计算两个日期相差的天数-Java实现

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这里用到了Java的Calendar类，首先创建两个Date类实例对象，然创建两个Calendar类的实例对象，使用Calendar对象的setTime(Date date) 方法分别为每个Calendar对象设置指定的时间，参数就是Date类对象。接下来分别获取两个Calendar对象的年份数和当前年份中的天数，再对年份进行闰年和平年判断，最后把两个日期全部转化成天数来计算

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class IntervalDay {

    public void compareDays(Date date1, Date date2) {
        Calendar calendar1 = Calendar.getInstance();
        Calendar calendar2 = Calendar.getInstance();
        calendar1.setTime(date1);
        calendar2.setTime(date2);
        int day1 = calendar1.get(Calendar.DAY_OF_YEAR);
        int day2 = calendar2.get(Calendar.DAY_OF_YEAR);
        int year1 = calendar1.get(Calendar.YEAR);
        int year2 = calendar2.get(Calendar.YEAR);
        if(year1 > year2) {
            int tempyear = year1;
            int tempday = day1;
            day1 = day2;
            day2 = tempday;
            year1 = year2;
            year2 = tempyear; 
        }
        if (year1 == year2) {
            System.out.printf("相隔的天数为:%s天", (day2 - day1));
        } else {
            int DayCount = 0;
            for (int i = year1; i < year2; i++) {
                if (i % 4 == 0 && i % 100 != 0 || i % 400 == 0) {
                    DayCount += 366;
                }else {
                    DayCount += 365;
                }
            }
            System.out.printf("相隔的天数为:%s天", DayCount+(day2-day1));
            
        }
    }

    public static void main(String[] args) {
        IntervalDay intervalDay = new IntervalDay();
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd H:m:s");
        Date date1 = null;
        Date date2 = null;
        try {
            date2 = dateFormat.parse("2012-08-02 12:01:32");
            date1 = dateFormat.parse("2018-08-07 13:01:32");
        } catch (ParseException e) {
            e.printStackTrace();
        }
        intervalDay .compareDays(date1, date2);
    }
}