Update a jList that contains user groups to display it to all connected users

Question

In my chat you have the option to create a user group, when a user connects to the chat, this option is available, and the user can create as many groups as he wants and he and other users connected to the chat can enter it, but initially, when there are no groups created yet, and only one user creates one or more groups, these groups will only be shown to other users who have created groups.

I created a button to update the group list, but it is not working. I would like to know if there is any way so that when only one user creates a group, that group will already be displayed to all other users who are connected in the chat.

Some code snippets:

ClientFrame:

package client;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.net.Socket;
import java.util.Set;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JList;
import javax.swing.JOptionPane;
import javax.swing.ListSelectionModel;
import server.ChatMessage;
import server.ChatMessage.Action;
import server.ServerService;

public class ClientFrame extends javax.swing.JFrame {
private Socket socket;
private ChatMessage message;
private ClientService service;

    public ClientFrame()throws IOException { 
      initComponents();
    }
    private class ListenerSocket implements Runnable {    
        private ObjectInputStream input;            
        public ListenerSocket (Socket socket) throws IOException {
            this.input = new ObjectInputStream (socket.getInputStream ());   
        }
        
        @Override
        public void run() {
           try {
            while((message = (ChatMessage) input.readObject()) != null){
               Action action = message.getAction();           
                if(action.equals(action.CONNECT)){
                   connected(message);                                         
                }else if(action.equals(action.USERS_ONLINE)){
                    RefreshOnlines(message);                   
                }else if(action.equals(action.ONLINE_GROUPS)){
                    RefreshOnlinesGroups(message);
                }
            }
        } catch (IOException ex) {
            dispose();
            
         Logger.getLogger (ServerService.class.getName()).log(Level.SEVERE, null, ex);
        } catch (ClassNotFoundException ex) {
            Logger.getLogger (ServerService.class.getName()).log(Level.SEVERE, null, ex);
        }        
        }
        private void connected (ChatMessage message) {
            if (message.getText().equals("NO")) {
            txtName.setText("");
                JOptionPane.showMessageDialog (null, "Connection not made. /n Try another name.");
           return;
            }
            message = message;
            btnConnect.setEnabled(false);
            txtName.setEditable(false);       
            txtNewGroup.setEnabled(true);
            btnCreateGroup.setEnabled(true);
            btnUpdateGroups.setEnabled(true);
            JOptionPane.showMessageDialog (null, "Connection successful");
        }
        private void RefreshOnlines (ChatMessage message) {
        System.out.println (message.getSetOnlines().toString());
            Set <String> names = message.getSetOnlines ();
            names.remove ((String) message.getName ());
            String [] array = (String []) names.toArray (new String [names.size ()]);
            listOnlines.setListData (array);
            listOnlines.setSelectionMode (ListSelectionModel.SINGLE_SELECTION);
            listOnlines.setLayoutOrientation (JList.VERTICAL);
        }
         
          private void RefreshOnlinesGroups (ChatMessage message) {          
           System.out.println (message.getSetOnlinesGroups().toString());
       
           Set <String> namesGroups = message.getSetOnlinesGroups ();
           String [] arrayGroup = (String []) namesGroups.toArray (new String [namesGroups.size ()]);
           listGroups.setListData (arrayGroup);
           listGroups.setSelectionMode (ListSelectionModel.SINGLE_SELECTION);
           listGroups.setLayoutOrientation (JList.VERTICAL);
        }
    }

    
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jScrollPane1 = new javax.swing.JScrollPane();
        jTextArea1 = new javax.swing.JTextArea();
        jButton1 = new javax.swing.JButton();
        jButton2 = new javax.swing.JButton();
        jScrollPane5 = new javax.swing.JScrollPane();
        jList1 = new javax.swing.JList<>();
        jPanel1 = new javax.swing.JPanel();
        txtName = new javax.swing.JTextField();
        btnConnect = new javax.swing.JButton();
        jPanel2 = new javax.swing.JPanel();
        jScrollPane4 = new javax.swing.JScrollPane();
        listOnlines = new javax.swing.JList<>();
        jScrollPane6 = new javax.swing.JScrollPane();
        listGroups = new javax.swing.JList<>();
        btnCreateGroup = new javax.swing.JButton();
        txtNewGroup = new javax.swing.JTextField();
        btnUpdateGroups = new javax.swing.JButton();
        jPanel3 = new javax.swing.JPanel();

        jTextArea1.setColumns(20);
        jTextArea1.setRows(5);
        jScrollPane1.setViewportView(jTextArea1);

        jButton1.setText("jButton1");

        jButton2.setText("jButton2");

        jList1.setModel(new javax.swing.AbstractListModel<String>() {
            String[] strings = { "Item 1", "Item 2", "Item 3", "Item 4", "Item 5" };
            public int getSize() { return strings.length; }
            public String getElementAt(int i) { return strings[i]; }
        });
        jScrollPane5.setViewportView(jList1);

