java Calendar add方法

public static Date addYears(Date date, int amount)

{

return add(date, 1, amount);

}

public static Date addMonths(Date date, int amount)

{

return add(date, 2, amount);

}

public static Date addWeeks(Date date, int amount)

{

return add(date, 3, amount);

}

public static Date addDays(Date date, int amount)

{

return add(date, 5, amount);

}

public static Date addHours(Date date, int amount)

{

return add(date, 11, amount);

}

public static Date addMinutes(Date date, int amount)

{

return add(date, 12, amount);

}

public static Date addSeconds(Date date, int amount)

{

return add(date, 13, amount);

}

public static Date addMilliseconds(Date date, int amount)

{

return add(date, 14, amount);

}

private static Date add(Date date, int calendarField, int amount)

{

if(date == null)

{

throw new IllegalArgumentException("The date must not be null");

} else

{

Calendar c = Calendar.getInstance();

c.setTime(date);

c.add(calendarField, amount);

return c.getTime();

}

}