Keyword Polymorphism Method Overriding Method Overloading vs Overriding Abstraction Abstract Classes Interfaces Abstract Class vs Interface Object Class & toString()

Packages in Java Creating Custom Packages import Statement Access Modifiers Overview public Modifier private Modifier protected Modifier default (package-private)

Inner Classes Anonymous Classes Enums Records (Java 16+)Sealed Classes (Java 17+)Annotations Built-in Annotations Custom Annotations Reflection API Design Patterns Overview

Collections Overview ArrayList LinkedList Stack Queue HashSet & LinkedHashSet TreeSet HashMap & LinkedHashMap TreeMap PriorityQueue Deque & ArrayDeque Iterator ListIterator Comparable Comparator Comparable vs Comparator Collections Utility Class Choosing the Right Collection Practice Questions

Generics Basics Generic Methods Generic Classes Bounded Type Parameters Wildcards Type Erasure

Java 8 Key Features Java 11 Features Java 17 Features (LTS)Java 21 Features (LTS)var (Local Type Inference)Text Blocks Pattern Matching Switch Expressions Virtual Threads (Java 21)

Exception Hierarchy try-catch finally Block try-with-resources throw Keyword throws Keyword Difference Between throw and throws Checked vs Unchecked Custom Exceptions Multi-catch Exception Propagation Practice Questions

File & Path Basics Reading Files Writing Files BufferedReader & Writer NIO.2 (java.nio)Serialization Externalization Serialization vs Externalization

Threads Basics Runnable & Callable Thread Lifecycle Synchronization volatile Keyword Race Conditions Deadlock wait, notify & notifyAll Executor Framework CompletableFuture Practice Questions

JVM Architecture Stack Memory Heap Memory Stack vs Heap Memory Garbage Collection ClassLoader JIT Compiler

Top Java Interview Q&A Core Java Interview Questions OOP Interview Questions String Interview Questions Array Interview Questions Collections Interview Q&A Multithreading Q&A Exception Handling Q&A Java 8+ Interview Q&A FAANG Java Questions Coding Challenges

Clean Code in Java SOLID Principles Effective Java Tips Common Anti-Patterns Code Review Checklist

Beginner Mistakes OOP Mistakes Collections Mistakes Streams Mistakes Exception Handling Mistakes Concurrency Mistakes Performance Pitfalls Memory Leaks

Java Tutorial

Our Java programming tutorial is designed for students and working professionals. Java is an object-oriented, class-based, platform-independent, and general-purpose programming language. It is one of the most widely used and robust technologies in the software industry.

Java follows the principle of Write Once, Run Anywhere (WORA) — code written and compiled on one machine runs on any device that has a Java Virtual Machine (JVM) installed, regardless of the operating system.

This tutorial covers everything from the very basics to advanced topics — OOP, Collections, Streams, Multithreading, and Modern Java 8–21 — with clear explanations and real code examples at every step.

What is Java?

Java is a programming language and a platform. It is high-level, robust, object-oriented, and secure. Java was originally developed by Sun Microsystems (now a subsidiary of Oracle) in 1995. James Gosling is known as the father of Java.

Platform: Any hardware or software environment in which a program runs is known as a platform. Since Java has a runtime environment (JRE) and its own API, it is called a platform.

Java is used to build Android apps, backend APIs, banking systems, desktop software, and large-scale enterprise applications. Companies like Amazon, Google, Netflix, and every major bank run Java in production.

New to programming? Start from Java Basics — we assume zero knowledge and explain every concept step by step. Already know C or Python? Jump to OOP Concepts →

Java Example

Let's have a quick look at a Java program. A detailed description of every line is available on the next page.

Java

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

Output:

Hello, World!

Click here for a detailed description of the above Java program.

Prerequisites

There are no prerequisites to learn Java. If you have a basic understanding of how a computer works, you can start right away. If you already know C or Python, you will find Java syntax very familiar and easy to pick up.

Who is this tutorial for?

This Java tutorial is designed for two groups of people:

›Beginners — who want to learn Java from the absolute basics with no prior experience.
›Working professionals — who want to strengthen their Java knowledge and prepare for technical interviews.

Java Tutorial Index

This tutorial is organized into the following sections. Click any topic to start learning it directly.

Java Introduction

Java Introduction · What is Java? · History & Features · JDK, JRE & JVM · How Java Works · Install Java & Setup · First Java Program · Java vs Other Languages

Java Basics

Syntax & Structure · Data Types · Variables · Type Casting · Operators · User Input (Scanner) · Comments

Control Flow

if / else / else-if · switch Statement · for Loop · while Loop · do-while Loop · break & continue · Nested Loops

Arrays & Strings

Arrays Basics · Multi-dimensional Arrays · Array Methods · String Basics · String Methods · StringBuilder · String Formatting

Methods

Defining Methods · Parameters & Return Types · Method Overloading · Recursion · Variable Arguments (varargs) · Common Mistakes

Object-Oriented Programming

Classes & Objects · Constructors · this Keyword · static Keyword · Encapsulation · Inheritance · super Keyword · Polymorphism · Method Overriding · Abstraction · Abstract Classes · Interfaces · Common Mistakes

Advanced OOP

Inner Classes · Anonymous Classes · Enums · Records (Java 16+) · Sealed Classes (Java 17+) · Design Patterns Overview

Exception Handling

try / catch / finally · throw & throws · Checked vs Unchecked · Custom Exceptions · Multi-catch & try-with-resources · Common Mistakes

Collections Framework

Collections Overview · ArrayList · LinkedList · Stack & Queue · HashSet & LinkedHashSet · TreeSet · HashMap & LinkedHashMap · TreeMap · PriorityQueue · Deque & ArrayDeque · Collections Utility Class · Choosing the Right Collection · Common Mistakes

Generics

Generics Basics · Generic Methods & Classes · Bounded Type Parameters · Wildcards

Functional Programming

Lambda Expressions · Functional Interfaces · Method References · Predicate, Function, Consumer · Optional · Common Mistakes

Streams API

Streams Basics · filter, map, forEach · reduce & collect · sorted, distinct, limit · Collectors & groupingBy · Parallel Streams · Common Mistakes

File I/O

File & Path Basics · Reading Files · Writing Files · BufferedReader & Writer · NIO.2 (java.nio) · Serialization

Multithreading

Threads Basics · Runnable & Callable · Thread Lifecycle · Synchronization · wait, notify & notifyAll · Executor Framework · CompletableFuture · Common Mistakes

JVM & Memory

JVM Architecture · Stack vs Heap Memory · Garbage Collection · ClassLoader · JIT Compiler

Modern Java (8–21)

Java 8 Key Features · Java 11 Features · Java 17 Features (LTS) · Java 21 Features (LTS) · var (Local Type Inference) · Text Blocks · Pattern Matching · Switch Expressions

Interview Preparation

Top Java Interview Q&A · OOP Interview Questions · Collections Interview Q&A · Multithreading Q&A · Java 8+ Interview Q&A · FAANG Java Questions · Coding Challenges

Best Practices

Clean Code in Java · SOLID Principles · Effective Java Tips · Common Anti-Patterns · Code Review Checklist

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