Java 8及更高版本

Question

如何知道特定年份的特定月份有多少天？

String date = "2010-01-19";
String[] ymd = date.split("-");
int year = Integer.parseInt(ymd[0]);
int month = Integer.parseInt(ymd[1]);
int day = Integer.parseInt(ymd[2]);
Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.YEAR,year);
calendar.set(Calendar.MONTH,month);
int daysQty = calendar.getDaysNumber(); // Something like this

Answer 1

Java 8及更高版本

@Warren M. Nocos。如果您尝试使用Java 8的新Date and Time API，则可以使用java.time.YearMonth类。请参阅Oracle Tutorial。

// Get the number of days in that month
YearMonth yearMonthObject = YearMonth.of(1999, 2);
int daysInMonth = yearMonthObject.lengthOfMonth(); //28

测试：在闰年尝试一个月：

yearMonthObject = YearMonth.of(2000, 2);
daysInMonth = yearMonthObject.lengthOfMonth(); //29

Java 7及更早版本

创建日历，设置年份和月份并使用getActualMaximum

int iYear = 1999;
int iMonth = Calendar.FEBRUARY; // 1 (months begin with 0)
int iDay = 1;

// Create a calendar object and set year and month
Calendar mycal = new GregorianCalendar(iYear, iMonth, iDay);

// Get the number of days in that month
int daysInMonth = mycal.getActualMaximum(Calendar.DAY_OF_MONTH); // 28

测试：在闰年尝试一个月：

mycal = new GregorianCalendar(2000, Calendar.FEBRUARY, 1);
daysInMonth= mycal.getActualMaximum(Calendar.DAY_OF_MONTH);      // 29

Answer 2

java.util.Calendar的代码

如果你必须使用java.util.Calendar，我怀疑你想要：

int days = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);

Joda时间代码

但就个人而言，我建议先使用Joda Time代替java.util.{Calendar, Date}，在这种情况下您可以使用：

int days = chronology.dayOfMonth().getMaximumValue(date);

请注意，不是单独解析字符串值，而是最好使用您用来解析它的日期/时间API。在java.util.*中，您可以使用SimpleDateFormat;在Joda Time中你使用DateTimeFormatter。

Answer 3

您可以使用Calendar.getActualMaximum方法：

Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.YEAR, year);
calendar.set(Calendar.MONTH, month);
int numDays = calendar.getActualMaximum(Calendar.DATE);

Answer 4

`java.time.LocalDate`

从Java 1.8开始，您可以使用lengthOfMonth上的方法java.time.LocalDate：

LocalDate date = LocalDate.of(2010, 1, 19);
int days = date.lengthOfMonth();

Answer 5

if (month == 4 || month == 6 || month == 9 || month == 11)

daysInMonth = 30;

else 

if (month == 2) 

daysInMonth = (leapYear) ? 29 : 28;

else 

daysInMonth = 31;

Answer 6

这是数学方式：

年，月（1至12）：

int daysInMonth = month == 2 ? 
    28 + (year % 4 == 0 ? 1:0) - (year % 100 == 0 ? (year % 400 == 0 ? 0 : 1) : 0) :
    31 - (month-1) % 7 % 2;

Answer 7

在Java8中，您可以使用日期字段中的get ValueRange。

LocalDateTime dateTime = LocalDateTime.now();

ChronoField chronoField = ChronoField.MONTH_OF_YEAR;
long max = dateTime.range(chronoField).getMaximum();

这允许您在该字段上进行参数化。

Answer 8

我会寻求这样的解决方案：

int monthNr = getMonth();
final Month monthEnum = Month.of(monthNr);
int daysInMonth;
if (monthNr == 2) {
    int year = getYear();
    final boolean leapYear = IsoChronology.INSTANCE.isLeapYear(year);
    daysInMonth = monthEnum.length(leapYear);
} else {
    daysInMonth = monthEnum.maxLength();
}

如果月份不是2月（占案例的92％），则仅取决于月份，并且不涉及年份会更有效。这样，您无需致电逻辑即可知道这是否是a年，并且无需在92％的情况下获得年份。而且它仍然是干净且可读性强的代码。

