code: public GlobalizationPreferences setDateFormat(int dateStyle, int timeStyle, DateFormat format) {
          if (isFrozen()) {
              throw new UnsupportedOperationException("Attempt to modify immutable object");
          }
          if (dateFormats == null) {
              dateFormats = new DateFormat[DF_LIMIT][DF_LIMIT];
          }
          dateFormats[dateStyle][timeStyle] = (DateFormat) format.clone(); // for safety
          return this;
      }
docs: Set an explicit date format. Overrides the locale priority list for
  a particular combination of dateStyle and timeStyle. DF_NONE should
  be used if for the style, where only the date or time format individually
  is being set.
  
  @param dateStyle DF_FULL, DF_LONG, DF_MEDIUM, DF_SHORT or DF_NONE
  @param timeStyle DF_FULL, DF_LONG, DF_MEDIUM, DF_SHORT or DF_NONE
  @param format The date format
  @return this, for chaining
  @hide draft / provisional / internal are hidden on Android