如何在数组中转换嵌套的 ArrayList? [英] How to convert nested ArrayList in Array?

问题描述

我必须将 ArrayList 的 ArrayList 转换为 Array.

I have to convert an ArrayList of ArrayList in to Array.

List<List<TockaXY>> clustersPorazdeljeni = new ArrayList<>(centers.size());

我知道可以将单个 ArrayList 转换为 Array 之类的

I know that is possible to convert a single ArrayList to Array like

 TockaXY[] arrayOfClusters = clustersPorazdeljeni.toArray(new TockaXY[centers.size()]);

但是这些不会转换嵌套部分.据我所知，现在是 ArrayLists 数组.那么是否有可能从嵌套的 ArrayLists 中获取一个 Array?

But these does not convert the nested part. As i understand is now array of ArrayLists. So is it possible to get an Array out of nested ArrayLists?

推荐答案

flatMap() 有线性替代方案:

There is linear alternative for flatMap():

    List<List<TockaXY>> clustersPorazdeljeni = new ArrayList<>();

    List<TockaXY> flatArray = new ArrayList<>();
    clustersPorazdeljeni.forEach(flatArray::addAll);
    TockaXY[] arrayOfClusters = flatArray.toArray(new TockaXY[0]);

或者使用 flatMap:

Or with flatMap:

TockaXY[] arrayOfClusters = clustersPorazdeljeni.stream().flatMap(Collection::stream).toArray(TockaXY[]::new);

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