如何将对象的两个字段收集到同一个列表中?

How to collect two fields of an object into the same list?(如何将对象的两个字段收集到同一个列表中?)

问题描述

我有一个商品对象，它有两个属性:firstCategoryId 和 secondCategoryId.我有一个商品清单，我想获取所有类别 ID(包括 firstCategoryId 和 secondCategoryId).

I have an Object of goods, which has two properties: firstCategoryId and secondCategoryId. I have a list of goods, and I want to get all category Ids (including both firstCategoryId and secondCategoryId).

我目前的解决方案是:

List<Integer> categoryIdList = goodsList.stream().map(g->g.getFirstCategoryId()).collect(toList());
categoryIdList.addAll(goodsList.stream().map(g->g.getSecondCategoryId()).collect(toList()));

有没有更方便的方式可以在一条语句中获取所有 categoryId?

Is there a more convenient manner I could get all the categoryIds in a single statement?

推荐答案

您可以使用 flatMap 使用单个 Stream 管道来完成:

You can do it with a single Stream pipeline using flatMap :

List<Integer> cats = goodsList.stream()
                              .flatMap(c->Stream.of(c.getFirstCategoryID(),c.getSecondCategoryID()))
                              .collect(Collectors.toList());

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