I need to compare two Dates (e.g. date1 and date2) and come up with a boolean sameDay which is true of the two Dates share the same day, and false if they are not.

How can I do this? There seems to be a whirlwind of confusion here... and I would like to avoid pulling in other dependencies beyond the JDK if at all possible.

to clarify: if date1 and date2 share the same year, month, and day, then sameDay is true, otherwise it is false. I realize this requires knowledge of a timezone... it would be nice to pass in a timezone but I can live with either GMT or local time as long as I k开发者_如何转开发now what the behavior is.

again, to clarify:

date1 = 2008 Jun 03 12:56:03
date2 = 2008 Jun 03 12:59:44
  => sameDate = true

date1 = 2009 Jun 03 12:56:03
date2 = 2008 Jun 03 12:59:44
  => sameDate = false

date1 = 2008 Aug 03 12:00:00
date2 = 2008 Jun 03 12:00:00
  => sameDate = false

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Calendar cal1 = Calendar.getInstance();
Calendar cal2 = Calendar.getInstance();
cal1.setTime(date1);
cal2.setTime(date2);
boolean sameDay = cal1.get(Calendar.DAY_OF_YEAR) == cal2.get(Calendar.DAY_OF_YEAR) &&
                  cal1.get(Calendar.YEAR) == cal2.get(Calendar.YEAR);

Note that "same day" is not as simple a concept as it sounds when different time zones can be involved. The code above will for both dates compute the day relative to the time zone used by the computer it is running on. If this is not what you need, you have to pass the relevant time zone(s) to the Calendar.getInstance() calls, after you have decided what exactly you mean with "the same day".

And yes, Joda Time's LocalDate would make the whole thing much cleaner and easier (though the same difficulties involving time zones would be present).

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How about:

SimpleDateFormat fmt = new SimpleDateFormat("yyyyMMdd");
return fmt.format(date1).equals(fmt.format(date2));

You can also set the timezone to the SimpleDateFormat, if needed.

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I use the "apache commons lang" package to do this (namely org.apache.commons.lang.time.DateUtils)

boolean samedate = DateUtils.isSameDay(date1, date2);  //Takes either Calendar or Date objects

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You can avoid external dependencies and the performance hit of using Calendar by calculating the Julian Day Number for each of the dates and then comparing these:

public static boolean isSameDay(Date date1, Date date2) {

    // Strip out the time part of each date.
    long julianDayNumber1 = date1.getTime() / MILLIS_PER_DAY;
    long julianDayNumber2 = date2.getTime() / MILLIS_PER_DAY;

    // If they now are equal then it is the same day.
    return julianDayNumber1 == julianDayNumber2;
}

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Joda-Time

As for adding a dependency, I'm afraid the java.util.Date & .Calendar really are so bad that the first thing I do to any new project is add the Joda-Time library. In Java 8 you can use the new java.time package, inspired by Joda-Time.

The core of Joda-Time is the DateTime class. Unlike java.util.Date, it understands its assigned time zone (DateTimeZone). When converting from j.u.Date, assign a zone.

DateTimeZone zone = DateTimeZone.forID( "America/Montreal" );
DateTime dateTimeQuébec = new DateTime( date , zone );

LocalDate

One way to verify if two date-times land on the same date is to convert to LocalDate objects.

That conversion depends on the assigned time zone. To compare LocalDate objects, they must have been converted with the same zone.

Here is a little utility method.

static public Boolean sameDate ( DateTime dt1 , DateTime dt2 )
{
    LocalDate ld1 = new LocalDate( dt1 );
    // LocalDate determination depends on the time zone.
    // So be sure the date-time values are adjusted to the same time zone.
    LocalDate ld2 = new LocalDate( dt2.withZone( dt1.getZone() ) );
    Boolean match = ld1.equals( ld2 );
    return match;
}

Better would be another argument, specifying the time zone rather than assuming the first DateTime object’s time zone should be used.

static public Boolean sameDate ( DateTimeZone zone , DateTime dt1 , DateTime dt2 )
{
    LocalDate ld1 = new LocalDate( dt1.withZone( zone ) );
    // LocalDate determination depends on the time zone.
    // So be sure the date-time values are adjusted to the same time zone.
    LocalDate ld2 = new LocalDate( dt2.withZone( zone ) );
    return ld1.equals( ld2 );
}

String Representation

Another approach is to create a string representation of the date portion of each date-time, then compare strings.

Again, the assigned time zone is crucial.

DateTimeFormatter formatter = ISODateTimeFormat.date();  // Static method.
String s1 = formatter.print( dateTime1 );
String s2 = formatter.print( dateTime2.withZone( dt1.getZone() )  );
Boolean match = s1.equals( s2 );
return match;

Span of Time

The generalized solution is to define a span of time, then ask if the span contains your target. This example code is in Joda-Time 2.4. Note that the "midnight"-related classes are deprecated. Instead use the withTimeAtStartOfDay method. Joda-Time offers three classes to represent a span of time in various ways: Interval, Period, and Duration.

Using the "Half-Open" approach where the beginning of the span is inclusive and the ending exclusive.

The time zone of the target can be different than the time zone of the interval.

DateTimeZone timeZone = DateTimeZone.forID( "Europe/Paris" );
DateTime target = new DateTime( 2012, 3, 4, 5, 6, 7, timeZone );
DateTime start = DateTime.now( timeZone ).withTimeAtStartOfDay();
DateTime stop = start.plusDays( 1 ).withTimeAtStartOfDay();
Interval interval = new Interval( start, stop );
boolean containsTarget = interval.contains( target );

java.time

Java 8 and later comes with the java.time framework. Inspired by Joda-Time, defined by JSR 310, and extended by the ThreeTen-Extra project. See Tutorial.

