Calendar instance = Calendar.getInstance();
		System.out.println(instance.getTime());
		instance.add(Calendar.MONTH, 1);//月份+1
		instance.set(Calendar.DAY_OF_MONTH, 1);//天设为一个月的第一天
		System.out.println(instance.getTime());
		instance.add(Calendar.DAY_OF_MONTH, -1);//本月最后一天
		System.out.println(instance.getTime());
		instance.add(Calendar.DAY_OF_MONTH,
				1 - instance.get(Calendar.DAY_OF_WEEK));//根据月末最后一天是星期几，向前偏移至最近的周日
		System.out.println(instance.getTime());