What is the difference of using TemporalAmount or TemporalUnit in Java 8?

Question

I write some piece of code in Java 8 which use time arithmetic. I realize that I can implement in differentways. Lets look at simple code below. Of course it is the same result but I confused which way is mostly applied or most efficient to make arithmetic operations in Java 8 ?

LocalTime time = LocalTime.now();
// 1st way
LocalTime plusOp = time.plus(Duration.ofMinutes(10L));
// 2nd way
LocalTime plusOp2 = time.plus(10L, ChronoUnit.MINUTES);
System.out.println(plusOp);
System.out.println(plusOp2);
// 3. way simply
 time.plusMinutes(10L);

Thanks in advance.

Answer 1

Duration can only handle fixed-length periods, such as "hours", "minutes", "seconds", "days" (where it assumes exactly 24 hours per day). You can't use "months" with Duration, because a month varies in length.

Period - the other common TemporalAmount implementation - represents years, months and days separately.

Personally I would recommend:

• When you know the unit beforehand, use the appropriate plusXxx method, e.g. time.plusMinutes(10). That's about as easy to read as it gets.
• When you're trying to represent "logical" calendar amounts, use Period
• When you're trying to represent "fixed length" amounts, use Duration

Here's an example of where Period and Duration can differ:

import java.time.*;

public class Test {
    public static void main(String[] args) {
        ZoneId zone = ZoneId.of("Europe/London");
        // At 2015-03-29T01:00:00Z, Europe/London goes from UTC+0 to UTC+1
        LocalDate transitionDate = LocalDate.of(2015, 3, 29);
        ZonedDateTime start = ZonedDateTime.of(transitionDate, LocalTime.MIDNIGHT, zone);
        ZonedDateTime endWithDuration = start.plus(Duration.ofDays(1));
        ZonedDateTime endWithPeriod = start.plus(Period.ofDays(1));
        System.out.println(endWithDuration); // 2015-03-30T01:00+01:00[Europe/London]
        System.out.println(endWithPeriod);   // 2015-03-30T00:00+01:00[Europe/London]
    }
}

I wouldn't worry about the efficiency until you really need to - at which point you should have a benchmark so you can test different options.

Answer 2

If you look at the source, the plus(long amountToAdd, TemporalUnit unit) method uses the plusXXX methods to produce the results. So there are no arguments here about efficiency.

Instead, you use whichever is most appropriate for your scenario. I would suggest that if you are using user input to decide whether to add hours, minutes, etc., then the plus() method is better. Otherwise, your code might be easier to read if you use plusXXX.