Pros and Cons of usage forEach and Stream

Question

Starts from java 8 to iterate throug list I can use both:

List list = new ArrayList();
1. list.forEach(...)
2. list.stream().forEach(...)

Is it any advantages of using second case? To convert list to stream?

score 6 · Accepted Answer · answered Feb 14 '18 at 21:30

6

There are no advantages of using the second case, unless you have a parallel stream. There is a disadvantage, namely that Stream.forEach() doesn't guarantee to respect encounter order. A more accurate (but still unnecessary) equivalent would be Stream.forEachOrdered().

answered Feb 14 '18 at 21:30

shmosel

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Does the non-guarantee of encounter order of `forEach` also apply to non parallel streams that have ordered source? – tsolakp Feb 14 '18 at 21:36
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@tsolakp Briefly, yes. See here for more: https://stackoverflow.com/q/34247318/1553851 – shmosel Feb 14 '18 at 21:40
Someone got to write better Javadoc:). Here is snippet from Javadoc as well. "If a stream is ordered, repeated execution of identical stream pipelines on an identical source will produce an identical result;" – tsolakp Feb 14 '18 at 21:48
@shmosel plus one, I just did not find the right words that even if forEach operates only via side-effects, adding elements to a list via `stream().forEach` is strongly discouraged and it might produce wrong results, while the other one would be ok. – Eugene Feb 14 '18 at 21:57
@tsolakp Presumably that doesn't apply to operations involving side-effects, since they depend on unknown variables. But I agree that the language could be tightened up. – shmosel Feb 14 '18 at 22:07
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@Eugene OP never mentioned such a use. As for side-effects in general, I'll just quote the docs: *A small number of stream operations, such as `forEach()` and `peek()`, can operate only via side-effects; these should be used with care.* – shmosel Feb 14 '18 at 22:14
@shmosel exactly, but that would count as a difference between them – Eugene Feb 15 '18 at 08:00
I don't see why. – shmosel Feb 15 '18 at 08:01

score 2 · Answer 2 · answered Feb 14 '18 at 21:37

No, in theory, the second option is worse than the first one - you pay the cost of instantiation/garbage-collection and calling a Stream instance and don't really get any benefit in return.

Additionally, in theory the iteration order of Stream.forEach() isn't deterministic.

Pros and Cons of usage forEach and Stream

2 Answers2