Java实现简单的万年历

import java.util.Scanner;

public class index {
    //每个月的天数
    public static int monthday(int month, int year) {
        if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
            int[] day = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
            return day[month];
        } else {
            int[] day = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
            return day[month];
        }
    }

    //月份总天数
    public static int monthdays(int month, int year) {
        int totaldays = 0;
        for (int i = 1; i < month; i++) {
            totaldays = totaldays + monthday(i, year);
        }
        return totaldays;
    }

    //距离1900年的年份总天数
    public static int yeardays(int year){
        int yeardays = 0;
        for (int i = 1900;i<year;i++){
            if ((i % 4 == 0 && i % 100 != 0) || i % 400 == 0) {
                yeardays = yeardays+366;
            } else {
                yeardays = yeardays+365;
            }
        }
        System.out.println(year+"年距离1900年的总天数"+yeardays);
        return yeardays;
    }

    //输出日历
    public static void printCalendar(int month,int year){
        int totaldays = 0;
        if (year > 0) {
            if (month > 0 && month < 13) {
                //距离1900年1月1日总天数
                totaldays = monthdays(month,year)+yeardays(year);
                System.out.println(year+"年"+month+"月1日距离1900年的总天数:"+totaldays);
                System.out.println("\n**********"+year+"年"+month+"月的日历为**********");
                System.out.println("一\t二\t三\t四\t五\t六\t日\t");
                int week = 1+totaldays%7;
                //根据1日为周几输出空格
                for(int i=1;i<week;i++){
                    System.out.print(" \t");
                }
                //输入具体日期
                for(int i=1;i<=monthday(month,year);i++){
                    System.out.print(i+"\t");
                    if(week==7){
                        week = 1;//重置为星期一
                        System.out.println();
                    }else{
                        week++;
                    }
                }
            } else {
                System.out.println("输入的月份不合法！");
            }
        } else {
            System.out.println("输入的年份不合法！");
        }
    }

    //主函数
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("***********************欢迎使用万年历**************************");
        System.out.println("*********请选择你需要进行的操作（输入进行操作之前的数字）**********");
        System.out.println("********************1.查询某年某月的日历************************");
        System.out.println("********************2.结束操作*********************************");
        System.out.print("\n请选择你需要进行的操作：");
        int a = scanner.nextInt();
        for (int i=0;i>=0;i++) {
            switch (a) {
                case 1:
                    System.out.print("请选择年份：");
                    int year = scanner.nextInt();
                    System.out.print("请选择月份：");
                    int month = scanner.nextInt();
                    printCalendar(month, year);
                    System.out.print("\n请选择你需要进行的操作：");
                    a = scanner.nextInt();
                    break;
                case 2:
                    System.out.println("退出程序成功！");
                    return;
            }
        }
    }
}