Time: How to get the next friday?

Question

How can I get the next friday with the Joda-Time API.

The LocalDate of today is today. It looks to me you have to decide whever you are before or after the friday of the current week. See this method:

private LocalDate calcNextFriday(LocalDate d) {
    LocalDate friday = d.dayOfWeek().setCopy(5);
    if (d.isBefore(friday)) {
        return d.dayOfWeek().setCopy(5);
    } else {
        return d.plusWeeks(1).dayOfWeek().setCopy(5);
    }
}

Is it possible to do it shorter or with a oneliner?

PS: Please don't advise me using JDKs date/time stuff. Joda-Time is a much better API.

Java 8 introduces java.time package (Tutorial) which is even better.

Solution 1

java.time

With the java.time framework built into Java 8 and later (Tutorial) you can use TemporalAdjusters to get next or previous day-of-week.

private LocalDate calcNextFriday(LocalDate d) {
  return d.with(TemporalAdjusters.next(DayOfWeek.FRIDAY));
}

Solution 2

It's possible to do it in a much easier to read way:

if (d.getDayOfWeek() < DateTimeConstants.FRIDAY) {
    return d.withDayOfWeek(DateTimeConstants.FRIDAY));
} else if (d.getDayOfWeek() == DateTimeConstants.FRIDAY) {
    // almost useless branch, could be merged with the one above
    return d;
} else {
    return d.plusWeeks(1).withDayOfWeek(DateTimeConstants.FRIDAY));
}

or in a bit shorter form

private LocalDate calcNextFriday(LocalDate d) {    
    if (d.getDayOfWeek() < DateTimeConstants.FRIDAY) {
        d = d.withDayOfWeek(DateTimeConstants.FRIDAY));
    } else {
        d = d.plusWeeks(1).withDayOfWeek(DateTimeConstants.FRIDAY));
    }    
    return d; // note that there's a possibility original object is returned
}

or even shorter

private LocalDate calcNextFriday(LocalDate d) {
    if (d.getDayOfWeek() >= DateTimeConstants.FRIDAY) {
        d = d.plusWeeks(1);
    }
    return d.withDayOfWeek(DateTimeConstants.FRIDAY);
}

PS. I didn't test the actual code! :)

Solution 3

Your code in 1 line

private LocalDate calcNextFriday3(LocalDate d) {
    return d.isBefore(d.dayOfWeek().setCopy(5))?d.dayOfWeek().setCopy(5):d.plusWeeks(1).dayOfWeek().setCopy(5);
}

Alternative approach

private LocalDate calcNextDay(LocalDate d, int weekday) {
    return (d.getDayOfWeek() < weekday)?d.withDayOfWeek(weekday):d.plusWeeks(1).withDayOfWeek(weekday);
}


private LocalDate calcNextFriday2(LocalDate d) {
    return calcNextDay(d,DateTimeConstants.FRIDAY);
}

somewhat tested ;-)

Solution 4

I just wasted like 30 minutes trying to figure this out myself but I needed to generically roll forward.

Anyway here is my solution:

public static DateTime rollForwardWith(ReadableInstant now, AbstractPartial lp) {
    DateTime dt = lp.toDateTime(now);
    while (dt.isBefore(now)) {
        dt = dt.withFieldAdded(lp.getFieldTypes()[0].getRangeDurationType(), 1);
    }
    return dt;
}

Now you just need to make a Partial (which LocalDate is) for the day of the week.

Partial().with(DateTimeFieldType.dayOfWeek(), DateTimeConstants.FRIDAY); 

Now whatever the most significant field is of the partial will be +1 if the current date is after it (now).

That is if you make a partial with March 2012 it will create a new datetime of March 2013 or <.

Solution 5

import java.util.Calendar;

private Calendar getNextweekOfDay(int weekOfDay) {
    Calendar today = Calendar.getInstance();
    int dayOfWeek = today.get(Calendar.DAY_OF_WEEK);
    int daysUntilNextWeekOfDay = weekOfDay - dayOfWeek;
    if (daysUntilNextWeekOfDay == 0) daysUntilNextWeekOfDay = 7;
    Calendar nextWeekOfDay = (Calendar)today.clone();
    nextWeekOfDay.add(Calendar.DAY_OF_WEEK, daysUntilNextWeekOfDay);
    return nextWeekOfDay;
}

// set alarm for next Friday 9am
public void setAlarm() {
    Calendar calAlarm = getNextweekOfDay(Calendar.FRIDAY);
    calAlarm.set(Calendar.HOUR_OF_DAY, 9);//9am
    calAlarm.set(Calendar.MINUTE, 0);
    calAlarm.set(Calendar.SECOND, 0);
    scheduleAlarm(calAlarm);// this is my own method to schedule a pendingIntent
}

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Comments

[michael.kebe]

Thanks for your answer. Your suggestion with the more general approach is nice. But the oneliner is awkward in term of readability.

[fvu]

@michaelkebe you asked for a oneliner, I just provided one... ;-)

[David Victor]

or compile it ... "DateTimeConstans"

[gyorgyabraham]

Your last snippet's "return" line contains a redundant ")" character. Anyways, thanks, great solution!

[gyorgyabraham]

@michael.kebe I usually place newlines with ternaries at "?" and ":", hit format in Eclipse and it arranges pretty well.

[Christopher Francisco]

Does this uses joda-time?

[michael.kebe]

No, but it developed from it. Here a quote from the joda time homepage: Joda-Time is the de facto standard date and time library for Java prior to Java SE 8. Users are now asked to migrate to java.time (JSR-310).

[Basil Bourque]

FYI, the java.time classes are built into Java 8 and later. Much of the java.time functionality has been back-ported to Java 6 & 7 in ThreeTen-Backport and further adapted to Android in ThreeTenABP. Also, see Oracle Tutorial to learn more.

[Basil Bourque]

FYI, the terribly troublesome old date-time classes such as java.util.Date, java.util.Calendar, and java.text.SimpleDateFormat are now legacy, supplanted by the java.time classes built into Java 8 and later. See Tutorial by Oracle.

[Basil Bourque]

FYI, the terribly troublesome old date-time classes such as java.util.Date, java.util.Calendar, and java.text.SimpleDateFormat are now legacy, supplanted by the java.time classes built into Java 8 and later. See Tutorial by Oracle.

[Breton F.]

Yes If you use java 8 or onwards version or Jodatime, this is not for you. I did say it but i was not clear. Thanks for commenting.

[Ole V.V.]

How is it better than the accepted answer? I guess it’s correct, but I have a very hard time convincing myself.

[Nestor Milyaev]

no-one saying it's better, just an alternative way of doing the same. I believe my answer has clear logic and it doesn't require knowledge/usage of different APIs/ classes other than LocalDate