I have problem using ObjectOutputStream with Multi-Thread

Question

I am writing a network rpg game for the project.
Because it is a network game, so i use thread to support multi-user.
When i using the string to store the command, and send to the server,
it still can work. You can downlod at http://ivebug.tripod.com/new-string.zip
(You cannot click the link, you must use [save target as] to save the file)
1. First compile the files then "java ChatServer",
2. Then you can execute "java ChatClient".
3. Input the name for username in the textfield and then press 'login button'.
4. A small square appear in the up-left corner.
5. Then you can click in the black panel to move the square.
6. If you want more than one square can be move, go step 2 to step 5 again.
It seems everthing is work, but i want more extention for future.
So i change to use object to encapsulate the command.
However, it can't work. It stops working after create the socket and
it can can't run to the line to create an ObjectInputStream and ObjectOutputStream. I don't know why. Who can tell me.
The program using object at http://ivebug.tripod.com/new-object.zip
(You cannot click the link, you must use [save target as] to save the file)

Answer 1

Thank you for solve my problem.
Now, i can send the object though the socket, however new problem occurs.
The problem is that after i sent the 'login' object to server,
the client lost the connection.
The program has lost connection problem : http://ivebug.tripod.com/new-lost.zip