code: protected final void validateField(int field, int min, int max) {
          int value = fields[field];
          if (value < min || value > max) {
              throw new IllegalArgumentException(fieldName(field) +
                      '=' + value + ", valid range=" +
                      min + ".." + max);
          }
      }
docs: Validate a single field of this calendar given its minimum and
  maximum allowed value.  If the field is out of range, throw a
  descriptive <code>IllegalArgumentException</code>.  Subclasses may
  use this method in their implementation of {@link
  #validateField(int)}.