Aurimas Liutikas | 88c7ff1 | 2023-08-10 12:42:26 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (c) 1997, 2019, 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.util.Map.Entry; |
| 28 | |
| 29 | /** |
| 30 | * This class provides a skeletal implementation of the {@code Map} |
| 31 | * interface, to minimize the effort required to implement this interface. |
| 32 | * |
| 33 | * <p>To implement an unmodifiable map, the programmer needs only to extend this |
| 34 | * class and provide an implementation for the {@code entrySet} method, which |
| 35 | * returns a set-view of the map's mappings. Typically, the returned set |
| 36 | * will, in turn, be implemented atop {@code AbstractSet}. This set should |
| 37 | * not support the {@code add} or {@code remove} methods, and its iterator |
| 38 | * should not support the {@code remove} method. |
| 39 | * |
| 40 | * <p>To implement a modifiable map, the programmer must additionally override |
| 41 | * this class's {@code put} method (which otherwise throws an |
| 42 | * {@code UnsupportedOperationException}), and the iterator returned by |
| 43 | * {@code entrySet().iterator()} must additionally implement its |
| 44 | * {@code remove} method. |
| 45 | * |
| 46 | * <p>The programmer should generally provide a void (no argument) and map |
| 47 | * constructor, as per the recommendation in the {@code Map} interface |
| 48 | * specification. |
| 49 | * |
| 50 | * <p>The documentation for each non-abstract method in this class describes its |
| 51 | * implementation in detail. Each of these methods may be overridden if the |
| 52 | * map being implemented admits a more efficient implementation. |
| 53 | * |
| 54 | * <p>This class is a member of the |
| 55 | * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> |
| 56 | * Java Collections Framework</a>. |
| 57 | * |
| 58 | * @param <K> the type of keys maintained by this map |
| 59 | * @param <V> the type of mapped values |
| 60 | * |
| 61 | * @author Josh Bloch |
| 62 | * @author Neal Gafter |
| 63 | * @see Map |
| 64 | * @see Collection |
| 65 | * @since 1.2 |
| 66 | */ |
| 67 | |
| 68 | public abstract class AbstractMap<K,V> implements Map<K,V> { |
| 69 | /** |
| 70 | * Sole constructor. (For invocation by subclass constructors, typically |
| 71 | * implicit.) |
| 72 | */ |
| 73 | protected AbstractMap() { |
| 74 | } |
| 75 | |
| 76 | // Query Operations |
| 77 | |
| 78 | /** |
| 79 | * {@inheritDoc} |
| 80 | * |
| 81 | * @implSpec |
| 82 | * This implementation returns {@code entrySet().size()}. |
| 83 | */ |
| 84 | public int size() { |
| 85 | return entrySet().size(); |
| 86 | } |
| 87 | |
| 88 | /** |
| 89 | * {@inheritDoc} |
| 90 | * |
| 91 | * @implSpec |
| 92 | * This implementation returns {@code size() == 0}. |
| 93 | */ |
| 94 | public boolean isEmpty() { |
| 95 | return size() == 0; |
| 96 | } |
| 97 | |
| 98 | /** |
| 99 | * {@inheritDoc} |
| 100 | * |
| 101 | * @implSpec |
| 102 | * This implementation iterates over {@code entrySet()} searching |
| 103 | * for an entry with the specified value. If such an entry is found, |
| 104 | * {@code true} is returned. If the iteration terminates without |
| 105 | * finding such an entry, {@code false} is returned. Note that this |
| 106 | * implementation requires linear time in the size of the map. |
| 107 | * |
| 108 | * @throws ClassCastException {@inheritDoc} |
| 109 | * @throws NullPointerException {@inheritDoc} |
| 110 | */ |
| 111 | public boolean containsValue(Object value) { |
| 112 | Iterator<Entry<K,V>> i = entrySet().iterator(); |
| 113 | if (value==null) { |
| 114 | while (i.hasNext()) { |
| 115 | Entry<K,V> e = i.next(); |
| 116 | if (e.getValue()==null) |
| 117 | return true; |
| 118 | } |
| 119 | } else { |
| 120 | while (i.hasNext()) { |
| 121 | Entry<K,V> e = i.next(); |
| 122 | if (value.equals(e.getValue())) |
| 123 | return true; |
| 124 | } |
| 125 | } |
| 126 | return false; |
| 127 | } |
| 128 | |
| 129 | /** |
| 130 | * {@inheritDoc} |
