java.md

🚀 Java Complete Notes + Roadmap + Project Checklist + Interview Checklist

📌 Table of Contents

• Java Notes
• Project-Based Java Learning Checklist
• Java Interview Preparation Checklist
• Java Beginner → Advanced Roadmap
• Resources

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Java Notes

📖 Introduction

• Java is a high-level, object-oriented programming language.
• Write Once, Run Anywhere.
• Platform Independent via JVM.
• Automatic Garbage Collection.

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🖋️ Basic Syntax

Hello World

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

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🔤 Data Types

Primitive Data Types

Type	Size	Example
byte	1 byte	10
short	2 bytes	1000
int	4 bytes	100000
long	8 bytes	10000000L
float	4 bytes	10.5f
double	8 bytes	10.5
char	2 bytes	'A'
boolean	1 bit	true/false

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➕ Operators

// Arithmetic
+ - * / %

// Relational
== != > < >= <=

// Logical
&& || !

// Assignment
= += -= *= /= %=

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🔁 Control Flow

if-else

if (condition) {
    // statements
} else {
    // statements
}

switch

switch (value) {
    case 1:
        // code
        break;
    default:
        // code
}

Loops

for (int i = 0; i < 5; i++) {}

while (condition) {}

do {} while (condition);

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🧱 OOP Concepts

Class & Object

class Car {
    String color;

    void drive() {
        System.out.println("Driving");
    }
}

Car myCar = new Car();
myCar.drive();

Inheritance

class Animal {
    void eat() {}
}

class Dog extends Animal {
    void bark() {}
}

Polymorphism

• Method Overloading
• Method Overriding

Abstraction

abstract class Shape {
    abstract void draw();
}

Encapsulation

private String name;

public String getName() {}
public void setName(String name) {}

Interface

interface Animal {
    void eat();
}

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🚨 Exception Handling

try {
    // code
} catch (Exception e) {
    System.out.println(e.getMessage());
} finally {
    // always runs
}

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🧵 Multithreading

class MyThread extends Thread {
    public void run() {}
}

MyThread t1 = new MyThread();
t1.start();

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📚 Java Collections Framework

List

ArrayList<String> list = new ArrayList<>();
list.add("Apple");

Set

HashSet<String> set = new HashSet<>();

Map

HashMap<Integer, String> map = new HashMap<>();

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🔀 Streams and Lambdas

Lambda Expression

Runnable r = () -> System.out.println("Running");
r.run();

Streams Example

List<String> names = Arrays.asList("John", "Jane");
names.stream().forEach(System.out::println);

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📂 File I/O

Read File

BufferedReader reader = new BufferedReader(new FileReader("file.txt"));

Write File

BufferedWriter writer = new BufferedWriter(new FileWriter("output.txt"));

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🗄️ JDBC Example

Connection con = DriverManager.getConnection(url, user, password);
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery("SELECT * FROM users");

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Project-Based Java Learning Checklist

✅ Hello World → Understand JVM, JDK, JRE
✅ Simple Calculator App → Basic OOP, operators
✅ Tic Tac Toe CLI Game → Control flow, Arrays
✅ Banking System → Classes, Encapsulation
✅ Address Book App → File I/O
✅ Multi-threaded Downloader → Multithreading
✅ Employee Management System → JDBC, Database
✅ Mini Web App with Spring Boot → Advanced Java + Web

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Java Interview Preparation Checklist

Core Java

✅ OOP Principles
✅ Collections (List, Set, Map)
✅ Exception Handling
✅ Threads & Concurrency
✅ String Handling
✅ File I/O
✅ Java 8 Features (Streams, Lambdas)

Advanced Topics

✅ JVM Internals
✅ Garbage Collection
✅ Design Patterns (Singleton, Factory, Observer, etc.)
✅ SOLID Principles

Coding Skills

✅ Data Structures
✅ Algorithms
✅ System Design Basics

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Java Beginner → Advanced Roadmap

1️⃣ Beginner

✅ Java Installation & Setup
✅ Hello World
✅ Basic Syntax
✅ Variables & Data Types
✅ Control Flow (if, loops)
✅ Methods

2️⃣ Object-Oriented Programming

✅ Classes & Objects
✅ Constructors
✅ Encapsulation
✅ Inheritance
✅ Polymorphism
✅ Abstraction
✅ Interface

3️⃣ Collections Framework

✅ ArrayList
✅ LinkedList
✅ HashSet
✅ TreeSet
✅ HashMap
✅ TreeMap

4️⃣ Advanced Java

✅ Exception Handling
✅ Multithreading
✅ Streams API
✅ Lambda Expressions
✅ File I/O
✅ JDBC

5️⃣ Frameworks (Optional)

✅ Maven
✅ Gradle
✅ Spring Boot
✅ Hibernate

6️⃣ Build Projects!

✅ CLI Apps
✅ Desktop Apps
✅ Web Apps (with Spring Boot)
✅ APIs (RESTful services)