Java Data Types

int age = 25;            // integer number
double salary = 75000.50; // decimal number
char grade = 'A';         // single character
boolean active = true;    // true or false
String name = "Arjun";    // text (reference type)

public class IntegerTypes {
    public static void main(String[] args) {
        byte smallNum = 127;            // -128 to 127
        short mediumNum = 32000;        // -32,768 to 32,767
        int regularNum = 2_000_000;     // Underscores for readability
        long bigNum = 9_999_999_999L;   // Note the 'L' suffix

        System.out.println("byte: " + smallNum);
        System.out.println("short: " + mediumNum);
        System.out.println("int: " + regularNum);
        System.out.println("long: " + bigNum);
    }
}

byte: 127
short: 32000
int: 2000000
long: 9999999999

public class FloatTypes {
    public static void main(String[] args) {
        float price = 99.99f;            // Must end with 'f'
        double pi = 3.141592653589793;   // More precise

        System.out.println("float: " + price);
        System.out.println("double: " + pi);

        // Scientific notation
        double distance = 1.496e8;       // 1.496 × 10⁸
        System.out.println("Distance to Sun: " + distance + " km");
    }
}

float: 99.99
double: 3.141592653589793
Distance to Sun: 1.496E8 km

public class CharType {
    public static void main(String[] args) {
        char letter = 'A';
        char digit = '7';
        char symbol = '@';
        char unicode = '\u0041';  // Unicode for 'A'
        char hindi = 'अ';         // Hindi character

        System.out.println(letter);   // A
        System.out.println(unicode);  // A
        System.out.println(hindi);    // अ

        // char is actually stored as a number (Unicode value)
        System.out.println((int) letter);  // 65
    }
}

public class BooleanType {
    public static void main(String[] args) {
        boolean isJavaFun = true;
        boolean isRaining = false;
        boolean isAdult = (18 >= 18);   // true

        System.out.println("Java is fun: " + isJavaFun);
        System.out.println("Is adult: " + isAdult);
    }
}

String greeting = "Hello, World!";
String name = new String("Arjun");  // Also valid, but not preferred

System.out.println(greeting.length());        // 13
System.out.println(greeting.toUpperCase());   // HELLO, WORLD!
System.out.println(greeting.charAt(0));       // H

int[] numbers = {10, 20, 30, 40, 50};
String[] names = {"Arjun", "Priya", "Rahul"};

System.out.println(numbers[0]);   // 10
System.out.println(names.length); // 3

Scanner scanner = new Scanner(System.in);

byte → short → int → long → float → double

int myInt = 100;
long myLong = myInt;       // Automatic: int → long
double myDouble = myLong;  // Automatic: long → double

System.out.println(myInt);     // 100
System.out.println(myLong);    // 100
System.out.println(myDouble);  // 100.0

double myDouble = 9.78;
int myInt = (int) myDouble;    // Manual: double → int

System.out.println(myDouble);  // 9.78
System.out.println(myInt);     // 9 (decimal part lost)

int largeNum = 130;
byte smallNum = (byte) largeNum;
System.out.println(smallNum);  // -126 (overflow!)

// Autoboxing: primitive → wrapper (automatic)
int num = 42;
Integer wrapped = num;

// Unboxing: wrapper → primitive (automatic)
int unwrapped = wrapped;

// Useful methods
int parsed = Integer.parseInt("123");          // String → int
String str = Integer.toString(123);            // int → String
int max = Integer.MAX_VALUE;                   // 2147483647

public class StudentProfile {
    public static void main(String[] args) {
        // Using different data types
        String name = "Arjun Kumar";
        int age = 22;
        double gpa = 8.75;
        char bloodGroup = 'O';
        boolean isGraduated = false;
        long aadhaarNumber = 1234_5678_9012L;
        byte semester = 6;

        System.out.println("=== Student Profile ===");
        System.out.printf("Name:       %s%n", name);
        System.out.printf("Age:        %d years%n", age);
        System.out.printf("GPA:        %.2f/10%n", gpa);
        System.out.printf("Blood Group: %c+%n", bloodGroup);
        System.out.printf("Graduated:  %b%n", isGraduated);
        System.out.printf("Aadhaar:    %d%n", aadhaarNumber);
        System.out.printf("Semester:   %d%n", semester);
    }
}

=== Student Profile ===
Name:       Arjun Kumar
Age:        22 years
GPA:        8.75/10
Blood Group: O+
Graduated:  false
Aadhaar:    123456789012
Semester:   6