| 131 | * |
| 132 | * @implSpec |
| 133 | * This implementation iterates over {@code entrySet()} searching |
| 134 | * for an entry with the specified key. If such an entry is found, |
| 135 | * {@code true} is returned. If the iteration terminates without |
| 136 | * finding such an entry, {@code false} is returned. Note that this |
| 137 | * implementation requires linear time in the size of the map; many |
| 138 | * implementations will override this method. |
| 139 | * |
| 140 | * @throws ClassCastException {@inheritDoc} |
| 141 | * @throws NullPointerException {@inheritDoc} |
| 142 | */ |
| 143 | public boolean containsKey(Object key) { |
| 144 | Iterator<Map.Entry<K,V>> i = entrySet().iterator(); |
| 145 | if (key==null) { |
| 146 | while (i.hasNext()) { |
| 147 | Entry<K,V> e = i.next(); |
| 148 | if (e.getKey()==null) |
| 149 | return true; |
| 150 | } |
| 151 | } else { |
| 152 | while (i.hasNext()) { |
| 153 | Entry<K,V> e = i.next(); |
| 154 | if (key.equals(e.getKey())) |
| 155 | return true; |
| 156 | } |
| 157 | } |
| 158 | return false; |
| 159 | } |
| 160 | |
| 161 | /** |
| 162 | * {@inheritDoc} |
| 163 | * |
| 164 | * @implSpec |
| 165 | * This implementation iterates over {@code entrySet()} searching |
| 166 | * for an entry with the specified key. If such an entry is found, |
| 167 | * the entry's value is returned. If the iteration terminates without |
| 168 | * finding such an entry, {@code null} is returned. Note that this |
| 169 | * implementation requires linear time in the size of the map; many |
| 170 | * implementations will override this method. |
| 171 | * |
| 172 | * @throws ClassCastException {@inheritDoc} |
| 173 | * @throws NullPointerException {@inheritDoc} |
| 174 | */ |
| 175 | public V get(Object key) { |
| 176 | Iterator<Entry<K,V>> i = entrySet().iterator(); |
| 177 | if (key==null) { |
| 178 | while (i.hasNext()) { |
| 179 | Entry<K,V> e = i.next(); |
| 180 | if (e.getKey()==null) |
| 181 | return e.getValue(); |
| 182 | } |
| 183 | } else { |
| 184 | while (i.hasNext()) { |
| 185 | Entry<K,V> e = i.next(); |
| 186 | if (key.equals(e.getKey())) |
| 187 | return e.getValue(); |
| 188 | } |
| 189 | } |
| 190 | return null; |
| 191 | } |
| 192 | |
| 193 | |
| 194 | // Modification Operations |
| 195 | |
| 196 | /** |
| 197 | * {@inheritDoc} |
| 198 | * |
| 199 | * @implSpec |
| 200 | * This implementation always throws an |
| 201 | * {@code UnsupportedOperationException}. |
| 202 | * |
| 203 | * @throws UnsupportedOperationException {@inheritDoc} |
| 204 | * @throws ClassCastException {@inheritDoc} |
| 205 | * @throws NullPointerException {@inheritDoc} |
| 206 | * @throws IllegalArgumentException {@inheritDoc} |
| 207 | */ |
| 208 | public V put(K key, V value) { |
| 209 | throw new UnsupportedOperationException(); |
| 210 | } |
| 211 | |
| 212 | /** |
| 213 | * {@inheritDoc} |
| 214 | * |
| 215 | * @implSpec |
| 216 | * This implementation iterates over {@code entrySet()} searching for an |
| 217 | * entry with the specified key. If such an entry is found, its value is |
| 218 | * obtained with its {@code getValue} operation, the entry is removed |
| 219 | * from the collection (and the backing map) with the iterator's |
| 220 | * {@code remove} operation, and the saved value is returned. If the |
| 221 | * iteration terminates without finding such an entry, {@code null} is |
| 222 | * returned. Note that this implementation requires linear time in the |
| 223 | * size of the map; many implementations will override this method. |
| 224 | * |
| 225 | * <p>Note that this implementation throws an |
| 226 | * {@code UnsupportedOperationException} if the {@code entrySet} |
| 227 | * iterator does not support the {@code remove} method and this map |
| 228 | * contains a mapping for the specified key. |
| 229 | * |
| 230 | * @throws UnsupportedOperationException {@inheritDoc} |
| 231 | * @throws ClassCastException {@inheritDoc} |
| 232 | * @throws NullPointerException {@inheritDoc} |