Answer 9

// 1 means Sunday ,2 means Monday .... 7 means Saturday
//month starts with 0 (January)

MonthDisplayHelper monthDisplayHelper = new MonthDisplayHelper(2019,4);
int numbeOfDaysInMonth = monthDisplayHelper.getNumberOfDaysInMonth();

Answer 10

就这么简单，不需要导入任何东西

public static int getMonthDays(int month, int year) {
    int daysInMonth ;
    if (month == 4 || month == 6 || month == 9 || month == 11) {
        daysInMonth = 30;
    }
    else {
        if (month == 2) {
            daysInMonth = (year % 4 == 0) ? 29 : 28;
        } else {
            daysInMonth = 31;
        }
    }
    return daysInMonth;
}

Answer 11

这对我来说很好。

This is a Sample Output

import java.util.*;

public class DaysInMonth { 

    public static void main(String args []) { 

        Scanner input = new Scanner(System.in); 
        System.out.print("Enter a year:"); 

        int year = input.nextInt(); //Moved here to get input after the question is asked 

        System.out.print("Enter a month:"); 
        int month = input.nextInt(); //Moved here to get input after the question is asked 

        int days = 0; //changed so that it just initializes the variable to zero
        boolean isLeapYear = (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0); 

        switch (month) { 
            case 1: 
                days = 31; 
                break; 
            case 2: 
                if (isLeapYear) 
                    days = 29; 
                else 
                    days = 28; 
                break; 
            case 3: 
                days = 31; 
                break; 
            case 4: 
                days = 30; 
                break; 
            case 5: 
                days = 31; 
                break; 
            case 6: 
                days = 30; 
                break; 
            case 7: 
                days = 31; 
                break; 
            case 8: 
                days = 31; 
                break; 
            case 9: 
                days = 30; 
                break; 
            case 10: 
                days = 31; 
                break; 
            case 11: 
                days = 30; 
                break; 
            case 12: 
                days = 31; 
                break; 
            default: 
                String response = "Have a Look at what you've done and try again";
                System.out.println(response); 
                System.exit(0); 
        } 

        String response = "There are " + days + " Days in Month " + month + " of Year " + year + ".\n"; 
        System.out.println(response); // new line to show the result to the screen. 
    } 
} //abhinavsthakur00@gmail.com

Answer 12

您可以使用Calendar.getActualMaximum方法：

    Calendar calendar = Calendar.getInstance();
    calendar.set(Calendar.YEAR, year);
    calendar.set(Calendar.MONTH, month-1);
    int numDays = calendar.getActualMaximum(Calendar.DATE);

而且月份1是因为月份采用其原始月份而在方法中采用如下参数在Calendar.class中

   public int getActualMaximum(int field) {
      throw new RuntimeException("Stub!");
   }

（int字段）如下所示。

    public static final int JANUARY = 0;
    public static final int NOVEMBER = 10;
    public static final int DECEMBER = 11;

Answer 13

public class Main {

    private static LocalDate local=LocalDate.now();
    public static void main(String[] args) {

            int month=local.lengthOfMonth();
            System.out.println(month);

    }
}

Answer 14

应避免使用过时的Calendar API。

在Java8或更高版本中，可以使用YearMonth完成此操作。

示例代码：

int year = 2011;
int month = 2;
YearMonth yearMonth = YearMonth.of(year, month);
int lengthOfMonth = yearMonth.lengthOfMonth();
System.out.println(lengthOfMonth);

Answer 15

以下方法将为您提供特定月份的天数

public static int getNoOfDaysInAMonth(String date) {

        Calendar cal = Calendar.getInstance();
        cal.setTime(date);
        return (cal.getActualMaximum(Calendar.DATE));
    }

Answer 16

String  MonthOfName = "";
int number_Of_DaysInMonth = 0;

//year,month
numberOfMonth(2018,11); // calling this method to assign values to the variables MonthOfName and number_Of_DaysInMonth 

