What's wrong there ?

DoubleLinked.java

import java.util.Iterator;

/**
 *
 */
public class DoubleLinked<Item> implements Iterable<Item>{

    private Node head;
    private Node tail;
    private int N;

    public DoubleLinked(){
        head = new Node();
        tail = new Node();

    }

    private class Node{
        Item item;
        Node left;
        Node right;
    }

    public int size(){
        return N;
    }

    public boolean isEmpty(){
        return size()==0;
    }

    public void push(Item item){
        if(isEmpty()){
            Node newFirst = new Node();
            newFirst.item=item;
            head.right = newFirst;
            tail.left=newFirst;

        }else {
            Node oldFirst = head.right;
            Node newFirst = new Node();
            newFirst.item=item;
            newFirst.right=oldFirst;
            oldFirst.left=newFirst;
            head.right=newFirst;
        }
        N++;
    }

    public Item remove(Node node){
        Item item = node.item;

        if(node==head.right){
            head.right = node.right;
            node=null;
        }else if(node==tail.left){
            tail.left=node.left;
            node=null;
        }else {
            Node last = node.left;
            Node next = node.right;
            last.right = next;
            next.left=last;
            node=null;
        }
        N--;
        return item;
    }
    @Override
    public ListIterator iterator() {
        return new ListIterator();
    }


    private class ListIterator implements Iterator<Item>{

        Node current = head.right;
        @Override
        public boolean hasNext() {
            if(current!=null && size()>0){
                return true;
            }else {
                return false;
            }

        }

        @Override
        public Item next() {
            Item item = current.item;
            //System.out.println("current:地址"+current);
            current=current.right;
            return item;
        }

        @Override
        public void remove() {

        }
    }

    public static void main(String[]args){
        DoubleLinked d = new DoubleLinked<Integer>();
        for(int i=0;i<5;i++) d.push(i);


        System.out.println(d.remove(d.tail.left));
//        System.out.println(d.remove(d.tail.left));


        int k = 0;
        for(Iterator i = d.iterator();i.hasNext();) {
            System.out.println("next:"+i.next());

            k++;
        }
        System.out.println("size:"+d.size());
        //System.out.println(d.tail.left.item);
    }
}