Return types array/list/stream [was: API question for point lambdafication]

Michael Nascimento misterm at
Wed Feb 20 08:46:50 PST 2013

Given your reasoning, shouldn't the default be Stream from now on?


On Wed, Feb 20, 2013 at 1:35 PM, Brian Goetz <brian.goetz at> wrote:
>> My preference would be as folows:
>> - only use array as a return type to match other methods in the same type
>> - prefer List to Set or Collection
>> - prefer Stream to Iterator and Enumeration (and probably Iterable)
>> - prefer List to Stream for small/bounded data sets
>> Thus, on the last point, I would argue that String.splitAsStream() is
>> wrong, and should be String.splitToList().  (As a side note, with my
>> general "arrays are bad" hat on, returning an array here was another
>> bad choice)
>> Users wanting a stream can easily get it from the list. The reverse is
>> not so true, and almost certainly more wasteful.
> This ignores a significant consideration -- List requires buffering all
> the matches before any work can be done, whereas Stream is lazy.  What
> if the List is potentially huge (or infinite)?  What if you're only
> going to look at the first few?  What if producing elements is
> expensive?  What if you have an expensive operation to perform on the
> results, and want to do so in parallel?  In all of these cases,
> preferring List over Stream gives up significant performance
> opportunities.  And, constructing lists is likely to be more expensive
> than constructing streams.
> The argument that we should "prefer List to Stream because you can
> always get a stream from a list" is too simplistic.
> Regex parsing is a good example of where you might want a stream rather
> than a list, as you might well not consume all the matches.

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