Calendar日期的计算

一，得到三月内的周六，周日

  Calendar calendar=Calendar.getInstance();//当前日期
		  Calendar calendar2=Calendar.getInstance();
		  int curYear = calendar2.get(Calendar.YEAR); // 得到系统年份
		  int curMonth = calendar2.get(Calendar.MONTH); // 得到系统月份
		  int curDay=calendar2.get(Calendar.DAY_OF_MONTH);
		  Calendar nowyear=Calendar.getInstance();
		  nowyear.set(curYear,curMonth, curDay);//将开始日期设置为当天，如7月17日
		  Calendar nexty=Calendar.getInstance();
		  calendar2.add(Calendar.MONTH,4);
		  nexty.set(calendar2.get(Calendar.YEAR),calendar2.get(Calendar.MONTH), 1);//将结束时间设置为三个月后的第一天，如10月1日
		  calendar.add(Calendar.DAY_OF_MONTH, -calendar.get(Calendar.DAY_OF_WEEK));//周六

		 SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
		 /**　初始化周六的日期*/
		 calendar.add(Calendar.DAY_OF_MONTH, -calendar.get(Calendar.DAY_OF_WEEK));//周六
		 Calendar SaturdayC=(Calendar) calendar.clone();

		 for(;SaturdayC.before(nexty);SaturdayC.add(Calendar.DAY_OF_YEAR,7)){

			 if(SaturdayC.after(nowyear)){
				 Date date = sdf.parse(SaturdayC.get(Calendar.YEAR)+"-"+(1+SaturdayC.get(Calendar.MONTH))+"-"+SaturdayC.get(Calendar.DATE));
				 String time=sdf.format(date);
				 SaturdayList.add(time);
			 }

		 }
		 /**　初始化周日的日期*/
		 calendar.add(Calendar.DAY_OF_MONTH,-calendar.get(Calendar.DAY_OF_WEEK)+1);//周日
		 Calendar SundayC=(Calendar) calendar.clone();
		 for(;SundayC.before(nexty);SundayC.add(Calendar.DAY_OF_YEAR,7)){
			 if(SundayC.after(nowyear)){
			 Date date = sdf.parse(SundayC.get(Calendar.YEAR)+"-"+(1+SundayC.get(Calendar.MONTH))+"-"+SundayC.get(Calendar.DATE));
			 String time=sdf.format(date);
			 SundayList.add(time);
			 }
		 }

二，得到三个月内的工作日

/**
		 * 得到三个月末的最后一天
		 */
		Calendar cal = Calendar.getInstance();
		  // 不加下面2行，就是取当前时间前一个月的第一天及最后一天
		cal.set(Calendar.YEAR,curYear);
		cal.set(Calendar.MONTH,curMonth+2);
		cal.set(Calendar.DAY_OF_MONTH, 1);
		cal.add(Calendar.DAY_OF_MONTH, -1);
		Date lastDate = cal.getTime();

		String start =curYear+"-"+curMonth+"-"+curDay;
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
		Date dBegin = null ;
		try {
			dBegin = sdf.parse(start);
		} catch (ParseException e) {
			e.printStackTrace();
		}
		 WorkdayList.add(sdf.format(dBegin));

		 Calendar calBegin = Calendar.getInstance();
		 // 使用给定的 Date 设置此 Calendar 的时间
		 calBegin.setTime(dBegin);
		 Calendar calEnd = Calendar.getInstance();
		 // 使用给定的 Date 设置此 Calendar 的时间
		 calEnd.setTime(lastDate);
		 // 测试此日期是否在指定日期之后
		 while (lastDate.after(calBegin.getTime())){
		   // 根据日历的规则，为给定的日历字段添加或减去指定的时间量
		   calBegin.add(Calendar.DAY_OF_MONTH, 1);
		   WorkdayList.add(sdf.format(calBegin.getTime()));
		 }  

		 WorkdayList.removeAll(SaturdayList);
		 WorkdayList.removeAll(SundayList);

三、日期间的比较大小

date1.after(date2)
date1.before(date2)

四、Calendar中add() 与set()的区别

add()是移位，set()是设置

Calendar日期的计算