Utilizando sockets para troca de mensagens. Lembrando que através dos Streams ObjectInputStream  & ObjectOutputStream é possível transmitir objetos pela rede.

--- Arquivo Client.java -----------------------

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStreamReader;

import java.io.PrintWriter;

import java.net.Socket;

public class Client

{

      public static void main(String[] args) throws IOException{

            Socket conexao = new Socket("127.0.0.1", 4444);

            BufferedReader in = new BufferedReader(new InputStreamReader(conexao.getInputStream()));

            PrintWriter out = new PrintWriter(conexao.getOutputStream());

           

           

            out.println("Sou o cliente");

            out.flush();

           

            String veioDoServidor = in.readLine();

            System.out.println("Servidor ->"+veioDoServidor);

           

           

            in.close();

            out.close();

      }

 

}

 

----- Arquivo  SocketServer.java ------------------

import java.io.BufferedReader;

import java.io.DataInputStream;

import java.io.InputStreamReader;

import java.io.PrintWriter;

import java.net.ServerSocket;

import java.net.Socket;

 

 

public class SocketServer

{

     

      public static void main(String[] args) throws Exception {

           

            //Criando um socket modo servidor              porta que vai escutar

            ServerSocket socketServer = new ServerSocket(4444);

           

            //Recebendo conexão de cliente

            while(true)

            {

                  Socket conexaoClient = socketServer.accept();

                  BufferedReader in = new BufferedReader(new InputStreamReader(conexaoClient.getInputStream()));

                  PrintWriter out = new PrintWriter(conexaoClient.getOutputStream());

                 

                 

                  String veioDoCliente = in.readLine();

                  System.out.println("Cliente ->"+veioDoCliente);

                 

                  out.println("Sou o servidor");

                  out.flush();

                  in.close();

                  out.close();

            }

           

      }

}

 

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