Java APIs

Hi,
I am following the above link to fetch the global IP address if we are in local network.

http://jstun.javawi.de/

In the source code i downloaded from the above link, DiscoveryTestDemo class is there, which on running provides the global ip address of our system.

Suppose if i want to connect to another system in another network and i want to interact with that system how this jstun application is useful.

Is the JStun application is only for finding the global address and not for hole punching.

Please suggest me if it is used for hole punching, how to run the source code given in that page.

Thanks
Rajasekhar