1 /* 2 * Copyright (c) 1997, 2023, 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 import java.util.function.Consumer; 29 import java.util.function.IntFunction; 30 import java.util.function.Predicate; 31 import java.util.stream.Stream; 32 33 /** 34 * This class provides a skeletal implementation of the {@code Map} 35 * interface, to minimize the effort required to implement this interface. 36 * 37 * <p>To implement an unmodifiable map, the programmer needs only to extend this 38 * class and provide an implementation for the {@code entrySet} method, which 39 * returns a set-view of the map's mappings. Typically, the returned set 40 * will, in turn, be implemented atop {@code AbstractSet}. This set should 41 * not support the {@code add} or {@code remove} methods, and its iterator 42 * should not support the {@code remove} method. 43 * 44 * <p>To implement a modifiable map, the programmer must additionally override 45 * this class's {@code put} method (which otherwise throws an 46 * {@code UnsupportedOperationException}), and the iterator returned by 47 * {@code entrySet().iterator()} must additionally implement its 48 * {@code remove} method. 49 * 50 * <p>The programmer should generally provide a void (no argument) and map 51 * constructor, as per the recommendation in the {@code Map} interface 52 * specification. 53 * 54 * <p>The documentation for each non-abstract method in this class describes its 55 * implementation in detail. Each of these methods may be overridden if the 56 * map being implemented admits a more efficient implementation. 57 * 58 * <p>This class is a member of the 59 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> 60 * Java Collections Framework</a>. 61 * 62 * @param <K> the type of keys maintained by this map 63 * @param <V> the type of mapped values 64 * 65 * @author Josh Bloch 66 * @author Neal Gafter 67 * @see Map 68 * @see Collection 69 * @since 1.2 70 */ 71 72 public abstract class AbstractMap<K,V> implements Map<K,V> { 73 /** 74 * Sole constructor. (For invocation by subclass constructors, typically 75 * implicit.) 76 */ AbstractMap()77 protected AbstractMap() { 78 } 79 80 // Query Operations 81 82 /** 83 * {@inheritDoc} 84 * 85 * @implSpec 86 * This implementation returns {@code entrySet().size()}. 87 */ size()88 public int size() { 89 return entrySet().size(); 90 } 91 92 /** 93 * {@inheritDoc} 94 * 95 * @implSpec 96 * This implementation returns {@code size() == 0}. 97 */ isEmpty()98 public boolean isEmpty() { 99 return size() == 0; 100 } 101 102 /** 103 * {@inheritDoc} 104 * 105 * @implSpec 106 * This implementation iterates over {@code entrySet()} searching 107 * for an entry with the specified value. If such an entry is found, 108 * {@code true} is returned. If the iteration terminates without 109 * finding such an entry, {@code false} is returned. Note that this 110 * implementation requires linear time in the size of the map. 111 * 112 * @throws ClassCastException {@inheritDoc} 113 * @throws NullPointerException {@inheritDoc} 114 */ containsValue(Object value)115 public boolean containsValue(Object value) { 116 Iterator<Entry<K,V>> i = entrySet().iterator(); 117 if (value==null) { 118 while (i.hasNext()) { 119 Entry<K,V> e = i.next(); 120 if (e.getValue()==null) 121 return true; 122 } 123 } else { 124 while (i.hasNext()) { 125 Entry<K,V> e = i.next(); 126 if (value.equals(e.getValue())) 127 return true; 128 } 129 } 130 return false; 131 } 132 133 /** 134 * {@inheritDoc} 135 * 136 * @implSpec 137 * This implementation iterates over {@code entrySet()} searching 138 * for an entry with the specified key. If such an entry is found, 139 * {@code true} is returned. If the iteration terminates without 140 * finding such an entry, {@code false} is returned. Note that this 141 * implementation requires linear time in the size of the map; many 142 * implementations will override this method. 