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 28 import java.io.IOException; 29 import java.io.ObjectInputStream; 30 import java.io.ObjectOutputStream; 31 import java.io.Serializable; 32 import java.lang.reflect.Array; 33 import java.util.function.BiConsumer; 34 import java.util.function.BiFunction; 35 import java.util.function.Consumer; 36 import java.util.function.Function; 37 import java.util.function.IntFunction; 38 import java.util.function.Predicate; 39 import java.util.function.UnaryOperator; 40 import java.util.stream.IntStream; 41 import java.util.stream.Stream; 42 import java.util.stream.StreamSupport; 43 import jdk.internal.access.SharedSecrets; 44 45 /** 46 * This class consists exclusively of static methods that operate on or return 47 * collections. It contains polymorphic algorithms that operate on 48 * collections, "wrappers", which return a new collection backed by a 49 * specified collection, and a few other odds and ends. 50 * 51 * <p>The methods of this class all throw a {@code NullPointerException} 52 * if the collections or class objects provided to them are null. 53 * 54 * <p>The documentation for the polymorphic algorithms contained in this class 55 * generally includes a brief description of the <i>implementation</i>. Such 56 * descriptions should be regarded as <i>implementation notes</i>, rather than 57 * parts of the <i>specification</i>. Implementors should feel free to 58 * substitute other algorithms, so long as the specification itself is adhered 59 * to. (For example, the algorithm used by {@code sort} does not have to be 60 * a mergesort, but it does have to be <i>stable</i>.) 61 * 62 * <p>The "destructive" algorithms contained in this class, that is, the 63 * algorithms that modify the collection on which they operate, are specified 64 * to throw {@code UnsupportedOperationException} if the collection does not 65 * support the appropriate mutation primitive(s), such as the {@code set} 66 * method. These algorithms may, but are not required to, throw this 67 * exception if an invocation would have no effect on the collection. For 68 * example, invoking the {@code sort} method on an unmodifiable list that is 69 * already sorted may or may not throw {@code UnsupportedOperationException}. 70 * 71 * <p>This class is a member of the 72 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> 73 * Java Collections Framework</a>. 74 * 75 * @author Josh Bloch 76 * @author Neal Gafter 77 * @see Collection 78 * @see Set 79 * @see List 80 * @see Map 81 * @since 1.2 82 */ 83 84 public class Collections { 85 // Suppresses default constructor, ensuring non-instantiability. 86 private Collections() { 87 } 88 89 // Algorithms 90 91 /* 92 * Tuning parameters for algorithms - Many of the List algorithms have 93 * two implementations, one of which is appropriate for RandomAccess 94 * lists, the other for "sequential." Often, the random access variant 95 * yields better performance on small sequential access lists. The 96 * tuning parameters below determine the cutoff point for what constitutes 97 * a "small" sequential access list for each algorithm. The values below 98 * were empirically determined to work well for LinkedList. Hopefully 99 * they should be reasonable for other sequential access List 100 * implementations. Those doing performance work on this code would 101 * do well to validate the values of these parameters from time to time. 102 * (The first word of each tuning parameter name is the algorithm to which 103 * it applies.) 104 */ 105 private static final int BINARYSEARCH_THRESHOLD = 5000; 106 private static final int REVERSE_THRESHOLD = 18; 107 private static final int SHUFFLE_THRESHOLD = 5; 108 private static final int FILL_THRESHOLD = 25; 109 private static final int ROTATE_THRESHOLD = 100; 110 private static final int COPY_THRESHOLD = 10; 111 private static final int REPLACEALL_THRESHOLD = 11; 112 private static final int INDEXOFSUBLIST_THRESHOLD = 35; 113 114 /** 115 * Sorts the specified list into ascending order, according to the 116 * {@linkplain Comparable natural ordering} of its elements. 117 * All elements in the list must implement the {@link Comparable} 118 * interface. Furthermore, all elements in the list must be 119 * <i>mutually comparable</i> (that is, {@code e1.compareTo(e2)} 120 * must not throw a {@code ClassCastException} for any elements 121 * {@code e1} and {@code e2} in the list). 122 * 123 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will 124 * not be reordered as a result of the sort. 125 * 126 * <p>The specified list must be modifiable, but need not be resizable. 127 * 128 * @implNote 129 * This implementation defers to the {@link List#sort(Comparator)} 130 * method using the specified list and a {@code null} comparator. 131 * 132 * @param <T> the class of the objects in the list 133 * @param list the list to be sorted. 134 * @throws ClassCastException if the list contains elements that are not 135 * <i>mutually comparable</i> (for example, strings and integers). 136 * @throws UnsupportedOperationException if the specified list's 137 * list-iterator does not support the {@code set} operation. 138 * @throws IllegalArgumentException (optional) if the implementation 139 * detects that the natural ordering of the list elements is 140 * found to violate the {@link Comparable} contract 141 * @see List#sort(Comparator) 142 */ 143 @SuppressWarnings("unchecked") 144 public static <T extends Comparable<? super T>> void sort(List<T> list) { 145 list.sort(null); 146 } 147 148 /** 149 * Sorts the specified list according to the order induced by the 150 * specified comparator. All elements in the list must be <i>mutually 151 * comparable</i> using the specified comparator (that is, 152 * {@code c.compare(e1, e2)} must not throw a {@code ClassCastException} 153 * for any elements {@code e1} and {@code e2} in the list). 154 * 155 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will 156 * not be reordered as a result of the sort. 157 * 158 * <p>The specified list must be modifiable, but need not be resizable. 159 * 160 * @implNote 161 * This implementation defers to the {@link List#sort(Comparator)} 162 * method using the specified list and comparator. 163 * 164 * @param <T> the class of the objects in the list 165 * @param list the list to be sorted. 166 * @param c the comparator to determine the order of the list. A 167 * {@code null} value indicates that the elements' <i>natural 168 * ordering</i> should be used. 169 * @throws ClassCastException if the list contains elements that are not 170 * <i>mutually comparable</i> using the specified comparator. 171 * @throws UnsupportedOperationException if the specified list's 172 * list-iterator does not support the {@code set} operation. 173 * @throws IllegalArgumentException (optional) if the comparator is 174 * found to violate the {@link Comparator} contract 175 * @see List#sort(Comparator) 176 */ 177 @SuppressWarnings({"unchecked", "rawtypes"}) 178 public static <T> void sort(List<T> list, Comparator<? super T> c) { 179 list.sort(c); 180 } 181 182 183 /** 184 * Searches the specified list for the specified object using the binary 185 * search algorithm. The list must be sorted into ascending order 186 * according to the {@linkplain Comparable natural ordering} of its 187 * elements (as by the {@link #sort(List)} method) prior to making this 188 * call. If it is not sorted, the results are undefined. If the list 189 * contains multiple elements equal to the specified object, there is no 190 * guarantee which one will be found. 191 * 192 * <p>This method runs in log(n) time for a "random access" list (which 193 * provides near-constant-time positional access). If the specified list 194 * does not implement the {@link RandomAccess} interface and is large, 195 * this method will do an iterator-based binary search that performs 196 * O(n) link traversals and O(log n) element comparisons. 197 * 198 * @param <T> the class of the objects in the list 199 * @param list the list to be searched. 200 * @param key the key to be searched for. 201 * @return the index of the search key, if it is contained in the list; 202 * otherwise, <code>(-(<i>insertion point</i>) - 1)</code>. The 203 * <i>insertion point</i> is defined as the point at which the 204 * key would be inserted into the list: the index of the first 205 * element greater than the key, or {@code list.size()} if all 206 * elements in the list are less than the specified key. Note 207 * that this guarantees that the return value will be >= 0 if 208 * and only if the key is found. 209 * @throws ClassCastException if the list contains elements that are not 210 * <i>mutually comparable</i> (for example, strings and 211 * integers), or the search key is not mutually comparable 212 * with the elements of the list. 213 */ 214 public static <T> 215 int binarySearch(List<? extends Comparable<? super T>> list, T key) { 216 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD) 217 return Collections.indexedBinarySearch(list, key); 218 else 219 return Collections.iteratorBinarySearch(list, key); 220 } 221 222 private static <T> 223 int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key) { 224 int low = 0; 225 int high = list.size()-1; 226 227 while (low <= high) { 228 int mid = (low + high) >>> 1; 229 Comparable<? super T> midVal = list.get(mid); 230 int cmp = midVal.compareTo(key); 231 232 if (cmp < 0) 233 low = mid + 1; 234 else if (cmp > 0) 235 high = mid - 1; 236 else 237 return mid; // key found 238 } 239 return -(low + 1); // key not found 240 } 241 242 private static <T> 243 int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key) 244 { 245 int low = 0; 246 int high = list.size()-1; 247 ListIterator<? extends Comparable<? super T>> i = list.listIterator(); 248 249 while (low <= high) { 250 int mid = (low + high) >>> 1; 251 Comparable<? super T> midVal = get(i, mid); 252 int cmp = midVal.compareTo(key); 253 254 if (cmp < 0) 255 low = mid + 1; 256 else if (cmp > 0) 257 high = mid - 1; 258 else 259 return mid; // key found 260 } 261 return -(low + 1); // key not found 262 } 263 264 /** 265 * Gets the ith element from the given list by repositioning the specified 266 * list listIterator. 267 */ 268 private static <T> T get(ListIterator<? extends T> i, int index) { 269 T obj = null; 270 int pos = i.nextIndex(); 271 if (pos <= index) { 272 do { 273 obj = i.next(); 274 } while (pos++ < index); 275 } else { 276 do { 277 obj = i.previous(); 278 } while (--pos > index); 279 } 280 return obj; 281 } 282 283 /** 284 * Searches the specified list for the specified object using the binary 285 * search algorithm. The list must be sorted into ascending order 286 * according to the specified comparator (as by the 287 * {@link #sort(List, Comparator) sort(List, Comparator)} 288 * method), prior to making this call. If it is 289 * not sorted, the results are undefined. If the list contains multiple 290 * elements equal to the specified object, there is no guarantee which one 291 * will be found. 292 * 293 * <p>This method runs in log(n) time for a "random access" list (which 294 * provides near-constant-time positional access). If the specified list 295 * does not implement the {@link RandomAccess} interface and is large, 296 * this method will do an iterator-based binary search that performs 297 * O(n) link traversals and O(log n) element comparisons. 298 * 299 * @param <T> the class of the objects in the list 300 * @param list the list to be searched. 301 * @param key the key to be searched for. 302 * @param c the comparator by which the list is ordered. 303 * A {@code null} value indicates that the elements' 304 * {@linkplain Comparable natural ordering} should be used. 305 * @return the index of the search key, if it is contained in the list; 306 * otherwise, <code>(-(<i>insertion point</i>) - 1)</code>. The 307 * <i>insertion point</i> is defined as the point at which the 308 * key would be inserted into the list: the index of the first 309 * element greater than the key, or {@code list.size()} if all 310 * elements in the list are less than the specified key. Note 311 * that this guarantees that the return value will be >= 0 if 312 * and only if the key is found. 313 * @throws ClassCastException if the list contains elements that are not 314 * <i>mutually comparable</i> using the specified comparator, 315 * or the search key is not mutually comparable with the 316 * elements of the list using this comparator. 317 */ 318 @SuppressWarnings("unchecked") 319 public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) { 320 if (c==null) 321 return binarySearch((List<? extends Comparable<? super T>>) list, key); 322 323 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD) 324 return Collections.indexedBinarySearch(list, key, c); 325 else 326 return Collections.iteratorBinarySearch(list, key, c); 327 } 328 329 private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) { 330 int low = 0; 331 int high = l.size()-1; 332 333 while (low <= high) { 334 int mid = (low + high) >>> 1; 335 T midVal = l.get(mid); 336 int cmp = c.compare(midVal, key); 337 338 if (cmp < 0) 339 low = mid + 1; 340 else if (cmp > 0) 341 high = mid - 1; 342 else 343 return mid; // key found 344 } 345 return -(low + 1); // key not found 346 } 347 348 private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) { 349 int low = 0; 350 int high = l.size()-1; 351 ListIterator<? extends T> i = l.listIterator(); 352 353 while (low <= high) { 354 int mid = (low + high) >>> 1; 355 T midVal = get(i, mid); 356 int cmp = c.compare(midVal, key); 357 358 if (cmp < 0) 359 low = mid + 1; 360 else if (cmp > 0) 361 high = mid - 1; 362 else 363 return mid; // key found 364 } 365 return -(low + 1); // key not found 366 } 367 368 /** 369 * Reverses the order of the elements in the specified list.<p> 370 * 371 * This method runs in linear time. 372 * 373 * @param list the list whose elements are to be reversed. 374 * @throws UnsupportedOperationException if the specified list or 375 * its list-iterator does not support the {@code set} operation. 376 */ 377 @SuppressWarnings({"rawtypes", "unchecked"}) 378 public static void reverse(List<?