Java 8 Stream添加元素以列出和求和 [英] Java 8 Stream add elements to list and sum

问题描述

我相信我可以在listOfPricedObjects上使用一个流操作：

I believe I can do next using one stream operation on listOfPricedObjects:

List<BigDecimal> myList = new ArrayList();
myList = listOfPricedObjects.stream().map(PricedObject::getPrice).collect(Collectors.toList());
BigDecimal sum = listOfPricedObjects.stream().map(PricedObject::getPrice).reduce(BigDecimal.ZERO, BigDecimal::add)

我如何使用流一次性填充myList的价格和计算价格的总和？
感谢

How I can fill myList with prices and calculate sum of prices using stream one time? Thanks

UPD：结果我需要myList填充价格和和变量sum。

UPD: As the result I need myList filled with prices and sum variable with sum. But not with usding stream() twice for that.

推荐答案

您可以使用 peek 并添加到新的列表同时应用缩减

You can use peek and add to a new list while applying the reduction

List<BigDecimal> newList = new ArrayList<>();
BigDecimal sum = list.stream()
                     .map(PricedObject::getPrice)
                     .peek(newList::add)
                     .reduce(BigDecimal.ZERO, BigDecimal::add);

请参考Tunaki的回答，如果你有兴趣使用 parallelStream 与非并发收集，这是有道理的，因为sum作为一个尴尬的并行任务。

Please look at Tunaki answer if you interested in using a parallelStream with a non concurrent collection which makes sense since sum as an embarrassingly parallel task.

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