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/*
 * 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.commons.collections4.map;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.lang.ref.Reference;

/**
 * A Map implementation that allows mappings to be
 * removed by the garbage collector and matches keys and values based
 * on == not equals().
 * 

*

* When you construct a ReferenceIdentityMap, you can specify what kind * of references are used to store the map's keys and values. * If non-hard references are used, then the garbage collector can remove * mappings if a key or value becomes unreachable, or if the JVM's memory is * running low. For information on how the different reference types behave, * see {@link Reference}. *

* Different types of references can be specified for keys and values. * The default constructor uses hard keys and soft values, providing a * memory-sensitive cache. *

* This map is similar to * {@link org.apache.commons.collections4.map.ReferenceMap ReferenceMap}. * It differs in that keys and values in this class are compared using ==. *

* 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. *

* This {@link java.util.Map Map} implementation does not allow null elements. * Attempting to add a null key or value to the map will raise a NullPointerException. *

* This implementation is not synchronized. * You can use {@link java.util.Collections#synchronizedMap} to * provide synchronized access to a ReferenceIdentityMap. * Remember that synchronization will not stop the garbage collector removing entries. *

* All the available iterators can be reset back to the start by casting to * ResettableIterator and calling reset(). *

* Note that ReferenceIdentityMap is not synchronized and is not thread-safe. * If you wish to use this map from multiple threads concurrently, you must use * appropriate synchronization. The simplest approach is to wrap this map * using {@link java.util.Collections#synchronizedMap}. This class may throw * exceptions when accessed by concurrent threads without synchronization. * * @see java.lang.ref.Reference * * @since 3.0 (previously in main package v2.1) * @version $Id: ReferenceIdentityMap.java 1477799 2013-04-30 19:56:11Z tn $ */ public class ReferenceIdentityMap extends AbstractReferenceMap implements Serializable { /** Serialization version */ private static final long serialVersionUID = -1266190134568365852L; /** * Constructs a new ReferenceIdentityMap that will * use hard references to keys and soft references to values. */ public ReferenceIdentityMap() { super(ReferenceStrength.HARD, ReferenceStrength.SOFT, DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, false); } /** * Constructs a new ReferenceIdentityMap that will * use the specified types of references. * * @param keyType the type of reference to use for keys; * must be {@link AbstractReferenceMap.ReferenceStrength#HARD HARD}, * {@link AbstractReferenceMap.ReferenceStrength#SOFT SOFT}, * {@link AbstractReferenceMap.ReferenceStrength#WEAK WEAK} * @param valueType the type of reference to use for values; * must be {@link AbstractReferenceMap.ReferenceStrength#HARD HARD}, * {@link AbstractReferenceMap.ReferenceStrength#SOFT SOFT}, * {@link AbstractReferenceMap.ReferenceStrength#WEAK WEAK} */ public ReferenceIdentityMap(final ReferenceStrength keyType, final ReferenceStrength valueType) { super(keyType, valueType, DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, false); } /** * Constructs a new ReferenceIdentityMap that will * use the specified types of references. * * @param keyType the type of reference to use for keys; * must be {@link AbstractReferenceMap.ReferenceStrength#HARD HARD}, * {@link AbstractReferenceMap.ReferenceStrength#SOFT SOFT}, * {@link AbstractReferenceMap.ReferenceStrength#WEAK WEAK} * @param valueType the type of reference to use for values; * must be {@link AbstractReferenceMap.ReferenceStrength#HARD HARD}, * {@link AbstractReferenceMap.ReferenceStrength#SOFT SOFT}, * {@link AbstractReferenceMap.ReferenceStrength#WEAK WEAK} * @param purgeValues should the value be automatically purged when the * key is garbage collected */ public ReferenceIdentityMap(final ReferenceStrength keyType, final ReferenceStrength valueType, final boolean purgeValues) { super(keyType, valueType, DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, purgeValues); } /** * Constructs a new ReferenceIdentityMap with the * specified reference types, load factor and initial capacity. * * @param keyType the type of reference to use for keys; * must be {@link AbstractReferenceMap.ReferenceStrength#HARD HARD}, * {@link AbstractReferenceMap.ReferenceStrength#SOFT SOFT}, * {@link AbstractReferenceMap.ReferenceStrength#WEAK WEAK} * @param valueType the type of reference to use for values; * must be {@link AbstractReferenceMap.ReferenceStrength#HARD HARD}, * {@link AbstractReferenceMap.ReferenceStrength#SOFT SOFT}, * {@link AbstractReferenceMap.ReferenceStrength#WEAK WEAK} * @param capacity the initial capacity for the map * @param loadFactor the load factor for the map */ public ReferenceIdentityMap(final ReferenceStrength keyType, final ReferenceStrength valueType, final int capacity, final float loadFactor) { super(keyType, valueType, capacity, loadFactor, false); } /** * Constructs a new ReferenceIdentityMap with the * specified reference types, load factor and initial capacity. * * @param keyType the type of reference to use for keys; * must be {@link AbstractReferenceMap.ReferenceStrength#HARD HARD}, * {@link AbstractReferenceMap.ReferenceStrength#SOFT SOFT}, * {@link AbstractReferenceMap.ReferenceStrength#WEAK WEAK} * @param valueType the type of reference to use for values; * must be {@link AbstractReferenceMap.ReferenceStrength#HARD HARD}, * {@link AbstractReferenceMap.ReferenceStrength#SOFT SOFT}, * {@link AbstractReferenceMap.ReferenceStrength#WEAK WEAK} * @param capacity the initial capacity for the map * @param loadFactor the load factor for the map * @param purgeValues should the value be automatically purged when the * key is garbage collected */ public ReferenceIdentityMap(final ReferenceStrength keyType, final ReferenceStrength valueType, final int capacity, final float loadFactor, final boolean purgeValues) { super(keyType, valueType, capacity, loadFactor, purgeValues); } //----------------------------------------------------------------------- /** * 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 */ @Override protected int hash(final Object key) { return System.identityHashCode(key); } /** * Gets the hash code for a MapEntry. *

* This implementation uses the identity hash code. * * @param key the key to get a hash code for, may be null * @param value the value to get a hash code for, may be null * @return the hash code, as per the MapEntry specification */ @Override protected int hashEntry(final Object key, final Object value) { return System.identityHashCode(key) ^ System.identityHashCode(value); } /** * Compares two keys for equals. *

* This implementation converts the key from the entry to a real reference * before comparison and uses ==. * * @param key1 the first key to compare passed in from outside * @param key2 the second key extracted from the entry via entry.key * @return true if equal by identity */ @Override protected boolean isEqualKey(final Object key1, Object key2) { key2 = isKeyType(ReferenceStrength.HARD) ? key2 : ((Reference) key2).get(); return key1 == key2; } /** * Compares two values for equals. *

* This implementation uses ==. * * @param value1 the first value to compare passed in from outside * @param value2 the second value extracted from the entry via getValue() * @return true if equal by identity */ @Override protected boolean isEqualValue(final Object value1, final Object value2) { return value1 == value2; } //----------------------------------------------------------------------- /** * Write the map out using a custom routine. */ private void writeObject(final ObjectOutputStream out) throws IOException { out.defaultWriteObject(); doWriteObject(out); } /** * Read the map in using a custom routine. */ private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException { in.defaultReadObject(); doReadObject(in); } }





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