获取星期几的开始日期（可配置的星期几开始日期）

Question

我有当前日期，还有一个常数，它指示星期几。我想基于该常数获取一周的开始日期。如果我将一周的第一天硬编码为星期一（或其他任何东西），那么这很简单。但是一周的第一天一直在变化。因此，我不想在每次更改第一天时都更改代码。

这是我尝试使用Java的Calendar的方法：

public static Date getLastWeekdayDate()
{
    Calendar calendar = new GregorianCalendar();
    int dayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);
    int daysToSubtractFromCurrentDate = 0;

    switch (dayOfWeek)
    {
    case Calendar.WEDNESDAY:
        daysToSubtractFromCurrentDate = 4;
        break;

    case Calendar.THURSDAY:
        daysToSubtractFromCurrentDate = 5;
        break;

    case Calendar.FRIDAY:
        daysToSubtractFromCurrentDate = 6;
        break;

    case Calendar.SATURDAY:
        daysToSubtractFromCurrentDate = 0;
        break;

    case Calendar.SUNDAY:
        daysToSubtractFromCurrentDate = 1;
        break;

    case Calendar.MONDAY:
        daysToSubtractFromCurrentDate = 2;
        break;

    case Calendar.TUESDAY:
        daysToSubtractFromCurrentDate = 3;
        break;
    }

    calendar.add(Calendar.DATE, -daysToSubtractFromCurrentDate);
    calendar.set(Calendar.AM_PM, Calendar.AM);
    calendar.set(Calendar.MINUTE, 0);
    calendar.set(Calendar.SECOND, 0);
    calendar.set(Calendar.HOUR, 0);
    calendar.set(Calendar.MILLISECOND, 0);

    return calendar.getTime();
}

我想获取一周的开始日期。上面的函数返回星期的第一天，并且星期开始日期被硬编码为星期六。每当星期开始日期以上的要求发生变化时，我都必须更改代码。

Answer 1

我使用以下方法：

/** 1 = Sunday, 2 = Monday, 3 = Tuesday, 4 = Wednesday, 5 = Thursday,
* 6 = Friday, 7 = Saturday
*/
public static Date getFirstDayOfWeekDate(int firstDay)
{
    // Calculate the date of the first day of the week

    // First get the today's date
    Calendar c = new GregorianCalendar();

    // Now set the day of week to the first day of week
    while (c.get(Calendar.DAY_OF_WEEK) != firstDay)
    {
        c.add(Calendar.DAY_OF_MONTH, -1);
    }

    return c.getTime();
}