Integer num2 = (Integer) f.getChildItem(Fraction.NUMERATOR);
Integer num2 = (Integer) f.getChild(Fraction.NUMERATOR);
    public void subtract(Fraction f) throws Exception {/*??        if (f != null) {            Integer num2 = (Integer) f.getChildItem(Fraction.NUMERATOR);            if (num2 != null) {                                Integer extnum2 = num2.multiplyWith((Integer) getChildItem(Fraction.DENOMINATOR));                Integer num1 = (Integer) getChildItem(Fraction.NUMERATOR);                                if (num1 != null) {                                        Integer extnum1 = num1.multiplyWith((Integer) f.getChildItem(Fraction.DENOMINATOR));                    if (extnum1 != null) {                        Integer den1 = (Integer) getChildItem(Fraction.DENOMINATOR);                                    if (den1 != null) {                                                        setChildItem(Fraction.NUMERATOR, extnum1.subtract(extnum2));                            setChildItem(Fraction.DENOMINATOR, den1.multiplyWith((Integer) f.getChildItem(Fraction.DENOMINATOR)));                            reduct();                                        } else {                                        throw new Exception("Could not subtract fraction. The denominator 1 is null.");                        }                    } else {                                throw new Exception("Could not subtract fraction. The extended numerator 1 is null.");                    }                                                } else {                        throw new Exception("Could not subtract fraction. The numerator 1 is null.");                }                } else {                throw new Exception("Could not subtract fraction. The numerator 2 is null.");            }        } else {                    throw new Exception("Could not subtract fraction. The fraction is null.");        }*/    }