The min non-null LocalDateTime of a list using stream

Question

I know how to get the min LocalDateTime of a list thanks to: https://stackoverflow.com/a/20996009/270143

e.g. LocalDateTime minLdt = list.stream().map(u -> u.getMyLocalDateTime()).min(LocalDateTime::compareTo).get();

My problem is slightly different though...

How would I go about doing that in a concise way?

Eugene · Accepted Answer · 2017-09-13T07:21:17.107

9

You could simply do:

Optional<LocalDateTime> op = list.stream()
        .filter(Objects::nonNull)
        .min(Comparator.naturalOrder());

And the absent value would indicate that there are only nulls in your List (or your List is empty)

edited Sep 13 '17 at 07:21

answered Sep 13 '17 at 07:18

Eugene

in my case an empty list will never occur - due to checks beforehand – ycomp Sep 13 '17 at 07:22
simple and effectively. – holi-java Sep 13 '17 at 11:21

score 4 · Answer 2 · edited Sep 13 '17 at 07:20

4

Something like this, maybe?

LocalDateTime minDate = list.stream()
    .filter(Objects::nonNull)
    .map(u -> u.date)
    .min(LocalDateTime::compareTo)
    .orElse(null);

edited Sep 13 '17 at 07:20

Andy Turner

answered Sep 13 '17 at 07:10

ah I guess I can just use the `Optional` being empty to indicate `null` – ycomp Sep 13 '17 at 07:12
1

@HubertGrzeskowiak probably `orElse(null)` instead of `get`, since the OP wants a `null` when all are null in the List – Eugene Sep 13 '17 at 07:15
2

Just a side note, when the element type implement `Comparable`, it’s preferable to use the existing `Comparator.naturalOrder()` instead of creating a new comparator via `ComparableType::compareTo`… – Holger Sep 13 '17 at 07:59

2 Answers2