如何在java中显示日历

Question

我目前正在做一个问题集，我必须创建一个显示一年中所有月份的日历，包括其中的月份中的日期。 但是，我对每个月第一行的间距有疑问。 在课堂上我们只学习了 switch 语句，if、else、while、do-while、for 循环

这是我的一个月中当前显示的内容：

输出图片 图片中没有显示我的输入，但我写的是 2016 年和 5 年开始的工作日。

所期望的输出图像 同样，所期望的图像。 我认为我的问题可能是我使用的方程式： int firstDayEachMonth = (daysMonth + firstDayYear)%7; 虽然老师把这个方程给了我们用，但是好像不行。

如您所见，第一行的空格一直在左侧，它应该与指定的日期对齐，在这种情况下为 1 月，1 月 1 日应与周五对齐，1 月 2 日应与周六对齐，但目前是周日和周一。

    import java.util.Scanner;

    public class DisplayCalendar
       {
        public static void main(String[] args)
        {
        //Create a new scanner 
        Scanner input = new Scanner(System.in);
        
        // Prompt user to enter year 
        System.out.print("Enter a year: ");
        int year = input.nextInt();
        
        // Prompt user to enter first day of the year
        System.out.print("Enter the weekday that the year starts: ");
        int firstDayYear = input.nextInt();
        
        // A for loop that prints out each month
        for(int month = 1; month <= 12; month++)
        {
            // Set the value of the amount of days in a month
            int daysMonth = 0;
            
            // Set value of the month 
            String monthDisplay = "";   
            
            // Find name of each month and number of days
            switch(month)
            {
                case 1: monthDisplay = "January"; 
                    daysMonth = 31;
                    break;
                
                case 2: 
                    monthDisplay = "February";
                    int leapYear = 0;
                    while (leapYear > -1)
                    {   
                        // Count all years that are divisible by 4 to be a leap year.
                        leapYear += 4;
                        
                        // If the year inputted is a leap year, the days of the month will be 29.
                        if (year == leapYear)
                        {
                            daysMonth = 29;
                            break;
                        }
                        
                        else 
                        {
                            daysMonth = 28;
                        }
                    }
                    break;

                case 3: monthDisplay = "March";
                    daysMonth = 31;
                    break;
                
                case 4: monthDisplay = "April";
                    daysMonth = 30;
                    break; 
                
                case 5: monthDisplay = "May";
                    daysMonth = 31;
                    break;
                
                case 6: monthDisplay = "June";
                    daysMonth = 30;
                    break; 
                
                case 7: monthDisplay = "July";
                    daysMonth = 31;
                    break;
                
                case 8: monthDisplay = "August";
                    daysMonth = 31;
                    break;
                
                case 9: monthDisplay = "September";
                    daysMonth = 30;
                    break;
            
                case 10: monthDisplay = "October";
                    daysMonth = 31;
                    break;
                
                case 11: monthDisplay = "November";
                    daysMonth = 30;
                    break;
                
                case 12: monthDisplay = "December";
                    daysMonth = 31;
                    break; 
                
                // If the month is not recognized, dialog box will be displayed, and then exits program. 
                default : System.out.print("Invalid: Your month is not recognized. ");
                    System.exit(0); 

            }
            // Display the month and year
            System.out.println("                      "+ monthDisplay + " " + year);
            
            // Display the lines
            System.out.println("_____________________________________");
            
            // Display the days of the week
            System.out.println("Sun     Mon     Tue     Wed     Thu     Fri     Sat");
            
            // Print spaces depending on the day the month starts.
            int firstDayEachMonth = (daysMonth + firstDayYear)%7;
            for (int space = 1; space <= firstDayEachMonth; space++)
                System.out.print("   ");

            // Print the days 
            for (int daysDisplay = 1; daysDisplay <= daysMonth; daysDisplay++)
            {
                if (firstDayYear%7 == 0)
                    System.out.println();
                
