--- old/src/java.base/share/classes/java/text/DateFormatSymbols.java	2017-12-19 12:00:12.000000000 +0530
+++ new/src/java.base/share/classes/java/text/DateFormatSymbols.java	2017-12-19 12:00:12.000000000 +0530
@@ -404,6 +404,12 @@
      * to the <a href="http://unicode.org/reports/tr35/#Calendar_Elements">
      * Calendar Elements in the Unicode Locale Data Markup Language
      * (LDML) specification</a> for more details.
+     * 
+     * @implNote The default implementation returns month string
+     * array of 13 elements, the thirteenth element is for
+     * {@link java.util.Calendar#UNDECIMBER Calendar.UNDECIMBER},
+     * in which an empty string is returned for
+     * {@code GregorianCalendar}.
      *
      * @return the month strings. Use
      * {@link java.util.Calendar#JANUARY Calendar.JANUARY},
@@ -438,6 +444,12 @@
      * Calendar Elements in the Unicode Locale Data Markup Language
      * (LDML) specification</a> for more details.
      *
+     * @implNote The default implementation returns short month string
+     * array of 13 elements, the thirteenth element is for
+     * {@link java.util.Calendar#UNDECIMBER Calendar.UNDECIMBER},
+     * in which an empty string is returned for
+     * {@code GregorianCalendar}.
+     * 
      * @return the short month strings. Use
      * {@link java.util.Calendar#JANUARY Calendar.JANUARY},
      * {@link java.util.Calendar#FEBRUARY Calendar.FEBRUARY},