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setResizable(false);

        jPanel1.setBorder(javax.swing.BorderFactory.createLineBorder(new java.awt.Color(0, 0, 0)));

        txtName.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                txtNameActionPerformed(evt);
            }
        });

        btnConnect.setText("Connect");
        btnConnect.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnConnectActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(txtName, javax.swing.GroupLayout.DEFAULT_SIZE, 289, Short.MAX_VALUE)
                .addContainerGap())
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addGap(106, 106, 106)
                .addComponent(btnConnect)
                .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(txtName, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(btnConnect)
                .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
        );

        jPanel2.setBorder(javax.swing.BorderFactory.createLineBorder(new java.awt.Color(0, 0, 0)));

        listOnlines.setSelectionMode(javax.swing.ListSelectionModel.SINGLE_INTERVAL_SELECTION);
        jScrollPane4.setViewportView(listOnlines);

        jScrollPane6.setViewportView(listGroups);

        btnCreateGroup.setText("Create Group");
        btnCreateGroup.setEnabled(false);
        btnCreateGroup.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnCreateGroupActionPerformed(evt);
            }
        });

        txtNewGroup.setEnabled(false);  
        btnUpdateGroups.setText("Update Groups");
        btnUpdateGroups.setEnabled(false);
        btnUpdateGroups.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnUpdateGroupsActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout jPanel2Layout = new javax.swing.GroupLayout(jPanel2);
        jPanel2.setLayout(jPanel2Layout);
        jPanel2Layout.setHorizontalGroup(
            jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel2Layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jScrollPane4, javax.swing.GroupLayout.PREFERRED_SIZE, 95, javax.swing.GroupLayout.PREFERRED_SIZE)                    .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 12, Short.MAX_VALUE)                    .addGroup(jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel2Layout.createSequentialGroup()                            .addGroup(jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)                                .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel2Layout.createSequentialGroup()
                                .addComponent(jScrollPane6, javax.swing.GroupLayout.PREFERRED_SIZE, 141, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addGap(35, 35, 35))
                            .addComponent(txtNewGroup, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.PREFERRED_SIZE, 216, javax.swing.GroupLayout.PREFERRED_SIZE))
                        .addContainerGap())
                    .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel2Layout.createSequentialGroup()                            .addGroup(jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addComponent(btnUpdateGroups)
                            .addComponent(btnCreateGroup))
                        .addGap(63, 63, 63))))
        );
        jPanel2Layout.setVerticalGroup(
            jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel2Layout.createSequentialGroup()
                .addContainerGap()                    .addGroup(jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(jScrollPane4, javax.swing.GroupLayout.PREFERRED_SIZE, 376, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addGroup(jPanel2Layout.createSequentialGroup()
                        .addComponent(jScrollPane6, javax.swing.GroupLayout.PREFERRED_SIZE, 292, javax.swing.GroupLayout.PREFERRED_SIZE)                            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                        .addComponent(txtNewGroup, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)                            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                        .addComponent(btnCreateGroup)                           .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                        .addComponent(btnUpdateGroups)))
                .addGap(0, 14, Short.MAX_VALUE)));    
     jPanel3.setBorder(javax.swing.BorderFactory.createLineBorder(new java.awt.Color(0, 0, 0)));    
            javax.swing.GroupLayout jPanel3Layout = new javax.swing.GroupLayout(jPanel3);
            jPanel3.setLayout(jPanel3Layout);
            jPanel3Layout.setHorizontalGroup(                jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGap(0, 309, Short.MAX_VALUE));
            jPanel3Layout.setVerticalGroup(              jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGap(0, 323, Short.MAX_VALUE));  
            javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
            getContentPane().setLayout(layout);
            layout.setHorizontalGroup(                layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(layout.createSequentialGroup()
                    .addContainerGap()                    .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false).addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                       .addComponent(jPanel3, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))                    .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
