Clash Royale CLAN TAG#URR8PPP

Lock underflow/overflow with Java LocalTime

When subtracting a given amount from a LocalTime object, I've realised that overflow/underflow can occur.

Example:

00:30 - 35 minutes = 23:55
23:30 + 35 minutes = 00:05


For my application, I would like lock times such that the above would generate 00:00 on underflow, and 23:59 on overflow.

00:00

23:59

Is this possible?

overflow

2 Answers
2

My suggestion is:

LocalTime orig = LocalTime.of(0, 30);
int minutesToSubtract = 35;
long minutesSinceMidnight = ChronoUnit.MINUTES.between(LocalTime.MIN, orig);
LocalTime result;
if (minutesToSubtract > minutesSinceMidnight)
// Subtracting the minutes will pass midnight at start of day
result = LocalTime.MIN;
else
// Normal case, no underflow
result = orig.minusMinutes(minutesToSubtract);

System.out.println(result);


The above assumes that minutesToSubtract is non-negative. If negative numbers may occur, you need to check for both underflow and overflow.

minutesToSubtract

The case of checking for overflow (more than 23:59:59.999999999) is similar. Use LocalTime.MAX for end of day.

23:59:59.999999999

LocalTime.MAX

Edit: JB Nizet’s code for the other operation in his comment deserves proper code formatting, so I am pasting it here:

public static LocalTime addWithoutOverflow(LocalTime baseTime, int minutes)
LocalTime maxTime = LocalTime.MAX;
long maxNanos = ChronoUnit.NANOS.between(baseTime, maxTime);
long nanos = Duration.ofMinutes(minutes).toNanos();
return baseTime.plusNanos(Math.min(maxNanos, nanos));



public static LocalTime addWithoutOverflow(LocalTime baseTime, int minutes) LocalTime maxTime = LocalTime.MAX; long maxNanos = ChronoUnit.NANOS.between(baseTime, maxTime); long nanos = Duration.ofMinutes(minutes).toNanos(); return baseTime.plusNanos(Math.min(maxNanos, nanos));

In this example, a route should be locked x amount of time before it starts.

1 |LocalTime firstStopTime = firstStop.getStopTime();
2 |LocalTime earliestTime = firstStopTime.minus(beforeRouteLockTimeMins % 1440, ChronoUnit.MINUTES);
3 |LocalTime latestTime = firstStopTime.plus(afterRouteTimeLockMins % 1440, ChronoUnit.MINUTES);
4 |
5 |// Handle underflow/overflow when getting earliest/latest time
6 |if (earliestTime.isAfter(firstStopTime)) earliestTime = LocalTime.MIN;
7 |if (latestTime.isBefore(firstStopTime)) latestTime = LocalTime.MAX;


On line 2 and 3, I am using % to avoid the lock time being greater than 24 hours. This way regardless of overflow/underflow, it can't pass the original time, so the checks on lines 6 and 7 will work.

I then assume that if the subtraction for earliest time is actually later than the stop, then it must have underflowed, therefore set it to 00:00, and the reverse for the latest time.

Finally, the times can be compared like so:

// Check route is within time constraint
if (currentTime.isBefore(earliestTime))
return new RouteAvailabilityResponseModel(false, "Too early to begin route.");
else if (currentTime.isAfter(latestTime))
return new RouteAvailabilityResponseModel(false, "Too late to begin route.");
else
return new RouteAvailabilityResponseModel(true, "Route can be started.");



Whilst this solution is working for me right now, I would like to see if there are any other less verbose options. (Then again this is Java.)

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