src/org/apache/xml/utils/Trie.java

/*
 * The Apache Software License, Version 1.1
 *
 *
 * Copyright (c) 1999 The Apache Software Foundation.  All rights 
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:  
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
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 * 4. The names "Xalan" and "Apache Software Foundation" must
 *    not be used to endorse or promote products derived from this
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 *
 * 5. Products derived from this software may not be called "Apache",
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 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation and was
 * originally based on software copyright (c) 1999, Lotus
 * Development Corporation., http://www.lotus.com.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */
package org.apache.xml.utils;

/**
 * <meta name="usage" content="internal"/>
 * A digital search trie for 7-bit ASCII text
 * The API is a subset of java.util.Hashtable
 * The key must be a 7-bit ASCII string
 * The value may be any Java Object
 */
public class Trie
{

  /** Size of the m_nextChar array.  */
  public static final int ALPHA_SIZE = 128;

  /** The root node of the tree.    */
  Node m_Root;

  /**
   * Construct the trie.
   */
  public Trie()
  {
    m_Root = new Node();
  }

  /**
   * Put an object into the trie for lookup.
   *
   * @param key must be a 7-bit ASCII string
   * @param value any java object.
   *
   * @return The old object that matched key, or null.
   */
  public Object put(String key, Object value)
  {

    final int len = key.length();
    Node node = m_Root;

    for (int i = 0; i < len; i++)
    {
      Node nextNode = node.m_nextChar[Character.toUpperCase(key.charAt(i))];

      if (nextNode != null)
      {
        node = nextNode;
      }
      else
      {
        for (; i < len; i++)
        {
          Node newNode = new Node();

          node.m_nextChar[Character.toUpperCase(key.charAt(i))] = newNode;
          node = newNode;
        }

        break;
      }
    }

    Object ret = node.m_Value;

    node.m_Value = value;

    return ret;
  }

  /**
   * Get an object that matches the key.
   *
   * @param key must be a 7-bit ASCII string
   *
   * @return The object that matches the key, or null.
   */
  public Object get(String key)
  {

    final int len = key.length();
    Node node = m_Root;

    for (int i = 0; i < len; i++)
    {
      try
      {
        node = node.m_nextChar[Character.toUpperCase(key.charAt(i))];
      }
      catch (ArrayIndexOutOfBoundsException e)
      {

        // the key is not 7-bit ASCII so we won't find it here
        node = null;
      }

      if (node == null)
        return null;
    }

    return node.m_Value;
  }

  /**
   * <meta name="usage" content="internal"/>
   * The node representation for the trie.
   */
  class Node
  {

    /**
     * Constructor, creates a Node[ALPHA_SIZE].
     */
    Node()
    {
      m_nextChar = new Node[ALPHA_SIZE];
      m_Value = null;
    }

    /** The next nodes.   */
    Node m_nextChar[];

    /** The value.   */
    Object m_Value;
  }
}