> list) { 379 int size = list.size(); 380 if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) { 381 for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--) 382 swap(list, i, j); 383 } else { 384 // instead of using a raw type here, it's possible to capture 385 // the wildcard but it will require a call to a supplementary 386 // private method 387 ListIterator fwd = list.listIterator(); 388 ListIterator rev = list.listIterator(size); 389 for (int i=0, mid=list.size()>>1; i<mid; i++) { 390 Object tmp = fwd.next(); 391 fwd.set(rev.previous()); 392 rev.set(tmp); 393 } 394 } 395 } 396 397 /** 398 * Randomly permutes the specified list using a default source of 399 * randomness. All permutations occur with approximately equal 400 * likelihood. 401 * 402 * <p>The hedge "approximately" is used in the foregoing description because 403 * default source of randomness is only approximately an unbiased source 404 * of independently chosen bits. If it were a perfect source of randomly 405 * chosen bits, then the algorithm would choose permutations with perfect 406 * uniformity. 407 * 408 * <p>This implementation traverses the list backwards, from the last 409 * element up to the second, repeatedly swapping a randomly selected element 410 * into the "current position". Elements are randomly selected from the 411 * portion of the list that runs from the first element to the current 412 * position, inclusive. 413 * 414 * <p>This method runs in linear time. If the specified list does not 415 * implement the {@link RandomAccess} interface and is large, this 416 * implementation dumps the specified list into an array before shuffling 417 * it, and dumps the shuffled array back into the list. This avoids the 418 * quadratic behavior that would result from shuffling a "sequential 419 * access" list in place. 420 * 421 * @param list the list to be shuffled. 422 * @throws UnsupportedOperationException if the specified list or 423 * its list-iterator does not support the {@code set} operation. 424 */ 425 public static void shuffle(List<?> list) { 426 Random rnd = r; 427 if (rnd == null) 428 r = rnd = new Random(); // harmless race. 429 shuffle(list, rnd); 430 } 431 432 private static Random r; 433 434 /** 435 * Randomly permute the specified list using the specified source of 436 * randomness. All permutations occur with equal likelihood 437 * assuming that the source of randomness is fair.<p> 438 * 439 * This implementation traverses the list backwards, from the last element 440 * up to the second, repeatedly swapping a randomly selected element into 441 * the "current position". Elements are randomly selected from the 442 * portion of the list that runs from the first element to the current 443 * position, inclusive.<p> 444 * 445 * This method runs in linear time. If the specified list does not 446 * implement the {@link RandomAccess} interface and is large, this 447 * implementation dumps the specified list into an array before shuffling 448 * it, and dumps the shuffled array back into the list. This avoids the 449 * quadratic behavior that would result from shuffling a "sequential 450 * access" list in place. 451 * 452 * @param list the list to be shuffled. 453 * @param rnd the source of randomness to use to shuffle the list. 454 * @throws UnsupportedOperationException if the specified list or its 455 * list-iterator does not support the {@code set} operation. 456 */ 457 @SuppressWarnings({"rawtypes", "unchecked"}) 458 public static void shuffle(List<?> list, Random rnd) { 459 int size = list.size(); 460 if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) { 461 for (int i=size; i>1; i--) 462 swap(list, i-1, rnd.nextInt(i)); 463 } else { 464 Object[] arr = list.toArray(); 465 466 // Shuffle array 467 for (int i=size; i>1; i--) 468 swap(arr, i-1, rnd.nextInt(i)); 469 470 // Dump array back into list 471 // instead of using a raw type here, it's possible to capture 472 // the wildcard but it will require a call to a supplementary 473 // private method 474 ListIterator it = list.listIterator(); 475 for (Object e : arr) { 476 it.next(); 477 it.set(e); 478 } 479 } 480 } 481 482 /** 483 * Swaps the elements at the specified positions in the specified list. 484 * (If the specified positions are equal, invoking this method leaves 485 * the list unchanged.) 486 * 487 * @param list The list in which to swap elements. 488 * @param i the index of one element to be swapped. 489 * @param j the index of the other element to be swapped. 490 * @throws IndexOutOfBoundsException if either {@code i} or {@code j} 491 * is out of range (i < 0 || i >= list.size() 492 * || j < 0 || j >= list.size()). 493 * @since 1.4 494 */ 495 @SuppressWarnings({"rawtypes", "unchecked"}) 496 public static void swap(List<?> list, int i, int j) { 497 // instead of using a raw type here, it's possible to capture 498 // the wildcard but it will require a call to a supplementary 499 // private method 500 final List l = list; 501 l.set(i, l.set(j, l.get(i))); 502 } 503 504 /** 505 * Swaps the two specified elements in the specified array. 506 */ 507 private static void swap(Object[] arr, int i, int j) { 508 Object tmp = arr[i]; 509 arr[i] = arr[j]; 510 arr[j] = tmp; 511 } 512 513 /** 514 * Replaces all of the elements of the specified list with the specified 515 * element. <p> 516 * 517 * This method runs in linear time. 518 * 519 * @param <T> the class of the objects in the list 520 * @param list the list to be filled with the specified element. 521 * @param obj The element with which to fill the specified list. 522 * @throws UnsupportedOperationException if the specified list or its 523 * list-iterator does not support the {@code set} operation. 524 */ 525 public static <T> void fill(List<? super T> list, T obj) { 526 int size = list.size(); 527 528 if (size < FILL_THRESHOLD || list instanceof RandomAccess) { 529 for (int i=0; i<size; i++) 530 list.set(i, obj); 531 } else { 532 ListIterator<? super T> itr = list.listIterator(); 533 for (int i=0; i<size; i++) { 534 itr.next(); 535 itr.set(obj); 536 } 537 } 538 } 539 540 /** 541 * Copies all of the elements from one list into another. After the 542 * operation, the index of each copied element in the destination list 543 * will be identical to its index in the source list. The destination 544 * list's size must be greater than or equal to the source list's size. 545 * If it is greater, the remaining elements in the destination list are 546 * unaffected. <p> 547 * 548 * This method runs in linear time. 549 * 550 * @param <T> the class of the objects in the lists 551 * @param dest The destination list. 552 * @param src The source list. 553 * @throws IndexOutOfBoundsException if the destination list is too small 554 * to contain the entire source List. 555 * @throws UnsupportedOperationException if the destination list's 556 * list-iterator does not support the {@code set} operation. 557 */ 558 public static <T> void copy(List<? super T> dest, List<? extends T> src) { 559 int srcSize = src.size(); 560 if (srcSize > dest.size()) 561 throw new IndexOutOfBoundsException("Source does not fit in dest"); 562 563 if (srcSize < COPY_THRESHOLD || 564 (src instanceof RandomAccess && dest instanceof RandomAccess)) { 565 for (int i=0; i<srcSize; i++) 566 dest.set(i, src.get(i)); 567 } else { 568 ListIterator<? super T> di=dest.listIterator(); 569 ListIterator<? extends T> si=src.listIterator(); 570 for (int i=0; i<srcSize; i++) { 571 di.next(); 572 di.set(si.next()); 573 } 574 } 575 } 576 577 /** 578 * Returns the minimum element of the given collection, according to the 579 * <i>natural ordering</i> of its elements. All elements in the 580 * collection must implement the {@code Comparable} interface. 581 * Furthermore, all elements in the collection must be <i>mutually 582 * comparable</i> (that is, {@code e1.compareTo(e2)} must not throw a 583 * {@code ClassCastException} for any elements {@code e1} and 584 * {@code e2} in the collection).<p> 585 * 586 * This method iterates over the entire collection, hence it requires 587 * time proportional to the size of the collection. 588 * 589 * @param <T> the class of the objects in the collection 590 * @param coll the collection whose minimum element is to be determined. 591 * @return the minimum element of the given collection, according 592 * to the <i>natural ordering</i> of its elements. 593 * @throws ClassCastException if the collection contains elements that are 594 * not <i>mutually comparable</i> (for example, strings and 595 * integers). 596 * @throws NoSuchElementException if the collection is empty. 597 * @see Comparable 598 */ 599 public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) { 600 Iterator<? extends T> i = coll.iterator(); 601 T candidate = i.next(); 602 603 while (i.hasNext()) { 604 T next = i.next(); 605 if (next.compareTo(candidate) < 0) 606 candidate = next; 607 } 608 return candidate; 609 } 610 611 /** 612 * Returns the minimum element of the given collection, according to the 613 * order induced by the specified comparator. All elements in the 614 * collection must be <i>mutually comparable</i> by the specified 615 * comparator (that is, {@code comp.compare(e1, e2)} must not throw a 616 * {@code ClassCastException} for any elements {@code e1} and 617 * {@code e2} in the collection).<p> 618 * 619 * This method iterates over the entire collection, hence it requires 620 * time proportional to the size of the collection. 621 * 622 * @param <T> the class of the objects in the collection 623 * @param coll the collection whose minimum element is to be determined. 624 * @param comp the comparator with which to determine the minimum element. 625 * A {@code null} value indicates that the elements' <i>natural 626 * ordering</i> should be used. 627 * @return the minimum element of the given collection, according 628 * to the specified comparator. 629 * @throws ClassCastException if the collection contains elements that are 630 * not <i>mutually comparable</i> using the specified comparator. 631 * @throws NoSuchElementException if the collection is empty. 632 * @see Comparable 633 */ 634 @SuppressWarnings({"unchecked", "rawtypes"}) 635 public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) { 636 if (comp==null) 637 return (T)min((Collection) coll); 638 639 Iterator<? extends T> i = coll.iterator(); 640 T candidate = i.next(); 641 642 while (i.hasNext()) { 643 T next = i.next(); 644 if (comp.compare(next, candidate) < 0) 645 candidate = next; 646 } 647 return candidate; 648 } 649 650 /** 651 * Returns the maximum element of the given collection, according to the 652 * <i>natural ordering</i> of its elements. All elements in the 653 * collection must implement the {@code Comparable} interface. 654 * Furthermore, all elements in the collection must be <i>mutually 655 * comparable</i> (that is, {@code e1.compareTo(e2)} must not throw a 656 * {@code ClassCastException} for any elements {@code e1} and 657 * {@code e2} in the collection).<p> 658 * 659 * This method iterates over the entire collection, hence it requires 660 * time proportional to the size of the collection. 661 * 662 * @param <T> the class of the objects in the collection 663 * @param coll the collection whose maximum element is to be determined. 664 * @return the maximum element of the given collection, according 665 * to the <i>natural ordering</i> of its elements. 666 * @throws ClassCastException if the collection contains elements that are 667 * not <i>mutually comparable</i> (for example, strings and 668 * integers). 669 * @throws NoSuchElementException if the collection is empty. 670 * @see Comparable 671 */ 672 public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) { 673 Iterator<? extends T> i = coll.iterator(); 674 T candidate = i.next(); 675 676 while (i.hasNext()) { 677 T next = i.next(); 678 if (next.compareTo(candidate) > 0) 679 candidate = next; 680 } 681 return candidate; 682 } 683 684 /** 685 * Returns the maximum element of the given collection, according to the 686 * order induced by the specified comparator. All elements in the 687 * collection must be <i>mutually comparable</i> by the specified 688 * comparator (that is, {@code comp.compare(e1, e2)} must not throw a 689 * {@code ClassCastException} for any elements {@code e1} and 690 * {@code e2} in the collection).<p> 691 * 692 * This method iterates over the entire collection, hence it requires 693 * time proportional to the size of the collection. 694 * 695 * @param <T> the class of the objects in the collection 696 * @param coll the collection whose maximum element is to be determined. 697 * @param comp the comparator with which to determine the maximum element. 698 * A {@code null} value indicates that the elements' <i>natural 699 * ordering</i> should be used. 700 * @return the maximum element of the given collection, according 701 * to the specified comparator. 702 * @throws ClassCastException if the collection contains elements that are 703 * not <i>mutually comparable</i> using the specified comparator. 704 * @throws NoSuchElementException if the collection is empty. 705 * @see Comparable 706 */ 707 @SuppressWarnings({"unchecked", "rawtypes"}) 708 public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) { 709 if (comp==null) 710 return (T)max((Collection) coll); 711 712 Iterator<? extends T> i = coll.iterator(); 713 T candidate = i.next(); 714 715 while (i.hasNext()) { 716 T next = i.next(); 717 if (comp.compare(next, candidate) > 0) 718 candidate = next; 719 } 720 return candidate; 721 } 722 723 /** 724 * Rotates the elements in the specified list by the specified distance. 725 * After calling this method, the element at index {@code i} will be 726 * the element previously at index {@code (i - distance)} mod 727 * {@code list.size()}, for all values of {@code i} between {@code 0} 728 * and {@code list.size()-1}, inclusive. (This method has no effect on 729 * the size of the list.) 730 * 731 * <p>For example, suppose {@code list} comprises{@code [t, a, n, k, s]}. 732 * After invoking {@code Collections.rotate(list, 1)} (or 733 * {@code Collections.rotate(list, -4)}), {@code list} will comprise 734 * {@code [s, t, a, n, k]}. 735 * 736 * <p>Note that this method can usefully be applied to sublists to 737 * move one or more elements within a list while preserving the 738 * order of the remaining elements. For example, the following idiom 739 * moves the element at index {@code j} forward to position 740 * {@code k} (which must be greater than or equal to {@code j}): 741 * <pre> 742 * Collections.rotate(list.subList(j, k+1), -1); 743 * </pre> 744 * To make this concrete, suppose {@code list} comprises 745 * {@code [a, b, c, d, e]}. To move the element at index {@code 1} 746 * ({@code b}) forward two positions, perform the following invocation: 747 * <pre> 748 * Collections.rotate(l.subList(1, 4), -1); 749 * </pre> 750 * The resulting list is {@code [a, c, d, b, e]}. 