JAVA取得1ヶ月の開始と終了時間および2つの日付が数ヶ月異なる

    /**
     *           
     * @param currentDate
     * @return
     */
    public static Date getStartDate(String currentDate){
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Calendar c = Calendar.getInstance();
        try {
            c.setTime(sdf.parse(currentDate));
            c.add(Calendar.MONTH, 0);
            //   1 ,           
            c.set(Calendar.DAY_OF_MONTH, 1);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return c.getTime();
    }

    /**
     *           
     * @param currentDate
     * @return
     */
    public static Date getEndDate(String currentDate){
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Calendar c = Calendar.getInstance();
        try {
            c.setTime(sdf.parse(currentDate));
            c.set(Calendar.DAY_OF_MONTH, c.getActualMaximum(Calendar.DAY_OF_MONTH));
            c.set(Calendar.HOUR_OF_DAY, 23);
            c.set(Calendar.MINUTE, 59);
            c.set(Calendar.SECOND, 59);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return c.getTime();
    }

    /**
     *            
     * @param start
     * @param end
     * @return
     */
    public static int getMonth(Date start, Date end) {
        if (start.after(end)) {
            Date t = start;
            start = end;
            end = t;
        }
        Calendar startCalendar = Calendar.getInstance();
        startCalendar.setTime(start);
        Calendar endCalendar = Calendar.getInstance();
        endCalendar.setTime(end);
        Calendar temp = Calendar.getInstance();
        temp.setTime(end);
        temp.add(Calendar.DATE, 1);
        int year = endCalendar.get(Calendar.YEAR) - startCalendar.get(Calendar.YEAR);
        int month = endCalendar.get(Calendar.MONTH) - startCalendar.get(Calendar.MONTH);
        if ((startCalendar.get(Calendar.DATE) == 1)&& (temp.get(Calendar.DATE) == 1)) {
            return year * 12 + month + 1;
        } else if ((startCalendar.get(Calendar.DATE) != 1) && (temp.get(Calendar.DATE) == 1)) {
            return year * 12 + month;
        } else if ((startCalendar.get(Calendar.DATE) == 1) && (temp.get(Calendar.DATE) != 1)) {
            return year * 12 + month;
        } else {
            return (year * 12 + month - 1) < 0 ? 0 : (year * 12 + month);
        }
    }

    public static void main(String[] args) throws ParseException{
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String startDate = "2018-10-15 00:00:00";
        String ednDate = "2019-11-10 23:59:59";
        Date sdate = getStartDate(startDate);
        Date edate = getEndDate(startDate);
        System.out.println("    ：" + sdf.format(sdate));
        System.out.println("    ：" + sdf.format(edate));
        int month = getMonth(sdf.parse(startDate), sdf.parse(ednDate));
        System.out.println("      ：" + month);
    }