[Java]两个有理数的加减乘除

public class Rational {
        private long num=0; //分子
        private long den=1; //分母
        /************Begin*****************/
        long i;
        public Rational(long num,long den){
            this.num=num;
            this.den=den;
        }
        public long getnum(){
            return num;
        }
        public long getden(){
            return den;
        }
        public Rational add(Rational r){
            long den1=this.den*(r.getden());
            long num1=this.num*(r.getden())+(r.getnum())*this.den;
            /*simplify(num1,den1);*/
            if(num1>=den1){
                for(i=num1;;i--)
                    if(num1%i==0&&den1%i==0) break;
            }
            else{
                for(i=den1;;i--)
                    if(num1%i==0&&den1%i==0) break;
            }
            num1=(num1/i);den1=(den1/i);

            return new Rational(num1,den1);
        }
        public Rational substract(Rational r){
            long den1=this.den*(r.getden());
            long num1=this.num*(r.getden())-(r.getnum())*this.den;
            /*simplify(num1,den1);*/
            if(num1>=den1){
                for(i=num1;;i--)
                    if(num1%i==0&&den1%i==0) break;
            }
            else{
                for(i=den1;;i--)
                    if(num1%i==0&&den1%i==0) break;
            }
            num1=(num1/i);den1=(den1/i);
            return new Rational(num1,den1);
        }
        public Rational multiply(Rational r){
            long den1=this.den*(r.getden());
            long num1=this.num*(r.getnum());
            /*simplify(num1,den1);*/
            if(num1>=den1){
                for(i=num1;;i--)
                    if(num1%i==0&&den1%i==0) break;
            }
            else{
                for(i=den1;;i--)
                    if(num1%i==0&&den1%i==0) break;
            }
            num1=(num1/i);den1=(den1/i);
            return new Rational(num1,den1);
        }
        public Rational divide(Rational r){
        long den1=this.den*(r.getnum());
        long num1=this.num*(r.getden());
        /*simplify(num1,den1);*/
            if(num1>=den1){
                for(i=num1;;i--)
                    if(num1%i==0&&den1%i==0) break;
            }
            else{
                for(i=den1;;i--)
                    if(num1%i==0&&den1%i==0) break;
            }
            num1=(num1/i);den1=(den1/i);
        return new Rational(num1,den1);
    }
    public String toString(){
        return num+"/"+den;
    }
}