Java 布尔值流，是真的吗？
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Stream of boolean values, is any true?
提问by S1lentSt0rm
I want to parallelize the following code snipped using a parallelStream:
我想并行化使用parallelStream截取的以下代码：
boolean anyTrue() {
for (Element e : setOfE) {
if (eval(e)) {
return true;
}
}
return false;
}
Will the following work on parallel streams and use regular short-circuit evaluation?
以下是否适用于并行流并使用常规短路评估？
setOfE.parallelStream().map(e -> eval(e)).reduce(false, (a,b) -> a || b))
采纳答案by Marko Topolnik
Streams API actually has first-class support for your requirement:
Streams API 实际上为您的需求提供一流的支持：
setOfE.parallelStream().anyMatch(e->eval(e));
As opposed to your approach with reduce, this is guaranteed to have short-circuit evaluation and optimally leverage parallelism.
与您使用 的方法相反reduce，这可以保证进行短路评估并最佳地利用并行性。
回答by Holger
No, reduction does not support short-circuit evaluation. The reason is that reducejust receives an arbitrary BinaryOperatorimplementation and has no idea about the possibilities of short-circuiting the particular operation.
不，减少不支持短路评估。原因是reduce只接收一个任意的BinaryOperator实现并且不知道短路特定操作的可能性。
But you can perform the entire operation much simpler:
但是您可以更简单地执行整个操作：
setOfE.parallelStream().filter(e -> eval(e)).findAny().isPresent()
This simply searches for an arbitrary item for which evalreturns trueand findAnyallows to end the operation as soon as one thread has encountered a match. The resulting Optionalcan be queried for being empty as you are not interested in the particular matching Element.
这只是搜索eval返回的任意项目，true并findAny允许在一个线程遇到匹配时立即结束操作。Optional由于您对特定匹配不感兴趣，因此可以查询结果是否为空Element。
Alternatively you can use as suggested by Marko Topolnik's comment:
或者，您可以按照 Marko Topolnik 评论的建议使用：
setOfE.parallelStream().anyMatch(e -> eval(e))
