package lrs;

/**
 * Represents the empty state. Singleton pattern.
 * @author Dung X. Nguyen  Copyright 2000 - All rights reserved.
 * @since 09/22/00
*/
class EmptyNode extends ANode
{
   /**
	 * Singleton Pattern.
	 */
	final static EmptyNode Singleton = new EmptyNode();
   private EmptyNode()
   {
   }

   /**
	 * Throws java.util.NoSuchElementException.
 	 */
	LRStruct getRest(LRStruct owner)
	{
	   throw new java.util.NoSuchElementException ("Empty list has no first.");
   }

   /**
	 * Throws java.util.NoSuchElementException.
 	 */
	Object getFirst(LRStruct owner)
	{
	   throw new java.util.NoSuchElementException ("Empty list has no first.");
   }

   /**
	 * Throws java.util.NoSuchElementException.
 	 */
	void setRest(LRStruct tail, LRStruct owner)
	{
	   throw new java.util.NoSuchElementException ("Empty list has no tail.");
   }

   /**
	 * Throws java.util.NoSuchElementException.
 	 */
	void setFirst(Object dat, LRStruct owner)
	{
	   throw new java.util.NoSuchElementException ("Empty list has no first.");
   }

	void insertFront(Object dat, LRStruct owner)
	{
	   owner.setHead(new NENode(dat));
   }

   /**
	 * Throws java.util.NoSuchElementException.
 	 */
	Object removeFront(LRStruct owner)
	{
	   throw new java.util.NoSuchElementException ("Empty list has no front.");
   }

   /**
   * Calls the visitor's empty case.
   */
   Object execute(IAlgo algo, Object input, LRStruct owner)
   {
      return algo.forEmpty(owner, input);
   }

}