Why would you need an iterator in the first place?
ArrayList is indexed with numbers, so it is quite simple to use a for loop.
It is possible to use advanced for loops...

I thought that it is same as in Java..

I think in Java the ArrayList changes its size dynamically.. When I iterate through a loop and I need to remove than one item it may cause a problem..

For example I have an ArrayList with apples.. 30 red, 20 green, 10 yellow..


for(i=0;i<ArrayList.size();i++){

if apple color is red then remove it..

}

The problem is that during initialization the I asked for the i to be less than 60. After a few removals the for loop will try to get an index that does not exist..

As far as I know this does not work in Java.. Does it work in processing? Does the arrayList change its size after the iteration is done?

You could just subtract one from i every time that you remove an item...

be careful though. if you are iterating from 0 to 10 and delete 5 then all the others will shuffle up. when you then carry on to item 6 you've skipped one - the one that was 6 but is now 5...

best way is to start from end and move forwards, from 10 to 0, so that deleting items only affects items you've already handled.

This is why I was wondering about Iterator in ArrayList, because I do not have to think all the extra cases..


I tried to use iterator with an ArrayList I got a few errors.. I 'll try again tomorrow..


Thanks guys!

Processing code is in fact Java  so the ArrayList in P5 is the Java ArrayList.

Using iterators to iterate over an entire ArrayList is slower than accessing the elements directy with ArrayList_variable.get(index), but unless you have very large ArrayLists or are perforimng a very large number of iterations then you will probably not notice the difference.

The reason for using iterators is because it is the easiest way to safely remove elements from an ArrayList while iterating over the list.

The following example deletes all 'Jack' elements (there are 2) from the list.

1. List<String> aList = new ArrayList<String>(); 
2. aList.add("Peter"); 
3. aList.add("Jack"); 
4. aList.add("Jill"); 
5. aList.add("Jack"); 
6. aList.add("Sarah"); 
7. aList.add("Maggie"); 
8. 
   
9. Iterator<String> itr = aList.iterator();
10. while (itr.hasNext()) { 
11.   String element = itr.next(); 
12.   if ("Jack".equals(element)) { 
13.     itr.remove();
14.   }
15. } 
16. println(aList); 

BTW HashMap does not have itearators

"HashMap does not have itearators"
True, but there are methods to get a Set or a Collection out of it, and these are Iterable.
(Just for the record.)

And good explanation on the usefulness of Iterator in a world where foreach loops tend to make it forgotten...

Or in this case: the simple and usual tip to go backward may be enough

Thank you guys!

I finally used iterators regarding to the quarks's example!

Until now it works fine!

You can also declare an iterator in a for-loop like this:

1. for (Iterator<String> i = stringList.iterator(); i.hasNext();) { 
2.   if (i.next().equals("Jack")) { 
3.     i.remove();
4.   }
5. }

It's the same thing as the while-loop, but the scope of the iterator variable is only in the for-loop curly braces