Java Lambda - 检查ArrayList to Stream是否为空 [英] Java Lambda - check if an ArrayList to Stream is empty

问题描述

我有以下lambda表达式，如果 bonusScheduleDurationContainers 不为空，则工作正常。如果它是空的，我得到一个 NoSuchElementException 。我如何在lambda表达式中检查这个？

I have the following lambda expression and if works fine when bonusScheduleDurationContainers is not empty. If it is empty, I get a NoSuchElementException. How do I check this in the lambda expression?

final List<ScheduleDurationContainer> bonusScheduleDurationContainers
        = scheduleDurationContainersOfWeek.stream()
                                          .filter(s -> s.getContainerType() == ScheduleIntervalContainerTypeEnum.BONUS)
                                          .collect(Collectors.toList());

final ScheduleDurationContainer bonusScheduleDurationContainer
        = bonusScheduleDurationContainers.stream()
                                         .filter(s -> s.getDayOfWeekStartingWithZero() == dayOfWeekTmp)
                                         .findFirst()
                                         .get();

推荐答案

Stream.findFirst 返回 可选 ，由您来检查可选项是否具有值而不是仅调用get。

Stream.findFirst returns an Optional, its up to you to check if the optional has a value rather than just calling get.

您可以使用 orElse 方法，如果可选项为空，则返回默认值。

You could use the orElse method to return a default value if the optional is empty.

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