Computer Science/61b/Homework/hw5/list/ListNode.java

This page contains computer code. Unlike all articles on the lensowiki, which are released under the GFDL, this code is released under the GPL.

Copyright 2006, 2007 Paul Borokhov. All rights reserved.

This code is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

The code is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

/* ListNode.java */

package list;

/**
 *  A ListNode is a mutable node in a list.  No implementation is provided.
 *
 *  DO NOT CHANGE THIS FILE.
 **/

public abstract class ListNode {

  /**
   *  item references the item stored in the current node.
   *  myList references the List that contains this node.
   *
   *  DO NOT CHANGE THE FOLLOWING FIELD DECLARATIONS.
   */

  protected Object item;
  protected List myList;

  /**
   *  isValidNode returns true if this node is valid; false otherwise.
   *  By default, an invalid node is one that doesn't belong to a list (myList
   *  is null), but subclasses can override this definition.
   *
   *  @return true if this node is valid; false otherwise.
   *
   *  Performance:  runs in O(1) time.
   */
  public boolean isValidNode() {
    return myList != null;
  }

  /**
   *  item() returns this node's item.  If this node is invalid,
   *  throws an exception.
   *
   *  @return the item stored in this node.
   *
   *  Performance:  runs in O(1) time.
   */
  public Object item() throws InvalidNodeException {
    if (!isValidNode()) {
      throw new InvalidNodeException();
    }
    return item;
  }

  /**
   *  setItem() sets this node's item to "item".  If this node is invalid,
   *  throws an exception.
   *
   *  Performance:  runs in O(1) time.
   */
  public void setItem(Object item) throws InvalidNodeException {
    if (!isValidNode()) {
      throw new InvalidNodeException();
    }
    this.item = item;
  }

  /**
   *  next() returns the node following this node.  If this node is invalid,
   *  throws an exception.
   *
   *  @return the node following this node.
   *  @exception InvalidNodeException if this node is not valid.
   */
  public abstract ListNode next() throws InvalidNodeException;

  /**
   *  prev() returns the node preceding this node.  If this node is invalid,
   *  throws an exception.
   *
   *  @param node the node whose predecessor is sought.
   *  @return the node preceding this node.
   *  @exception InvalidNodeException if this node is not valid.
   */
  public abstract ListNode prev() throws InvalidNodeException;

  /**
   *  insertAfter() inserts an item immediately following this node.  If this
   *  node is invalid, throws an exception.
   *
   *  @param item the item to be inserted.
   *  @exception InvalidNodeException if this node is not valid.
   */
  public abstract void insertAfter(Object item) throws InvalidNodeException;

  /**
   *  insertBefore() inserts an item immediately preceding this node.  If this
   *  node is invalid, throws an exception.
   *
   *  @param item the item to be inserted.
   *  @exception InvalidNodeException if this node is not valid.
   */
  public abstract void insertBefore(Object item) throws InvalidNodeException;

  /**
   *  remove() removes this node from its List.  If this node is invalid,
   *  throws an exception.
   *
   *  @exception InvalidNodeException if this node is not valid.
   */
  public abstract void remove() throws InvalidNodeException; 
}