检查流中的 instanceof

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2022-01-01

Check instanceof in stream(检查流中的 instanceof)

本文介绍了检查流中的 instanceof的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

I have the following expression:

scheduleIntervalContainers.stream()
        .filter(sic -> ((ScheduleIntervalContainer) sic).getStartTime() != ((ScheduleIntervalContainer)sic).getEndTime())
        .collect(Collectors.toList());

...where scheduleIntervalContainers has element type ScheduleContainer:

final List<ScheduleContainer> scheduleIntervalContainers

Is it possible to check the type before the filter?

解决方案

You can apply another filter in order to keep only the ScheduleIntervalContainer instances, and adding a map will save you the later casts :

scheduleIntervalContainers.stream()
    .filter(sc -> sc instanceof ScheduleIntervalContainer)
    .map (sc -> (ScheduleIntervalContainer) sc)
    .filter(sic -> sic.getStartTime() != sic.getEndTime())
    .collect(Collectors.toList());

Or, as Holger commented, you can replace the lambda expressions with method references if you prefer that style:

scheduleIntervalContainers.stream()
    .filter(ScheduleIntervalContainer.class::isInstance)
    .map (ScheduleIntervalContainer.class::cast)
    .filter(sic -> sic.getStartTime() != sic.getEndTime())
    .collect(Collectors.toList());

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本文标题为：检查流中的 instanceof