1 #import "HashMap.h" 2 /** 3 * <p>Hash table and linked list implementation of the <tt>Map</tt> interface, 4 * with predictable iteration order. This implementation differs from 5 * <tt>HashMap</tt> in that it maintains a doubly-linked list running through 6 * all of its entries. This linked list defines the iteration ordering, 7 * which is normally the order in which keys were inserted into the map 8 * (<i>insertion-order</i>). Note that insertion order is not affected 9 * if a key is <i>re-inserted</i> into the map. (A key <tt>k</tt> is 10 * reinserted into a map <tt>m</tt> if <tt>m.put(k, v)</tt> is invoked when 11 * <tt>m.containsKey(k)</tt> would return <tt>true</tt> immediately prior to 12 * the invocation.) 13 * 14 * <p>This implementation spares its clients from the unspecified, generally 15 * chaotic ordering provided by {@link HashMap} (and {@link Hashtable}), 16 * without incurring the increased cost associated with {@link TreeMap}. It 17 * can be used to produce a copy of a map that has the same order as the 18 * original, regardless of the original map's implementation: 19 * <pre> 20 * void foo(Map m) { 21 * Map copy = new LinkedHashMap(m); 22 * ... 23 * } 24 * </pre> 25 * This technique is particularly useful if a module takes a map on input, 26 * copies it, and later returns results whose order is determined by that of 27 * the copy. (Clients generally appreciate having things returned in the same 28 * order they were presented.) 29 * 30 * <p>A special {@link #LinkedHashMap(NSInteger,float,boolean) constructor} is 31 * provided to create a linked hash map whose order of iteration is the order 32 * in which its entries were last accessed, from least-recently accessed to 33 * most-recently (<i>access-order</i>). This kind of map is well-suited to 34 * building LRU caches. Invoking the <tt>put</tt> or <tt>get</tt> method 35 * results in an access to the corresponding entry (assuming it exists after 36 * the invocation completes). The <tt>putAll</tt> method generates one entry 37 * access for each mapping in the specified map, in the order that key-value 38 * mappings are provided by the specified map's entry set iterator. <i>No 39 * other methods generate entry accesses.</i> In particular, operations on 40 * collection-views do <i>not</i> affect the order of iteration of the backing 41 * map. 42 * 43 * <p>The {@link #removeEldestEntry(Map.Entry)} method may be overridden to 44 * impose a policy for removing stale mappings automatically when new mappings 45 * are added to the map. 46 * 47 * <p>This class provides all of the optional <tt>Map</tt> operations, and 48 * permits null elements. Like <tt>HashMap</tt>, it provides constant-time 49 * performance for the basic operations (<tt>add</tt>, <tt>contains</tt> and 50 * <tt>remove</tt>), assuming the hash function disperses elements 51 * properly among the buckets. Performance is likely to be just slightly 52 * below that of <tt>HashMap</tt>, due to the added expense of maintaining the 53 * linked list, with one exception: Iteration over the collection-views 54 * of a <tt>LinkedHashMap</tt> requires time proportional to the <i>size</i> 55 * of the map, regardless of its capacity. Iteration over a <tt>HashMap</tt> 56 * is likely to be more expensive, requiring time proportional to its 57 * <i>capacity</i>. 58 * 59 * <p>A linked hash map has two parameters that affect its performance: 60 * <i>initial capacity</i> and <i>load factor</i>. They are defined precisely 61 * as for <tt>HashMap</tt>. Note, however, that the penalty for choosing an 62 * excessively high value for initial capacity is less severe for this class 63 * than for <tt>HashMap</tt>, as iteration times for this class are unaffected 64 * by capacity. 65 * 66 * <p><strong>Note that this implementation is not synchronized.</strong> 67 * If multiple threads access a linked hash map concurrently, and at least 68 * one of the threads modifies the map structurally, it <em>must</em> be 69 * synchronized externally. This is typically accomplished by 70 * synchronizing on some object that naturally encapsulates the map. 71 * 72 * If no such object exists, the map should be "wrapped" using the 73 * {@link Collections#synchronizedMap Collections.synchronizedMap} 74 * method. This is best done at creation time, to prevent accidental 75 * unsynchronized access to the map:<pre> 76 * Map m = Collections.synchronizedMap(new LinkedHashMap(...));</pre> 77 * 78 * A structural modification is any operation that adds or deletes one or more 79 * mappings or, in the case of access-ordered linked hash maps, affects 80 * iteration order. In insertion-ordered linked hash maps, merely changing 81 * the value associated with a key that is already contained in the map is not 82 * a structural modification. <strong>In access-ordered linked hash maps, 83 * merely querying the map with <tt>get</tt> is a structural 84 * modification.