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From: Eric Sosman <esosman@comcast-dot-net.invalid> (Eric Sosman)
Newsgroups: comp.lang.java.programmer
Subject: Re: Can I put a filter into a lambda?
Date: Mon, 04 Dec 2017 09:29:10 +1200
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On 12/4/2017 8:32 AM, Eric Douglas wrote:
> On Monday, December 4, 2017 at 8:20:59 AM UTC-5, Eric Sosman wrote:
>>       If it *must* be an ArrayList (and not some other kind of List),
>> you might want to change the last bit to
>>
>>      .collect(Collectors.toCollection(ArrayList::new));
>>
>> Although the toList() method appears to use ArrayList anyhow, it
>> doesn't guarantee to do so -- meaning that it might use some other
>> List in a future Java, or in circumstances I haven't studies (e.g.,
>> it might behave differently with a parallel stream).
>>
> ok, thanks, I'll keep that in mind.  I'll have to test if the variable can be
assigned and if that would be more efficient.  Currently it doesn't matter what
 kind of list because I made the rowToModelIndex variable final, just calling
clear() then addAll().

     If you'd rather clear and repopulate the same List (as opposed
to making a new one each time), you could use forEach():

        rowModelIndex.clear();
        IntStream.range(0, modelRowCount)
             .filter((value) -> include(value))
            .forEach((value) -> rowModelIndex.add(value);

or

        rowModelIndex.clear();
        IntStream.range(0, modelRowCount)
            .forEach((value) ->
                if (include(value)) rowModelIndex.add(value));

I don't know which of these might be faster, or whether either might be faster
than a plain old `for' loop.  (Research project.)

     FWIW, Brian Goetz (who knows far more about JVM performance
issues than I ever will) indicates that object allocation and collection is
cheaper than commonly thought, so there's little if any advantage to re-using
the same List object:

https://www.ibm.com/developerworks/java/library/j-jtp09275/index.html

... which means even more research may be indicated.  (The cited article is
twelve years old, and we may expect that JVM's have continued to improve
meanwhile).

--
esosman@comcast-dot-net.invalid
Eleven hundred forty-three days to go.