| 233 | */ |
| 234 | public V remove(Object key) { |
| 235 | Iterator<Entry<K,V>> i = entrySet().iterator(); |
| 236 | Entry<K,V> correctEntry = null; |
| 237 | if (key==null) { |
| 238 | while (correctEntry==null && i.hasNext()) { |
| 239 | Entry<K,V> e = i.next(); |
| 240 | if (e.getKey()==null) |
| 241 | correctEntry = e; |
| 242 | } |
| 243 | } else { |
| 244 | while (correctEntry==null && i.hasNext()) { |
| 245 | Entry<K,V> e = i.next(); |
| 246 | if (key.equals(e.getKey())) |
| 247 | correctEntry = e; |
| 248 | } |
| 249 | } |
| 250 | |
| 251 | V oldValue = null; |
| 252 | if (correctEntry !=null) { |
| 253 | oldValue = correctEntry.getValue(); |
| 254 | i.remove(); |
| 255 | } |
| 256 | return oldValue; |
| 257 | } |
| 258 | |
| 259 | |
| 260 | // Bulk Operations |
| 261 | |
| 262 | /** |
| 263 | * {@inheritDoc} |
| 264 | * |
| 265 | * @implSpec |
| 266 | * This implementation iterates over the specified map's |
| 267 | * {@code entrySet()} collection, and calls this map's {@code put} |
| 268 | * operation once for each entry returned by the iteration. |
| 269 | * |
| 270 | * <p>Note that this implementation throws an |
| 271 | * {@code UnsupportedOperationException} if this map does not support |
| 272 | * the {@code put} operation and the specified map is nonempty. |
| 273 | * |
| 274 | * @throws UnsupportedOperationException {@inheritDoc} |
| 275 | * @throws ClassCastException {@inheritDoc} |
| 276 | * @throws NullPointerException {@inheritDoc} |
| 277 | * @throws IllegalArgumentException {@inheritDoc} |
| 278 | */ |
| 279 | public void putAll(Map<? extends K, ? extends V> m) { |
| 280 | for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) |
| 281 | put(e.getKey(), e.getValue()); |
| 282 | } |
| 283 | |
| 284 | /** |
| 285 | * {@inheritDoc} |
| 286 | * |
| 287 | * @implSpec |
| 288 | * This implementation calls {@code entrySet().clear()}. |
| 289 | * |
| 290 | * <p>Note that this implementation throws an |
| 291 | * {@code UnsupportedOperationException} if the {@code entrySet} |
| 292 | * does not support the {@code clear} operation. |
| 293 | * |
| 294 | * @throws UnsupportedOperationException {@inheritDoc} |
| 295 | */ |
| 296 | public void clear() { |
| 297 | entrySet().clear(); |
| 298 | } |
| 299 | |
| 300 | |
| 301 | // Views |
| 302 | |
| 303 | /** |
| 304 | * Each of these fields are initialized to contain an instance of the |
| 305 | * appropriate view the first time this view is requested. The views are |
| 306 | * stateless, so there's no reason to create more than one of each. |
| 307 | * |
| 308 | * <p>Since there is no synchronization performed while accessing these fields, |
| 309 | * it is expected that java.util.Map view classes using these fields have |
| 310 | * no non-final fields (or any fields at all except for outer-this). Adhering |
| 311 | * to this rule would make the races on these fields benign. |
| 312 | * |
| 313 | * <p>It is also imperative that implementations read the field only once, |
| 314 | * as in: |
| 315 | * |
| 316 | * <pre> {@code |
| 317 | * public Set<K> keySet() { |
| 318 | * Set<K> ks = keySet; // single racy read |
| 319 | * if (ks == null) { |
| 320 | * ks = new KeySet(); |
| 321 | * keySet = ks; |
| 322 | * } |
| 323 | * return ks; |
| 324 | * } |
| 325 | *}</pre> |
| 326 | */ |
| 327 | transient Set<K> keySet; |
| 328 | transient Collection<V> values; |
| 329 | |
| 330 | /** |
| 331 | * {@inheritDoc} |
| 332 | * |
| 333 | * @implSpec |
| 334 | * This implementation returns a set that subclasses {@link AbstractSet}. |
| 335 | * The subclass's iterator method returns a "wrapper object" over this |
| 336 | * map's {@code entrySet()} iterator. The {@code size} method |
| 337 | * delegates to this map's {@code size} method and the |
| 338 | * {@code contains} method delegates to this map's |
| 339 | * {@code containsKey} method. |
| 340 | * |
| 341 | * <p>The set is created the first time this method is called, |
