CODEWITHSUNDEEP
javajava-8functional-programmingjava-stream
coder
coder

Reputation: 43

Java 8 collecting the list that is already present in object

I was just searching for better way to handle this scenario using java 8 streams. Object A has list of object b. What I get is a list of object A (List). I need to stream through list of object A and get all the listB's in each of the object A as a one single list. 

class A {
    List<B> listB
}

I have tried the below way it throws compilation

List<A> as = someObject.getAs();
List<B> listofBs = as.stream().map(in -> in.getListB()).collect(Collectors.toList());

Upvotes: 1

Views: 326

Answers (2)

Erics Nguyen
Erics Nguyen

Reputation: 380

Class A{
  List<B> listB
};
List<A> listA;
listA.stream().map(
 a->{
  //some code for A
  a.ListB.stream().map(
   b->{
    // some code for B
  })
});

may be help you

Upvotes: 0

Naman
Naman

Reputation: 31968

To get a single list of all B's, you should use flatMap as:

List<B> listOfBs = listOfAs.stream()
        .flatMap(a -> a.getListB().stream())
        .collect(Collectors.toList());

Upvotes: 4

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