docs: public static boolean isDecimal(String str, int beginIndex, int endIndex)
      {
          if ( str.charAt(str.length() - 1) == '.'
                  || str.charAt(0) == '.' ) {
              return false;
          }
  
          char c;
          int p= 0;        //number of point
          for ( int j = 1; j < str.length(); j++ ) {
              c = str.charAt(j);
              if ( c == '.' ) {
                  p++;
              } else {
                  //make full-width half-width
                  if ( c > 65280 ) c -= 65248;
                  if ( c < 48 || c > 57 ) return false;
              }
          }
  
          return (p==1);
      }