             .addComponent(jPanel2, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE).addContainerGap()));
            layout.setVerticalGroup(                layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(layout.createSequentialGroup()
                    .addContainerGap()                    .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING).addComponent(jPanel2, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE).addGroup(layout.createSequentialGroup().addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, 72, javax.swing.GroupLayout.PREFERRED_SIZE)
                            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(jPanel3, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))).addContainerGap()));    
        pack();
    }// </editor-fold>                            
    private void txtNameActionPerformed(java.awt.event.ActionEvent evt) {                                            
    }                                           
    private void btnConnectActionPerformed(java.awt.event.ActionEvent evt) {                                           
       String name = this.txtName.getText ();
        if (! name.isEmpty ()) {
            this.message = new ChatMessage ();
            this.message.setAction (Action.CONNECT);
            this.message.setName (name);    
                this.service = new ClientService();
                try {
                    this.socket = this.service.connect ();
                } catch (IOException ex) {
                    JOptionPane.showMessageDialog(null, "Server not connected");                        Logger.getLogger(ClientFrame.class.getName()).log(Level.SEVERE, null, ex);
                }
                try {
                    new Thread (new ListenerSocket (this.socket)). start ();
                } catch (IOException ex) {                        Logger.getLogger(ClientFrame.class.getName()).log(Level.SEVERE, null, ex);
                }                
            try {
               setTitle(name);
               this.service.send(message);
            } catch (IOException ex) {
                Logger.getLogger (ClientFrame.class.getName()).log(Level.SEVERE, null, ex);
           }
        }
    }                                              
    private void btnCreateGroupActionPerformed(java.awt.event.ActionEvent evt) {                                               
      this.message = new ChatMessage ();
        String newGroup = this.txtNewGroup.getText ();
        if (! newGroup.isEmpty ()) {              
            this.message.setAction (Action.NEW_GROUP);
             this.message.setGroupReserved(newGroup);
              try {
                  this.service.send (this.message);
              } catch (IOException ex) {
                  Logger.getLogger (ClientFrame.class.getName()).log(Level.SEVERE, null, ex);
              }
       }else{
                         JOptionPane.showMessageDialog (null, "Enter a name to create a group");
       }
    }                                                 
    private void btnUpdateGroupsActionPerformed(java.awt.event.ActionEvent evt) {                                                
        this.message = new ChatMessage();        
        this.message.setAction(Action.ONLINE_GROUPS);
    try {
        this.service.send(this.message);
    } catch (IOException ex) {
        Logger.getLogger(ClientFrame.class.getName()).log(Level.SEVERE, null, ex);
    }
    }                                                   
    // Variables declaration - do not modify                     
    private static javax.swing.JButton btnConnect;
    private javax.swing.JButton btnCreateGroup;
    private javax.swing.JButton btnUpdateGroups;
    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    private javax.swing.JList<String> jList1;
    private javax.swing.JPanel jPanel1;
    private javax.swing.JPanel jPanel2;
    private javax.swing.JPanel jPanel3;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JScrollPane jScrollPane4;
    private javax.swing.JScrollPane jScrollPane5;
    private javax.swing.JScrollPane jScrollPane6;
    private javax.swing.JTextArea jTextArea1;
    private javax.swing.JList<String> listGroups;
    private javax.swing.JList<String> listOnlines;
    private javax.swing.JTextField txtName;
    public static javax.swing.JTextField txtNewGroup;
    // End of variables declaration                   
}

ServerService:

    package server;
    import java.io.IOException;
    import java.io.ObjectInputStream;
    import java.io.ObjectOutputStream;
    import java.net.ServerSocket;
    import java.net.Socket;
    import java.util.HashMap;
    import java.util.HashSet;
    import java.util.Map;
    import java.util.Set;
    import java.util.logging.Level;
    import java.util.logging.Logger;
    import javax.swing.JOptionPane;
    import server.ChatMessage.Action;

    public class ServerService {
    private ServerSocket serverSocket;
    private Socket socket;     
    public static Map<String, ObjectOutputStream>mapOnlines = new 
    HashMap<String, ObjectOutputStream>(); 
    private static Map<String, ObjectOutputStream>mapGroup = new 
    HashMap<String, ObjectOutputStream>();   

