public class LinkedStack{
    private int size;
    private Node head;

    public LinkedStack(){
        head=new Node(null);
        size=0;
    }

    public void push(Object data){
        Node temp=new Node(data);
        temp.next=head.next;
        head.next=temp;
        size++;

    }

    public void pop(){
        if(size==0){
            System.out.println("Stack Under Flow");
        }
        else{
            size--;
            Node temp= head;
            temp.next=temp.next.next;
        }
    }

    public Object top(){
        return head.next.data;
    }

    public boolean isEmpty(){
        return (size==0);
    }

    public boolean isFull(){
        return false;
    }

    public void display(){
        if(isEmpty()){
            System.out.println("(Empty)");
        }
        else{
            System.out.println("xxxxxx");
            Node temp=head.next;
            while(temp!=null){
                System.out.printf("|%4d",temp.data);
                System.out.println("|");

                temp=temp.next;
            }
            System.out.println("xxxxxx");
        }
    }

    private class Node
    {
        protected Node next;
        protected Object data;

        public Node(Object _data)
        {
            next = null;
            data = _data;
        }

        public Node(Object _data, Node _next)
        {
            next = _next;
            data = _data;
        }

    }
}