identitymap.java

rule engine drools-2.0-beta-18

package org.drools.util;
/*
 *  Copyright 2003-2004 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.
 */

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Map;

/**
 * A <code>Map</code> implementation that matches keys and values based on
 * <code>==</code> not <code>equals()</code>.
 * <p>
 * This map will violate the detail of various Map and map view contracts. As a
 * general rule, don't compare this map to other maps.
 * 
 * @since Commons Collections 3.0
 * @version $Revision: 1.2 $ $Date: 2004/11/19 02:15:18 $
 * 
 * @author java util HashMap
 * @author Stephen Colebourne
 */
public class IdentityMap extends AbstractHashedMap
    implements
    Serializable,
    Cloneable
{

    /** Serialisation version */
    private static final long serialVersionUID = 2028493495224302329L;

    /**
     * Constructs a new empty map with default size and load factor.
     */
    public IdentityMap()
    {
        super( DEFAULT_CAPACITY,
               DEFAULT_LOAD_FACTOR,
               DEFAULT_THRESHOLD );
    }

    /**
     * Constructs a new, empty map with the specified initial capacity.
     * 
     * @param initialCapacity
     *            the initial capacity
     * @throws IllegalArgumentException
     *             if the initial capacity is less than one
     */
    public IdentityMap(int initialCapacity)
    {
        super( initialCapacity );
    }

    /**
     * Constructs a new, empty map with the specified initial capacity and load
     * factor.
     * 
     * @param initialCapacity
     *            the initial capacity
     * @param loadFactor
     *            the load factor
     * @throws IllegalArgumentException
     *             if the initial capacity is less than one
     * @throws IllegalArgumentException
     *             if the load factor is less than zero
     */
    public IdentityMap(int initialCapacity,
                       float loadFactor)
    {
        super( initialCapacity,
               loadFactor );
    }

    /**
     * Constructor copying elements from another map.
     * 
     * @param map
     *            the map to copy
     * @throws NullPointerException
     *             if the map is null
     */
    public IdentityMap(Map map)
    {
        super( map );
    }

    // -----------------------------------------------------------------------
    /**
     * Gets the hash code for the key specified. This implementation uses the
     * identity hash code.
     * 
     * @param key
     *            the key to get a hash code for
     * @return the hash code
     */
    protected int hash(Object key)
    {
        return System.identityHashCode( key );
    }

    /**
     * Compares two keys for equals. This implementation uses <code>==</code>.
     * 
     * @param key1
     *            the first key to compare
     * @param key2
     *            the second key to compare
     * @return true if equal by identity
     */
    protected boolean isEqualKey(Object key1,
                                 Object key2)
    {
        return (key1 == key2);
    }

    /**
     * Compares two values for equals. This implementation uses <code>==</code>.
     * 
     * @param value1
     *            the first value to compare
     * @param value2
     *            the second value to compare
     * @return true if equal by identity
     */
    protected boolean isEqualValue(Object value1,
                                   Object value2)
    {
        return (value1 == value2);
    }

    /**
     * Creates an entry to store the data. This implementation creates an
     * IdentityEntry instance.
     * 
     * @param next
     *            the next entry in sequence
     * @param hashCode
     *            the hash code to use
     * @param key
     *            the key to store
     * @param value
     *            the value to store
     * @return the newly created entry
     */
    protected HashEntry createEntry(HashEntry next,
                                    int hashCode,
                                    Object key,
                                    Object value)
    {
        return new IdentityEntry( next,
                                  hashCode,
                                  key,
                                  value );
    }

    // -----------------------------------------------------------------------
    /**
     * HashEntry
     */
    protected static class IdentityEntry extends HashEntry
    {

        protected IdentityEntry(HashEntry next,
                                int hashCode,
                                Object key,
                                Object value)
        {
            super( next,
                   hashCode,
                   key,
                   value );
        }

        public boolean equals(Object obj)
        {
            if ( obj == this )
            {
                return true;
            }
            if ( obj instanceof Map.Entry == false )
            {
                return false;
            }
            Map.Entry other = (Map.Entry) obj;
            return (getKey( ) == other.getKey( )) && (getValue( ) == other.getValue( ));
        }

        public int hashCode()
        {
            return System.identityHashCode( getKey( ) ) ^ System.identityHashCode( getValue( ) );
        }
    }

    // -----------------------------------------------------------------------
    /**
     * Clones the map without cloning the keys or values.
     * 
     * @return a shallow clone
     */
    public Object clone()
    {
        return super.clone( );
    }

    /**
     * Write the map out using a custom routine.
     */
    private void writeObject(ObjectOutputStream out) throws IOException
    {
        out.defaultWriteObject( );
        doWriteObject( out );
    }

    /**
     * Read the map in using a custom routine.
     */
    private void readObject(ObjectInputStream in) throws IOException,
                                                 ClassNotFoundException
    {
        in.defaultReadObject( );
        doReadObject( in );
    }

}