code: public TimeZoneFormat setTimeZoneNames(TimeZoneNames tznames) {
          if (isFrozen()) {
              throw new UnsupportedOperationException("Attempt to modify frozen object");
          }
         _tznames = tznames;
         // TimeZoneGenericNames must be changed to utilize the new TimeZoneNames instance.
         _gnames = new TimeZoneGenericNames(_locale, _tznames);
         return this;
      }
docs: Sets the time zone display name data to this instance.
  
  @param tznames the time zone display name data.
  @return this object.
  @throws UnsupportedOperationException when this object is frozen.
  @see #getTimeZoneNames()