Khanh Stack

public class Stack {

        private Node first = null;
        private class Node
        {
            String item;
            Node next = null;
        }

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

        public void push(String item)
        {
            Node oldfirst = first;
            first = new Node();
            first.item = item;
            first.next = oldfirst;
        }
        public void pop()
        {
            if(isEmpty()){
                System.out.print("Stack underflow");
                return;
            }
            String item = first.item;
            first = first.next;
        }

        public String peek(){
            if(isEmpty())
                System.out.print("Stack underflow");
            return first.item;
        }


    public static void main(String[] args) {
        Stack list = new Stack();
        list.push("co");
        list.push("bao");
        list.push("gio");
        list.push("em");
        list.push("nghi");
        list.push("nghi");
        list.push("ve");
        list.push("anh");

        while (!list.isEmpty()) {
            System.out.println(list.peek());
            list.pop();
        }
    }
}