How to block access to objects from outside the library?

Question

I am developing a library has too many objects on android. So I must group the classes with package. I want to access A class from C but I want to prevent this objects accessible from Project X. So I can't use private-package (default) and "public" identifiers.

--PROJECT X (The project that uses the library.)
    --library src
         ---packagex
             ----Class A
             ----Class B
         ---packagey
             ----Class C

Is it possible ? Is there anyway to group classes without package? Thanks.