【2019.07.03】java 编写一个程序，显示给定年月的日历

方法抽象、逐步求精

将方法的使用和她的实现分离
自顶向下设计
自底向上实现

package com.ybs.practice;

import java.util.Scanner;

/**
* @Description 类描述：输入年份和月份，然后显示该月的整个日历
* @ClassName 类名称：
* @author yb.w
* @version 创建时间：2019年7月3日 下午4:42:01
*/
public class PrintCalendar {
	public static void main(String[] args) {
		@SuppressWarnings("resource")
		Scanner input = new Scanner(System.in);
		System.out.println("Enter full year (e.g., 2012): ");
		int year = input.nextInt();
		
		System.out.println("Enter month as a number between 1 and 12: ");
		int month = input.nextInt();
		
		printMonth(year, month);
		
	}

	private static void printMonth(int year, int month) {
		printMonthTitle(year, month);
		printMonthBody(year, month);
	}
	
	private 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");
	}
	
	private 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();
		 }
	}
	
	private static String getMonthName(int month) {
		String monthName = "";
		switch (month) {
		case 1: monthName = "January"; break;
		case 2: monthName = "Febrary"; 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 = "Auguest"; break;
		case 9: monthName = "September"; break;
		case 10: monthName = "October"; break;
		case 11: monthName = "Nobermber"; break;
		case 12: monthName = "December"; 
		}
		return monthName;
	}
	
	private static int getStartDay(int year, int month) {
		//  获取月初第一日是星期几
		final int START_DAY_FOR_1_1800 = 3;
		int totalNumberOfDays = getTotalNumberOfDays(year, month);
		
		return (totalNumberOfDays + START_DAY_FOR_1_1800) % 7;
	}
	
	private static int getTotalNumberOfDays(int year, int month) {
		//  1800年起到当前月第一日的总天数
		int total = 0;
		for (int i = 1800; i < year; i++) 
			if (isLeapYear(year))
				total += 366;
			else
				total += 365;
		
		// Add days form jan to the month prior to the calendar month
		for (int i = 1; i < month; i++)
			total += getNumberOfDaysInMonth(year, i);
		
		return total;
	}
	
	private static int getNumberOfDaysInMonth(int year, int month) {
		//  获取这个月共多少天
		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; // If month is incorrect
	}
	
	private static boolean isLeapYear(int year) {
		return year % 400 == 0 || (year % 4 == 0 && year % 100 != 0); 
	}
}