如何在java中显示日历

Question

I'm currently doing a problem set where I have to create a calendar displaying all the months of a year, including the days of the month within it. However I'm having issues with the spacing of the first line of each month. In class we have only learned switch statements, if, else, while, do-while, for loops

Here is what is currently displayed for one of my months:

Image of output In the picture is doesn't show my inputs, but what I wrote was 2016 for the year and 5 for the weekday that the year starts in.

Image of output of what what is desired Again, a picture of what is desired. I think my problem is possibly the equation I used which is: int firstDayEachMonth = (daysMonth + firstDayYear)%7; though the teacher gave this equation to us to use, but it seems like it doesn't work.

As you can see the spaces on the first line is all the way to the left, it should be aligned with the designated dates, in this case for January, Jan 1st should align on Friday and Jan 2nd should align with Saturday but it is currently on Sunday and Monday.

    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();
        }
            
    }
}   

We can't use the different libraries (like Calendar ), only keeping with scanner.

Answer 1

Can you try this example? I can see the following output:

   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

Since this seems to be a homework, I won't bother to give you the right algorithm. That would defeat the purpose of you - or other people with the same problem - practice your programming and analytical skills.

In this line for (int space = 1; space <= firstDayEachMonth; space++) you can totally ignore firstDayEachMonth result and use your firstDayYear counter. This counter has the starting weekday of the year and it is incremented each day that passes. Also, it is necessary to define if your week starts in 0 or 1.

In this part, you are already setting a line break for the end of the week here in:

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

I would reset firstDayYear when you reach this condition because since you are using it as parameter to set your spaces, you'll never have this number going greater than 7. This way you have each week line laid out correctly on the calendar and the only problem would be presenting it in the right format on the screen.

When you print the days of the week header like this System.out.println("Sun Mon Tue Wed Thu Fri Sat"); mind that you have the names with length 3 plus 5 whitespaces. So this line System.out.printf("%3d ", daysDisplay); should have a digit with a width of 3 spaces, which explains the use of %3d , plus 5 whitespaces. In this case you have 6 whitespace that you always give you the wrong offset and will cause some hell on some lines.

These are the things I've noticed and I hope it helps. Peace!

Answer 3

java.time

I recommend you do it using the modern Date-Time API ^* which has been part of the standard library since Java SE 8.

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();
            }
        }
    }
}

A sample run:

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  

Learn more about the modern Date-Time API from Trail: Date Time .

---

^{* For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7. If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project .}

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

import java.util.Scanner;

public class 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

This is the Calendar for the whole year:

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("");
       }
     }
 }

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