The makers of Joda-Time have instructed us all to move to java.time as soon as is convenient. In the meantime Joda-Time continues as an actively maintained project. But expect future work to occur only in java.time and ThreeTen-Extra rather than Joda-Time.

To summarize java.time in a nutshell… An Instant is a moment on the timeline in UTC. Apply a time zone (ZoneId) to get a ZonedDateTime object. To move off the timeline, to get the vague indefinite idea of a date-time, use the "local" classes: LocalDateTime, LocalDate, LocalTime.

The logic discussed in the Joda-Time section of this Answer applies to java.time.

The old java.util.Date class has a new toInstant method for conversion to java.time.

Instant instant = yourJavaUtilDate.toInstant(); // Convert into java.time type.

Determining a date requires a time zone.

ZoneId zoneId = ZoneId.of( "America/Montreal" );

We apply that time zone object to the Instant to obtain a ZonedDateTime. From that we extract a date-only value (a LocalDate) as our goal is to compare dates (not hours, minutes, etc.).

ZonedDateTime zdt1 = ZonedDateTime.ofInstant( instant , zoneId );
LocalDate localDate1 = LocalDate.from( zdt1 );

Do the same to the second java.util.Date object we need for comparison. I’ll just use the current moment instead.

ZonedDateTime zdt2 = ZonedDateTime.now( zoneId );
LocalDate localDate2 = LocalDate.from( zdt2 );

Use the special isEqual method to test for the same date value.

Boolean sameDate = localDate1.isEqual( localDate2 );

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Convert dates to Java 8 java.time.LocalDate as seen here.

LocalDate localDate1 = date1.toInstant().atZone(ZoneId.systemDefault()).toLocalDate();
LocalDate localDate2 = date2.toInstant().atZone(ZoneId.systemDefault()).toLocalDate();

// compare dates
assertTrue("Not on the same day", localDate1.equals(localDate2));

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Java 8

If you are using Java 8 in your project and comparing java.sql.Timestamp, you could use the LocalDate class:

sameDate = date1.toLocalDateTime().toLocalDate().equals(date2.toLocalDateTime().toLocalDate());

If you are using java.util.Date, have a look at Istvan answer which is less ambiguous.

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private boolean isSameDay(Date date1, Date date2) {
        Calendar calendar1 = Calendar.getInstance();
        calendar1.setTime(date1);
        Calendar calendar2 = Calendar.getInstance();
        calendar2.setTime(date2);
        boolean sameYear = calendar1.get(Calendar.YEAR) == calendar2.get(Calendar.YEAR);
        boolean sameMonth = calendar1.get(Calendar.MONTH) == calendar2.get(Calendar.MONTH);
        boolean sameDay = calendar1.get(Calendar.DAY_OF_MONTH) == calendar2.get(Calendar.DAY_OF_MONTH);
        return (sameDay && sameMonth && sameYear);
    }

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FOR ANDROID USERS:

You can use DateUtils.isToday(dateMilliseconds) to check whether the given date is current day or not.

API reference: https://developer.android.com/reference/android/text/format/DateUtils.html#isToday(long)

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For Kotlin devs this is the version with comparing formatted strings approach:

val sdf = SimpleDateFormat("yyMMdd")
if (sdf.format(date1) == sdf.format(date2)) {
    // same day
}

It's not the best way, but it's short and working.

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in addition to Binil Thomas solution

public static boolean isOnSameDay(Timestamp... dates) {
    SimpleDateFormat fmt = new SimpleDateFormat("yyyyMMdd");
    String date1 = fmt.format(dates[0]);
    for (Timestamp date : dates) {
        if (!fmt.format(date).equals(date1)) {
            return false;
        }
    }
    return true;
}

usage

    isOnSameDay(date1,date2,date3 ...);
//or 
    isOnSameDay(mydates);

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With JAVA 8 we can convert Date object to LocalDate object, hence we can do this:

public static boolean isDatesAreDifferentDays(Date date1,Date date2)
{
    LocalDate d1 = date1.toInstant().atZone(ZoneId.systemDefault()).toLocalDate();
    LocalDate d2 = date2.toInstant().atZone(ZoneId.systemDefault()).toLocalDate();
    if(d1.getDayOfMonth() != d2.getDayOfMonth())
    {
        return false;
    }
    else if(d1.getMonth() != d2.getMonth())
    {
        return false;
    }
    else if(d1.getYear() != d2.getYear())
    {
        return false;
    }
    else
    {
        return true;
    }
}

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FASTER SOLUTION

Like @AyeJay solution but correct for all timezones, that add a offset in timestamp.

  public static boolean isSameDay(Date dateA, Date dateB) {
    int offset = TimeZone.getDefault().getRawOffset();
    try {
        long julianDayNumber1 = (dateA.getTime() + offset) / MILLIS_PER_DAY;
        long julianDayNumber2 = (dateB.getTime() + offset) / MILLIS_PER_DAY;
        return julianDayNumber1 == julianDayNumber2;
    } catch (Exception e) {
        return false;
    }
}

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you can apply the same logic as the SimpleDateFormat solution without relying on SimpleDateFormat

date1.getFullYear()*10000 + date1.getMonth()*100 + date1.getDate() == 
date2.getFullYear()*10000 + date2.getMonth()*100 + date2.getDate()