The ip you use on which the server is hosted off of is usually "127.0.0.1" or "0.0.0.0".
You have to make a copy of your client for your friend with the server's ip in that spot.
To find this go into client.java, then press ctrl - f , then type "server =", type the ip into this spot.
Your "server =" should be 127.0.0.1, or 0.0.0.0 , His should be the no-ip.org one.
Hope this helps.