JAVA : On Network

I know that java.net.* have tons of classes for Networking.

Any one which classes I should use to let all clients on the computer to comunite each other or maybe see the message was post by the administration?

For example: If an Admin. maybe changed some texts in a specify folder, then the Java updated the file once it's save. And when the client open it up, it show the current messages. I am thinking doing this in Java Applet.

no offence but.. wah!?!?! i didnt get a word of that :confused:

you can use tcp with sockets to connect client applets to a server application (threaded for multiple users)

or udp packets (but this is quite unreliable apparently)

or multicast to broadcast messages even if no1 is listening(not in an applet)

im makeing a chatroom for my ict coursework and im using threaded tcp sockets (its all cofusing me but it should work :))