class WizardPanel1Excel implements WizardDescriptor.Panel {

    private final ImporterSpreadsheetExcel importer;
    private final Set<ChangeListener> listeners = new HashSet<>(1); // or can use ChangeSupport in NB 6.0
    /**
     * The visual component that displays this panel. If you need to access the
     * component from this class, just use getComponent().
     */
    private WizardVisualPanel1Excel component;

    public WizardPanel1Excel(ImporterSpreadsheetExcel importer) {
        this.importer = importer;
    }

    // Get the visual component for the panel. In this template, the component
    // is kept separate. This can be more efficient: if the wizard is created
    // but never displayed, or not all panels are displayed, it is better to
    // create only those which really need to be visible.
    @Override
    public Component getComponent() {
        if (component == null) {
            component = new WizardVisualPanel1Excel(importer, this);
        }
        return component.getValidationPanel();
    }

    @Override
    public HelpCtx getHelp() {
        // Show no Help button for this panel:
        return HelpCtx.DEFAULT_HELP;
        // If you have context help:
        // return new HelpCtx(SampleWizardPanel1.class);
    }

    @Override
    public boolean isValid() {
        return component.isValidData();
    }

    @Override
    public final void addChangeListener(ChangeListener l) {
        synchronized (listeners) {
            listeners.add(l);
        }
    }

    @Override
    public final void removeChangeListener(ChangeListener l) {
        synchronized (listeners) {
            listeners.remove(l);
        }
    }

    protected final void fireChangeEvent() {<FILL_FUNCTION_BODY>}

    // You can use a settings object to keep track of state. Normally the
    // settings object will be the WizardDescriptor, so you can use
    // WizardDescriptor.getProperty & putProperty to store information entered
    // by the user.
    @Override
    public void readSettings(Object settings) {
        component.refreshPreviewTable();
    }

    @Override
    public void storeSettings(Object settings) {
        importer.setMode(component.getSelectedMode());
        importer.setSheetIndex(component.getSelectedSheetIndex());
    }
}

        Iterator<ChangeListener> it;
        synchronized (listeners) {
            it = new HashSet<>(listeners).iterator();
        }
        ChangeEvent ev = new ChangeEvent(this);
        while (it.hasNext()) {
            it.next().stateChanged(ev);
        }
    
<no_super_class>