Rational Numbers in Groovy

//  Class RationalNumber Author: Lewis/Loftus
//  http://www.cs.dartmouth.edu/~cs5/examples/chap06/RationalNumber.java
//
//  Represents one rational number with a numerator and denominator.
//
// --> Slightly adapted by R. Plantiko,
// It remains more or less a POJO
// But the method naming is important in Groovy:
//   x * y will automatically be bound to plus(x,y) if plus() has a signature that fits
// The same for minus, multiply, div.
// And, as in Java, equals() and toString() have special meaning
// Handling of denominator 0: Computations can be continued, but any div by 0 gives a
// normalized representation NaN = (1,0) which makes it identifiable

public class RationalNumber
{
   private int numerator, denominator;

   public static final RationalNumber DIV_BY_ZERO = new RationalNumber(1,0);

   //-----------------------------------------------------------------
   //  Constructor: Sets up the rational number by ensuring a nonzero
   //  denominator and making only the numerator signed.
   //-----------------------------------------------------------------
   public RationalNumber (int numer, int denom)
   {

// Normalize all "Div-By-Zero" fractions
      if (denom == 0) {
         numerator = 1;
         denominator = 0;
         }

      // Make the numerator "store" the sign
      else {

         if (denom < 0) {
           numer = numer * -1;
           denom = denom * -1;
           }

         numerator = numer;
         denominator = denom;

         reduce();

       }

  }

   //-----------------------------------------------------------------
   //  Returns the numerator of this rational number.
   //-----------------------------------------------------------------
   public int getNumerator ()
   {
      return numerator;
   }

   //-----------------------------------------------------------------
   //  Returns the denominator of this rational number.
   //-----------------------------------------------------------------
   public int getDenominator ()
   {
      return denominator;
   }

   //-----------------------------------------------------------------
   //  Returns the reciprocal of this rational number.
   //-----------------------------------------------------------------
   public RationalNumber reciprocal ()
   {
      return new RationalNumber (denominator, numerator);
   }

   //-----------------------------------------------------------------
   //  Adds this rational number to the one passed as a parameter.
   //  A common denominator is found by multiplying the individual
   //  denominators.
   //-----------------------------------------------------------------
   public RationalNumber plus(RationalNumber op2)
   {
      int commonDenominator = denominator * op2.getDenominator();
      int numerator1 = numerator * op2.getDenominator();
      int numerator2 = op2.getNumerator() * denominator;
      int sum = numerator1 + numerator2;

      return new RationalNumber (sum, commonDenominator);
   }

   //-----------------------------------------------------------------
   //  Subtracts the rational number passed as a parameter from this
   //  rational number.
   //-----------------------------------------------------------------
   public RationalNumber minus(RationalNumber op2)
   {
      int commonDenominator = denominator * op2.getDenominator();
      int numerator1 = numerator * op2.getDenominator();
      int numerator2 = op2.getNumerator() * denominator;
      int difference = numerator1 - numerator2;

      return new RationalNumber (difference, commonDenominator);
   }

   //-----------------------------------------------------------------
   //  Multiplies this rational number by the one passed as a
   //  parameter.
   //-----------------------------------------------------------------
   public RationalNumber multiply (RationalNumber op2)
   {
      int numer = numerator * op2.getNumerator();
      int denom = denominator * op2.getDenominator();

      return new RationalNumber (numer, denom);
   }

   //-----------------------------------------------------------------
   //  Divides this rational number by the one passed as a parameter
   //  by multiplying by the reciprocal of the second rational.
   //-----------------------------------------------------------------
   public RationalNumber div(RationalNumber op2)
   {
      return multiply (op2.reciprocal());
   }

   //-----------------------------------------------------------------
   //  Determines if this rational number is equal to the one passed
   //  as a parameter.  Assumes they are both reduced.
   //-----------------------------------------------------------------
   public boolean equals (RationalNumber op2)
   {
      return ( numerator == op2.getNumerator() &&
               denominator == op2.getDenominator() );
   }

   //-----------------------------------------------------------------
   //  Returns this rational number as a string.
   //-----------------------------------------------------------------
   public String toString ()
   {
      String result;

      if (numerator == 0)
         result = "0";
      else
         if (denominator == 1)
            result = numerator + "";
         else if (denominator == 0)
            result = "NaN"
         else
            result = numerator + "/" + denominator;

      return result;
   }

   //-----------------------------------------------------------------
   //  Reduces this rational number by dividing both the numerator
   //  and the denominator by their greatest common divisor.
   //-----------------------------------------------------------------
   private void reduce ()
   {
      if (numerator != 0)
      {
         int common = gcd (Math.abs(numerator), denominator);

         numerator = numerator / common;
         denominator = denominator / common;
      }
   }

   //-----------------------------------------------------------------
   //  Computes and returns the greatest common divisor of the two
   //  positive parameters. Uses Euclid's algorithm.
   //-----------------------------------------------------------------
   private int gcd (int num1, int num2)
   {
      while (num1 != num2)
         if (num1 > num2)
            num1 = num1 - num2;
         else
            num2 = num2 - num1;

      return num1;
   }
}