751 * 752 * <p>To move more than one element forward, increase the absolute value 753 * of the rotation distance. To move elements backward, use a positive 754 * shift distance. 755 * 756 * <p>If the specified list is small or implements the {@link 757 * RandomAccess} interface, this implementation exchanges the first 758 * element into the location it should go, and then repeatedly exchanges 759 * the displaced element into the location it should go until a displaced 760 * element is swapped into the first element. If necessary, the process 761 * is repeated on the second and successive elements, until the rotation 762 * is complete. If the specified list is large and doesn't implement the 763 * {@code RandomAccess} interface, this implementation breaks the 764 * list into two sublist views around index {@code -distance mod size}. 765 * Then the {@link #reverse(List)} method is invoked on each sublist view, 766 * and finally it is invoked on the entire list. For a more complete 767 * description of both algorithms, see Section 2.3 of Jon Bentley's 768 * <i>Programming Pearls</i> (Addison-Wesley, 1986). 769 * 770 * @param list the list to be rotated. 771 * @param distance the distance to rotate the list. There are no 772 * constraints on this value; it may be zero, negative, or 773 * greater than {@code list.size()}. 774 * @throws UnsupportedOperationException if the specified list or 775 * its list-iterator does not support the {@code set} operation. 776 * @since 1.4 777 */ 778 public static void rotate(List<?> list, int distance) { 779 if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD) 780 rotate1(list, distance); 781 else 782 rotate2(list, distance); 783 } 784 785 private static <T> void rotate1(List<T> list, int distance) { 786 int size = list.size(); 787 if (size == 0) 788 return; 789 distance = distance % size; 790 if (distance < 0) 791 distance += size; 792 if (distance == 0) 793 return; 794 795 for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) { 796 T displaced = list.get(cycleStart); 797 int i = cycleStart; 798 do { 799 i += distance; 800 if (i >= size) 801 i -= size; 802 displaced = list.set(i, displaced); 803 nMoved ++; 804 } while (i != cycleStart); 805 } 806 } 807 808 private static void rotate2(List<?> list, int distance) { 809 int size = list.size(); 810 if (size == 0) 811 return; 812 int mid = -distance % size; 813 if (mid < 0) 814 mid += size; 815 if (mid == 0) 816 return; 817 818 reverse(list.subList(0, mid)); 819 reverse(list.subList(mid, size)); 820 reverse(list); 821 } 822 823 /** 824 * Replaces all occurrences of one specified value in a list with another. 825 * More formally, replaces with {@code newVal} each element {@code e} 826 * in {@code list} such that 827 * {@code (oldVal==null ? e==null : oldVal.equals(e))}. 828 * (This method has no effect on the size of the list.) 829 * 830 * @param <T> the class of the objects in the list 831 * @param list the list in which replacement is to occur. 832 * @param oldVal the old value to be replaced. 833 * @param newVal the new value with which {@code oldVal} is to be 834 * replaced. 835 * @return {@code true} if {@code list} contained one or more elements 836 * {@code e} such that 837 * {@code (oldVal==null ? e==null : oldVal.equals(e))}. 838 * @throws UnsupportedOperationException if the specified list or 839 * its list-iterator does not support the {@code set} operation. 840 * @since 1.4 841 */ 842 public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) { 843 boolean result = false; 844 int size = list.size(); 845 if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) { 846 if (oldVal==null) { 847 for (int i=0; i<size; i++) { 848 if (list.get(i)==null) { 849 list.set(i, newVal); 850 result = true; 851 } 852 } 853 } else { 854 for (int i=0; i<size; i++) { 855 if (oldVal.equals(list.get(i))) { 856 list.set(i, newVal); 857 result = true; 858 } 859 } 860 } 861 } else { 862 ListIterator<T> itr=list.listIterator(); 863 if (oldVal==null) { 864 for (int i=0; i<size; i++) { 865 if (itr.next()==null) { 866 itr.set(newVal); 867 result = true; 868 } 869 } 870 } else { 871 for (int i=0; i<size; i++) { 872 if (oldVal.equals(itr.next())) { 873 itr.set(newVal); 874 result = true; 875 } 876 } 877 } 878 } 879 return result; 880 } 881 882 /** 883 * Returns the starting position of the first occurrence of the specified 884 * target list within the specified source list, or -1 if there is no 885 * such occurrence. More formally, returns the lowest index {@code i} 886 * such that {@code source.subList(i, i+target.size()).equals(target)}, 887 * or -1 if there is no such index. (Returns -1 if 888 * {@code target.size() > source.size()}) 889 * 890 * <p>This implementation uses the "brute force" technique of scanning 891 * over the source list, looking for a match with the target at each 892 * location in turn. 893 * 894 * @param source the list in which to search for the first occurrence 895 * of {@code target}. 896 * @param target the list to search for as a subList of {@code source}. 897 * @return the starting position of the first occurrence of the specified 898 * target list within the specified source list, or -1 if there 899 * is no such occurrence. 900 * @since 1.4 901 */ 902 public static int indexOfSubList(List<?> source, List<?> target) { 903 int sourceSize = source.size(); 904 int targetSize = target.size(); 905 int maxCandidate = sourceSize - targetSize; 906 907 if (sourceSize < INDEXOFSUBLIST_THRESHOLD || 908 (source instanceof RandomAccess&&target instanceof RandomAccess)) { 909 nextCand: 910 for (int candidate = 0; candidate <= maxCandidate; candidate++) { 911 for (int i=0, j=candidate; i<targetSize; i++, j++) 912 if (!eq(target.get(i), source.get(j))) 913 continue nextCand; // Element mismatch, try next cand 914 return candidate; // All elements of candidate matched target 915 } 916 } else { // Iterator version of above algorithm 917 ListIterator<?> si = source.listIterator(); 918 nextCand: 919 for (int candidate = 0; candidate <= maxCandidate; candidate++) { 920 ListIterator<?> ti = target.listIterator(); 921 for (int i=0; i<targetSize; i++) { 922 if (!eq(ti.next(), si.next())) { 923 // Back up source iterator to next candidate 924 for (int j=0; j<i; j++) 925 si.previous(); 926 continue nextCand; 927 } 928 } 929 return candidate; 930 } 931 } 932 return -1; // No candidate matched the target 933 } 934 935 /** 936 * Returns the starting position of the last occurrence of the specified 937 * target list within the specified source list, or -1 if there is no such 938 * occurrence. More formally, returns the highest index {@code i} 939 * such that {@code source.subList(i, i+target.size()).equals(target)}, 940 * or -1 if there is no such index. (Returns -1 if 941 * {@code target.size() > source.size()}) 942 * 943 * <p>This implementation uses the "brute force" technique of iterating 944 * over the source list, looking for a match with the target at each 945 * location in turn. 946 * 947 * @param source the list in which to search for the last occurrence 948 * of {@code target}. 949 * @param target the list to search for as a subList of {@code source}. 950 * @return the starting position of the last occurrence of the specified 951 * target list within the specified source list, or -1 if there 952 * is no such occurrence. 953 * @since 1.4 954 */ 955 public static int lastIndexOfSubList(List<?> source, List<?> target) { 956 int sourceSize = source.size(); 957 int targetSize = target.size(); 958 int maxCandidate = sourceSize - targetSize; 959 960 if (sourceSize < INDEXOFSUBLIST_THRESHOLD || 961 source instanceof RandomAccess) { // Index access version 962 nextCand: 963 for (int candidate = maxCandidate; candidate >= 0; candidate--) { 964 for (int i=0, j=candidate; i<targetSize; i++, j++) 965 if (!eq(target.get(i), source.get(j))) 966 continue nextCand; // Element mismatch, try next cand 967 return candidate; // All elements of candidate matched target 968 } 969 } else { // Iterator version of above algorithm 970 if (maxCandidate < 0) 971 return -1; 972 ListIterator<?> si = source.listIterator(maxCandidate); 973 nextCand: 974 for (int candidate = maxCandidate; candidate >= 0; candidate--) { 975 ListIterator<?> ti = target.listIterator(); 976 for (int i=0; i<targetSize; i++) { 977 if (!eq(ti.next(), si.next())) { 978 if (candidate != 0) { 979 // Back up source iterator to next candidate 980 for (int j=0; j<=i+1; j++) 981 si.previous(); 982 } 983 continue nextCand; 984 } 985 } 986 return candidate; 987 } 988 } 989 return -1; // No candidate matched the target 990 } 991 992 993 // Unmodifiable Wrappers 994 995 /** 996 * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the 997 * specified collection. Query operations on the returned collection "read through" 998 * to the specified collection, and attempts to modify the returned 999 * collection, whether direct or via its iterator, result in an 1000 * {@code UnsupportedOperationException}.<p> 1001 * 1002 * The returned collection does <i>not</i> pass the hashCode and equals 1003 * operations through to the backing collection, but relies on 1004 * {@code Object}'s {@code equals} and {@code hashCode} methods. This 1005 * is necessary to preserve the contracts of these operations in the case 1006 * that the backing collection is a set or a list.<p> 1007 * 1008 * The returned collection will be serializable if the specified collection 1009 * is serializable. 1010 * 1011 * @param <T> the class of the objects in the collection 1012 * @param c the collection for which an unmodifiable view is to be 1013 * returned. 1014 * @return an unmodifiable view of the specified collection. 1015 */ 1016 public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) { 1017 return new UnmodifiableCollection<>(c); 1018 } 1019 1020 /** 1021 * @serial include 1022 */ 1023 static class UnmodifiableCollection<E> implements Collection<E>, Serializable { 1024 private static final long serialVersionUID = 1820017752578914078L; 1025 1026 final Collection<? extends E> c; 1027 1028 UnmodifiableCollection(Collection<? extends E> c) { 1029 if (c==null) 1030 throw new NullPointerException(); 1031 this.c = c; 1032 } 1033 1034 public int size() {return c.size();} 1035 public boolean isEmpty() {return c.isEmpty();} 1036 public boolean contains(Object o) {return c.contains(o);} 1037 public Object[] toArray() {return c.toArray();} 1038 public <T> T[] toArray(T[] a) {return c.toArray(a);} 1039 public <T> T[] toArray(IntFunction<T[]> f) {return c.toArray(f);} 1040 public String toString() {return c.toString();} 1041 1042 public Iterator<E> iterator() { 1043 return new Iterator<E>() { 1044 private final Iterator<? extends E> i = c.iterator(); 1045 1046 public boolean hasNext() {return i.hasNext();} 1047 public E next() {return i.next();} 1048 public void remove() { 1049 throw new UnsupportedOperationException(); 1050 } 1051 @Override 1052 public void forEachRemaining(Consumer<? super E> action) { 1053 // Use backing collection version 1054 i.forEachRemaining(action); 1055 } 1056 }; 1057 } 1058 1059 public boolean add(E e) { 1060 throw new UnsupportedOperationException(); 1061 } 1062 public boolean remove(Object o) { 1063 throw new UnsupportedOperationException(); 1064 } 1065 1066 public boolean containsAll(Collection<?> coll) { 1067 return c.containsAll(coll); 1068 } 1069 public boolean addAll(Collection<? extends E> coll) { 1070 throw new UnsupportedOperationException(); 1071 } 1072 public boolean removeAll(Collection<?> coll) { 1073 throw new UnsupportedOperationException(); 1074 } 1075 public boolean retainAll(Collection<?> coll) { 1076 throw new UnsupportedOperationException(); 1077 } 1078 public void clear() { 1079 throw new UnsupportedOperationException(); 1080 } 1081 1082 // Override default methods in Collection 1083 @Override 1084 public void forEach(Consumer<? super E> action) { 1085 c.forEach(action); 1086 } 1087 @Override 1088 public boolean removeIf(Predicate<? super E> filter) { 1089 throw new UnsupportedOperationException(); 1090 } 1091 @SuppressWarnings("unchecked") 1092 @Override 1093 public Spliterator<E> spliterator() { 1094 return (Spliterator<E>)c.spliterator(); 1095 } 1096 @SuppressWarnings("unchecked") 1097 @Override 1098 public Stream<E> stream() { 1099 return (Stream<E>)c.stream(); 1100 } 1101 @SuppressWarnings("unchecked") 1102 @Override 1103 public Stream<E> parallelStream() { 1104 return (Stream<E>)c.parallelStream(); 1105 } 1106 } 1107 1108 /** 1109 * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the 1110 * specified set. Query operations on the returned set "read through" to the specified 1111 * set, and attempts to modify the returned set, whether direct or via its 1112 * iterator, result in an {@code UnsupportedOperationException}.<p> 1113 * 1114 * The returned set will be serializable if the specified set 1115 * is serializable. 1116 * 1117 * @param <T> the class of the objects in the set 1118 * @param s the set for which an unmodifiable view is to be returned. 1119 * @return an unmodifiable view of the specified set. 1120 */ 1121 public static <T> Set<T> unmodifiableSet(Set<? extends T> s) { 1122 return new UnmodifiableSet<>(s); 1123 } 1124 1125 /** 1126 * @serial include 1127 */ 1128 static class UnmodifiableSet<E> extends UnmodifiableCollection<E> 1129 implements Set<E>, Serializable { 1130 private static final long serialVersionUID = -9215047833775013803L; 1131 1132 UnmodifiableSet(Set<? extends E> s) {super(s);} 1133 public boolean equals(Object o) {return o == this || c.equals(o);} 1134 public int hashCode() {return c.hashCode();} 1135 } 1136 1137 /** 1138 * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the 1139 * specified sorted set. Query operations on the returned sorted set "read 1140 * through" to the specified sorted set. Attempts to modify the returned 1141 * sorted set, whether direct, via its iterator, or via its 1142 * {@code subSet}, {@code headSet}, or {@code tailSet} views, result in 1143 * an {@code UnsupportedOperationException}.<p> 1144 * 1145 * The returned sorted set will be serializable if the specified sorted set 1146 * is serializable. 1147 * 1148 * @param <T> the class of the objects in the set 1149 * @param s the sorted set for which an unmodifiable view is to be 1150 * returned. 