| 342 | * and returned in response to all subsequent calls. No synchronization |
| 343 | * is performed, so there is a slight chance that multiple calls to this |
| 344 | * method will not all return the same set. |
| 345 | */ |
| 346 | public Set<K> keySet() { |
| 347 | Set<K> ks = keySet; |
| 348 | if (ks == null) { |
| 349 | ks = new AbstractSet<K>() { |
| 350 | public Iterator<K> iterator() { |
| 351 | return new Iterator<K>() { |
| 352 | private Iterator<Entry<K,V>> i = entrySet().iterator(); |
| 353 | |
| 354 | public boolean hasNext() { |
| 355 | return i.hasNext(); |
| 356 | } |
| 357 | |
| 358 | public K next() { |
| 359 | return i.next().getKey(); |
| 360 | } |
| 361 | |
| 362 | public void remove() { |
| 363 | i.remove(); |
| 364 | } |
| 365 | }; |
| 366 | } |
| 367 | |
| 368 | public int size() { |
| 369 | return AbstractMap.this.size(); |
| 370 | } |
| 371 | |
| 372 | public boolean isEmpty() { |
| 373 | return AbstractMap.this.isEmpty(); |
| 374 | } |
| 375 | |
| 376 | public void clear() { |
| 377 | AbstractMap.this.clear(); |
| 378 | } |
| 379 | |
| 380 | public boolean contains(Object k) { |
| 381 | return AbstractMap.this.containsKey(k); |
| 382 | } |
| 383 | }; |
| 384 | keySet = ks; |
| 385 | } |
| 386 | return ks; |
| 387 | } |
| 388 | |
| 389 | /** |
| 390 | * {@inheritDoc} |
| 391 | * |
| 392 | * @implSpec |
| 393 | * This implementation returns a collection that subclasses {@link |
| 394 | * AbstractCollection}. The subclass's iterator method returns a |
| 395 | * "wrapper object" over this map's {@code entrySet()} iterator. |
| 396 | * The {@code size} method delegates to this map's {@code size} |
| 397 | * method and the {@code contains} method delegates to this map's |
| 398 | * {@code containsValue} method. |
| 399 | * |
| 400 | * <p>The collection is created the first time this method is called, and |
| 401 | * returned in response to all subsequent calls. No synchronization is |
| 402 | * performed, so there is a slight chance that multiple calls to this |
| 403 | * method will not all return the same collection. |
| 404 | */ |
| 405 | public Collection<V> values() { |
| 406 | Collection<V> vals = values; |
| 407 | if (vals == null) { |
| 408 | vals = new AbstractCollection<V>() { |
| 409 | public Iterator<V> iterator() { |
| 410 | return new Iterator<V>() { |
| 411 | private Iterator<Entry<K,V>> i = entrySet().iterator(); |
| 412 | |
| 413 | public boolean hasNext() { |
| 414 | return i.hasNext(); |
| 415 | } |
| 416 | |
| 417 | public V next() { |
| 418 | return i.next().getValue(); |
| 419 | } |
| 420 | |
| 421 | public void remove() { |
| 422 | i.remove(); |
| 423 | } |
| 424 | }; |
| 425 | } |
| 426 | |
| 427 | public int size() { |
| 428 | return AbstractMap.this.size(); |
| 429 | } |
| 430 | |
| 431 | public boolean isEmpty() { |
| 432 | return AbstractMap.this.isEmpty(); |
| 433 | } |
| 434 | |
| 435 | public void clear() { |
| 436 | AbstractMap.this.clear(); |
| 437 | } |
| 438 | |
| 439 | public boolean contains(Object v) { |
| 440 | return AbstractMap.this.containsValue(v); |
| 441 | } |
| 442 | }; |
| 443 | values = vals; |
| 444 | } |
| 445 | return vals; |
| 446 | } |
| 447 | |
| 448 | public abstract Set<Entry<K,V>> entrySet(); |
| 449 | |
| 450 | |
| 451 | // Comparison and hashing |
| 452 | |
| 453 | /** |
| 454 | * Compares the specified object with this map for equality. Returns |
| 455 | * {@code true} if the given object is also a map and the two maps |
| 456 | * represent the same mappings. More formally, two maps {@code m1} and |
| 457 | * {@code m2} represent the same mappings if |
| 458 | * {@code m1.entrySet().equals(m2.entrySet())}. This ensures that the |
| 459 | * {@code equals} method works properly across different implementations |
| 460 | * of the {@code Map} interface. |
| 461 | * |
| 462 | * @implSpec |
| 463 | * This implementation first checks if the specified object is this map; |
| 464 | * if so it returns {@code true}. Then, it checks if the specified |
