You should use writeEmptyElement(...)
for this:
xtw.writeStartDocument("utf-8", "1.0");
xtw.writeEmptyElement("Buddy");
xtw.writeAttribute("Name", "AB");
xtw.writeAttribute("Age", "25");
xtw.writeAttribute("petName", "XX");
xtw.writeEndDocument();
No writeEndElement()
is needed for empty elements.