There are two commonly used data types in java namely Primitive and Reference Data type.
Primitive Data Type
Primitive data type specifies the size and type of variable values, and has no additional method. These data types are predefined in java. Makes use of camel case. Ie It is used for storing simple values.
Reference Data Types
Reference data types are used for storing complex objects. Such as mail messages, dates etc. These are not predefined unlike the primitive type.