Hello Emily,
as Ulf Dittmer suggests, most common way to achieve this is exporting (in rmi sense) a listener object client side.
This lead to open a ServerSocket client side, with can be problematic in almost all network environments.
Other way is using long lived connections as i suggest in this post:
RMI client behind NAT. Callback implementation .
Recommended way in production environments is using a polling mecanishm.
Regards,
Oricio
[ July 29, 2007: Message edited by: Oricio Ocle ]