Inheritance In Swing

Question

Hi,
I have a confusion in understanding the behaviour of below code
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
public class Test extends JPanel
     private static final String butHireLabel = "Hire";
     private static final String butFireLabel = "Fire";
     private JButton butFire;
     private JButton butHire;
     private JTextField txtEmployeeName;
     public Test()
          super(new BorderLayout());
          butHire = new JButton(butHireLabel);
          butHire.setEnabled(false);
          butFire = new JButton(butFireLabel);
          txtEmployeeName = new JTextField(10);
          //Create a panel that uses BoxLayout.
        JPanel buttonPane = new JPanel();
        buttonPane.setLayout(new BoxLayout(buttonPane,
                                           BoxLayout.LINE_AXIS));
        buttonPane.add(butFire);
        buttonPane.add(Box.createHorizontalStrut(5));
        //buttonPane.add(new JSeparator(SwingConstants.VERTICAL));
        buttonPane.add(txtEmployeeName);
        buttonPane.add(Box.createHorizontalStrut(5));
        buttonPane.add(butHire);
        buttonPane.setBorder(BorderFactory.createEmptyBorder(5,5,5,5));
        add(buttonPane, BorderLayout.PAGE_END);          
     public static void createAndShowGUI()
          //Window decoration
          JFrame.setDefaultLookAndFeelDecorated(true);
          //Create and setup window
          JFrame frame = new JFrame("List Demo");
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          //Create and setup window pane
          JComponent newContentPane = new Test();          newContentPane.setOpaque(true);
          frame.setContentPane(newContentPane);
          //Display window
          frame.pack();
          frame.setVisible(true);
     public static void main(String[] args)
          // Schedule a job for event-dispatching thread
          // Creating and displaying this application GUI
          javax.swing.SwingUtilities.invokeLater(new Runnable()
               public void run()
                    createAndShowGUI();
When I extend JFrame the code marked bold gives type casting error.
This may be very trivial but as I am in the learning stage I cannot understand the behaviour.
Thanks,
Reena

Answer 1

Sorry the line of error wasn't clear in my previous post.
When JFrame is extended instead of JPanel in the above code the typecasting error is generated at below line
JComponent newContentPane = new Test();
Thanks,
Reena