code: public void setFallbackIntervalPattern(String fallbackPattern)
      {
          if ( frozen ) {
              throw new UnsupportedOperationException("no modification is allowed after DII is frozen");
          }
          int firstPatternIndex = fallbackPattern.indexOf("{0}");
          int secondPatternIndex = fallbackPattern.indexOf("{1}");
          if ( firstPatternIndex == -1 || secondPatternIndex == -1 ) {
              throw new IllegalArgumentException("no pattern {0} or pattern {1} in fallbackPattern");
          }
          if ( firstPatternIndex > secondPatternIndex ) {
              fFirstDateInPtnIsLaterDate = true;
          }
          fFallbackIntervalPattern = fallbackPattern;
      }
docs: Re-set the fallback interval pattern.
  
  In construction, default fallback pattern is set as "{0} - {1}".
  And constructor taking locale as parameter will set the
  fallback pattern as what defined in the locale resource file.
  
  This method provides a way for user to replace the fallback pattern.
  
  @param fallbackPattern                 fall-back interval pattern.
  @throws UnsupportedOperationException  if the object is frozen
  @throws IllegalArgumentException       if there is no pattern {0} or
  pattern {1} in fallbakckPattern