System.out.print("Number Of Days: "+number_Of_DaysInMonth+"   name of the month: "+  MonthOfName );

public void numberOfMonth(int year, int month) {
    switch (month) {
        case 1:
            MonthOfName = "January";
            number_Of_DaysInMonth = 31;
            break;
        case 2:
            MonthOfName = "February";
            if ((year % 400 == 0) || ((year % 4 == 0) && (year % 100 != 0))) {
                number_Of_DaysInMonth = 29;
            } else {
                number_Of_DaysInMonth = 28;
            }
            break;
        case 3:
            MonthOfName = "March";
            number_Of_DaysInMonth = 31;
            break;
        case 4:
            MonthOfName = "April";
            number_Of_DaysInMonth = 30;
            break;
        case 5:
            MonthOfName = "May";
            number_Of_DaysInMonth = 31;
            break;
        case 6:
            MonthOfName = "June";
            number_Of_DaysInMonth = 30;
            break;
        case 7:
            MonthOfName = "July";
            number_Of_DaysInMonth = 31;
            break;
        case 8:
            MonthOfName = "August";
            number_Of_DaysInMonth = 31;
            break;
        case 9:
            MonthOfName = "September";
            number_Of_DaysInMonth = 30;
            break;
        case 10:
            MonthOfName = "October";
            number_Of_DaysInMonth = 31;
            break;
        case 11:
            MonthOfName = "November";
            number_Of_DaysInMonth = 30;
            break;
        case 12:
            MonthOfName = "December";
            number_Of_DaysInMonth = 31;
    }
}

Answer 17

如果您不想对年份和月份的值进行硬编码，而又想从当前日期和时间中获取该值，则可以轻松进行以下操作：

Date d = new Date();
String myDate = new SimpleDateFormat("dd/MM/yyyy").format(d);
int iDayFromDate = Integer.parseInt(myDate.substring(0, 2));
int iMonthFromDate = Integer.parseInt(myDate.substring(3, 5));
int iYearfromDate = Integer.parseInt(myDate.substring(6, 10));

YearMonth CurrentYear = YearMonth.of(iYearfromDate, iMonthFromDate);
int lengthOfCurrentMonth = CurrentYear.lengthOfMonth();
System.out.println("Total number of days in current month is " + lengthOfCurrentMonth );

Answer 18

    String date = "11-02-2000";
    String[] input = date.split("-");
    int day = Integer.valueOf(input[0]);
    int month = Integer.valueOf(input[1]);
    int year = Integer.valueOf(input[2]);
    Calendar cal=Calendar.getInstance();
    cal.set(Calendar.YEAR,year);
    cal.set(Calendar.MONTH,month-1);
    cal.set(Calendar.DATE, day);
    //since month number starts from 0 (i.e jan 0, feb 1), 
    //we are subtracting original month by 1
    int days = cal.getActualMaximum(Calendar.DAY_OF_MONTH);
    System.out.println(days);

Answer 19

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

/*
 * 44. Return the number of days in a month
 * , where month and year are given as input.
 */
public class ex44 {
    public static void dateReturn(int m,int y)
    {
        int m1=m;
        int y1=y;
        String str=" "+ m1+"-"+y1;
        System.out.println(str);
        SimpleDateFormat sd=new SimpleDateFormat("MM-yyyy");

        try {
            Date d=sd.parse(str);
            System.out.println(d);
            Calendar c=Calendar.getInstance();
            c.setTime(d);
            System.out.println(c.getActualMaximum(Calendar.DAY_OF_MONTH));
        } catch (ParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
    public static void main(String[] args) {
dateReturn(2,2012);


    }

}

Answer 20

最佳和高效的方差：

public static int daysInMonth(int month, int year) {
    if (month != 2) {
        return 31 - (month - 1) % 7 % 2;
    }
    else {
        if ((year & 3) == 0 && ((year % 25) != 0 || (year & 15) == 0)) { // leap year
            return 29;
        } else {
            return 28;
        }
    }
}

有关跳跃算法的更多详细信息，请检查here

Answer 21

特定年份的天数-Java 8+解决方案

Year.now().length()

特定年份的特定月份的天数？

21 个答案:

Java 8及更高版本

Java 7及更早版本

java.util.Calendar的代码

Joda时间代码

`java.time.LocalDate`