                System.out.printf("%3d      ", daysDisplay);
                firstDayYear += 1;
            }
            System.out.println();
        }
            
    }
}   

我们不能使用不同的库（如Calendar ），只能使用扫描仪。

Answer 1

你能试试这个例子吗？ 我可以看到以下输出：

   February 2016
   Sun  Mon Tue   Wed Thu   Fri  Sat
        1    2    3    4    5    6 
   7    8    9   10   11   12   13 
  14   15   16   17   18   19   20 
  21   22   23   24   25   26   27 
  28   29

package general;

import java.util.Scanner;

public class DisplayCalendar {

    public static void main(String[] args) {
        int Y = 2016;    // year
        int startDayOfMonth = 5;
        int spaces = startDayOfMonth;

        // startDayOfMonth

        // months[i] = name of month i
        String[] months = {
                "",                               // leave empty so that we start with months[1] = "January"
                "January", "February", "March",
                "April", "May", "June",
                "July", "August", "September",
                "October", "November", "December"
            };

            // days[i] = number of days in month i
            int[] days = {
                0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
            };

            for (int M = 1; M <= 12; M++) {

            // check for leap year
            if  ((((Y % 4 == 0) && (Y % 100 != 0)) ||  (Y % 400 == 0)) && M == 2)
                days[M] = 29;

            
            // print calendar header
            // Display the month and year
            System.out.println("          "+ months[M] + " " + Y);

            // Display the lines
            System.out.println("_____________________________________");
            System.out.println("   Sun  Mon Tue   Wed Thu   Fri  Sat");

            // spaces required
               spaces = (days[M-1] + spaces)%7;
            
            // print the calendar
            for (int i = 0; i < spaces; i++)
                System.out.print("     ");
            for (int i = 1; i <= days[M]; i++) {
                System.out.printf(" %3d ", i);
                if (((i + spaces) % 7 == 0) || (i == days[M])) System.out.println();
            }
            
            System.out.println();
        }
    }
}

Answer 2

由于这似乎是一项家庭作业，因此我不会费心为您提供正确的算法。 这将违背你——或其他有同样问题的人——练习你的编程和分析技能的目的。

在for (int space = 1; space <= firstDayEachMonth; space++)这一行中for (int space = 1; space <= firstDayEachMonth; space++)您可以完全忽略firstDayEachMonth结果并使用您的firstDayYear计数器。 该计数器具有一年中的起始工作日，并且它在经过的每一天递增。 此外，有必要定义您的一周是从 0 还是 1 开始。

在这部分中，您已经在此处设置了本周末的换行符：

if (firstDayYear%7 == 0)
   System.out.println();

当你达到这个条件时，我会重置firstDayYear因为因为你使用它作为参数来设置你的空间，你永远不会让这个数字大于 7。这样你就可以在日历上正确布置每周的行，并且唯一的问题是在屏幕上以正确的格式呈现它。

当您像这样打印星期System.out.println("Sun Mon Tue Wed Thu Fri Sat"); 请注意，您的名称长度为 3 加 5 个空格。 所以这一行System.out.printf("%3d ", daysDisplay); 应该有一个宽度为 3 个空格的数字，这解释了%3d的用法，加上 5 个空格。 在这种情况下，你有 6 个空格，你总是给你错误的偏移量，并且会在某些行上造成一些麻烦。

这些是我注意到的事情，我希望它有所帮助。 和平！

Answer 3

时间

我建议您使用现代 Date-Time API ^{* 来完成}，它自 Java SE 8 以来一直是标准库的一部分。

import java.time.LocalDate;
import java.time.YearMonth;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Test harness
        Scanner input = new Scanner(System.in);
        System.out.print("Please enter a month between 1 and 12 (e.g. 5): ");
        int m = input.nextInt();

