How have two people using diff clients but same app, and have app know that

Question

I want to have an app called XMLReader that reads an xml file and then puts it into a JTree. Then I want the person to be able to edit it. But I also want to be able to lock it (using mutex or synchronization) so if someone else on the same network opens up XMLReader, then they cannot edit it at the same time. Also, when they open their app and then Person A edits it, I want it to notify Person B's app.
Does anyone know how to do this? Can it be done with the two instances and no server?

Answer 1

I want to have an app called XMLReader that reads an
xml file and then puts it into a JTree. Then I want
the person to be able to edit it. But I also want to
be able to lock it (using mutex or synchronization) so
if someone else on the same network opens up
XMLReader, then they cannot edit it at the same time.
Also, when they open their app and then Person A edits
it, I want it to notify Person B's app.
Does anyone know how to do this? Can it be done with
the two instances and no server?quite interesting
ok
i try
my solution is
make a interface which has the method which edit the xmlreader to the user whom u want to give the access of
editing make all the other methods which the other users can use in a different interface and give that instances to them
hope u will understand the hints if u want more explanation i will give
in this case make all the other users to register with the Xml reader to get the notifications if the Xml reader is changed by the user who can access
so it will be quite easy for u now to notify the users when the file is edited
it can be done both in single JVM and also in different JVM(client server)
regards
kamal