Send class with client-server

[Gal]

Hi all,
I am working on server-client project. I found a simple example where you send string like this:

output = new PrintWriter(socket.getOutputStream(),true);
output.println(lineToBeSent);

and receive:

input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
String message = input.readLine();

my question is how can I send and receive a class if the class is the same in both server and client?