Test Doubly Linked list

DoublyLinkedListImpl.java

public class DoublyLinkedListImpl {

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

    public DoublyLinkedListImpl() {
        size = 0;
    }
    /**
     * this class keeps track of each data
     */
    private class Node {
        int data;
        Node next;
        Node prev;

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

    /**
     * adds data at the starting of the linked list
     * @param data
     */
    public void addFirst(int data) {
        Node tmp = new Node(data, head, null);
        if(head != null ) {head.prev = tmp;}
        head = tmp;
        if(tail == null) { tail = tmp;}
        size++;
        System.out.println("adding: "+data);
    }

    /**
     * adds data at the end of the linked list
     * @param data
     */
    public void addLast(int data) {

        Node tmp = new Node(data, null, tail);
        if(tail != null) {tail.next = tmp;}
        tail = tmp;
        if(head == null) { head = tmp;}
        size++;
        System.out.println("adding: "+data);
    }

    /**
     * this method walks forward through the linked list
     */
    public void iterate(){

        System.out.println("iterating forward..");
        Node tmp = head;
        while(tmp != null){
            System.out.print(tmp.data+",");
            tmp = tmp.next;
        }
        System.out.println();
    }

    /**
     * this method removes all the nodes that has data greater than x
     * @param head
     * @param x
     */
    public void deleteNode(Node head, int x)
    {
        if(head==null)
            return;
        if(size == 1 && head.data > x){
            head.next.prev = null;
            return;
        }

        Node temp = head;
        while (temp.next != null){
            Node current = temp.next;
            if(current.data > x){
                current.prev.next = current.next;
                if(current.next != null)
                    current.next.prev = current.prev;
            }
            temp = current;
        }
        return;
    }

    public static void main(String a[]){

        DoublyLinkedListImpl dll = new DoublyLinkedListImpl();
        dll.addFirst(10);
        dll.addFirst(34);
        dll.addLast(56);
        dll.addLast(364);
        dll.addLast(1200);
        dll.addLast(589);
        dll.addLast(12);
        dll.addLast(5000);
        dll.iterate();
        dll.deleteNode(dll.head, 50);
        dll.iterate();
    }
}