Iterators in C++ (stl) vs Java, is there a conceptual difference?

Perhaps a bit more theoretical. Mathematically, collections in C++ can be described as a half-open interval of iterators, namely one iterator pointing to the start of the collection and one iterator pointing just behind the last element.

This convention opens up a host of possibilities. The way algorithms work in C++, they can all be applied to subsequences of a larger collection. To make such a thing work in Java, you have to create a wrapper around an existing collection that returns a different iterator.

Another important aspect of iterators has already been mentioned by Frank. There are different concepts of iterators. Java iterators correspond to C++' input iterators, i.e. they are read-only iterators that can only be incremented one step at a time and can't go backwards.

On the other extreme, you have C pointers which correspond exactly to C++' concept of a random access iterator.

All in all, C++ offers a much richer and purer concept that can be applied to a much wider variety of tasks than either C pointers or Java iterators.

Yes, there is a large conceptual difference. C++ utilizes different "classes" of iterators. Some are used for random access (unlike Java), some are used for forward access (like java). While even others are used for writing data (for use with, say, transform).

See the iterators concept in the C++ Documentation:

• Input Iterator
• Output Iterator
• Forward Iterator
• Bidirectional Iterator
• Random Access Iterator

These are far more interesting and powerful compared to Java/C#'s puny iterators. Hopefully these conventions will be codified using C++0x's Concepts.