Java对日期Date类进行加减运算，年份加减，月份加减

conclusions:

1 create specific date rather than current date.

a. using SimpleDateFormat and Callendar.

eg: SimpleDateFormat sdf=new SimpleDateFormat("yyyyMMdd"); String str="20110823"; Date dt=sdf.parse(str); Calendar rightNow = Calendar.getInstance(); rightNow.setTime(dt);

2. using GregorianCalendar .

   Calendar cal = GregorianCalendar(int year,int month,int date);

1.用java.util.Calender来实现

Calendar calendar=Calendar.getInstance(); calendar.setTime(new Date()); System.out.println(calendar.get(Calendar.DAY_OF_MONTH));//今天的日期 calendar.set(Calendar.DAY_OF_MONTH,calendar.get(Calendar.DAY_OF_MONTH)+1);//让日期加1 System.out.println(calendar.get(Calendar.DATE));//加1之后的日期Top

SimpleDateFormat sdf=new SimpleDateFormat("yyyyMMdd");String str="20110823";Date dt=sdf.parse(str);Calendar rightNow = Calendar.getInstance();rightNow.setTime(dt);rightNow.add(Calendar.YEAR,-1);//日期减1年rightNow.add(Calendar.MONTH,3);//日期加3个月rightNow.add(Calendar.DAY_OF_YEAR,10);//日期加10天Date dt1=rightNow.getTime();String reStr = sdf.format(dt1);System.out.println(reStr);

2.用GregorianCalendar来实现

*gc.add(1,-1)表示年份减一.*gc.add(2,-1)表示月份减一.*gc.add(3.-1)表示周减一.*gc.add(5,-1)表示天减一.

*GregorianCalendar类的add(int field,int amount)方法表示年月日加减.*field参数表示年,月.日等.*amount参数表示要加减的数量.

你所缺少的部分，也早已被我用想像的画笔填满。