QueueNode(將書中後續的Iterable補全)

package 數據結構.Queue;

import java.util.Iterator;

public class QueueNode<Item> implements Iterable {

    private class Node{
        Item item;
        Node next;
    }
    Node first;
    Node last;
    int N=0;
    public int size(){
        return N;
    }
    public boolean isEmpty(){
        return N==0;
    }
    public void enqueue(Item item){
        Node oldfirst=last;
        last=new Node();
        last.item=item;
        last.next=null;
        if (isEmpty()) {
            first=last;
        } else{
            oldfirst.next=last;
        }
        N++;
    }
    public Item dequeue(){
        Item item =first.item;
        first=first.next;
        //當注意對象的引用變量是多個時，要注意剩下的引用變量會使得對象無法被回收。
        if (isEmpty())last=null;
        N--;
        return item;
    }
    @Override
    public Iterator iterator() {
        return new QueueNodeIterator();
    }
    private class QueueNodeIterator<Item> implements Iterator<Item> {
        Node temp =first;
        int j=N;
        @Override
        public boolean hasNext() {
            return j>0;
        }

        @Override
        public Item next() {
            Item item=(Item) temp.item;
            temp = temp.next;
            j--;
            return item;
        }

        @Override
        public void remove() {

        }
    }
}