Algs4-1.3.41复制队列采用for方式实现

1.3.41复制队列。编写一个新的构造函数，使用以下代码Queue<Item> r=new Queue<Item>(q);得到的r指向队列q的一个新的独立的副本。可以对q或r进行任意入列或出列操作但它们不会相互影响。提示：从q中取出所有元素再将它们插入q和r。
答：
 
 import java.util.Iterator;
public class Queue<Item> implements Iterable<Item>
{
    private int N;
    private Node first;
    private Node last;
    
    private class Node
    {
        Item item;
        Node next;
    }
    
    public Queue()
    {
    }
    public  Queue(Queue q)
    {
         for(Object i:q)
        {
           //
           Node oldlast=last;
           last=new Node();
           last.item=(Item) i;
           last.next=null;
           if(isEmpty())
               first=last;
           else
                oldlast.next=last;
           N++;
        }
     }
    
    public boolean isEmpty()
    {return N==0;}
    
    public int size()
    {return N;}
    
    public void enqueue(Item item)
    {
        Node oldlast=last;
        last=new Node();
        last.item=item;
        last.next=null;
        if(isEmpty())
            first=last;
        else
            oldlast.next=last;
        N++;
    }
    
    public Item dequeue()
    {
        Item item=first.item;
        first=first.next;
        if(isEmpty()) last=null;
        N--;
        return item;
   }
    
    public Iterator<Item> iterator()  {return new ListIterator();}
    
    private class ListIterator implements Iterator<Item>
    {
        private Node current=first;
        public boolean hasNext(){return current!=null;}
        public void remove(){}
        public Item next()
        {
            Item item=current.item;
            current=current.next;
            return item;
        }//end next
      }//end class ListIterator
    public static void main(String[] args)
    {
        Queue<String> q=new Queue<String>();
        while(!StdIn.isEmpty())
        {
            String item=StdIn.readString();
            q.enqueue(item);
        }//end while
        

        StdOut.println("---Queue q is:");
        for(String item:q)
        StdOut.println(item+" ");
        //
        Queue<String> r=new Queue<String>(q);
        //
        StdOut.println("---After r=new Queue<Item>(q)  q is:");
        for(String item:q)
        StdOut.println(item+" ");
        //
        q.dequeue();
        StdOut.println("---After q.dequeue  q is:");
        for(String item:q)
        StdOut.println(item+" ");
        //
        StdOut.println("---Queue r is:");
        for(String item:r)
          StdOut.println(item+" ");
        
    }//end main
}//end class