What You Need

• JDK: Java Development Kit
• Code editor: IntelliJ IDEA, Eclipse, NetBeans, or VS Code
• Command Prompt or Terminal

Install JDK on Windows

1. Download and install the latest JDK from Oracle or OpenJDK distribution.
2. Install it normally.
3. Set environment variable if needed.
4. Open Command Prompt and check:

java -version
javac -version

Important Tools

Compile and Run Java

javac Main.java
java Main

What is Java?

Java is a high-level, class-based, object-oriented programming language. It is used to create desktop applications, Android apps, enterprise systems, web applications, banking systems, and backend services.

Features of Java

JDK, JRE, JVM

Hello World Program

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

Explanation

Variables

A variable is a named memory location used to store data.

int age = 20;
double price = 99.99;
char grade = 'A';
boolean isPassed = true;
String name = "Ravi";

Primitive Data Types

Taking Input Using Scanner

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter your name: ");
        String name = input.nextLine();

        System.out.print("Enter your age: ");
        int age = input.nextInt();

        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
    }
}

Type Casting

int a = 10;
double b = a; // automatic casting

double x = 10.75;
int y = (int) x; // manual casting

System.out.println(b);
System.out.println(y);

Arithmetic Operators

Comparison Operators

int a = 10;
int b = 5;

System.out.println(a == b);
System.out.println(a != b);
System.out.println(a > b);
System.out.println(a <= b);

Logical Operators

int age = 20;
boolean hasId = true;

if (age >= 18 && hasId) {
    System.out.println("Allowed");
}

Assignment Operators

int x = 10;
x += 5;
x -= 2;
x *= 3;
System.out.println(x);

if Statement

int age = 18;

if (age >= 18) {
    System.out.println("Adult");
}

if else

int marks = 45;

if (marks >= 50) {
    System.out.println("Pass");
} else {
    System.out.println("Fail");
}

else if Ladder

int marks = 78;

if (marks >= 75) {
    System.out.println("A Grade");
} else if (marks >= 65) {
    System.out.println("B Grade");
} else if (marks >= 50) {
    System.out.println("C Grade");
} else {
    System.out.println("Fail");
}

switch

int day = 2;

switch (day) {
    case 1:
        System.out.println("Monday");
        break;
    case 2:
        System.out.println("Tuesday");
        break;
    default:
        System.out.println("Invalid day");
}

for Loop

for (int i = 1; i <= 5; i++) {
    System.out.println(i);
}

while Loop

int i = 1;

while (i <= 5) {
    System.out.println(i);
    i++;
}

do while Loop

int i = 1;

do {
    System.out.println(i);
    i++;
} while (i <= 5);

Array

An array stores multiple values of the same type.

int[] numbers = {10, 20, 30, 40};

System.out.println(numbers[0]);
System.out.println(numbers.length);

Loop Through Array

int[] marks = {75, 80, 65};

for (int i = 0; i < marks.length; i++) {
    System.out.println(marks[i]);
}

Enhanced for Loop

String[] names = {"Ravi", "Kavi", "Meena"};

for (String name : names) {
    System.out.println(name);
}

Two-Dimensional Array

int[][] matrix = {
    {1, 2, 3},
    {4, 5, 6}
};

System.out.println(matrix[0][1]);

String Basics

String text = "Java Programming";

System.out.println(text.length());
System.out.println(text.toUpperCase());
System.out.println(text.toLowerCase());
System.out.println(text.charAt(0));
System.out.println(text.substring(0, 4));
System.out.println(text.contains("Java"));

StringBuilder

StringBuilder is useful when you need to modify text many times.

StringBuilder sb = new StringBuilder("Java");
sb.append(" Course");
System.out.println(sb);

A method is a block of code that performs a specific task.

Simple Method

public class Main {
    static void greet() {
        System.out.println("Hello Student");
    }

    public static void main(String[] args) {
        greet();
    }
}

Method with Parameters

public class Main {
    static void greet(String name) {
        System.out.println("Hello " + name);
    }

    public static void main(String[] args) {
        greet("Ravi");
    }
}

Method with Return Value

public class Main {
    static int add(int a, int b) {
        return a + b;
    }

    public static void main(String[] args) {
        int result = add(10, 20);
        System.out.println(result);
    }
}

Method Overloading

Method overloading means using the same method name with different parameters.

public class Main {
    static int add(int a, int b) {
        return a + b;
    }

    static double add(double a, double b) {
        return a + b;
    }

    public static void main(String[] args) {
        System.out.println(add(5, 10));
        System.out.println(add(5.5, 10.5));
    }
}

