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Groups > comp.lang.java.programmer > #33356

Re: streams list in list reduce

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On 12/16/2015 5:52 AM, Philipp Kraus wrote:
> I have got a definition like
>
> interface Execute { Collection<Term> exec(); }
>
> and run vai streams over my data
>
> List<Execute> x; // x is filled
>
> And I would like to create List<Term> y = x.stream().map( i ->
> i.exec()).collect( ?? toList() );
>
> I would like to run addAll on the collect and build a concatinated
> list if all lists which are return by the exec method. How can I
> create this concatinated list?

Demo of one approach:

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

public class LotsOfLists {
	public static interface Execute
	{
	     public Collection<Integer> exec();
	}
	public static class ExecuteImpl implements Execute {
		private List<Integer> data = new ArrayList<>();
		public ExecuteImpl(int... vals) {
			for(int val : vals) data.add(val);
		}
		@Override
		public Collection<Integer> exec() {
			return data;
		}
	}
	public static void main(String[] args) {
		List<Execute> x = new ArrayList<>();
		x.add(new ExecuteImpl(1));
		x.add(new ExecuteImpl(2, 3));
		List<Integer> res = x.stream().collect(ArrayList<Integer>::new, 
(acc,elm) -> acc.addAll(elm.exec()), ArrayList<Integer>::addAll);
		System.out.println(res);
	}

}

Arne

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streams list in list reduce Philipp Kraus <philipp.kraus.flashpixx@gmail.com> - 2015-12-16 02:52 -0800
  Re: streams list in list reduce Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-12-16 09:23 -0500
  Re: streams list in list reduce Arne Vajhøj <arne@vajhoej.dk> - 2015-12-16 21:14 -0500
    Re: streams list in list reduce Philipp Kraus <philipp.kraus.flashpixx@gmail.com> - 2015-12-16 23:41 -0800

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