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| 1 | /* | ||
| 2 | * Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved. | ||
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 4 | * | ||
| 5 | * This code is free software; you can redistribute it and/or modify it | ||
| 6 | * under the terms of the GNU General Public License version 2 only, as | ||
| 7 | * published by the Free Software Foundation. Oracle designates this | ||
| 8 | * particular file as subject to the "Classpath" exception as provided | ||
| 9 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 10 | * | ||
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 14 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 15 | * accompanied this code). | ||
| 16 | * | ||
| 17 | * You should have received a copy of the GNU General Public License version | ||
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 20 | * | ||
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * questions. | ||
| 24 | */ | ||
| 25 | |||
| 26 | package java.util; | ||
| 27 | import java.io.*; | ||
| 28 | |||
| 29 | /** | ||
| 30 | * <p>Hash table and linked list implementation of the <tt>Map</tt> interface, | ||
| 31 | * with predictable iteration order. This implementation differs from | ||
| 32 | * <tt>HashMap</tt> in that it maintains a doubly-linked list running through | ||
| 33 | * all of its entries. This linked list defines the iteration ordering, | ||
| 34 | * which is normally the order in which keys were inserted into the map | ||
| 35 | * (<i>insertion-order</i>). Note that insertion order is not affected | ||
| 36 | * if a key is <i>re-inserted</i> into the map. (A key <tt>k</tt> is | ||
| 37 | * reinserted into a map <tt>m</tt> if <tt>m.put(k, v)</tt> is invoked when | ||
| 38 | * <tt>m.containsKey(k)</tt> would return <tt>true</tt> immediately prior to | ||
| 39 | * the invocation.) | ||
| 40 | * | ||
| 41 | * <p>This implementation spares its clients from the unspecified, generally | ||
| 42 | * chaotic ordering provided by {@link HashMap} (and {@link Hashtable}), | ||
| 43 | * without incurring the increased cost associated with {@link TreeMap}. It | ||
| 44 | * can be used to produce a copy of a map that has the same order as the | ||
| 45 | * original, regardless of the original map's implementation: | ||
| 46 | * <pre> | ||
| 47 | * void foo(Map m) { | ||
| 48 | * Map copy = new LinkedHashMap(m); | ||
| 49 | * ... | ||
| 50 | * } | ||
| 51 | * </pre> | ||
| 52 | * This technique is particularly useful if a module takes a map on input, | ||
| 53 | * copies it, and later returns results whose order is determined by that of | ||
| 54 | * the copy. (Clients generally appreciate having things returned in the same | ||
| 55 | * order they were presented.) | ||
| 56 | * | ||
| 57 | * <p>A special {@link #LinkedHashMap(int,float,boolean) constructor} is | ||
| 58 | * provided to create a linked hash map whose order of iteration is the order | ||
| 59 | * in which its entries were last accessed, from least-recently accessed to | ||
| 60 | * most-recently (<i>access-order</i>). This kind of map is well-suited to | ||
| 61 | * building LRU caches. Invoking the <tt>put</tt> or <tt>get</tt> method | ||
| 62 | * results in an access to the corresponding entry (assuming it exists after | ||
| 63 | * the invocation completes). The <tt>putAll</tt> method generates one entry | ||
| 64 | * access for each mapping in the specified map, in the order that key-value | ||
| 65 | * mappings are provided by the specified map's entry set iterator. <i>No | ||
| 66 | * other methods generate entry accesses.</i> In particular, operations on | ||
| 67 | * collection-views do <i>not</i> affect the order of iteration of the backing | ||
| 68 | * map. | ||
| 69 | * | ||
| 70 | * <p>The {@link #removeEldestEntry(Map.Entry)} method may be overridden to | ||
