如何在数组中转换嵌套的ArrayList? [英] How to convert nested ArrayList in Array?
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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转换成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.据我了解,现在是ArrayLists的数组.那么有可能从嵌套的ArrayList中获取一个Array吗?
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]);
或使用flatMap:
Or with flatMap:
TockaXY[] arrayOfClusters = clustersPorazdeljeni.stream().flatMap(Collection::stream).toArray(TockaXY[]::new);
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