List of Lists into a List (Stream)

Required

Stream Support Since Java 1.8

Use FlatMap

Use FlatMap to flatten the internal lists into a single Stream, and the collect the result into a list:

List<List<Object>> list = .....
List<Object> flat = list.stream()
                .flatMap(List::stream)
                .collect(Collectors.toList());

Stream (Java Platform SE 8 )docs.oracle.com