Doubly Linked List - removal method

Question

I am trying too delete a node in a doubly linked list, by an index that a user inputs. It seems to make sense for me but after "removing the node" and reprinting the list's contents, nothing has changed. I'm sure it's something stupid that I'm missing. Any advice?

public void removeEntryNode() {
    System.out
            .println("We delete by index here. Type in the number you want to delete");
    // print list for selection
    temp = head;
    while (temp != null && temp.getFirstName() != null) {
        System.out.print(temp.getIndex() + " " + temp.getFirstName() + " ");
        System.out.print(temp.getLastName() + " ");
        System.out.println(" ");
        temp = temp.getNext();
    }

    int selection = keyboard.nextInt();

    // Gets node matching index with selection and deletes it
    // Next two lines loop through list
    while (temp != null && temp.getIndex() != selection) {
        temp = temp.getNext();
    }

    // if it is the head
    if (selection == 0) {
        head = temp.getNext();
        temp.getNext().setPrev(null);
        temp.setNext(null);
        counter--;
    }
    // if it is the tail
    else if (selection == size()) {
        tail = temp.getPrev();
        temp.setPrev(null);
        temp.setNext(null);
        temp.getPrev().setNext(null);
        counter--;
    } else {
        temp.getPrev().setNext(temp.getNext());
        temp.getNext().setPrev(temp.getPrev());
        temp.setNext(null);
        temp.setPrev(null);
        counter--;
    }

    System.out.println("Successfully deleted ");
    menu();
}

Answer 1

It's impossible to pinpoint the exact problem without seeing your entire code.

Nonetheless, I'll give you some pointers:

1.

... temp.getIndex() != selection ...

It is generally not a good idea for an element in a linked list to keep track of its own index. To keep the indices correct, every insertion or removal would require traversing the list just to update the indices.

2.

    else if (selection == size()){

There is probably an off-by-one error here.

3.

        temp.setPrev(null);
        temp.setNext(null);
        temp.getPrev().setNext(null);

The last line is guaranteed to throw a NullPointerException.

Once you fix these problems, I recommend stepping through your program in a debugger, to see whether what actually happens is what you expect to happen at each step.

Answer 2

after you listed all the elements your temp pointer points to the end of the list, before you search for the element you should make the temp pointer point to the head again.

   temp = head;
    //Gets node matching index with selection and deletes it
    //Next two lines loop through list
    while (temp!=null && temp.getIndex() != selection) {
        temp = temp.getNext();
    }

Answer 3

a double linkedlist has two pointers, to it's previous and it's next.

if you are trying to remove that node, make sure to set the previous.next point to the node's next, and the next.previous to node's previous.

about maintaining the index value, i also disagree, but it's okay if you can do that perfectly,.