Java deque Deque

import java.util.Iterator;
public class Deque<Item> implements Iterable<Item> {
    private class Node {
        Item item;
        Node next;
        Node pre;
    }
    private class QueueIterator implements Iterator<Item> {
        public boolean hasNext() {
            return current != null;
        }
        public Item next() {
            Item tmp = current.item;
            current = current.next;
            return tmp;
        }
        private Node current = front;
    }
    public Iterator<Item> iterator() {
        return new QueueIterator();
    }
    boolean isEmtpy() {
        return front == null;
    }
    int size() {
        return n;
    }
    void pushLeft(Item x) {
        Node oldfront = front;
        front = new Node();
        front.item = x;
        front.next = oldfront;
        front.pre = null;
        if(oldfront == null)
            rear = front;
        else
            oldfront.pre = front;
        n++;
    }
    void pushRight(Item x) {
        Node oldrear = rear;
        rear = new Node();
        rear.item = x;
        rear.next = null;
        rear.pre = oldrear;
        if(oldrear != null)
            oldrear.next = rear;
        else
            front = rear;
        n++;
    }
    Item popLeft() {
        if(isEmtpy())
            return null;
        Item tmp = front.item;
        front = front.next;
        if(front == null)
            rear = null;
        else
            front.pre = null;
        n--;
        return tmp;
    }
    Item popRight() {
        if(isEmtpy())
            return null;
        Item tmp = rear.item;
        rear = rear.pre;
        if(rear != null)
            rear.next = null;
        else
            front = null;
        n--;
        return tmp;
    }
    private Node front;
    private Node rear;
    int n;
}