What data types exist in Java?

In Java, there are two main data types:

1. Primitive Data Types: Store simple values. Their size and range are predefined by the JLS (Java Language Specification).

   • Logical: boolean (stores true or false).
   • Integer:
     • byte (1 byte, from -128 to 127)
     • short (2 bytes, from -32,768 to 32,767)
     • int (4 bytes, from -2^31 to 2^31-1)
     • long (8 bytes, from -2^63 to 2^63-1)
     • char (2 bytes, stores a single Unicode character)
   • Floating point:
     • float (4 bytes, single precision)
     • double (8 bytes, double precision)

2. Reference Data Types: Store references (addresses) to objects in memory. Include predefined Java classes, arrays, and user-defined classes, interfaces, and enums.

   • Classes (class)
   • Interfaces (interface)
   • Enums (enum)
   • Arrays (array)

Examples:

// Primitive types
int count = 10;
boolean isValid = true;
char initial = 'J';
double price = 99.99;

// Reference types
String name = "Java"; // String is a class
int[] numbers = {1, 2, 3}; // Array
Object obj = new Object(); // Object class

Differences:

Attribute	Primitive Types	Reference Types
Storage	Actual value	Reference (address) to object in memory
Default value	Depends on type (0, false, '\u0000')	null
Size	Fixed	Depends on object and JVM platform
Memory handling	Placed on stack (usually)	Objects are placed on heap, references on stack