Java merges list method instance code

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List includes the List interface and all the implementation classes of the List interface. Because the List interface implements the Collection interface, the List interface has all the common methods provided by the Collection interface, and because the List is a list type, the List interface also provides some common methods suitable for itself.

method one

List reduce = list.stream() .map(x -> x.getChildren()) .reduce(new ArrayList(), (all, item) -> { all.addAll(item); return all; }); System.out.println(reduce);

methodology II

List collect = list.stream() .map(Employee::getChildren) .flatMap(Collection::stream) .distinct().collect(Collectors.toList());----------------------------List childrens1 = new ArrayList();for (long i =0;i