How to do a cyclic doubly link list add method in java

Question

I am implementing the add(E) method in the cyclic DoublyLinkedList class as well as the Node inner class.

Node should be implemented as a private inner class.

D

Answer 1

EDIT:

One mistake is here: Instead of this line this.next = prev; it should have this.prev = prev;

However, if you fix this line the code will still not work. This is a simplified version of your code that works.

public class DoublyLinkedList {

    private static class Node {

        private final E data;
        private Node next;
        private Node prev;

        Node(E data) {
            this.data = data;
            this.next = this;
            this.prev = this;
        }

        Node(E data, Node next) {
            this.data = data;
            this.next = next;
            next.prev = this;
        }
    }

    private Node head;
    private Node tail;
    private int size;

    public void add(E value) {
        if (this.head == null) {
            this.head = new Node<>(value);
            this.tail = head;
        } else {
            this.head = new Node<>(value, head);
            this.head.prev = this.tail;
            this.tail.next = head;
        }
        size++;
    }

    public void forEach(Consumer consumer) {
        Node node = this.head;

        if (node != null) {
            do {
                consumer.accept(node.data);
                node = node.next;
            } while (node != this.head);
        }
    }

    public static void main(String[] args) {
        DoublyLinkedList list = new DoublyLinkedList<>();

        list.add(1);
        list.add(2);
        list.add(3);

        list.forEach(e -> System.out.print(e + ", "));
    }

}

What I've done: in order to create a circular double linked list I keep a reference to the tail.