| 465 | * object is a map whose size is identical to the size of this map; if |
| 466 | * not, it returns {@code false}. If so, it iterates over this map's |
| 467 | * {@code entrySet} collection, and checks that the specified map |
| 468 | * contains each mapping that this map contains. If the specified map |
| 469 | * fails to contain such a mapping, {@code false} is returned. If the |
| 470 | * iteration completes, {@code true} is returned. |
| 471 | * |
| 472 | * @param o object to be compared for equality with this map |
| 473 | * @return {@code true} if the specified object is equal to this map |
| 474 | */ |
| 475 | public boolean equals(Object o) { |
| 476 | if (o == this) |
| 477 | return true; |
| 478 | |
| 479 | if (!(o instanceof Map<?, ?> m)) |
| 480 | return false; |
| 481 | if (m.size() != size()) |
| 482 | return false; |
| 483 | |
| 484 | try { |
| 485 | for (Entry<K, V> e : entrySet()) { |
| 486 | K key = e.getKey(); |
| 487 | V value = e.getValue(); |
| 488 | if (value == null) { |
| 489 | if (!(m.get(key) == null && m.containsKey(key))) |
| 490 | return false; |
| 491 | } else { |
| 492 | if (!value.equals(m.get(key))) |
| 493 | return false; |
| 494 | } |
| 495 | } |
| 496 | } catch (ClassCastException unused) { |
| 497 | return false; |
| 498 | } catch (NullPointerException unused) { |
| 499 | return false; |
| 500 | } |
| 501 | |
| 502 | return true; |
| 503 | } |
| 504 | |
| 505 | /** |
| 506 | * Returns the hash code value for this map. The hash code of a map is |
| 507 | * defined to be the sum of the hash codes of each entry in the map's |
| 508 | * {@code entrySet()} view. This ensures that {@code m1.equals(m2)} |
| 509 | * implies that {@code m1.hashCode()==m2.hashCode()} for any two maps |
| 510 | * {@code m1} and {@code m2}, as required by the general contract of |
| 511 | * {@link Object#hashCode}. |
| 512 | * |
| 513 | * @implSpec |
| 514 | * This implementation iterates over {@code entrySet()}, calling |
| 515 | * {@link Map.Entry#hashCode hashCode()} on each element (entry) in the |
| 516 | * set, and adding up the results. |
| 517 | * |
| 518 | * @return the hash code value for this map |
| 519 | * @see Map.Entry#hashCode() |
| 520 | * @see Object#equals(Object) |
| 521 | * @see Set#equals(Object) |
| 522 | */ |
| 523 | public int hashCode() { |
| 524 | int h = 0; |
| 525 | for (Entry<K, V> entry : entrySet()) |
| 526 | h += entry.hashCode(); |
| 527 | return h; |
| 528 | } |
| 529 | |
| 530 | /** |
| 531 | * Returns a string representation of this map. The string representation |
| 532 | * consists of a list of key-value mappings in the order returned by the |
| 533 | * map's {@code entrySet} view's iterator, enclosed in braces |
| 534 | * ({@code "{}"}). Adjacent mappings are separated by the characters |
| 535 | * {@code ", "} (comma and space). Each key-value mapping is rendered as |
| 536 | * the key followed by an equals sign ({@code "="}) followed by the |
| 537 | * associated value. Keys and values are converted to strings as by |
| 538 | * {@link String#valueOf(Object)}. |
| 539 | * |
| 540 | * @return a string representation of this map |
| 541 | */ |
| 542 | public String toString() { |
| 543 | Iterator<Entry<K,V>> i = entrySet().iterator(); |
| 544 | if (! i.hasNext()) |
| 545 | return "{}"; |
| 546 | |
| 547 | StringBuilder sb = new StringBuilder(); |
| 548 | sb.append('{'); |
| 549 | for (;;) { |
| 550 | Entry<K,V> e = i.next(); |
| 551 | K key = e.getKey(); |
| 552 | V value = e.getValue(); |
| 553 | sb.append(key == this ? "(this Map)" : key); |
| 554 | sb.append('='); |
| 555 | sb.append(value == this ? "(this Map)" : value); |
| 556 | if (! i.hasNext()) |
| 557 | return sb.append('}').toString(); |
| 558 | sb.append(',').append(' '); |
| 559 | } |
| 560 | } |
| 561 | |
| 562 | /** |
| 563 | * Returns a shallow copy of this {@code AbstractMap} instance: the keys |
| 564 | * and values themselves are not cloned. |
| 565 | * |
| 566 | * @return a shallow copy of this map |
