What Are Advantages Java Reference Type Variables?

Reference variables :

* All non-primitive variables contain only references to objects on the heap.
They never contain the object. C++ object variables may be either,
but Java supports only object references.

For Example :

Book bookvar = new Book("Java");


bookvar is not an object, it's a variable which contains a reference to an object.
Objects don't have names, just types and locations in memory (and, of course,
fields and methods).

Create a new Book object in memory.
Initialize it with the data sent as arguments to a constructor.
When created, assign a reference to that object to the Book variable bookvar.
"bookvar" is a reference or object type variable which may reference a Book object or
an object of any subclass of Book.