Performance difference from for simple and for iterator

Question

Performance difference from for simple and for iterator

Asked 6 years, 10 months ago

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5

I have a list of customers and on a certain screen the user can do a search and edit the clients of the list that is quite extensive, comparing these two examples which would be the best to work?

Example 1:

for (int i = 0, tamI = listAll.size(); i< tamI;i++)
           if (listAll.get(i).getNome().toLowerCase().startsWith(query.toLowerCase()))
                listResult.add(listAll.get(i));

Example 2:

for (Cliente item : listAll)
            if(item.getNome().toLowerCase().startsWith(query.toLowerCase()))
                listResult.add(item);

1

Related : https://answall.com/questions/63005/qual-possuí-um-performant-bestfor-ou-foreachrange

– viana

2017/08/23 at 13:55
1

There is difference between reporting the size in the loop condition or outside of it?

– rray

2017/08/23 at 13:55
1

This site is great for comparing Javascript/Jquery methods : https://jsperf.com/

– Bruno

2017/08/23 at 13:58
5

@Bruno but no Javascript/Jquery code here!

– viana

2017/08/23 at 13:59
I am using the second example, because it is an implementation of the language I believe it is optimized for these situations

– GabrielLocalhost

2017/08/23 at 14:05
1

@Gabriellocalhost Did the answer resolve what was in doubt? Do you need something else to be improved? Do you think it is possible to accept it now?

– Maniero

2017/08/28 at 12:37

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1 answer

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by Maniero • **444,682** points · Answer 1 · 2017-08-23T14:18:44+00:00

Depends a little on what it is ListAll, can be various types of structure, each with a different complexity commitment. It has collection that the calculus of size() can be huge and an iteration can be absurdly faster. But considering that the size() has complexity O(1) low the difference should be very small, often varying according to other circumstances.

Therefore, use the most readable flow control structure, which better shows the intention and avoids more errors should be preferred, so the one that uses the iterator (for each) would be better.

It may be that some case has better performance the for simple, but would have to analyze case by case. Do not assume you know which one will be faster, can break your face. There are optimizations that can give different result than intuitive. And can change according to the compiler version or the framework.