Getting Java to talk to Python, C, C++, and Ruby
You should probably use a standard interprocess mechanism like a pipe or socket.
All of these languages have libraries available for both, and this strategy allows communication between any 2 of your processes (Java/Ruby, Ruby/Python, Java/C, etc)
I have succeeded in getting ProcessBuilder to run external scripts, but I still have to get Java to communicate with the external scripts. I figure that I should get the input/output streams from the process, and use those to send and receive data. I'm having a the most trouble with giving input to the scripts. It seems that I can get output from the scripts by using the script's print function, but I can't seem to get the scripts to register input from the main java program. 
This question involves four languages, so it's fine if you post only the answer regarding one language.