</strong>) 85 * 86 * <p>The iterators returned by the <tt>iterator</tt> method of the collections 87 * returned by all of this class's collection view methods are 88 * <em>fail-fast</em>: if the map is structurally modified at any time after 89 * the iterator is created, in any way except through the iterator's own 90 * <tt>remove</tt> method, the iterator will throw a {@link 91 * ConcurrentModificationException}. Thus, in the face of concurrent 92 * modification, the iterator fails quickly and cleanly, rather than risking 93 * arbitrary, non-deterministic behavior at an undetermined time in the future. 94 * 95 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed 96 * as it is, generally speaking, impossible to make any hard guarantees in the 97 * presence of unsynchronized concurrent modification. Fail-fast iterators 98 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. 99 * Therefore, it would be wrong to write a program that depended on this 100 * exception for its correctness: <i>the fail-fast behavior of iterators 101 * should be used only to detect bugs.</i> 102 * 103 * <p>This class is a member of the 104 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 105 * Java Collections Framework</a>. 106 * 107 * @param <K> the type of keys maintained by this map 108 * @param <V> the type of mapped values 109 * 110 * @author Josh Bloch 111 * @see Object#hashCode() 112 * @see Collection 113 * @see Map 114 * @see HashMap 115 * @see TreeMap 116 * @see Hashtable 117 * @since 1.4 118 */ 119 @class LinkedHashMap; 120 121 /** 122 * LinkedHashMap entry. 123 */ 124 125 @interface LHMEntry : HMEntry 126 { 127 LHMEntry *before; 128 LHMEntry *after; 129 BOOL accessOrder; 130 } 131 132 @property (retain) LHMEntry *before; 133 @property (retain) LHMEntry *after; 134 @property (assign) BOOL accessOrder; 135 136 - (id) newEntry:(NSInteger)aHash key:(NSString *)aKey value:(id)aValue next:(LHMEntry *)aNext; 137 138 - (id) init:(NSInteger)hash key:(NSString *)key value:(id)value next:(LHMEntry *)next; 139 - (void) recordAccess:(LinkedHashMap *)m; 140 - (void) recordRemoval:(LinkedHashMap *)m; 141 142 @end 143 144 /** 145 * LinkedHashMapIterator. 146 */ 147 148 @interface LinkedHashIterator : HashIterator 149 { 150 LHMEntry *nextEntry; 151 LHMEntry *lastReturned; 152 LinkedHashMap *lhm; 153 } 154 155 @property (retain) LHMEntry *nextEntry; 156 @property (retain) LHMEntry *lastReturned; 157 @property (retain) LinkedHashMap *lhm; 158 159 + (LinkedHashIterator *) newIterator:(LinkedHashMap *)aLHM; 160 161 - (id) init:(LinkedHashMap *)aLHM; 162 - (BOOL) hasNext; 163 - (void) remove; 164 - (LHMEntry *) nextEntry; 165 @end 166 167 @interface LHMEntryIterator : LinkedHashIterator 168 { 169 } 170 171 + (LHMEntryIterator *)newIterator:(LinkedHashMap *)aHM; 172 173 - (id) init:(LinkedHashMap *)aHM; 174 - (LHMEntry *) next; 175 @end 176 177 @interface LHMKeyIterator : LinkedHashIterator 178 { 179 } 180 181 + (LHMKeyIterator *)newIterator:(LinkedHashMap *)aHM; 182 183 - (id) init:(LinkedHashMap *)aHM; 184 - (NSString *) next; 185 @end 186 187 @interface LHMValueIterator : LinkedHashIterator 188 { 189 } 190 191 + (LHMValueIterator *)newIterator:(LinkedHashMap *)aHM; 192 193 - (id) init:(LinkedHashMap *)aHM; 194 - (id) next; 195 @end 196 197 198 @interface LinkedHashMap : HashMap 199 { 200 201 /** 202 * The head of the doubly linked list. 203 */ 204 LHMEntry *header; 205 /** 206 * The iteration ordering method for this linked hash map: <tt>true</tt> 207 * for access-order, <tt>false</tt> for insertion-order. 208 * 209 * @serial 210 */ 211 BOOL accessOrder; 212 213 } 214 215 @property (retain) LHMEntry *header; 216 @property (assign) BOOL accessOrder; 217 218 + (id) newLinkedHashMap:(NSInteger)anInitialCapacity; 219 + (id) newLinkedHashMap:(NSInteger)anInitialCapacity 220 loadFactor:(float)loadFactor; 221 + (id) newLinkedHashMap:(NSInteger)anInitialCapacity 222 loadFactor:(float)loadFactor 223 accessOrder:(BOOL)anAccessOrder; 224 225 - (id) init:(NSInteger)initialCapacity loadFactor:(float)loadFactor accessOrder:(BOOL)accessOrder; 226 - (id) init:(NSInteger)initialCapacity loadFactor:(float)loadFactor; 227 - (id) init:(NSInteger)initialCapacity; 228 - (id) init; 229 - (id) initWithM:(AMutableDictionary *)m; 230 - (void) transfer:(NSArray *)newTable; 231 - (BOOL) containsValue:(NSObject *)value; 232 - (id) get:(NSString *)key; 233 - (void) clear; 234 - (LHMEntryIterator *) newEntryIterator; 235 - (LHMKeyIterator *) newKeyIterator; 236 - (LHMValueIterator *) newValueIterator; 237 - (void) addEntry:(NSInteger)hash key:(NSString *)key value:(id)value bucketIndex:(NSInteger)bucketIndex; 238 - (void) createEntry:(NSInteger)hash key:(NSString *)key value:(id)value bucketIndex:(NSInteger)bucketIndex; 239 - (BOOL) removeEldestEntry:(LHMEntry *)eldest; 240 @end 241