ICU4J defines *Format.Field constants like this one in NumberFormat:
It would be easier to use ICU4J together with JDK API if we did this instead:
where java.* has an equivalent constant.
Is it necessary that a Field constant be of type Field rather than base class type Format.Field?
If so, the second-best approach might be to add an instance member of type Format.Field, and a getter, so that ICU `Field.SIGN.getJavaTextField() == java.text.NumberFormat.Field.SIGN`.
It would also be useful to have a converter method from Java Field to ICU Field.