What is the difference between primitive and reference data types?

Primitive data types store the value directly, whereas reference data types store a reference (memory address) to an object.

Primitive types:

• Always have a value (cannot be null).
• Occupy a fixed amount of memory.
• Are passed by value.
• Examples: byte, short, int, long, float, double, char, boolean.

Reference types:

• Can accept the value null.
• Occupy different amounts of memory depending on the object.
• Are passed by reference.
• Examples: classes (String, Object, arrays), interfaces.

Comparison:

Characteristic	Primitive types	Reference types
Data storage	The value itself	Reference to an object in memory
Null value	Cannot be null	Can be null
Memory size	Fixed	Variable
Passed to methods	By value	By reference