- /*
- * 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.commons.collections.map;
-
- import java.io.IOException;
- import java.io.ObjectInputStream;
- import java.io.ObjectOutputStream;
- import java.io.Serializable;
- import java.lang.ref.Reference;
-
- /**
- * A <code>Map</code> implementation that allows mappings to be
- * removed by the garbage collector and matches keys and values based
- * on <code>==</code> not <code>equals()</code>.
- * <p>
- * <p>
- * When you construct a <code>ReferenceIdentityMap</code>, 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}.
- * <p>
- * 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.
- * <p>
- * This map is similar to
- * {@link org.apache.commons.collections.map.ReferenceMap ReferenceMap}.
- * It differs in that keys and values in this class are compared using <code>==</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.
- * <p>
- * This {@link Map} implementation does <i>not</i> allow null elements.
- * Attempting to add a null key or value to the map will raise a <code>NullPointerException</code>.
- * <p>
- * This implementation is not synchronized.
- * You can use {@link java.util.Collections#synchronizedMap} to
- * provide synchronized access to a <code>ReferenceIdentityMap</code>.
- * Remember that synchronization will not stop the garbage collecter removing entries.
- * <p>
- * All the available iterators can be reset back to the start by casting to
- * <code>ResettableIterator</code> and calling <code>reset()</code>.
- *
- * @see java.lang.ref.Reference
- *
- * @since Commons Collections 3.0 (previously in main package v2.1)
- * @version $Revision: 1.1 $ $Date: 2004/04/27 21:37:32 $
- *
- * @author Stephen Colebourne
- */
- public class ReferenceIdentityMap extends AbstractReferenceMap implements Serializable {
-
- /** Serialization version */
- private static final long serialVersionUID = -1266190134568365852L;
-
- /**
- * Constructs a new <code>ReferenceIdentityMap</code> that will
- * use hard references to keys and soft references to values.
- */
- public ReferenceIdentityMap() {
- super(HARD, SOFT, DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, false);
- }
-
- /**
- * Constructs a new <code>ReferenceIdentityMap</code> that will
- * use the specified types of references.
- *
- * @param keyType the type of reference to use for keys;
- * must be {@link #HARD}, {@link #SOFT}, {@link #WEAK}
- * @param valueType the type of reference to use for values;
- * must be {@link #HARD}, {@link #SOFT}, {@link #WEAK}
- */
- public ReferenceIdentityMap(int keyType, int valueType) {
- super(keyType, valueType, DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, false);
- }
-
- /**
- * Constructs a new <code>ReferenceIdentityMap</code> that will
- * use the specified types of references.
- *
- * @param keyType the type of reference to use for keys;
- * must be {@link #HARD}, {@link #SOFT}, {@link #WEAK}
- * @param valueType the type of reference to use for values;
- * must be {@link #HARD}, {@link #SOFT}, {@link #WEAK}
- * @param purgeValues should the value be automatically purged when the
- * key is garbage collected
- */
- public ReferenceIdentityMap(int keyType, int valueType, boolean purgeValues) {
- super(keyType, valueType, DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, purgeValues);
- }
-
- /**
- * Constructs a new <code>ReferenceIdentityMap</code> with the
- * specified reference types, load factor and initial capacity.
- *
- * @param keyType the type of reference to use for keys;
- * must be {@link #HARD}, {@link #SOFT}, {@link #WEAK}
- * @param valueType the type of reference to use for values;
- * must be {@link #HARD}, {@link #SOFT}, {@link #WEAK}
- * @param capacity the initial capacity for the map
- * @param loadFactor the load factor for the map
- */
- public ReferenceIdentityMap(int keyType, int valueType, int capacity, float loadFactor) {
- super(keyType, valueType, capacity, loadFactor, false);
- }
-
- /**
- * Constructs a new <code>ReferenceIdentityMap</code> with the
- * specified reference types, load factor and initial capacity.
- *
- * @param keyType the type of reference to use for keys;
- * must be {@link #HARD}, {@link #SOFT}, {@link #WEAK}
- * @param valueType the type of reference to use for values;
- * must be {@link #HARD}, {@link #SOFT}, {@link #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(int keyType, int valueType, int capacity,
- float loadFactor, boolean purgeValues) {
- super(keyType, valueType, capacity, loadFactor, purgeValues);
- }
-
- //-----------------------------------------------------------------------
- /**
- * Gets the hash code for the key specified.
- * <p>
- * 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);
- }
-
- /**
- * Gets the hash code for a MapEntry.
- * <p>
- * 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
- */
- protected int hashEntry(Object key, Object value) {
- return System.identityHashCode(key) ^
- System.identityHashCode(value);
- }
-
- /**
- * Compares two keys for equals.
- * <p>
- * This implementation converts the key from the entry to a real reference
- * before comparison and uses <code>==</code>.
- *
- * @param key1 the first key to compare passed in from outside
- * @param key2 the second key extracted from the entry via <code>entry.key</code>
- * @return true if equal by identity
- */
- protected boolean isEqualKey(Object key1, Object key2) {
- key2 = (keyType > HARD ? ((Reference) key2).get() : key2);
- return (key1 == key2);
- }
-
- /**
- * Compares two values for equals.
- * <p>
- * This implementation uses <code>==</code>.
- *
- * @param value1 the first value to compare passed in from outside
- * @param value2 the second value extracted from the entry via <code>getValue()</code>
- * @return true if equal by identity
- */
- protected boolean isEqualValue(Object value1, Object value2) {
- return (value1 == value2);
- }
-
- //-----------------------------------------------------------------------
- /**
- * 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);
- }
-
- }