| 71 | * impose a policy for removing stale mappings automatically when new mappings | ||
| 72 | * are added to the map. | ||
| 73 | * | ||
| 74 | * <p>This class provides all of the optional <tt>Map</tt> operations, and | ||
| 75 | * permits null elements. Like <tt>HashMap</tt>, it provides constant-time | ||
| 76 | * performance for the basic operations (<tt>add</tt>, <tt>contains</tt> and | ||
| 77 | * <tt>remove</tt>), assuming the hash function disperses elements | ||
| 78 | * properly among the buckets. Performance is likely to be just slightly | ||
| 79 | * below that of <tt>HashMap</tt>, due to the added expense of maintaining the | ||
| 80 | * linked list, with one exception: Iteration over the collection-views | ||
| 81 | * of a <tt>LinkedHashMap</tt> requires time proportional to the <i>size</i> | ||
| 82 | * of the map, regardless of its capacity. Iteration over a <tt>HashMap</tt> | ||
| 83 | * is likely to be more expensive, requiring time proportional to its | ||
| 84 | * <i>capacity</i>. | ||
| 85 | * | ||
| 86 | * <p>A linked hash map has two parameters that affect its performance: | ||
| 87 | * <i>initial capacity</i> and <i>load factor</i>. They are defined precisely | ||
| 88 | * as for <tt>HashMap</tt>. Note, however, that the penalty for choosing an | ||
| 89 | * excessively high value for initial capacity is less severe for this class | ||
| 90 | * than for <tt>HashMap</tt>, as iteration times for this class are unaffected | ||
| 91 | * by capacity. | ||
| 92 | * | ||
| 93 | * <p><strong>Note that this implementation is not synchronized.</strong> | ||
| 94 | * If multiple threads access a linked hash map concurrently, and at least | ||
| 95 | * one of the threads modifies the map structurally, it <em>must</em> be | ||
| 96 | * synchronized externally. This is typically accomplished by | ||
| 97 | * synchronizing on some object that naturally encapsulates the map. | ||
| 98 | * | ||
| 99 | * If no such object exists, the map should be "wrapped" using the | ||
| 100 | * {@link Collections#synchronizedMap Collections.synchronizedMap} | ||
| 101 | * method. This is best done at creation time, to prevent accidental | ||
| 102 | * unsynchronized access to the map:<pre> | ||
| 103 | * Map m = Collections.synchronizedMap(new LinkedHashMap(...));</pre> | ||
| 104 | * | ||
| 105 | * A structural modification is any operation that adds or deletes one or more | ||
| 106 | * mappings or, in the case of access-ordered linked hash maps, affects | ||
| 107 | * iteration order. In insertion-ordered linked hash maps, merely changing | ||
| 108 | * the value associated with a key that is already contained in the map is not | ||
| 109 | * a structural modification. <strong>In access-ordered linked hash maps, | ||
| 110 | * merely querying the map with <tt>get</tt> is a structural | ||
| 111 | * modification.</strong>) | ||
| 112 | * | ||
| 113 | * <p>The iterators returned by the <tt>iterator</tt> method of the collections | ||
| 114 | * returned by all of this class's collection view methods are | ||
| 115 | * <em>fail-fast</em>: if the map is structurally modified at any time after | ||
| 116 | * the iterator is created, in any way except through the iterator's own | ||
| 117 | * <tt>remove</tt> method, the iterator will throw a {@link | ||
| 118 | * ConcurrentModificationException}. Thus, in the face of concurrent | ||
| 119 | * modification, the iterator fails quickly and cleanly, rather than risking | ||
| 120 | * arbitrary, non-deterministic behavior at an undetermined time in the future. | ||
| 121 | * | ||
| 122 | * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed | ||
| 123 | * as it is, generally speaking, impossible to make any hard guarantees in the | ||
| 124 | * presence of unsynchronized concurrent modification. Fail-fast iterators | ||
| 125 | * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. | ||