| 567 | */ |
| 568 | protected Object clone() throws CloneNotSupportedException { |
| 569 | AbstractMap<?,?> result = (AbstractMap<?,?>)super.clone(); |
| 570 | result.keySet = null; |
| 571 | result.values = null; |
| 572 | return result; |
| 573 | } |
| 574 | |
| 575 | /** |
| 576 | * Utility method for SimpleEntry and SimpleImmutableEntry. |
| 577 | * Test for equality, checking for nulls. |
| 578 | * |
| 579 | * NB: Do not replace with Object.equals until JDK-8015417 is resolved. |
| 580 | */ |
| 581 | private static boolean eq(Object o1, Object o2) { |
| 582 | return o1 == null ? o2 == null : o1.equals(o2); |
| 583 | } |
| 584 | |
| 585 | // Implementation Note: SimpleEntry and SimpleImmutableEntry |
| 586 | // are distinct unrelated classes, even though they share |
| 587 | // some code. Since you can't add or subtract final-ness |
| 588 | // of a field in a subclass, they can't share representations, |
| 589 | // and the amount of duplicated code is too small to warrant |
| 590 | // exposing a common abstract class. |
| 591 | |
| 592 | |
| 593 | /** |
| 594 | * An Entry maintaining a key and a value. The value may be |
| 595 | * changed using the {@code setValue} method. Instances of |
| 596 | * this class are not associated with any map's entry-set view. |
| 597 | * |
| 598 | * @apiNote |
| 599 | * This class facilitates the process of building custom map |
| 600 | * implementations. For example, it may be convenient to return |
| 601 | * arrays of {@code SimpleEntry} instances in method |
| 602 | * {@code Map.entrySet().toArray}. |
| 603 | * |
| 604 | * @since 1.6 |
| 605 | */ |
| 606 | public static class SimpleEntry<K,V> |
| 607 | implements Entry<K,V>, java.io.Serializable |
| 608 | { |
| 609 | @java.io.Serial |
| 610 | private static final long serialVersionUID = -8499721149061103585L; |
| 611 | |
| 612 | @SuppressWarnings("serial") // Conditionally serializable |
| 613 | private final K key; |
| 614 | @SuppressWarnings("serial") // Conditionally serializable |
| 615 | private V value; |
| 616 | |
| 617 | /** |
| 618 | * Creates an entry representing a mapping from the specified |
| 619 | * key to the specified value. |
| 620 | * |
| 621 | * @param key the key represented by this entry |
| 622 | * @param value the value represented by this entry |
| 623 | */ |
| 624 | public SimpleEntry(K key, V value) { |
| 625 | this.key = key; |
| 626 | this.value = value; |
| 627 | } |
| 628 | |
| 629 | /** |
| 630 | * Creates an entry representing the same mapping as the |
| 631 | * specified entry. |
| 632 | * |
| 633 | * @param entry the entry to copy |
| 634 | */ |
| 635 | public SimpleEntry(Entry<? extends K, ? extends V> entry) { |
| 636 | this.key = entry.getKey(); |
| 637 | this.value = entry.getValue(); |
| 638 | } |
| 639 | |
| 640 | /** |
| 641 | * Returns the key corresponding to this entry. |
| 642 | * |
| 643 | * @return the key corresponding to this entry |
| 644 | */ |
| 645 | public K getKey() { |
| 646 | return key; |
| 647 | } |
| 648 | |
| 649 | /** |
| 650 | * Returns the value corresponding to this entry. |
| 651 | * |
| 652 | * @return the value corresponding to this entry |
| 653 | */ |
| 654 | public V getValue() { |
| 655 | return value; |
| 656 | } |
| 657 | |
| 658 | /** |
| 659 | * Replaces the value corresponding to this entry with the specified |
| 660 | * value. |
| 661 | * |
| 662 | * @param value new value to be stored in this entry |
| 663 | * @return the old value corresponding to the entry |
| 664 | */ |
| 665 | public V setValue(V value) { |
| 666 | V oldValue = this.value; |
| 667 | this.value = value; |
| 668 | return oldValue; |
| 669 | } |
| 670 | |
| 671 | /** |
| 672 | * Compares the specified object with this entry for equality. |
| 673 | * Returns {@code true} if the given object is also a map entry and |
| 674 | * the two entries represent the same mapping. More formally, two |
| 675 | * entries {@code e1} and {@code e2} represent the same mapping |
