Java求前一天和后一天、相差天数

Java求前一天和后一天、相差天数

1. 日期（年、月、日）

2.+1天        -1天

3.返回当前日期的字符串

package mjh.week.day6;

//约束要求
//1.year只能从1000-3000
//2.month只能从1-12
//3.day每个月都不同
public class Date {
    private int year;
    private int month;
    private int day;

    public Date(int year, int month, int day) {
        if (!checkYear(year)) {
            throw new RuntimeException("year必须是[1000,3000]:year = " + year);
        }
        if (!checkMonth(month)) {
            throw new RuntimeException("month必须是[1,12]: month = " + month);
        }
        if (!checkDay(year, month, day)) {
            throw new RuntimeException("day必须满足正确的范围：day = " + day);
        }
        //这里已经可以保证数据一定是正确的，可以保存在属性之中了
        this.year = year;
        this.month = month;
        this.day = day;
    }

    public String toString() {
        return String.format("%04d-%02d-%02d", year, month, day);
    }

    public void 往前一天() {
        day--;
        if (day > 0) {
            return;
        }
        month--;
        if (month == 0) {
            year--;
            month = 12;
        }
        day = 根据月取边界(year, month);
    }

    public void 往后一天() {
        day++;

        int dayBound = 根据月取边界(year, month);
        if (day <= dayBound) {
            return;
        }
        month++;
        day = 1;

        if (month <= 12) {
            return;
        }
        year++;
        month = 1;
    }

    private int 根据月取边界(int year, int month) {
        int dayBound;
        if (month == 2) {
            return isLeapyear(year) ? 29 : 28;
           
        } else {
            
            
            return DAY_OF_MONTH[month - 1];
        }
    }

    private static final int[] DAY_OF_MonTH = {
            31, 28, 31, 30, 31, 30,
            31, 31, 30, 31, 30, 31
    };

    private static boolean isLeapyear(int year) {
        if (year % 400 == 0) {
            return true;
        }
        return year % 4 == 0 && year % 100 != 0;
    }

    private static boolean checkDay(int year, int month, int day) {
        if (month != 2) {
            int i = month - 1;
            return day >= 1 && day <= DAY_OF_MONTH[i];
        }
        if (isLeapyear(year)) {
            return day >= 1 && day <= 29;
        }
        return day >= 1 && day <= 28;
    }

    private static boolean checkMonth(int month) {
        return month >= 1 && month <= 12;
    }

    private static boolean checkYear(int year) {
        return year >= 1000 && year <= 3000;
    }
}

package mjh.week.day6;

public class UseDate {
    public static void main(String[] args) {
        Date d1 = new Date(2020, 1, 1);
        
        
        for (int i = 0; i <= 300; i++) {
            d1.往前一天();
            if (i % 15 == 0) {
                System.out.println(d1.toString());
            }
        }
    }
}