code: public static String product(String... factors) {
  
          if (factors == null || factors.length == 0) {
              return null;
          }
  
          BigDecimal prodcut;
          try {
              prodcut = new BigDecimal(factors[0]);
              for (int i = 1; i < factors.length; i++) {
                  prodcut = prodcut.multiply(new BigDecimal(factors[i]));
              }
              return prodcut.toString();
          } catch (Exception e) {
              return null;
          }
      }
docs: Get the product of all input numbers
  
  Any numeric string recognized by {@code BigDecimal} is supported.
  
  @param factors one or more valid number strings
  
  @return <code>factors[0] * factors[1] * ...</code>
  
  @see BigDecimal