Fraction class

package kr_2;

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

    public Fraction(int num, int denum) {
        this.numerator = num;
        this.denominator = denum;
    }

    public Fraction(String txt) {
        String[] nums = txt.split("/");
        this.numerator = Integer.parseInt(nums[0]);
        this.denominator = Integer.parseInt(nums[1]);
    }

    @Override
    public String toString() {
        String str = this.numerator + "/" + this.denominator;
        return str;
    }

    public Fraction sum(Fraction anotherFr) {
        int num = this.numerator * anotherFr.denominator + anotherFr.numerator * this.denominator;
        int denum = this.denominator * anotherFr.denominator;
        Fraction fr = new Fraction(num, denum);
        fr.sakrati();
        return fr;
    }

    public Fraction subtract(Fraction anotherFr) {
        int num = this.numerator * anotherFr.denominator - anotherFr.numerator * this.denominator;
        int denum = this.denominator * anotherFr.denominator;
        Fraction fr = new Fraction(num, denum);
        fr.sakrati();
        return fr;
    }

    public Fraction multiply(Fraction anotherFr) {
        int num = this.numerator * anotherFr.numerator;
        int denum = this.denominator * anotherFr.denominator;
        Fraction fr = new Fraction(num, denum);
        fr.sakrati();
        return fr;
    }

    public Fraction divide(Fraction anotherFr) {
        int num = this.numerator * anotherFr.denominator;
        int denum = this.denominator * anotherFr.numerator;
        Fraction fr = new Fraction(num, denum);
        fr.sakrati();
        return fr;
    }

    private int gcd(int a, int b) {
        if (b == 0) {
            return a;
        } else {
            return gcd(b, a % b);
        }
    }

    public void sakrati() {
        int div = gcd(this.denominator, this.numerator);
        this.numerator /= div;
        this.denominator /= div;
    }

}