1.First off, download no-ip and create a host for example "yourhost.no-ip.biz"
2.then you port forward 43594, then you turn your server on and dont forget to edit the run.bat and put your jdk version or jre version in so the run works.
3.then go to your client and go to client.java search for "server" until you see the old ip or it will say 127.0.0.1 and change it to your server ip from no-ip.
4.compile after you do that and the client will now connect to your server.
Also if you don't know how to port forward, use the search bar and search "how to portforward", ik there's a few ways to portforward. Only way I know is through Utorrent by going preferences > connection then put port 43594 and press apply.