獲取過去某一天的日期，然後可以利用for 迴圈，從高到低（或者從低到高，決定日期陣列的順序），獲取過去任意天數內的日期，同理可以寫出未來任意天數的方法。

 /**
     * 獲取過去或者未來 任意天內的日期陣列
     * @param intervals      intervals天內
     * @return              日期陣列
     */
    public static ArrayList<String> test(int intervals ) {
        ArrayList<String> pastDaysList = new ArrayList<>();
        ArrayList<String> fetureDaysList = new ArrayList<>();
        for (int i = 0; i <intervals; i++) {
            pastDaysList.add(getPastDate(i));
            fetureDaysList.add(getFetureDate(i));
        }
        return pastDaysList;
    }

    /**
     * 獲取過去第幾天的日期
     *
     * @param past
     * @return
     */
    public static String getPastDate(int past) {
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.DAY_OF_YEAR, calendar.get(Calendar.DAY_OF_YEAR) - past);
        Date today = calendar.getTime();
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
        String result = format.format(today);
        Log.e(null, result);
        return result;
    }

    /**
     * 獲取未來 第 past 天的日期
     * @param past
     * @return
     */
    public static String getFetureDate(int past) {
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.DAY_OF_YEAR, calendar.get(Calendar.DAY_OF_YEAR) + past);
        Date today = calendar.getTime();
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
        String result = format.format(today);
        Log.e(null, result);
        return result;
    }