public void leaveUser(ChatUser u) throws RemoteException {
if (userstable.containsKey(u.getName())) {
userstable.remove(u.getName());
broadcastLeaving(u.getName());
}
}
public void joinUser(ChatUser u) throws java.rmi.RemoteException {
if (!userstable.containsKey(u.getName())) {
userstable.put(u.getName(), u);
broadcastJoining(u.getName());
}
}