Issues with Code Not Working , does not add all the numbers to the output, requirements are not being met, Please Help

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Hello All, I though I was on the right track to fix this problem but then I get the requirements are not being met. I then realized only 2 - 9 is being output. How do i fix this ?

It's time to get acquainted with doubly linked lists. By solving this task, you will understand how a doubly linked list works and you'll be able to add elements to it. You have a StringLinkedList class, which has first and last fields that point to the first and last elements respectively.
You need to implement the logic of the add method, which will add elements to the list.

Hints:

To achieve the correct implementation, it is important to understand that you can iterate over the list both from the first element to the last, and vice versa. So when you add new elements, don't forget to change the references in the adjacent elements.
The add method must create a new Node object, which will store the passed value. Before adding a new node, you need to change the last node's reference so that it points to the newly created one, and the newly created node will become the last node.
If there is a single element in the list, then the first.next and last.prev fields both point to it.
The printAll method was created for debugging. It is not involving in verifying the task.

Important:
Node first should not store a value. It only points to the first element (first.next);
Node last also does not store a value. It only points to the last element (last.prev).

Requirements:

When a new element is added, existing elements should get a reference it.
When a new element is added, it should store a reference to the previous element.
The StringLinkedList class's first field should always refer to the first element and not contain the value of the previous element (prev field) or a reference to it.
The StringLinkedList class's last field should always refer to the last element and not contain the value of the next element (next field) or a reference to it.

package en.codegym.task.pro.task13.task1313; /* StringLinkedList It's time to get acquainted with doubly linked lists. By solving this task, you will understand how a doubly linked list works and you'll be able to add elements to it. You have a StringLinkedList class, which has first and last fields that point to the first and last elements respectively. You need to implement the logic of the add method, which will add elements to the list. */ public class Solution { public static void main(String[] args) { StringLinkedList stringLinkedList = new StringLinkedList(); stringLinkedList.add("1"); stringLinkedList.add("2"); stringLinkedList.add("3"); stringLinkedList.add("4"); stringLinkedList.add("5"); stringLinkedList.add("6"); stringLinkedList.add("7"); stringLinkedList.add("8"); stringLinkedList.add("9"); stringLinkedList.printAll(); } }

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Thomas

Level 41 , Bayreuth, Germany

30 November 2023, 17:37

You probably have overseen that first an last node should contain no values. So when you add the first element the first nodes next property points to that added element and the last nodes prev property points also to that added element. All further elements you add using the last and the prev.last nodes these two you need to unlink and in between you need to place the new node. Just a hint, you may need a construct like last.prev.next = (from the last node you select the previous one and now you change the next property to the new node). That's four assignments. Try also to output from last to first to verify all is working, like (as addition to printAll):

System.out.println("last -> first");
currentElement = last;
while((currentElement = currentElement.prev) != null) {
    System.out.println(currentElement.value);
}

// or
System.out.println("9th element");
System.out.println(first.next.next.next.next.next.next.next.next.next.value);