value of selected checkbox is "Off"

Hi Eveybody

I've got a PDF with 3 Checkboxes.
One of these Checkboxes is selected, as can be seen in the attached PDF
and in the attached screenshot.

When I analyse the pdf file with following code i get this result:

 for (Map.Entry<String, AcroFields.Item> entry :
acroFields.getFields().entrySet()) {
      String fieldName = entry.getKey();
      String value = acroFields.getField(fieldName);
      if (acroFields.getFieldType(fieldName) ==
AcroFields.FIELD_TYPE_CHECKBOX) {
        String[] appearanceStates =
acroFields.getAppearanceStates(fieldName);
        System.out.println("Checkbox: " + fieldName + " Value:" + value
+
            " AvailableValues:" + StringUtil.concatWithDelimiter(",",
appearanceStates));
      }
    }

Result:
Checkbox: CheckBox_Group1 Value:Off AvailableValues:chk1,Off
Checkbox: CheckBox_Group2 Value:Off AvailableValues:chk2,Off
Checkbox: CheckBox_Group3 Value:Off AvailableValues:Off,chk3

So all of the values are "Off".
Is there something wrong with my pdf file or have I completely
misunderstood something?

Thanks for your help and kind regards
Thomas

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