| 126 | * Therefore, it would be wrong to write a program that depended on this | ||
| 127 | * exception for its correctness: <i>the fail-fast behavior of iterators | ||
| 128 | * should be used only to detect bugs.</i> | ||
| 129 | * | ||
| 130 | * <p>This class is a member of the | ||
| 131 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> | ||
| 132 | * Java Collections Framework</a>. | ||
| 133 | * | ||
| 134 | * @param <K> the type of keys maintained by this map | ||
| 135 | * @param <V> the type of mapped values | ||
| 136 | * | ||
| 137 | * @author Josh Bloch | ||
| 138 | * @see Object#hashCode() | ||
| 139 | * @see Collection | ||
| 140 | * @see Map | ||
| 141 | * @see HashMap | ||
| 142 | * @see TreeMap | ||
| 143 | * @see Hashtable | ||
| 144 | * @since 1.4 | ||
| 145 | */ | ||
| 146 | |||
| 147 | public class LinkedHashMap<K,V> | ||
| 148 | extends HashMap<K,V> | ||
| 149 | implements Map<K,V> | ||
| 150 | { | ||
| 151 | |||
| 152 | private static final long serialVersionUID = 3801124242820219131L; | ||
| 153 | |||
| 154 | /** | ||
| 155 | * The head of the doubly linked list. | ||
| 156 | */ | ||
| 157 | private transient Entry<K,V> header; | ||
| 158 | |||
| 159 | /** | ||
| 160 | * The iteration ordering method for this linked hash map: <tt>true</tt> | ||
| 161 | * for access-order, <tt>false</tt> for insertion-order. | ||
| 162 | * | ||
| 163 | * @serial | ||
| 164 | */ | ||
| 165 | private final boolean accessOrder; | ||
| 166 | |||
| 167 | /** | ||
| 168 | * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance | ||
| 169 | * with the specified initial capacity and load factor. | ||
| 170 | * | ||
| 171 | * @param initialCapacity the initial capacity | ||
| 172 | * @param loadFactor the load factor | ||
| 173 | * @throws IllegalArgumentException if the initial capacity is negative | ||
| 174 | * or the load factor is nonpositive | ||
| 175 | */ | ||
| 176 | public LinkedHashMap(int initialCapacity, float loadFactor) { | ||
| 177 | super(initialCapacity, loadFactor); | ||
| 178 | accessOrder = false; | ||
| 179 | } | ||
| 180 | |||
| 181 | /** | ||
| 182 | * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance | ||
| 183 | * with the specified initial capacity and a default load factor (0.75). | ||
| 184 | * | ||
| 185 | * @param initialCapacity the initial capacity | ||
| 186 | * @throws IllegalArgumentException if the initial capacity is negative | ||
| 187 | */ | ||
| 188 | public LinkedHashMap(int initialCapacity) { | ||
| 189 | super(initialCapacity); | ||
| 190 | accessOrder = false; | ||
| 191 | } | ||
| 192 | |||
| 193 | /** | ||
| 194 | * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance | ||
| 195 | * with the default initial capacity (16) and load factor (0.75). | ||
| 196 | */ | ||
| 197 | public LinkedHashMap() { | ||
| 198 | super(); | ||
| 199 | accessOrder = false; | ||
| 200 | } | ||
| 201 | |||
| 202 | /** | ||
| 203 | * Constructs an insertion-ordered <tt>LinkedHashMap</tt> instance with | ||
| 204 | * the same mappings as the specified map. The <tt>LinkedHashMap</tt> | ||
| 205 | * instance is created with a default load factor (0.75) and an initial | ||
| 206 | * capacity sufficient to hold the mappings in the specified map. | ||
| 207 | * | ||
| 208 | * @param m the map whose mappings are to be placed in this map | ||
| 209 | * @throws NullPointerException if the specified map is null | ||
| 210 | */ | ||
| 211 | public LinkedHashMap(Map<? extends K, ? extends V> m) { | ||
| 212 | super(m); | ||
| 213 | accessOrder = false; | ||
| 214 | } | ||
| 215 | |||
| 216 | /** | ||
| 217 | * Constructs an empty <tt>LinkedHashMap</tt> instance with the | ||
| 218 | * specified initial capacity, load factor and ordering mode. | ||
| 219 | * | ||
| 220 | * @param initialCapacity the initial capacity | ||
