Data Types

A data type defines the kind of data a variable can hold and how much memory it uses and what operations can be performed on it.

Java has two categories of data types:

1. Primitive data types
2. Reference data types

Primitive Data Types

Primitive types are the basic building blocks and are not objects.

Data Type	Size	Description	Range	Example
byte	8 bits	Integer	-128 to 127	byte b = 100;
short	16 bits	Integer	-32,768 to 32,767	short s = 10000;
int	32 bits	Integer	-2³¹ to 2³¹-1	int i = 100000;
long	64 bits	Integer	-2⁶³ to 2⁶³-1	long l = 100000L;
float	32 bits	Floating-point	~±3.402…	float f = 3.14f;
double	64 bits	Floating-point	~±1.797…	double d = 3.14159;
char	16 bits	Unicode character	0 to 65,535	char c = 'A';
boolean	1 bit	True/false value	true or false	boolean flag = true;

Integer Types

byte smallNumber = 127;
short mediumNumber = 32767;
int regularNumber = 2147483647;
long largeNumber = 9223372036854775807L; // Note the 'L' suffix

Floating-Point Types

float simpleDecimal = 3.14f;  // Note the 'f' suffix
double preciseDecimal = 3.141592653589793;

Character Type

char letter = 'A';
char unicodeChar = '\u00A9';  // Copyright symbol ©

Boolean Type

boolean isActive = true;
boolean hasPermission = false;

Reference Data Types

Reference types are derived from classes and interfaces.

String

String greeting = "Hello, Java!";
String empty = "";  // Empty string
String nullString = null;  // Null reference

Arrays

int[] numbers = {1, 2, 3, 4, 5};
String[] names = new String[3];
names[0] = "Alice";
names[1] = "Bob";
names[2] = "Charlie";

Classes and Objects

// Define a class
class Person {
  String name;
  int age;
}

// Create an object
Person person = new Person();
person.name = "John";
person.age = 30;

Wrapper Classes

Every primitive type has a corresponding wrapper class:

Primitive Type	Wrapper Class
byte	Byte
short	Short
int	Integer
long	Long
float	Float
double	Double
char	Character
boolean	Boolean

Integer wrappedInt = 42;

Differences

Feature	Primitive Data Types	Reference Data Types
Storage	Store actual values directly in memory	Store references (addresses) to objects in memory
Definition	Predefined by the Java language	Created from classes or interfaces (can be user-defined)
Size	Fixed size	Size can vary (depends on the object)
Are they objects?	No	Yes
Examples	int, double, char, boolean	String, arrays, all class objects

Best Practices

1. Use the appropriate type for the data you’re storing
2. Use int for most integer values unless you need a larger range
3. Use double for most floating-point calculations
4. Use wrapper classes when you need to treat primitives as objects
5. Be careful with type conversions to avoid data loss