JAVA基础：万年历 【习题笔记】

 public static void main(String[] args) {
        System.out.println("请输入年份：");
        Scanner input = new Scanner(System.in);
        int year = input.nextInt();
        System.out.println("请输入月份：");
        int month = input.nextInt();

        //计算这个月有多少天
        int days = 0;
        if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12) {
            days = 31;
        } else if (month == 4 || month == 6 || month == 9 || month == 11) {
            days = 30;
        } else {
            if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
                days = 29;
            } else {
                days = 28;
            }
        }
        //2.算输入月份的1号是星期几
        //2.1先算 你输进来的年份year年 距离 1900年相差的整年天数差
        int sumYear = 0;
        for (int i = 1900; i < year; i++) {
            if (i % 4 == 0 && i % 100 != 0 || i % 400 == 0) {
                sumYear += 366;
            } else {
                sumYear += 365;
            }
        }
        //2.2再算year年的一月 距离month月的天数差
        int sumMonth = 0;
        for (int i = 1; i < month; i++) {
            if (i == 1 || i == 3 || i == 5 || i == 7 || i == 8 || i == 10 || i == 12) {
                sumMonth += 31;
            } else if (i == 4 || i == 6 || i == 9 || i == 11) {
                sumMonth += 30;
            } else {
                if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
                    sumMonth += 29;
                } else {
                    sumMonth += 28;
                }
            }
        }
        //2.3计算year年month月1号是星期几？
        int week = (sumYear + sumMonth + 1) % 7;
        if (week == 0) {
            week = 7;
        }
        //3.打印日历
        System.out.println(year + "年" + month + "月");
        System.out.println("一\t二\t三\t四\t五\t六\t日");
        for (int i = 1; i < week; i++) {//挤出前面
            System.out.print("\t");//直接输出
        }
        for (int i = 1; i <= days; i++) {//日历内容
            System.out.print(i + "\t");//直接输出

            if ((sumMonth + sumYear + i) % 7 == 0) {//换行
                System.out.println();//输出后换行
            }
        }


    }

最基础的写法，代码量大，但是思路最为清晰，新手必学！！！

 public static void main4(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.println("请输入年份");
        int year = input.nextInt();
        System.out.println("请输入月份");
        int month = input.nextInt();
        Calendar calendar = Calendar.getInstance();//当前时间
        calendar.set(Calendar.YEAR, year);
        calendar.set(Calendar.MONTH, month - 1);
        //这个月有多少天？
        int days = calendar.getActualMaximum(Calendar.DATE);
        //这个月的1号是星期几？
        calendar.set(Calendar.DATE, 1);
        int week = calendar.get(Calendar.DAY_OF_WEEK) == 1 ? 7 : calendar.get(Calendar.DAY_OF_WEEK) - 1;
        //calendar .get(Calendar.DAY_OF_WEEK) :获取1号是本周的第几天
        //打印日历
        System.out.println("一\t二\t三\t四\t五\t六\t日\t");
        for (int i = 1; i < week; i++) {
            System.out.print("\t");
        }
        for (int i = 1; i <= days; i++) {
            System.out.print(i + "\t");
            calendar.set(Calendar.DATE, i);
            if (calendar.get(Calendar.DAY_OF_WEEK) == 1) {
                System.out.println();
            }
        }


    }

采用日期时间类，使用Canlendar，代码更加简单，更加便捷。