I would to pick up a new programming language - Java, having been using Python for some time. But it seems most things that can be done with Java can be done with Python. So I would like to know

What kind of things can be done with Java but not Python?

mobile programming (Android).
POSIX Threads Programming.

Conversely, What kind of things can be done with Python but not Java if any?

clarification:
I hope to get an answer from a practical point of view but not a theoretical point of view and it should be about the current status, not future. So theoretically all programming languages can perform any task, practically each is limited in some way.
CPython has a lot of libraries with bindings to native libraries--not so Java.
What kind of things can be done with Java but not Python?