    public ServerService() throws IOException{
        try{
            serverSocket = new ServerSocket(5555);            
            System.out.println("Server ON");          
        }catch(IOException ex){
            Logger.getLogger(ServerService.class.getName()).log(Level.SEVERE, 
      null, ex);
        }
  
    while(true){
     socket = serverSocket.accept();
    new Thread(new ListenerSocket(socket)).start();
    }
     }
    private class ListenerSocket implements Runnable {

    private ObjectOutputStream output;
    private ObjectInputStream input;
    
    public ListenerSocket(Socket socket) throws IOException{
        this.output = new ObjectOutputStream(socket.getOutputStream());
        this.input = new ObjectInputStream(socket.getInputStream());
    }
        public void run() {
            ChatMessage message = null;
            sendOnlinesGroups();
        try {
            while((message = (ChatMessage) input.readObject()) != null){
                Action action = message.getAction(); 
                
                if(action.equals(action.CONNECT)){
                  boolean  isConnect = connect(message, output);
                  if(isConnect){
                      mapOnlines.put(message.getName(), output);                                    
                      sendOnlines(); 
                  }
                  }else if(action.equals(action.NEW_GROUP)){
                  if(mapGroup.containsKey(message.getGroupReserved())){
                    JOptionPane.showMessageDialog(null, "A group with that 
      name already exists");
                   }else{
                  JOptionPane.showMessageDialog(null, "Successfully created 
      group");    
                  mapGroup.put(message.getGroupReserved(), output);
                  sendOnlinesGroups();
                  }             
                }else if(action.equals(action.ONLINE_GROUPS)){
                    sendOnlinesGroups();
                }
            }
        }catch(IOException ex){               Logger.getLogger(ServerService.class.getName()).log(Level.SEVERE, 
    null, ex);
        } catch (ClassNotFoundException ex){
            Logger.getLogger(ServerService.class.getName()).log(Level.SEVERE, 
      null, ex);
        }
        }  
    }

     private boolean connect(ChatMessage message, ObjectOutputStream output) 
     throws IOException{
    if(mapOnlines.size()== 0){
        message.setText("YES");
        send(message, output);
        return true;
    }
        if(mapOnlines.containsKey(message.getName())){
            message.setText("NO");
            send(message,output);
            return false;
        }else{
            message.setText("YES");
            send(message,output);
            return true;
        }    
     }

    private void send(ChatMessage message, ObjectOutputStream output) throws 
     IOException{
    output.writeObject(message);
     }
    private void sendOnlines(){
    Set<String> setNames = new HashSet<String>();
    for(Map.Entry<String, ObjectOutputStream> kv : mapOnlines.entrySet()){
        setNames.add(kv.getKey());
    }

    ChatMessage message = new ChatMessage();
    message.setAction(Action.USERS_ONLINE);
    message.setSetOnlines(setNames);
    
    for (Map.Entry<String, ObjectOutputStream> kv : mapOnlines.entrySet()){
        message.setName(kv.getKey());
        try{        
        kv.getValue().writeObject(message);
        }catch(IOException ex) {               Logger.getLogger(ServerService.class.getName()).log(Level.SEVERE, 
     null, ex);
        }            
        }       
    }
    private void sendOnlinesGroups(){
    Set<String> setNamesGroups = new HashSet<String>();
    for(Map.Entry<String, ObjectOutputStream> kv : mapGroup.entrySet()){
        setNamesGroups.add(kv.getKey());
    }
    ChatMessage message = new ChatMessage();
    message.setAction(Action.ONLINE_GROUPS);
    message.setSetOnlinesGroups(setNamesGroups);
    for (Map.Entry<String, ObjectOutputStream> kv : mapGroup.entrySet()){
        message.setGroupReserved(kv.getKey());
        try {
        kv.getValue().writeObject(message);
        }catch(IOException ex) {                Logger.getLogger(ServerService.class.getName()).log(Level.SEVERE, 
     null, ex);
        }      
        }        
    }

     public static boolean criarGrupo(){    
    ChatMessage message = new ChatMessage();
    if(mapGroup.containsKey(message.getGroupReserved())){
        JOptionPane.showMessageDialog(null, "A group with that name already 
     exists");
        return false;
    }else{
        JOptionPane.showMessageDialog(null, "Successfully created group");
        return true;
    }
    }
    }

