I wonder if ArrayList<SimpleObject> and ArrayList<ComplexObject> has different performance effect if we are concerning on memory usage and navigating speed (foreach, getAt())? Why?
Thanks,
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2Can you clarify your question? At the moment it doesn't make a lot of sense.T.J. Crowder– T.J. Crowder2011-08-09 11:09:16 +00:00Commented Aug 9, 2011 at 11:09
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look at your question again..? its asking for nothing valid...ngesh– ngesh2011-08-09 11:10:38 +00:00Commented Aug 9, 2011 at 11:10
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I think he means ArrayList and ArrayList<K>Marcus Johansson– Marcus Johansson2011-08-09 11:11:30 +00:00Commented Aug 9, 2011 at 11:11
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Thanks sepp2k for editing the format. It lost <K>. It's correct now.Loc Phan– Loc Phan2011-08-09 11:17:03 +00:00Commented Aug 9, 2011 at 11:17
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3 Answers
Your question isn't very clear on what you are looking for, so I've made a few assumptions about what you are seeking.
If your concern is of the memory used by the list, then it will depend on the actual size of the objects being managed by the ArrayList. If SimpleObjects are lightweight compared to ComplexObjects then the memory consumed on the heap will be higher in the latter case. However, the actual memory consumed by the array lists will be more or less constant for arraylists of equal number of objects, as the lists only contain references to the actual objects on the heap.
On the topic of runtime performance, this depends on the method being invoked. Methods like get(int index) and add(E element) will always have the same runtime performance characteristics irrespective of the type being used. This is due to the nature of the method: their behavior does not depend on the type of the Object present in the list.
On the other hand, the performance of indexOf(Object object) will depend on how the equals method is implemented. For trivial cases, it would easy to infer that indexOf will run faster for ArrayList<SimpleObject> than for ArrayList<ComplexObject>, assuming that the equals() implementation of SimpleObject will run faster than that of ComplexObject.
If your concern is of memory consumption during execution of the ArrayList methods, then it is not bound to be different as most of the methods work off references of objects. There are exceptions like toArray() which would require less memory for SimpleObject than for ComplexObject.
1 Comment
Loc Phan
Why is it "more memory for SimpleObject than for ComplexObject"in toArray()?
No, there is no performance difference. There are two very simple arguments to explain this:
- An
ArrayListonly ever handles references and references are always the same size, no matter how complex the thing is they point to. - Generics are implemented using erasure, which essentially means that at runtime the information that one is an
ArrayList<SimpleObject>and the other is anArrayList<ComplexObject>is not available, they are justArrayListobjects to the runtime.
Comments
it does make no difference, because what we store in ArrayList() is just an object reference and not the memory. so no issue what kind of class you put in to it.. so there is no performance hindrance for large class and no enhanced performance for smaller classes..
