In Java, data types are classified into two categories: primitive and non-primitive data types. Primitive data types are predefined by the programming language, while non-primitive data types are created by the programmer and are not predefined. Non-primitive data types are also called reference types because they refer to objects. Examples of non-primitive data types include Strings, Arrays, Classes, Interface, etc. .

The main differences between primitive and non-primitive data types in Java are:

• Primitive types are predefined in Java, while non-primitive types are created by the programmer.
• 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.
• A primitive type starts with a lowercase letter, while non-primitive types start with an uppercase letter.

In Java, all non-primitive data types are simply called objects that are created by instantiating a class. Non-primitive data types are also referred to as referenced data types or object reference variables.