| 221 | * @param loadFactor the load factor | ||
| 222 | * @param accessOrder the ordering mode - <tt>true</tt> for | ||
| 223 | * access-order, <tt>false</tt> for insertion-order | ||
| 224 | * @throws IllegalArgumentException if the initial capacity is negative | ||
| 225 | * or the load factor is nonpositive | ||
| 226 | */ | ||
| 227 | public LinkedHashMap(int initialCapacity, | ||
| 228 | float loadFactor, | ||
| 229 | boolean accessOrder) { | ||
| 230 | super(initialCapacity, loadFactor); | ||
| 231 | this.accessOrder = accessOrder; | ||
| 232 | } | ||
| 233 | |||
| 234 | /** | ||
| 235 | * Called by superclass constructors and pseudoconstructors (clone, | ||
| 236 | * readObject) before any entries are inserted into the map. Initializes | ||
| 237 | * the chain. | ||
| 238 | */ | ||
| 239 | void init() { | ||
| 240 | header = new Entry<>(-1, null, null, null); | ||
| 241 | header.before = header.after = header; | ||
| 242 | } | ||
| 243 | |||
| 244 | /** | ||
| 245 | * Transfers all entries to new table array. This method is called | ||
| 246 | * by superclass resize. It is overridden for performance, as it is | ||
| 247 | * faster to iterate using our linked list. | ||
| 248 | */ | ||
| 249 | void transfer(HashMap.Entry[] newTable) { | ||
| 250 | int newCapacity = newTable.length; | ||
| 251 | for (Entry<K,V> e = header.after; e != header; e = e.after) { | ||
| 252 | int index = indexFor(e.hash, newCapacity); | ||
| 253 | e.next = newTable[index]; | ||
| 254 | newTable[index] = e; | ||
| 255 | } | ||
| 256 | } | ||
| 257 | |||
| 258 | |||
| 259 | /** | ||
| 260 | * Returns <tt>true</tt> if this map maps one or more keys to the | ||
| 261 | * specified value. | ||
| 262 | * | ||
| 263 | * @param value value whose presence in this map is to be tested | ||
| 264 | * @return <tt>true</tt> if this map maps one or more keys to the | ||
| 265 | * specified value | ||
| 266 | */ | ||
| 267 | public boolean containsValue(Object value) { | ||
| 268 | // Overridden to take advantage of faster iterator | ||
| 269 | if (value==null) { | ||
| 270 | for (Entry e = header.after; e != header; e = e.after) | ||
| 271 | if (e.value==null) | ||
| 272 | return true; | ||
| 273 | } else { | ||
| 274 | for (Entry e = header.after; e != header; e = e.after) | ||
| 275 | if (value.equals(e.value)) | ||
| 276 | return true; | ||
| 277 | } | ||
| 278 | return false; | ||
| 279 | } | ||
| 280 | |||
| 281 | /** | ||
| 282 | * Returns the value to which the specified key is mapped, | ||
| 283 | * or {@code null} if this map contains no mapping for the key. | ||
| 284 | * | ||
| 285 | * <p>More formally, if this map contains a mapping from a key | ||
| 286 | * {@code k} to a value {@code v} such that {@code (key==null ? k==null : | ||
| 287 | * key.equals(k))}, then this method returns {@code v}; otherwise | ||
| 288 | * it returns {@code null}. (There can be at most one such mapping.) | ||
| 289 | * | ||
| 290 | * <p>A return value of {@code null} does not <i>necessarily</i> | ||
| 291 | * indicate that the map contains no mapping for the key; it's also | ||
| 292 | * possible that the map explicitly maps the key to {@code null}. | ||
| 293 | * The {@link #containsKey containsKey} operation may be used to | ||
| 294 | * distinguish these two cases. | ||
| 295 | */ | ||
| 296 | public V get(Object key) { | ||
| 297 | Entry<K,V> e = (Entry<K,V>)getEntry(key); | ||
| 298 | if (e == null) | ||
| 299 | return null; | ||
| 300 | e.recordAccess(this); | ||
| 301 | return e.value; | ||
| 302 | } | ||
| 303 | |||
| 304 | /** | ||
| 305 | * Removes all of the mappings from this map. | ||
| 306 | * The map will be empty after this call returns. | ||
| 307 | */ | ||
| 308 | public void clear() { | ||
| 309 | super.clear(); | ||
| 310 | header.before = header.after = header; | ||
| 311 | } | ||
| 312 | |||
| 313 | /** | ||
| 314 | * LinkedHashMap entry. | ||
