Listing 1.
import java.rmi.*;
public interface Talker extends Remote {
  public String getName() throws RemoteException;
  public void recvMsg(String from, String msg) throws RemoteException;
  public void add(Talker talker) throws RemoteException;
  public void remove(Talker talker) throws RemoteException;
}

Listing 2.
import java.rmi.*;
public interface TalkerServer extends Remote {

  public void register(Talker talker) throws RemoteException;
  public void unRegister(Talker talker) throws RemoteException;
  public Talker[] lookup() throws RemoteException;
  public void shutdown() throws RemoteException;
}

Listing 3.
import java.rmi.*;
import java.rmi.server.UnicastRemoteObject;
import java.rmi.registry.LocateRegistry;
import java.util.*;

public class TalkerServerImpl extends UnicastRemoteObject implements TalkerServer {

  private Vector v = new Vector();

  public TalkerServerImpl() throws RemoteException {
    super();
  }

  public synchronized void register(Talker talker) throws RemoteException {
    if (!v.contains(talker)) {
      v.addElement(talker);
      for (int i = 0; i < v.size(); i++)
        ((Talker)v.elementAt(i)).add(talker);
    }
  }

  public synchronized void unRegister(Talker talker) throws RemoteException {
    for (int i = 0; i < v.size(); i++)
      ((Talker)v.elementAt(i)).remove(talker);
    v.removeElement(talker);
  }

  public synchronized Talker[] lookup() throws RemoteException {
    Talker[] talkers = new Talker[v.size()];
    v.copyInto(talkers);
    return talkers;
  }

  public void shutdown() throws RemoteException {
    System.exit(0);
  }

  public static void main(String args[]) {

    System.setSecurityManager(new RMISecurityManager());

    try {
      System.out.println("TalkerServer.main: creating registry");
      LocateRegistry.createRegistry(2006);

      System.out.println("TalkerServer.main: creating server");
      TalkerServerImpl talkerServer = new TalkerServerImpl();

      System.out.println("TalkerServer.main: binding server");
      Naming.rebind("//:2006/TalkerServer", talkerServer);

      System.out.println("TalkerServer.main: done");
    } catch (Exception ex) {
      System.err.println("TalkerServer.main: exception: " + ex.getMessage());
      ex.printStackTrace();
    }

  }

}

Listing 4.
import java.rmi.*;
import java.rmi.server.UnicastRemoteObject;

class TalkerImpl extends UnicastRemoteObject implements Talker {

  private TalkerApplet applet;
  private String name;

  public TalkerImpl(TalkerApplet applet, String name) throws RemoteException {
    this.applet = applet;
    this.name = name;
  }

  public String getName() throws RemoteException {
    return name;
  }

  public void recvMsg(String from, String msg) throws RemoteException {
    applet.addToMsg(from, msg);
  }

  public void add(Talker talker) throws RemoteException {
    applet.addTalker(talker, talker.getName());
  }

  public void remove(Talker talker) throws RemoteException {
    applet.removeTalker(talker, talker.getName());
  }

}

Listing 5.
import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.net.*;
import java.rmi.*;
import java.util.*;

public class TalkerApplet extends Applet {

  class StartListener implements ActionListener {
    TalkerApplet applet;
    public StartListener(TalkerApplet applet) {
      this.applet = applet;
    }
    public void actionPerformed(ActionEvent ev) {
      field.setEditable(false);
      start.setEnabled(false);
      stop.setEnabled(true);
      try {
        initList();
        talker = new TalkerImpl(applet, field.getText());
        server.register(talker);
      } catch (Exception ex) {
      }
    }
  }

  class StopListener implements ActionListener {
    public void actionPerformed(ActionEvent ev) {
      field.setEditable(true);
      start.setEnabled(true);
      stop.setEnabled(false);
      try {
        server.unRegister(talker);
        talker = null;
      } catch (Exception ex) {
      }
    }
  }

  class ShutdownListener implements ActionListener {
    public void actionPerformed(ActionEvent ev) {
      shutdown.setEnabled(false);
      try {
        server.shutdown();
      } catch (Exception ex) {
      }
    }
  }

  class TextAreaListener extends KeyAdapter {
    public void keyReleased(KeyEvent ev) {
      String s;
      String s1;
      String s2;
      int i1;
      int i2;
      if (talker != null && ev.getKeyCode() == KeyEvent.VK_ENTER) {

