Client

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.Scanner;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Client {

    public static void main(String[] args) {

        try {
            Socket s = new Socket("localhost",2009);

            Scanner input = new Scanner(System.in);

            System.out.println("Donner un nombre");

            double number = input.nextDouble();

            DataOutputStream out = new DataOutputStream(s.getOutputStream());

            out.writeDouble(number);

            /*
            OutputStreamWriter out = new OutputStreamWriter(s.getOutputStream());
            PrintWriter pw = new PrintWriter(out);

            pw.write(number);
            out.flush();
            */

            DataInputStream in = new DataInputStream(s.getInputStream());

            double data = in.readDouble();
            /*
            BufferedReader br = new BufferedReader(new InputStreamReader(s.getInputStream()));
            int data = br.read();
            */
            System.out.println("Le resultat est "+data);

            s.close();

        } catch (IOException ex) {
            Logger.getLogger(Client.class.getName()).log(Level.SEVERE, null, ex);
        }


    }

}