万年历

首先位java的结构图

然后是第一种代码（第一种完全在主函数中编写）：

  1 package com.cal;
  2 public class MyCalendar01 {
  3     public static void main(String[] args) {
  4         int year = 2017;
  5         //显示某一年的日历
  6         System.out.println(year + "年的日历");
  7         for (int i = 1; i < 13; i++) {
  8             int month = i;
  9             //显示某一月的开头
 10             System.out.println(year + "年" + month + "月的日历");
 11             System.out.println("日	一	二	三	四	五	六");
 12             
 13             int monthDays = 0;
 14             //判断此月有多少天
 15             switch (month) {
 16             case 1:
 17             case 3:
 18             case 5:
 19             case 7:
 20             case 8:
 21             case 10:
 22             case 12:
 23                 monthDays = 31;
 24                 break;
 25             case 4:
 26             case 6:
 27             case 9:
 28             case 11:
 29                 monthDays = 30;
 30                 break;
 31             case 2:
 32                 //判断是否为闰年
 33                 if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
 34                     monthDays = 29;
 35                 } else {
 36                     monthDays = 28;
 37                 }
 38                 break;
 39             default:
 40                 break;
 41             }
 42             //计算每月为星期几，weekday是某月星期几
 43             int weekDay = 0;
 44             //计算1900年到该年之间一共有多少天
 45             int days = 0;
 46             for (int j = 1900; j < year; j++) {
 47                 int currentYear = j;
 48                 if (currentYear % 4 == 0 && currentYear % 100 != 0
 49                         || currentYear % 400 == 0) {
 50                     days = days + 366;
 51                 } else {
 52                     days = days + 365;
 53                 }
 54             }
 55             //算出该年某月之前有多少天
 56             for (int j = 1; j < month; j++) {
 57                 int currentmonth = j;
 58                 switch (currentmonth) {
 59                 case 1:
 60                 case 3:
 61                 case 5:
 62                 case 7:
 63                 case 8:
 64                 case 10:
 65                 case 12:
 66                     days = days + 31;
 67                     break;
 68                 case 4:
 69                 case 6:
 70                 case 9:
 71                 case 11:
 72                     days = days + 30;
 73                     break;
 74                 case 2:
 75                     if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
 76                         days = days + 29;
 77                     } else {
 78                         days = days + 28;
 79                     }
 80                     break;
 81                 default:
 82                     break;
 83                 }
 84             }
 85             weekDay = (days % 7 + 1) % 7;
 86             //显示某月主题部分
 87             for (int j = 0; j < weekDay; j++) {
 88                 System.out.print("	");
 89             }
 90             for (int j = 1; j < monthDays + 1; j++) {
 91                 int day = j;
 92                 System.out.print(day + "	");
 93                 if ((day + weekDay) % 7 == 0) {
 94                     System.out.println();
 95                 }
 96             }
 97             System.out.println();
 98 
 99         }
100     }
101 }

第二种代码将某些功能写成一块一块的函数：

package com.Calendar;

public class MyCalendar {
    public static void main(String[] args) {
        int year = 2017;
        // System.out.println();
        //printCalendarofMonth(year, 2);
        printCalendar(year);
    }

    // 显示每个月的开头
    static void printHeader(int year, int month) {
        System.out.println(year + "年" + month + "月");
        System.out.println("日	一	二	三	四	五	六");
    }

    // 某年某月是否为闰月
    static boolean isYear(int year) {
        boolean result;
        if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
            result = true;
        } else {
            result = false;
        }
        return result;
    }

    // 获得某年的天数
    static int getDayofYear(int year) {
        int days = 0;
        if (isYear(year) == true) {
            days = 366;
        } else {
            days = 365;
        }
        return days;
    }

    // 获得某年某月的天数
    static int getDaysofMonth(int year, int month) {
        int days = 0;
        switch (month) {
        case 1:
        case 3:
        case 7:
        case 8:
        case 10:
        case 12:
        case 5:
            days = 31;
            break;
        case 4:
        case 6:
        case 9:
        case 11:
            days = 30;
            break;
        case 2:
            if (isYear(year) == true) {
                days = 29;
            } else {
                days = 28;
            }
            break;
        default:
            days = 0;
            break;
        }
        return days;
    }

