3 ways to flatten a list of lists. Is there a reason to prefer one of them?

Question

Assume we have a list as follows. CoreResult has a field of type List.

final List list = new LinkedList         


        

Answer 1

I'm not sure about the performance of each one, but an important aspect of the builder pattern utilized by java streams is that it allows for readability. I personally find the option 2 to be the most readable. Option 3 is good, too. I would avoid option one because it kind of "cheats" the flattening of the collection.

Put each method on its own line and determine which is the most intuitive to read. I rather like the second one:

final List B = list.stream()
                           .map(CoreResult::getField)
                           .flatMap(Collection::stream)
                           .collect(Collectors.toList());