java 获取两个时间相差天数

    public static int getIntervalDays(Date oldDate,Date newDate){        if(oldDate.after(newDate)){            throw new  IllegalArgumentException("时间先后顺序不对!");        }        //将转换的两个时间对象转换成Calendard对象        Calendar can1 = Calendar.getInstance();        can1.setTime(oldDate);        Calendar can2 = Calendar.getInstance();        can2.setTime(newDate);        //拿出两个年份        int year1 = can1.get(Calendar.YEAR);        int year2 = can2.get(Calendar.YEAR);        //天数        int days = 0;        Calendar can = null;        //减去小的时间在这一年已经过了的天数        //加上大的时间已过的天数        days -= can1.get(Calendar.DAY_OF_YEAR);        days += can2.get(Calendar.DAY_OF_YEAR);        can = can1;        for (int i = 0; i < Math.abs(year2-year1); i++) {            //获取小的时间当前年的总天数            days += can.getActualMaximum(Calendar.DAY_OF_YEAR);            //再计算下一年。            can.add(Calendar.YEAR, 1);        }        return days;    }