    // 获得某年某月的1号是星期几
    static int getWeekDayofMonth(int year, int month) {
        int days = 0;
        int weekday;
        // 累计每年天数
        for (int i = 1900; i < year; i++) {
            int currentyear = i;
            if (isYear(currentyear) == true) {
                days += 366;
            } else {
                days += 365;
            }
        }
        // 累计该年前几月的天数
        for (int j = 1; j < month; j++) {
            int currentmonth = j;
            days += getDaysofMonth(year, currentmonth);
        }
        weekday = (days % 7 + 1) % 7;
        return weekday;
    }

    // 显示某月的日历主题部分
    static void printCalendarofMonth(int year, int month) {
        int days = 0;
        printHeader(year, month);
        int weekday = getWeekDayofMonth(year, month);
        for (int i = 0; i < weekday; i++) {
            System.out.print("	");
        }
        days = getDaysofMonth(year, month);
        for (int i = 0; i < days; i++) {
            int day = i + 1;
            System.out.print(day + "	");
            if ((weekday + day) % 7 == 0) {
                System.out.println();
            }
        }
        System.out.println();
    }
    //显示某年日历
    static void printCalendar(int year){
        for (int i = 1; i <13; i++) {
            int month=i;
            printCalendarofMonth(year, month);
        }
    }

}

第三种为偷懒的办法，从主函数开始写分支函数，然后用ctl+1来建立分支函数，可以更快点：

package com.cal;

public class MyCalendar {
    public static void main(String[] args) {
        int year = 2017;
        //System.out.println(getDays(year,2));
        //打印某一年的日历
        printYearCalendar(year);
    }

    private static void printYearCalendar(int year) {
        System.out.println(year + "年的日历");
        for (int i = 0; i < 12; i++) {
            int month = i + 1;
            System.out.println(year + "年" + month + "月");
            System.out.println("日	一	二	三	四	五	六");
            printMonthofHeader(year, month);
        }
    }

    private static void printMonthofHeader(int year, int month) {
        // 某月的开始为星期几
        int weekday = getFirstDayofMonth(year, month);
        for (int i = 0; i < weekday; i++) {
            System.out.print("	");
        }
        //根据年份和月份得到某个月共有几天
        int days = getDays(year, month);
        for (int i = 0; i < days; i++) {
            int day = i + 1;
            System.out.print(day + "	");
            if ((weekday + day) % 7 == 0) {
                System.out.println();
            }
        }
        System.out.println();

    }

    //获得某年某个月的1号是星期几
    private static int getFirstDayofMonth(int year, int month) {
        int weekday;
        int days=0;
        // 计算从1900年1月1日以来的整年天数
        for (int i = 1900; i <year; i++) {
            int currentyear=i;
            days+=getDaysofYear(currentyear);            
        }
        // 计算当前年份当前月份之前整月的天数
        for (int i = 1; i < month; i++) {
            int currentmonth=i;
            days+=getDays(year, currentmonth);
        }
        // 根据总天数计算这一天是星期几
        weekday=(days%7+1)%7;
        return weekday;
    }
    //获得某年的天数
    private static int getDaysofYear(int year) {
        if(isLeapYear(year)==true){
            return 366;
        }else{
            return 365;
        }
    }

    //根据年份和月份得到某个月共有几天
    private static int getDays(int year, int month) {
        int days = 0;
        switch (month) {
        case 1:
        case 3:
        case 5:
        case 7:
        case 8:
        case 10:
        case 12:
            days = 31;
            break;
        case 4:
        case 6:
        case 9:
        case 11:
            days=30;
            break;
        case 2:
            if(isLeapYear(year)==true){
                days=29;
            }else{
                days=28;
            }
            break;
        default:
            days = 0;
            break;
        }
        return days;
    }
    //判断某个年份是否为闰年
    private static boolean isLeapYear(int year) {
        boolean result;
        if(year%4==0&&year%100!=0||year%400==0){
            result= true;
        }else{
            result= false;
        }
        return result;
    }
}