examples of sanity code java for a doubly linked list

Example: double linked list java

class doublelinkedlist{  
    Node head;
    Node tail;

    static class Node{
        int data;
        Node previous;
        Node next;

        Node(int data) { this.data = data; }
    }

    public void addLink(int data) {
        Node node = new Node(data);

        if(head == null) {
            head = tail = node;
            head.previous = null;
        } else {
            tail.next = node;
            node.previous = tail;
            tail = node;
        }
        tail.next = null;
    }
}