143 * 144 * @throws ClassCastException {@inheritDoc} 145 * @throws NullPointerException {@inheritDoc} 146 */ containsKey(Object key)147 public boolean containsKey(Object key) { 148 Iterator<Map.Entry<K,V>> i = entrySet().iterator(); 149 if (key==null) { 150 while (i.hasNext()) { 151 Entry<K,V> e = i.next(); 152 if (e.getKey()==null) 153 return true; 154 } 155 } else { 156 while (i.hasNext()) { 157 Entry<K,V> e = i.next(); 158 if (key.equals(e.getKey())) 159 return true; 160 } 161 } 162 return false; 163 } 164 165 /** 166 * {@inheritDoc} 167 * 168 * @implSpec 169 * This implementation iterates over {@code entrySet()} searching 170 * for an entry with the specified key. If such an entry is found, 171 * the entry's value is returned. If the iteration terminates without 172 * finding such an entry, {@code null} is returned. Note that this 173 * implementation requires linear time in the size of the map; many 174 * implementations will override this method. 175 * 176 * @throws ClassCastException {@inheritDoc} 177 * @throws NullPointerException {@inheritDoc} 178 */ get(Object key)179 public V get(Object key) { 180 Iterator<Entry<K,V>> i = entrySet().iterator(); 181 if (key==null) { 182 while (i.hasNext()) { 183 Entry<K,V> e = i.next(); 184 if (e.getKey()==null) 185 return e.getValue(); 186 } 187 } else { 188 while (i.hasNext()) { 189 Entry<K,V> e = i.next(); 190 if (key.equals(e.getKey())) 191 return e.getValue(); 192 } 193 } 194 return null; 195 } 196 197 198 // Modification Operations 199 200 /** 201 * {@inheritDoc} 202 * 203 * @implSpec 204 * This implementation always throws an 205 * {@code UnsupportedOperationException}. 206 * 207 * @throws UnsupportedOperationException {@inheritDoc} 208 * @throws ClassCastException {@inheritDoc} 209 * @throws NullPointerException {@inheritDoc} 210 * @throws IllegalArgumentException {@inheritDoc} 211 */ put(K key, V value)212 public V put(K key, V value) { 213 throw new UnsupportedOperationException(); 214 } 215 216 /** 217 * {@inheritDoc} 218 * 219 * @implSpec 220 * This implementation iterates over {@code entrySet()} searching for an 221 * entry with the specified key. If such an entry is found, its value is 222 * obtained with its {@code getValue} operation, the entry is removed 223 * from the collection (and the backing map) with the iterator's 224 * {@code remove} operation, and the saved value is returned. If the 225 * iteration terminates without finding such an entry, {@code null} is 226 * returned. Note that this implementation requires linear time in the 227 * size of the map; many implementations will override this method. 228 * 229 * <p>Note that this implementation throws an 230 * {@code UnsupportedOperationException} if the {@code entrySet} 231 * iterator does not support the {@code remove} method and this map 232 * contains a mapping for the specified key. 233 * 234 * @throws UnsupportedOperationException {@inheritDoc} 235 * @throws ClassCastException {@inheritDoc} 236 * @throws NullPointerException {@inheritDoc} 237 */ remove(Object key)238 public V remove(Object key) { 239 Iterator<Entry<K,V>> i = entrySet().iterator(); 240 Entry<K,V> correctEntry = null; 241 if (key==null) { 242 while (correctEntry==null && i.hasNext()) { 243 Entry<K,V> e = i.next(); 244 if (e.getKey()==null) 245 correctEntry = e; 246 } 247 } else { 248 while (correctEntry==null && i.hasNext()) { 249 Entry<K,V> e = i.next(); 250 if (key.equals(e.getKey())) 251 correctEntry = e; 252 } 253 } 254 255 V oldValue = null; 256 if (correctEntry !=null) { 257 oldValue = correctEntry.getValue(); 258 i.remove(); 259 } 260 return oldValue; 261 } 262 263 264 // Bulk Operations 265 266 /** 267 * {@inheritDoc} 268 * 269 * @implSpec 270 * This implementation iterates over the specified map's 271 * {@code entrySet()} collection, and calls this map's {@code put} 272 * operation once for each entry returned by the iteration. 273 * 274 * <p>Note that this implementation throws an 275 * {@code UnsupportedOperationException} if this map does not support 276 * the {@code put} operation and the specified map is nonempty. 277 * 278 * @throws UnsupportedOperationException {@inheritDoc} 279 * @throws ClassCastException {@inheritDoc} 280 * @throws NullPointerException {@inheritDoc} 281 * @throws IllegalArgumentException {@inheritDoc} 282 */ putAll(Map<? extends K, ? extends V> m)283 public void putAll(Map<? extends K, ? extends V> m) { 284 for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) 285 put(e.getKey(), e.getValue()); 286 } 287 288 /** 289 * {@inheritDoc} 290 * 291 * @implSpec 292 * This implementation calls {@code entrySet().clear()}. 293 * 294 * <p>Note that this implementation throws an 295 * {@code UnsupportedOperationException} if the {@code entrySet} 296 * does not support the {@code clear} operation. 