[FIXED] Java program runs slow?

Issue

I don't understand why my Program need 0 second to run if there're these 2 lines in "private int ggT(int a, int b)" >>> if (a < 0) a *= -1; if (b < 0 ) b *= -1;

If I delete these 2 lines it needs more than 30 seconds to run. I just want to understand what these 2 lines do, because I did'nt write the code. And I think these 2 lines are superfluous.

Btw I'm coding in Netbeans with java 8.0 I guess.

Here is the whole program:

public class Bruch {

    private int zaehler;
    private int nenner;
    
    public Bruch(int zaehler, int nenner){
        this.zaehler = zaehler;
        this.nenner = nenner;
        if (zaehler < 0 & nenner < 0) {
            this.nenner *= -1;
            this.zaehler *= -1;
        }
        kuerzeDich();
           
    }
           
    private int min(int a, int b) {
        if (a < b) return a;
        return b;
    }

    private int ggT(int a, int b) {
        if (a < 0) a *= -1;
        if (b <0 ) b *= -1;
    
        int ggTeiler = min(a, b);
        while (a%ggTeiler != 0 || b%ggTeiler != 0) {
           ggTeiler--;
        }
        return ggTeiler;
    }

    private void kuerzeDich() {
        int ggTeiler = ggT(zaehler, nenner);
        zaehler = zaehler / ggTeiler;
        nenner = nenner / ggTeiler;
    }

    @Override
    public String toString() {
        return String.valueOf(zaehler + "/" + nenner);
    }

    public Bruch kehrwert() {
        return new Bruch(nenner, zaehler);
    }

    public Bruch add(Bruch pOther) {
        int ggTeiler = ggT(nenner, pOther.nenner);
        int kgV = nenner * pOther.nenner / ggTeiler;
        int neuerZaehler = zaehler * (kgV/nenner) + pOther.zaehler * (kgV/pOther.nenner);
        return new Bruch(neuerZaehler, kgV);
    }

    public Bruch sub(Bruch pOther) {
        int ggTeiler = ggT(nenner, pOther.nenner);
        int kgV = nenner * pOther.nenner / ggTeiler;
        int neuerZaehler = zaehler * (kgV/nenner) - pOther.zaehler * (kgV/pOther.nenner);
        return new Bruch(neuerZaehler, kgV);
    }

    public Bruch mul(Bruch pOther) {
        int neuerzaehler = zaehler * pOther.zaehler;
        int neuernenner = nenner * pOther.nenner;
        return new Bruch(neuerzaehler, neuernenner);
    } 

    public Bruch div(Bruch pOther) {
        return new Bruch(zaehler,nenner).mul(pOther.kehrwert());
    }


    public static void main(String[] args) {
        Bruch b1 = new Bruch(1, 6);
        Bruch b2 = new Bruch(3, 4);
        System.out.println(b1.add(b2));
        System.out.println(b1.sub(b2));
       System.out.println(b1.mul(b2));
        System.out.println(b1.div(b2));
    }
}

Solution

My assumption is when performing mathematic operations on them, it goes below 0 which are then assigned to back to zaehler nenner.
The reason it takes more time is because of this code(modulus)

int ggTeiler = min(a, b);
while (a%ggTeiler != 0 || b%ggTeiler != 0) {
     ggTeiler--;
}

x % y always equals x % -y
You can think of the sign of the second operand as being ignored. x % 5 (which is the same as x % -5).

-5 %  11 == -5
 5 % -11 ==  5
-5 % -11 == -5

Suppose one of them is -11 and 5. -11 is smaller than 5 which is then assigned to ggTeiler.
Now, 5 % -11 = 5 which is != 0 and the loop continues.
ggTeiler-- -> -11-1=-12.
5 % -12 = 5 which remains 5 all the time and the loop continues.
until ggTeiler it goes from minimum integer to maximum integer value. Refer this
So then from maximum postive int value, it'll come to a value where both 5 % ggTeiler != 0 and -11 % ggTeiler != 0 becomes false when ggTeiler = -1.
Then the loop exits.

Practice tracing your program. You'll undertand what each line does.

Answered By - sittsering
Answer Checked By - Marie Seifert (JavaFixing Admin)