使用链接的

import static java.lang.System.out;
/* 来自 nowjava.com - 时  代  Java*/

import java.util.Iterator;

import java.util.NoSuchElementException;


public class Queue<Item> implements Iterable<Item> {


    private Node first, last;

    

    private class Node {

        private Item item;

        private Node next;

    }

  

    public boolean isEmpty() {

        return first == null;

    }

    

    public void enqueue(Item item) {

        Node oldlast = last;

        last = new Node();

        last.item = item;/*n o w j a v a . c o m - 时代Java 提 供*/

        last.next = null;

        

        if (isEmpty())

            first = last;

        else

            oldlast.next = last;

    }

    

    public Item dequeue() {

        Item item = first.item;

        first = first.next;

        

        if (isEmpty()) 

            last = null;

    

        return item;

    }

    

    /**

     * Implements a iterator for Queue, using FIFO.

     * 

     * <h5>Lecture: Iterators (Week 2)</h5>

     */

    private class QueueIterator implements Iterator<Item> {

        

        private Node current = first;

        

        public boolean hasNext() {

            return current != null;

        }

        

        public Item next() {

            if (!hasNext())

                throw new NoSuchElementException();

            

            Item item = current.item;

            current = current.next;

            return item;

        }

        

        public void remove() {

            throw new UnsupportedOperationException();

        }

    }

  

    @Override

    public Iterator<Item> iterator() {

        return new QueueIterator();

    }


    public static void main(String[] args) {

      Queue<String> queue =