        System.out.print("Please enter a full year (e.g. 2018): ");
        int y = input.nextInt();
        printMonth(y, m);
    }

    static void printMonth(int year, int month) {
        YearMonth ym = YearMonth.of(year, month);
        System.out.println("Sun Mon Tue Wed Thu Fri Sat");
        int counter = 1;

        // Get day of week of 1st date of the month and print space for as many days as
        // distant from SUN
        int dayValue = LocalDate.of(year, month, 1).getDayOfWeek().getValue();
        if (dayValue != 7)
            for (int i = 0; i < dayValue; i++, counter++) {
                System.out.printf("%-4s", "");
            }

        for (int i = 1; i <= ym.getMonth().length(ym.isLeapYear()); i++, counter++) {
            System.out.printf("%-4d", i);

            // Break the line if the value of the counter is multiple of 7
            if (counter % 7 == 0) {
                System.out.println();
            }
        }
    }
}

示例运行：

Please enter a month between 1 and 12 (e.g. 5): 9
Please enter a full year (e.g. 2018): 2020
Sun Mon Tue Wed Thu Fri Sat
        1   2   3   4   5   
6   7   8   9   10  11  12  
13  14  15  16  17  18  19  
20  21  22  23  24  25  26  
27  28  29  30  

从Trail: Date Time 中了解有关现代日期时间 API 的更多信息。

---

^{* 出于任何原因，如果您必须坚持使用 Java 6 或 Java 7，您可以使用ThreeTen-Backport，它将大部分java.time功能向后移植到 Java 6 和 7。如果您正在为 Android 项目和您的 Android API 工作级别仍然不符合 Java-8，请检查 通过 desugaring和How to use ThreeTenABP in Android Project 可用的 Java 8+ APIs 。}

Answer 4

public class Exercice5_29DisplayCalenderDay {

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
      //Create a new scanner 
    Scanner input = new Scanner(System.in);

    // Prompt user to enter year 
    System.out.print("Enter a year: ");
    int year = input.nextInt();

    // Prompt user to enter first day of the year
    System.out.println("Enter the weekday that the year starts: ");
    int day = input.nextInt();
    int dayCounter = day;
     int nbrOfDays = 0;
     String  monthx = ""; 
    for (int month= 1; month <=12; month++)
    {

                        // Switch to chose the month 
              switch (month)
             {
                  case 1: monthx = "January";
                             nbrOfDays = 31;
                             break;
                  case 2: monthx = "February";
                                     if ( year % 4 == 0 && year % 100 !=0 || year % 400 == 0)
                      {
                             nbrOfDays = 29;
                             break;
                      }
                                     else
                         {  nbrOfDays = 28;
                             break;
                         }
                 case 3: monthx = "March";
                             nbrOfDays = 31;
                             break; 
                  case 4: monthx = "April";
                             nbrOfDays = 30;
                             break; 
                         case 5: monthx = "May";
                             nbrOfDays = 31;
                             break;

                         case 6: monthx = "June";
                             nbrOfDays = 30;
                             break;
                          case 7: monthx = "July";
                             nbrOfDays = 31;
                             break;
                          case 8: monthx = "August";
                             nbrOfDays = 31;
                             break;
                    case 9: monthx = "September";
                             nbrOfDays = 30;
                             break; 
                    case 10: monthx = "October";
                             nbrOfDays = 31;
                             break; 
                    case 11: monthx = "November";
                             nbrOfDays = 30;
                             break; 
                         case 12: monthx = "December";
                             nbrOfDays = 31;
                             break;                  
             }

                 System.out.printf("%15s %d  \n", monthx , year);
                 System.out.println("----------------------------");
                 System.out.printf("%s %s %s %s %s %s %s\n ", "Sun","Mon","Tue", "Wed", "Thu","Fri","Sat");

                 for (int space =1; space<=day; space++) 
                 {
                     System.out.printf("%4s", "    ");
                 }
                 for (int i = 1; i <=nbrOfDays; i++)
                 {
                    dayCounter++;
                    if ( dayCounter% 7==0)
                     System.out.printf("%- 4d\n", i);
                    else
                    System.out.printf("%-4d", i);

