I'm adding an interface org.jboss.io.Immutable that can be used to Mark Immutable user classes. If you use that interface and you have two identical objects ( by hashCode and equals definitions) these will be replaced by a single reference when the streaming is being parsed. This didn't add any incompatibility issues as this change only affects how IDs are generated on writeObject. This didn't cause any change on the protocol. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4036065#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...