Socket programming in Java

Hello.
I have a problem with client-server programming. I put the information I want to send to the server in a object. I serialize the object and sends it, and on the server side I deserialize it and reads the information. This works the first time I try it, but when I want to send an updated object to the same stream something goes wrong. The server still has the old object after deserialization.

I would be really greatful if someone could give me some advise how to solve this problem.
Thanks

Tobias
*****client side code**********
BufferedOutputStream out=null;  
Socket ServSocket = new Socket('localhost',4444);
out=new BufferedOutputStream(ServSocket.getOutputStream());

//this is the object I want to send to the server    
Client_server_message message=new Client_server_message();
ObjectOutputStream oos=new ObjectOutputStream(out);
message.message='s';  
oos.writeObject(message);
oos.flush();

//and then I update the object and send it again  
message.message='u';
oos.writeObject(message);
oos.flush();
*********server side code**************    
ServerSocket serverSocket = new ServerSocket(4444);
Socket clientSocket = serverSocket.accept();
//open a new thread for one user
new PrivateConnection(clientSocket);

********The thread class PrivateConnection*******  
Socket clientSocket=null;
PrivateConnection(Socket s)
 {
  clientSocket = s;
  start();
 }      
  public void run()
 {      
 BufferedInputStream in = new BufferedInputStream(clientSocket.getInputStream());
     
//deserialize
Client_server_message message=new Client_server_message();
ObjectInputStream ois=new ObjectInputStream(in);

//here comes the first object and it works fine
message=(Client_server_message)ois.readObject();

//when this second object is deserialized it still contains the old information, message.message is still ='s'.
message=(Client_server_message)ois.readObject();
}//run