Ho eseguito pari pari questo esempio:
http://download.oracle.com/javase/tu...settingup.html
ecco il codice del CelsiusConverterGUI.java generato da NetBeans 6.9.1
codice:
/*
 * CelsiusConverterGUI.java
 *
 * Created on May 17, 2011, 1:03:29 PM
 */

package learn;

/**
 *
 * @author neorf
 */
public class CelsiusConverterGUI extends javax.swing.JFrame {

    /** Creates new form CelsiusConverterGUI */
    public CelsiusConverterGUI() {
        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() {

        tempTextField = new javax.swing.JTextField();
        celsiusLabel = new javax.swing.JLabel();
        convertButton = new javax.swing.JButton();
        fahrenheitLabel = new javax.swing.JLabel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setTitle("Celsius Converter's neorf");

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

        celsiusLabel.setText("Celsius");

        convertButton.setText("Convert");
        convertButton.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                convertButtonActionPerformed(evt);
            }
        });

        fahrenheitLabel.setText("Fahrenheit");

        org.jdesktop.layout.GroupLayout layout = new org.jdesktop.layout.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
            .add(layout.createSequentialGroup()
                .addContainerGap()
                .add(layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING, false)
                    .add(layout.createSequentialGroup()
                        .add(tempTextField, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE)
                        .addPreferredGap(org.jdesktop.layout.LayoutStyle.RELATED)
                        .add(celsiusLabel))
                    .add(layout.createSequentialGroup()
                        .add(convertButton)
                        .addPreferredGap(org.jdesktop.layout.LayoutStyle.RELATED, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                        .add(fahrenheitLabel)))
                .addContainerGap(49, Short.MAX_VALUE))
        );

        layout.linkSize(new java.awt.Component[] {convertButton, tempTextField}, org.jdesktop.layout.GroupLayout.HORIZONTAL);

        layout.setVerticalGroup(
            layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
            .add(layout.createSequentialGroup()
                .addContainerGap()
                .add(layout.createParallelGroup(org.jdesktop.layout.GroupLayout.BASELINE)
                    .add(tempTextField, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE)
                    .add(celsiusLabel))
                .addPreferredGap(org.jdesktop.layout.LayoutStyle.UNRELATED)
                .add(layout.createParallelGroup(org.jdesktop.layout.GroupLayout.BASELINE)
                    .add(convertButton)
                    .add(fahrenheitLabel))
                .addContainerGap(org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
        );

        pack();
    }// </editor-fold>                        

    private void tempTextFieldActionPerformed(java.awt.event.ActionEvent evt) {                                              
        // TODO add your handling code here:
    }                                             

    private void convertButtonActionPerformed(java.awt.event.ActionEvent evt) {                                              
        // TODO add your handling code here:
        int tempFahr = (int)((Double.parseDouble(tempTextField.getText())) * 1.8 + 32);
        fahrenheitLabel.setText(tempFahr + " Fahrenheit");
    }                                             

    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new CelsiusConverterGUI().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JLabel celsiusLabel;
    private javax.swing.JButton convertButton;
    private javax.swing.JLabel fahrenheitLabel;
    private javax.swing.JTextField tempTextField;
    // End of variables declaration                   

}