How do I go from Stream>> to ArrayList

Question

I have a Stream<ArrayList<Object>> and I want to "extract" the ArrayList from it and assign it to a variable. How do I do that?

My resulting variable needs to be of type ArrayList<Object> so I can iterate over it and do stuff.

Do you want to add all elements from every `ArrayList` in the stream into a single big `ArrayList`? Do note that you can iterate over stream and do stuff, tell us what are you trying to do. — Karol Dowbecki, Jan 17 '20 at 16:43
Could you provide some small sample data and what you need as the result? — Thorbjørn Ravn Andersen, Jan 17 '20 at 16:48
check this link https://www.geeksforgeeks.org/how-to-get-arraylist-from-stream-in-java-8/ — Marwen Jaffel, Jan 17 '20 at 16:49
And provide your attempt(s). We are not a code-writing service. — Turing85, Jan 17 '20 at 16:49

YCF_L · Accepted Answer · 2020-01-17T16:54:30.147

3

If you want to get one ArrayList then use

ArrayList<Object> result = strm.flatMap(ArrayList::stream)
        .collect(Collectors.toCollection(ArrayList::new));

edited Jan 17 '20 at 16:54

answered Jan 17 '20 at 16:50

YCF_L

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score 1 · Answer 2 · answered Jan 17 '20 at 16:51

Stream.flatMap method lets you replace each value of a stream with another stream and then concatenates all the generated streams into a single stream.

List<Object> objectList = new ArrayList<>();
        List<Object> collect = Stream.of(objectList)
                .flatMap(m -> m.stream())
                .collect(Collectors.toList());

How do I go from Stream>> to ArrayList

2 Answers2

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