@Override
        public int hashCode()
        {
            return Objects.hash(serviceId, nodeId, itemId);
        }
A unique identifier for an item, in context of all nodes of all services in the system.

The properties that uniquely identify an item are its node, and its itemId.
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/PublishedItem.java