Trying to implement my own iterator in Java

[trouty323]

Homework Statement

Basically, I am assigned to implement my own iterator using a Doubly Linked List. The methods, of course, are hasNext(), next(), and remove(). The one that is giving me the most grief is the remove() method.

Homework Equations

The Attempt at a Solution

The code that I have currently is:

public void remove() {
	lastItemReturned = lastItemReturned.prev;
	nextItem = lastItemReturned.next.next;
	index--;
}

Now, this could actually be right and I may be messing up somewhere else in the code, but I have a feeling this is not the case. Does anybody know if this part of code is right?

 

[KataKoniK]

Dear student,

Thank you for reaching out for help with your iterator implementation. The remove() method in your code looks like it may be incorrect. It is important to remember that when removing an item from a linked list, you need to update the pointers of the previous and next nodes in order to maintain the integrity of the list.

Here is a possible solution for your remove() method:

public void remove() {
if(lastItemReturned == null) {
throw new IllegalStateException("No item to remove.");
}
// check if lastItemReturned is the first node
if(lastItemReturned.prev == null) {
// update the next node's prev pointer
lastItemReturned.next.prev = null;
// update the nextItem pointer
nextItem = lastItemReturned.next;
} else {
// update the previous node's next pointer
lastItemReturned.prev.next = lastItemReturned.next;
// update the next node's prev pointer
lastItemReturned.next.prev = lastItemReturned.prev;
// update the nextItem pointer
nextItem = lastItemReturned.next;
}
// update the index
index--;
// set lastItemReturned to null
lastItemReturned = null;
}

I hope this helps you with your implementation. Remember to thoroughly test your code and consider edge cases to ensure it is functioning correctly. Good luck!