Shuyi Chen | d7955ce | 2013-05-22 14:51:55 -0700 | [diff] [blame^] | 1 | // GenericsNote: Converted. |
| 2 | /* |
| 3 | * Copyright 2002-2004 The Apache Software Foundation |
| 4 | * |
| 5 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 6 | * you may not use this file except in compliance with the License. |
| 7 | * You may obtain a copy of the License at |
| 8 | * |
| 9 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 10 | * |
| 11 | * Unless required by applicable law or agreed to in writing, software |
| 12 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 13 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 14 | * See the License for the specific language governing permissions and |
| 15 | * limitations under the License. |
| 16 | */ |
| 17 | package org.jivesoftware.smack.util.collections; |
| 18 | |
| 19 | import java.io.IOException; |
| 20 | import java.io.ObjectInputStream; |
| 21 | import java.io.ObjectOutputStream; |
| 22 | import java.io.Serializable; |
| 23 | |
| 24 | /** |
| 25 | * A <code>Map</code> implementation that allows mappings to be |
| 26 | * removed by the garbage collector. |
| 27 | * <p/> |
| 28 | * When you construct a <code>ReferenceMap</code>, you can specify what kind |
| 29 | * of references are used to store the map's keys and values. |
| 30 | * If non-hard references are used, then the garbage collector can remove |
| 31 | * mappings if a key or value becomes unreachable, or if the JVM's memory is |
| 32 | * running low. For information on how the different reference types behave, |
| 33 | * see {@link java.lang.ref.Reference}. |
| 34 | * <p/> |
| 35 | * Different types of references can be specified for keys and values. |
| 36 | * The keys can be configured to be weak but the values hard, |
| 37 | * in which case this class will behave like a |
| 38 | * <a href="http://java.sun.com/j2se/1.4/docs/api/java/util/WeakHashMap.html"> |
| 39 | * <code>WeakHashMap</code></a>. However, you can also specify hard keys and |
| 40 | * weak values, or any other combination. The default constructor uses |
| 41 | * hard keys and soft values, providing a memory-sensitive cache. |
| 42 | * <p/> |
| 43 | * This map is similar to ReferenceIdentityMap. |
| 44 | * It differs in that keys and values in this class are compared using <code>equals()</code>. |
| 45 | * <p/> |
| 46 | * This {@link java.util.Map} implementation does <i>not</i> allow null elements. |
| 47 | * Attempting to add a null key or value to the map will raise a <code>NullPointerException</code>. |
| 48 | * <p/> |
| 49 | * This implementation is not synchronized. |
| 50 | * You can use {@link java.util.Collections#synchronizedMap} to |
| 51 | * provide synchronized access to a <code>ReferenceMap</code>. |
| 52 | * Remember that synchronization will not stop the garbage collecter removing entries. |
| 53 | * <p/> |
| 54 | * All the available iterators can be reset back to the start by casting to |
| 55 | * <code>ResettableIterator</code> and calling <code>reset()</code>. |
| 56 | * <p/> |
| 57 | * NOTE: As from Commons Collections 3.1 this map extends <code>AbstractReferenceMap</code> |
| 58 | * (previously it extended AbstractMap). As a result, the implementation is now |
| 59 | * extensible and provides a <code>MapIterator</code>. |
| 60 | * |
| 61 | * @author Paul Jack |
| 62 | * @author Matt Hall, John Watkinson, Stephen Colebourne |
| 63 | * @version $Revision: 1.1 $ $Date: 2005/10/11 17:05:32 $ |
| 64 | * @see java.lang.ref.Reference |
| 65 | * @since Commons Collections 3.0 (previously in main package v2.1) |
| 66 | */ |
| 67 | public class ReferenceMap <K,V> extends AbstractReferenceMap<K, V> implements Serializable { |
| 68 | |
| 69 | /** |
| 70 | * Serialization version |
| 71 | */ |
| 72 | private static final long serialVersionUID = 1555089888138299607L; |
| 73 | |
| 74 | /** |
