1.2 Pushdown stack (linked-list implementation)

Stack.java

package containers;

import java.util.Iterator;

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

    private Node first;
    private int size;

    private class Node {
        T item;
        Node next;
    }

    public boolean isEmpty(){
      return first == null;
    }

    public int size() {
        return size;
    }


    public void push(T item){
        Node oldFirst = this.first;
        first = new Node();
        first.item = item;
        first.next = oldFirst;
        size++;
    }

    public T pop() {
        T result = first.item;
        first = first.next;
        size--;
        return result;

    }

    public Iterator<T> iterator() {

           return new ReverseArrayIterator();
       }

       private class ReverseArrayIterator<T> implements Iterator<T> {

           private int index = size;

           public boolean hasNext() {
               return index>0;
           }

           public T next() {
               return (T) items[--index];
           }

           public void remove() {
           }
       }
}