org.apache.xml.dtm.ref.DTMStringPool Maven / Gradle / Ivy
/*
* 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