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Where are all the resources?
No one has posted anything :S
I remember having a link to an excellent article about real time multiplayer games…I seem to have lost it now 
EDIT: BAM! FOUND IT!
For now, this post about UDP vs TCP is very useful 
This also may be interesting: https://developer.valvesoftware.com/wiki/Source_Multiplayer_Networking
Good read: http://www.gamasutra.com/view/feature/3094/1500_archers_on_a_288_network_.php
Not Java, but good resource:
http://docs.unity3d.com/Documentation/Manual/NetworkedMultiplayer.html
http://www.java-samples.com/showtutorial.php?tutorialid=1167
Extremely simple tcp server/client example. Great to learn from
Great to learn bad exception and resource handling, as well as cpu munching.
I’m still looking for more resources, but one that had a lot of general networking tips + solutions was the book:
“ActionScript for Multiplayer Games and Virtual Worlds”: http://www.amazon.com/ActionScript-Multiplayer-Games-Virtual-Worlds/dp/0321643364/ref=sr_1_11?ie=UTF8&qid=1359883942&sr=8-11&keywords=multiplayer+flash.
They use their own socket server, but they go through some stuff on syncing the client/server, interpolation, lots of stuff that helped when I was working with kyronet. More concepts, and things to think about when trying to work on multiplayer programming.