Iterator

import java.util.Iterator;
public class LinkedListStackOfStrings{
    private class Node{
        private String item;
        private Node next;
    }
    public class ListIterator implements Iterator{
        private Node current=first;
        public boolean hasNext(){
            return current!=null;
        }
        public void remove(){
            ;
        }
        public String next(){
            String s=current.item;
            current=current.next;
            return s;
        }
    }
    private Node first=null;
    
    public Iterator iterator(){
        return new ListIterator();
    }
    public boolean isEmpty(){
        if(first==null)
            return true;
        else
            return false;
    }
    public void push(String s){
        Node oldfirst=first;
        first=new Node();
        first.item=s;
        first.next=oldfirst;
             }
    public String pop(){
        if(!isEmpty()){
        String s=first.item;
        first=first.next;
        return s;
        }
        else 
        throw new IllegalArgumentException("Invalid operation!");
    }
}