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Java Tutorial

Last Updated : 22 Aug, 2025

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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#.

Try our ongoing free courses Java Skillup and Advance Java Skillup with weekly topic coverage, notes, daily quizzes and coding problems.

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 and reusable code.
It runs on all platforms Windows, Mac, and Linux using the JVM.
Top companies like Amazon, Netflix, and LinkedIn use Java.

Java Hello World Program

Here is a simple Java program that prints "Hello World".

Java

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

Output

Hello World

Java Basics

Java basics form the foundation of your programming journey, covering essential concepts like syntax, data types, variables, loops, and conditionals. Mastering these fundamentals is key to building strong, error-free Java applications:

Introduction
Download and Install Java
JDK vs JRE vs JVM
Identifiers
Keywords
Quiz: Java Basics and Identifiers
Data Types
Variables
Operators
Quiz: Variables, Operator
Decision Making (if, if-else, switch, break, continue, jump)
Loops
Quiz: Control Statements and Loops
Project: Number Guessing Game

Java 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:

Introduction to Methods
Static Methods vs Instance Methods
Access Modifiers
Command Line Arguments
Variable Arguments (Varargs)
Quiz: Methods

Java 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:

Introduction to Arrays
Declare and Initialize Arrays
Multi-Dimensional Arrays
Quiz: Java Arrays
Jagged Arrays
Arrays Class
Final Arrays
Java Array Programs
Quiz: Array Programs
Projects: Tic-Tac-Toe Game

Java 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:

Introduction of Strings
Why Strings are Immutable?
Java String Concatenation
Quiz: String Basics
String Class
StringBuffer Class
StringBuilder Class
Quiz:String Classes
Strings vs StringBuffer vs StringBuilder
Java String Programs

Java 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:

What are OOP Concepts?
Classes and Objects
Quiz: Classes and Objects
Constructors
Quiz: Constructors
Object Class
Abstraction
Encapsulation
Inheritance
Quiz: Inheritance and Abstraction
Polymorphism
Compile-Time Polymorphism (Method Overloading)
Runtime Polymorphism (Method Overriding)
Packages
Quiz: Polymorphism and Packages
Project: Simple Banking Application

Java 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:

Java Interfaces
Interfaces and Inheritance
Class vs Interface
Quiz: Interfaces
Functional Interface
Nested Interface
Marker Interface
Comparator Interface
Quiz: Interface types and Comparator
Project: Employee Management System

Java 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:

Java Collection Framework
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

Java Exception Handling

ava 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:

Java Exceptions
Checked vs Unchecked Exceptions
Try Catch Block
Quiz: Java Exceptions
Final, Finally and Finalize
Throw and Throws
Customized Exception Handling
Chained Exceptions
Null Pointer Exceptions
Exception Handling with Method Overriding
Quiz: Exception Handling

Java Multithreading

Java Multithreading allows concurrent execution of two or more threads, enabling efficient CPU utilization and faster program performance. It is commonly used for tasks like parallel processing and responsive applications:

Introduction to Java Multithreading
Threads
Thread Class
Runnable Interface
Quiz: Thread Basics and Lifecycle
Lifecycle and States of a Thread
Main Thread
Thread Priority in Multithreading
Naming & Feteching Name of Current Thread
Thread.start() vs Thread.run() Method
Thread.sleep() Method
Daemon Thread
Quiz: Thread Methods and Daemon Threads
Thread Safety
Thread Pools
Project: Snake Game

Java 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:

File Handling
File Class
Create Files
Read Files
Quiz:File Handling
Write on Files
Delete File
FileReader Class
FileWriter Class
Quiz:File Writing
FilePermission Class
FileDescriptor Class

Java Streams and Lambda Expressions

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 Stream - Complete Tutorial
Quiz:Lambda Expressions and Streams
Java 8 Features - Complete Tutorial

Java IO

Java IO (Input/Output) provides a set of classes and streams to read and write data from various sources like files, consoles, and network connections. It is part of the java.io package and supports both byte and character streams:

Introduction to Java IO
Reader Class
Writer Class
FileInput Stream
Quiz: IO Basics
FileOutput Stream
BufferedReader Input Stream
BufferedReader Output stream
BufferedReader vs Scanner
Fast I/O
Quiz: BufferedReader vs Scanner and Fast I/O
Project: Text Editor

Java Synchronization

Java Synchronization is used to control access to shared resources in multithreaded environments. It ensures that only one thread can access a critical section at a time, preventing data inconsistency:

Java Synchronization
Importance of Thread Synchronization
Method and Block Synchronization
Quiz: Synchronization Basics
Atomic vs Volatile vs Synchronized
Local Frameworks vs Thread Synchronization
Deadlock in Multithreading
Quiz: Deadlocks and Synchronization
Deadlock Prevention and Avoidance
Lock vs Monitor in Concurrency
Reentrant Lock
Quiz: Concurrency Locks and Reentrant Locks

Java 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:

What is Java Regex?
Pattern Class
Matcher Class
Character Class
Quiz: Regex Basics and Pattern Matching
Quantifiers

Java 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:

Introduction to Java Networking
TCP Architecture
UDP Architecture
IPV4 vs IPV6
Quiz: Networking Basics and Protocols
Connection-Oriented vs Connectionless Protocols
Socket Programming
Server Socket Class
Quiz: Sockets and Server Communication
URL Class and Methods
Project: Chat Application

Java Database Connectivity(JDBC)

Introduction to Java JDBC
JDBC Driver
JDBC Connection
Types of Statements in JDBC
Quiz: JDBC

Java 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:

Java Memory Management
How Java Objects Stored in Memory?
Quiz: Java Memory Allocation
Stack vs Heap Memory Allocation
Quiz: Heap vs Stack
Java Virtual Machine(JVM) Stack Area
Types of Memory Areas Allocated by JVM
Garbage Collection
Quiz: JVM Memory Management and Garbage Collection
Types of JVM Garbage Collectors
Heap and Stack Memory Allocation
Memory Leaks

Java 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:

200+ Core Java Interview Questions and Answers
Java MCQ

Important Links

Comparison of various programming languages
Companies That Use Java
Careers & Jobs in Java

Java Practice

Java Exercises – Basic to Advanced Java Practice Programs
Java Coding Practice Problems
Java Language MCQs with Answers

Introduction to Java

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Introduction to Java

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Writing First Program in Java

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Variables and Primitive DataTypes

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Non Primitive DataTypes

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Type Conversion in Java

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Input in Java

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