Problem with socket object writing

Question

hi,
I made this little programm , with a class point , a server and a client.
I try to send via the socket several point object.
If send differents objects ( with several new point(... )) it works fine , but if i send the same object changing only the properties it doesn't work. Changing are not applicate.
Here is the code.
// POINT
import java.io.Serializable;
import java.awt.*;
public class point implements Serializable{
    private int x_;
    private int y_;
    private Color c_;
    public point(int x, int y, Color c) {
       x_=x;
       y_=y;
       c_=c;
    public int get_x() { return x_ ; }
    public int get_y() { return y_ ; }
    public void set_x(int x) { x_=x ; }
    public void set_y(int y) { y_=y ; }
    public Color get_color() { return c_ ; }
// SERVER
import java.io.*;
import java.net.*;
public class s {
    public s()
        try
            ServerSocket server = new java.net.ServerSocket(80);
            java.net.Socket client  = server.accept();
            ObjectInputStream Istream_ = new ObjectInputStream(client.getInputStream());
            ObjectOutputStream Ostream_ = new ObjectOutputStream(client.getOutputStream());
            for(int i=0;i<4;i++)
                point p_read = (point)Istream_.readObject();
                System.out.print("x="+p_read.get_x());
                System.out.println(" y="+p_read.get_y());
         catch (Exception exception) { exception.printStackTrace(); }
    public static void main(String args[])
     s s_ = new s();
// CLIENT
import java.io.*;
import java.net.*;
import java.awt.*;
public class c {
    public c()
        try
            ipJDialog ipjd = new ipJDialog();
            String ip = ipjd.getvalue();
            Socket socket  = new Socket(ip,80);
            System.out.println("connection avec serveur reussi");
            ObjectOutputStream Ostream_ = new ObjectOutputStream(socket.getOutputStream());
            ObjectInputStream Istream_ = new ObjectInputStream(socket.getInputStream());
            point p1 = new point(50,50, new Color(255,0,0));
            Ostream_.writeObject(p1);
            point p2 = new point(22,30, new Color(255,0,0));
            Ostream_.writeObject(p2);
            point p3 = new point(8,7, new Color(255,0,0));
            Ostream_.writeObject(p3);
            point p4 = new point(2,1, new Color(255,0,0));
            Ostream_.writeObject(p4);
         catch (Exception exception) {exception.printStackTrace();}
    public static void main(String args[])
     c c_ = new c();
// DIALOG TO GET IP FROM INPUTBOX
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
public class ipJDialog extends JDialog implements ActionListener {
    private String ip_;
    private JTextArea jta_;
    private JTextField jtf_;
    private JButton jb1_;
    public ipJDialog()
        this.getContentPane().setLayout(null);
        this.setTitle("Entrez l'IP du serveur");
        this.setSize(220,100);
        this.setModal(true);
        ip_= "localhost";
        jta_ = new JTextArea("IP du serveur :");
        jta_.setBounds(10,5, 90,20);
        jta_.setOpaque(false);
        jta_.setEditable(false);
        getContentPane().add(jta_);
        jtf_ = new JTextField();
        jtf_.setBounds(110,5, 90,20);
        jtf_.requestFocus();
        getContentPane().add(jtf_);
        jb1_ = new JButton("OK");
        jb1_.setBounds(10,30, 90,30);
        jb1_.addActionListener(this);
        getContentPane().add(jb1_);
        this.setVisible(true);
    public String getvalue() { return ip_ ; }
    public void actionPerformed(ActionEvent evt)
        String ChoixOption = evt.getActionCommand();
     if(ChoixOption.equals("OK"))
            ip_=jtf_.getText();
            this.setVisible(false);
if I replace in client :
         point p1 = new point(50,50, new Color(255,0,0));
            Ostream_.writeObject(p1);
            point p2 = new point(22,30, new Color(255,0,0));
            Ostream_.writeObject(p2);
            point p3 = new point(8,7, new Color(255,0,0));
            Ostream_.writeObject(p3);
            point p4 = new point(2,1, new Color(255,0,0));
            Ostream_.writeObject(p4);
by :
         point p = new point(50,50, new Color(255,0,0));
            Ostream_.writeObject(p);
            p.set_x(20);
            p.set_x(22);
            Ostream_.writeObject(p);
            p.set_x(55);
            p.set_x(32);
            Ostream_.writeObject(p);
            p.set_x(14);
            p.set_x(88);
            Ostream_.writeObject(p);
I doesn't work , i receive a point with 50,50 ( the first one ) four times ...If you can explain me me why and what can I do ...
Thx.

Answer 1

For ObjectOutputStream, multiple references to a single object are encoded using a reference sharing mechanism so that graphs of objects can be restored to the same shape as when the original was written. State of a object will be recorded so that the ObjectOutputStream doesn't writes the same object to the outputstream when the object was refered by multiple references. So, when you tried to write the same object agains into the ObjectOutputStream, the ObjectOutputStream doesn't write the object, but passed the as a reference to the outputstream... In this case, on the other side, the ObjectInputStream will receive this reference and it will return the reference of this object (which is previous created when this object was passed over on the 1st time). This caused the ObjectInputStream will return a "unchanged" object even your object have changed before you write it agains to the ObjectOutputStream.
My explaination maybe not that good... hope you can understand... :)