Java.lang.NoSuchMethodError: main Exception in thread main

Question

I am a student currently trying to teach myself java with the aid of sams teach yourself java book, but whilst doing one of the examples I have become stuck.
I get the message that I have posted as the subject title, the book is designed to use java 2 with netbeans 4.0 java 1.5 I think which I guess the code is written for,
but at uni they have netbeans 3.6 java 1.4 so we have been advised to use this so there is no problems when working on the same projects and uni and at home,
anyway can someone please help the code is posted below.
thanx in advance
import java.awt.*;
import javax.swing.*;
public class MessagePanel extends JPanel {
    GridBagLayout gridbag = new GridBagLayout();
    public MessagePanel() {
        super();
        GridBagConstraints constraints;
        setLayout(gridbag);
        JLabel toLabel = new JLabel("To: ");
        JTextField to = new JTextField();
        JLabel subjectLabel = new JLabel("Subject: ");
        JTextField subject = new JTextField();
        JLabel ccLabel = new JLabel("CC: ");
        JTextField cc = new JTextField();
        JLabel bccLabel = new JLabel("BCC: ");
        JTextField bcc = new JTextField();
        addComponent(toLabel, 0, 0 , 1, 1, 10, 100,
            GridBagConstraints.NONE, GridBagConstraints.EAST);
        addComponent(to, 1, 0, 9, 1, 90, 100,
            GridBagConstraints.HORIZONTAL, GridBagConstraints.WEST);
        addComponent(subjectLabel, 0, 1, 1, 1, 10, 100,
            GridBagConstraints.NONE, GridBagConstraints.EAST);
        addComponent(subject, 1, 1, 9, 1, 90, 100,
            GridBagConstraints.HORIZONTAL, GridBagConstraints.WEST);
     addComponent(ccLabel, 0, 2, 1, 1, 10, 100,
            GridBagConstraints.NONE, GridBagConstraints.EAST);
        addComponent(cc, 1, 2, 4, 1, 40, 100,
            GridBagConstraints.HORIZONTAL, GridBagConstraints.WEST);
        addComponent(bccLabel, 5, 2, 1, 1, 10, 100,
            GridBagConstraints.NONE, GridBagConstraints.EAST);
        addComponent(bcc, 6, 2, 4, 1, 40, 100,
            GridBagConstraints.HORIZONTAL, GridBagConstraints.WEST);
    private void addComponent(Component component, int gridx, int gridy,
        int gridwidth, int gridheight, int weightx, int weighty, int fill,
        int anchor) {
        GridBagConstraints constraints = new GridBagConstraints();
        constraints.gridx = gridx;
        constraints.gridy = gridy;
        constraints.gridwidth = gridwidth;
        constraints.gridheight = gridheight;
        constraints.weightx = weightx;
        constraints.weighty = weighty;
        constraints.fill = fill;
        constraints.anchor = anchor;
        gridbag.setConstraints(component, constraints);
        add(component);
}I have copied exactly what the book says and downloaded the files from the website and everything is the same but it just won't work?

Answer 1

My guess is that the main method is in another class. It would probably look something like this:
public static void main(String[] args)
     JFrame f = new JFrame();
     f.setSize(500, 500);
     f.setLocation(20, 20);
     f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     f.setContentPane(new MessagePanel());
     f.setVisible(true);
}