ChatMessage:

      package server;
      import java.io.Serializable;
      import java.util.HashSet;
      import java.util.Set;

    public class ChatMessage implements Serializable{
    String name;
    private Set<String> setOnlinesGroups = new HashSet<String>();
    String groupReserved;   
    String text; 
    private String nameReserved;
    private Set<String> setOnlines = new HashSet<String>();   
    private Set<String> setOnlinesPrivate = new HashSet<String>();   
    private Action action;
    
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    public String getText() {
        return text;
    }
    public void setText(String text) {
        this.text = text;
    }
    public String getNameReserved() {
        return nameReserved;
    }
    public void setNameReserved(String nameReserved) {
        this.nameReserved = nameReserved;
    }
    public Action getAction() {
        return action;
    }

    public void setAction(Action action) {
       this.action = action;
    }
    
    public Set<String> getSetOnlines() {
        return setOnlines;
    }

    public void setSetOnlines(Set<String> setOnlines) {
        this.setOnlines = setOnlines;
    }

    public Set<String> getSetOnlinesPrivate() {
        return setOnlinesPrivate;
    }

    public void setSetOnlinesPrivate(Set<String> setOnlinesPrivate) {
        this.setOnlinesPrivate = setOnlinesPrivate;
    }

    public Set<String> getSetOnlinesGroups() {
        return setOnlinesGroups;
    }

    public void setSetOnlinesGroups(Set<String> setOnlinesGroups) {
        this.setOnlinesGroups = setOnlinesGroups;
    }
    public String getGroupReserved() {
        return groupReserved;
    }

    public void setGroupReserved(String groupReserved) {
        this.groupReserved = groupReserved;
    }
    public enum Action {
    CONNECT,DISCONNECT,SEND_ONE,SEND_ONE2, 
    SEND_ALL,USERS_ONLINE,ONLINE_GROUPS,NEW_GROUP,REMOVE_GROUP,SEND_GROUP,
    } 
     }

Client:

    package client;  
    import java.io.IOException;
    import java.util.logging.Level;
    import java.util.logging.Logger;

    public class Client {
    public static void main(String args[]) {   
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    new ClientFrame().setVisible(true);
                } catch (IOException ex) {
                    Logger.getLogger(Client.class.getName()).log(Level.SEVERE, 
        null, ex);
                }
            }
        });
    }
      }

ClientService:

    package client;
    import java.io.IOException;
    import java.io.ObjectOutputStream;
    import java.net.Socket;
    import server.ChatMessage;
    public class ClientService {
    private Socket socket;
    private ObjectOutputStream output;
    public static int hostt;
    
    public Socket connect() throws IOException{
        this.socket = new Socket("localhost",5555);
        this.output = new ObjectOutputStream(socket.getOutputStream());
        return socket;            
        }
    public void send(ChatMessage message) throws IOException{
     output.writeObject(message);
    } 
    }

Server:

package server;
import java.io.IOException;
public class Server {
public static void main(String[] args) throws IOException {
new ServerService();
}
}

