LinkedList.java

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<T>();
    
    public T pop(){
      T result = top.item;
      if(!top.end()){
        top = top.next;
      }
      return result;
    }
    
    public void push(T item){
      top = new Node<T>(item, top);
    }
  }
}