Problemas com JList

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package chat;

import java.awt.event.KeyEvent;
import javax.swing.DefaultListModel;
import javax.swing.JTextField;

/**
 *
 * @author moska
 */
public class ChatWindow extends javax.swing.JFrame {

    /**
     * Creates new form ChatWindow
     */
    public ChatWindow() {
        initComponents();
    }

    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jPanel1 = new javax.swing.JPanel();
        lblChat = new javax.swing.JLabel();
        lblCursor = new javax.swing.JLabel();
        jScrollPane1 = new javax.swing.JScrollPane();
        lstCompletion = new javax.swing.JList();
        txtChat = new javax.swing.JTextField();
        txtChat.setFocusTraversalKeysEnabled(false);

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jPanel1.setBorder(javax.swing.BorderFactory.createTitledBorder("Chat"));

        lblChat.setText("Chat");

        lblCursor.setText("Cursor");

        lstCompletion.setSelectionMode(javax.swing.ListSelectionModel.SINGLE_SELECTION);
        jScrollPane1.setViewportView(lstCompletion);

        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()
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(lblChat)
                    .addComponent(lblCursor))
                .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
                .addContainerGap(343, Short.MAX_VALUE)
                .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 68, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap())
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(lblChat)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(lblCursor)
                .addGap(21, 21, 21)
                .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 125, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
        );

        txtChat.addKeyListener(new java.awt.event.KeyAdapter() {
            public void keyPressed(java.awt.event.KeyEvent evt) {
                txtChatKeyPressed(evt);
            }
        });

        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)
                    .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addComponent(txtChat))
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(txtChat, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(20, Short.MAX_VALUE))
        );

        pack();
    }// </editor-fold>                        
    
    private void autoCompletion(int carretPosition) {
        String fullText = txtChat.getText();
        int textSize = fullText.length();
        
        DefaultListModel completion = (DefaultListModel) lstCompletion.getModel();
        
        completion.addElement("teste1");
        completion.addElement("teste2");
        
    }
    
    private void txtChatKeyPressed(java.awt.event.KeyEvent evt) {                                   
        int key = evt.getKeyCode();
        switch (key) {
            case KeyEvent.VK_ENTER:
                lblChat.setText(txtChat.getText());
                txtChat.setText(null);
                break;
            case KeyEvent.VK_TAB:
                lblCursor.setText("Tab!");
                autoCompletion(txtChat.getCaretPosition());
                break;
        }
    }                                  

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(ChatWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(ChatWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(ChatWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(ChatWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                new ChatWindow().setVisible(true);
            }
        });
    }
    // Variables declaration - do not modify                     
    private javax.swing.JPanel jPanel1;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JLabel lblChat;
    private javax.swing.JLabel lblCursor;
    private javax.swing.JList lstCompletion;
    private javax.swing.JTextField txtChat;
    // End of variables declaration                   
}

Erro:

Exception in thread “AWT-EventQueue-0” java.lang.ClassCastException: javax.swing.JList$3 cannot be cast to javax.swing.DefaultListModel

at chat.ChatWindow.autoCompletion(ChatWindow.java:113)

at chat.ChatWindow.txtChatKeyPressed(ChatWindow.java:129)

at chat.ChatWindow.access$000(ChatWindow.java:15)

at chat.ChatWindow$1.keyPressed(ChatWindow.java:81)

at java.awt.Component.processKeyEvent(Component.java:6094)

at javax.swing.JComponent.processKeyEvent(JComponent.java:2801)

at java.awt.Component.processEvent(Component.java:5913)

at java.awt.Container.processEvent(Container.java:2105)

at java.awt.Component.dispatchEventImpl(Component.java:4497)

at java.awt.Container.dispatchEventImpl(Container.java:2163)

at java.awt.Component.dispatchEvent(Component.java:4323)

at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1860)

at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:749)

at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:1025)

at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:892)

at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:713)

at java.awt.Component.dispatchEventImpl(Component.java:4367)

at java.awt.Container.dispatchEventImpl(Container.java:2163)

at java.awt.Window.dispatchEventImpl(Window.java:2478)

at java.awt.Component.dispatchEvent(Component.java:4323)

at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:649)

at java.awt.EventQueue.access$000(EventQueue.java:96)

at java.awt.EventQueue$1.run(EventQueue.java:608)

at java.awt.EventQueue$1.run(EventQueue.java:606)

at java.security.AccessController.doPrivileged(Native Method)

at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:105)

at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:116)

at java.awt.EventQueue$2.run(EventQueue.java:622)

at java.awt.EventQueue$2.run(EventQueue.java:620)

at java.security.AccessController.doPrivileged(Native Method)

at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:105)

at java.awt.EventQueue.dispatchEvent(EventQueue.java:619)

at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:275)

at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:200)

at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190)

at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:185)

at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:177)

at java.awt.EventDispatchThread.run(EventDispatchThread.java:138)