1151 * @return an unmodifiable view of the specified sorted set. 1152 */ 1153 public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) { 1154 return new UnmodifiableSortedSet<>(s); 1155 } 1156 1157 /** 1158 * @serial include 1159 */ 1160 static class UnmodifiableSortedSet<E> 1161 extends UnmodifiableSet<E> 1162 implements SortedSet<E>, Serializable { 1163 private static final long serialVersionUID = -4929149591599911165L; 1164 private final SortedSet<E> ss; 1165 1166 UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;} 1167 1168 public Comparator<? super E> comparator() {return ss.comparator();} 1169 1170 public SortedSet<E> subSet(E fromElement, E toElement) { 1171 return new UnmodifiableSortedSet<>(ss.subSet(fromElement,toElement)); 1172 } 1173 public SortedSet<E> headSet(E toElement) { 1174 return new UnmodifiableSortedSet<>(ss.headSet(toElement)); 1175 } 1176 public SortedSet<E> tailSet(E fromElement) { 1177 return new UnmodifiableSortedSet<>(ss.tailSet(fromElement)); 1178 } 1179 1180 public E first() {return ss.first();} 1181 public E last() {return ss.last();} 1182 } 1183 1184 /** 1185 * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the 1186 * specified navigable set. Query operations on the returned navigable set "read 1187 * through" to the specified navigable set. Attempts to modify the returned 1188 * navigable set, whether direct, via its iterator, or via its 1189 * {@code subSet}, {@code headSet}, or {@code tailSet} views, result in 1190 * an {@code UnsupportedOperationException}.<p> 1191 * 1192 * The returned navigable set will be serializable if the specified 1193 * navigable set is serializable. 1194 * 1195 * @param <T> the class of the objects in the set 1196 * @param s the navigable set for which an unmodifiable view is to be 1197 * returned 1198 * @return an unmodifiable view of the specified navigable set 1199 * @since 1.8 1200 */ 1201 public static <T> NavigableSet<T> unmodifiableNavigableSet(NavigableSet<T> s) { 1202 return new UnmodifiableNavigableSet<>(s); 1203 } 1204 1205 /** 1206 * Wraps a navigable set and disables all of the mutative operations. 1207 * 1208 * @param <E> type of elements 1209 * @serial include 1210 */ 1211 static class UnmodifiableNavigableSet<E> 1212 extends UnmodifiableSortedSet<E> 1213 implements NavigableSet<E>, Serializable { 1214 1215 private static final long serialVersionUID = -6027448201786391929L; 1216 1217 /** 1218 * A singleton empty unmodifiable navigable set used for 1219 * {@link #emptyNavigableSet()}. 1220 * 1221 * @param <E> type of elements, if there were any, and bounds 1222 */ 1223 private static class EmptyNavigableSet<E> extends UnmodifiableNavigableSet<E> 1224 implements Serializable { 1225 private static final long serialVersionUID = -6291252904449939134L; 1226 1227 public EmptyNavigableSet() { 1228 super(new TreeSet<>()); 1229 } 1230 1231 private Object readResolve() { return EMPTY_NAVIGABLE_SET; } 1232 } 1233 1234 @SuppressWarnings("rawtypes") 1235 private static final NavigableSet<?> EMPTY_NAVIGABLE_SET = 1236 new EmptyNavigableSet<>(); 1237 1238 /** 1239 * The instance we are protecting. 1240 */ 1241 private final NavigableSet<E> ns; 1242 1243 UnmodifiableNavigableSet(NavigableSet<E> s) {super(s); ns = s;} 1244 1245 public E lower(E e) { return ns.lower(e); } 1246 public E floor(E e) { return ns.floor(e); } 1247 public E ceiling(E e) { return ns.ceiling(e); } 1248 public E higher(E e) { return ns.higher(e); } 1249 public E pollFirst() { throw new UnsupportedOperationException(); } 1250 public E pollLast() { throw new UnsupportedOperationException(); } 1251 public NavigableSet<E> descendingSet() 1252 { return new UnmodifiableNavigableSet<>(ns.descendingSet()); } 1253 public Iterator<E> descendingIterator() 1254 { return descendingSet().iterator(); } 1255 1256 public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) { 1257 return new UnmodifiableNavigableSet<>( 1258 ns.subSet(fromElement, fromInclusive, toElement, toInclusive)); 1259 } 1260 1261 public NavigableSet<E> headSet(E toElement, boolean inclusive) { 1262 return new UnmodifiableNavigableSet<>( 1263 ns.headSet(toElement, inclusive)); 1264 } 1265 1266 public NavigableSet<E> tailSet(E fromElement, boolean inclusive) { 1267 return new UnmodifiableNavigableSet<>( 1268 ns.tailSet(fromElement, inclusive)); 1269 } 1270 } 1271 1272 /** 1273 * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the 1274 * specified list. Query operations on the returned list "read through" to the 1275 * specified list, and attempts to modify the returned list, whether 1276 * direct or via its iterator, result in an 1277 * {@code UnsupportedOperationException}.<p> 1278 * 1279 * The returned list will be serializable if the specified list 1280 * is serializable. Similarly, the returned list will implement 1281 * {@link RandomAccess} if the specified list does. 1282 * 1283 * @param <T> the class of the objects in the list 1284 * @param list the list for which an unmodifiable view is to be returned. 1285 * @return an unmodifiable view of the specified list. 1286 */ 1287 public static <T> List<T> unmodifiableList(List<? extends T> list) { 1288 return (list instanceof RandomAccess ? 1289 new UnmodifiableRandomAccessList<>(list) : 1290 new UnmodifiableList<>(list)); 1291 } 1292 1293 /** 1294 * @serial include 1295 */ 1296 static class UnmodifiableList<E> extends UnmodifiableCollection<E> 1297 implements List<E> { 1298 private static final long serialVersionUID = -283967356065247728L; 1299 1300 final List<? extends E> list; 1301 1302 UnmodifiableList(List<? extends E> list) { 1303 super(list); 1304 this.list = list; 1305 } 1306 1307 public boolean equals(Object o) {return o == this || list.equals(o);} 1308 public int hashCode() {return list.hashCode();} 1309 1310 public E get(int index) {return list.get(index);} 1311 public E set(int index, E element) { 1312 throw new UnsupportedOperationException(); 1313 } 1314 public void add(int index, E element) { 1315 throw new UnsupportedOperationException(); 1316 } 1317 public E remove(int index) { 1318 throw new UnsupportedOperationException(); 1319 } 1320 public int indexOf(Object o) {return list.indexOf(o);} 1321 public int lastIndexOf(Object o) {return list.lastIndexOf(o);} 1322 public boolean addAll(int index, Collection<? extends E> c) { 1323 throw new UnsupportedOperationException(); 1324 } 1325 1326 @Override 1327 public void replaceAll(UnaryOperator<E> operator) { 1328 throw new UnsupportedOperationException(); 1329 } 1330 @Override 1331 public void sort(Comparator<? super E> c) { 1332 throw new UnsupportedOperationException(); 1333 } 1334 1335 public ListIterator<E> listIterator() {return listIterator(0);} 1336 1337 public ListIterator<E> listIterator(final int index) { 1338 return new ListIterator<E>() { 1339 private final ListIterator<? extends E> i 1340 = list.listIterator(index); 1341 1342 public boolean hasNext() {return i.hasNext();} 1343 public E next() {return i.next();} 1344 public boolean hasPrevious() {return i.hasPrevious();} 1345 public E previous() {return i.previous();} 1346 public int nextIndex() {return i.nextIndex();} 1347 public int previousIndex() {return i.previousIndex();} 1348 1349 public void remove() { 1350 throw new UnsupportedOperationException(); 1351 } 1352 public void set(E e) { 1353 throw new UnsupportedOperationException(); 1354 } 1355 public void add(E e) { 1356 throw new UnsupportedOperationException(); 1357 } 1358 1359 @Override 1360 public void forEachRemaining(Consumer<? super E> action) { 1361 i.forEachRemaining(action); 1362 } 1363 }; 1364 } 1365 1366 public List<E> subList(int fromIndex, int toIndex) { 1367 return new UnmodifiableList<>(list.subList(fromIndex, toIndex)); 1368 } 1369 1370 /** 1371 * UnmodifiableRandomAccessList instances are serialized as 1372 * UnmodifiableList instances to allow them to be deserialized 1373 * in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList). 1374 * This method inverts the transformation. As a beneficial 1375 * side-effect, it also grafts the RandomAccess marker onto 1376 * UnmodifiableList instances that were serialized in pre-1.4 JREs. 1377 * 1378 * Note: Unfortunately, UnmodifiableRandomAccessList instances 1379 * serialized in 1.4.1 and deserialized in 1.4 will become 1380 * UnmodifiableList instances, as this method was missing in 1.4. 1381 */ 1382 private Object readResolve() { 1383 return (list instanceof RandomAccess 1384 ? new UnmodifiableRandomAccessList<>(list) 1385 : this); 1386 } 1387 } 1388 1389 /** 1390 * @serial include 1391 */ 1392 static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E> 1393 implements RandomAccess 1394 { 1395 UnmodifiableRandomAccessList(List<? extends E> list) { 1396 super(list); 1397 } 1398 1399 public List<E> subList(int fromIndex, int toIndex) { 1400 return new UnmodifiableRandomAccessList<>( 1401 list.subList(fromIndex, toIndex)); 1402 } 1403 1404 private static final long serialVersionUID = -2542308836966382001L; 1405 1406 /** 1407 * Allows instances to be deserialized in pre-1.4 JREs (which do 1408 * not have UnmodifiableRandomAccessList). UnmodifiableList has 1409 * a readResolve method that inverts this transformation upon 1410 * deserialization. 1411 */ 1412 private Object writeReplace() { 1413 return new UnmodifiableList<>(list); 1414 } 1415 } 1416 1417 /** 1418 * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the 1419 * specified map. Query operations on the returned map "read through" 1420 * to the specified map, and attempts to modify the returned 1421 * map, whether direct or via its collection views, result in an 1422 * {@code UnsupportedOperationException}.<p> 1423 * 1424 * The returned map will be serializable if the specified map 1425 * is serializable. 1426 * 1427 * @param <K> the class of the map keys 1428 * @param <V> the class of the map values 1429 * @param m the map for which an unmodifiable view is to be returned. 1430 * @return an unmodifiable view of the specified map. 1431 */ 1432 public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) { 1433 return new UnmodifiableMap<>(m); 1434 } 1435 1436 /** 1437 * @serial include 1438 */ 1439 private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable { 1440 private static final long serialVersionUID = -1034234728574286014L; 1441 1442 private final Map<? extends K, ? extends V> m; 1443 1444 UnmodifiableMap(Map<? extends K, ? extends V> m) { 1445 if (m==null) 1446 throw new NullPointerException(); 1447 this.m = m; 1448 } 1449 1450 public int size() {return m.size();} 1451 public boolean isEmpty() {return m.isEmpty();} 1452 public boolean containsKey(Object key) {return m.containsKey(key);} 1453 public boolean containsValue(Object val) {return m.containsValue(val);} 1454 public V get(Object key) {return m.get(key);} 1455 1456 public V put(K key, V value) { 1457 throw new UnsupportedOperationException(); 1458 } 1459 public V remove(Object key) { 1460 throw new UnsupportedOperationException(); 1461 } 1462 public void putAll(Map<? extends K, ? extends V> m) { 1463 throw new UnsupportedOperationException(); 1464 } 1465 public void clear() { 1466 throw new UnsupportedOperationException(); 1467 } 1468 1469 private transient Set<K> keySet; 1470 private transient Set<Map.Entry<K,V>> entrySet; 1471 private transient Collection<V> values; 1472 1473 public Set<K> keySet() { 1474 if (keySet==null) 1475 keySet = unmodifiableSet(m.keySet()); 1476 return keySet; 1477 } 1478 1479 public Set<Map.Entry<K,V>> entrySet() { 1480 if (entrySet==null) 1481 entrySet = new UnmodifiableEntrySet<>(m.entrySet()); 1482 return entrySet; 1483 } 1484 1485 public Collection<V> values() { 1486 if (values==null) 1487 values = unmodifiableCollection(m.values()); 1488 return values; 1489 } 1490 1491 public boolean equals(Object o) {return o == this || m.equals(o);} 1492 public int hashCode() {return m.hashCode();} 1493 public String toString() {return m.toString();} 1494 1495 // Override default methods in Map 1496 @Override 1497 @SuppressWarnings("unchecked") 1498 public V getOrDefault(Object k, V defaultValue) { 1499 // Safe cast as we don't change the value 1500 return ((Map<K, V>)m).getOrDefault(k, defaultValue); 1501 } 1502 1503 @Override 1504 public void forEach(BiConsumer<? super K, ? super V> action) { 1505 m.forEach(action); 1506 } 1507 1508 @Override 1509 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 1510 throw new UnsupportedOperationException(); 1511 } 1512 1513 @Override 1514 public V putIfAbsent(K key, V value) { 1515 throw new UnsupportedOperationException(); 1516 } 1517 1518 @Override 1519 public boolean remove(Object key, Object value) { 1520 throw new UnsupportedOperationException(); 1521 } 1522 1523 @Override 1524 public boolean replace(K key, V oldValue, V newValue) { 1525 throw new UnsupportedOperationException(); 1526 } 1527 1528 @Override 1529 public V replace(K key, V value) { 1530 throw new UnsupportedOperationException(); 1531 } 1532 1533 @Override 1534 public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) { 1535 throw new UnsupportedOperationException(); 1536 } 1537 1538 @Override 1539 public V computeIfPresent(K key, 1540 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 1541 throw new UnsupportedOperationException(); 1542 } 1543 1544 @Override 1545 public V compute(K key, 1546 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 1547 throw new UnsupportedOperationException(); 1548 } 1549 1550 @Override 1551 public V merge(K key, V value, 1552 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 1553 throw new UnsupportedOperationException(); 1554 } 1555 1556 /** 1557 * We need this class in addition to UnmodifiableSet as 1558 * Map.Entries themselves permit modification of the backing Map 1559 * via their setValue operation. This class is subtle: there are 1560 * many possible attacks that must be thwarted. 