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 } 162
