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From: Eric Sosman <esosman@comcast-dot-net.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: stream collect with own class
Date: Sat, 5 Dec 2015 08:34:02 -0500
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On 12/4/2015 5:46 PM, Philipp Kraus wrote:
> Am Freitag, 4. Dezember 2015 14:58:48 UTC+1 schrieb Eric Sosman:
>> On 12/4/2015 8:12 AM, Philipp Kraus wrote:
>>> Hello,
>>>
>>> I'm using streams and I would like to create "fuzzy logic implications". In short call, I have a collection with
>>>
>>> Set<IFuzzy> x;
>>>
>>> and my IFuzzy interface is defined like
>>>
>>> public interface IFuzzy
>>> {
>>>        public Boolean getResult();
>>>
>>>        public Double getFuzzy();
>>> }
>>>
>>> I run in my code
>>>
>>> IFuzzy y = x.stream()......
>>>
>>> I would like to implode / aggregate each IFuzzy object into one result, so I need to call on each element from x the getResult() and the getFuzzy() method and collect / implode the data.
>>>
>>> How can I do this call with a stream operation? IMHO I need to write an operator like allMatch()
>>
>>       If I understand you correctly, you want to combine information
>> from many IFuzzy's into a single IFuzzy instance.  (Just ignore me
>> if I've understood *in*correctly.)  In that case, you need some kind
>> of a .reduce() operation, either something from the Collectors class
>> or something you write yourself.
>
> Yes, that's correct. I have found the Collector<T,A,B> interface, but how I can implement this in a correct way (for stream and parallelstream)? IMHO T is the type IFuzyy, but A and B? Is is correct to define T=A=B => Collector<T,T,T> ?

     Why would you want a Collector?  You're trying to combine a Set of
IFuzzy's into *one* IFuzzy, not into a collection of (modified, derived,
whatever) IFuzzy's.

     (Aside: The JavaDoc for SE 8 lists gives Collector's type parameters
as <T,A,R>, not <T,A,B>.  Did you misread R as B, or are you looking at
some other description?)

     I'm still not clear on what you're trying to do.  Perhaps it would
help me understand if you showed the IFuzzy's => IFuzzy transformation:
How would you write it using a plain old `for(IFuzzy i : x)' loop?

-- 
esosman@comcast-dot-net.invalid
"Don't be afraid of work. Make work afraid of you." -- TLM