No-reuse-streams (original) (raw)

Paul Sandoz paul.sandoz at oracle.com
Mon Nov 26 09:22:52 PST 2012

On Nov 26, 2012, at 5:45 PM, Henry Jen <henry.jen at oracle.com> wrote:

On Nov 26, 2012, at 8:21 AM, "David M. Lloyd" <david.lloyd at redhat.com> wrote:

Should the following throw an ISE on the last line of the following? Stream s = .. Object i1 = s.findFirst(); Stream s1 = s.map(...); i.e. should we fail on the s.map(...) or just when a terminal operation occurs, if at all? I agree with you and Rémi - this should fail. While it may be "consistent", what is the obvious alternative when need to do something like this? A use case like this is probably following, For a input stream, find a marker, and then continue to process the rest of stream.

That seems like a use-case for dropWhile or skipWhile.

I guess the general question is: how does one control the flow of the stream? How do we continue the stream after a terminal op which does not consume whole stream.

It's a bit funky but one could do:

Stream s = ... Iterator i = s.iterator(); Object first = i.next(); i.stream()....; // Not yet supported but IIRC we have talked about making Iterator streamable.

If the source is an iterator of some sorts i think detached streams might be useful for repeated processing of such a source.

Note that for a parallel stream findFirst and findAny (or anyMatch) may consume more elements than the equivalent sequential stream.

Paul.

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