                 }
                 day = (day + nbrOfDays)%7;

                         System.out.println();

    }    

}
}

Answer 5

导入 java.util.Scanner;

公共类 DisplayCalendar {

public static void main(String[] args) {
    String Months[] = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
    int numday[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

    Scanner in = new Scanner(System.in);
    System.out.println("enter the year");
    int year = in.nextInt();
    if ((((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0))) {
        numday[1] = 29;
    }
    System.out.println("enter the day start the year ");
    int day = in.nextInt();
    for (int i = 1; i <= 12; i++) {
        System.out.println("\t" + Months[i - 1]+" "+ year);
        System.out.println("ـــــــــــــــــــــــــ");
        System.out.printf("%-4s%-4s%-4s%-4s%-4s%-4s%-4s\n","Sun","Mon","Tue","Wed","Thu","Fri","Sat");
        day = manh(day, numday[i - 1]);
    }

}

public static int manh(int day, int numday) {
    int a[][] = new int[6][7];
    int counter = 1;
    int j = 0;
    for (int i = 0; i < 6; i++) {
        for (j = day; j < 7; j++) {
            a[i][j] = counter;
            day++;
            counter++;
            if (counter == numday + 1) {
                break;
            }
        }
        day = 0;
        if (counter == numday + 1) {
            break;
        }

    }
    for (int i = 0; i < 6; i++) {
        for (int f = 0; f < 7; f++) {
            System.out.printf("%-4s", a[i][f] == 0 ? "" : a[i][f]);
        }
        System.out.println();

    }
    int dayret = j + 1;
    return dayret >= 7 ? 0 : dayret;
}

}

Answer 6

这是全年的日历：

public class Main { 

    /***************************************************************************
     *  Given the month, day, and year, return which day
     *  of the week it falls on according to the Gregorian calendar.
     *  For month, use 1 for January, 2 for February, and so forth.
     *  Returns 0 for Sunday, 1 for Monday, and so forth.
     ***************************************************************************/
     public static int day(int month, int day, int year) {
         int y = year - (14 - month) / 12;
         int x = y + y/4 - y/100 + y/400;
         int m = month + 12 * ((14 - month) / 12) - 2;
         int d = (day + x + (31*m)/12) % 7;
         return d;
     }
 
     // return true if the given year is a leap year
     public static boolean isLeapYear(int year) {
         if  ((year % 4 == 0) && (year % 100 != 0)) return true;
         if  (year % 400 == 0) return true;
         return false;
     }
 
     public static void main(String[] args) {
         int[] a = {1,2,3,4,5,6,7,8,9,10,11,12};   // month (Jan = 1, Dec = 12)
         int year = 2022; // year
         
         // months[i] = name of month i
         String[] months = {
             "",                               // leave empty so that months[1] = "January"
             "January", "February", "March",
             "April", "May", "June",
             "July", "August", "September",
             "October", "November", "December"
         };
 
         // days[i] = number of days in month i
         int[] days = {
             0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
         };
         
         for(int month : a){
 
         // check for leap year
         if (month == 2 && isLeapYear(year)) days[month] = 29;
 
 
         // print calendar header
         System.out.println("   " + months[month] + " " + year);
         System.out.println(" S  M Tu  W Th  F  S");
 
         // starting day
         int d = day(month, 1, year);
 
         // print the calendar
         for (int i = 0; i < d; i++)
             System.out.print("   ");
         for (int i = 1; i <= days[month]; i++) {
             System.out.printf("%2d ", i);
             if (((i + d) % 7 == 0) || (i == days[month])) System.out.println();
         }
         System.out.println("");
       }
     }
 }

参考： https ://introcs.cs.princeton.edu/java/21function/Calendar.java.html