Java Calendar的用法

/**
	 * 计算指定日期为当年第几周
	 * 
	 * @param year
	 *            指定的年份
	 * @param month
	 *            指定的月份
	 * @param day
	 *            指定的日
	 * @return 指定日期为当年的第几周
	 */
	public static int caculateWeekOfYear(int year, int month, int day) {
		Calendar c = Calendar.getInstance();
		c.set(Calendar.YEAR, year);
		c.set(Calendar.MONTH, month - 1);
		c.set(Calendar.DATE, day);
		return c.get(Calendar.WEEK_OF_YEAR);
	}

	/**
	 * 获取本月第一天是星期几
	 * 
	 * @return
	 */
	public static int getWeekOfFirstDay(Calendar c) {
		Calendar calendar = c;
		calendar.set(Calendar.DAY_OF_MONTH, 1);
		return calendar.get(Calendar.DAY_OF_WEEK);
	}

	/**
	 * 获取本月1号是该年的第几周
	 * 
	 * @return
	 */
	public static int getMonthStartWeek(Calendar c) {
		Calendar calendar = c;
		calendar.set(Calendar.DATE, 1);
		return calendar.get(Calendar.WEEK_OF_YEAR);
	}

	/**
	 * 获取当天是该年的第几周
	 */
	public static int getCurrentWeekOfYear() {
		Calendar calendar = Calendar.getInstance();
		return calendar.get(Calendar.WEEK_OF_YEAR);
	}

	/**
	 * 获取上月的总天数
	 * 
	 * @return
	 */
	public static int getLastMonthDays(Calendar c) {
		Calendar calendar = c;
		calendar.set(Calendar.MONTH, calendar.get(Calendar.MONTH) - 1);
		return calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
	}

	/**
	 * 获取指定月份的总天数
	 * 
	 * @return
	 */
	public static int getCurrentMonthDays(int month) {
		Calendar c = Calendar.getInstance();
		c.set(Calendar.MONTH, month);
		return c.getActualMaximum(Calendar.DAY_OF_MONTH);
	}

	/**
	 * 获取指定年份有多少周
	 * 
	 * @param year
	 * @return
	 */
	public static int getTotalWeekOfYear(int year) {
		Calendar c = Calendar.getInstance();
		return c.getActualMaximum(Calendar.WEEK_OF_YEAR);
	}

	/**
	 * 判断指定月份是否是当前月
	 * 
	 * @param month
	 * @return
	 */
	public static boolean isCurrentMonth(int month) {

		Calendar c = Calendar.getInstance();

		return (c.get(Calendar.MONTH) == month) ? true : false;

	}

	/**
	 * 计算指定的月份共有多少天
	 */
	public static int getTotalDaysOfMonth(int year, int month) {
		Calendar c = Calendar.getInstance();
		c.set(Calendar.YEAR, year);
		c.set(Calendar.MONTH, month);
		c.set(Calendar.DATE, 1);
		/**
		 * 计算这个月有多少天
		 */
		return c.getActualMaximum(Calendar.DAY_OF_MONTH);
	}