getYear() is a value between -(10^9-1) to (10^9)-1
or Javax.Xml.Datatype.DatatypeConstants.FieldUndefined. Javax.Xml.Datatype.XMLGregorianCalendar.Eon is high order year value in billion of years. getEon() has values greater than or equal to (10^9) or less than or equal to -(10^9).
A value of null indicates field is undefined.
Given that states that the year zero
will be a valid lexical value in a future version of XML Schema,
this class allows the year field to be set to zero. Otherwise,
the year field value is handled exactly as described
in the errata and [ISO-8601-1988]. Note that W3C XML Schema 1.0
validation does not allow for the year field to have a value of zero.