Java Socket passing a class object from the client to the server

I'm studying Java Socket and the client server part, I don't understand the moment of transferring the class object (names and values of variables for performing calculations) from the client to the server, I Googled it and decided to try transmitting it via json. There is a class

public class CalculatorModel
{
    private String JSON;    
    private double number;
    private double sizeCredit;

    // Конструктор
    public CalculatorModel(number, sizeCredit)
    {
        this.number=number;
        this. sizeCredit = sizeCredit;
    }

    // У него метод читающий данные из csv файла и кидающий их в лист
    public void readFile() throws IOException

    // Метод инициализации данных
    public void initialization()
    {
        for(int i=0; i<value.size(); i++)     
        {
            number = value.get(i);
            sizeCredit = value.get(i+1)

            Gson gson = new Gson();
            JSON  = gson.toJson(new CalculatorModel(number, sizeCredit));
        }
     }

    // Метод производит вычисления и бросает данные в лист
    calculation throws IOException ();
    {
        Возвращает List<String> exitData
    }
}

Client

public class CalculatorClientIO implements Runnable
{
    @Override
    public void run()
    {
        int serverPort=8080;
        String adress="127.0.0.1";
        try
        {
            Socket socket = new Socket(adress, serverPort);
            System.out.println("Устанавливаем соединение");
            DataInputStream in = new DataInputStream(socket.getInputStream());
            DataOutputStream out = new DataOutputStream(socket.getOutputStream());

            out.write ????????;
            out.flush();
            String line = in.readUTF();
            System.out.println("Сервер ответил:  " + line);
        }
        catch(Exception er)
        {
           er.printStackTrace();
        }
    }
}

Server

public class CalculatorServerIO
{
    public static void main(String[] args)
    {
        int port=8080;
        CalculatorClientIO se=new CalculatorClientIO();
        Thread th=new Thread(se);
        th.start();
        try
        {
            ServerSocket ss = new ServerSocket(port);
            while(true)
            {
                Socket socket = ss.accept();
                System.out.println("Есть контакт !");
                DataInputStream in = new DataInputStream(socket.getInputStream());
                DataOutputStream out = new DataOutputStream(socket.getOutputStream());

                String line = in.read ??????;
                System.out.println("Клиент прислал : " + line);

                System.out.println("Отправляем ему в ответ: );
                out.write??????;
                out.flush();
            }
        }
        catch(Exception er)
        {
            er.printStackTrace();
        }
    }
}