Trouble simplifying fractions in java

Question

I'm trying to make a program that takes two fractions and then adds, subtracts, multiplies, and divides them, then puts them in simplest form if necessary.

The only problem I've run into is that the fractions are not simplifying and I'm not sure why.

For example, right now when I run the fractions 3/4 and 1/4 through it gives me these answers: Addition: 4/4 Subtraction: 2/4 Multiplication: 3/16 Division: 12/4

I want addition to be 1/1, subtraction 1/2, and division 3/1. Below is my code.

import java.util.*;
public class RationalNumber
{
private int numerator;
private int denominator;//instance variables
//constructor
public RationalNumber()
{
    numerator = 0;
    denominator = 1;
}

public RationalNumber(int num, int den)
{
    setNumerator(num);
    setDenominator(den);
    int gcf= greatestCommonFactor(num, den);

    num = num/gcf;
    den = den/gcf;
    /*num = num/(greatestCommonFactor(num, den));
    den = den/(greatestCommonFactor(num, den));*/
}

//getters
public int getDenominator()
{
    return denominator;
}

public int getNumerator()
{
    return numerator;
}

//setters
public void setNumerator(int num)
{
    numerator = num;
}

public void setDenominator(int den)
{
    denominator = den;
}

//adds the rational numbers
public RationalNumber add(RationalNumber two)
{
    RationalNumber add = new RationalNumber();
    if(getDenominator() == two.getDenominator())
    {
        int newNum = numerator + two.numerator;//simply adds the numerators if the denominators are the same
        /*newNum = newNum/(greatestCommonFactor(newNum, denominator));
        int newDen = denominator/(greatestCommonFactor(newNum, denominator));//simplification*/
        return new RationalNumber(newNum, denominator);
    }
    else
    {
        int newDen = getDenominator() * two.getDenominator();
        int leftNum = getNumerator() * two.getDenominator();
        int rightNum = getDenominator() * two.getNumerator();//cross multiplication

        /*int newNum = (leftNum + rightNum)/(greatestCommonFactor((leftNum + rightNum), getDenominator()));//simplification
        newDen = denominator/(greatestCommonFactor(newNum, getDenominator()));*/

        return new RationalNumber(leftNum + rightNum, newDen);
    }
}

//subtracts the rational numbers, same math as the add method but with subtraction signs
public RationalNumber sub(RationalNumber two)
{
    RationalNumber sub = new RationalNumber();

    if(this.getDenominator() == two.getDenominator())
    {
        int newNum = this.numerator - two.numerator;
        return new RationalNumber(newNum, this.getDenominator());
    }
    else
    {
        int newDen = this.getDenominator() * two.getDenominator();
        int leftNum = this.getNumerator() * two.getDenominator();
        int rightNum = this.getDenominator() * two.getNumerator();
        return new RationalNumber(leftNum - rightNum, newDen);
    }

}

//multiplies the two rational numbers
public RationalNumber mult(RationalNumber two)
{
    RationalNumber mult = new RationalNumber();
    mult.denominator = denominator * two.denominator;
    mult.numerator = numerator * two.numerator;

    return mult;
}

//divides the rational numbers
public RationalNumber div(RationalNumber two)
{
    RationalNumber div = new RationalNumber();
    div.denominator = denominator * (two.numerator);
    div.numerator = numerator * two.denominator;//multiply by reciprocal in order to divide

    return div;
}

//returns the reciprocal of a rational number
public RationalNumber reciprocal(RationalNumber two)
{
    RationalNumber reciprocal = new RationalNumber();
    reciprocal.denominator = numerator;
    reciprocal.numerator = denominator;
    return reciprocal;
}

//returns the inverse of a rational number
public RationalNumber inverse(RationalNumber two)
{
    RationalNumber inverse = new RationalNumber();
    inverse.numerator = (numerator*-1);
    return inverse;
}

//finds the greatest common factor, used in simplifying
public int greatestCommonFactor(int num, int den)
{
    for(int i = (Math.max(num,den)/2)+1; i > 0; i--)
    {
        if((num/i) == Math.round(num/i) && (den/i) == Math.round(den/i))
            return i;//loop finds the GCF by finding if numerator & denominator divided by i is an even number
    }
    return 1;
}

public String toString()
{
    return numerator + "/" + denominator;//prints the numerator and denominator as a string
}
}

Answer 1

Your greatestCommonFactor function was giving me wrong results. Try testing with this one (this is using Euclid's method):

//finds the greatest common factor, used in simplifying
public int greatestCommonFactor(int num, int den)
{
    if(den == 0){
        return num;
    }
    return greatestCommonFactor(den, num % den);
}

Also you don't set numerator or denominator to their simplified form:

public RationalNumber(int num, int den)
{
    //setNumerator(num);
    //setDenominator(den);
    int gcf= greatestCommonFactor(num, den);
    setNumerator(num/gcf);
    setDenominator(den/gcf);
}