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Java Forum / General / November 2007vector element iterator
Hi all, Any performance advantage for traversing elements from list using Iterator over get(int index) ? thanks, ronan > Hi all, > > Any performance advantage for traversing elements > from list using Iterator over get(int index) ? It depends on the list. For an ArrayList or Vector[0], there isn't a noticable speed difference between using an iterator or an index, and only a minimal (one-object) difference in memory use. For other List implementations that doesn't always hold: iterating a LinkedList using get(int index) is O(n*n), because each call to get counts from the nearest end of the list and iterates to the target index from scratch, whereas using an iterator is O(n), because the iterator remembers the last element you looked at for you. There are some clarity tradeoffs involved; explicitly using an iterator is, in my opinion, very slightly less readable than calling get, but implicit iterator use with the for-each syntax is much clearer than either. -Owen [0] and you should really look at using ArrayList instead of Vector, if you are using the latter; if nothing else, it doesn't impose synchronization on you All The Time. > Any performance advantage for traversing elements >from list using Iterator over get(int index) ? Depends on the list implementation, but generally an iterator is as fast or faster. For instance, it's about the same between the two for an ArrayList, but it'll be O(n) to use an Iterator over a LinkedList, and O(n*n) to use get(index) for each element. -- Mark Rafn dagon@dagon.net <http://www.dagon.net/> >> Any performance advantage for traversing elements >>from list using Iterator over get(int index) ? [quoted text clipped - 6 lines] > -- > Mark Rafn dagon@dagon.net <http://www.dagon.net/> All of them are much slower than using an array. If performance is really the issue then you don't want to use any of the Collection objects. But usually speed isn't the most important thing. And the collection classes are very easy to use.  SignatureKnute Johnson email s/nospam/knute/ On Nov 25, 9:50 pm, Knute Johnson <nos...@rabbitbrush.frazmtn.com> wrote: > All of them are much slower than using an array. If performance is > really the issue then you don't want to use any of the Collection > objects. But usually speed isn't the most important thing. And the > collection classes are very easy to use. To add to Knute's point, if you look up Vector's source code, the get(int index) uses direct access to an array's index. -cheers, Manish >>> Any performance advantage for traversing elements >>>from list using Iterator over get(int index) ? >> Depends on the list implementation, but generally an iterator is as fast or >> faster. For instance, it's about the same between the two for an ArrayList, >> but it'll be O(n) to use an Iterator over a LinkedList, and O(n*n) to use >> get(index) for each element. >All of them are much slower than using an array. Hardly. For some operations, they're massively faster. Try implementing a queue, or anything that requires inserts and deletes from the head. Let me know when you're tired of copying your array... >If performance is really the issue then you don't want to use any of the >Collection objects. Disagree. Even if perf is the issue, choosing the correct data structure for your use will outweigh the tiny (if any) advantage of arrays over array-backed Collections. >But usually speed isn't the most important thing. And the collection >classes are very easy to use. Fully agreed. And using an iterator rather than get(int) is generally the right way to use a collection. This way it works well regardless of underlying structure. -- Mark Rafn dagon@dagon.net <http://www.dagon.net/> On Sun, 25 Nov 2007 20:13:05 -0800 (PST), "rony.john@gmail.com" <rony.john@gmail.com> wrote, quoted or indirectly quoted someone who said : > Any performance advantage for traversing elements >from list using Iterator over get(int index) ? Even if there were, the use of for:each is preferred to make code clear. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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