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HSQLDB example source code file (HashIndex.java)

This example HSQLDB source code file (HashIndex.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - HSQLDB tags/keywords

hashindex, hashindex

The HSQLDB HashIndex.java source code

/* Copyright (c) 2001-2008, The HSQL Development Group
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer.
 *
 * 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.
 *
 * Neither the name of the HSQL Development Group nor the names of its
 * contributors may be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL HSQL DEVELOPMENT GROUP, HSQLDB.ORG,
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */


package org.hsqldb.store;

/**
 * A chained bucket hash index implementation.
 *
 * hashTable and linkTable are arrays of signed integral types. This
 * implementation uses int as the type but short or byte can be used for
 * smaller index sizes (cardinality).
 *
 * hashTable[index] contains the pointer to the first node with
 * (index == hash modulo hashTable.length) or -1 if there is no corresponding
 * node. linkTable[{0,newNodePointer}] (the range between 0 and newNodePointer)
 * contains either the pointer to the next node or -1 if there is no
 * such node. reclaimedNodeIndex contains a pointer to an element
 * of linkTable which is the first element in the list of reclaimed nodes
 * (nodes no longer in index) or -1 if there is no such node.
 *
 * elemenet at and above linkTable[newNodePointer] have never been used
 * as a node and their contents is not significant.
 *
 * @author fredt@users
 * @version 1.7.2
 * @since 1.7.2
 */
class HashIndex {

    int[]   hashTable;
    int[]   linkTable;
    int     newNodePointer;
    int     elementCount;
    int     reclaimedNodePointer = -1;
    boolean fixedSize;

    HashIndex(int hashTableSize, int capacity, boolean fixedSize) {

        reset(hashTableSize, capacity);

        this.fixedSize = fixedSize;
    }

    /**
     * Reset the structure with a new size as empty.
     *
     * @param hashTableSize
     * @param capacity
     */
    void reset(int hashTableSize, int capacity) {

        int[] newHT = new int[hashTableSize];
        int[] newLT = new int[capacity];

        // allocate memory before assigning
        hashTable = newHT;
        linkTable = newLT;

        resetTables();
    }

    void resetTables() {

        int   to       = hashTable.length;
        int[] intArray = hashTable;

        while (--to >= 0) {
            intArray[to] = -1;
        }

        newNodePointer       = 0;
        elementCount         = 0;
        reclaimedNodePointer = -1;
    }

    /**
     * Reset the index as empty.
     */
    void clear() {

        int   to       = linkTable.length;
        int[] intArray = linkTable;

        while (--to >= 0) {
            intArray[to] = 0;
        }

        resetTables();
    }

    /**
     * @param hash
     */
    int getHashIndex(int hash) {
        return (hash & 0x7fffffff) % hashTable.length;
    }

    /**
     * Return the array index for a hash.
     *
     * @param hash the hash value used for indexing
     * @return either -1 or the first node for this hash value
     */
    int getLookup(int hash) {

        int index = (hash & 0x7fffffff) % hashTable.length;

        return hashTable[index];
    }

    /**
     * This looks from a given node, so the parameter is always > -1.
     *
     * @param valid lookup node to look from
     * @return either -1 or the next node from this node
     */
    int getNextLookup(int lookup) {
        return linkTable[lookup];
    }

    /**
     * Link a new node to the end of the linked for a hash index.
     *
     * @param index an index into hashTable
     * @param lastLookup either -1 or the node to which the new node will be linked
     * @return the new node
     */
    int linkNode(int index, int lastLookup) {

        // get the first reclaimed slot
        int lookup = reclaimedNodePointer;

        if (lookup == -1) {
            lookup = newNodePointer++;
        } else {

            // reset the first reclaimed slot
            reclaimedNodePointer = linkTable[lookup];
        }

        // link the node
        if (lastLookup == -1) {
            hashTable[index] = lookup;
        } else {
            linkTable[lastLookup] = lookup;
        }

        linkTable[lookup] = -1;

        elementCount++;

        return lookup;
    }

    /**
     * Unlink a node from a linked list and link into the reclaimed list.
     *
     * @param index an index into hashTable
     * @param lastLookup either -1 or the node to which the target node is linked
     * @param lookup the node to remove
     */
    void unlinkNode(int index, int lastLookup, int lookup) {

        // unlink the node
        if (lastLookup == -1) {
            hashTable[index] = linkTable[lookup];
        } else {
            linkTable[lastLookup] = linkTable[lookup];
        }

        // add to reclaimed list
        linkTable[lookup]    = reclaimedNodePointer;
        reclaimedNodePointer = lookup;

        elementCount--;
    }

    /**
     * Remove a node that has already been unlinked. This is not required
     * for index operations. It is used only when the row needs to be removed
     * from the data structures that store the actual indexed data and the
     * nodes need to be contiguous.
     *
     * @param lookup the node to remove
     * @return true if node found in unlinked state
     */
    boolean removeEmptyNode(int lookup) {

        boolean found      = false;
        int     lastLookup = -1;

        for (int i = reclaimedNodePointer; i >= 0;
                lastLookup = i, i = linkTable[i]) {
            if (i == lookup) {
                if (lastLookup == -1) {
                    reclaimedNodePointer = linkTable[lookup];
                } else {
                    linkTable[lastLookup] = linkTable[lookup];
                }

                found = true;

                break;
            }
        }

        if (!found) {
            return false;
        }

        for (int i = 0; i < newNodePointer; i++) {
            if (linkTable[i] > lookup) {
                linkTable[i]--;
            }
        }

        System.arraycopy(linkTable, lookup + 1, linkTable, lookup,
                         newNodePointer - lookup - 1);

        linkTable[newNodePointer - 1] = 0;

        newNodePointer--;

        for (int i = 0; i < hashTable.length; i++) {
            if (hashTable[i] > lookup) {
                hashTable[i]--;
            }
        }

        return true;
    }
}

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