297 * 298 * @throws UnsupportedOperationException {@inheritDoc} 299 */ clear()300 public void clear() { 301 entrySet().clear(); 302 } 303 304 305 // Views 306 307 /** 308 * Each of these fields are initialized to contain an instance of the 309 * appropriate view the first time this view is requested. The views are 310 * stateless, so there's no reason to create more than one of each. 311 * 312 * <p>Since there is no synchronization performed while accessing these fields, 313 * it is expected that java.util.Map view classes using these fields have 314 * no non-final fields (or any fields at all except for outer-this). Adhering 315 * to this rule would make the races on these fields benign. 316 * 317 * <p>It is also imperative that implementations read the field only once, 318 * as in: 319 * 320 * <pre> {@code 321 * public Set<K> keySet() { 322 * Set<K> ks = keySet; // single racy read 323 * if (ks == null) { 324 * ks = new KeySet(); 325 * keySet = ks; 326 * } 327 * return ks; 328 * } 329 *}</pre> 330 */ 331 transient Set<K> keySet; 332 transient Collection<V> values; 333 334 /** 335 * {@inheritDoc} 336 * 337 * @implSpec 338 * This implementation returns a set that subclasses {@link AbstractSet}. 339 * The subclass's iterator method returns a "wrapper object" over this 340 * map's {@code entrySet()} iterator. The {@code size} method 341 * delegates to this map's {@code size} method and the 342 * {@code contains} method delegates to this map's 343 * {@code containsKey} method. 344 * 345 * <p>The set is created the first time this method is called, 346 * and returned in response to all subsequent calls. No synchronization 347 * is performed, so there is a slight chance that multiple calls to this 348 * method will not all return the same set. 349 */ keySet()350 public Set<K> keySet() { 351 Set<K> ks = keySet; 352 if (ks == null) { 353 ks = new AbstractSet<K>() { 354 public Iterator<K> iterator() { 355 return new Iterator<K>() { 356 private Iterator<Entry<K,V>> i = entrySet().iterator(); 357 358 public boolean hasNext() { 359 return i.hasNext(); 360 } 361 362 public K next() { 363 return i.next().getKey(); 364 } 365 366 public void remove() { 367 i.remove(); 368 } 369 }; 370 } 371 372 public int size() { 373 return AbstractMap.this.size(); 374 } 375 376 public boolean isEmpty() { 377 return AbstractMap.this.isEmpty(); 378 } 379 380 public void clear() { 381 AbstractMap.this.clear(); 382 } 383 384 public boolean contains(Object k) { 385 return AbstractMap.this.containsKey(k); 386 } 387 }; 388 keySet = ks; 389 } 390 return ks; 391 } 392 393 /** 394 * {@inheritDoc} 395 * 396 * @implSpec 397 * This implementation returns a collection that subclasses {@link 398 * AbstractCollection}. The subclass's iterator method returns a 399 * "wrapper object" over this map's {@code entrySet()} iterator. 400 * The {@code size} method delegates to this map's {@code size} 401 * method and the {@code contains} method delegates to this map's 402 * {@code containsValue} method. 403 * 404 * <p>The collection is created the first time this method is called, and 405 * returned in response to all subsequent calls. No synchronization is 406 * performed, so there is a slight chance that multiple calls to this 407 * method will not all return the same collection. 408 */ values()409 public Collection<V> values() { 410 Collection<V> vals = values; 411 if (vals == null) { 412 vals = new AbstractCollection<V>() { 413 public Iterator<V> iterator() { 414 return new Iterator<V>() { 415 private Iterator<Entry<K,V>> i = entrySet().iterator(); 416 417 public boolean hasNext() { 418 return i.hasNext(); 419 } 420 421 public V next() { 422 return i.next().getValue(); 423 } 424 425 public void remove() { 426 i.remove(); 427 } 428 }; 429 } 430 431 public int size() { 432 return AbstractMap.this.size(); 433 } 434 435 public boolean isEmpty() { 436 return AbstractMap.this.isEmpty(); 437 } 438 439 public void clear() { 440 AbstractMap.this.clear(); 441 } 442 443 public boolean contains(Object v) { 444 return AbstractMap.this.containsValue(v); 445 } 446 }; 447 values = vals; 448 } 449 return vals; 450 } 451 entrySet()452 public abstract Set<Entry<K,V>> entrySet(); 453 454 455 // Comparison and hashing 456 457 /** 458 * Compares the specified object with this map for equality. Returns 459 * {@code true} if the given object is also a map and the two maps 460 * represent the same mappings. More formally, two maps {@code m1} and 461 * {@code m2} represent the same mappings if 462 * {@code m1.entrySet().equals(m2.entrySet())}. This ensures that the 463 * {@code equals} method works properly across different implementations 464 * of the {@code Map} interface. 