javajava-8integerjava-stream

Java 8 primitive stream to collection mapping methods

Is there any significant difference (in performance or best practices) between those two stream creation methods?

int[] arr2 = {1,2,3,4,5,6};

Arrays.stream(arr2)
      .map((in)->in*2)
      .mapToObj((in) -> new Integer(in))
      .collect(Collectors.toCollection(()-> new ArrayList<>()));

Arrays.stream(arr2)
      .map(in->in*2)
      .boxed()
      .collect(Collectors.toCollection(()-> new ArrayList<>()));

EDIT

Thanks to Stack Community answers I can add some addons to question completeness for new readers:

As many pointed out, .boxed() IntStream method is defined as:

@Override
    public final Stream<Integer> boxed() {
        return mapToObj(Integer::valueOf);
    }

What basically re-defines issue to which one of following is better:

.mapToObj(in -> new Integer(in))

or

.mapToObj(in -> Integer.valueOf(in))
Solution

  • Yes, boxed() uses Integer.valueOf which can retrieve some Integer instances from a cache.

    So you should either use the version with boxed() (preferably), or use Integer.valueOf instead of new Integer(). Note that boxed() is in fact shorthand for mapToObj(Integer::valueOf).