Tauziehen! HighScorers Prime vs. United DownCounters​

package hausuebung7;

import acm.program.*;
import java.math.*;

public class Rational extends ConsoleProgram{
    
    public Rational() {
        this(0);
    }
    
    public Rational (int n) {
        this(n, 1);
    }

    public Rational (int x, int y) {
        int g = gcd(Math.abs(x),Math.abs(y));
        num = num.add(BigInteger.valueOf(x).divide(BigInteger.valueOf(g)));
        //num = x/g;
        den = den.add(BigInteger.valueOf(Math.abs(y)).divide(BigInteger.valueOf(g)));
        if (y < 0) num = num.multiply(BigInteger.valueOf(-1));
    }
    
    public Rational add(Rational r) {
        return new Rational(num.add(BigInteger.valueOf(r.den)));
    }
    
    /**public Rational add(Rational r) {
    *    return new Rational(this.num * r.den + r.num * this.den, this.den * r.den);
    *}
    */
    
    public Rational substract(Rational r) {
        return new Rational(this.num.multiply(BigInteger.valueOf(r.den)).substract(BigInteger.valueOf(this.den)), 
                this.den.multiply(BigInteger.valueOf(r.den)));
    }
    
    /**public Rational substract(Rational r) {
    *    return new Rational(this.num * r.den - r.num * this.den, this.den * r.den);
    *}
    */
    
    public Rational multiply(Rational r) {
        return new Rational(this.num.multiply(BigInteger.valueOf(r.num)), 
                this.den.multiply(BigInteger.valueOf(r.den)));
    }
    
    /**public Rational multiply(Rational r) {
    *    return new Rational(this.num * r.num, this.den * r.den);
    *}
    */
    
    public Rational divide(Rational r) {
        return new Rational(this.num.multiply(BigInteger.valueOf(r.den)), 
                this.den.multiply(BigInteger.valueOf(r.num)));
    }
    
    /**public Rational divide(Rational r) {
    *    return new Rational(this.num * r.den, this.den * r.num);
    *}
    */
    
    public String toString() {
        if (den.equals(1))
        //if (den == 1) {
            return "" + intValue(num);
        } else {
            return intValue(num) + "/" + intValue(den);
        }
    }
    
    /* Größter gemeinsamer Teiler (gcd) nach euklidischem Algorithmus berechnen */
    private int gcd(int x, int y) {
        int r = x % y;
        while (r != 0) {
            x = y;
            y = r;
            r = x % y;
        }
        return y;
    }
    
    /* private Variablen deklarieren*/
    private new BigInteger num;
    private new BigInteger den;
    
    /* Run Methode */
    public void run() {
        Rational a= new Rational(1, 2);
        Rational b= new Rational(1, 3);
        Rational c= new Rational(1, 6);
        Rational sum = a.add(b).add(c);
        println(a + " + " + b + " + " + c + " = " + sum);
    }
}