如何计算Java中日期的星期几？

如何用Java编写一个方法，当我以

computeDayOfWeek（Month，date）

格式键入日期时，该方法将告诉我一周中的哪一天？

如果您正在使用Java。您可以使用Joda Time API来实现这一点： 检查此处的文档：

示例：

DateTime dt = new DateTime()
System.out.println(dt.dayOfWeek().getAsText());

---

如果你正在寻找Java。您可以使用Joda Time API来实现这一点： 检查此处的文档：

示例：

DateTime dt = new DateTime()
System.out.println(dt.dayOfWeek().getAsText());

---

不需要外部库

java.util.Calendar

类处理这些内容

Calendar c = Calendar.getInstance();
c.setTime(put a java.util.Date instance here);
int dow = c.get(Calendar.DAY_OF_WEEK); //1=sunday, 2=monday, 3=Calendar.WEDNESDAY...

---

不需要外部库

java.util.Calendar

类处理这些内容

Calendar c = Calendar.getInstance();
c.setTime(put a java.util.Date instance here);
int dow = c.get(Calendar.DAY_OF_WEEK); //1=sunday, 2=monday, 3=Calendar.WEDNESDAY...

---

如果您需要自己计算，而不是使用预先制作的库函数，请查看

---

我在去年实施了这项计划，然后纠正了学生们提出的大约40个解决方案（其中相当一部分学生是第一个真正的解决方案），他们试图自己动手——这里有很多方法会犯错误。确保测试不同日期（1月、2月、其他月份、正常年份、闰年、2000年（是闰年）和1900年（不是闰年））。

如果需要自己计算，而不是使用预先制作的库函数，请查看

---

我在去年实施了这项计划，然后纠正了学生们提出的大约40个解决方案（其中相当一部分学生是第一个真正的解决方案），他们试图自己动手——这里有很多方法会犯错误。确保你测试不同的日期（1月、2月、其他月份、正常年份、闰年、2000年（是闰年）和1900年（不是闰年））。

大约10年前我写了一节有趣的小课。我只是为了好玩而做的，从来没有使用过，但是请随意使用和改进它（给我发邮件）。相当可怕的代码，因为我当时是初学者

package se.danero.calendar.util;

import java.lang.NullPointerException;

/**
 * This is a Calendar that is meant to be used as a utility. To come up with this class, I analyzed the gregorian calendar, and I searched the web for
 * useful, free algorithms. Then I put them together to create this version of of the Calendar.<BR>
 * <BR>
 * <B>The analyze</B><BR>
 * In my analyze of the gregorian calendar, I have come to the conclution that<BR>
 * there are 8 different types of year endings. These endings have a recurring<BR>
 * cycle of 28 years. The pattern repeats itself over 28 years, continiously.<BR>
 * <BR>
 * The pattern consists of 8 different types of year-endings. These are listed below <BR>
 * <BR>
 * <B>Type</B><BR>
 * 1 = 4 times over a period of 28 year period<BR>
 * 2 = 4 times over a period of 28 year period<BR>
 * 3 = 3 times ... <BR>
 * 4 = 4 times ... <BR>
 * 5 = 4 times ... <BR>
 * 6 = 4 times ... <BR>
 * 7 = 4 times ... <BR>
 * 8 = 1 time ... <BR>
 * <BR>
 * 
 * @author Robert Nordin, robert.nordin@bredband.net
 * @version 0.5
 * 
 */
public class Calendar {
    // ****************************************************************************
    // *** MEMBERS
    // ****************************************************************************
    // *** Type of year break; beginning with break 1980/1981 ***
    private final int types[] = { 1, 2, 3, 4, 5, 6, 1, 2, 4, 7, 5, 6, 2, 3, 4, 7, 6, 1, 2, 3, 7, 5, 6, 1, 8, 4, 7, 5 };

    // *** Week of the last week of the year and the first week of the new year ***
    private final int weeks[][] = { { 52, 1 }, { 52, 53 }, { 52, 1 }, { 52, 1 }, { 52, 1 }, { 52, 1 }, { 52, 1 }, { 52, 53 } };

