fraction codecheck v2

Fraction2.java

/*
 * The Fraction class from http://skylit.com/javamethods3/studentfiles.zip
 * where the following are also implemented:
 * - all methods of FractionI;
 * 
  * JM3e Chapter 10.3 - Author: Alex
 * @author EZRA GOLDNER <24goldnere@brooklinek12.org>
 */

public class Fraction implements FractionI, Comparable<Fraction>
{
    /////////////////////////////// FIELDS ///////////////////////////////

    private int num;
    private int den;

    //////////////////////////// CONSTRUCTORS ////////////////////////////

    public Fraction() {             // no-args constructor
        num = 0;
        den = 1;
    }

    public Fraction(int n) {
        num = n;
        den = 1;
    }

    public Fraction(int num, int den) {
        if (den == 0)
            throw new IllegalArgumentException(
                "Fraction construction error: denominator is 0");
        // Otherwise... initialize fields and reduce to canonical form
        this.num = num;
        this.den = den;
        this.reduce();
    }

    // Copy constructor
    public Fraction(Fraction other) {
        num = other.num;
        den = other.den;
    }

    ////////////////////////////// METHODS ///////////////////////////////

    // Accessor methods
    public int getNumerator() { return num; }
    public int getDenominator() { return den; }

    // Returns the value of this fraction as a double
    public double doubleValue() {
        return (double) num / (double) den;
    }

    // Returns a string representation of this fraction
    @Override
    public String toString() {
        return num + "/" + den;
    }

    // Returns the sum of this fraction and other
    public Fraction add(Fraction other) {
        int common = gcd(this.den, other.den);
        int thisDivided = this.den / common;
        int thatDivided = other.den / common;
        return new Fraction(this.num * thatDivided + other.num * thisDivided, this.den * thatDivided);
    }

    // Returns the sum of this fraction and m
    public Fraction add(int m) {
        return add(new Fraction(m));
    }

    // Returns the product of this fraction and other
    public Fraction multiply(Fraction other) {
        int aDcommon = gcd(this.num, other.den);
        int bCcommon = gcd(this.den, other.num);
        int thisNewNum = this.num / aDcommon;
        int thatNewDen = other.den / aDcommon;
        int thisNewDen = this.den / bCcommon;
        int thatNewNum = other.num / bCcommon;
        return new Fraction(thisNewNum * thatNewNum, thisNewDen * thatNewDen);
    }

    // Returns the product of this fraction and m
    public Fraction multiply(int m) {
        // return new Fraction(num * m, den);
        return multiply(new Fraction(m));
    }

    // Returns the opposite of this fraction
    public Fraction negate() {
        return multiply(-1);
    }

    // Returns the difference of this fraction and other
    public Fraction subtract(Fraction other) {
        return add(other.negate()); 
    }

    // Returns the difference of this fraction and m
    public Fraction subtract(int m) {
        return add(m * -1);
    }

    // Returns the reciprocal of this fraction
    public Fraction reciprocal() {
        return new Fraction(den, num);
    }

    // Returns the quotient of this fraction and other
    public Fraction divide(Fraction other) {
        return multiply(other.reciprocal());
    }

    // Returns the quotient of this fraction and m
    public Fraction divide(int m) {
        return multiply(new Fraction(1, m));
    }

    // Return a negative integer, zero, or a positive integer as this Fraction is <, ==, > than the other Fraction.
    public int compareTo(Fraction other) {
        Fraction subtracted = subtract(other);
        if (subtracted.num < 0)
            return -1;
        else if (subtracted.num > 0)
            return 1;
        return 0;
    }

    // Return true if this equals that
    public boolean equals(Fraction that) {
        return that.num == num && that.den == den;
    }

    // http://www.technofundo.com/tech/java/equalhash.html

    // Returns true if this has the same value as other, otherwise false
    @Override
    public boolean equals(Object other) {
        if (other == this) return true;
        if (other == null) return false;
        if (other.getClass() != this.getClass()) return false;
        Fraction that = (Fraction) other;
        return equals(that);
    }

    // Return a hashcode for this fraction
    @Override
    public int hashCode() {
        int hash = 17;
        hash = 31 * hash + num;
        hash = 31 * hash + den;
        return hash;
    }

    ////////////////////////// PRIVATE METHODS ///////////////////////////

    // Reduce this fraction to canonical form: gcd(num, den) == 1 and den > 0
    private void reduce() {
        if (num == 0) {
            den = 1;
            return;
        }
        
        if (den < 0) {
            num = -num;
            den = -den;
        }
        
        int q = gcd(num, den);
        num /= q;
        den /= q;
    }

    // Returns the greatest common divisor of two integers
    private static int gcd(int n, int d) {
        if (d == 0) return Math.abs(n);
        return gcd(d, n % d);
    }
}