flatmap for inner classes

Question

I have a class. I want to get list of objects that will contain all this parameters flat. For now I'm doing it with foreach. Is there a way to do it with flatMap?

public class A{
  String parA;
  List<B> parB;

  public static class B{
    String parC;
    String parD;
    List<C> parE;
  }

  public static class C{
    String parF;
    String parG;
    String parH;
    String parJ;
  }
}

I want to have list of objects :

public class Out{
  String parA;
  String parC;
  String parD;
  String parF;
  String parG;
  String parH;
  String parJ;
}

So, instead of having object A with String parA and List, would you like to have object A with parA, parC, parD, parF... etc? — mlewandowski, Apr 12 '16 at 09:09
This is really unclear. Please show an example of input / output. — Tunaki, Apr 12 '16 at 09:10
This is still unclear. You haven't shown what you have as input and what you want as output. — Tunaki, Apr 12 '16 at 12:17

Flown · Accepted Answer · 2016-04-12T11:39:56.350

2

Assuming you have a given A a = ... the more concise and clean approach would be two nested loops like:

List<Out> list = new ArrayList<>();
for (B b : a.parB) {
  for (C c : b.parE) {
    list.add(new Out(a.parA, b.parC, b.parD, c.parF, c.parG, c.parH, c.parJ));
  }
}

Since you've asked for a Stream solution here you go:

List<Out> list = Stream.of(a).flatMap(aa -> 
  aa.parB.stream().flatMap(bb -> 
    bb.parE.stream().map(cc -> 
      new Out(aa.parA, bb.parC, bb.parD, cc.parF, cc.parG, cc.parH, cc.parJ))
  )
).collect(Collectors.toList());

edited Apr 12 '16 at 11:39

answered Apr 12 '16 at 11:15

Flown

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Thank you, that was what i meant! – janneob Apr 12 '16 at 13:14

flatmap for inner classes

1 Answers1