    // Date of the last day of the last week and the last date of the first
    // week in the new year
    // private final int dates[][] = {{28, 4}, {27, 3}, { 2, 9}, { 1, 8},
    // {30, 6}, {29, 5}, {31, 7}, {26, 2}};

    private boolean initiated = false;
    private int year = 0;
    private int preMonths = 0;
    private int aftMonths = 0;

    // ****************************************************************************
    // *** CONSTRUCTORS
    // ****************************************************************************
    public Calendar() {
    }

    // ****************************************************************************
    public Calendar(int year) throws OutOfRangeException {
        if (!isYearValid(year)) {
            throw new OutOfRangeException(OutOfRangeException.TYPE_YEAR, "Year[" + year + "]");
        } else {
            this.year = year;
            initiated = true;
        }
    }

    // ****************************************************************************
    public Calendar(int year, int preMonths, int aftMonths) throws OutOfRangeException {
        if (!isYearValid(year)) {
            throw new OutOfRangeException(OutOfRangeException.TYPE_YEAR, "Year[" + year + "]");
        } else {
            this.year = year;
            initiated = true;
        }
        this.preMonths = ((preMonths >= 0) && (preMonths <= 12)) ? preMonths : 0;
        this.aftMonths = ((aftMonths >= 0) && (aftMonths <= 12)) ? aftMonths : 0;
    }

    // ****************************************************************************
    private boolean isYearValid(int year) {
        return ((year >= Date.MIN_YEAR) && (year <= Date.MAX_YEAR)) ? true : false;
    }

    // ****************************************************************************
    private int[] getWeeks(int type) {
        int retval[] = null;
        int arrayindex = type - 1;
        try {
            retval = weeks[arrayindex];
        } catch (Exception ex) {
            System.err.println("getWeeks(): Type is not inside valid range");
        }
        return retval;
    }

    // ****************************************************************************
    private int getType(int index) {
        int retval = types[index];
        if ((retval < 1) || (retval > 8)) {
            System.err.println("getType(): Index is not inside valid range");
        }
        return retval;
    }

    // ****************************************************************************
    private int getFirstWeek(int type) {
        int retval = 1;
        if (type == 3 || type == 4) {
            retval = 52;
        } else
            if (type == 2 || type == 8) {
                retval = 53;
            }
        return retval;
    }

    // ****************************************************************************
    private int getLastWeek(int type) {
        int retval = 52;
        if (type == 1 || type == 5 || type == 6) {
            retval = 1;
        } else
            if (type == 2 || type == 8) {
                retval = 53;
            }
        return retval;
    }

    // ****************************************************************************
    public String intToWeekday(int day, boolean longVersion) {
        String retval = "";
        /*
        if (day == 1) {
            retval = (longVersion) ? "Monday" : "Mon";
        } else
            if (day == 2) {
                retval = (longVersion) ? "Tuesday" : "Tue";
            } else
                if (day == 3) {
                    retval = (longVersion) ? "Wednesday" : "Wed";
                } else
                    if (day == 4) {
                        retval = (longVersion) ? "Thursday" : "Thu";
                    } else
                        if (day == 5) {
                            retval = (longVersion) ? "Friday" : "Fri";
                        } else
                            if (day == 6) {
                                retval = (longVersion) ? "Saturday" : "Sat";
                            } else
                                if (day == 7) {
                                    retval = (longVersion) ? "Sunday" : "Sun";
                                } else {
                                    System.err.println("intToWeekday(): Day is not inside valid range");
                                }
         */
        switch (day) {
        case 1: 
            retval = (longVersion) ? "Monday" : "Mon";
            break;
        case 2: 
            retval = (longVersion) ? "Tuesday" : "Tue";
            break;
        case 3: 
            retval = (longVersion) ? "Wednesday" : "Wed";
            break;
        case 4: 
            retval = (longVersion) ? "Thursday" : "Thu";
            break;
        case 5: 
            retval = (longVersion) ? "Friday" : "Fri";
            break;
        case 6: 
            retval = (longVersion) ? "Saturday" : "Sat";
            break;
        case 7: 
            retval = (longVersion) ? "Sunday" : "Sun";
            break;
        default: 
            System.err.println("intToWeekday(): Day is not inside valid range");
        }           
        return retval;
    }