465 * 466 * @implSpec 467 * This implementation first checks if the specified object is this map; 468 * if so it returns {@code true}. Then, it checks if the specified 469 * object is a map whose size is identical to the size of this map; if 470 * not, it returns {@code false}. If so, it iterates over this map's 471 * {@code entrySet} collection, and checks that the specified map 472 * contains each mapping that this map contains. If the specified map 473 * fails to contain such a mapping, {@code false} is returned. If the 474 * iteration completes, {@code true} is returned. 475 * 476 * @param o object to be compared for equality with this map 477 * @return {@code true} if the specified object is equal to this map 478 */ equals(Object o)479 public boolean equals(Object o) { 480 if (o == this) 481 return true; 482 483 if (!(o instanceof Map<?, ?> m)) 484 return false; 485 if (m.size() != size()) 486 return false; 487 488 try { 489 for (Entry<K, V> e : entrySet()) { 490 K key = e.getKey(); 491 V value = e.getValue(); 492 if (value == null) { 493 if (!(m.get(key) == null && m.containsKey(key))) 494 return false; 495 } else { 496 if (!value.equals(m.get(key))) 497 return false; 498 } 499 } 500 } catch (ClassCastException | NullPointerException unused) { 501 return false; 502 } 503 504 return true; 505 } 506 507 /** 508 * Returns the hash code value for this map. The hash code of a map is 509 * defined to be the sum of the hash codes of each entry in the map's 510 * {@code entrySet()} view. This ensures that {@code m1.equals(m2)} 511 * implies that {@code m1.hashCode()==m2.hashCode()} for any two maps 512 * {@code m1} and {@code m2}, as required by the general contract of 513 * {@link Object#hashCode}. 514 * 515 * @implSpec 516 * This implementation iterates over {@code entrySet()}, calling 517 * {@link Map.Entry#hashCode hashCode()} on each element (entry) in the 518 * set, and adding up the results. 519 * 520 * @return the hash code value for this map 521 * @see Map.Entry#hashCode() 522 * @see Object#equals(Object) 523 * @see Set#equals(Object) 524 */ hashCode()525 public int hashCode() { 526 int h = 0; 527 for (Entry<K, V> entry : entrySet()) 528 h += entry.hashCode(); 529 return h; 530 } 531 532 /** 533 * Returns a string representation of this map. The string representation 534 * consists of a list of key-value mappings in the order returned by the 535 * map's {@code entrySet} view's iterator, enclosed in braces 536 * ({@code "{}"}). Adjacent mappings are separated by the characters 537 * {@code ", "} (comma and space). Each key-value mapping is rendered as 538 * the key followed by an equals sign ({@code "="}) followed by the 539 * associated value. Keys and values are converted to strings as by 540 * {@link String#valueOf(Object)}. 541 * 542 * @return a string representation of this map 543 */ toString()544 public String toString() { 545 Iterator<Entry<K,V>> i = entrySet().iterator(); 546 if (! i.hasNext()) 547 return "{}"; 548 549 StringBuilder sb = new StringBuilder(); 550 sb.append('{'); 551 for (;;) { 552 Entry<K,V> e = i.next(); 553 K key = e.getKey(); 554 V value = e.getValue(); 555 sb.append(key == this ? "(this Map)" : key); 556 sb.append('='); 557 sb.append(value == this ? "(this Map)" : value); 558 if (! i.hasNext()) 559 return sb.append('}').toString(); 560 sb.append(',').append(' '); 561 } 562 } 563 564 /** 565 * Returns a shallow copy of this {@code AbstractMap} instance: the keys 566 * and values themselves are not cloned. 567 * 568 * @return a shallow copy of this map 569 */ clone()570 protected Object clone() throws CloneNotSupportedException { 571 AbstractMap<?,?> result = (AbstractMap<?,?>)super.clone(); 572 result.keySet = null; 573 result.values = null; 574 return result; 575 } 576 577 /** 578 * Utility method for SimpleEntry and SimpleImmutableEntry. 579 * Test for equality, checking for nulls. 580 * 581 * NB: Do not replace with Object.equals until JDK-8015417 is resolved. 