Rationals

public class Rational {

    // Creating instance variables for the numerator and denominator
    private long numerator;
    private long denominator;

    // Constructor that creates a new Rational object, making sure the denominator is not 0 or negative.
    public Rational (long numer, long denom){

        if (denom == 0){
            throw new RuntimeException("Error, can't have a denominator of 0.");
        }

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

        long greatestCommonDivisor = gcd(numer, denom);
        numerator = numer / greatestCommonDivisor;
        denominator = denom / greatestCommonDivisor;

    }

    // This method takes two rational numbers and adds them together
    public Rational plus(Rational b){
        Rational answer = new Rational (this.numerator * b.denominator + b.numerator * this.denominator, b.denominator * this.denominator);

        return answer;
    }

    //This method takes two rational numbers and subtracts them
    public Rational minus (Rational b){
        Rational answer = new Rational (this.numerator * b.denominator - b.numerator * this.denominator, b.denominator * this.denominator);


        return answer;
    }

    //This method takes two rational numbers and multiplies them
    public Rational times (Rational b){
        Rational answer = new Rational (this.numerator * b.numerator, this.denominator * b.denominator);

        return answer;
    }



    // This method uses Euclid's algorithm  which calculates the greatest common divisor
    public static long gcd(long p, long q){
        if (q==0) return p;
        long r = p % q;
        return gcd(q, r);
    }

    // This method produces a string representation of values
    public String toString(){
        if (denominator == 1)
            return numerator + "";
        else
            return numerator + "/" + denominator;
    }


    // Test client
    public static void main (String args[]){
        Rational p = new Rational (1, 6);
        Rational q = new Rational (4, 8);

        Rational r = p.minus(q);
        System.out.println(r);
    }


}