    // ****************************************************************************
    private int getYearType(int year) {
        int retval = -1;
        if (year >= 1980) {
            retval = getType(((year - 1980) % 28));
        } else
            if (year == 1979) {
                retval = 5;
            } else {
                System.err.println("getYearType(): Year is not inside valid range");
            }
        return retval;
    }

    /**
     * Compute the sequential number of a day in the year (1-Jan=1, 31-Dec=365/366). The algorithm used: J.D. Robertson: Remark on Algorithm 398,
     * Comm. ACM 13, 10 (Oct. 1972), p. 918
     * 
     * @param date
     *            a date of the day you query about
     * @return returns an integer between 1 and 365/366. 366 if it is a leapyear.
     * @throw NullPointerException if the date is null.
     */
    public int getDayInYear(Date date) throws NullPointerException {
        if (date == null)
            throw new NullPointerException("Date cannot be null");
        int y = date.getYear();
        int m = date.getMonth();
        int d = date.getDay();
        int lm = (m + 10) / 13;
        return (int) (((long) 3055 * (long) (m + 2)) / 100 - 2 * lm - 91
                + (1 - (y - (y / 4) * 4 + 3) / 4 + (y - (y / 100) * 100 + 99) / 100 - (y - (y / 400) * 400 + 399) / 400) * lm + d);
    }

    /**
     * Returns an array of dates that conforms to a year and a week.
     * 
     * @param year
     *            the year in the form eg. 1980. Must be within Date.MIN_YEAR and Date.MAX_YEAR.
     * @param week
     *            the week. Must be less than 54
     * @return returns a full week of valid ISODates if inparameters are within the given range. returns a full week of null pointers if not.
     */
    public Date[] getWeekDates(int year, int week) {
        Date retval[] = new Date[7];
        if ((isYearValid(year)) && ((week > 0) && (week < 54))) {
            int dayCounter = 0;
            for (int i = 1; i < 13; i++) {
                for (int j = 1; j <= Date.getDaysInMonth(year, i); j++) {
                    Date tmp = new Date(year, i, j);

                    if (this.getWeekNumber(tmp) == week) {
                        retval[dayCounter] = tmp;
                        if (dayCounter == 7) {
                            i = 13;
                            j = 31;
                        }
                        if (dayCounter < 6) {
                            dayCounter++;
                        }
                    }
                }
            }
        }
        return retval;
    }

    /**
     * Returns the weeknumber of the given date.
     * 
     * @param date
     *            a date that you want to know in what week it is.
     * @return returns the weeknumber as an integer.
     * @throws NullPointerException
     *             if the parameter is null.
     */
    public int getWeekNumber(Date date) throws NullPointerException {
        int retval = -1;
        if (date == null)
            throw new NullPointerException("ISODate cannot be null");
        // *** Incoming data ***
        int year = date.getYear();
        int month = date.getMonth();
        int day = date.getDay();

        if (isYearValid(year)) {
            int targetDay = getDayInYear(date);
            int firstWeek = getFirstWeek(getYearType((year - 1)));
            int lastWeek = getLastWeek(getYearType(year));
            Date oneone = new Date(year, 1, 1);

            int firstDay = getDayInWeek(oneone);
            int dayCounter = 0;
            int weekCounter = firstWeek;
            int dayInWeek = firstDay;

            while (dayCounter != targetDay) {
                if (dayInWeek == 8) {
                    dayInWeek = 1;
                    if ((weekCounter > 51) && (dayCounter < 10)) {
                        weekCounter = 1;
                    } else
                        if ((dayCounter > 360) && (weekCounter > lastWeek)) {
                            weekCounter = lastWeek;
                        } else {
                            weekCounter++;
                        }
                }
                dayCounter++;
                dayInWeek++;
            }
            retval = weekCounter;
        }
        return retval;
    }