OOP Concepts

Class and Object

class Student {
    String name;
    int age;

    void display() {
        System.out.println(name);
        System.out.println(age);
    }
}

public class Main {
    public static void main(String[] args) {
        Student s1 = new Student();
        s1.name = "Ravi";
        s1.age = 20;
        s1.display();
    }
}

Constructor

class Student {
    String name;
    int age;

    Student(String n, int a) {
        name = n;
        age = a;
    }

    void display() {
        System.out.println(name + " " + age);
    }
}

public class Main {
    public static void main(String[] args) {
        Student s1 = new Student("Kavi", 21);
        s1.display();
    }
}

this Keyword

class Student {
    String name;

    Student(String name) {
        this.name = name;
    }
}

Encapsulation

class BankAccount {
    private double balance;

    public void deposit(double amount) {
        if (amount > 0) {
            balance += amount;
        }
    }

    public double getBalance() {
        return balance;
    }
}

Inheritance

class Animal {
    void eat() {
        System.out.println("Animal is eating");
    }
}

class Dog extends Animal {
    void bark() {
        System.out.println("Dog is barking");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog d = new Dog();
        d.eat();
        d.bark();
    }
}

Method Overriding

class Animal {
    void sound() {
        System.out.println("Animal sound");
    }
}

class Dog extends Animal {
    @Override
    void sound() {
        System.out.println("Dog barks");
    }
}

Polymorphism

class Animal {
    void sound() {
        System.out.println("Animal sound");
    }
}

class Cat extends Animal {
    void sound() {
        System.out.println("Meow");
    }
}

class Dog extends Animal {
    void sound() {
        System.out.println("Bark");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal a;

        a = new Cat();
        a.sound();

        a = new Dog();
        a.sound();
    }
}

Abstract Class

abstract class Shape {
    abstract void draw();

    void message() {
        System.out.println("Drawing shape");
    }
}

class Circle extends Shape {
    void draw() {
        System.out.println("Drawing circle");
    }
}

Interface

interface Payment {
    void pay();
}

class CardPayment implements Payment {
    public void pay() {
        System.out.println("Paid by card");
    }
}

Abstract Class vs Interface

Package

A package groups related classes together.

package mypackage;

public class Student {
    public void display() {
        System.out.println("Student class");
    }
}

Import Package

import java.util.Scanner;
import java.util.ArrayList;

Access Modifiers

An exception is an error that occurs during program execution. Java uses exception handling to keep programs safe and stable.

try catch

public class Main {
    public static void main(String[] args) {
        try {
            int result = 10 / 0;
            System.out.println(result);
        } catch (ArithmeticException e) {
            System.out.println("Cannot divide by zero");
        }
    }
}

finally

try {
    int[] numbers = {1, 2, 3};
    System.out.println(numbers[5]);
} catch (ArrayIndexOutOfBoundsException e) {
    System.out.println("Invalid array index");
} finally {
    System.out.println("Program completed");
}

throw

public class Main {
    static void checkAge(int age) {
        if (age < 18) {
            throw new ArithmeticException("Not eligible");
        } else {
            System.out.println("Eligible");
        }
    }

    public static void main(String[] args) {
        checkAge(16);
    }
}

throws

import java.io.FileReader;
import java.io.IOException;

public class Main {
    static void readFile() throws IOException {
        FileReader file = new FileReader("data.txt");
    }
}

The Java Collections Framework provides ready-made data structures like ArrayList, LinkedList, HashSet, HashMap, and Queue.

ArrayList

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        ArrayList<String> names = new ArrayList<>();

        names.add("Ravi");
        names.add("Kavi");
        names.add("Meena");

        System.out.println(names.get(0));
        System.out.println(names.size());
    }
}

LinkedList

import java.util.LinkedList;

LinkedList<String> list = new LinkedList<>();
list.add("A");
list.addFirst("Start");
list.addLast("End");

HashSet

import java.util.HashSet;

HashSet<Integer> numbers = new HashSet<>();
numbers.add(10);
numbers.add(20);
numbers.add(10);

System.out.println(numbers);

HashMap

import java.util.HashMap;

HashMap<String, Integer> marks = new HashMap<>();
marks.put("Ravi", 80);
marks.put("Kavi", 90);

System.out.println(marks.get("Ravi"));

Collection Comparison

Write File

import java.io.FileWriter;
import java.io.IOException;

public class Main {
    public static void main(String[] args) {
        try {
            FileWriter writer = new FileWriter("notes.txt");
            writer.write("Java file handling example.");
            writer.close();
            System.out.println("File written successfully.");
        } catch (IOException e) {
            System.out.println("Error occurred.");
        }
    }
}

Read File

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        try {
            File file = new File("notes.txt");
            Scanner reader = new Scanner(file);

            while (reader.hasNextLine()) {
                String line = reader.nextLine();
                System.out.println(line);
            }

            reader.close();
        } catch (FileNotFoundException e) {
            System.out.println("File not found.");
        }
    }
}

Wrapper Classes

Wrapper classes convert primitive types into objects.

