Queue Implementation

import java.util.Iterator;

public class MyQueue<Item> implements Iterable<Item> {
    private class Node {
        Item val;
        Node next;
        Node(Item val) {
            this.val = val;
        }
    }

    private Node head = null;
    private Node tail = null;
    private int size;

    MyQueue() {
        this.size = 0;
    }

    public void offer(Item item) {
        Node node = new Node(item);
        if (head == null) {
        head = node;
        tail = node;
        } else {
            Node oldtail = tail;
            oldtail.next = node;
            tail = node;
        }
        size++;
    }

    public Item poll() {

        if (head == null) {
            return null;
        }
        Item oldItem = head.val;
        head = head.next;
        if (head == null) {
            tail = null;
        }
        size--;
        return oldItem;
    }

    public boolean isEmpty() {
        return head == null;
    }

    public int size() {
        return size;
    }

    public Iterator<Item> iterator() {
        return new queueIterator();
    }

    private class queueIterator implements Iterator<Item> {

        private int i = size;
        private Node oldhead = head;
        public boolean hasNext() {
            return i != 0;
        }
        public Item next() {
            Item cur = oldhead.val;
            oldhead = oldhead.next;
            i--;
            return cur;
        }

        public void remove() {
            throw new UnsupportedOperationException();
        }
    }

    public static void main(String[] args) {
        MyQueue<String> q = new MyQueue<String>();
        q.offer("first");
        q.offer("second");
        q.offer("third");
        for (String s : q) {
            System.out.println(s);
        }
        System.out.println("First test");
        q.poll();
        for (String s : q) {
            System.out.println(s);
        }
        System.out.println("Second test");
        q.offer("fourth");
        q.offer("fifth");
        for (String s : q) {
            System.out.println(s);
        }
        System.out.println("Third test");
    }


}