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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the  "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * $Id: DTMStringPool.java 468653 2006-10-28 07:07:05Z minchau $
 */

package org.apache.xml.dtm.ref;

import java.util.Vector;

import org.apache.xml.utils.IntVector;

/** 

DTMStringPool is an "interning" mechanism for strings. It will * create a stable 1:1 mapping between a set of string values and a set of * integer index values, so the integers can be used to reliably and * uniquely identify (and when necessary retrieve) the strings.

* *

Design Priorities: *

    *
  • String-to-index lookup speed is critical.
  • *
  • Index-to-String lookup speed is slightly less so.
  • *
  • Threadsafety is not guaranteed at this level. * Enforce that in the application if needed.
  • *
  • Storage efficiency is an issue but not a huge one. * It is expected that string pools won't exceed about 2000 entries.
  • *
*

* *

Implementation detail: A standard Hashtable is relatively * inefficient when looking up primitive int values, especially when * we're already maintaining an int-to-string vector. So I'm * maintaining a simple hash chain within this class.

* *

NOTE: There is nothing in the code that has a real dependency upon * String. It would work with any object type that implements reliable * .hashCode() and .equals() operations. The API enforces Strings because * it's safer that way, but this could trivially be turned into a general * ObjectPool if one was needed.

* *

Status: Passed basic test in main().

* */ public class DTMStringPool { Vector m_intToString; static final int HASHPRIME=101; int[] m_hashStart=new int[HASHPRIME]; IntVector m_hashChain; public static final int NULL=-1; /** * Create a DTMStringPool using the given chain size * * @param chainSize The size of the hash chain vector */ public DTMStringPool(int chainSize) { m_intToString=new Vector(); m_hashChain=new IntVector(chainSize); removeAllElements(); // -sb Add this to force empty strings to be index 0. stringToIndex(""); } public DTMStringPool() { this(512); } public void removeAllElements() { m_intToString.removeAllElements(); for(int i=0;i




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