Generics

Generics allow classes and methods to work with different data types safely.

class Box<T> {
    T value;

    void setValue(T value) {
        this.value = value;
    }

    T getValue() {
        return value;
    }
}

public class Main {
    public static void main(String[] args) {
        Box<String> box = new Box<>();
        box.setValue("Java");
        System.out.println(box.getValue());
    }
}

Enum

enum Day {
    MONDAY, TUESDAY, WEDNESDAY
}

public class Main {
    public static void main(String[] args) {
        Day today = Day.MONDAY;
        System.out.println(today);
    }
}

Lambda Expression

Lambda expressions make code shorter when working with functional interfaces.

interface Greeting {
    void sayHello();
}

public class Main {
    public static void main(String[] args) {
        Greeting g = () -> System.out.println("Hello Java");
        g.sayHello();
    }
}

Lambda with Parameters

interface Add {
    int sum(int a, int b);
}

public class Main {
    public static void main(String[] args) {
        Add add = (a, b) -> a + b;
        System.out.println(add.sum(10, 20));
    }
}

Stream API

import java.util.Arrays;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);

        numbers.stream()
               .filter(n -> n % 2 == 0)
               .forEach(n -> System.out.println(n));
    }
}

map and collect

import java.util.*;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        List<String> names = Arrays.asList("ravi", "kavi", "meena");

        List<String> upperNames = names.stream()
            .map(name -> name.toUpperCase())
            .collect(Collectors.toList());

        System.out.println(upperNames);
    }
}

Multithreading means running multiple parts of a program at the same time.

Thread Using Thread Class

class MyThread extends Thread {
    public void run() {
        System.out.println("Thread is running");
    }
}

public class Main {
    public static void main(String[] args) {
        MyThread t1 = new MyThread();
        t1.start();
    }
}

Thread Using Runnable Interface

class MyTask implements Runnable {
    public void run() {
        System.out.println("Task running");
    }
}

public class Main {
    public static void main(String[] args) {
        Thread t1 = new Thread(new MyTask());
        t1.start();
    }
}

sleep

public class Main {
    public static void main(String[] args) {
        try {
            Thread.sleep(1000);
            System.out.println("After 1 second");
        } catch (InterruptedException e) {
            System.out.println(e);
        }
    }
}

synchronized

synchronized helps control access when multiple threads use the same resource.

class Counter {
    int count = 0;

    synchronized void increment() {
        count++;
    }
}

JDBC means Java Database Connectivity. It allows Java programs to connect with databases like MySQL, PostgreSQL, Oracle, and SQLite.

JDBC Steps

1. Import JDBC package.
2. Load database driver if needed.
3. Create connection.
4. Create statement or prepared statement.
5. Execute query.
6. Process result.
7. Close connection.

Basic MySQL Connection Example

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;

public class Main {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/school";
        String user = "root";
        String password = "";

        try {
            Connection con = DriverManager.getConnection(url, user, password);
            Statement stmt = con.createStatement();

            String sql = "CREATE TABLE students (id INT, name VARCHAR(100))";
            stmt.executeUpdate(sql);

            System.out.println("Table created successfully");

            con.close();
        } catch (Exception e) {
            System.out.println(e);
        }
    }
}

Insert Data

String sql = "INSERT INTO students VALUES (1, 'Ravi')";
stmt.executeUpdate(sql);

Read Data

import java.sql.ResultSet;

ResultSet rs = stmt.executeQuery("SELECT * FROM students");

while (rs.next()) {
    System.out.println(rs.getInt("id") + " " + rs.getString("name"));
}

PreparedStatement

import java.sql.PreparedStatement;

String sql = "INSERT INTO students VALUES (?, ?)";
PreparedStatement ps = con.prepareStatement(sql);

ps.setInt(1, 2);
ps.setString(2, "Meena");

ps.executeUpdate();

Important Coding Questions for Practice

1. Write a Java program to check odd or even number.
2. Write a Java program to find largest of three numbers.
3. Write a Java program to print multiplication table.
4. Write a Java program to reverse a string.
5. Write a Java program to find factorial of a number.
6. Write a Java program to check prime number.
7. Write a Java program to sort an array.
8. Create a Student class and display student details.
9. Create a BankAccount class using encapsulation.
10. Create a To-Do app using ArrayList.