I understand and have coded up some RMI code and it works. I can create a RMIServer object and a RMIClient object and the client can send messages to the server and the server receives it perfectly.
My question is how do I communicate between two different computers in different parts of the world?
When you connect to the RMI server you provide an IP or name of the machine hosting the server. You will simply provide the IP/name of the RMI server in place of the one you're currently using.