关于calendar修改前的代码和修改后的代码

Java编写的日历，输入年月，输出这个月的日期与星期

修改前的代码：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;

	public class calendar {
	    static int year, month, yearFirstDay, monthFirstDay; // 定义静态变量，以便其它类调用

	    public static boolean isLeapYear(int y) {// 判断是否是闰年
	        return ((y % 4 == 0 && y % 100 != 0) || (y % 400 == 0));
	    }

	    public static int getMonthDay(int m) {// 获取每个月的天数
	        switch (m) {
	        case 1:
	        case 3:
	        case 5:
	        case 7:
	        case 8:
	        case 10:
	        case 12:
	            return 31;
	        case 4:
	        case 6:
	        case 9:
	        case 11:
	            return 30;
	        case 2:
	            if (isLeapYear(year))// 判断是否是闰年
	                return 29;
	            else
	                return 28;
	        default:
	            return 0;
	        }
	    }

	    public static void getYearFirstDay() {// 计算该年第一天是星期几
	        long n = year * 365;
	        for (int i = 1; i < year; i++)
	            if (isLeapYear(i))// 判断是否是闰年
	                n += 1;
	        yearFirstDay = (int) n % 7;
	    }

	    public static void getMonthFirstDay() {// 计算该年第一天是星期几
	        getYearFirstDay();
	        int n = yearFirstDay;
	        for (int i = 1; i < month; i++)
	            n += getMonthDay(i);
	        monthFirstDay = n % 7;
	    }

	    public static void printTitleWeek() {// 打印表头
	        System.out.println("===========================");
	        System.out.println("日  一  二  三   四  五   六");
	    }

	    public static void printMonths() {// 逐月打印该年的日历
	        for (int m = 1; m <= 12; m++) // 循环月份
	        {
	            System.out.println(m + "月");
	            printTitleWeek();
	            for (int j = 1; j <= yearFirstDay; j++) {// 按每个月第一天是星期几打印相应的空格
	                System.out.print("    ");
	            }
	            int monthDay = getMonthDay(m); // 获取每个月的天数
	            for (int d = 1; d <= monthDay; d++) {
	                if (d < 10)// 以下4行对输出格式化
	                    System.out.print(d + "   ");
	                else
	                    System.out.print(d + "  ");
	                yearFirstDay = (yearFirstDay + 1) % 7; // 每打印一天后，反应第二天是星期几
	                if (yearFirstDay == 0) // 如果第二天是星期天，便换行。
	                    System.out.println();
	            }
	            System.out.println('\n');
	        }
	    }

	    public static void printMonth() {// 只打印该月的日历
	        System.out.println(month + "月");
	        printTitleWeek();
	        for (int j = 1; j <= monthFirstDay; j++) {// 按每个月第一天是星期几打印相应的空格
	            System.out.print("    ");
	        }
	        int monthDay = getMonthDay(month); // 获取每个月的天数
	        for (int d = 1; d <= monthDay; d++) {
	            if (d < 10)// 以下4行对输出格式化
	                System.out.print(d + "   ");
	            else
	                System.out.print(d + "  ");
	            monthFirstDay = (monthFirstDay + 1) % 7; // 每打印一天后，反应第二天是星期几
	            if (monthFirstDay == 0) // 如果第二天是星期天，便换行。
	                System.out.println();
	        }
	        System.out.println('\n');
	    }

	    public static void main(String[] args) throws IOException {
	        InputStreamReader ir; // 以下接受从控制台输入
	        BufferedReader in;
	        ir = new InputStreamReader(System.in);
	        in = new BufferedReader(ir);
	        System.out.print("请输入年份：");
	        String y = in.readLine();
	        year = Integer.parseInt(y);
	        System.out.print("请输入月份：");
	        String m = in.readLine();
	        month = Integer.parseInt(m);
	        //getYearFirstDay(); // 计算该年第一天是星期几
	        getMonthFirstDay(); // 计算该月第一天是星期几
	        System.out.println("\n          " + year + "年          ");
	        //printMonths();
	        printMonth();
	    }
	}

修改后的代码：

import java.util.Scanner;

	public class calendar {
	    public static void main(String[] args) {
	        for (int g = 0; g < 100; g++) {
	            Scanner in = new Scanner(System.in);
	            System.out.println("\n请输入年份：");
	            int year = in.nextInt();
	            System.out.println("请输入月份：");
	            int month = in.nextInt();
	            int sum = 0;
	            int k = 0;
	            for (int i = 1; i <= month - 1; i++) {
	                if (i == 2) {
	                    if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
	                        sum = sum + 29;
	                    } else {
	                        sum = sum + 28;
	                    }
	                } else {
	                    if (i == 4 || i == 6 || i == 9 || i == 11) {
	                        sum = sum + 30;
	                    } else {
	                        sum = sum + 31;
	                    }
	                }
	            }
	            for (int a = 1900; a <= year - 1; a++) {
	                if (a % 4 == 0 && a % 100 != 0 || a % 400 == 0) {
	                    sum = sum + 366;
	                } else {
	                    sum += 365;
	                }
	            }
	            sum += 1;
	            int wekday = sum % 7;
	            System.out.println("日\t一\t二\t三\t四\t五\t六");
	            for (int j = 1; j <= wekday; j++) {
	                System.out.print("\t");
	            }
	            if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
	                if (month == 2) {
	                    k = 29;
	                } else if (month == 4 || month == 6 || month == 9 || month == 11) {
	                    k = 30;
	                } else {
	                    k = 31;
	                }
	            } else {
	                if (month == 2) {
	                    k = 28;
	                } else if (month == 4 || month == 6 || month == 9 || month == 11) {
	                    k = 30;
	                } else {
	                    k = 31;
	                }
	            }
	            for (int i = 1; i <= k; i++) {
	                if (sum % 7 == 6) {
	                    System.out.print(i + "\n");
	                } else {
	                    System.out.print(i + "\t");
	                }
	                sum++;
	            }
	        }
	    }
	}