582 */ eq(Object o1, Object o2)583 private static boolean eq(Object o1, Object o2) { 584 return o1 == null ? o2 == null : o1.equals(o2); 585 } 586 587 // Implementation Note: SimpleEntry and SimpleImmutableEntry 588 // are distinct unrelated classes, even though they share 589 // some code. Since you can't add or subtract final-ness 590 // of a field in a subclass, they can't share representations, 591 // and the amount of duplicated code is too small to warrant 592 // exposing a common abstract class. 593 594 595 /** 596 * An Entry maintaining a key and a value. The value may be 597 * changed using the {@code setValue} method. Instances of 598 * this class are not associated with any map nor with any 599 * map's entry-set view. 600 * 601 * @apiNote 602 * This class facilitates the process of building custom map 603 * implementations. For example, it may be convenient to return 604 * arrays of {@code SimpleEntry} instances in method 605 * {@code Map.entrySet().toArray}. 606 * 607 * @param <K> the type of key 608 * @param <V> the type of the value 609 * 610 * @since 1.6 611 */ 612 public static class SimpleEntry<K,V> 613 implements Entry<K,V>, java.io.Serializable 614 { 615 @java.io.Serial 616 private static final long serialVersionUID = -8499721149061103585L; 617 618 @SuppressWarnings("serial") // Conditionally serializable 619 private final K key; 620 @SuppressWarnings("serial") // Conditionally serializable 621 private V value; 622 623 /** 624 * Creates an entry representing a mapping from the specified 625 * key to the specified value. 626 * 627 * @param key the key represented by this entry 628 * @param value the value represented by this entry 629 */ SimpleEntry(K key, V value)630 public SimpleEntry(K key, V value) { 631 this.key = key; 632 this.value = value; 633 } 634 635 /** 636 * Creates an entry representing the same mapping as the 637 * specified entry. 638 * 639 * @param entry the entry to copy 640 */ SimpleEntry(Entry<? extends K, ? extends V> entry)641 public SimpleEntry(Entry<? extends K, ? extends V> entry) { 642 this.key = entry.getKey(); 643 this.value = entry.getValue(); 644 } 645 646 /** 647 * Returns the key corresponding to this entry. 648 * 649 * @return the key corresponding to this entry 650 */ getKey()651 public K getKey() { 652 return key; 653 } 654 655 /** 656 * Returns the value corresponding to this entry. 657 * 658 * @return the value corresponding to this entry 659 */ getValue()660 public V getValue() { 661 return value; 662 } 663 664 /** 665 * Replaces the value corresponding to this entry with the specified 666 * value. 667 * 668 * @param value new value to be stored in this entry 669 * @return the old value corresponding to the entry 670 */ setValue(V value)671 public V setValue(V value) { 672 V oldValue = this.value; 673 this.value = value; 674 return oldValue; 675 } 676 677 /** 678 * Compares the specified object with this entry for equality. 679 * Returns {@code true} if the given object is also a map entry and 680 * the two entries represent the same mapping. More formally, two 681 * entries {@code e1} and {@code e2} represent the same mapping 682 * if<pre> 683 * (e1.getKey()==null ? 684 * e2.getKey()==null : 685 * e1.getKey().equals(e2.getKey())) 686 * && 687 * (e1.getValue()==null ? 688 * e2.getValue()==null : 689 * e1.getValue().equals(e2.getValue()))</pre> 690 * This ensures that the {@code equals} method works properly across 691 * different implementations of the {@code Map.Entry} interface. 692 * 693 * @param o object to be compared for equality with this map entry 694 * @return {@code true} if the specified object is equal to this map 695 * entry 696 * @see #hashCode 697 */ equals(Object o)698 public boolean equals(Object o) { 699 return o instanceof Map.Entry<?, ?> e 700 && eq(key, e.getKey()) 701 && eq(value, e.getValue()); 702 } 703 704 /** 705 * Returns the hash code value for this map entry. The hash code 706 * of a map entry {@code e} is defined to be: <pre> 707 * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^ 708 * (e.getValue()==null ? 0 : e.getValue().hashCode())</pre> 709 * This ensures that {@code e1.equals(e2)} implies that 710 * {@code e1.hashCode()==e2.hashCode()} for any two Entries 711 * {@code e1} and {@code e2}, as required by the general 712 * contract of {@link Object#hashCode}. 