MCS-378 Lab 4: Distributed Communication, Fall 1999

Due: December 10, 1999

Goals of the lab

In this lab, your team will get some experience using RMI, the Java Remote Method Invocation facility, which is one example of a modern distributed object system. To do this, you will write a simple "chat" program, which can be used to converse with other network users. Each user of the chat program identifies himself/herself with a "handle" (name) which can be the same as the username or chosen arbitrarily. Each user also selects a chat "channel" to participate in. Any message sent to that channel will appear, prefixed by the sender's handle. A message can at any time be sent to the selected channel. If the channel is changed, the area displaying received messages is cleared out.


You can use as starting point a dummy chat program, which I have as a file linked to the web version of this lab handout. This provides the graphical user interface, but doesn't actually do any network communication. Instead, it just displays your own messages locally. (You are welcome to improve on the user interface if you want, but that isn't the focus of the lab. The focus should be on adding the RMI communications to make the chat program real.)

You will probably want to consult the RMI documentation, which is on the web at In particular, this includes the RMI Tutorial, the code from which I showed on the overhead in class.

You may also need to look at some other Java documentation, such as that for the Choice class, which is used for the channel selector.

Your friendly neighborhood instructor is also a resource.


Remember that the client and the server are quite asymmetrical. The clients will need to find the server by name, but can then register with the server, so that the server knows the clients without doing a naming lookup. Similarly, when the client discovers that the server has failed, that is quite a different matter than when the server discovers that the client has failed.

You will almost certainly find it less hassle to leave the client a stand-alone application program rather than make it an applet.

You will also almost certainly find it less hassle to have all messages go by way of the server rather than directly from one client to the other clients on the same channel.

Possible extension

There are lots of extensions you could do, but one that comes particularly to mind is making the choice of channels more flexible. Right now, the client program has built into it the names of the channels. Instead, you could have that knowledge only in the server, with the clients retrieving an array of channel names from the server.

Instructor: Max Hailperin