code: public static String extractDigit(String string) {
          StringBuilder res = new StringBuilder();
          if (HAS_DIGIT_PATTERN.matcher(string).matches()) {
              string = string.replaceAll("(\\s|[a-zA-Z])+", "");
              res = new StringBuilder(string.indexOf("-") == 0 ? "-" : "");
              int dotIdx = string.lastIndexOf(".");
              for (int i = 0; i < string.length(); i++) {
                  char c = string.charAt(i);
                  if (Character.isDigit(c) || i == dotIdx) {
                      res.append(c);
                  }
              }
              if (res.indexOf(ValueConsts.DOT_SIGN) == 0) {
                  res.insert(0, "0");
              } else if (res.indexOf(ValueConsts.NEGATIVE_DOT_SIGN) == 0) {
                  res = new StringBuilder("-0." + res.substring(2, res.length()));
              }
          }
          return res.toString();
      }
docs: 抽取字符串的数字（包括最后一个点号）
  
  @param string {@link String}
  
  @return {@link String}