713 * 714 * @return the hash code value for this map entry 715 * @see #equals 716 */ hashCode()717 public int hashCode() { 718 return (key == null ? 0 : key.hashCode()) ^ 719 (value == null ? 0 : value.hashCode()); 720 } 721 722 /** 723 * Returns a String representation of this map entry. This 724 * implementation returns the string representation of this 725 * entry's key followed by the equals character ("{@code =}") 726 * followed by the string representation of this entry's value. 727 * 728 * @return a String representation of this map entry 729 */ toString()730 public String toString() { 731 return key + "=" + value; 732 } 733 734 } 735 736 /** 737 * An unmodifiable Entry maintaining a key and a value. This class 738 * does not support the {@code setValue} method. Instances of 739 * this class are not associated with any map nor with any map's 740 * entry-set view. 741 * 742 * @apiNote 743 * Instances of this class are not necessarily immutable, as the key 744 * and value may be mutable. An instance of <i>this specific class</i> 745 * is unmodifiable, because the key and value references cannot be 746 * changed. A reference of this <i>type</i> may not be unmodifiable, 747 * as a subclass may be modifiable or may provide the appearance of modifiability. 748 * <p> 749 * This class may be convenient in methods that return thread-safe snapshots of 750 * key-value mappings. For alternatives, see the 751 * {@link Map#entry Map::entry} and {@link Map.Entry#copyOf Map.Entry::copyOf} 752 * methods. 753 * 754 * @param <K> the type of the keys 755 * @param <V> the type of the value 756 * @since 1.6 757 */ 758 public static class SimpleImmutableEntry<K,V> 759 implements Entry<K,V>, java.io.Serializable 760 { 761 @java.io.Serial 762 private static final long serialVersionUID = 7138329143949025153L; 763 764 @SuppressWarnings("serial") // Not statically typed as Serializable 765 private final K key; 766 @SuppressWarnings("serial") // Not statically typed as Serializable 767 private final V value; 768 769 /** 770 * Creates an entry representing a mapping from the specified 771 * key to the specified value. 772 * 773 * @param key the key represented by this entry 774 * @param value the value represented by this entry 775 */ SimpleImmutableEntry(K key, V value)776 public SimpleImmutableEntry(K key, V value) { 777 this.key = key; 778 this.value = value; 779 } 780 781 /** 782 * Creates an entry representing the same mapping as the 783 * specified entry. 784 * 785 * @param entry the entry to copy 786 */ SimpleImmutableEntry(Entry<? extends K, ? extends V> entry)787 public SimpleImmutableEntry(Entry<? extends K, ? extends V> entry) { 788 this.key = entry.getKey(); 789 this.value = entry.getValue(); 790 } 791 792 /** 793 * Returns the key corresponding to this entry. 794 * 795 * @return the key corresponding to this entry 796 */ getKey()797 public K getKey() { 798 return key; 799 } 800 801 /** 802 * Returns the value corresponding to this entry. 803 * 804 * @return the value corresponding to this entry 805 */ getValue()806 public V getValue() { 807 return value; 808 } 809 810 /** 811 * Replaces the value corresponding to this entry with the specified 812 * value (optional operation). This implementation simply throws 813 * {@code UnsupportedOperationException}, as this class implements 814 * an unmodifiable map entry. 815 * 816 * @implSpec 817 * The implementation in this class always throws {@code UnsupportedOperationException}. 818 * 819 * @param value new value to be stored in this entry 820 * @return (Does not return) 821 * @throws UnsupportedOperationException always 822 */ setValue(V value)823 public V setValue(V value) { 824 throw new UnsupportedOperationException(); 825 } 826 827 /** 828 * Compares the specified object with this entry for equality. 829 * Returns {@code true} if the given object is also a map entry and 830 * the two entries represent the same mapping. More formally, two 831 * entries {@code e1} and {@code e2} represent the same mapping 832 * if<pre> 833 * (e1.getKey()==null ? 834 * e2.getKey()==null : 835 * e1.getKey().equals(e2.getKey())) 836 * && 837 * (e1.getValue()==null ? 838 * e2.getValue()==null : 839 * e1.getValue().equals(e2.getValue()))</pre> 840 * This ensures that the {@code equals} method works properly across 841 * different implementations of the {@code Map.Entry} interface. 