// generics/LinkedStack.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// A stack implemented with an internal linked structure

public class LinkedStack<T> {
 private static class Node<U> {
 U item;
 Node<U> next;
 Node() { item = null; next = null; }
 Node(U item, Node<U> next) {
 this.item = item;
 this.next = next;
 }
 boolean end() {
 return item == null && next == null;
 }
 }
 private Node<T> top = new Node<>(); // End sentinel
 public void push(T item) {
 top = new Node<>(item, top);
 }
 public T pop() {
 T result = top.item;
 if(!top.end())
 top = top.next;
 return result;
 }
 public static void main(String[] args) {
 LinkedStack<String> lss = new LinkedStack<>();
 for(String s : "Phasers on stun!".split(" "))
 lss.push(s);
 String s;
 while((s = lss.pop()) != null)
 System.out.println(s);
 }
}
/* Output:
stun!
on
Phasers
*/