| 676 | * if<pre> |
| 677 | * (e1.getKey()==null ? |
| 678 | * e2.getKey()==null : |
| 679 | * e1.getKey().equals(e2.getKey())) |
| 680 | * && |
| 681 | * (e1.getValue()==null ? |
| 682 | * e2.getValue()==null : |
| 683 | * e1.getValue().equals(e2.getValue()))</pre> |
| 684 | * This ensures that the {@code equals} method works properly across |
| 685 | * different implementations of the {@code Map.Entry} interface. |
| 686 | * |
| 687 | * @param o object to be compared for equality with this map entry |
| 688 | * @return {@code true} if the specified object is equal to this map |
| 689 | * entry |
| 690 | * @see #hashCode |
| 691 | */ |
| 692 | public boolean equals(Object o) { |
| 693 | return o instanceof Map.Entry<?, ?> e |
| 694 | && eq(key, e.getKey()) |
| 695 | && eq(value, e.getValue()); |
| 696 | } |
| 697 | |
| 698 | /** |
| 699 | * Returns the hash code value for this map entry. The hash code |
| 700 | * of a map entry {@code e} is defined to be: <pre> |
| 701 | * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^ |
| 702 | * (e.getValue()==null ? 0 : e.getValue().hashCode())</pre> |
| 703 | * This ensures that {@code e1.equals(e2)} implies that |
| 704 | * {@code e1.hashCode()==e2.hashCode()} for any two Entries |
| 705 | * {@code e1} and {@code e2}, as required by the general |
| 706 | * contract of {@link Object#hashCode}. |
| 707 | * |
| 708 | * @return the hash code value for this map entry |
| 709 | * @see #equals |
| 710 | */ |
| 711 | public int hashCode() { |
| 712 | return (key == null ? 0 : key.hashCode()) ^ |
| 713 | (value == null ? 0 : value.hashCode()); |
| 714 | } |
| 715 | |
| 716 | /** |
| 717 | * Returns a String representation of this map entry. This |
| 718 | * implementation returns the string representation of this |
| 719 | * entry's key followed by the equals character ("{@code =}") |
| 720 | * followed by the string representation of this entry's value. |
| 721 | * |
| 722 | * @return a String representation of this map entry |
| 723 | */ |
| 724 | public String toString() { |
| 725 | return key + "=" + value; |
| 726 | } |
| 727 | |
| 728 | } |
| 729 | |
| 730 | /** |
| 731 | * An unmodifiable Entry maintaining a key and a value. This class |
| 732 | * does not support the {@code setValue} method. Instances of |
| 733 | * this class are not associated with any map's entry-set view. |
| 734 | * |
| 735 | * @apiNote |
| 736 | * Instances of this class are not necessarily immutable, as the key |
| 737 | * and value may be mutable. An instance of <i>this specific class</i> |
| 738 | * is unmodifiable, because the key and value references cannot be |
| 739 | * changed. A reference of this <i>type</i> may not be unmodifiable, |
| 740 | * as a subclass may be modifiable or may provide the appearance of modifiability. |
| 741 | * <p> |
| 742 | * This class may be convenient in methods that return thread-safe snapshots of |
| 743 | * key-value mappings. For alternatives, see the |
| 744 | * {@link Map#entry Map::entry} and {@link Map.Entry#copyOf Map.Entry::copyOf} |
| 745 | * methods. |
| 746 | * |
| 747 | * @since 1.6 |
| 748 | */ |
| 749 | public static class SimpleImmutableEntry<K,V> |
| 750 | implements Entry<K,V>, java.io.Serializable |
| 751 | { |
| 752 | @java.io.Serial |
| 753 | private static final long serialVersionUID = 7138329143949025153L; |
| 754 | |
| 755 | @SuppressWarnings("serial") // Not statically typed as Serializable |
| 756 | private final K key; |
| 757 | @SuppressWarnings("serial") // Not statically typed as Serializable |
| 758 | private final V value; |
| 759 | |
| 760 | /** |
| 761 | * Creates an entry representing a mapping from the specified |
| 762 | * key to the specified value. |
| 763 | * |
| 764 | * @param key the key represented by this entry |
| 765 | * @param value the value represented by this entry |
| 766 | */ |
| 767 | public SimpleImmutableEntry(K key, V value) { |
| 768 | this.key = key; |
| 769 | this.value = value; |
| 770 | } |
| 771 | |
