Need help fixing this piece of code

Question

public class Number {
private int numerator;
private int denominator;

public Number(int numerator, int denominator) {
    this.numerator = numerator;
    this.denominator = denominator;
}

public Number() {
    this.numerator = 0;
    this.denominator = 1;
}

public int getDenominator() {
    return denominator;
}

public int getNumerator() { 
    return numerator;
}

public String toString() {
    if (numerator == 0) {
        return "0";
    } else if (denominator == 1) {
        return denominator + "";
    }
    return numerator + "/" + denominator;
}

public Number subtract(Number other) {
    numerator = (this.getNumerator() * other.getDenominator()) - (other.getNumerator() * this.getDenominator());
    denominator = this.getDenominator() * other.getDenominator();

    return this;
}

////
public class test {
public static void main(String[] args) {
    Number n1 = new Number(1, 2);
    Number n2 = new Number(3, 5);
    Number n4 = new Number(7, 40);
    Number test = n2.subtract(n1);
    System.out.println(test);
    Number test2 = n4.subtract(n1);
    System.out.println(test2);
    Number test3 = n1.subtract(n4);
    System.out.println(test3);
    Number test4 = n2.subtract(n1);
    System.out.println(test4);

}
}

I'm having trouble with the Number subtract() method. When I call it from the client, it works some of the time, but after several successive calls, I am getting unexpected outputs. The first two calls work fine, then I start to get results which are way off. I know that I am missing something in the subtract() method, just not sure what it is.

Any help would be appreciated.

Answer 1

I ended up solving my own problem but I appreciate everyones help. I know this might not be the most efficient way to solve this problem, but I am only a first year CS student. If anyone has any suggestions to clean this code up, I would love to hear it. Thanks!

public class Number {
private int numerator;
private int denominator;

public Number(int numerator, int denominator) {
    reduce(numerator, denominator);
}

public Number() {
    this.numerator = 0;
    this.denominator = 1;
}

public int getDenominator() {
    return denominator;
}

public int getNumerator() { 
    return numerator;
}

public String toString() {
    if (numerator == 0) {
        return "0";
    } else if (denominator == 1) {
        return numerator + "";
    }
    return numerator + "/" + denominator;
}

public Number add(RationalNumber other) {
    int numerator1 = (numerator * other.getDenominator()) + (other.getNumerator() * denominator);
    int denominator1 = denominator * other.getDenominator();

    return new Number(numerator1, denominator1);
}

public Number subtract(RationalNumber other) {
    int numerator1 = (numerator * other.getDenominator()) - (other.getNumerator() * denominator);
    int denominator1 = denominator * other.getDenominator();

    return new Number(numerator1, denominator1);
}

public Number multiply(RationalNumber other) {
    int numerator1 = numerator * other.getNumerator();
    int denominator1 = denominator * other.getDenominator();

    return new Number(numerator1, denominator1);
}

public Number divide(RationalNumber other) {
    int numerator1 = numerator * other.getDenominator();
    int denominator1 = denominator * other.getNumerator();

    return new Number(numerator1, denominator1);
}   

private void reduce(int numerator, int denominator) {
    int factor = 1;
    int temp = 0;
    if (Math.abs(numerator) > Math.abs(denominator)) {
        temp = Math.abs(numerator);
    } else if (Math.abs(denominator) > Math.abs(numerator)) {
        temp = Math.abs(denominator);
    }
    for (int i = temp; i > 0; i --) {
        if ((numerator %i == 0) && (denominator %i == 0)) {
            factor = i;
            i = 0;
        }
    }
    numerator = numerator / factor;
    denominator = denominator / factor;
    rightForm(numerator, denominator);
}
private void rightForm(int numerator, int denominator) {
    if (numerator > 0 && denominator < 0) {
        this.numerator = numerator - numerator - numerator;
        this.denominator = Math.abs(denominator);
    } else if (numerator < 0 && denominator < 0) {
        this.numerator = Math.abs(numerator);
        this.denominator = Math.abs(denominator);
    } else {
        this.numerator = numerator;
        this.denominator = denominator;
    }
}

}

Answer 2

If you use subtract method on object, change last line to return this. By the way, your substraction for ratio types is wrong.