package t234;
/**
 * Represents the empty state of a 2-3-4 tree.  EmptyNode is an example of the
 * Null object pattern.
 *
 * Since there is conceptually only one empty state for all the 2-3-4 trees,
 * EmptyNode is implemented with the Singleton pattern.
 *
 * @since 04/18/01
 * @author Dung X. Nguyen, Copyright 2000 - All Rights Reserved.
 * @author Alan L. Cox
 */
class EmptyNode extends ANode234
{
  final public static EmptyNode Singleton = new EmptyNode();

  private EmptyNode()
  {
  }

  final boolean isEmpty(Tree234 owner)
  {
    return true;
  }

  /**
   * Inserts an Integer into the owner tree without duplication.
   *
   * This is the EmptyNode.  So just asks the owner to change its
   * state to a Node2.
   *
   * @param n != null.
   * @param owner the owner of this EmptyNode.
   */
  final void insert(Tree234 owner, Integer n)
  {
    owner.changeRoot(new Node2(n));
  }

  final void insertHelper(Tree234 ownerPo, Tree234 owner, Integer n)
  {
    owner.insert(n);	// can call insert(owner, n) instead.
  }

  /**
   * @throw IllegalStateException("Empty tree cannot be a parent!").
   */
  final void attach(Tree234 owner, Tree234 lTree, Integer n, Tree234 rTree)
  {
    throw new IllegalStateException("Empty tree cannot be a parent!");
  }

  final void drawRootAndSubtrees(int level)
  {
    System.out.print("{}");
  }
}