1561 * 1562 * @serial include 1563 */ 1564 static class UnmodifiableEntrySet<K,V> 1565 extends UnmodifiableSet<Map.Entry<K,V>> { 1566 private static final long serialVersionUID = 7854390611657943733L; 1567 1568 @SuppressWarnings({"unchecked", "rawtypes"}) 1569 UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) { 1570 // Need to cast to raw in order to work around a limitation in the type system 1571 super((Set)s); 1572 } 1573 1574 static <K, V> Consumer<Map.Entry<? extends K, ? extends V>> entryConsumer( 1575 Consumer<? super Entry<K, V>> action) { 1576 return e -> action.accept(new UnmodifiableEntry<>(e)); 1577 } 1578 1579 public void forEach(Consumer<? super Entry<K, V>> action) { 1580 Objects.requireNonNull(action); 1581 c.forEach(entryConsumer(action)); 1582 } 1583 1584 static final class UnmodifiableEntrySetSpliterator<K, V> 1585 implements Spliterator<Entry<K,V>> { 1586 final Spliterator<Map.Entry<K, V>> s; 1587 1588 UnmodifiableEntrySetSpliterator(Spliterator<Entry<K, V>> s) { 1589 this.s = s; 1590 } 1591 1592 @Override 1593 public boolean tryAdvance(Consumer<? super Entry<K, V>> action) { 1594 Objects.requireNonNull(action); 1595 return s.tryAdvance(entryConsumer(action)); 1596 } 1597 1598 @Override 1599 public void forEachRemaining(Consumer<? super Entry<K, V>> action) { 1600 Objects.requireNonNull(action); 1601 s.forEachRemaining(entryConsumer(action)); 1602 } 1603 1604 @Override 1605 public Spliterator<Entry<K, V>> trySplit() { 1606 Spliterator<Entry<K, V>> split = s.trySplit(); 1607 return split == null 1608 ? null 1609 : new UnmodifiableEntrySetSpliterator<>(split); 1610 } 1611 1612 @Override 1613 public long estimateSize() { 1614 return s.estimateSize(); 1615 } 1616 1617 @Override 1618 public long getExactSizeIfKnown() { 1619 return s.getExactSizeIfKnown(); 1620 } 1621 1622 @Override 1623 public int characteristics() { 1624 return s.characteristics(); 1625 } 1626 1627 @Override 1628 public boolean hasCharacteristics(int characteristics) { 1629 return s.hasCharacteristics(characteristics); 1630 } 1631 1632 @Override 1633 public Comparator<? super Entry<K, V>> getComparator() { 1634 return s.getComparator(); 1635 } 1636 } 1637 1638 @SuppressWarnings("unchecked") 1639 public Spliterator<Entry<K,V>> spliterator() { 1640 return new UnmodifiableEntrySetSpliterator<>( 1641 (Spliterator<Map.Entry<K, V>>) c.spliterator()); 1642 } 1643 1644 @Override 1645 public Stream<Entry<K,V>> stream() { 1646 return StreamSupport.stream(spliterator(), false); 1647 } 1648 1649 @Override 1650 public Stream<Entry<K,V>> parallelStream() { 1651 return StreamSupport.stream(spliterator(), true); 1652 } 1653 1654 public Iterator<Map.Entry<K,V>> iterator() { 1655 return new Iterator<Map.Entry<K,V>>() { 1656 private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator(); 1657 1658 public boolean hasNext() { 1659 return i.hasNext(); 1660 } 1661 public Map.Entry<K,V> next() { 1662 return new UnmodifiableEntry<>(i.next()); 1663 } 1664 public void remove() { 1665 throw new UnsupportedOperationException(); 1666 } 1667 public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action) { 1668 i.forEachRemaining(entryConsumer(action)); 1669 } 1670 }; 1671 } 1672 1673 @SuppressWarnings("unchecked") 1674 public Object[] toArray() { 1675 Object[] a = c.toArray(); 1676 for (int i=0; i<a.length; i++) 1677 a[i] = new UnmodifiableEntry<>((Map.Entry<? extends K, ? extends V>)a[i]); 1678 return a; 1679 } 1680 1681 @SuppressWarnings("unchecked") 1682 public <T> T[] toArray(T[] a) { 1683 // We don't pass a to c.toArray, to avoid window of 1684 // vulnerability wherein an unscrupulous multithreaded client 1685 // could get his hands on raw (unwrapped) Entries from c. 1686 Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0)); 1687 1688 for (int i=0; i<arr.length; i++) 1689 arr[i] = new UnmodifiableEntry<>((Map.Entry<? extends K, ? extends V>)arr[i]); 1690 1691 if (arr.length > a.length) 1692 return (T[])arr; 1693 1694 System.arraycopy(arr, 0, a, 0, arr.length); 1695 if (a.length > arr.length) 1696 a[arr.length] = null; 1697 return a; 1698 } 1699 1700 /** 1701 * This method is overridden to protect the backing set against 1702 * an object with a nefarious equals function that senses 1703 * that the equality-candidate is Map.Entry and calls its 1704 * setValue method. 1705 */ 1706 public boolean contains(Object o) { 1707 if (!(o instanceof Map.Entry)) 1708 return false; 1709 return c.contains( 1710 new UnmodifiableEntry<>((Map.Entry<?,?>) o)); 1711 } 1712 1713 /** 1714 * The next two methods are overridden to protect against 1715 * an unscrupulous List whose contains(Object o) method senses 1716 * when o is a Map.Entry, and calls o.setValue. 1717 */ 1718 public boolean containsAll(Collection<?> coll) { 1719 for (Object e : coll) { 1720 if (!contains(e)) // Invokes safe contains() above 1721 return false; 1722 } 1723 return true; 1724 } 1725 public boolean equals(Object o) { 1726 if (o == this) 1727 return true; 1728 1729 if (!(o instanceof Set)) 1730 return false; 1731 Set<?> s = (Set<?>) o; 1732 if (s.size() != c.size()) 1733 return false; 1734 return containsAll(s); // Invokes safe containsAll() above 1735 } 1736 1737 /** 1738 * This "wrapper class" serves two purposes: it prevents 1739 * the client from modifying the backing Map, by short-circuiting 1740 * the setValue method, and it protects the backing Map against 1741 * an ill-behaved Map.Entry that attempts to modify another 1742 * Map Entry when asked to perform an equality check. 1743 */ 1744 private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> { 1745 private Map.Entry<? extends K, ? extends V> e; 1746 1747 UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) 1748 {this.e = Objects.requireNonNull(e);} 1749 1750 public K getKey() {return e.getKey();} 1751 public V getValue() {return e.getValue();} 1752 public V setValue(V value) { 1753 throw new UnsupportedOperationException(); 1754 } 1755 public int hashCode() {return e.hashCode();} 1756 public boolean equals(Object o) { 1757 if (this == o) 1758 return true; 1759 if (!(o instanceof Map.Entry)) 1760 return false; 1761 Map.Entry<?,?> t = (Map.Entry<?,?>)o; 1762 return eq(e.getKey(), t.getKey()) && 1763 eq(e.getValue(), t.getValue()); 1764 } 1765 public String toString() {return e.toString();} 1766 } 1767 } 1768 } 1769 1770 /** 1771 * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the 1772 * specified sorted map. Query operations on the returned sorted map "read through" 1773 * to the specified sorted map. Attempts to modify the returned 1774 * sorted map, whether direct, via its collection views, or via its 1775 * {@code subMap}, {@code headMap}, or {@code tailMap} views, result in 1776 * an {@code UnsupportedOperationException}.<p> 1777 * 1778 * The returned sorted map will be serializable if the specified sorted map 1779 * is serializable. 1780 * 1781 * @param <K> the class of the map keys 1782 * @param <V> the class of the map values 1783 * @param m the sorted map for which an unmodifiable view is to be 1784 * returned. 1785 * @return an unmodifiable view of the specified sorted map. 1786 */ 1787 public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) { 1788 return new UnmodifiableSortedMap<>(m); 1789 } 1790 1791 /** 1792 * @serial include 1793 */ 1794 static class UnmodifiableSortedMap<K,V> 1795 extends UnmodifiableMap<K,V> 1796 implements SortedMap<K,V>, Serializable { 1797 private static final long serialVersionUID = -8806743815996713206L; 1798 1799 private final SortedMap<K, ? extends V> sm; 1800 1801 UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m; } 1802 public Comparator<? super K> comparator() { return sm.comparator(); } 1803 public SortedMap<K,V> subMap(K fromKey, K toKey) 1804 { return new UnmodifiableSortedMap<>(sm.subMap(fromKey, toKey)); } 1805 public SortedMap<K,V> headMap(K toKey) 1806 { return new UnmodifiableSortedMap<>(sm.headMap(toKey)); } 1807 public SortedMap<K,V> tailMap(K fromKey) 1808 { return new UnmodifiableSortedMap<>(sm.tailMap(fromKey)); } 1809 public K firstKey() { return sm.firstKey(); } 1810 public K lastKey() { return sm.lastKey(); } 1811 } 1812 1813 /** 1814 * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the 1815 * specified navigable map. Query operations on the returned navigable map "read 1816 * through" to the specified navigable map. Attempts to modify the returned 1817 * navigable map, whether direct, via its collection views, or via its 1818 * {@code subMap}, {@code headMap}, or {@code tailMap} views, result in 1819 * an {@code UnsupportedOperationException}.<p> 1820 * 1821 * The returned navigable map will be serializable if the specified 1822 * navigable map is serializable. 1823 * 1824 * @param <K> the class of the map keys 1825 * @param <V> the class of the map values 1826 * @param m the navigable map for which an unmodifiable view is to be 1827 * returned 1828 * @return an unmodifiable view of the specified navigable map 1829 * @since 1.8 1830 */ 1831 public static <K,V> NavigableMap<K,V> unmodifiableNavigableMap(NavigableMap<K, ? extends V> m) { 1832 return new UnmodifiableNavigableMap<>(m); 1833 } 1834 1835 /** 1836 * @serial include 1837 */ 1838 static class UnmodifiableNavigableMap<K,V> 1839 extends UnmodifiableSortedMap<K,V> 1840 implements NavigableMap<K,V>, Serializable { 1841 private static final long serialVersionUID = -4858195264774772197L; 1842 1843 /** 1844 * A class for the {@link EMPTY_NAVIGABLE_MAP} which needs readResolve 1845 * to preserve singleton property. 1846 * 1847 * @param <K> type of keys, if there were any, and of bounds 1848 * @param <V> type of values, if there were any 1849 */ 1850 private static class EmptyNavigableMap<K,V> extends UnmodifiableNavigableMap<K,V> 1851 implements Serializable { 1852 1853 private static final long serialVersionUID = -2239321462712562324L; 1854 1855 EmptyNavigableMap() { super(new TreeMap<>()); } 1856 1857 @Override 1858 public NavigableSet<K> navigableKeySet() 1859 { return emptyNavigableSet(); } 1860 1861 private Object readResolve() { return EMPTY_NAVIGABLE_MAP; } 1862 } 1863 1864 /** 1865 * Singleton for {@link emptyNavigableMap()} which is also immutable. 1866 */ 1867 private static final EmptyNavigableMap<?,?> EMPTY_NAVIGABLE_MAP = 1868 new EmptyNavigableMap<>(); 1869 1870 /** 1871 * The instance we wrap and protect. 1872 */ 1873 private final NavigableMap<K, ? extends V> nm; 1874 1875 UnmodifiableNavigableMap(NavigableMap<K, ? extends V> m) 1876 {super(m); nm = m;} 1877 1878 public K lowerKey(K key) { return nm.lowerKey(key); } 1879 public K floorKey(K key) { return nm.floorKey(key); } 1880 public K ceilingKey(K key) { return nm.ceilingKey(key); } 1881 public K higherKey(K key) { return nm.higherKey(key); } 1882 1883 @SuppressWarnings("unchecked") 1884 public Entry<K, V> lowerEntry(K key) { 1885 Entry<K,V> lower = (Entry<K, V>) nm.lowerEntry(key); 1886 return (null != lower) 1887 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(lower) 1888 : null; 1889 } 1890 1891 @SuppressWarnings("unchecked") 1892 public Entry<K, V> floorEntry(K key) { 1893 Entry<K,V> floor = (Entry<K, V>) nm.floorEntry(key); 1894 return (null != floor) 1895 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(floor) 1896 : null; 1897 } 1898 1899 @SuppressWarnings("unchecked") 1900 public Entry<K, V> ceilingEntry(K key) { 1901 Entry<K,V> ceiling = (Entry<K, V>) nm.ceilingEntry(key); 1902 return (null != ceiling) 1903 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(ceiling) 1904 : null; 1905 } 1906 1907 1908 @SuppressWarnings("unchecked") 1909 public Entry<K, V> higherEntry(K key) { 1910 Entry<K,V> higher = (Entry<K, V>) nm.higherEntry(key); 1911 return (null != higher) 1912 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(higher) 1913 : null; 1914 } 1915 1916 @SuppressWarnings("unchecked") 1917 public Entry<K, V> firstEntry() { 1918 Entry<K,V> first = (Entry<K, V>) nm.firstEntry(); 1919 return (null != first) 1920 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(first) 1921 : null; 1922 } 1923 1924 @SuppressWarnings("unchecked") 1925 public Entry<K, V> lastEntry() { 1926 Entry<K,V> last = (Entry<K, V>) nm.lastEntry(); 1927 return (null != last) 1928 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(last) 1929 : null; 1930 } 1931 1932 public Entry<K, V> pollFirstEntry() 1933 { throw new UnsupportedOperationException(); } 1934 public Entry<K, V> pollLastEntry() 1935 { throw new UnsupportedOperationException(); } 1936 public NavigableMap<K, V> descendingMap() 1937 { return unmodifiableNavigableMap(nm.descendingMap()); } 1938 public NavigableSet<K> navigableKeySet() 1939 { return unmodifiableNavigableSet(nm.navigableKeySet()); } 1940 public NavigableSet<K> descendingKeySet() 1941 { return unmodifiableNavigableSet(nm.descendingKeySet()); } 1942 1943 public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) { 1944 return unmodifiableNavigableMap( 1945 nm.subMap(fromKey, fromInclusive, toKey, toInclusive)); 1946 } 1947 1948 public NavigableMap<K, V> headMap(K toKey, boolean inclusive) 1949 { return unmodifiableNavigableMap(nm.headMap(toKey, inclusive)); } 1950 public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) 1951 { return unmodifiableNavigableMap(nm.tailMap(fromKey, inclusive)); } 1952 } 1953 1954 // Synch Wrappers 1955 1956 /** 1957 * Returns a synchronized (thread-safe) collection backed by the specified 1958 * collection. In order to guarantee serial access, it is critical that 1959 * <strong>all</strong> access to the backing collection is accomplished 1960 * through the returned collection.<p> 1961 * 1962 * It is imperative that the user manually synchronize on the returned 1963 * collection when traversing it via {@link Iterator}, {@link Spliterator} 1964 * or {@link Stream}: 1965 * <pre> 1966 * Collection c = Collections.synchronizedCollection(myCollection); 1967 * ... 1968 * synchronized (c) { 1969 * Iterator i = c.iterator(); // Must be in the synchronized block 1970 * while (i.hasNext()) 1971 * foo(i.next()); 1972 * } 1973 * </pre> 1974 * Failure to follow this advice may result in non-deterministic behavior. 1975 * 1976 * <p>The returned collection does <i>not</i> pass the {@code hashCode} 1977 * and {@code equals} operations through to the backing collection, but 1978 * relies on {@code Object}'s equals and hashCode methods. This is 1979 * necessary to preserve the contracts of these operations in the case 1980 * that the backing collection is a set or a list.<p> 1981 * 1982 * The returned collection will be serializable if the specified collection 1983 * is serializable. 1984 * 1985 * @param <T> the class of the objects in the collection 1986 * @param c the collection to be "wrapped" in a synchronized collection. 1987 * @return a synchronized view of the specified collection. 