日历本

打印日历，已知1800.1.1是星期三（START_DAY_FOR_JAN-1_1800=3）,打印某年某月的日历

package choice;

import java.util.Scanner;
public class Choose{
	public static void main(String[] args){
		Scanner input = new Scanner (System.in);
		
		//prompt the user to enter year
		System.out.print("Enter full year(e.g.,2012): ");
		int year = input.nextInt();
		
		//prompt the user to enter month
		System.out.print("Enter moth as a number between 1 and 12: ");
		int month = input.nextInt();
		
		//print calendar for the month of the year
		printMonth(year,month);
	}
	
	/**print the calendar for a month in a year**/
	public static void printMonth (int year ,int month){
		//print the headings of the calendar
		printMonthTitle(year,month);
		
		//print the body of the calendar
		printMonthBody(year,month);
	}
	
	/**print the month title, e.g., March 2012*/
	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");
	}
	
	/**get the English name for the month*/
	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 = "Augeust"; break;
		case 9: monthName = "September"; break;
		case 10: monthName = "October"; break;
		case 11: monthName = "November"; break;
		case 12: monthName = "December"; 			
		}
		return monthName;
	}
	
	/**print month body*/
	public static void printMonthBody(int year,int month){
		//get start day of the week for the first data in the month
		int startDay = getStartDay(year,month);
		
		//Get number of days in the month
		int numberOfDaysInMonth = getNumberOfDaysInMonth(year,month);
		
		//pad space before the first day of the 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();
	}
	
	/**get the start day of month/1/year*/
	public static int getStartDay(int year ,int month){
		final int START_DAY_FOR_JAN_1_1800 = 3;
		//get total number of days from 1/1/1800 to month/1/year
		int totalNumberOfDays = getTotalNamerOfDays(year ,month);
		
		//return the start day for month/1/year
		return (totalNumberOfDays + START_DAY_FOR_JAN_1_1800 % 7);
	}
	
	/**get the total number of days since January 1,1800*/
	public static int getTotalNamerOfDays(int year, int month){
		int total = 0;
		
		//get the total days from 1800 to 1/1 year
		for(int i = 1800;i<year;i++)
			if(isLeapYear(i))
				total +=366;
			else
				total += 365;
			
		//add days from Jan to the month prior to thar=e calender month
		for(int i=1 ;i< month;i++)
			total = total +getNumberOfDaysInMonth(year,i);
		return total;	
	}
	
	/**get the number of days in month*/
	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;
		else if(month == 4 || month == 6 || month == 9|| month == 11)
			return 30;
		else if( month == 2)
			return isLeapYear(year) ? 29 : 28;
		return 0;
	}
	
	/**determine if it is a leap year*/
	public static boolean isLeapYear(int year){
		return year % 400 == 0 ||(year %4 == 0 && year %100 != 0);
	}
}