@classmethod
def _get_kdj_default(cls, df):
    """ default KDJ, 9 days

        :param df: k line data frame
        :return: None
        """
    df['kdjk'] = df['kdjk_{}'.format(cls.KDJ_WINDOW)]
    df['kdjd'] = df['kdjd_{}'.format(cls.KDJ_WINDOW)]
    df['kdjj'] = df['kdjj_{}'.format(cls.KDJ_WINDOW)]
