[JAVA]计算两个日期相差的天数

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算法的主要思路：

首先保证输入的年份要合法，即开始日期一定要小于结束日期

这里利用了两个辅助函数，一个是判断是否为闰年的isLeapYear；另一个是计算传入的某个日期在那一年的第几天theDayInTheYear(Date)

阐述一下计算的主要想法：

分为三种情况：

1.当输入的年份是同一年时，直接用计算出的两个日期所占这一年的天数差即可

2.当计算两个相邻年份时，计算(365（或366）-theDayInTheYear(beginDate))+theDayInTheYear(endDate)即可

3.当计算的两个日期相差大于至少一年时，只要按照2中的计算再加上相差年份的天数总和即可（注意相差年份中是闰年要加上366，平年加上365）

package class4_3;public class Date {private int year;private int month;private int day;public int getYear() {return year;}public void setYear(int year) {this.year = year;}public int getMonth() {return month;}public void setMonth(int month) {this.month = month;}public int getDay() {return day;}public void setDay(int day) {this.day = day;}}

package class4_3;import java.util.Scanner;public class DateCalc {private static int monthDay[] = { 31, 0, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };private static boolean isLeapYear(Date date) {// （辅助函数）判断是否为闰年int year = date.getYear();if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0)return true;elsereturn false;}private static boolean isLeapYear(int year) {// TODO Auto-generated method stubif (year % 4 == 0 && year % 100 != 0 || year % 400 == 0)return true;elsereturn false;}private static int theDayInTheYear(Date date) {// （辅助函数）计算传入日期在这一年的第几天int result = 0;int day = date.getMonth();if (isLeapYear(date))monthDay[1] = 29;elsemonthDay[1] = 28;for (int i = 0; i < (day - 1); i++) {result += monthDay[i];}return (result + day);}private static int calc(Date beiginDate, Date endDate) {// 计算日期差(非法计算返回-1，否则返回日期差)// 确保日期可以计算（beginDate早于endDate）if (beiginDate.getYear() > endDate.getYear()|| beiginDate.getYear() == endDate.getYear() && theDayInTheYear(beiginDate) > theDayInTheYear(endDate))return -1;// 预先计算各自日期在当年的第几天int begin = theDayInTheYear(beiginDate);int end = theDayInTheYear(endDate);// case 1：若为同一年if (beiginDate.getYear() == endDate.getYear()) {return (end - begin);}// case 2:若为相邻年份else if ((beiginDate.getYear() + 1) == endDate.getYear()) {int beginYearDays = 365;if (isLeapYear(beiginDate))beginYearDays = 366;begin = beginYearDays - begin;return (begin + end);}// case 3:相差一年以上else {int beginYearDays = 365;if (isLeapYear(beiginDate))beginYearDays = 366;begin = beginYearDays - begin;int yearDay = 0;// 计算相隔年的天数和for (int i = (beiginDate.getYear() + 1); i < endDate.getYear(); i++) {if (isLeapYear(i))yearDay += 366;elseyearDay += 365;}return (begin + end + yearDay);}}public static void main(String[] args) {// 驱动函数Date beginDate = new Date();Date endDate = new Date();Scanner in = new Scanner(System.in);System.out.print("请输入起始年：");beginDate.setYear(in.nextInt());System.out.print("请输入起始月：");beginDate.setMonth(in.nextInt());System.out.print("请输入起始日：");beginDate.setDay(in.nextInt());System.out.print("请输入结束年：");endDate.setYear(in.nextInt());System.out.print("请输入结束月：");endDate.setMonth(in.nextInt());System.out.print("请输入结束日：");endDate.setDay(in.nextInt());int result = calc(beginDate, endDate);if (result == -1)System.out.println("您的输入有误！");elseSystem.out.println("结果为：" + result);}}

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