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java- ip address command
I'm not expert on java, but i can tell u that (from what it sounds like you're trying to do) java is not the best language for you, java has very little direct computer interaction, but the good thing about it is that it is well documented on java.sun.com. Try this Google "java ip address" and see what comes up, i did just to see and i think it might steer u in the right direction. sorry i couldn't help more
Among that list is the java.net library (probably best), and executing ipconfig through cmd.