Non-primitive data types are called reference types because they refer to objects. They are called “non-primitive” because they do not represent simple values like integers or characters but instead represent complex objects that may contain multiple pieces of data and behavior.

eg. String, Arrays, Classes.

Whenever a non-primitive data type is defined, it refers a memory location where the data is stored in heap memory i.e., it refers to the memory location where an object is placed. Therefore, a non-primitive data type variable is also called referenced data type or simply object reference variable.

An object reference variable lives on the stack memory and the object to which it points always lives on the heap memory. The stack holds a pointer to the object on the heap.

They are defined by the user/developer/programmer, not Java.

Non-primitive types can be used to call methods to perform certain operations, while primitive types cannot.

A primitive type has always a value, while non-primitive types can be null.

Non-primitive data types are stored in the heap memory area, unlike primitive data types that are stored in the stack memory.

Non-primitive data types are stored in the heap memory area, unlike primitive data types that are stored in the stack memory.