创造实验数据
// 现在的时间
Date nowDate = new Date();
// 设置三天后的时间
Calendar c = Calendar.getInstance();
c.setTime(nowDate);
c.add(Calendar.DATE,3);
Date afterThreeDay = c.getTime();
默认向下取整天数
// 一天的毫秒数
long DAY = 24L * 60L * 60L * 1000L;
// 加一秒
Long dayNumberOne = (endDate.getTime() + 1000 - startDate.getTime()) / DAY;
但是有的时候,我们需要向上取整
Calendar c = Calendar.getInstance();
c.setTime(nowDate);
// 增加两天多一个小时
c.add(Calendar.HOUR,49);
Date afterTwoDay = c.getTime();
// 先转成double类型
Long afterTwoDayDouble = afterTwoDay .getTime()+1000;
Long nowDateDouble = nowDate.getTime();
Double dayNumber2 = (afterTwoDayDouble .doubleValue() - nowDateDouble .doubleValue()) / DAY;
// 获取的double类型的天数向上取整
int dayNumInt =(int)Math.ceil(dayNumber2);