package Stack_Java;

import java.util.*;

public class LinkedStack2 {
  private static class Node {
    private Object data;
    private Node next = null;
    private Node(Object dataItem, Node nextRef) {
      data = dataItem;
      next = nextRef;
    }
  } //end of the private class Node

  private Node stackTop = null;
  
  public Object push(Object item) {
    stackTop = new Node(item, stackTop);
    return item;
  }

  public Object pop() {
      if (empty()) {
      throw new EmptyStackException();
    }
    else {
      Object result = stackTop.data;
      stackTop = stackTop.next;
      return result;
    }
  }

  public Object peek() {
      if (empty()) {
      throw new EmptyStackException();
    }
    else {
      return stackTop.data;
    }
  }

  public boolean empty() {
    return stackTop == null;
  }
}