| 315 | */ | ||
| 316 | private static class Entry<K,V> extends HashMap.Entry<K,V> { | ||
| 317 | // These fields comprise the doubly linked list used for iteration. | ||
| 318 | Entry<K,V> before, after; | ||
| 319 | |||
| 320 | Entry(int hash, K key, V value, HashMap.Entry<K,V> next) { | ||
| 321 | super(hash, key, value, next); | ||
| 322 | } | ||
| 323 | |||
| 324 | /** | ||
| 325 | * Removes this entry from the linked list. | ||
| 326 | */ | ||
| 327 | private void remove() { | ||
| 328 | before.after = after; | ||
| 329 | after.before = before; | ||
| 330 | } | ||
| 331 | |||
| 332 | /** | ||
| 333 | * Inserts this entry before the specified existing entry in the list. | ||
| 334 | */ | ||
| 335 | private void addBefore(Entry<K,V> existingEntry) { | ||
| 336 | after = existingEntry; | ||
| 337 | before = existingEntry.before; | ||
| 338 | before.after = this; | ||
| 339 | after.before = this; | ||
| 340 | } | ||
| 341 | |||
| 342 | /** | ||
| 343 | * This method is invoked by the superclass whenever the value | ||
| 344 | * of a pre-existing entry is read by Map.get or modified by Map.set. | ||
| 345 | * If the enclosing Map is access-ordered, it moves the entry | ||
| 346 | * to the end of the list; otherwise, it does nothing. | ||
| 347 | */ | ||
| 348 | void recordAccess(HashMap<K,V> m) { | ||
| 349 | LinkedHashMap<K,V> lm = (LinkedHashMap<K,V>)m; | ||
| 350 | if (lm.accessOrder) { | ||
| 351 | lm.modCount++; | ||
| 352 | remove(); | ||
| 353 | addBefore(lm.header); | ||
| 354 | } | ||
| 355 | } | ||
| 356 | |||
| 357 | void recordRemoval(HashMap<K,V> m) { | ||
| 358 | remove(); | ||
| 359 | } | ||
| 360 | } | ||
| 361 | |||
| 362 | private abstract class LinkedHashIterator<T> implements Iterator<T> { | ||
| 363 | Entry<K,V> nextEntry = header.after; | ||
| 364 | Entry<K,V> lastReturned = null; | ||
| 365 | |||
| 366 | /** | ||
| 367 | * The modCount value that the iterator believes that the backing | ||
| 368 | * List should have. If this expectation is violated, the iterator | ||
| 369 | * has detected concurrent modification. | ||
| 370 | */ | ||
| 371 | int expectedModCount = modCount; | ||
| 372 | |||
| 373 | public boolean hasNext() { | ||
| 374 | return nextEntry != header; | ||
| 375 | } | ||
| 376 | |||
| 377 | public void remove() { | ||
| 378 | if (lastReturned == null) | ||
| 379 | throw new IllegalStateException(); | ||
| 380 | if (modCount != expectedModCount) | ||
| 381 | throw new ConcurrentModificationException(); | ||
| 382 | |||
| 383 | LinkedHashMap.this.remove(lastReturned.key); | ||
| 384 | lastReturned = null; | ||
| 385 | expectedModCount = modCount; | ||
| 386 | } | ||
| 387 | |||
| 388 | Entry<K,V> nextEntry() { | ||
| 389 | if (modCount != expectedModCount) | ||
| 390 | throw new ConcurrentModificationException(); | ||
| 391 | if (nextEntry == header) | ||
| 392 | throw new NoSuchElementException(); | ||
| 393 | |||
| 394 | Entry<K,V> e = lastReturned = nextEntry; | ||
| 395 | nextEntry = e.after; | ||
| 396 | return e; | ||
| 397 | } | ||
| 398 | } | ||
| 399 | |||
| 400 | private class KeyIterator extends LinkedHashIterator<K> { | ||
| 401 | public K next() { return nextEntry().getKey(); } | ||
| 402 | } | ||
| 403 | |||
| 404 | private class ValueIterator extends LinkedHashIterator<V> { | ||
| 405 | public V next() { return nextEntry().value; } | ||
| 406 | } | ||
| 407 | |||
| 408 | private class EntryIterator extends LinkedHashIterator<Map.Entry<K,V>> { | ||
| 409 | public Map.Entry<K,V> next() { return nextEntry(); } | ||
| 410 | } | ||
| 411 | |||
| 412 | // These Overrides alter the behavior of superclass view iterator() methods | ||
| 413 | Iterator<K> newKeyIterator() { return new KeyIterator(); } | ||
| 414 | Iterator<V> newValueIterator() { return new ValueIterator(); } | ||
| 415 | Iterator<Map.Entry<K,V>> newEntryIterator() { return new EntryIterator(); } | ||
