PrintCalendar – 源码巴士

import java.util.Scanner;

public class PrintCalendar {
   public static void main(String[] args) {
       Scanner input = new Scanner(System.in);

       System.out.print("Enter a year: ");
       int year = 0;
       while(year < 1800)
           year = input.nextInt();

       System.out.print("Enter a month: ");
       int month = 0;
       while(month < 1 || month >12)
           month = input.nextInt();

       printCalendar(year, month);

   }

   static final int MONTH_DAYS[] = {0, 31, 59, 90, 120, 151, 181,
           212, 243, 273, 304, 334, 365};

   public static void printCalendar(int year, int month) {
       printMonthTitle(year, month);
       printMonthBody(year, month);
   }

   public static void printMonthTitle(int year, int month) {
       System.out.println(" "+year + " " + getMonthName(month));
       System.out.println(" SUN MON TUE WED THU FRI SAT");

   }

   public static String getMonthName(int month) {
       switch(month) {
       case 1: return "January";
       case 2: return "February";
       case 3: return "March";
       case 4: return "April";
       case 5: return "May";
       case 6: return "June";
       case 7: return "July";
       case 8: return "August";
       case 9: return "September";
       case 10: return "October";
       case 11: return "November";
       default: return "December";
       }
   }

   public static void printMonthBody(int year, int month) {
       int startDay = getStartDay(year, month);
       int numberOfDaysInMonth =
               getNumberOfDaysInMonth(year, month);
       for(int i = 0; i < startDay; i++)
           System.out.print("    ");
       for(int i = 0; i < numberOfDaysInMonth; i++) {
           if((i + startDay) % 7 == 0)
               System.out.printf("\n%4s", i + 1);
           else
               System.out.printf("%4s", i + 1);
       }
   }

   public static int getStartDay(int year, int month) {
       return
               (getTotalNumberOfDays(year, month) + 3)% 7;
   }

   public static int getTotalNumberOfDays(
           int year, int month) {
       int totalNumberOfDays = 0;

       for(int i = 1800; i < year; i++) {
           if(isLeapYear(i))
               totalNumberOfDays += 366;
           else totalNumberOfDays += 365;
           }
       totalNumberOfDays += MONTH_DAYS[month - 1];

       if(isLeapYear(year) && month > 1)
           return totalNumberOfDays++;
       else return totalNumberOfDays;
   }

   public static int getNumberOfDaysInMonth(
           int year, int month) {
       if (isLeapYear(year) == true && month == 2)
           return MONTH_DAYS[month] - MONTH_DAYS[month - 1] + 1;
       else return MONTH_DAYS[month] - MONTH_DAYS[month - 1];
   }

   public static boolean isLeapYear(int year) {
       return year % 400 ==0 || year % 4 ==0 && year % 100 != 0;
   }

}

Enter a year: 2014
Enter a month: 4
2014 April
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