java - Collect results from parallel stream -

i have piece of code this:

list<egg> eggs = hens.parallelstream().map(hen -> {     arraylist<egg> eggs = new arraylist<>();     while (hen.hasegg()) {         eggs.add(hen.getegg());     }     return eggs; }).flatmap(collection::stream).collect(collectors.tolist()); 

but in way have create arraylist every hen, , eggs not collected until hen 100% processed. this:

list<egg> eggs = hens.parallelstream().map(hen -> {     while (hen.hasegg()) {         yield return hen.getegg();     } }).collect(collectors.tolist()); 

but java not have yield return. there way implement it?

your hen class poorly adapted stream api. provided cannot change , has no other useful methods (like collection<egg> getalleggs() or iterator<egg> eggiterator()), can create egg stream this:

public static stream<egg> eggs(hen hen) {     iterator<egg> = new iterator<egg>() {         @override         public boolean hasnext() {             return hen.hasegg();         }          @override         public egg next() {             return hen.getegg();         }     };     return streamsupport.stream(spliterators.spliteratorunknownsize(it, 0), false); } 

now can use in following manner:

list<egg> eggs = hens.parallelstream()                      .flatmap(hen -> eggs(hen))                      .collect(collectors.tolist()); 

of course better stream implementation might possible if can change hen class.