what is this.service? your code is not well format and It is not useful for the problem described. There is not JList in your list, or some implementation of List — vincenzopalazzo, May 15 '21 at 23:49
@vincenzopalazzo: it looks like the OP may be updating the JList's model within the `RefreshOnlinesGroups(...)` method. To Andre, your code appears to have potential Swing-threading issues in that you call methods that appear to mutate Swing GUI state, but does so off of the event dispatch thread. I don't know if this is contributing to your problem or not. My big problem is to not have runnable code to test or play with. Consider creating a [mre] or code as close to a MRE as possible and posting it, code we can run, test and modify. — Hovercraft Full Of Eels, May 15 '21 at 23:52
@Hovercraft Full Of Eels, excuse. That was the first question I asked at StackOverFlow. I will edit and post the complete code so that I can test it. — Andre, May 16 '21 at 00:03
I'm not sure that the full code will fit or be allowed, and it is certainly not what we want or need. No, instead best for you to try to create and post the [mre] (please check out the link to this valuable tool). — Hovercraft Full Of Eels, May 16 '21 at 00:05
@Hovercraft Full Of Eels ,i edited the code, removing features from the program that are not relevant to my question Now the code can be run for testing. — Andre, May 16 '21 at 02:03
@vincenzopalazzo, sorry, this is my first question here at StackOverFlow. Now I have edited the code so that it is executable. — Andre, May 16 '21 at 02:06
Your question is too complex in terms of code, and your GUI code is the Netbinse code, this means that is out of the Java guide line. This is a little bit frustrating because the reader can have not accessed this question. No, all people are able to read the text as normal people. But any way I can't change the world with this comment — vincenzopalazzo, May 16 '21 at 10:36
@Abra I means the Java Guide line of the code style. For people that have problem in to read like dyslexia the formatting code is very important — vincenzopalazzo, May 16 '21 at 10:59
@Abra The GroupLayout is under the Java JDK but the method on how it is used is not very readable at all because it is autogenerated from Netbeans and this means that inside this initComponents there is code to change the Layout, code to change the color of component and method to change the model of UI. In fact, the bug in this answer is that the List model is used from netbinse and not from the programmer. Maybe it don't know that the list has a model. — vincenzopalazzo, May 16 '21 at 11:03
@vincenzopalazzo I use Netbeans. I use it in a way such that it never generates the code. As to the formatting, I agree it's not well formatted and that also messes with my ability to read it. I need to load it into an IDE and do a quick format before it becomes comprehensible. **OP:** In Netbeans, use `Ctrl` + `Shift` + `F` to have it auto format code. — Andrew Thompson, May 16 '21 at 11:35

vincenzopalazzo · Answer 1 · 2021-05-16T11:08:54.487

Before proposing the solution to this problem I want to add a small comment that the code that you post is in bad format and it is too complex, so my understanding of the problem can be wrong.

Possible solution

During the reading of your code, I noted that your service performs an action, like that

public void send(ChatMessage message) throws IOException {
   output.writeObject(message);
}

This action doesn't throw any propriety change, read here for more details How to use propriety change listener in Java.

Another simple solution is to change the code in your JFrame and add some code like the following one in your update action.

private void btnUpdateGroupsActionPerformed(java.awt.event.ActionEvent evt) {                                                
    this.message = new ChatMessage();        
    this.message.setAction(Action.ONLINE_GROUPS);
    try {
       this.service.send(this.message);
       this.jList1.add(this.message.toString()); // This in according with your ListModel
       this.jList1.updateUI(); // Usually this is enough, you it not work, try revalidate();
    } catch (IOException ex) {
        Logger.getLogger(ClientFrame.class.getName())
                .log(Level.SEVERE, null, ex);
    }
}

Critical comments

This question looks like a university project, and there is nothing wrong with that, the thing that I don't agree with is that your problem is "How to use the JList in Swing" and not "My JList View is not working with the update".

I'm saying that because I know that a lot of university use Netbinse as an example of Java Beans and it only use the UI to autogenerate the code, without help the people to understand how in reality work a Java Framework as Swing.

Your code generator hides one of the most important concepts in Swing, that is the Model of one component like JList, JTree e so on.

    jList1.setModel(new javax.swing.AbstractListModel<String>() {
        String[] strings = { "Item 1", "Item 2", "Item 3", "Item 4", "Item 5" };
        public int getSize() { return strings.length; }
        public String getElementAt(int i) { return strings[i]; }
    });

This is your bug! You need to create the model for JList and use that to update.

More details on how to add a component in the JList

@Andre there are three types of change proposed in this post. without a minimal runnable example, I can not propose a solution that works for your case. This post suggests you only some possible changes to solve your problem. — vincenzopalazzo, May 16 '21 at 14:09
@vincenzopalazzo, regarding the first change, the send method has the function of making the user connect to the chat, unrelated to the problem I am having. In the second change, if I add the line this.jList1.add(this.message.toString ()) to the code, it gives an error. In the third change, I created a DefaultListModel model = new DefaultListModel in the RefreshOnlinesGroups method of the ClientFrame class, using a for and using the model.addElement (arrayGroup [i]) line inside the for to add the elements, and at the end I use a listGroups.setModel(model), but is not updating. — Andre, May 16 '21 at 14:34
without a runnable code, I can't help you sorry. If you can reproduce the error in a minimal example, I will fix the error that you find in my answer. I know that this work because I use this logic in on of my library, but I'm read to have some proof that my code don't work — vincenzopalazzo, May 16 '21 at 15:01

Update a jList that contains user groups to display it to all connected users

1 Answers1

Possible solution

Critical comments