Iterate through ArrayList with If condition and return boolean flag with stream api

Question

I am trying to make myself more comfortable with Java 8 Stream api. Currently I want to translate something like as stream, but it seems I am still not comfortable enough, because I have no idea how to do this.

boolean isTrue = false;

for (Integer integer : intList) {
    if (integer > 10) {
        isTrue = true;
        break;
    }
}

Eugene · Accepted Answer · 2018-08-23T13:44:52.680

13

All you care about is if at least one input from your list is bigger than 10, thus anyMatch:

boolean isTrue = intList.stream()
                        .anyMatch(x -> x > 10);

edited Aug 23 '18 at 13:44

answered Aug 23 '18 at 13:27

Eugene

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can cause NPE ? – VedantK Jul 09 '20 at 01:45
@VdeX I need some context to your question, please – Eugene Jul 09 '20 at 01:47
sorry `intList.stream()` can cause NPE,isnt it? – VedantK Jul 09 '20 at 01:55
@VdeX if the `intList` itself is `null`? of course. I don't get it... – Eugene Jul 09 '20 at 01:56
I mean we should consider using optional. :) – VedantK Jul 09 '20 at 02:00
1

@VdeX finally :) why not make it clear from the beginning? `Optional.ofNullable(intList).orElse(Collections.emptyList()).anyMatch(x -> x > 10)` – Eugene Jul 09 '20 at 02:01
1

So sorry, yea I was too abstract :( – VedantK Jul 09 '20 at 02:34

davidxxx · Answer 2 · 2018-08-23T13:40:16.547

3

you iterate a List of Integer. So use Collection.stream()
you compare numeric value. So use Stream.mapToInt() to work with int rather than Integer that is more efficient. Here it doesn't change many things but if you change the stream to do some other numerical operations, you already use the correct way.
you value a boolean (result) as soon as a condition is met. Otherwise false I assume. So use Stream.anyMatch(Predicate).

So this corresponds :

boolean result =
intList.stream()
       .mapToInt(i-> i)
       .anyMatch(i-> i > 10);

edited Aug 23 '18 at 13:40

answered Aug 23 '18 at 13:29

davidxxx

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Why the `mapToInt()` though to work with a primitive `int` instead of object `Integer`? The `Integer` will get unboxed to `int` anyway at `i -> i > 10` (like in *Eugene*'s answer) without it. And in your answer it still gets auto-unboxed at `i -> i`. – Kevin Cruijssen Aug 23 '18 at 13:33
@Kevin Cruijssen Right. But suppose you modify the stream later to have other processings , some boxing operations could occur. Using `mapToInt()` here is more a way to write a robust code. – davidxxx Aug 23 '18 at 13:38
Hmm, hadn't thought about that. I still feel like it's a bit redundant in this case, but I can understand your reasoning behind it now. – Kevin Cruijssen Aug 23 '18 at 13:47

Iterate through ArrayList with If condition and return boolean flag with stream api

2 Answers2