What you asking for is something pretty complex and at the leading edge of computing. Text to speech and speech to text, though it has been done reasonably now, it still sounds very synthetic and the world is always trying to improve this stuff. You should probably have
tried Google'ing this before asking on CP, as it is in the CP guidelines and we're unlikely to be able to give you much help based on this short question. Have a look at this search:
http://lmgtfy.com/?q=convert%20text%20to%20audio%20java[
^]
Hope this helps,
Ed :)