Use a for-loop or a for-each loop?

Question

Should we prefer the for-each loop instead of the traditional for-loops? Is the while-loop advantageous?

List<String> names = Arrays.asList("John", "Jeff", "Mary", "Elise");

//for-each loop
for(String name: names){
    log(name);
}

//traditional for-loop
for(int index=0; index < 10; ++index){
    log(names.get(index));
}

//Iterator while
Iterator<String> iter1 = names.iterator();
while (iter1.hasNext()) {
    log(iter1.next());
}

//Iterator for loop
for(Iterator<String> iter2 = names.iterator(); iter2.hasNext();){
    log(iter2.next());
}

What is the best flavor to use?

Do whatever you feel like. But hopefully, you'll want to maximize readability. I use `for each` when I don't need the index — keyser, Aug 06 '13 at 11:01
http://stackoverflow.com/questions/9226483/java-loop-efficiency-for-vs-foreach — bas, Aug 06 '13 at 11:02
The traditional loop can load to errors, especially when an index starts from 1, while arrays are zero based. — Dimitri Dewaele, Aug 06 '13 at 15:17

score 2 · Answer 1 · answered Aug 06 '13 at 11:07

Loops 1, 3 and 4 are essentially the same and probably compile to the same bytecode. So use the first one which is more readable.

Loop 2 should be avoided if you don't know what list implementation you are dealing with. In particular, list.get(i) can be an O(n) operation on some lists (LinkedLists for example), making the performance of loop 2 an O(n^2) operation = bad.

score 2 · Accepted Answer · answered Aug 06 '13 at 11:08

2

Are are same. But some case one is more favourable then others

Case 1:

//for-each loop
for(String name: names){
    log(name);
}

Favourable :

When you want to iterate over collection
no adding or deletion over array.
No need of index of item you iterate

Case 2:

//traditional for-loop
for(int index=0; index < 10; ++index){
    log(names.get(index));
}

Favourable :

When you want to iterate over collection
you need to work on index of item you iterate. So for that you always have value of index you currently on.

Case 3:

Iterator<String> iter1 = names.iterator();
while (iter1.hasNext()) {
    log(iter1.next());
}

and

//Iterator for loop
for(Iterator<String> iter2 = names.iterator(); iter2.hasNext();){
    log(iter2.next());
}

Favourable :

When you want to iterate over collection
Addition or deletion take ||ly while iterating.

answered Aug 06 '13 at 11:08

Ashish Aggarwal

3,018
2
23
46

I think he already know that, he just want to know which one is better, and I think it's impossible to tell which one is better:) – Azad Aug 06 '13 at 11:10
@Azad yes it is impposible to tell which one is better. But from the post I didn't found anything which will show that whether he will know this facts or not. – Ashish Aggarwal Aug 06 '13 at 11:42
Loop 2 should be avoided, because this can more easily lead to errors. Typically with the start of your index = 1; list.get(index) and also when using index++ inside the loop. – Dimitri Dewaele Aug 08 '13 at 06:22

Evgeniy Dorofeev · Answer 3 · 2013-08-06T11:17:57.070

2

Options 1 is just a shorten version of 3 and 4. Out of them #1 is preferrable as it easier to write and read. Option 2 may be better in microperformance as it does not create an Iterator object but only in case you use a RandomAccess list like ArrayList

edited Aug 06 '13 at 11:17

answered Aug 06 '13 at 11:09

Evgeniy Dorofeev

133,369
30
199
275

score 1 · Answer 4 · answered Aug 06 '13 at 11:08

1

Don't use foreach loop when you want to delete some elements inside this loop. Instead use classic for loop, when you can decrease iterator after removing element from collection.

answered Aug 06 '13 at 11:08

MGorgon

2,547
23
41

score 0 · Answer 5 · answered Aug 06 '13 at 11:08

0

For and foreach differ slightly in performance. They are approximately the same speed. But the foreach loop uses more stack space for local variables.

For more detials about this please refer

http://forums.asp.net/t/1209455.aspx/1

answered Aug 06 '13 at 11:08

RAJESH KUMAR

497
4
13

score 0 · Answer 6 · answered Aug 06 '13 at 11:08

0

As long as the container implements Iterable, use for each, as long as mentioned above you do not need an index. Altought probablly you will use the Objects id field instead of a for id.

answered Aug 06 '13 at 11:08

Bogdan M.

2,161
6
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Use a for-loop or a for-each loop?

6 Answers6

Linked