code: public Rational multiply(Rational value)
      {
          return new Rational(numerator * value.getNumerator(),
                              denominator * value.getDenominator());
      }
docs: Multiply this rational by the specified value and return the result as a new
  object (also a Rational).
  @param value The amount to multiply by.
  @return A new rational value that is the result of multiplying this value by
  the specified value.