MAX in Stack

class Stack {
  private Node last;

  public void push(Integer value) {

  	if (last == null) {
      last = new Node(value, null, value);
    }
    else {
      Node node = new Node(value, last, (value != null) ?
                           (last.value != null ? Math.max(value, last.value) : value) : last.value);
      last = node;
    }
  }

  public Integer pop() { // get should return the value, not the node

    if (last == null)
      throw new IllegalStateException();

    Node node = last;
    last = last.next;

    return node.value;
  }

  public Integer top() {

    if (last == null)
      throw new IllegalStateException();

    return last.value;
  }

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

  public Optional<Integer> max() { // const
    return Optional.ofNullable(last).map(Node::getMax);
  }

  static class Node {
    public Integer value;
    public Node next;
    public Integer max;

    Node(Integer value, Node next, Integer max) {
      this.value = value;
      this.next = next;
      this.max = max;
    }

    public Integer getMax() {
      return max;
    }

    // getters
  }
}