code: public static String substract(String minuend, String... subtrahends) {
  
          if (subtrahends == null) {
              return minuend;
          }
  
          BigDecimal difference;
          try {
              difference = new BigDecimal(minuend);
              for (int i = 0; i < subtrahends.length; i++) {
                  difference = difference.subtract(new BigDecimal(subtrahends[i]));
              }
              return difference.toString();
          } catch (Exception e) {
              return null;
          }
      }
docs: Get the difference of minuend and all subtrahends
  
  Any numeric string recognized by {@code BigDecimal} is supported.
  
  @param minuend A valid number string
  @param subtrahends one or more valid number strings
  
  @return <code>minuend - subtrahends[0] - subtrahends[1] - ...</code>
  
  @see BigDecimal