Time consts in Java?

Question

Is there a Java package with all the annoying time constants like milliseconds/seconds/minutes in a minute/hour/day/year? I'd hate to duplicate something like that.

Solution 1

Joda-Time contains classes such as Days, which contain methods such as toStandardSeconds(). So you can write:

int seconds = Days.ONE.toStandardSeconds();

although it seems a little verbose, and perhaps is only useful for more complex scenarios such as leap years etc.

Solution 2

I would go with java TimeUnit if you are not including joda-time in your project already. You don't need to include an external lib and it is fairly straightforward.

Whenever you need those "annoying constants" you usually need them to mutliply some number for cross-unit conversion. Instead you can use TimeUnit to simply convert the values without explicit multiplication.

This:

long millis = hours * MINUTES_IN_HOUR * SECONDS_IN_MINUTE * MILLIS_IN_SECOND;

becomes this:

long millis = TimeUnit.HOURS.toMillis(hours);

If you expose a method that accepts some value in, say, millis and then need to convert it, it is better to follow what java concurrency API does:

public void yourFancyMethod(long somePeriod, TimeUnit unit) {
    int iNeedSeconds = unit.toSeconds(somePeriod);
}

If you really need the constants very badly you can still get i.e. seconds in an hour by calling:

int secondsInHour = TimeUnit.HOURS.toSeconds(1);

Solution 3

Java 8 / java.time solution

As an alternative to TimeUnit, you might for some reason prefer the Duration class from java.time package:

Duration.ofDays(1).getSeconds()     // returns 86400;
Duration.ofMinutes(1).getSeconds(); // 60
Duration.ofHours(1).toMinutes();    // also 60
//etc.

Additionally, if you would go deeper and have analyzed how Duration.ofDays(..) method works, you would see the following code:

return create(Math.multiplyExact(days, SECONDS_PER_DAY), 0);

where SECONDS_PER_DAY is a package protected static constant from LocalTime class.

/**
 * Seconds per day.
 */
static final int SECONDS_PER_DAY = SECONDS_PER_HOUR * HOURS_PER_DAY;

//there are also many others, like HOURS_PER_DAY, MINUTES_PER_HOUR, etc.

I think it is safe to assume that if there would be any package, which would defined "all the annoying time constants like miliseconds/seconds/minutes" as you call them, I believe Java SDK Developers would have use them.

Why are this LocalTime constants package protected and not public that is a good question, I believe there is a reason for that. For now it looks like you really have to copy them and maintain on your own.

Solution 4

If on android, I suggest:

android.text.format.DateUtils

DateUtils.SECOND_IN_MILLIS
DateUtils.MINUTE_IN_MILLIS
DateUtils.HOUR_IN_MILLIS
DateUtils.DAY_IN_MILLIS
DateUtils.WEEK_IN_MILLIS
DateUtils.YEAR_IN_MILLIS

Solution 5

The Java TimeUnit seems to be what you want

View more solutions

Comments

[kanso]

duffymo: You're right , of course , but for our needs , 60 seconds in a minute is a good enough approximation

[Basil Bourque]

See the DateTimeConstants class in Joda-Time as well.

[M. Atif Riaz]

Totally agree with your solution to avoid unnecessary dependency on third party library

[Basil Bourque]

FYI: The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

[Basil Bourque]

FYI: The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

[simpleuser]

any comments on why someone might prefer Duration over TimeUnit?

[Yoory N.]

Duration.ofDays(1).getSeconds() will create and throw away an object to do its work, comparing to TimeUnit.DAYS.toSeconds(1) that only performs calculations.

[theadam]

I think there is absolutely no reason to use Duration if all you need them to do is convert to a value. It is preferable to use Duration though in your API if that's what you need, in some cases this will be more readable then specifying value and unit as 2 separate arguments. I will remember to update my answer sometimes soon to indicate that.

[Kong]

Another bonus of this solution is that it works if you need constants rather than method calls, such as when using them in annotations.

[Vassilis]

The drawback is that you cannot use them in annotations, as they have to be compile time constants

[walv]

exactly what I was looking for, thank you

[zypA13510]

What about readability? I, for one, think ofDays(1) is clearer than toSeconds(1) in its meaning - I cannot imagine anyone to mistake 1 as the number of seconds when I do ofDays(1), but I can imagine that happening for toSeconds(1).