栈和队列的java实现

package test4;

import java.util.Iterator;

//队列

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

   private Node frist;

   private Node last;

   private int N;

   private class Node{ 
  Item item;
  Node next;

   }
public boolean isEmpty(){ 
return frist==null;
}
public int size(){ 
return N;
}
public void enqueue(Item item){ 
Node old=last;
last=new Node();
last.item=item;
last.next=null;
if(isEmpty()) frist=last;
else old=null;
N++;

}
public Item dequeue(){ 
Item item=frist.item;
frist=frist.next;
if(isEmpty()) last=frist;
N--;
return item;
}

@Override
public Iterator<Item> iterator() {
// TODO Auto-generated method stub
return null;
}

}

import java.util.Iterator;

// 栈

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

    private Node frist;

    private int N;

    private class Node{ 

    Item item;

    Node next;

    }

public boolean isEmpty(){ 
return frist==null;
}
public int size(){ 
return N;
}
public void push(Item item){ 
Node old=frist;
frist=new Node();
frist.item=item;
frist.next=old;
N++;
}
public Item pop(){ 
Item item=frist.item;
frist=frist.next;
N--;
return item;
}

@Override
public Iterator<Item> iterator() {
// TODO Auto-generated method stub
return null;
}

}