如何获取两个日期之间的天数 - `java.util.Calendar` [重复]

Question

我正在尝试获取两个日期之间的天数。我在 JFXtras 的 Agenda 工作。

开始时间 = getStartTime() 返回java.util.Calendar
结束时间 = getEndTime() 返回java.util.Calendar

这是我目前得到的：

void printAppointment(Appointment a) throws ParseException {
        System.out.println(a.getSummary());
        System.out.println(a.getDescription());

        DateFormat formatter = new SimpleDateFormat("yyyy, MMM dd h:mm:ss a z");
        System.out.println(formatter.format(a.getStartTime().getTime()));
        System.out.println(formatter.format(a.getEndTime().getTime()));
        System.out.println(a.getAppointmentGroup());
        System.out.println(a.getLocation());

        // My problem starts here
        Calendar cal1 = new GregorianCalendar();
        Calendar cal2 = new GregorianCalendar();

        SimpleDateFormat sdf = new SimpleDateFormat("ddMMyyyy");

        Date date = sdf.parse(formatter.format(a.getStartTime().getTime()));
        cal1.setTime(date);
        date = sdf.parse(formatter.format(a.getEndTime().getTime()));
        cal2.setTime(date);
        // System.out.println("Days difference = " + daysBetween(cal1.getTime(), cal2.getTime()));
        System.out.println("Days difference = can't be set");
    }

    private int daysBetween(Date d1, Date d2) {
        return (int) ((d2.getTime() - d1.getTime()) / (1000 * 60 * 60 * 24));
    }

// My problem starts here 之后我什么也得不到。打印以下内容：

Another Morning appointment
Another Description of morning appointment
2014, Jun 12 6:00:00 AM PDT
2014, Jun 13 2:00:00 AM PDT
jfxtras.labs.scene.control.Agenda$AppointmentGroupImpl@16e4577
null

请注意，天数的差异会被忽略。

如果有人可以帮助我，我会非常感激。谢谢大家。

更新：

这是最终的工作实现，它以天、小时、分钟和秒为单位，如下面的尝试所示。

Pel
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2014. Jun Mon.9 3:18PM
2014. Jun Wed.11 3:18PM
jfxtras.labs.scene.control.Agenda$AppointmentGroupImpl@12e3872
null
diffSeconds difference = 172800
diffMinutes difference = 2880
diffHours difference = 48
diffDays difference = 2

这是执行此操作的代码

void printAppointment(Appointment a) {
    System.out.println(a.getSummary());
    System.out.println(a.getDescription());

    DateFormat formatter = new SimpleDateFormat("yyyy. MMM EEE.d h:mma");
    System.out.println(formatter.format(a.getStartTime().getTime()));
    System.out.println(formatter.format(a.getEndTime().getTime()));
    System.out.println(a.getAppointmentGroup());
    System.out.println(a.getLocation());
    this.daysBetween(a.getStartTime().getTimeInMillis(), a.getEndTime().getTimeInMillis());

}

private void daysBetween(long t1, long t2) {
    int diff = (int) (t2 - t1);

    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("diffSeconds difference = " + diffSeconds);
    System.out.println("diffMinutes difference = " + diffMinutes);
    System.out.println("diffHours difference = " + diffHours);
    System.out.println("diffDays difference = " + diffDays);
}

Answer 1

不要将 Date 传递给 daysBetween，而是传递一个 long。您可以使用 getTimeInMillis() 从日历中获取当前时间（自 1970 年 1 月 1 日起）。您的代码现在如下所示：

void printAppointment(Appointment a) throws ParseException {
    System.out.println(a.getSummary());
    System.out.println(a.getDescription());

    System.out.println(formatter.format(a.getStartTime().getTime()));
    System.out.println(formatter.format(a.getEndTime().getTime()));
    System.out.println(a.getAppointmentGroup());
    System.out.println(a.getLocation());


    System.out.println("Days difference = " + daysBetween(a.getStartTime().getTimeInMillis(), a.getEndTime().getTimeInMillis()));
}

private int daysBetween(long t1, long t2) {
    return (int) ((t2 - t1) / (1000 * 60 * 60 * 24));
} 

Answer 2

如果您被允许使用 Java 8，那么您应该查看 https://stackoverflow.com/users/288671/vitalii-fedorenko 对问题 Difference in days between two dates in Java? 的回答

在 Java 8 中引入新 API 有几个原因 - 正确处理时差是其中一个原因。 （在某些时区可能会发生影响计算的变化 - 因此，如果有白天调整或类似的事情，仅除以毫秒为单位的差异会导致意外结果）