How to avoid negative time between time difference?

Question

I'm developing an app in which I'm using Java8 Time. I'm facing an issue.

Let's say Time A is 08:00 and Time B is 17:00, so the difference of between these two times will be 9h which in my case is correct, but if Time A is 18:00 and Time B is 02:00 it should be 8h, but in my case my program is returning -16. Kindly someone guide me how to solve this.

My code:

@Test
public void testTime()
{
    DateTimeFormatter format = DateTimeFormatter.ofPattern("HH:mm");

    String s = "18:00";
    String e = "02:00";

    // Parse datetime string to java.time.LocalDateTime instance
    LocalTime startTime = LocalTime.parse(s, format);
    LocalTime endTime = LocalTime.parse(e, format);

    String calculatedTime = ChronoUnit.HOURS.between(startTime, endTime)%24 + ":"
            + ChronoUnit.MINUTES.between(startTime, endTime)%60;

    System.out.println(calculatedTime);

}

Answer 1

Why not use the Duration class? It’s meant for situations like yours.

    Duration calculatedTime = Duration.between(startTime, endTime);
    if (calculatedTime.isNegative()) {
        calculatedTime = calculatedTime.plusDays(1);
    }

    System.out.println(calculatedTime);

This prints the duration in ISO 8601 format:

PT8H

To format it in Java 8:

    long hours = calculatedTime.toHours();
    calculatedTime = calculatedTime.minusHours(hours);
    String formattedTime = String.format(Locale.getDefault(), "%d:%02d",
                                         hours, calculatedTime.toMinutes());
    System.out.println(formattedTime);

This prints

8:00

To format in Java 9 (not tested):

    String formattedTime = String.format("%d:%02d", 
                                         calculatedTime.toHoursPart(),
                                         calculatedTime.toMinutesPart());