Modifying lists with ListIterator

1. Modifying lists with ListIterator

In the last video, we explored `Iterator` for iterating through collections. Now, we extend this concept with `ListIterator`, which provides more control over list traversal.

2. Iterator vs ListIterator

Unlike a regular `Iterator`, `ListIterator` allows moving forward and backward within a list, modifying existing elements and adding new elements dynamically. However, `ListIterator` only works for `List` collections while `Iterator` works for all data collections.

3. Sample ArrayList

To start, we will create an `ArrayList` named `names`, which contains `Alice`, `Bob` and `Charlie`, to showcase `ListIterator` functionality.

4. Traversing a list with ListIterator

To iterate through the list, we start by importing the `ListIterator` class Then, we call `.listIterator()` on the `names` list to create a `ListIterator` object. After that, we use `.hasNext()` and `.next()` to move forward through the list, printing each element. As a result, the code outputs all the names line by line

5. Moving backward with ListIterator

One of `ListIterator`’s key advantages is moving backward through a list. If we need to traverse backward, we must initialize `ListIterator` at the end of the list by calling `.listIterator(names.size())`. Instead of `.hasNext()`, we use `.hasPrevious()` to check if an earlier element exists. Calling `.previous()` moves the iterator backward and retrieves the previous element so we can print it.

6. Modifying elements during iteration

With `ListIterator`, we can modify elements while iterating using the `.set()` method. First, we call `.listIterator()` on the `names` list to create a `ListIterator` object. Then we loop through `names`, checking if an element equals `Bob`. When found, we replace `Bob` with `Bobby` using `.set()`. After modification, the `names` list now contains 3 elements: `Alice`, `Bobby` and `Charlie`.

7. Adding elements during iteration

With `ListIterator`, we can insert elements dynamically using the `.add()` method. First, we call `.listIterator()` on the `names` list to create a `ListIterator` object. Then, we traverse `names`, checking for `Charlie`. When `Charlie` is found, `David` is inserted right after position of `Charlie`. After insertion, the `names` list now contains 4 elements: `Alice`, `Bobby`, `Charlie` and `David`.

8. Summary

In this video, we explored `ListIterator`, an enhanced version of `Iterator` that allows both forward and backward traversal while modifying lists safely. We covered key operations like `.next()` and `.previous()` to navigate, `.set()` to modify elements, `.add()` to insert, and `.remove()` for safe deletion. Since `ListIterator` only works on Lists, it provides more flexibility than a standard Iterator but is not compatible with `Set` or `Map`.

9. Let's practice!

Now it's time for you to practice!

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