| 416 | |||
| 417 | /** | ||
| 418 | * This override alters behavior of superclass put method. It causes newly | ||
| 419 | * allocated entry to get inserted at the end of the linked list and | ||
| 420 | * removes the eldest entry if appropriate. | ||
| 421 | */ | ||
| 422 | void addEntry(int hash, K key, V value, int bucketIndex) { | ||
| 423 | createEntry(hash, key, value, bucketIndex); | ||
| 424 | |||
| 425 | // Remove eldest entry if instructed, else grow capacity if appropriate | ||
| 426 | Entry<K,V> eldest = header.after; | ||
| 427 | if (removeEldestEntry(eldest)) { | ||
| 428 | removeEntryForKey(eldest.key); | ||
| 429 | } else { | ||
| 430 | if (size >= threshold) | ||
| 431 | resize(2 * table.length); | ||
| 432 | } | ||
| 433 | } | ||
| 434 | |||
| 435 | /** | ||
| 436 | * This override differs from addEntry in that it doesn't resize the | ||
| 437 | * table or remove the eldest entry. | ||
| 438 | */ | ||
| 439 | void createEntry(int hash, K key, V value, int bucketIndex) { | ||
| 440 | HashMap.Entry<K,V> old = table[bucketIndex]; | ||
| 441 | Entry<K,V> e = new Entry<>(hash, key, value, old); | ||
| 442 | table[bucketIndex] = e; | ||
| 443 | e.addBefore(header); | ||
| 444 | size++; | ||
| 445 | } | ||
| 446 | |||
| 447 | /** | ||
| 448 | * Returns <tt>true</tt> if this map should remove its eldest entry. | ||
| 449 | * This method is invoked by <tt>put</tt> and <tt>putAll</tt> after | ||
| 450 | * inserting a new entry into the map. It provides the implementor | ||
| 451 | * with the opportunity to remove the eldest entry each time a new one | ||
| 452 | * is added. This is useful if the map represents a cache: it allows | ||
| 453 | * the map to reduce memory consumption by deleting stale entries. | ||
| 454 | * | ||
| 455 | * <p>Sample use: this override will allow the map to grow up to 100 | ||
| 456 | * entries and then delete the eldest entry each time a new entry is | ||
| 457 | * added, maintaining a steady state of 100 entries. | ||
| 458 | * <pre> | ||
| 459 | * private static final int MAX_ENTRIES = 100; | ||
| 460 | * | ||
| 461 | * protected boolean removeEldestEntry(Map.Entry eldest) { | ||
| 462 | * return size() > MAX_ENTRIES; | ||
| 463 | * } | ||
| 464 | * </pre> | ||
| 465 | * | ||
| 466 | * <p>This method typically does not modify the map in any way, | ||
| 467 | * instead allowing the map to modify itself as directed by its | ||
| 468 | * return value. It <i>is</i> permitted for this method to modify | ||
| 469 | * the map directly, but if it does so, it <i>must</i> return | ||
| 470 | * <tt>false</tt> (indicating that the map should not attempt any | ||
| 471 | * further modification). The effects of returning <tt>true</tt> | ||
| 472 | * after modifying the map from within this method are unspecified. | ||
| 473 | * | ||
| 474 | * <p>This implementation merely returns <tt>false</tt> (so that this | ||
| 475 | * map acts like a normal map - the eldest element is never removed). | ||
| 476 | * | ||
| 477 | * @param eldest The least recently inserted entry in the map, or if | ||
| 478 | * this is an access-ordered map, the least recently accessed | ||
| 479 | * entry. This is the entry that will be removed it this | ||
| 480 | * method returns <tt>true</tt>. If the map was empty prior | ||
| 481 | * to the <tt>put</tt> or <tt>putAll</tt> invocation resulting | ||
| 482 | * in this invocation, this will be the entry that was just | ||
| 483 | * inserted; in other words, if the map contains a single | ||
| 484 | * entry, the eldest entry is also the newest. | ||
| 485 | * @return <tt>true</tt> if the eldest entry should be removed | ||
| 486 | * from the map; <tt>false</tt> if it should be retained. | ||
| 487 | */ | ||
| 488 | protected boolean removeEldestEntry(Map.Entry<K,V> eldest) { | ||
| 489 | return false; | ||
| 490 | } | ||
| 491 | } | ||