Question

Find last element in list using lambda expressions

Answer 1

Where data.careas is a List<CArea>:

CArea first = data.careas.stream()

.filter(c -> c.bbox.orientationHorizontal).findFirst().get();

CArea last = data.careas.stream()

.filter(c -> c.bbox.orientationHorizontal)

.collect(Collectors.toList()).; //how to?

As you can see getting the first element, with a certain filter, is not hard.

However getting the last element in a one-liner is a real pain:

It seems I cannot obtain it directly from a Stream. (It would only make sense for finite streams)

It also seems that you cannot get things like first() and last() from the List interface, which is really a pain.

I do not see any argument for not providing a first() and last() method in the List interface, as the elements in there, are ordered, and moreover the size is known.

But as per the original answer: How to get the last element of a finite Stream?

Personally, this is the closest I could get:

int lastIndex = data.careas.stream()

.filter(c -> c.bbox.orientationHorizontal)

.mapToInt(c -> data.careas.indexOf(c)).max().getAsInt();

CArea last = data.careas.get(lastIndex);

However it does involve, using an indexOf on every element, which is most likely not you generally want as it can impair performance.