java计算两个日期相差的天数

    /**
     * 计算两个日期相差的天数
     * @param oldDate
     * @param newDate
     * @return
     * @author WangLiping
     */
    public static int comparePastDate(String oldDate,String nowDate){
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Calendar calendar = Calendar.getInstance();
        Date old;
        int day=0;
        try {
            old = sdf.parse(oldDate);
            calendar.setTime(old);
            Long oTime = calendar.getTimeInMillis();

            Date now = sdf.parse(nowDate);
            calendar.setTime(now);
            Long nTime = calendar.getTimeInMillis();

            day=(int) ((nTime - oTime)/(3600F * 1000 * 24));
        } catch (ParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return day;
    }