Chapter Thirty-fourth Question (Print calendar)

Chapter Thirty-fourth Question (Print calendar)

• **6.34 (Printing Calendar) Programming Practice Problem 3.21 uses the Zeller consistency principle to calculate the day of the week. Use Zeller's algorithm to simplify the program Listing 6-12 to get the day of the week when the first day of each month starts.
  **6.34(Print calendar) Programming Exercise 3.21 uses Zeller's congruence to calculate the day of the week. Simplify Listing 6.12, PrintCalendar.java, using Zeller's algorithm to get the start day of the month.
• Reference Code:

package chapter06;

import java.util.Scanner;

public class Code_34 {
    
    
    public static void main(String[] args) {
    
    
        Scanner input = new Scanner(System.in);
        System.out.print("Enter full year (e.g., 2012): ");
        int year = input.nextInt();
        System.out.print("Enter month as a number between 1 and 12: ");
        int month = input.nextInt();
        printMonth(year, month);
    }
    public static void printMonth(int year, int month) {
    
    
        printMonthTitle(year, month);
        printMonthBody(year, month);
    }
    public static void printMonthTitle(int year, int month) {
    
    
        System.out.println(" " + getMonthName(month) + " " + year);
        System.out.println("-----------------------------");
        System.out.println(" Sun Mon Tue Wed Thu Fri Sat");
    }
    public static String getMonthName(int month) {
    
    
        String monthName = "";
        switch (month) {
    
    
            case 1:
                monthName = "January";
                break;
            case 2:
                monthName = "February";
                break;
            case 3:
                monthName = "March";
                break;
            case 4:
                monthName = "April";
                break;
            case 5:
                monthName = "May";
                break;
            case 6:
                monthName = "June";
                break;
            case 7:
                monthName = "July";
                break;
            case 8:
                monthName = "August";
                break;
            case 9:
                monthName = "September";
                break;
            case 10:
                monthName = "October";
                break;
            case 11:
                monthName = "November";
                break;
            case 12:
                monthName = "December";
        }
        return monthName;
    }
    public static void printMonthBody(int year, int month) {
    
    
        int startDay = getStartDay(year, month);
        int numberOfDaysInMonth = getNumberOfDaysInMonth(year, month);
        int i = 0;
        for (i = 0; i < startDay; i++)
            System.out.print("    ");
        for (i = 1; i <= numberOfDaysInMonth; i++) {
    
    
            System.out.printf("%4d", i);

            if ((i + startDay) % 7 == 0)
                System.out.println();
        }
        System.out.println();
    }
    public static int getStartDay(int year, int month) {
    
    
        int day = 1, h, q, m, j, k,statement;
        q = day;
        if(month == 1 || month == 2) {
    
    
            month += 12;
            year -= 1;
        }
        m = month;
        j = year / 100;
        k = year % 100;
        h = (q + (26 * (m + 1) / 10) + k + k / 4 + j / 4 + 5 * j) % 7;
        switch(h) {
    
    
            case 0:
                statement = 6; break;
            case 1:
                statement = 0; break;
            case 2:
                statement = 1; break;
            case 3:
                statement = 2; break;
            case 4:
                statement = 3; break;
            case 5:
                statement = 4; break;
            case 6:
                statement = 5; break;
            default:
                statement = -1;
        }
        return statement;
    }
    public static int getNumberOfDaysInMonth(int year, int month) {
    
    
        if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12)
            return 31;
        if (month == 4 || month == 6 || month == 9 || month == 11)
            return 30;
        if (month == 2)
            return isLeapYear(year) ? 29 : 28;
        return 0;
    }
    public static boolean isLeapYear(int year) {
    
    
        return year % 400 == 0 || (year % 4 == 0 && year % 100 != 0);
    }
}

• The results show that:

Enter full year (e.g., 2012): 2012
Enter month as a number between 1 and 12: 2
 February 2012
-----------------------------
 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

Process finished with exit code 0