    /**
     * Returns an integer that tells you what day of the week the date specifies. The algorithm used is Zeller's congruence for the Gregorian
     * calendar.
     * 
     * @param date
     *            a date that points out the day you want to know the weekday of.
     * 
     * @return returns the weekday in the form of an integer. 1=Monday, 2=Tuesday...
     * @throws NullPointerException
     *             if the parameter is null.
     */
    public int getDayInWeek(Date date) throws NullPointerException {
        if (date == null)
            throw new NullPointerException("ISODate cannot be null");
        int year = date.getYear();
        int month = date.getMonth();
        int day = date.getDay();
        if (month < 3) {
            month += 12;
            year--;
        }
        return ((13 * month + 3) / 5 + day + year + year / 4 - year / 100 + year / 400) % 7 + 1;
    }
}

包se.danero.calendar.util；
导入java.lang.NullPointerException；
/**
*这是一个打算用作实用程序的日历。为了上这门课，我分析了公历，并在网上搜索了
*有用的免费算法。然后我将它们放在一起创建这个版本的日历。

*

*分析

*在我对公历的分析中，我得出的结论是

*有8种不同类型的年终。这些结尾具有重复性

*周期为28年。这种模式持续重复了28年。

*

*该模式包括8种不同类型的年终。下面列出了它们

*

*类型

*1=28年期间的4次

*2=28年期间的4次

*3=3次

*4=4次

*5=4次

*6=4次

*7=4次

*8=1次

*

* 
*@作者罗伯特·诺丁，罗伯特。nordin@bredband.net
*@version 0.5
* 
*/
公课日历{
// ****************************************************************************
//***成员
// ****************************************************************************
//***年假类型；从1980/1981年的年假开始***
私有final int类型[]={1,2,3,4,5,6,1,2,4,7,5,6,2,3,4,7,6,1,2,3,7,5,6,1,8,4,7,5}；
//***一年中最后一周的一周和新年的第一周***
私人最后整数周[][]={{52,1}，{52,53}，{52,1}，{52,1}，{52,1}，{52,1}，{52,1}，{52,1}，{52,53}；
//上周最后一天的日期和第一周最后一天的日期
//新年的一周
//私人最终整数日期[][]={{28,4}，{27,3}，{2,9}，{1,8}，
// {30, 6}, {29, 5}, {31, 7}, {26, 2}};
私有布尔值=false；
私家车整年=0；
私有整数前几个月=0；
私人月数=0；
// ****************************************************************************
//***施工人员
// ****************************************************************************
公历（）{
}
// ****************************************************************************
公共日历（整数年）抛出范围异常{
如果（！isYearValid（年））{
抛出新的OutOfRangeException（OutOfRangeException.TYPE_YEAR，“YEAR[“+YEAR+”]）；
}否则{
今年=年；
启动=真；
}
}
// ****************************************************************************
公历（整数年、整数前月、整数后月）抛出范围异常{
如果（！isYearValid（年））{
抛出新的OutOfRangeException（OutOfRangeException.TYPE_YEAR，“YEAR[“+YEAR+”]）；
}否则{
今年=年；
启动=真；
}
this.preMonths=（（preMonths>=0）和&（preMonths=0）和&（aftmounts=Date.minu YEAR）和&（YEAR 8））{
System.err.println（“getType（）：索引不在有效范围内”）；
}
返回返回；
}
// ****************************************************************************
私有整数getFirstWeek（整数类型）{
int-retval=1；
如果（类型==3 | |类型==4）{
retval=52；
}否则
如果（类型==2 | |类型==8）{
retval=53；
}
返回返回；
}
// ****************************************************************************
私有整数getLastWeek（整数类型）{
int-retval=52；
如果（类型==1 | |类型==5 | |类型==6）{
retval=1；
}否则
如果（类型==2 | |类型==8）{
retval=53；
}
返回返回；
}
// ****************************************************************************
公共字符串intToWeekday（int-day，布尔长版本）{
字符串retval=“”；
/*
如果（天==1）{
电视转播