1988 */ 1989 public static <T> Collection<T> synchronizedCollection(Collection<T> c) { 1990 return new SynchronizedCollection<>(c); 1991 } 1992 1993 static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) { 1994 return new SynchronizedCollection<>(c, mutex); 1995 } 1996 1997 /** 1998 * @serial include 1999 */ 2000 static class SynchronizedCollection<E> implements Collection<E>, Serializable { 2001 private static final long serialVersionUID = 3053995032091335093L; 2002 2003 final Collection<E> c; // Backing Collection 2004 final Object mutex; // Object on which to synchronize 2005 2006 SynchronizedCollection(Collection<E> c) { 2007 this.c = Objects.requireNonNull(c); 2008 mutex = this; 2009 } 2010 2011 SynchronizedCollection(Collection<E> c, Object mutex) { 2012 this.c = Objects.requireNonNull(c); 2013 this.mutex = Objects.requireNonNull(mutex); 2014 } 2015 2016 public int size() { 2017 synchronized (mutex) {return c.size();} 2018 } 2019 public boolean isEmpty() { 2020 synchronized (mutex) {return c.isEmpty();} 2021 } 2022 public boolean contains(Object o) { 2023 synchronized (mutex) {return c.contains(o);} 2024 } 2025 public Object[] toArray() { 2026 synchronized (mutex) {return c.toArray();} 2027 } 2028 public <T> T[] toArray(T[] a) { 2029 synchronized (mutex) {return c.toArray(a);} 2030 } 2031 public <T> T[] toArray(IntFunction<T[]> f) { 2032 synchronized (mutex) {return c.toArray(f);} 2033 } 2034 2035 public Iterator<E> iterator() { 2036 return c.iterator(); // Must be manually synched by user! 2037 } 2038 2039 public boolean add(E e) { 2040 synchronized (mutex) {return c.add(e);} 2041 } 2042 public boolean remove(Object o) { 2043 synchronized (mutex) {return c.remove(o);} 2044 } 2045 2046 public boolean containsAll(Collection<?> coll) { 2047 synchronized (mutex) {return c.containsAll(coll);} 2048 } 2049 public boolean addAll(Collection<? extends E> coll) { 2050 synchronized (mutex) {return c.addAll(coll);} 2051 } 2052 public boolean removeAll(Collection<?> coll) { 2053 synchronized (mutex) {return c.removeAll(coll);} 2054 } 2055 public boolean retainAll(Collection<?> coll) { 2056 synchronized (mutex) {return c.retainAll(coll);} 2057 } 2058 public void clear() { 2059 synchronized (mutex) {c.clear();} 2060 } 2061 public String toString() { 2062 synchronized (mutex) {return c.toString();} 2063 } 2064 // Override default methods in Collection 2065 @Override 2066 public void forEach(Consumer<? super E> consumer) { 2067 synchronized (mutex) {c.forEach(consumer);} 2068 } 2069 @Override 2070 public boolean removeIf(Predicate<? super E> filter) { 2071 synchronized (mutex) {return c.removeIf(filter);} 2072 } 2073 @Override 2074 public Spliterator<E> spliterator() { 2075 return c.spliterator(); // Must be manually synched by user! 2076 } 2077 @Override 2078 public Stream<E> stream() { 2079 return c.stream(); // Must be manually synched by user! 2080 } 2081 @Override 2082 public Stream<E> parallelStream() { 2083 return c.parallelStream(); // Must be manually synched by user! 2084 } 2085 private void writeObject(ObjectOutputStream s) throws IOException { 2086 synchronized (mutex) {s.defaultWriteObject();} 2087 } 2088 } 2089 2090 /** 2091 * Returns a synchronized (thread-safe) set backed by the specified 2092 * set. In order to guarantee serial access, it is critical that 2093 * <strong>all</strong> access to the backing set is accomplished 2094 * through the returned set.<p> 2095 * 2096 * It is imperative that the user manually synchronize on the returned 2097 * collection when traversing it via {@link Iterator}, {@link Spliterator} 2098 * or {@link Stream}: 2099 * <pre> 2100 * Set s = Collections.synchronizedSet(new HashSet()); 2101 * ... 2102 * synchronized (s) { 2103 * Iterator i = s.iterator(); // Must be in the synchronized block 2104 * while (i.hasNext()) 2105 * foo(i.next()); 2106 * } 2107 * </pre> 2108 * Failure to follow this advice may result in non-deterministic behavior. 2109 * 2110 * <p>The returned set will be serializable if the specified set is 2111 * serializable. 2112 * 2113 * @param <T> the class of the objects in the set 2114 * @param s the set to be "wrapped" in a synchronized set. 2115 * @return a synchronized view of the specified set. 2116 */ 2117 public static <T> Set<T> synchronizedSet(Set<T> s) { 2118 return new SynchronizedSet<>(s); 2119 } 2120 2121 static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) { 2122 return new SynchronizedSet<>(s, mutex); 2123 } 2124 2125 /** 2126 * @serial include 2127 */ 2128 static class SynchronizedSet<E> 2129 extends SynchronizedCollection<E> 2130 implements Set<E> { 2131 private static final long serialVersionUID = 487447009682186044L; 2132 2133 SynchronizedSet(Set<E> s) { 2134 super(s); 2135 } 2136 SynchronizedSet(Set<E> s, Object mutex) { 2137 super(s, mutex); 2138 } 2139 2140 public boolean equals(Object o) { 2141 if (this == o) 2142 return true; 2143 synchronized (mutex) {return c.equals(o);} 2144 } 2145 public int hashCode() { 2146 synchronized (mutex) {return c.hashCode();} 2147 } 2148 } 2149 2150 /** 2151 * Returns a synchronized (thread-safe) sorted set backed by the specified 2152 * sorted set. In order to guarantee serial access, it is critical that 2153 * <strong>all</strong> access to the backing sorted set is accomplished 2154 * through the returned sorted set (or its views).<p> 2155 * 2156 * It is imperative that the user manually synchronize on the returned 2157 * sorted set when traversing it or any of its {@code subSet}, 2158 * {@code headSet}, or {@code tailSet} views via {@link Iterator}, 2159 * {@link Spliterator} or {@link Stream}: 2160 * <pre> 2161 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet()); 2162 * ... 2163 * synchronized (s) { 2164 * Iterator i = s.iterator(); // Must be in the synchronized block 2165 * while (i.hasNext()) 2166 * foo(i.next()); 2167 * } 2168 * </pre> 2169 * or: 2170 * <pre> 2171 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet()); 2172 * SortedSet s2 = s.headSet(foo); 2173 * ... 2174 * synchronized (s) { // Note: s, not s2!!! 2175 * Iterator i = s2.iterator(); // Must be in the synchronized block 2176 * while (i.hasNext()) 2177 * foo(i.next()); 2178 * } 2179 * </pre> 2180 * Failure to follow this advice may result in non-deterministic behavior. 2181 * 2182 * <p>The returned sorted set will be serializable if the specified 2183 * sorted set is serializable. 2184 * 2185 * @param <T> the class of the objects in the set 2186 * @param s the sorted set to be "wrapped" in a synchronized sorted set. 2187 * @return a synchronized view of the specified sorted set. 2188 */ 2189 public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) { 2190 return new SynchronizedSortedSet<>(s); 2191 } 2192 2193 /** 2194 * @serial include 2195 */ 2196 static class SynchronizedSortedSet<E> 2197 extends SynchronizedSet<E> 2198 implements SortedSet<E> 2199 { 2200 private static final long serialVersionUID = 8695801310862127406L; 2201 2202 private final SortedSet<E> ss; 2203 2204 SynchronizedSortedSet(SortedSet<E> s) { 2205 super(s); 2206 ss = s; 2207 } 2208 SynchronizedSortedSet(SortedSet<E> s, Object mutex) { 2209 super(s, mutex); 2210 ss = s; 2211 } 2212 2213 public Comparator<? super E> comparator() { 2214 synchronized (mutex) {return ss.comparator();} 2215 } 2216 2217 public SortedSet<E> subSet(E fromElement, E toElement) { 2218 synchronized (mutex) { 2219 return new SynchronizedSortedSet<>( 2220 ss.subSet(fromElement, toElement), mutex); 2221 } 2222 } 2223 public SortedSet<E> headSet(E toElement) { 2224 synchronized (mutex) { 2225 return new SynchronizedSortedSet<>(ss.headSet(toElement), mutex); 2226 } 2227 } 2228 public SortedSet<E> tailSet(E fromElement) { 2229 synchronized (mutex) { 2230 return new SynchronizedSortedSet<>(ss.tailSet(fromElement),mutex); 2231 } 2232 } 2233 2234 public E first() { 2235 synchronized (mutex) {return ss.first();} 2236 } 2237 public E last() { 2238 synchronized (mutex) {return ss.last();} 2239 } 2240 } 2241 2242 /** 2243 * Returns a synchronized (thread-safe) navigable set backed by the 2244 * specified navigable set. In order to guarantee serial access, it is 2245 * critical that <strong>all</strong> access to the backing navigable set is 2246 * accomplished through the returned navigable set (or its views).<p> 2247 * 2248 * It is imperative that the user manually synchronize on the returned 2249 * navigable set when traversing it, or any of its {@code subSet}, 2250 * {@code headSet}, or {@code tailSet} views, via {@link Iterator}, 2251 * {@link Spliterator} or {@link Stream}: 2252 * <pre> 2253 * NavigableSet s = Collections.synchronizedNavigableSet(new TreeSet()); 2254 * ... 2255 * synchronized (s) { 2256 * Iterator i = s.iterator(); // Must be in the synchronized block 2257 * while (i.hasNext()) 2258 * foo(i.next()); 2259 * } 2260 * </pre> 2261 * or: 2262 * <pre> 2263 * NavigableSet s = Collections.synchronizedNavigableSet(new TreeSet()); 2264 * NavigableSet s2 = s.headSet(foo, true); 2265 * ... 2266 * synchronized (s) { // Note: s, not s2!!! 2267 * Iterator i = s2.iterator(); // Must be in the synchronized block 2268 * while (i.hasNext()) 2269 * foo(i.next()); 2270 * } 2271 * </pre> 2272 * Failure to follow this advice may result in non-deterministic behavior. 2273 * 2274 * <p>The returned navigable set will be serializable if the specified 2275 * navigable set is serializable. 2276 * 2277 * @param <T> the class of the objects in the set 2278 * @param s the navigable set to be "wrapped" in a synchronized navigable 2279 * set 2280 * @return a synchronized view of the specified navigable set 2281 * @since 1.8 2282 */ 2283 public static <T> NavigableSet<T> synchronizedNavigableSet(NavigableSet<T> s) { 2284 return new SynchronizedNavigableSet<>(s); 2285 } 2286 2287 /** 2288 * @serial include 2289 */ 2290 static class SynchronizedNavigableSet<E> 2291 extends SynchronizedSortedSet<E> 2292 implements NavigableSet<E> 2293 { 2294 private static final long serialVersionUID = -5505529816273629798L; 2295 2296 private final NavigableSet<E> ns; 2297 2298 SynchronizedNavigableSet(NavigableSet<E> s) { 2299 super(s); 2300 ns = s; 2301 } 2302 2303 SynchronizedNavigableSet(NavigableSet<E> s, Object mutex) { 2304 super(s, mutex); 2305 ns = s; 2306 } 2307 public E lower(E e) { synchronized (mutex) {return ns.lower(e);} } 2308 public E floor(E e) { synchronized (mutex) {return ns.floor(e);} } 2309 public E ceiling(E e) { synchronized (mutex) {return ns.ceiling(e);} } 2310 public E higher(E e) { synchronized (mutex) {return ns.higher(e);} } 2311 public E pollFirst() { synchronized (mutex) {return ns.pollFirst();} } 2312 public E pollLast() { synchronized (mutex) {return ns.pollLast();} } 2313 2314 public NavigableSet<E> descendingSet() { 2315 synchronized (mutex) { 2316 return new SynchronizedNavigableSet<>(ns.descendingSet(), mutex); 2317 } 2318 } 2319 2320 public Iterator<E> descendingIterator() 2321 { synchronized (mutex) { return descendingSet().iterator(); } } 2322 2323 public NavigableSet<E> subSet(E fromElement, E toElement) { 2324 synchronized (mutex) { 2325 return new SynchronizedNavigableSet<>(ns.subSet(fromElement, true, toElement, false), mutex); 2326 } 2327 } 2328 public NavigableSet<E> headSet(E toElement) { 2329 synchronized (mutex) { 2330 return new SynchronizedNavigableSet<>(ns.headSet(toElement, false), mutex); 2331 } 2332 } 2333 public NavigableSet<E> tailSet(E fromElement) { 2334 synchronized (mutex) { 2335 return new SynchronizedNavigableSet<>(ns.tailSet(fromElement, true), mutex); 2336 } 2337 } 2338 2339 public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) { 2340 synchronized (mutex) { 2341 return new SynchronizedNavigableSet<>(ns.subSet(fromElement, fromInclusive, toElement, toInclusive), mutex); 2342 } 2343 } 2344 2345 public NavigableSet<E> headSet(E toElement, boolean inclusive) { 2346 synchronized (mutex) { 2347 return new SynchronizedNavigableSet<>(ns.headSet(toElement, inclusive), mutex); 2348 } 2349 } 2350 2351 public NavigableSet<E> tailSet(E fromElement, boolean inclusive) { 2352 synchronized (mutex) { 2353 return new SynchronizedNavigableSet<>(ns.tailSet(fromElement, inclusive), mutex); 2354 } 2355 } 2356 } 2357 2358 /** 2359 * Returns a synchronized (thread-safe) list backed by the specified 2360 * list. In order to guarantee serial access, it is critical that 2361 * <strong>all</strong> access to the backing list is accomplished 2362 * through the returned list.<p> 2363 * 2364 * It is imperative that the user manually synchronize on the returned 2365 * list when traversing it via {@link Iterator}, {@link Spliterator} 2366 * or {@link Stream}: 2367 * <pre> 2368 * List list = Collections.synchronizedList(new ArrayList()); 2369 * ... 2370 * synchronized (list) { 2371 * Iterator i = list.iterator(); // Must be in synchronized block 2372 * while (i.hasNext()) 2373 * foo(i.next()); 2374 * } 2375 * </pre> 2376 * Failure to follow this advice may result in non-deterministic behavior. 2377 * 2378 * <p>The returned list will be serializable if the specified list is 2379 * serializable. 2380 * 2381 * @param <T> the class of the objects in the list 2382 * @param list the list to be "wrapped" in a synchronized list. 2383 * @return a synchronized view of the specified list. 2384 */ 2385 public static <T> List<T> synchronizedList(List<T> list) { 2386 return (list instanceof RandomAccess ? 2387 new SynchronizedRandomAccessList<>(list) : 2388 new SynchronizedList<>(list)); 2389 } 2390 2391 static <T> List<T> synchronizedList(List<T> list, Object mutex) { 2392 return (list instanceof RandomAccess ? 