batik-dom/src/main/java/org/apache/batik/dom/util/HashTable.java

/*

   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.

 */
package org.apache.batik.dom.util;

import java.io.Serializable;

/**
 * A simple hashtable, not synchronized, with fixed load factor.
 *
 * @author <a href="mailto:stephane@hillion.org">Stephane Hillion</a>
 * @version $Id$
 */
public class HashTable implements Serializable {

    /**
     * The initial capacity
     */
    protected static final int INITIAL_CAPACITY = 11;

    /**
     * The underlying array
     */
    protected Entry[] table;

    /**
     * The number of entries
     */
    protected int count;

    /**
     * Creates a new table.
     */
    public HashTable() {
        table = new Entry[INITIAL_CAPACITY];
    }

    /**
     * Creates a new table.
     *
     * @param c The initial capacity.
     */
    public HashTable( int c ) {
        table = new Entry[c];
    }

    /**
     * Creates a copy of the given HashTable object.
     * @param t The table to copy.
     */
    public HashTable( HashTable t ) {
        count = t.count;
        table = new Entry[t.table.length];
        for ( int i = 0; i < table.length; i++ ) {
            Entry e = t.table[ i ];
            Entry n = null;
            if ( e != null ) {
                n = new Entry( e.hash, e.key, e.value, null );
                table[ i ] = n;
                e = e.next;
                while ( e != null ) {
                    n.next = new Entry( e.hash, e.key, e.value, null );
                    n = n.next;
                    e = e.next;
                }
            }
        }
    }

    /**
     * Returns the size of this table.
     */
    public int size() {
        return count;
    }

    /**
     * Gets the value of a variable
     * @return the value or null
     */
    public Object get(Object key) {
        int hash  = key == null ? 0 : key.hashCode() & 0x7FFFFFFF;
        int index = hash % table.length;

        for (Entry e = table[index]; e != null; e = e.next) {
            if (e.hash == hash
                          && (e.key == null && key == null
                              || e.key != null && e.key.equals(key))) {
                return e.value;
            }
        }
        return null;
    }

    /**
     * Sets a new value for the given variable
     * @return the old value or null
     */
    public Object put(Object key, Object value) {
        int hash  = key == null ? 0 : key.hashCode() & 0x7FFFFFFF;
        int index = hash % table.length;

        for (Entry e = table[index]; e != null; e = e.next) {
            if (e.hash == hash
                          && (e.key == null && key == null
                              || e.key != null && e.key.equals(key))) {
                Object old = e.value;
                e.value = value;
                return old;
            }
        }

        // The key is not in the hash table
        int len = table.length;
        if (count++ >= (len - ( len >> 2 ))) {
            // more than 75% loaded: grow
            rehash();
            index = hash % table.length;
        }

        Entry e = new Entry(hash, key, value, table[index]);
        table[index] = e;
        return null;
    }

    /**
     * Removes an entry from the table.
     *
     * @return the value or null.
     */
    public Object remove( Object key ) {
        int hash = key == null ? 0 : key.hashCode() & 0x7FFFFFFF;
        int index = hash % table.length;

        Entry p = null;
        for ( Entry e = table[ index ]; e != null; e = e.next ) {
            if ( e.hash == hash
                    && ( e.key == null && key == null
                    || e.key != null && e.key.equals( key ) ) ) {
                Object result = e.value;
                if ( p == null ) {
                    table[ index ] = e.next;
                } else {
                    p.next = e.next;
                }
                count--;
                return result;
            }
            p = e;
        }
        return null;
    }

    /**
     * Returns the key at the given position or null.
     */
    public Object key( int index ) {
        if ( index < 0 || index >= count ) {
            return null;
        }
        int j = 0;
        for (Entry aTable : table) {
            Entry e = aTable;
            if (e == null) {
                continue;
            }
            do {
                if (j++ == index) {
                    return e.key;
                }
                e = e.next;
            } while (e != null);
        }
        return null;
    }

    /**
     * Returns the item at the given position.
     */
    public Object item( int index ) {
        if ( index < 0 || index >= count ) {
            return null;
        }
        int j = 0;
        for (Entry aTable : table) {
            Entry e = aTable;
            if (e == null) {
                continue;
            }
            do {
                if (j++ == index) {
                    return e.value;
                }
                e = e.next;
            } while (e != null);
        }
        return null;
    }

    /**
     * Clears the map.
     */
    public void clear() {
        for ( int i = 0; i < table.length; i++ ) {
            table[ i ] = null;
        }
        count = 0;
    }

    /**
     * Rehash the table
     */
    protected void rehash() {
        Entry[] oldTable = table;

        table = new Entry[oldTable.length * 2 + 1];

        for ( int i = oldTable.length - 1; i >= 0; i-- ) {
            for ( Entry old = oldTable[ i ]; old != null; ) {
                Entry e = old;
                old = old.next;

                int index = e.hash % table.length;
                e.next = table[ index ];
                table[ index ] = e;
            }
        }
    }

    /**
     * To manage collisions
     */
    protected static class Entry
            implements Serializable {

        /**
         * The hash code
         */
        public int hash;

        /**
         * The key
         */
        public Object key;

        /**
         * The value
         */
        public Object value;

        /**
         * The next entry
         */
        public Entry next;

        /**
         * Creates a new entry
         */
        public Entry( int hash, Object key, Object value, Entry next ) {
            this.hash = hash;
            this.key = key;
            this.value = value;
            this.next = next;
        }
    }
}