Why is an iterator used instead of a for loop?

Question

I'm looking at this code: https://www.geeksforgeeks.org/bridge-in-a-graph/

Iterator<Integer> i = adj[u].iterator();
while (i.hasNext())
{
    int v = i.next();  // v is current adjacent of u
    ...

Why didn't the author just use a for loop? Wouldn't this be the same?

for (int v: adj[u])

Please include the definition of `adj`. Collection iterators can do certain things which enhanced for loops cannot, e.g. delete from the collection while iterating. This must be a duplicate of some other question. — Tim Biegeleisen, Jan 26 '18 at 01:43
"Why didn't the author just use a for loop?" You should ask the author, we can't look inside the author's mind. Possible reasons: the code might be very old, from before the enhanded for-loop was introduced. Or the author is not familiar with Java and used whatever they knew about it. For anyone else than the author, this is an opinion-based question. — Erwin Bolwidt, Jan 26 '18 at 01:47
They are the same ... unless the "..." code is doing something with the iterator. — Stephen C, Jan 26 '18 at 01:56

Jacob G. · Accepted Answer · 2018-01-26T01:49:48.363

In Java, one use of Iterator<E> is to remove elements from a Collection<E> while iterating. If you were to attempt to remove the same element from the same Collection while iterating over it with for (int v : adj[u]), then a ConcurrentModificationException would be thrown.

If no element is being removed, then yes, both choices of syntax would suffice.

As for why the author of that article didn't use a for-loop, you'd have to ask them. Their code doesn't seem to be removing any elements from the LinkedList<Integer> within the loop, so it was most likely a subconscious choice.

Why is an iterator used instead of a for loop?

1 Answers1