使用 Java 进行日期比较

Date Comparison using Java

提问by minil

I have two dates:

我有两个日期：

1. toDate(user input in MM/dd/yyyyformat)
2. currentDate(obtained by new Date())

1. toDate（用户输入MM/dd/yyyy格式）
2. currentDate（由 获得new Date()）

I need to compare the currentDatewith toDate. I have to display a report only when the toDateis equal to or more than currentDate. How can I do that?

我需要currentDate与toDate. 仅当toDate等于或大于时，我才必须显示报告currentDate。我怎样才能做到这一点？

回答by Bozho

Date#equals()and Date#after()

Date#equals()和 Date#after()

If there is a possibility that the hourand minutefields are != 0, you'd have to set them to 0.

如果hour和minute字段可能为 != 0，则必须将它们设置为 0。

I can't forget to mention that using java.util.Dateis considered a bad practice, and most of its methods are deprecated. Use java.util.Calendaror JodaTime, if possible.

我不能忘记提到使用java.util.Date被认为是一种不好的做法，并且它的大部分方法都已弃用。如果可能，请使用java.util.Calendar或JodaTime。

回答by Vaishak Suresh

Use java.util.Calendarif you have extensive date related processing.

使用java.util.Calendar，如果你有大量的日期相关的处理。

Date has before(), after()methods. you could use them as well.

日期有before()，after()方法。你也可以使用它们。

回答by tkr

You are probably looking for:

您可能正在寻找：

!toDate.before(currentDate)

before() and after() test whether the date is strictly before or after. So you have to take the negation of the other one to get non strict behaviour.

before() 和 after() 测试日期是严格之前还是之后。因此，您必须否定另一个才能获得非严格行为。

回答by Abdel Raoof

It is easier to compare dates using the java.util.Calendar. Here is what you might do:

使用java.util.Calendar. 以下是您可以执行的操作：

Calendar toDate = Calendar.getInstance();
Calendar nowDate = Calendar.getInstance();
toDate.set(<set-year>,<set-month>,<set-day>);  
if(!toDate.before(nowDate)) {
    //display your report
} else {
    // don't display the report
}

回答by Powerlord

If you're set on using Java Dates rather than, say, JodaTime, use a java.text.DateFormatto convert the string to a Date, then compare the two using .equals:

如果您打算使用 Java 日期而不是 JodaTime，请使用 ajava.text.DateFormat将字符串转换为日期，然后使用 .equals 比较两者：

I almost forgot: You need to zero out the hours, minutes, seconds, and milliseconds on the current date before comparing them. I used a Calendarobject below to do it.

我差点忘了：在比较它们之前，您需要将当前日期的小时、分钟、秒和毫秒归零。我使用Calendar下面的一个对象来做到这一点。

import java.text.DateFormat;
import java.util.Calendar;
import java.util.Date;

// Other code here
    String toDate;
    //toDate = "05/11/2010";

    // Value assigned to toDate somewhere in here

    DateFormat df = DateFormat.getDateInstance(DateFormat.SHORT);
    Calendar currDtCal = Calendar.getInstance();

    // Zero out the hour, minute, second, and millisecond
    currDtCal.set(Calendar.HOUR_OF_DAY, 0);
    currDtCal.set(Calendar.MINUTE, 0);
    currDtCal.set(Calendar.SECOND, 0);
    currDtCal.set(Calendar.MILLISECOND, 0);

    Date currDt = currDtCal.getTime();

    Date toDt;
    try {
        toDt = df.parse(toDate);
    } catch (ParseException e) {
        toDt = null;
        // Print some error message back to the user
    }

    if (currDt.equals(toDt)) {
        // They're the same date
    }

回答by BalusC

This is one of the ways:

这是其中一种方式：

String toDate = "05/11/2010";

if (new SimpleDateFormat("MM/dd/yyyy").parse(toDate).getTime() / (1000 * 60 * 60 * 24) >= System.currentTimeMillis() / (1000 * 60 * 60 * 24)) {
    System.out.println("Display report.");
} else {
    System.out.println("Don't display report.");
}

A bit more easy interpretable:

更容易解释：

String toDateAsString = "05/11/2010";
Date toDate = new SimpleDateFormat("MM/dd/yyyy").parse(toDateAsString);
long toDateAsTimestamp = toDate.getTime();
long currentTimestamp = System.currentTimeMillis();
long getRidOfTime = 1000 * 60 * 60 * 24;
long toDateAsTimestampWithoutTime = toDateAsTimestamp / getRidOfTime;
long currentTimestampWithoutTime = currentTimestamp / getRidOfTime;

if (toDateAsTimestampWithoutTime >= currentTimestampWithoutTime) {
    System.out.println("Display report.");
} else {
    System.out.println("Don't display report.");
}

Oh, as a bonus, the JodaTime's variant:

哦，作为奖励，JodaTime的变体：

String toDateAsString = "05/11/2010";
DateTime toDate = DateTimeFormat.forPattern("MM/dd/yyyy").parseDateTime(toDateAsString);
DateTime now = new DateTime();

if (!toDate.toLocalDate().isBefore(now.toLocalDate())) {
    System.out.println("Display report.");
} else {
    System.out.println("Don't display report.");
}

回答by BlairHippo

If for some reason you're intent on using Dateobjects for your solution, you'll need to do something like this:

如果出于某种原因，您打算在Date解决方案中使用对象，则需要执行以下操作：

    // Convert user input into year, month, and day integers
    Date toDate = new Date(year - 1900, month - 1, day + 1);
    Date currentDate = new Date();
    boolean runThatReport = toDate.after(currentDate);

Shifting the toDateahead to midnight of the next day will take care of the bug I've whined about in the comments to other answers. But, note that this approach uses a deprecated constructor; any approach relying on Datewill use one deprecated method or another, and depending on how you do it may lead to race conditions as well (if you base toDateoff of new Date()and then fiddle around with the year, month, and day, for instance). Use Calendar, as described elsewhere.

将toDate提前到第二天的午夜将解决我在其他答案的评论中抱怨的错误。但是，请注意，这种方法使用了不推荐使用的构造函数；任何方法依赖于Date将使用一个过时的方法或另一种，取决于你怎么做就可能导致竞争条件，以及（如果你基地toDate关闭的new Date()，然后反复折腾的年，月，日，例如）。使用Calendar，如别处所述。

回答by Mark Z

Date long getTime()returns the number of milliseconds since January 1, 1970, 00:00:00 GMTrepresented by this Date object.

Date long getTime()返回自此January 1, 1970, 00:00:00 GMTDate 对象表示以来经过的毫秒数。

//test if date1 is before date2
if(date1.getTime() < date2.getTime()) {
....
}

回答by Viren Savaliya

private boolean checkDateLimit() {

    long CurrentDateInMilisecond = System.currentTimeMillis(); // Date 1
    long Date1InMilisecond = Date1.getTimeInMillis(); //Date2

    if (CurrentDateInMilisecond <= Date1InMilisecond) {
        return true;
    } else {
        return false;
    }

}

// Convert both date into milisecond value .

// 将两个日期都转换为毫秒值。