Java 8 - 转换列表的最佳方法：map还是foreach？ [英] Java 8 - Best way to transform a list: map or foreach?

问题描述

我有一个列表 myListToParse 其中我想过滤元素并对每个元素应用一个方法，并将结果添加到另一个列表中 myFinalList 。

I have a list myListToParse where I want to filter the elements and apply a method on each element, and add the result in another list myFinalList.

在Java 8中，我注意到我可以通过两种不同的方式来实现。我想知道他们之间更有效的方式，并理解为什么一种方式比另一种更好。

With Java 8 I noticed that I can do it in 2 different ways. I would like to know the more efficient way between them and understand why one way is better than the other one.

我对任何有关第三种方式的建议持开放态度。

I'm open for any suggestion about a third way.

方法1：

myFinalList = new ArrayList<>();
myListToParse.stream()
        .filter(elt -> elt != null)
        .forEach(elt -> myFinalList.add(doSomething(elt)));

方法2：

myFinalList = myListToParse.stream()
        .filter(elt -> elt != null)
        .map(elt -> doSomething(elt))
        .collect(Collectors.toList()); 

推荐答案

不要担心任何性能差异，他们'在这种情况下通常会最小化。

Don't worry about any performance differences, they're going to be minimal in this case normally.

方法2是首选，因为

1. 它不需要改变存在于lambda表达式之外的集合，

1. it doesn't require mutating a collection that exists outside the lambda expression,

它更具可读性，因为它在收集管道按顺序写入（首先是过滤操作，然后是地图操作，然后收集结果），
（有关收集管道的好处的更多信息，请参阅Martin Fowler的优秀文章）

it's more readable because the different steps that are performed in the collection pipeline are written sequentially (first a filter operation, then a map operation, then collecting the result), (for more info on the benefits of collection pipelines, see Martin Fowler's excellent article)

您可以通过替换<$来轻松更改收集值的方式c $ c>使用的收集器。在某些情况下，您可能需要编写自己的收集器，但之后的好处是您可以轻松地重复使用它。

you can easily change the way values are collected by replacing the Collector that is used. In some cases you may need to write your own Collector, but then the benefit is that you can easily reuse that.

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