Groups > comp.lang.java.programmer > #33858

Re: stream filter twice

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From	Robert Klemme <shortcutter@googlemail.com>
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Subject	Re: stream filter twice
Date	Sun, 21 Feb 2016 12:58:18 +0100
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On 21.02.2016 04:20, Arne Vajhøj wrote:

> What is your goal? To produce easily understandable code? To save
> a few micro seconds?

That is really the first question to answer.

> If the first then I think you current code is fine.
>
> If the second then you will need to be creative.
>
> Here is my attempt to be creative:

I'm a bit more old fashioned, maybe that's why I do not find the 
advantage of streams so big here.  I was also considering, we might not 
know how large the initial collection is.  So the cost of iterating 
twice could be significant.  So:

     public static List<myClass> test_2(final Collection<myClass> 
myclasscollection) {
         final List<myClass> x = new ArrayList<>();
         final List<myClass> y = new ArrayList<>();

         for (final myClass i : myclasscollection) {
             if (i.filter())
                 x.add(i);
             else if (i.anotherfilter()) // "else" is optimization!
                 y.add(i);
         }

         if (!x.isEmpty()) {
             return x;
         } else if (!y.isEmpty()) {
             return y;
         } else
             return new ArrayList<>(myclasscollection);
     }

     public static List<myClass> test_3(final Collection<myClass> 
myclasscollection) {
         final List<myClass> x = new ArrayList<>();
         final List<myClass> y = new ArrayList<>();

         for (final myClass i : myclasscollection) {
             if (i.filter())
                 x.add(i);
             else if (i.anotherfilter()) // "else" is optimization!
                 y.add(i);
         }

         return x.isEmpty() ?
           (y.isEmpty() ? new ArrayList<>(myclasscollection) : y) :
           x;
     }

Note: formatting suffered a bit.

Kind regards

	robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

Thread

stream filter twice Philipp Kraus <philipp.kraus.flashpixx@gmail.com> - 2016-02-20 04:28 -0800
  Re: stream filter twice Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-02-20 08:16 -0500
  Re: stream filter twice Arne Vajhøj <arne@vajhoej.dk> - 2016-02-20 22:20 -0500
    Re: stream filter twice Robert Klemme <shortcutter@googlemail.com> - 2016-02-21 12:58 +0100
      Re: stream filter twice Arne Vajhøj <arne@vajhoej.dk> - 2016-02-21 09:52 -0500
      Re: stream filter twice Sebastian <news@seyweiler.dyndns.org> - 2016-02-22 00:13 +0100

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