        // send the last line of text
        s1 = senderText.getText();
        i1 = s1.lastIndexOf('\n');
        if (i1 == 0) s = s1;
        else {
          s2 = s1.substring(0, i1);
          i2 = s2.lastIndexOf('\n');
          if (i2 == -1) s = s1;
          else s = s2.substring(i2+1, s2.length()) + '\n';
        }

        // and send it!!
        String[] names = list.getSelectedItems();
        for (int i = 0; i < names.length; i++)
          for (int j = 0; j < talkersNames.size(); j++)
            if (names[i].equals((String)talkersNames.elementAt(j))) {
              try {
                ((Talker)talkers.elementAt(j)).recvMsg(field.getText(), s);
              } catch (RemoteException ex) {
              }
            }
      }
    }
  }

  Button start, stop, shutdown;
  TextField field;
  List list;
  TextArea receiverText;
  TextArea senderText;
  TalkerImpl talker;
  TalkerServer server;
  java.util.Vector talkers = new java.util.Vector();
  java.util.Vector talkersNames = new java.util.Vector();

  public void init() {

    try {
      server = (TalkerServer)Naming.lookup("//pluto:2006/TalkerServer");
    } catch (Exception ex) {
      ex.printStackTrace();
      return;
    }

    setSize(550, 450);

    GridBagLayout layout = new GridBagLayout();
    GridBagConstraints c = new GridBagConstraints();
    c.anchor = GridBagConstraints.NORTHWEST;
    c.insets = new Insets(4, 4, 4, 4);

    Panel p1 = new Panel();
    p1.setLayout(layout);

    c.gridx = 0; c.gridy = 0;
    Label label1 = new Label("Name:");
    layout.setConstraints(label1, c);
    p1.add(label1);

    c.gridx = 1;
    field = new TextField(15);
    layout.setConstraints(field, c);
    p1.add(field);

    c.gridx = 0; c.gridy = 1;
    Label label2 = new Label("Talk to:");
    layout.setConstraints(label2, c);
    p1.add(label2);

    c.gridx = 1;
    list = new List(5, false);
    list.setMultipleMode(true);
    layout.setConstraints(list, c);
    p1.add(list);

    c.gridx = 0; c.gridy = 2;
    Label sender = new Label("Send message:");
    layout.setConstraints(sender, c);
    p1.add(sender);

    c.gridx = 1;
    senderText = new TextArea(5, 50);
    senderText.addKeyListener(new TextAreaListener());
    layout.setConstraints(senderText, c);
    p1.add(senderText);

    c.gridx = 0; c.gridy = 3;
    Label receiver = new Label("Receive message:");
    layout.setConstraints(receiver, c);
    p1.add(receiver);

    c.gridx = 1;
    receiverText = new TextArea(5, 50);
    layout.setConstraints(receiverText, c);
    p1.add(receiverText);

    Panel p2 = new Panel();
    p2.setLayout(new FlowLayout(FlowLayout.CENTER));
    start = new Button("Start");
    start.addActionListener(new StartListener(this));
    p2.add(start);
    stop = new Button("Stop");
    stop.setEnabled(false);
    stop.addActionListener(new StopListener());
    p2.add(stop);
    shutdown = new Button("Shutdown Server");
    shutdown.addActionListener(new ShutdownListener());
    p2.add(shutdown);

    add(p1);
    add(p2);
    initList();

  }

  void initList() {
    Talker[] talkersArray;
    try {
      talkersArray = server.lookup();
    } catch (RemoteException ex) {
      ex.printStackTrace();
      return;
    }
    list.removeAll();
    talkers.removeAllElements();
    talkersNames.removeAllElements();
    for (int i = 0; i < talkersArray.length; i++) {
      try {
        list.add(talkersArray[i].getName());
        talkers.addElement(talkersArray[i]);
        talkersNames.addElement(talkersArray[i].getName());
      } catch (RemoteException ex) {
      }
    }
  }

  public void addToMsg(String from, String msg) {
    receiverText.append(from + ": " + msg);
  }

  public void addTalker(Talker talker, String name) {
    list.add(name);
    talkers.addElement(talker);
    talkersNames.addElement(name);
  }

  public void removeTalker(Talker talker, String name) {
    list.remove(name);
    talkers.removeElement(talker);
  }

}