Why do we need to use iterator on ArrayList in Java? [duplicate]

Question

I was reading the answer mentioned to the question "Do we ever need to use Iterators on ArrayList?".

In the answer, the user stated something like this: "A big use case of iterators with ArrayLists is when you want to remove elements while iterating".

This could be achieved even using remove method of ArrayList in Java. My question is why we need iterator in ArrayList?

Consider the code:

import java.util.*; public class ocajp66 {     public static void main(String[] args) {         ArrayList a = new ArrayList();         for (int i = 0; i < 10; i++) {             a.add(i);         }         System.out.printf("BEFORE ITERATOR\n");         for (int i = 0; i < a.size(); i++) {             System.out.printf("I:%d\n", a.get(i));         }         System.out.printf("AFTER ITERATOR\n");         Iterator i = a.iterator();         while (i.hasNext()) {             System.out.printf("I:%d\n", i.next());         }     } } 

Can anybody explain the significance of the iterator? It would be wonderful if you could explain me with code.

Answer 1

As you have stated iterator is used when you want to remove stuff whilst you iterate over the array contents. If you don't use an iterator but simply have a for loop and inside it use the remove method you will get exceptions because the contents of the array changes while you iterate through. e.g: you might think array size is 10 at the start of the for loop but it wont be the case once you remove stuff.. so when u reach the last loops probably there will be IndexOutofBoundsException etc.