| 75 | * Constructs a new <code>ReferenceMap</code> that will |
| 76 | * use hard references to keys and soft references to values. |
| 77 | */ |
| 78 | public ReferenceMap() { |
| 79 | super(HARD, SOFT, DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, false); |
| 80 | } |
| 81 | |
| 82 | /** |
| 83 | * Constructs a new <code>ReferenceMap</code> that will |
| 84 | * use the specified types of references. |
| 85 | * |
| 86 | * @param keyType the type of reference to use for keys; |
| 87 | * must be {@link #HARD}, {@link #SOFT}, {@link #WEAK} |
| 88 | * @param valueType the type of reference to use for values; |
| 89 | * must be {@link #HARD}, {@link #SOFT}, {@link #WEAK} |
| 90 | */ |
| 91 | public ReferenceMap(int keyType, int valueType) { |
| 92 | super(keyType, valueType, DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, false); |
| 93 | } |
| 94 | |
| 95 | /** |
| 96 | * Constructs a new <code>ReferenceMap</code> that will |
| 97 | * use the specified types of references. |
| 98 | * |
| 99 | * @param keyType the type of reference to use for keys; |
| 100 | * must be {@link #HARD}, {@link #SOFT}, {@link #WEAK} |
| 101 | * @param valueType the type of reference to use for values; |
| 102 | * must be {@link #HARD}, {@link #SOFT}, {@link #WEAK} |
| 103 | * @param purgeValues should the value be automatically purged when the |
| 104 | * key is garbage collected |
| 105 | */ |
| 106 | public ReferenceMap(int keyType, int valueType, boolean purgeValues) { |
| 107 | super(keyType, valueType, DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, purgeValues); |
| 108 | } |
| 109 | |
| 110 | /** |
| 111 | * Constructs a new <code>ReferenceMap</code> with the |
| 112 | * specified reference types, load factor and initial |
| 113 | * capacity. |
| 114 | * |
| 115 | * @param keyType the type of reference to use for keys; |
| 116 | * must be {@link #HARD}, {@link #SOFT}, {@link #WEAK} |
| 117 | * @param valueType the type of reference to use for values; |
| 118 | * must be {@link #HARD}, {@link #SOFT}, {@link #WEAK} |
| 119 | * @param capacity the initial capacity for the map |
| 120 | * @param loadFactor the load factor for the map |
| 121 | */ |
| 122 | public ReferenceMap(int keyType, int valueType, int capacity, float loadFactor) { |
| 123 | super(keyType, valueType, capacity, loadFactor, false); |
| 124 | } |
| 125 | |
| 126 | /** |
| 127 | * Constructs a new <code>ReferenceMap</code> with the |
| 128 | * specified reference types, load factor and initial |
| 129 | * capacity. |
| 130 | * |
| 131 | * @param keyType the type of reference to use for keys; |
| 132 | * must be {@link #HARD}, {@link #SOFT}, {@link #WEAK} |
| 133 | * @param valueType the type of reference to use for values; |
| 134 | * must be {@link #HARD}, {@link #SOFT}, {@link #WEAK} |
| 135 | * @param capacity the initial capacity for the map |
| 136 | * @param loadFactor the load factor for the map |
| 137 | * @param purgeValues should the value be automatically purged when the |
| 138 | * key is garbage collected |
| 139 | */ |
| 140 | public ReferenceMap(int keyType, int valueType, int capacity, float loadFactor, boolean purgeValues) { |
| 141 | super(keyType, valueType, capacity, loadFactor, purgeValues); |
| 142 | } |
| 143 | |
| 144 | //----------------------------------------------------------------------- |
| 145 | /** |
| 146 | * Write the map out using a custom routine. |
| 147 | */ |
| 148 | private void writeObject(ObjectOutputStream out) throws IOException { |
| 149 | out.defaultWriteObject(); |
| 150 | doWriteObject(out); |
| 151 | } |
| 152 | |
| 153 | /** |
| 154 | * Read the map in using a custom routine. |
| 155 | */ |
| 156 | private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { |
| 157 | in.defaultReadObject(); |
| 158 | doReadObject(in); |
| 159 | } |
| 160 | |
| 161 | } |