java计算两个日期中间的时间

如果想要计算两个日期中间的时间，可以使用Java的Date和Calendar类来处理，具体步骤如下：

1. 使用SimpleDateFormat类将输入的两个日期字符串转换为Date对象。

String startDate = "2021-01-01";
String endDate =  "2021-06-30";
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Date date1 = sdf.parse(startDate);
Date date2 = sdf.parse(endDate);

1. 使用Calendar类获取两个日期的毫秒差。

Calendar calendar1 = Calendar.getInstance();
Calendar calendar2 = Calendar.getInstance();
calendar1.setTime(date1);
calendar2.setTime(date2);
long millis1 = calendar1.getTimeInMillis();
long millis2 = calendar2.getTimeInMillis();
long diff = millis2 - millis1;

1. 将毫秒差转换为时间间隔（天、小时、分、秒）。

long diffSeconds = diff / 1000;
long diffMinutes = diff / (60 * 1000);
long diffHours = diff / (60 * 60 * 1000);
long diffDays = diff / (24 * 60 * 60 * 1000);

以下是完整的计算两个日期中间时间的代码：

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

public class DateIntervalExample {
    public static void main(String[] args) {
        String startDate = "2021-01-01";
        String endDate =  "2021-06-30";
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        try {
            Date date1 = sdf.parse(startDate);
            Date date2 = sdf.parse(endDate);
            Calendar calendar1 = Calendar.getInstance();
            Calendar calendar2 = Calendar.getInstance();
            calendar1.setTime(date1);
            calendar2.setTime(date2);
            long millis1 = calendar1.getTimeInMillis();
            long millis2 = calendar2.getTimeInMillis();
            long diff = millis2 - millis1;
            long diffSeconds = diff / 1000;
            long diffMinutes = diff / (60 * 1000);
            long diffHours = diff / (60 * 60 * 1000);
            long diffDays = diff / (24 * 60 * 60 * 1000);
            System.out.println("Difference in seconds: " + diffSeconds + " seconds.");
            System.out.println("Difference in minutes: " + diffMinutes + " minutes.");
            System.out.println("Difference in hours: " + diffHours + " hours.");
            System.out.println("Difference in days: " + diffDays + " days.");
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
}

输出结果：

Difference in seconds: 15552000 seconds.
Difference in minutes: 259200 minutes.
Difference in hours: 4320 hours.
Difference in days: 180 days.

另外一个示例：

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

public class DateIntervalExample {
    public static void main(String[] args) {
        String startDate = "2021-03-01";
        String endDate =  "2021-03-10";
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        try {
            Date date1 = sdf.parse(startDate);
            Date date2 = sdf.parse(endDate);
            Calendar calendar1 = Calendar.getInstance();
            Calendar calendar2 = Calendar.getInstance();
            calendar1.setTime(date1);
            calendar2.setTime(date2);
            long millis1 = calendar1.getTimeInMillis();
            long millis2 = calendar2.getTimeInMillis();
            long diff = millis2 - millis1;
            long diffSeconds = diff / 1000;
            long diffMinutes = diff / (60 * 1000);
            long diffHours = diff / (60 * 60 * 1000);
            long diffDays = diff / (24 * 60 * 60 * 1000);
            System.out.println("Difference in seconds: " + diffSeconds + " seconds.");
            System.out.println("Difference in minutes: " + diffMinutes + " minutes.");
            System.out.println("Difference in hours: " + diffHours + " hours.");
            System.out.println("Difference in days: " + diffDays + " days.");
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
}

输出结果：

Difference in seconds: 777600 seconds.
Difference in minutes: 12960 minutes.
Difference in hours: 216 hours.
Difference in days: 9 days.