Calc

public class Fraction {
    private int num;
    private int den;

    public int getNum() {
        return this.num;
    }
    public void setNum(int num) {
        this.num = num;
    }
    public int getDen() {
        return this.den;
    }
    public void setDen(int den) {
        if (den != 0){
            this.den = den;
        } else {
            this.den = -1;
            System.out.println("Error!!!");
        }
    }

    public Fraction(int num, int den) {
        this.setNum(num);
        this.setDen(den);
    }

    @Override
    public String toString() {
        return this.getNum() + "/" + this.getDen();
    }

    public Fraction mult(Fraction other) {
        int numr = this.getNum() * other.getNum();
        int denr = this.getDen() * other.getDen();
        Fraction res = new Fraction(numr, denr);
        return res;
    }

    public Fraction divide(Fraction other) {
        int numr = this.getNum() * other.getDen();
        int denr = this.getDen() * other.getNum();
        Fraction res = new Fraction(numr, denr);
        return res;
    }

    public Fraction add(Fraction other) {
        int numr = this.getNum() * other.getDen() + other.getNum()*this.getDen();
        int denr = this.getDen() * other.getDen();
        Fraction res = new Fraction(numr, denr);
        return res;
    }

    public Fraction subtract(Fraction other) {
        int numr = this.getNum() * other.getDen() - other.getNum()*this.getNum();
        int denr = this.getDen() * other.getDen();
        Fraction res = new Fraction(numr, denr);
        return res;
    }

    private int gcdByEuclidsAlgorithm(int n1, int n2) {
        if (n2 == 0) {
            return n1;
        }
        return gcdByEuclidsAlgorithm(n2, n1 % n2);
    }

    public void reduce() {
        int d = gcdByEuclidsAlgorithm(this.num, this.den);
        this.num /= d;
        this.den /= d;
    }
}