2393 new SynchronizedRandomAccessList<>(list, mutex) : 2394 new SynchronizedList<>(list, mutex)); 2395 } 2396 2397 /** 2398 * @serial include 2399 */ 2400 static class SynchronizedList<E> 2401 extends SynchronizedCollection<E> 2402 implements List<E> { 2403 private static final long serialVersionUID = -7754090372962971524L; 2404 2405 final List<E> list; 2406 2407 SynchronizedList(List<E> list) { 2408 super(list); 2409 this.list = list; 2410 } 2411 SynchronizedList(List<E> list, Object mutex) { 2412 super(list, mutex); 2413 this.list = list; 2414 } 2415 2416 public boolean equals(Object o) { 2417 if (this == o) 2418 return true; 2419 synchronized (mutex) {return list.equals(o);} 2420 } 2421 public int hashCode() { 2422 synchronized (mutex) {return list.hashCode();} 2423 } 2424 2425 public E get(int index) { 2426 synchronized (mutex) {return list.get(index);} 2427 } 2428 public E set(int index, E element) { 2429 synchronized (mutex) {return list.set(index, element);} 2430 } 2431 public void add(int index, E element) { 2432 synchronized (mutex) {list.add(index, element);} 2433 } 2434 public E remove(int index) { 2435 synchronized (mutex) {return list.remove(index);} 2436 } 2437 2438 public int indexOf(Object o) { 2439 synchronized (mutex) {return list.indexOf(o);} 2440 } 2441 public int lastIndexOf(Object o) { 2442 synchronized (mutex) {return list.lastIndexOf(o);} 2443 } 2444 2445 public boolean addAll(int index, Collection<? extends E> c) { 2446 synchronized (mutex) {return list.addAll(index, c);} 2447 } 2448 2449 public ListIterator<E> listIterator() { 2450 return list.listIterator(); // Must be manually synched by user 2451 } 2452 2453 public ListIterator<E> listIterator(int index) { 2454 return list.listIterator(index); // Must be manually synched by user 2455 } 2456 2457 public List<E> subList(int fromIndex, int toIndex) { 2458 synchronized (mutex) { 2459 return new SynchronizedList<>(list.subList(fromIndex, toIndex), 2460 mutex); 2461 } 2462 } 2463 2464 @Override 2465 public void replaceAll(UnaryOperator<E> operator) { 2466 synchronized (mutex) {list.replaceAll(operator);} 2467 } 2468 @Override 2469 public void sort(Comparator<? super E> c) { 2470 synchronized (mutex) {list.sort(c);} 2471 } 2472 2473 /** 2474 * SynchronizedRandomAccessList instances are serialized as 2475 * SynchronizedList instances to allow them to be deserialized 2476 * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList). 2477 * This method inverts the transformation. As a beneficial 2478 * side-effect, it also grafts the RandomAccess marker onto 2479 * SynchronizedList instances that were serialized in pre-1.4 JREs. 2480 * 2481 * Note: Unfortunately, SynchronizedRandomAccessList instances 2482 * serialized in 1.4.1 and deserialized in 1.4 will become 2483 * SynchronizedList instances, as this method was missing in 1.4. 2484 */ 2485 private Object readResolve() { 2486 return (list instanceof RandomAccess 2487 ? new SynchronizedRandomAccessList<>(list) 2488 : this); 2489 } 2490 } 2491 2492 /** 2493 * @serial include 2494 */ 2495 static class SynchronizedRandomAccessList<E> 2496 extends SynchronizedList<E> 2497 implements RandomAccess { 2498 2499 SynchronizedRandomAccessList(List<E> list) { 2500 super(list); 2501 } 2502 2503 SynchronizedRandomAccessList(List<E> list, Object mutex) { 2504 super(list, mutex); 2505 } 2506 2507 public List<E> subList(int fromIndex, int toIndex) { 2508 synchronized (mutex) { 2509 return new SynchronizedRandomAccessList<>( 2510 list.subList(fromIndex, toIndex), mutex); 2511 } 2512 } 2513 2514 private static final long serialVersionUID = 1530674583602358482L; 2515 2516 /** 2517 * Allows instances to be deserialized in pre-1.4 JREs (which do 2518 * not have SynchronizedRandomAccessList). SynchronizedList has 2519 * a readResolve method that inverts this transformation upon 2520 * deserialization. 2521 */ 2522 private Object writeReplace() { 2523 return new SynchronizedList<>(list); 2524 } 2525 } 2526 2527 /** 2528 * Returns a synchronized (thread-safe) map backed by the specified 2529 * map. In order to guarantee serial access, it is critical that 2530 * <strong>all</strong> access to the backing map is accomplished 2531 * through the returned map.<p> 2532 * 2533 * It is imperative that the user manually synchronize on the returned 2534 * map when traversing any of its collection views via {@link Iterator}, 2535 * {@link Spliterator} or {@link Stream}: 2536 * <pre> 2537 * Map m = Collections.synchronizedMap(new HashMap()); 2538 * ... 2539 * Set s = m.keySet(); // Needn't be in synchronized block 2540 * ... 2541 * synchronized (m) { // Synchronizing on m, not s! 2542 * Iterator i = s.iterator(); // Must be in synchronized block 2543 * while (i.hasNext()) 2544 * foo(i.next()); 2545 * } 2546 * </pre> 2547 * Failure to follow this advice may result in non-deterministic behavior. 2548 * 2549 * <p>The returned map will be serializable if the specified map is 2550 * serializable. 2551 * 2552 * @param <K> the class of the map keys 2553 * @param <V> the class of the map values 2554 * @param m the map to be "wrapped" in a synchronized map. 2555 * @return a synchronized view of the specified map. 2556 */ 2557 public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) { 2558 return new SynchronizedMap<>(m); 2559 } 2560 2561 /** 2562 * @serial include 2563 */ 2564 private static class SynchronizedMap<K,V> 2565 implements Map<K,V>, Serializable { 2566 private static final long serialVersionUID = 1978198479659022715L; 2567 2568 private final Map<K,V> m; // Backing Map 2569 final Object mutex; // Object on which to synchronize 2570 2571 SynchronizedMap(Map<K,V> m) { 2572 this.m = Objects.requireNonNull(m); 2573 mutex = this; 2574 } 2575 2576 SynchronizedMap(Map<K,V> m, Object mutex) { 2577 this.m = m; 2578 this.mutex = mutex; 2579 } 2580 2581 public int size() { 2582 synchronized (mutex) {return m.size();} 2583 } 2584 public boolean isEmpty() { 2585 synchronized (mutex) {return m.isEmpty();} 2586 } 2587 public boolean containsKey(Object key) { 2588 synchronized (mutex) {return m.containsKey(key);} 2589 } 2590 public boolean containsValue(Object value) { 2591 synchronized (mutex) {return m.containsValue(value);} 2592 } 2593 public V get(Object key) { 2594 synchronized (mutex) {return m.get(key);} 2595 } 2596 2597 public V put(K key, V value) { 2598 synchronized (mutex) {return m.put(key, value);} 2599 } 2600 public V remove(Object key) { 2601 synchronized (mutex) {return m.remove(key);} 2602 } 2603 public void putAll(Map<? extends K, ? extends V> map) { 2604 synchronized (mutex) {m.putAll(map);} 2605 } 2606 public void clear() { 2607 synchronized (mutex) {m.clear();} 2608 } 2609 2610 private transient Set<K> keySet; 2611 private transient Set<Map.Entry<K,V>> entrySet; 2612 private transient Collection<V> values; 2613 2614 public Set<K> keySet() { 2615 synchronized (mutex) { 2616 if (keySet==null) 2617 keySet = new SynchronizedSet<>(m.keySet(), mutex); 2618 return keySet; 2619 } 2620 } 2621 2622 public Set<Map.Entry<K,V>> entrySet() { 2623 synchronized (mutex) { 2624 if (entrySet==null) 2625 entrySet = new SynchronizedSet<>(m.entrySet(), mutex); 2626 return entrySet; 2627 } 2628 } 2629 2630 public Collection<V> values() { 2631 synchronized (mutex) { 2632 if (values==null) 2633 values = new SynchronizedCollection<>(m.values(), mutex); 2634 return values; 2635 } 2636 } 2637 2638 public boolean equals(Object o) { 2639 if (this == o) 2640 return true; 2641 synchronized (mutex) {return m.equals(o);} 2642 } 2643 public int hashCode() { 2644 synchronized (mutex) {return m.hashCode();} 2645 } 2646 public String toString() { 2647 synchronized (mutex) {return m.toString();} 2648 } 2649 2650 // Override default methods in Map 2651 @Override 2652 public V getOrDefault(Object k, V defaultValue) { 2653 synchronized (mutex) {return m.getOrDefault(k, defaultValue);} 2654 } 2655 @Override 2656 public void forEach(BiConsumer<? super K, ? super V> action) { 2657 synchronized (mutex) {m.forEach(action);} 2658 } 2659 @Override 2660 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 2661 synchronized (mutex) {m.replaceAll(function);} 2662 } 2663 @Override 2664 public V putIfAbsent(K key, V value) { 2665 synchronized (mutex) {return m.putIfAbsent(key, value);} 2666 } 2667 @Override 2668 public boolean remove(Object key, Object value) { 2669 synchronized (mutex) {return m.remove(key, value);} 2670 } 2671 @Override 2672 public boolean replace(K key, V oldValue, V newValue) { 2673 synchronized (mutex) {return m.replace(key, oldValue, newValue);} 2674 } 2675 @Override 2676 public V replace(K key, V value) { 2677 synchronized (mutex) {return m.replace(key, value);} 2678 } 2679 @Override 2680 public V computeIfAbsent(K key, 2681 Function<? super K, ? extends V> mappingFunction) { 2682 synchronized (mutex) {return m.computeIfAbsent(key, mappingFunction);} 2683 } 2684 @Override 2685 public V computeIfPresent(K key, 2686 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 2687 synchronized (mutex) {return m.computeIfPresent(key, remappingFunction);} 2688 } 2689 @Override 2690 public V compute(K key, 2691 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 2692 synchronized (mutex) {return m.compute(key, remappingFunction);} 2693 } 2694 @Override 2695 public V merge(K key, V value, 2696 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 2697 synchronized (mutex) {return m.merge(key, value, remappingFunction);} 2698 } 2699 2700 private void writeObject(ObjectOutputStream s) throws IOException { 2701 synchronized (mutex) {s.defaultWriteObject();} 2702 } 2703 } 2704 2705 /** 2706 * Returns a synchronized (thread-safe) sorted map backed by the specified 2707 * sorted map. In order to guarantee serial access, it is critical that 2708 * <strong>all</strong> access to the backing sorted map is accomplished 2709 * through the returned sorted map (or its views).<p> 2710 * 2711 * It is imperative that the user manually synchronize on the returned 2712 * sorted map when traversing any of its collection views, or the 2713 * collections views of any of its {@code subMap}, {@code headMap} or 2714 * {@code tailMap} views, via {@link Iterator}, {@link Spliterator} or 2715 * {@link Stream}: 2716 * <pre> 2717 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap()); 2718 * ... 2719 * Set s = m.keySet(); // Needn't be in synchronized block 2720 * ... 2721 * synchronized (m) { // Synchronizing on m, not s! 2722 * Iterator i = s.iterator(); // Must be in synchronized block 2723 * while (i.hasNext()) 2724 * foo(i.next()); 2725 * } 2726 * </pre> 2727 * or: 2728 * <pre> 2729 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap()); 2730 * SortedMap m2 = m.subMap(foo, bar); 2731 * ... 2732 * Set s2 = m2.keySet(); // Needn't be in synchronized block 2733 * ... 2734 * synchronized (m) { // Synchronizing on m, not m2 or s2! 2735 * Iterator i = s2.iterator(); // Must be in synchronized block 2736 * while (i.hasNext()) 2737 * foo(i.next()); 2738 * } 2739 * </pre> 2740 * Failure to follow this advice may result in non-deterministic behavior. 2741 * 2742 * <p>The returned sorted map will be serializable if the specified 2743 * sorted map is serializable. 2744 * 2745 * @param <K> the class of the map keys 2746 * @param <V> the class of the map values 2747 * @param m the sorted map to be "wrapped" in a synchronized sorted map. 2748 * @return a synchronized view of the specified sorted map. 2749 */ 2750 public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) { 2751 return new SynchronizedSortedMap<>(m); 2752 } 2753 2754 /** 2755 * @serial include 2756 */ 2757 static class SynchronizedSortedMap<K,V> 2758 extends SynchronizedMap<K,V> 2759 implements SortedMap<K,V> 2760 { 2761 private static final long serialVersionUID = -8798146769416483793L; 2762 2763 private final SortedMap<K,V> sm; 2764 2765 SynchronizedSortedMap(SortedMap<K,V> m) { 2766 super(m); 2767 sm = m; 2768 } 2769 SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) { 2770 super(m, mutex); 2771 sm = m; 2772 } 2773 2774 public Comparator<? super K> comparator() { 2775 synchronized (mutex) {return sm.comparator();} 2776 } 2777 2778 public SortedMap<K,V> subMap(K fromKey, K toKey) { 2779 synchronized (mutex) { 2780 return new SynchronizedSortedMap<>( 2781 sm.subMap(fromKey, toKey), mutex); 2782 } 2783 } 2784 public SortedMap<K,V> headMap(K toKey) { 2785 synchronized (mutex) { 2786 return new SynchronizedSortedMap<>(sm.headMap(toKey), mutex); 2787 } 2788 } 2789 public SortedMap<K,V> tailMap(K fromKey) { 2790 synchronized (mutex) { 2791 return new SynchronizedSortedMap<>(sm.tailMap(fromKey),mutex); 2792 } 2793 } 2794 2795 public K firstKey() { 2796 synchronized (mutex) {return sm.firstKey();} 2797 } 2798 public K lastKey() { 2799 synchronized (mutex) {return sm.lastKey();} 2800 } 2801 } 2802 2803 /** 2804 * Returns a synchronized (thread-safe) navigable map backed by the 2805 * specified navigable map. In order to guarantee serial access, it is 2806 * critical that <strong>all</strong> access to the backing navigable map is 2807 * accomplished through the returned navigable map (or its views).<p> 2808 * 2809 * It is imperative that the user manually synchronize on the returned 2810 * navigable map when traversing any of its collection views, or the 2811 * collections views of any of its {@code subMap}, {@code headMap} or 2812 * {@code tailMap} views, via {@link Iterator}, {@link Spliterator} or 2813 * {@link Stream}: 2814 * <pre> 2815 * NavigableMap m = Collections.synchronizedNavigableMap(new TreeMap()); 2816 * ... 2817 * Set s = m.keySet(); // Needn't be in synchronized block 2818 * ... 2819 * synchronized (m) { // Synchronizing on m, not s! 2820 * Iterator i = s.iterator(); // Must be in synchronized block 2821 * while (i.hasNext()) 2822 * foo(i.next()); 2823 * } 2824 * </pre> 2825 * or: 2826 * <pre> 2827 * NavigableMap m = Collections.synchronizedNavigableMap(new TreeMap()); 2828 * NavigableMap m2 = m.subMap(foo, true, bar, false); 2829 * ... 2830 * Set s2 = m2.keySet(); // Needn't be in synchronized block 2831 * ... 2832 * synchronized (m) { // Synchronizing on m, not m2 or s2! 2833 * Iterator i = s.iterator(); // Must be in synchronized block 2834 * while (i.hasNext()) 2835 * foo(i.next()); 2836 * } 2837 * </pre> 2838 * Failure to follow this advice may result in non-deterministic behavior. 2839 * 2840 * <p>The returned navigable map will be serializable if the specified 2841 * navigable map is serializable. 2842 * 2843 * @param <K> the class of the map keys 2844 * @param <V> the class of the map values 2845 * @param m the navigable map to be "wrapped" in a synchronized navigable 2846 * map 2847 * @return a synchronized view of the specified navigable map. 2848 * @since 1.8 2849 */ 2850 public static <K,V> NavigableMap<K,V> synchronizedNavigableMap(NavigableMap<K,V> m) { 2851 return new SynchronizedNavigableMap<>(m); 2852 } 2853 2854 /** 2855 * A synchronized NavigableMap. 