[JAVA]计算两个日期相差的天数

Posted 2023-02-26 yccy1230

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;
		else
			return false;
	

	private static boolean isLeapYear(int year) 
		// TODO Auto-generated method stub
		if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0)
			return true;
		else
			return 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;
		else
			monthDay[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;
				else
					yearDay += 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！");
		else
			System.out.println("结果为：" + result);