Swing error ClassCastException

Question

This is the Code I typed

// loading all distict age on to list bix from student table
 private void b1ActionPerformed(java.awt.event.ActionEvent evt) {                                   
DefaultTableModel tb = (DefaultTableModel)tb1.getModel();
tb.setRowCount(0);
String sql = "select * from student";
try
{
Class.forName("java.sql.Driver");
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/info","root","");  
Statement s = con.createStatement();
ResultSet rs = s.executeQuery(sql);
while(rs.next())
{
    int s_rno = rs.getInt(1);
    String s_name = rs.getString(2);
    int s_age = rs.getInt(3);
    double s_marks = rs.getDouble(4);
    tb.addRow(new Object[]{s_rno, s_name, s_age, s_marks});
    tb1.setModel(tb);
}
rs.close();
s.close();
con.close();
}
catch(Exception e)
{
    JOptionPane.showMessageDialog(this, e.getMessage());
}        
}

And when I run the program, the GUI appears, but on pressing the button, nothing happens, and there is the following error on my output window

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: JDBC2$2 cannot be cast to javax.swing.DefaultListModel at JDBC2.b1ActionPerformed(JDBC2.java:74) at JDBC2.access$000(JDBC2.java:9) at JDBC2$1.actionPerformed(JDBC2.java:36) at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022) at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348) at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402) at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252) at java.awt.Component.processMouseEvent(Component.java:6535) at javax.swing.JComponent.processMouseEvent(JComponent.java:3324) at java.awt.Component.processEvent(Component.java:6300) at java.awt.Container.processEvent(Container.java:2236) at java.awt.Component.dispatchEventImpl(Component.java:4891) at java.awt.Container.dispatchEventImpl(Container.java:2294) at java.awt.Component.dispatchEvent(Component.java:4713) at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888) at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466) at java.awt.Container.dispatchEventImpl(Container.java:2280) at java.awt.Window.dispatchEventImpl(Window.java:2750) at java.awt.Component.dispatchEvent(Component.java:4713) at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758) at java.awt.EventQueue.access$500(EventQueue.java:97) at java.awt.EventQueue$3.run(EventQueue.java:709) at java.awt.EventQueue$3.run(EventQueue.java:703) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76) at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86) at java.awt.EventQueue$4.run(EventQueue.java:731) at java.awt.EventQueue$4.run(EventQueue.java:729) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76) at java.awt.EventQueue.dispatchEvent(EventQueue.java:728) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93) at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

I need more help , how i can comprehend the error.

Can you replace this statement Class.forName("java.sql.Driver"); with this statement DriverManager.registerDriver(new com.mysql.jdbc.Driver()); and let me know the status? — N00b Pr0grammer
@N00bPr0grammer Why? Neither is necessary, and neither has anything to do with the exception. — user207421
@OP Which is line 74? And Class.forName("java.sql.Driver"); accomplishes nothing and should be removed, and Netbeans has nothing to do with it. — user207421

Joop Eggen Joop Eggen · Accepted Answer · 2016-09-13T16:00:01

Look at line 74; that must be where the error happens.

You are doing a bit of heavy work when the action event is handled. The following postpones this a bit by invokeLater so that at least the immediate GUI response is visible.

I have corrected the usage of the table model a bit. Still a bit too many messages will be fired.

private void b1ActionPerformed(java.awt.event.ActionEvent evt) {
    SwingUtilities.invokeLater(new Runnable() {

        @Override
        public void run() {
            DefaultTableModel tb = (DefaultTableModel) tb1.getModel();
            tb.setRowCount(0);
            String sql = "select * from student";
            try (Connection con = DriverManager.getConnection("jdbc:...", "...", "");
                    Statement s = con.createStatement();
                    ResultSet rs = s.executeQuery(sql)) {
                while (rs.next()) {
                    int s_rno = rs.getInt(1);
                    String s_name = rs.getString(2);
                    int s_age = rs.getInt(3);
                    double s_marks = rs.getDouble(4);
                    tb.addRow(new Object[] { s_rno, s_name, s_age, s_marks });
                }
            } catch (SQLException e) {
                JOptionPane.showMessageDialog(this, e.getMessage());
            }
        }
    });
}

Where it might happen is:

            DefaultTableModel tb = (DefaultTableModel) tb1.getModel();

(Is this line 74?)

In general it might be better to create a new DefaultTableModel (AbstractTableModel?), and at the end of the method do tb1.setModel(tb).

By the way there are already TableModels for ResultSets in the net.

Swing error ClassCastException

1 Answers