Difference between summarizingInt and Collectors.summarizingInt?

Question

I am working with the IntSummaryStatistics class to calculate out the statistics for my class. I searched for three particular ways to calculate statistics. Here is my code:

IntSummaryStatistics stats1 = orderEntries.stream()
            .mapToInt((x) -> x.getAmount()).summaryStatistics();

IntSummaryStatistics stats2 = orderEntries.stream().collect(
            Collectors.summarizingInt(o -> o.getAmount()));

IntSummaryStatistics istats2 = orderEntries.stream().
                            collect( 
                                    () -> new IntSummaryStatistics(),
                                    (i,o) -> i.accept(o.getAmount()),
                                    (i1, i2) -> i1.combine(i2));
IntSummaryStatistics istats = IntStream.of(51,22,50,27,35).
        collect(IntSummaryStatistics::new, IntSummaryStatistics::accept, 
                IntSummaryStatistics::combine);

Which one is the better approach? Which one we should prefer over other?

@Holger The third entry just i got from internet. It is not in sync with orderEnteries. — KayV, Dec 06 '16 at 09:03
Please don't (significantly) change the code your options. I refer to that in my answer and now you've made that reference baseless. — lexicore, Dec 06 '16 at 09:14
See also [“Collectors.summingInt() vs mapToInt().sum()”](http://stackoverflow.com/q/37023822/2711488) — Holger, Dec 06 '16 at 10:46

score 4 · Accepted Answer · answered Dec 06 '16 at 08:10

4

I'd opt to:

IntSummaryStatistics stats = orderEntries
    .stream()
    .collect(Collectors.summarizingInt(OrderEntry::getAmount));

This option:

IntSummaryStatistics istats = IntStream.of(51,22,50,27,35).
            collect(IntSummaryStatistics::new, IntSummaryStatistics::accept, 
                    IntSummaryStatistics::combine);

is the worst, it's exactly what IntStream.summaryStatistics does, just written explicitly. So no advantage of the first option.

I'd go with a slightly modified second option because the collector better represents the business operation "summarization of order entry amounts" from my point of view.

answered Dec 06 '16 at 08:10

lexicore

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1

There’s no fundamental difference between `.mapToInt(OrderEntry::getAmount).summaryStatistics()` and `.collect(Collectors.summarizingInt(OrderEntry::getAmount))`. That’s more a matter of taste. – Holger Dec 06 '16 at 09:03
@lexicore I think collect(Collectors.summarizingInt(OrderEntry::getAmount)) and collect( Collectors.summarizingInt(o -> o.getAmount())); are the same. Isn't it? – KayV Dec 06 '16 at 09:05
2

@KaranVerma Yes and no. Yes, this will give you the same result. No, in the second case you write out a lambda instead of using an existing method. I'd definitely prefer `OrderEntry::getAmount`. Why writing lambdas if the method is already there? – lexicore Dec 06 '16 at 09:12

Difference between summarizingInt and Collectors.summarizingInt?

1 Answers1