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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 08:20:38 +1200
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On 12/4/2017 8:03 AM, Eric Douglas wrote:
> On Friday, December 1, 2017 at 4:28:26 PM UTC-5, Eric Sosman wrote:
>>       It's not clear what your filter loop is actually doing:
>> the RowFilter seems never to be used, and I can't find any
>> one-argument include() method in any Java SE (8 or 9) class.
>> (You also haven't shown what rowToModelIndex is, but I'll
>> guess it's a Collection<Integer>, possibly List<Integer>).
>> So I'll restate the problem without the table trappings:
>>
>>       1) If getRowFilter() returns null, you want a List of
>>          all the values 0 through modelRowCount-1, in order.
>>
>>       2) If getRowFilter() returns non-null, you want a List
>>          of the same values, excluding those for which the
>>          boolean-valued include(int) method returns false.
>>
>>       If that's not the goal, read no further.  But if it is
>> (or is close enough for jazz), both cases can be written
>> more simply:
>>
>>      // Case 1:
>>      rowModelIndex = IntStream.range(0, modelRowCount)
>>          .mapToObj(Integer::valueOf)
>>          .collect(Collectors.toList());
>>
>>      // Case 2:
>>      rowModelIndex = IntStream.range(0, modelRowCount)
>>          .filter((value) -> include(value))
>>          .mapToObj(Integer::valueOf)
>>          .collect(Collectors.toList());
>>
>>       Final point: If you can't stop worrying about efficiency,
>> at the very least stop *guessing* about it!
>>
> rowToModelIndex is an ArrayList<Integer>.

     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).

> Milliseconds do count in a row filtering method which executes thousands of
times.

     If performance is important, measure.  Don't guess.

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