How to write expression in java8?

I’m trying to write this function with java 8 , but i didn’t succeeded.
This is my code :

private LocalTime getAbsenceParJour(List<test> tests) {
    LocalTime absenceParJourTime = null;
    Duration sum = Duration.ZERO;
    for (test perPrestation : tests) {
        if (perPrestation.getTypeContactLibre().equalsIgnoreCase("absence")) {
            Duration duration = Duration.between(perPrestation.getHeureDebut(), perPrestation.getHeureFin());
            sum = sum.plus(duration);
        }
    }
    if (sum != null) {
        long m = sum.toMinutes() % 60;
        long s = sum.toHours() % 60;
        absenceParJourTime = LocalTime.of(Long.valueOf(s).intValue(), Long.valueOf(m).intValue());
    }
    return absenceParJourTime;
}

where test is a class java this is :

public class Prestation {
   private LocalTime heureDebut;
   private LocalTime heureFin;
   private String typeContactLibre;
}

Any help thanks in advance.

>Solution :

private LocalTime getAbsenceParJour(List<test> tests) {
    Duration sum = tests.stream()
        .filter(P-> P.getTypeContactLibre().equalsIgnoreCase("absence"))
        .reduce(null, (sum, p) ->
            (sum == null ? Duration.ZERO : sum)
              .plus(Duration.between(p.getHeureDebut(), p.getHeureFin()));
    LocalTime absenceParJourTime = null;
    if (sum != null) {
        int m = (int)(sum.toMinutes() % 60);
        int s = (int)(sum.toHours() % 60);
        absenceParJourTime = LocalTime.of(s, m);
    }
    return absenceParJourTime;
}

Use of Stream is tricky here:

• There is a .sum but not for Duration. So you must use reduce.
• You want to distinguish between a Duration.ZERO found, and nothing found.

For durations I think you could do without the use of null.