Data Types

Data types

Java has eight primitive data types:

byte

• size - 1 byte (8 bits)
• stores whole number from -128 to 127

byte smallNumber = 100;

short

• size - 2 bytes (16 bits)
• stores value from - 32,768 to 32,767

short mediumNumber = 30000;

int

• size - 4 bytes (32 bits)
• stores values from —2,147,483,648 to 2,147,483,647

int number = 100000;

long

• size - 8 bytes (64 bits)
• stores values from -2^63 to 2^63 - 1

long bigNumber = 9223372036854775807L; // Add 'L' at the end

float

• size - 4 bytes (32 bits)
• stores decimal values with ~7 decimal precision

float decimalNumber = 3.14f; // Add 'f' at the end

double

• size - 8 bytes (64 bits)
• stores decimal values with ~15 decimal precision

double preciseNumber = 3.14159265358979;

char

• size - 2 bytes (16 bits)
• stores a single unicode character.

char letter = 'A';

boolean

• size - 1 bit

boolean yes = true;

default values

Data Type	Default Value
byte	0
short	0
int	0
long	0L
float	0.0f
double	0.0d
char	’\u0000’ (null character)
boolean	false

Variables

A variable is a named storage location in memory. It has:

1. Data type (primitive or reference type)
2. Name (identifier)
3. Value (stored data)

int age = 20;        // Declaration + Initialization
double price;        // Declaration only
price = 99.99;       // Assigning a value later

Variable Naming Rules

• Can contain letters, digits, underscores (_) and dollar signs ($)
• Cannot start with a number
• Cannot use reserved keywords (e.g., int, class)
• Java follows camelCase naming convention:

  int studentAge = 25;