package data;
import java.io.Serializable;

public class User implements Serializable {

    /**
     *
     */
    public static final long serialVersionUID = 1L;
    private String username = null;
    private String hashedPassword = null;
    private Integer code = null;
    private String from = null;
    private String to = null;
    private Object data = null;

    public User() {

    }

    public User(Integer code) {
        this.code = code;
    }

    public User(Integer code, Object data) {
        this.code = code;
        this.data = data;
    }

    public User(String username, String hashedPassword, Integer code, String from, String to, Object data) {
        this.username = username;
        this.hashedPassword = hashedPassword;
        this.code = code;
        this.from = from;
        this.to = to;
        this.data = data;
    }

    public Integer getCode() {
        return code;
    }
    // other getters and setters
}

package tankclient;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;
import data.*;

public class Main {
    public static void main(String args[]) {
        Socket socket = null;
        ObjectOutputStream oos = null;
        ObjectInputStream ois = null;
        boolean isConnected = false;
        String ipServer = "localhost";
        int portServer = 4444;
        try {
            // Print("connecting to server...");
            socket = new Socket(ipServer, portServer);
            isConnected = true;
            oos = new ObjectOutputStream(socket.getOutputStream());
            ois = new ObjectInputStream(socket.getInputStream());
            oos.writeObject(new User());
            // Print("connect server success");
        } catch (Exception ex) {
            isConnected = false;
            ex.printStackTrace();
        }
        // DataTransfer transfer = new DataTransfer();
        // //transfer.SendDataRequest(new DataRequest(3));
        // transfer.TestSend();
    }
}

package tankserver;

import data.*;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class Main {

    public static void main(String args[]) {
        ServerSocket serverSocket = null;
        Socket socket = null;
        ObjectOutputStream oos = null;
        ObjectInputStream ois = null;
        boolean isConnected = false;
        int portServer = 4444;
        try {
            System.out.println("waiting for client to connect ...");
            serverSocket = new ServerSocket(portServer);
            socket = serverSocket.accept();
            oos = new ObjectOutputStream(socket.getOutputStream());
            ois = new ObjectInputStream(socket.getInputStream());
            isConnected = true;
            System.out.println("connected");
            User obj = (User) ois.readObject();
            System.out.println(obj.toString());
        } catch (Exception ex) {
            isConnected = false;
            ex.printStackTrace();
        }
        //DataTransfer transfer = new DataTransfer();

        //transfer.GetDataRequest();
        //transfer.TestRecieve();
    }

}