Smack isnt designed to send java objects via xmpp- you would need to marshal your object in such a way that it can be represented in an xmpp packet (XML, base64, something), then you need something on the other end that can unmarshal it in the same way.
I then have ‘obj’ on my end of the chat and am free to do as I wish with it. Sending java-objects simply involves setting a property in the Message object. Check out the link in my first post.