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The Apache Commons Codec package contains simple encoder and decoders for various formats such as Base64 and Hexadecimal. In addition to these widely used encoders and decoders, the codec package also maintains a collection of phonetic encoding utilities.
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/*   Copyright 2004 The Apache Software Foundation
 *
 *   Licensed 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.
 */

package org.apache.xmlbeans;

import javax.xml.namespace.QName;

/**
 * A cache that can be used to pool QName instances.  Each thread has one.
 */ 
public final class QNameCache
{
    private static final float DEFAULT_LOAD = 0.70f;
    private final float loadFactor;
    private int numEntries = 0;
    private int threshold;
    private int hashmask;
    private QName[] table;

    /**
     * Creates a QNameCache with the given initialCapacity and loadFactor.
     * 
     * @param initialCapacity the number of entries to initially make space for
     * @param loadFactor a number to control the density of the hashtable
     */ 
    public QNameCache(int initialCapacity, float loadFactor)
    {
        assert initialCapacity > 0;
        assert loadFactor > 0 && loadFactor < 1;

        // Find a power of 2 >= initialCapacity
        int capacity = 16;
        while (capacity < initialCapacity) 
            capacity <<= 1;
    
        this.loadFactor = loadFactor;
        this.hashmask = capacity - 1;
        threshold = (int)(capacity * loadFactor);
        table = new QName[capacity];
    }

    /**
     * Creates a QNameCache with the given initialCapacity.
     * 
     * @param initialCapacity the number of entries to initially make space for
     */ 
    public QNameCache(int initialCapacity)
    {
        this(initialCapacity, DEFAULT_LOAD);
    }

    public QName getName(String uri, String localName)
    {
        return getName( uri, localName, "" );
    }
    
    /**
     * Fetches a QName with the given namespace and localname.
     * Creates one if one is not found in the cache.
     * 
     * @param uri the namespace
     * @param localName the localname
     * @param prefix the prefix
     * @return the cached QName
     */ 
    public QName getName(String uri, String localName, String prefix)
    {
        /*
        return new QName(uri, localName, prefix);
        */
        assert localName != null;
        
        if (uri == null) uri = "";
        if (prefix == null) prefix = "";

        int index = hash(uri, localName, prefix) & hashmask;
        while (true) {
            QName q = table[index];
            if (q == null)
            {
                numEntries++;
                if (numEntries >= threshold)
                    rehash();

                return table[index] = new QName(uri, localName, prefix);
            }
            else if (equals(q, uri, localName, prefix))
                return q;
            else 
                index = (index-1) & hashmask;
        }
    }

    private void rehash()
    {
        int newLength = table.length * 2;
        QName[] newTable = new QName[newLength];
        int newHashmask = newLength - 1;

        for (int i = 0 ; i < table.length ; i++)
        {
            QName q = table[i];
            if (q != null)
            {
                int newIndex =
                    hash( q.getNamespaceURI(), q.getLocalPart(), q.getPrefix() ) & newHashmask;
                
                while (newTable[newIndex] != null)
                    newIndex = (newIndex - 1) & newHashmask;
                
                newTable[newIndex] = q;
            }
        }

        table = newTable;
        hashmask = newHashmask;
        threshold = (int) (newLength * loadFactor);
    }
    
    private static int hash(String uri, String localName, String prefix)
    {
        int h = 0;

        h += prefix.hashCode() << 10;
        h += uri.hashCode() << 5;
        h += localName.hashCode();

        return h;
    }

    private static boolean equals(QName q, String uri, String localName, String prefix)
    {
        return
            q.getLocalPart().equals(localName) &&
                q.getNamespaceURI().equals(uri) &&
                    q.getPrefix().equals(prefix);
    }
}