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

*** 699,708 ****
--- 699,712 ----
       * @param newFormat the format to use for the specified format element
       * @exception ArrayIndexOutOfBoundsException if {@code formatElementIndex} is equal to or
       *            larger than the number of format elements in the pattern string
       */
      public void setFormat(int formatElementIndex, Format newFormat) {
+ 
+         if (formatElementIndex > maxOffset) {
+             throw new ArrayIndexOutOfBoundsException(formatElementIndex);
+         }
          formats[formatElementIndex] = newFormat;
      }
  
      /**
       * Gets the formats used for the values passed into