public Set<String> getOnValues()
    {
        // we need a set as the field can appear multiple times
        Set<String> onValues = new LinkedHashSet<>();
        List<String> exportValues = getExportValues();
        if (!exportValues.isEmpty())
        {
            onValues.addAll(exportValues);
            return onValues;
        }
        
        List<PDAnnotationWidget> widgets = this.getWidgets();
        for (PDAnnotationWidget widget : widgets)
        {
            onValues.add(getOnValueForWidget(widget));
        }        
        return onValues;
    }
@Test
    void retrieveAcrobatRadioButtonProperties()
    {
        PDRadioButton radioButton = (PDRadioButton) acrobatAcroForm.getField("RadioButtonGroup");
        assertNotNull(radioButton);
        assertEquals(2, radioButton.getOnValues().size());
        assertTrue(radioButton.getOnValues().contains("RadioButton01"));
        assertTrue(radioButton.getOnValues().contains("RadioButton02"));
    }