Question

I am trying to Implement a doubly linked with null objects at the beginning and end of the list using null object design pattern. So an empty list will contain two null objects. So I wrote this code Does this follow null object design pattern? If not how can I achieve that. ANy suggestions will be appreciated.

Updated Code-

// Creating a doubly linked list.
        doubleLinkedList = new DoubleLinkedList();

    class DoubleLinkedList {

        private NewLink firstNode;
        private NewLink lastNode;
        private NewLink rootNode;



        public DoubleLinkedList() {

//So this satisfies my question that I have asked meaning null objects at beginning and last node or something else I have to do.
            firstNode = NewLink.NULL_NODE;
            lastNode  = NewLink.NULL_NODE;

        }

    }



    class NewLink {

        public String  data;
        public NewLink nextPointer;
        public NewLink previousPointer;


public static final NewLink NULL_NODE = new NewLink(); 



        public NewLink(String id) {

            data = id;

        }

public NewLink() {

    }
        // Overriding toString method to return the actual data of the node
        public String toString() {

            return "{" + data + "} ";

        }
    }

Answer 1

public static final NewLink NULL_NODE = new NewLink(); 

must be in NewLink class

so

firstNode = NewLink.NULL_NODE;
secondNode = NewLink.NULL_NODE;

also you can make all methods from NewLink – abstract
and make two nested classes: for NULL objects and for not NULL object.
It’s can be very helpful in difficult situations