recursion - How to recursively iterate over Lists of Lists in JAVA 8 -

i have following scenario

 object has  -- list<b>  -- list<c>       -- object 

object contains: list<b> , list<c>

i want collect objects of type 'b' in list after traversal in given object 'a'.

note: list<c> may contain object 'a', iteration becomes recursive.

i/p: object  = {list<b>,list<c>} o/p: list<b>//list of objects of type b 

what best way iterate on , collect objects of type 'b' list in java 8.

thanks

what don't understand why has done soly stream? why don't create recursive function? , list<a> not contain list<a> , list<b>, object a contains 2 lists.

here simple recursive method should you, keep in mind did not provide code of , b cannot know:

    public list<b> getallbs(list<a> alist) {     return alist.stream()                 .map(a -> getallbs(a))                 .collect(collectors.tolist()); }  private list<b> getallbs(a somea) {     list<b> returnlist = new arraylist<b>();     returnlist.addall(somea.getlistofb());      for(a othera: somea.getlistofa()) {         returnlist.addall(getallbs(othera);     }      return returnlist; }