| 772 | /** |
| 773 | * Creates an entry representing the same mapping as the |
| 774 | * specified entry. |
| 775 | * |
| 776 | * @param entry the entry to copy |
| 777 | */ |
| 778 | public SimpleImmutableEntry(Entry<? extends K, ? extends V> entry) { |
| 779 | this.key = entry.getKey(); |
| 780 | this.value = entry.getValue(); |
| 781 | } |
| 782 | |
| 783 | /** |
| 784 | * Returns the key corresponding to this entry. |
| 785 | * |
| 786 | * @return the key corresponding to this entry |
| 787 | */ |
| 788 | public K getKey() { |
| 789 | return key; |
| 790 | } |
| 791 | |
| 792 | /** |
| 793 | * Returns the value corresponding to this entry. |
| 794 | * |
| 795 | * @return the value corresponding to this entry |
| 796 | */ |
| 797 | public V getValue() { |
| 798 | return value; |
| 799 | } |
| 800 | |
| 801 | /** |
| 802 | * Replaces the value corresponding to this entry with the specified |
| 803 | * value (optional operation). This implementation simply throws |
| 804 | * {@code UnsupportedOperationException}, as this class implements |
| 805 | * an unmodifiable map entry. |
| 806 | * |
| 807 | * @implSpec |
| 808 | * The implementation in this class always throws {@code UnsupportedOperationException}. |
| 809 | * |
| 810 | * @param value new value to be stored in this entry |
| 811 | * @return (Does not return) |
| 812 | * @throws UnsupportedOperationException always |
| 813 | */ |
| 814 | public V setValue(V value) { |
| 815 | throw new UnsupportedOperationException(); |
| 816 | } |
| 817 | |
| 818 | /** |
| 819 | * Compares the specified object with this entry for equality. |
| 820 | * Returns {@code true} if the given object is also a map entry and |
| 821 | * the two entries represent the same mapping. More formally, two |
| 822 | * entries {@code e1} and {@code e2} represent the same mapping |
| 823 | * if<pre> |
| 824 | * (e1.getKey()==null ? |
| 825 | * e2.getKey()==null : |
| 826 | * e1.getKey().equals(e2.getKey())) |
| 827 | * && |
| 828 | * (e1.getValue()==null ? |
| 829 | * e2.getValue()==null : |
| 830 | * e1.getValue().equals(e2.getValue()))</pre> |
| 831 | * This ensures that the {@code equals} method works properly across |
| 832 | * different implementations of the {@code Map.Entry} interface. |
| 833 | * |
| 834 | * @param o object to be compared for equality with this map entry |
| 835 | * @return {@code true} if the specified object is equal to this map |
| 836 | * entry |
| 837 | * @see #hashCode |
| 838 | */ |
| 839 | public boolean equals(Object o) { |
| 840 | return o instanceof Map.Entry<?, ?> e |
| 841 | && eq(key, e.getKey()) |
| 842 | && eq(value, e.getValue()); |
| 843 | } |
| 844 | |
| 845 | /** |
| 846 | * Returns the hash code value for this map entry. The hash code |
| 847 | * of a map entry {@code e} is defined to be: <pre> |
| 848 | * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^ |
| 849 | * (e.getValue()==null ? 0 : e.getValue().hashCode())</pre> |
| 850 | * This ensures that {@code e1.equals(e2)} implies that |
| 851 | * {@code e1.hashCode()==e2.hashCode()} for any two Entries |
| 852 | * {@code e1} and {@code e2}, as required by the general |
| 853 | * contract of {@link Object#hashCode}. |
| 854 | * |
| 855 | * @return the hash code value for this map entry |
| 856 | * @see #equals |
| 857 | */ |
| 858 | public int hashCode() { |
| 859 | return (key == null ? 0 : key.hashCode()) ^ |
| 860 | (value == null ? 0 : value.hashCode()); |
| 861 | } |
| 862 | |
| 863 | /** |
| 864 | * Returns a String representation of this map entry. This |
| 865 | * implementation returns the string representation of this |
| 866 | * entry's key followed by the equals character ("{@code =}") |
| 867 | * followed by the string representation of this entry's value. |
| 868 | * |
| 869 | * @return a String representation of this map entry |
| 870 | */ |
| 871 | public String toString() { |
| 872 | return key + "=" + value; |
| 873 | } |
| 874 | |
| 875 | } |
| 876 | |
| 877 | } |