How to add dateTime values in a stream(java)?

Question

Today I started learning Java 8, so I\'m quite new to Java 8 and it\'s stuff. I have a list of activities. An activity has name, startTime, endTime. For startTime and endTi

Answer 1

First start to use Java 8 DateTime API. There is a built-in Duration class. Then you can use:

Map map = list.stream().collect(
    Collectors.groupingBy(a -> a.activityLabel, 
        Collectors.reducing(Duration.ZERO, 
            a -> Duration.between(a.startTime, a.endTime).abs(), Duration::plus
        )
    ));

---

EDIT

Since you've to use Joda you can get the same results with (using Period instead of Duration):

Map map = list.stream().collect(
    Collectors.groupingBy(a -> a.activityLabel, 
        Collectors.reducing(Period.ZERO, 
            a -> new Period(a.startTime, a.endTime), Period::plus
        )
    ));