How to access iterator?

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Todd - 17 Dec 2007 23:04 GMT

Hello,

In the brief form of the loop {for( double value : collection )} can
one access the iterator that is created to perform the loop?

I ask as there are times that I would like to reassign the i-th value
in collection to the result of an operation on value.

Thanks for any insights,
Todd

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Mark Rafn - 18 Dec 2007 00:07 GMT

>In the brief form of the loop {for( double value : collection )} can
>one access the iterator that is created to perform the loop?

Nope.

>I ask as there are times that I would like to reassign the i-th value
>in collection to the result of an operation on value.

There's no great way to do this. Actually, having access to the Iterator
wouldn't help you either - imagine the old-style version of the loop:

Iterator it = myCollection.iterator();
while (it.hasNext) {
Object myObj = it.next();
...
}

Even though the iterator is in scope, you don't have any data about the index.
This is good, generally - you don't know that you're iterating over something
that CAN be accessed by index, and certainly don't know that it would be
efficient.

I generally end up doing something like:
int idx=0;
for (Object myObj : myCollection) {
...
idx++;
}

Gross, but it works, and it's often simpler than trying to refactor my data
structures so that such usage isn't needed.
--
Mark Rafn dagon@dagon.net <http://www.dagon.net/>

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Lew - 18 Dec 2007 00:53 GMT

> I generally end up doing something like:
> int idx=0;
> for (Object myObj : myCollection) {
> ...
> idx++;
> }

That idiom relies on having an ordered collection.
If you have a RandomAccess collection such as ArrayList you can also use:

for ( int ix = 0; ix < list.size; ++ix )
{
doSomething( list.get( ix ));
}

Signature

Lew

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Hendrik Maryns - 18 Dec 2007 11:46 GMT

Lew schreef:

>> I generally end up doing something like:
>> int idx=0;
[quoted text clipped - 10 lines]
> doSomething( list.get( ix ));
> }

Or indeed use a ListIterator, which has set(E element). (Though of
course, this could throw an UnsupportedOperationException.)

H.

Signature

Hendrik Maryns
http://tcl.sfs.uni-tuebingen.de/~hendrik/
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Owen Jacobson - 18 Dec 2007 00:14 GMT

> Hello,
>
[quoted text clipped - 3 lines]
> I ask as there are times that I would like to reassign the i-th value
> in collection to the result of an operation on value.

No. If you need to access an iterator, you must create the iterator
yourself and assign it a name in your program. (Furthermore, the
feature you want -- replacing elements in the collection -- is only
available through certain Iterator subclasses such as ListIterator,
which aren't involved in for-each loops at all.)

Hope that helps,
-o

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How to access iterator?

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