Java: Long (class) vs long (primitive)

A Long is a class, or a reference type, defined in the standard library. It stores a reference to an object containing a value (a "box").

A long on the other hand, is a primitive type and part of the language itself. It stores an actual value.

We say that Long is the wrapper type for long, and objects of type Long are boxed values.

Continue reading here:

Java: Primitives vs Objects and References
Java: Wrapper Types