Primitive Array vs ArrayList

Question

I am receiving XML and need to convert to either a primitive Array or ArrayList. Is there much difference in terms of performance in terms of memory and garbage collection? My application will be creating thousand of these objects every second and I need to minimize GC as I need real-time performance.

Thxs

This might answer your question: http://stackoverflow.com/questions/716597/array-or-list-in-java-which-is-faster — euphoria83, Oct 23 '11 at 21:09

score 7 · Accepted Answer · answered Oct 23 '11 at 21:11

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Primitive arrays are much more efficient, as they don't require wrapper objects. Guava has List implementations that are backed by primitive arrays (example: Ints.asList(int[])), perhaps that could be a reasonable solution for you: get the power of a collection but only use Objects when you actually need them.

answered Oct 23 '11 at 21:11

Sean Patrick Floyd

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Aren't Guava List implementations also wrapper objects? – Ted Hopp Oct 23 '11 at 21:14
Do you have any quantitative details of how much more efficient they are? – DD. Oct 23 '11 at 21:15
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@TedHopp yes, one wrapper object per array, but not one per array element – Sean Patrick Floyd Oct 23 '11 at 21:15
@DD. no, but you can ask the google guys on the guava mailing list – Sean Patrick Floyd Oct 23 '11 at 21:16
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"_but not one per array element" -- ArrayList has no such object-per-element overhead. They are, I believe, as space efficient as raw arrays (which, by the way, are also wrapper objects containing a contiguous block of references and a count). – Ted Hopp Oct 23 '11 at 21:17
@TedHopp yes there is, you need to convert the primitive array to an array of wrapper Objects first, potentially creating up to one Object per entry (depending on the JVM's Integer caching). – Sean Patrick Floyd Oct 23 '11 at 21:19
Ah. I read OP's use of "primitive Array" to mean what I call a "raw array", not "an array of primitive types". If OP meant the latter, then you are, of course, correct. – Ted Hopp Oct 23 '11 at 21:21
@TedHopp and otherwise, you are :-) – Sean Patrick Floyd Oct 23 '11 at 21:21

score 3 · Answer 2 · answered Sep 26 '13 at 06:26

Primitive arrays are always more efficient, but by how much depends on the exact details of your use case. I've recently sped up performance by a factor of 7, by ripping out the ArrayLists, and replacing them with primitive arrays, in the inner-most loops. The use case was an O(n^2) algorithm applied to lists 100-1000 characters long. I then did a controlled experiment, comparing the performance of a int[] array to a ArrayList, and interestingly, as the array/list sizes get bigger, the JIT compiler seems to kick in, and the performance penalty becomes a lot less (only ~20%). But for list sizes less than 500, the performance penalty of an ArrayList can be up to a factor of 10. So if you've got a frequently called method, which is manipulating lots of small lists or arrays (as was with my use case), using primitave arrays can have a big performance impact.

score 0 · Answer 3 · answered Dec 17 '18 at 09:02

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Linked lists are good for inserts/deletes, and arrays are good for random access.

answered Dec 17 '18 at 09:02

salmanseifian

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score 0 · Answer 4 · answered Oct 24 '11 at 07:06

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As Sean Patrick Floyd pointed out, primitive arrays are much more efficient. However, there are cases where one would definitely prefer Collections. But as long as you just iterate over the Objects, there is no need for Collections.

answered Oct 24 '11 at 07:06

Oskar

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Primitive Array vs ArrayList

4 Answers4

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