Java 8 stream - cast list items to type of subclass

Question

I have a list of ScheduleContainer objects and in the stream each element should be casted to type ScheduleIntervalContainer. Is there a way of doing this?

final List<ScheduleContainer> scheduleIntervalContainersReducedOfSameTimes

final List<List<ScheduleContainer>> scheduleIntervalContainerOfCurrentDay = new ArrayList<>(
        scheduleIntervalContainersReducedOfSameTimes.stream()
            .sorted(Comparator.comparing(ScheduleIntervalContainer::getStartDate).reversed())
            .filter(s -> s.getStartDate().withTimeAtStartOfDay().isEqual(today.withTimeAtStartOfDay())).collect(Collectors
                .groupingBy(ScheduleIntervalContainer::getStartDate, LinkedHashMap::new, Collectors.<ScheduleContainer> toList()))
            .values());

Answer 1

It's possible, but you should first consider if you need casting at all or just the function should operate on subclass type from the very beginning.

Downcasting requires special care and you should first check if given object can be casted down by:

object instanceof ScheduleIntervalContainer

Then you can cast it nicely by:

use functional method to cast like ScheduleIntervalContainer.class::cast

So, the whole flow should look like:

collection.stream()
    .filter(obj -> obj instanceof ScheduleIntervalContainer)
    .map(ScheduleIntervalContainer.class::cast)
    // other operations