calendar前推n天_Java获取N天前，N天后的日期（如3天）详解

3天前：取负值

Calendar calendar1 = Calendar.getInstance();

SimpleDateFormat sdf1 = new SimpleDateFormat("yyyyMMdd");

calendar1.add(Calendar.DATE, -3);

String three_days_ago = sdf1.format(calendar1.getTime());

System.out.println(three_days_ago);

同理，3天后，取正值即可：

Calendar calendar2 = Calendar.getInstance();

SimpleDateFormat sdf2 = new SimpleDateFormat("yyyyMMdd");

calendar2.add(Calendar.DATE, 3);

String three_days_after = sdf2.format(calendar2.getTime());

System.out.println(three_days_after);