src/java.base/share/classes/java/text/DateFormatSymbols.java

*** 403,412 ****
--- 403,418 ----
       * form. This method returns {@code "ledna"} in this case. Refer
       * 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},
       * {@link java.util.Calendar#FEBRUARY Calendar.FEBRUARY},
       * etc. to index the result array.
       */
*** 436,445 ****
--- 442,457 ----
       * form. This method returns {@code "de gen."} in this case. Refer
       * 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 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},
       * etc. to index the result array.
       */