Data Types in Java

Java data types define the kind of data a variable can hold and how memory is allocated. Learn about primitive types, reference types, and memory storage.

Overview of Data Types

Data types in Java are broadly categorized into:

Primitive Data Types: Store simple values directly in memory.
Non-Primitive (Reference) Data Types: Store memory references to objects.

How Primitive Variables Are Stored

Primitive types store the actual value directly in the stack memory.

Example:

int x = 10;

The variable x is stored in the stack.
The value 10 is also in the stack.

✔ Primitive = store REAL value in stack

How Non-Primitive Variables Are Stored

Non-primitive types store a reference in the stack, but the actual object is stored in the heap memory.

Example:

String name = new String("John");

Memory behavior:

name → stored in stack
"John" object → stored in heap
Stack variable name stores a reference to the heap object.

✔ Non-primitive = stack holds reference, heap holds actual object

Primitive Data Types

Java has eight primitive data types. They store single values directly and are stored in stack memory.

Type	Description	Default	Size	Example	Range
boolean	Logical values	false	1 byte (JVM dependent)	true, false	—
byte	8-bit signed integer	0	1 byte	10	-128 to 127
char	16-bit Unicode character	\u0000	2 bytes	'A', '\u0041'	0 to 65,535
short	16-bit signed integer	0	2 bytes	2000	-32,768 to 32,767
int	32-bit signed integer	0	4 bytes	1000, -500	-2,147,483,648 to 2,147,483,647
long	64-bit signed integer	0L	8 bytes	123456789L	±9.22e18
float	32-bit floating point	0.0f	4 bytes	3.14f	~6–7 digits precision
double	64-bit floating point	0.0d	8 bytes	3.14159d	~15–16 digits precision