Iterator

[Tony Johansson]

Hello!
Why should an Iterator be used instead of using index when going through a
collection for example ArrayList

//Tony

[Alf P. Steinbach]

* Tony Johansson:

Why should an Iterator be used instead of using index when going through a
collection for example ArrayList

ArrayList is not a standard class, so no answer is possible.

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A: Top-posting.
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[Rapscallion]

Alf P. Steinbach wrote:

ArrayList is not a standard class

It is - in Java :-)

[Ioannis Vranos]

Tony Johansson wrote:

Hello!
Why should an Iterator be used instead of using index when going through a
collection for example ArrayList

When the container contents can be accessed efficiently with indices, then indices are
provided. Consider vector, valarray, bitset, etc.

--
Ioannis Vranos

http://www23.brinkster.com/noicys

[Rolf Magnus]

Rapscallion wrote:

Alf P. Steinbach wrote:

ArrayList is not a standard class

It is - in Java :-)

Just out of interest: What is it? An array or a list?

[Andrew McDonagh]

Rolf Magnus wrote:

Rapscallion wrote:

Alf P. Steinbach wrote:

ArrayList is not a standard class

It is - in Java :-)

Just out of interest: What is it? An array or a list?

List is the interface (i.e. Java's pure abstract class 'like' construct)
http://java.sun.com/j2se/1.4.2/docs/...util/List.html
An ArrayList is an implementation of the List interface which is backed
by an array - so 'get(int position)' maps nicely to 'array[position]'

There's also LinkedList - which implements the List interface using a
doubly linked list.

[Ioannis Vranos]

Andrew McDonagh wrote:

An ArrayList is an implementation of the List interface which is backed
by an array - so 'get(int position)' maps nicely to 'array[position]'

There's also LinkedList - which implements the List interface using a
doubly linked list.

So, what has it to do with C++? C++ vector provides both random access iterators and
indices. Under .NET, in VS 2005, a managed vector version inheriting from .NET IList<T>
interface will also be provided.

--
Ioannis Vranos

http://www23.brinkster.com/noicys

[Andrew McDonagh]

Ioannis Vranos wrote:

Andrew McDonagh wrote:

An ArrayList is an implementation of the List interface which is
backed by an array - so 'get(int position)' maps nicely to
'array[position]'

There's also LinkedList - which implements the List interface using a
doubly linked list.
So, what has it to do with C++?

Absolutely nothing, I was just answering Rolf's question.
C++ vector provides both random access
iterators and indices.
Great aren't they.

Under .NET, in VS 2005, a managed vector version
inheriting from .NET IList<T> interface will also be provided.

What's this got to do with standard C++ ?

[Ioannis Vranos]

Andrew McDonagh wrote:

So, what has it to do with C++?

Absolutely nothing, I was just answering Rolf's question.

My mistake, I thought you were the original poster. :-)

--
Ioannis Vranos

http://www23.brinkster.com/noicys

[Cy Edmunds]

"Tony Johansson" <jo*****************@telia.com> wrote in message
news:Y1*********************@newsc.telia.net...

Hello!
Why should an Iterator be used instead of using index when going through a
collection for example ArrayList

//Tony

There may or not be a speed advantage, but there is almost certainly a
maintainability advantage if your algorithms don't actually need
subscripting. Consider:

#include <vector>
typedef std::vector<double> t_coll;
t_coll c;
....
for (t_coll::iterator i = c.begin(); i != c.end(); ++i)
*i = 2.2;

Now let's say that after some new requirements come in you find that you
must frequently delete items from the middle of your collection. You need to
use a list instead of a vector for efficient performance. No problem:

#include <list> // change this
typedef std::list<double> t_coll; // and this
t_coll c; // same
....
for (t_coll::iterator i = c.begin(); i != c.end(); ++i) // same
*i = 2.2; // same

Now if you had written you loops as

for (unsigned i = 0; i < c.size(); ++i)
c[i] = 2.2;

you would have to change them all.

--
Cy
http://home.rochester.rr.com/cyhome/