package t234;
/**
* Represents the empty state of a 2-3-4 tree.  EmptyNode is an example of the
* Null object pattern.
<pre>
Since there is conceptually only one empty state for all the 2-3-4 trees,
EmptyNode is implemented with the Singleton pattern.
</pre>
* @since 11/13/01
* @author Dung X. Nguyen, Copyright 2001 - All Rights Reserved.
*/
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: just asks the owner to change its state to a Node2.
    * @param n
    * @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 ("{}");
    }
}