There are two problems here:

1. The spec for is
"protected DateFormat.Field(String name,
                           int calendarField)
    Creates a Field with the specified name. calendarField is used to identify the Calendar field this attribute represents. Use -1 if this field does not have a corresponding Calendar value."

The behaviour of constructor is undefined when calendarField is not from
range -1 .. Calendar.FIELD_COUNT (not legal calendar field and not -1).
It is not very clear if any out of range value is allowed or not.


2) The spec for getCalendarField() states that method returns -1 if the value is out of range. However, when running the following testcode on jdk6, it returns the value passed to the constructor.

Here is the test code:
===========================================================
 public class Test {

     public void case1() {
         int[] values = { Integer.MIN_VALUE, -100, Integer.MAX_VALUE };
         for(int i = 0; i < values.length; i++) {
             StubDateFormatField mF = new StubDateFormatField("Test", values[i]);
             if (mF.getCalendarField() != -1) {
                 System.out.println("getCalendarField() returns non -1 for "+ values[i]);
             } else {
                 System.out.println("ok");
            }
        }
     }

     public static void main(String[] args) {
         Test t = new Test();
         t.case1();
     }
 }

 class StubDateFormatField extends Field {
     public StubDateFormatField(String name, int calendarField) {
         super(name, calendarField);
     }
  }
==================================================================================
Here is the result on jdk6:
getCalendarField() returns non -1 for -2147483648
getCalendarField() returns non -1 for -100
getCalendarField() returns non -1 for 2147483647

So the implementation is inconsistent with the spec, and either one should be fixed.