code: public static Nature getNature(String natureStr) {
          Nature nature = NATUREMAP.get(natureStr);
          if (nature == null) {
              nature = new Nature(natureStr, FYI, FYI, YI);
              NATUREMAP.put(natureStr, nature);
              return nature;
          }
          return nature;
      }
docs: 根据字符串得道词性.没有就创建一个
  
  @param natureStr
  @return