/*

 * Cay S. Horstmann & Gary Cornell, Core Java

 * Published By Sun Microsystems Press/Prentice-Hall

 * Copyright (C) 1997 Sun Microsystems Inc.

 * All Rights Reserved.

 *

 * Permission to use, copy, modify, and distribute this 

 * software and its documentation for NON-COMMERCIAL purposes

 * and without fee is hereby granted provided that this 

 * copyright notice appears in all copies. 

 * 

 * THE AUTHORS AND PUBLISHER MAKE NO REPRESENTATIONS OR 

 * WARRANTIES ABOUT THE SUITABILITY OF THE SOFTWARE, EITHER 

 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE 

 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A 

 * PARTICULAR PURPOSE, OR NON-INFRINGEMENT. THE AUTHORS

 * AND PUBLISHER SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED 

 * BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING 

 * THIS SOFTWARE OR ITS DERIVATIVES.

 */

 

/**

 * A simple implementation of a linked list

 * @version 1.02 07 Sep 1996 

 * @author Cay Horstmann

 */



package corejava;



public class LinkedList

{  

  /** 

   * resets the cursor

   */

   

   public void reset()



   {  pre = null;

   }







   /**

    * @return true iff the cursor is not at the end of the

    * list 

    */

   public boolean hasMoreElements() 

   {  return cursor() != null;

   }





   /**

    * move the cursor to the next position

    * @return the current element (before advancing the 

    * position)

    * @exception java.util.NoSuchElementException if already at the

    * end of the list

    */

   public Object nextElement()

   {  if (pre == null) pre = head; else pre = pre.next;

      if (pre == null) 

         throw new java.util.NoSuchElementException();

      return pre.data;

   }





   /**

    * @return the current element under the cursor

    * @exception java.util.NoSuchElementException if already at the

    * end of the list

    */

   

   public Object currentElement() 

   {  Link cur = cursor();

      if (cur == null) 

         throw new java.util.NoSuchElementException();

      return cur.data;

   }



   /**

    * insert before the iterator position

    * @param n the object to insert

    */



   public void insert(Object n)

   {  Link p = new Link(n, cursor());



      if (pre != null)

      {  pre.next = p;

         if (pre == tail) tail = p;

      }

      else

      {  if (head == null) tail = p;

         head = p;

      }



      pre = p;

      len++;

   }



   /**

    * insert after the tail of the list

    * @param n - the value to insert

    */

   

   public void append(Object n)

   {  Link p = new Link(n, null);

      if (head == null) head = tail = p;

      else

      {  tail.next = p;

         tail = p;

      }

      len++;

   }



   /**

    * remove the element under the cursor

    * @return the removed element

    * @exception java.util.NoSuchElementException if already at the 

    * end of the list

    */



   public Object remove()

   {  Link cur = cursor();

      if (cur == null) 

         throw new java.util.NoSuchElementException();

      if (tail == cur) tail = pre;

      if (pre != null)

         pre.next = cur.next;

      else

         head = cur.next;

      len--;

      return cur.data;

   }





   /**

    * @return the number of elements in the list

    */



   public int size() 

   {  return len;

   }



   /**

    * @return an enumeration to iterate through all elements

    * in the list

    */



   public java.util.Enumeration elements() 

   {  return new ListEnumeration(head); 

   }



   public static void main(String[] args)

   {  LinkedList a = new LinkedList();

      for (int i = 1; i <= 10; i++) 

         a.insert(new Integer(i));

      java.util.Enumeration e = a.elements();

      while (e.hasMoreElements())

         System.out.println(e.nextElement());



      a.reset();

      while (a.hasMoreElements())

      {  a.remove();

         a.nextElement();

      }

      a.reset();

      while (a.hasMoreElements())

         System.out.println(a.nextElement());

   }

   

   private Link cursor() 

   {  if (pre == null) return head; else return pre.next;

   }

   

   private Link head;

   private Link tail;

   private Link pre; // predecessor of cursor

   private int len;

}



class Link

{  Object data;

   Link next;

   Link(Object d, Link n) { data = d; next = n; }

}

    /**

    * A class for enumerating a linked list

    * implements the Enumeration interface

    */

    

class ListEnumeration implements java.util.Enumeration

{  public ListEnumeration( Link l)

   {  cursor = l;

   }



   /**

    * @return true iff the iterator is not at the end of the

    * list

    */

   public boolean hasMoreElements() 

   {  return cursor != null;

   }



   /**

    * move the iterator to the next position

    * @return the current element (before advancing the 

    * position)

    * @exception NoSuchElementException if already at the

    * end of the list

    */



   public Object nextElement()

   {  if (cursor == null) 

      throw new java.util.NoSuchElementException();

      Object r = cursor.data;

      cursor = cursor.next;

      return r;

   }

   

   private Link cursor;

}