用链表实现栈demo

package cn.aust.zyw.demo;

import java.util.Iterator;

/**
 * Created by zyw on 2016/2/20.
 */
public class Stack<Item> implements Iterable<Item>{
    private Node first;
    private int N;
    private class Node{
        private Item item;
        private Node next;
    }
    public boolean isEmpty(){return first==null;}
    public int size(){return N;}
    public void push(Item item){
        Node oldfirst=first;
        first=new Node();
        first.item=item;
        first.next=oldfirst;
        N++;
    }
    public Item pop(){
        Item item=first.item;
        first=first.next;
        N--;
        return item;
    }
    @Override
    public Iterator<Item> iterator() {
        return new Iterator<Item>() {
            private int i=N;
            @Override
            public boolean hasNext() {
                if(i-->0) return true;
                return false;
            }
            @Override
            public Item next() {
                Item item=first.item;
                first=first.next;
                return item;
            }
        };
    }
    public static void main(String args[]){
        Stack<Double> mystack=new Stack<>();
        mystack.push(1.5);
        mystack.push(1.3);
        mystack.push(1.0);
        Iterator iter=mystack.iterator();
        while(iter.hasNext()){
            System.out.println(iter.next());
        }
    }
}