842 * 843 * @param o object to be compared for equality with this map entry 844 * @return {@code true} if the specified object is equal to this map 845 * entry 846 * @see #hashCode 847 */ equals(Object o)848 public boolean equals(Object o) { 849 return o instanceof Map.Entry<?, ?> e 850 && eq(key, e.getKey()) 851 && eq(value, e.getValue()); 852 } 853 854 /** 855 * Returns the hash code value for this map entry. The hash code 856 * of a map entry {@code e} is defined to be: <pre> 857 * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^ 858 * (e.getValue()==null ? 0 : e.getValue().hashCode())</pre> 859 * This ensures that {@code e1.equals(e2)} implies that 860 * {@code e1.hashCode()==e2.hashCode()} for any two Entries 861 * {@code e1} and {@code e2}, as required by the general 862 * contract of {@link Object#hashCode}. 863 * 864 * @return the hash code value for this map entry 865 * @see #equals 866 */ hashCode()867 public int hashCode() { 868 return (key == null ? 0 : key.hashCode()) ^ 869 (value == null ? 0 : value.hashCode()); 870 } 871 872 /** 873 * Returns a String representation of this map entry. This 874 * implementation returns the string representation of this 875 * entry's key followed by the equals character ("{@code =}") 876 * followed by the string representation of this entry's value. 877 * 878 * @return a String representation of this map entry 879 */ toString()880 public String toString() { 881 return key + "=" + value; 882 } 883 } 884 885 /** 886 * Delegates all Collection methods to the provided non-sequenced map view, 887 * except add() and addAll(), which throw UOE. This provides the common 888 * implementation of each of the sequenced views of the SequencedMap. 889 * Each view implementation is a subclass that provides an instance of the 890 * non-sequenced view as a delegate and an implementation of reversed(). 891 * Each view also inherits the default implementations for the sequenced 892 * methods from SequencedCollection or SequencedSet. 893 * <p> 894 * Ideally this would be a private class within SequencedMap, but private 895 * classes aren't permitted within interfaces. 896 * <p> 897 * The non-sequenced map view is obtained by calling the abstract view() 898 * method for each operation. 899 * 900 * @param <E> the view's element type 901 */ 902 /* non-public */ abstract static class ViewCollection<E> implements Collection<E> { uoe()903 UnsupportedOperationException uoe() { return new UnsupportedOperationException(); } view()904 abstract Collection<E> view(); 905 add(E t)906 public boolean add(E t) { throw uoe(); } addAll(Collection<? extends E> c)907 public boolean addAll(Collection<? extends E> c) { throw uoe(); } clear()908 public void clear() { view().clear(); } contains(Object o)909 public boolean contains(Object o) { return view().contains(o); } containsAll(Collection<?> c)910 public boolean containsAll(Collection<?> c) { return view().containsAll(c); } forEach(Consumer<? super E> c)911 public void forEach(Consumer<? super E> c) { view().forEach(c); } isEmpty()912 public boolean isEmpty() { return view().isEmpty(); } iterator()913 public Iterator<E> iterator() { return view().iterator(); } parallelStream()914 public Stream<E> parallelStream() { return view().parallelStream(); } remove(Object o)915 public boolean remove(Object o) { return view().remove(o); } removeAll(Collection<?> c)916 public boolean removeAll(Collection<?> c) { return view().removeAll(c); } removeIf(Predicate<? super E> filter)917 public boolean removeIf(Predicate<? super E> filter) { return view().removeIf(filter); } retainAll(Collection<?> c)918 public boolean retainAll(Collection<?> c) { return view().retainAll(c); } size()919 public int size() { return view().size(); } spliterator()920 public Spliterator<E> spliterator() { return view().spliterator(); } stream()921 public Stream<E> stream() { return view().stream(); } toArray()922 public Object[] toArray() { return view().toArray(); } toArray(IntFunction<T[]> generator)923 public <T> T[] toArray(IntFunction<T[]> generator) { return view().toArray(generator); } toArray(T[] a)924 public <T> T[] toArray(T[] a) { return view().toArray(a); } toString()925 public String toString() { return view().toString(); } 926 } 927 } 928