Whether java is fully object oriented or partially?
That depends on your definition of "object-oriented".
For example, according to Alan Kay, who coined the word "object-oriented", the only object-oriented languages today are Smalltalk and Lisp. I assume that he probably also would include Self, Newspeak, Io, Ioke, Seph and Erlang, but definitely not Java.
Why its called as fully object oriented or partially?
You would have to ask the people who call it that.
In the case of Alan Kay, it is because it is missing the most important concept of object-orientation: Messaging.
What is Object oriented programming?
Programming with messages.
What is a class ?
Classes were an initial attempt at implementing inheritance in the 1960s. We have since learnt that we don't actually need them.
What is object?
An object is an entity that can send and receive messages. You can think of it as a little computer on a network or as a cell in a complex organism.