public class LinkedStack<E> extends AbstractStack<E> {

private class Node<E> {

E data;

Node<E> next;

Node(E data, Node<E> next) {

this.data = data;

this.next = next;

}

}

private Node<E> head;

public void push(E item) {

head = new Node<E>(item, head);

}

public E removeNext() {

E answer = head.data;

head = head.next;

return answer;

}

public boolean isEmpty() {

return (head == null);

}

public static void main(String[] args) {

LinkedStack<Integer> ints = new LinkedStack<>();

ints.push(1);

ints.push(2);

ints.push(3);

System.out.println(ints.pop());

System.out.println(ints.pop());

System.out.println(ints.pop());

System.out.println(ints.pop());

}

}