LinkedListQueue.java

import java.util.NoSuchElementException;
import java.util.Iterator;

public class LinkedListQueue<Item> implements Iterable<Item>{
    private class Node{
        Item item;
        Node next;
    }
    
    private Node head; // head of the queue; we dequeue at the head
    private Node tail; // tail of the queue; we add new node to the tail
    private int count; // the number of element in the queue
    
    public LinkedListQueue(){
        head = tail = null;
        count = 0;
    }
    
    public void enqueue(Item item){
        Node n = new Node();
        n.item = item;
        n.next = null;
        if (count == 0){
            head = tail = n;
        }else{
            tail.next = n;
            tail = n;
        }
        count++;
    }
    
    public Item dequeue(){
        if (count == 0) throw new NoSuchElementException("The queue is already!");
        Item item = head.item;
        head = head.next;
        count--;
        if (count == 0) tail = null; // avoid loitering
        return item;
    }
    
    public int size(){
        return count;
    }
    
    public Iterator<Item> iterator(){
        return new LinkedListIterator();
    }
    
    private LinkedListIterator() implements Iterator<Item>{
        private Node current = head;
        public boolean hasNext(){return current != null;}
        public void remove() {throw new UnsupportedOperationException();}
        public Item next() {
            if (!hasNext()) throw new NoSuchElementException("Queue is empty!");
            Item item = current.item;
            current = current.next;
            return item;
        }
    }
    
    public String toString(){
        // since we have an iterator implemented, we could use the foreach method instead
        // use StringBuilder instead of concantenating the string
        StringBuilder builder = new StringBuilder();
        for(Item item: this){
            builder.append(item);
            builder.append(" ");
        }
        return builder.toString();
    }
}

For a LinkedListQueue, it should be head -> N2 ->N3 -> ..... -> tail -> null

A few place where we should add the generic type:
The outer class LinkedListQueue implements Iterable

The Iterator iterator() method

The inner class LinkedListIterator implements Iterator