2856 * 2857 * @serial include 2858 */ 2859 static class SynchronizedNavigableMap<K,V> 2860 extends SynchronizedSortedMap<K,V> 2861 implements NavigableMap<K,V> 2862 { 2863 private static final long serialVersionUID = 699392247599746807L; 2864 2865 private final NavigableMap<K,V> nm; 2866 2867 SynchronizedNavigableMap(NavigableMap<K,V> m) { 2868 super(m); 2869 nm = m; 2870 } 2871 SynchronizedNavigableMap(NavigableMap<K,V> m, Object mutex) { 2872 super(m, mutex); 2873 nm = m; 2874 } 2875 2876 public Entry<K, V> lowerEntry(K key) 2877 { synchronized (mutex) { return nm.lowerEntry(key); } } 2878 public K lowerKey(K key) 2879 { synchronized (mutex) { return nm.lowerKey(key); } } 2880 public Entry<K, V> floorEntry(K key) 2881 { synchronized (mutex) { return nm.floorEntry(key); } } 2882 public K floorKey(K key) 2883 { synchronized (mutex) { return nm.floorKey(key); } } 2884 public Entry<K, V> ceilingEntry(K key) 2885 { synchronized (mutex) { return nm.ceilingEntry(key); } } 2886 public K ceilingKey(K key) 2887 { synchronized (mutex) { return nm.ceilingKey(key); } } 2888 public Entry<K, V> higherEntry(K key) 2889 { synchronized (mutex) { return nm.higherEntry(key); } } 2890 public K higherKey(K key) 2891 { synchronized (mutex) { return nm.higherKey(key); } } 2892 public Entry<K, V> firstEntry() 2893 { synchronized (mutex) { return nm.firstEntry(); } } 2894 public Entry<K, V> lastEntry() 2895 { synchronized (mutex) { return nm.lastEntry(); } } 2896 public Entry<K, V> pollFirstEntry() 2897 { synchronized (mutex) { return nm.pollFirstEntry(); } } 2898 public Entry<K, V> pollLastEntry() 2899 { synchronized (mutex) { return nm.pollLastEntry(); } } 2900 2901 public NavigableMap<K, V> descendingMap() { 2902 synchronized (mutex) { 2903 return 2904 new SynchronizedNavigableMap<>(nm.descendingMap(), mutex); 2905 } 2906 } 2907 2908 public NavigableSet<K> keySet() { 2909 return navigableKeySet(); 2910 } 2911 2912 public NavigableSet<K> navigableKeySet() { 2913 synchronized (mutex) { 2914 return new SynchronizedNavigableSet<>(nm.navigableKeySet(), mutex); 2915 } 2916 } 2917 2918 public NavigableSet<K> descendingKeySet() { 2919 synchronized (mutex) { 2920 return new SynchronizedNavigableSet<>(nm.descendingKeySet(), mutex); 2921 } 2922 } 2923 2924 2925 public SortedMap<K,V> subMap(K fromKey, K toKey) { 2926 synchronized (mutex) { 2927 return new SynchronizedNavigableMap<>( 2928 nm.subMap(fromKey, true, toKey, false), mutex); 2929 } 2930 } 2931 public SortedMap<K,V> headMap(K toKey) { 2932 synchronized (mutex) { 2933 return new SynchronizedNavigableMap<>(nm.headMap(toKey, false), mutex); 2934 } 2935 } 2936 public SortedMap<K,V> tailMap(K fromKey) { 2937 synchronized (mutex) { 2938 return new SynchronizedNavigableMap<>(nm.tailMap(fromKey, true),mutex); 2939 } 2940 } 2941 2942 public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) { 2943 synchronized (mutex) { 2944 return new SynchronizedNavigableMap<>( 2945 nm.subMap(fromKey, fromInclusive, toKey, toInclusive), mutex); 2946 } 2947 } 2948 2949 public NavigableMap<K, V> headMap(K toKey, boolean inclusive) { 2950 synchronized (mutex) { 2951 return new SynchronizedNavigableMap<>( 2952 nm.headMap(toKey, inclusive), mutex); 2953 } 2954 } 2955 2956 public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) { 2957 synchronized (mutex) { 2958 return new SynchronizedNavigableMap<>( 2959 nm.tailMap(fromKey, inclusive), mutex); 2960 } 2961 } 2962 } 2963 2964 // Dynamically typesafe collection wrappers 2965 2966 /** 2967 * Returns a dynamically typesafe view of the specified collection. 2968 * Any attempt to insert an element of the wrong type will result in an 2969 * immediate {@link ClassCastException}. Assuming a collection 2970 * contains no incorrectly typed elements prior to the time a 2971 * dynamically typesafe view is generated, and that all subsequent 2972 * access to the collection takes place through the view, it is 2973 * <i>guaranteed</i> that the collection cannot contain an incorrectly 2974 * typed element. 2975 * 2976 * <p>The generics mechanism in the language provides compile-time 2977 * (static) type checking, but it is possible to defeat this mechanism 2978 * with unchecked casts. Usually this is not a problem, as the compiler 2979 * issues warnings on all such unchecked operations. There are, however, 2980 * times when static type checking alone is not sufficient. For example, 2981 * suppose a collection is passed to a third-party library and it is 2982 * imperative that the library code not corrupt the collection by 2983 * inserting an element of the wrong type. 2984 * 2985 * <p>Another use of dynamically typesafe views is debugging. Suppose a 2986 * program fails with a {@code ClassCastException}, indicating that an 2987 * incorrectly typed element was put into a parameterized collection. 2988 * Unfortunately, the exception can occur at any time after the erroneous 2989 * element is inserted, so it typically provides little or no information 2990 * as to the real source of the problem. If the problem is reproducible, 2991 * one can quickly determine its source by temporarily modifying the 2992 * program to wrap the collection with a dynamically typesafe view. 2993 * For example, this declaration: 2994 * <pre> {@code 2995 * Collection<String> c = new HashSet<>(); 2996 * }</pre> 2997 * may be replaced temporarily by this one: 2998 * <pre> {@code 2999 * Collection<String> c = Collections.checkedCollection( 3000 * new HashSet<>(), String.class); 3001 * }</pre> 3002 * Running the program again will cause it to fail at the point where 3003 * an incorrectly typed element is inserted into the collection, clearly 3004 * identifying the source of the problem. Once the problem is fixed, the 3005 * modified declaration may be reverted back to the original. 3006 * 3007 * <p>The returned collection does <i>not</i> pass the hashCode and equals 3008 * operations through to the backing collection, but relies on 3009 * {@code Object}'s {@code equals} and {@code hashCode} methods. This 3010 * is necessary to preserve the contracts of these operations in the case 3011 * that the backing collection is a set or a list. 3012 * 3013 * <p>The returned collection will be serializable if the specified 3014 * collection is serializable. 3015 * 3016 * <p>Since {@code null} is considered to be a value of any reference 3017 * type, the returned collection permits insertion of null elements 3018 * whenever the backing collection does. 3019 * 3020 * @param <E> the class of the objects in the collection 3021 * @param c the collection for which a dynamically typesafe view is to be 3022 * returned 3023 * @param type the type of element that {@code c} is permitted to hold 3024 * @return a dynamically typesafe view of the specified collection 3025 * @since 1.5 3026 */ 3027 public static <E> Collection<E> checkedCollection(Collection<E> c, 3028 Class<E> type) { 3029 return new CheckedCollection<>(c, type); 3030 } 3031 3032 @SuppressWarnings("unchecked") 3033 static <T> T[] zeroLengthArray(Class<T> type) { 3034 return (T[]) Array.newInstance(type, 0); 3035 } 3036 3037 /** 3038 * @serial include 3039 */ 3040 static class CheckedCollection<E> implements Collection<E>, Serializable { 3041 private static final long serialVersionUID = 1578914078182001775L; 3042 3043 final Collection<E> c; 3044 final Class<E> type; 3045 3046 @SuppressWarnings("unchecked") 3047 E typeCheck(Object o) { 3048 if (o != null && !type.isInstance(o)) 3049 throw new ClassCastException(badElementMsg(o)); 3050 return (E) o; 3051 } 3052 3053 private String badElementMsg(Object o) { 3054 return "Attempt to insert " + o.getClass() + 3055 " element into collection with element type " + type; 3056 } 3057 3058 CheckedCollection(Collection<E> c, Class<E> type) { 3059 this.c = Objects.requireNonNull(c, "c"); 3060 this.type = Objects.requireNonNull(type, "type"); 3061 } 3062 3063 public int size() { return c.size(); } 3064 public boolean isEmpty() { return c.isEmpty(); } 3065 public boolean contains(Object o) { return c.contains(o); } 3066 public Object[] toArray() { return c.toArray(); } 3067 public <T> T[] toArray(T[] a) { return c.toArray(a); } 3068 public <T> T[] toArray(IntFunction<T[]> f) { return c.toArray(f); } 3069 public String toString() { return c.toString(); } 3070 public boolean remove(Object o) { return c.remove(o); } 3071 public void clear() { c.clear(); } 3072 3073 public boolean containsAll(Collection<?> coll) { 3074 return c.containsAll(coll); 3075 } 3076 public boolean removeAll(Collection<?> coll) { 3077 return c.removeAll(coll); 3078 } 3079 public boolean retainAll(Collection<?> coll) { 3080 return c.retainAll(coll); 3081 } 3082 3083 public Iterator<E> iterator() { 3084 // JDK-6363904 - unwrapped iterator could be typecast to 3085 // ListIterator with unsafe set() 3086 final Iterator<E> it = c.iterator(); 3087 return new Iterator<E>() { 3088 public boolean hasNext() { return it.hasNext(); } 3089 public E next() { return it.next(); } 3090 public void remove() { it.remove(); } 3091 public void forEachRemaining(Consumer<? super E> action) { 3092 it.forEachRemaining(action); 3093 } 3094 }; 3095 } 3096 3097 public boolean add(E e) { return c.add(typeCheck(e)); } 3098 3099 private E[] zeroLengthElementArray; // Lazily initialized 3100 3101 private E[] zeroLengthElementArray() { 3102 return zeroLengthElementArray != null ? zeroLengthElementArray : 3103 (zeroLengthElementArray = zeroLengthArray(type)); 3104 } 3105 3106 @SuppressWarnings("unchecked") 3107 Collection<E> checkedCopyOf(Collection<? extends E> coll) { 3108 Object[] a; 3109 try { 3110 E[] z = zeroLengthElementArray(); 3111 a = coll.toArray(z); 3112 // Defend against coll violating the toArray contract 3113 if (a.getClass() != z.getClass()) 3114 a = Arrays.copyOf(a, a.length, z.getClass()); 3115 } catch (ArrayStoreException ignore) { 3116 // To get better and consistent diagnostics, 3117 // we call typeCheck explicitly on each element. 3118 // We call clone() to defend against coll retaining a 3119 // reference to the returned array and storing a bad 3120 // element into it after it has been type checked. 3121 a = coll.toArray().clone(); 3122 for (Object o : a) 3123 typeCheck(o); 3124 } 3125 // A slight abuse of the type system, but safe here. 3126 return (Collection<E>) Arrays.asList(a); 3127 } 3128 3129 public boolean addAll(Collection<? extends E> coll) { 3130 // Doing things this way insulates us from concurrent changes 3131 // in the contents of coll and provides all-or-nothing 3132 // semantics (which we wouldn't get if we type-checked each 3133 // element as we added it) 3134 return c.addAll(checkedCopyOf(coll)); 3135 } 3136 3137 // Override default methods in Collection 3138 @Override 3139 public void forEach(Consumer<? super E> action) {c.forEach(action);} 3140 @Override 3141 public boolean removeIf(Predicate<? super E> filter) { 3142 return c.removeIf(filter); 3143 } 3144 @Override 3145 public Spliterator<E> spliterator() {return c.spliterator();} 3146 @Override 3147 public Stream<E> stream() {return c.stream();} 3148 @Override 3149 public Stream<E> parallelStream() {return c.parallelStream();} 3150 } 3151 3152 /** 3153 * Returns a dynamically typesafe view of the specified queue. 3154 * Any attempt to insert an element of the wrong type will result in 3155 * an immediate {@link ClassCastException}. Assuming a queue contains 3156 * no incorrectly typed elements prior to the time a dynamically typesafe 3157 * view is generated, and that all subsequent access to the queue 3158 * takes place through the view, it is <i>guaranteed</i> that the 3159 * queue cannot contain an incorrectly typed element. 3160 * 3161 * <p>A discussion of the use of dynamically typesafe views may be 3162 * found in the documentation for the {@link #checkedCollection 3163 * checkedCollection} method. 3164 * 3165 * <p>The returned queue will be serializable if the specified queue 3166 * is serializable. 3167 * 3168 * <p>Since {@code null} is considered to be a value of any reference 3169 * type, the returned queue permits insertion of {@code null} elements 3170 * whenever the backing queue does. 3171 * 3172 * @param <E> the class of the objects in the queue 3173 * @param queue the queue for which a dynamically typesafe view is to be 3174 * returned 3175 * @param type the type of element that {@code queue} is permitted to hold 3176 * @return a dynamically typesafe view of the specified queue 3177 * @since 1.8 3178 */ 3179 public static <E> Queue<E> checkedQueue(Queue<E> queue, Class<E> type) { 3180 return new CheckedQueue<>(queue, type); 3181 } 3182 3183 /** 3184 * @serial include 3185 */ 3186 static class CheckedQueue<E> 3187 extends CheckedCollection<E> 3188 implements Queue<E>, Serializable 3189 { 3190 private static final long serialVersionUID = 1433151992604707767L; 3191 final Queue<E> queue; 3192 3193 CheckedQueue(Queue<E> queue, Class<E> elementType) { 3194 super(queue, elementType); 3195 this.queue = queue; 3196 } 3197 3198 public E element() {return queue.element();} 3199 public boolean equals(Object o) {return o == this || c.equals(o);} 3200 public int hashCode() {return c.hashCode();} 3201 public E peek() {return queue.peek();} 3202 public E poll() {return queue.poll();} 3203 public E remove() {return queue.remove();} 3204 public boolean offer(E e) {return queue.offer(typeCheck(e));} 3205 } 3206 3207 /** 3208 * Returns a dynamically typesafe view of the specified set. 3209 * Any attempt to insert an element of the wrong type will result in 3210 * an immediate {@link ClassCastException}. Assuming a set contains 3211 * no incorrectly typed elements prior to the time a dynamically typesafe 3212 * view is generated, and that all subsequent access to the set 3213 * takes place through the view, it is <i>guaranteed</i> that the 3214 * set cannot contain an incorrectly typed element. 3215 * 3216 * <p>A discussion of the use of dynamically typesafe views may be 3217 * found in the documentation for the {@link #checkedCollection 3218 * checkedCollection} method. 3219 * 3220 * <p>The returned set will be serializable if the specified set is 3221 * serializable. 3222 * 3223 * <p>Since {@code null} is considered to be a value of any reference 3224 * type, the returned set permits insertion of null elements whenever 3225 * the backing set does. 3226 * 3227 * @param <E> the class of the objects in the set 3228 * @param s the set for which a dynamically typesafe view is to be 3229 * returned 3230 * @param type the type of element that {@code s} is permitted to hold 3231 * @return a dynamically typesafe view of the specified set 3232 * @since 1.5 3233 */ 3234 public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) { 3235 return new CheckedSet<>(s, type); 3236 } 3237 3238 /** 3239 * @serial include 3240 */ 3241 static class CheckedSet<E> extends CheckedCollection<E> 3242 implements Set<E>, Serializable 3243 { 3244 private static final long serialVersionUID = 4694047833775013803L; 3245 3246 CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); } 3247 3248 public boolean equals(Object o) { return o == this || c.equals(o); } 3249 public int hashCode() { return c.hashCode(); } 3250 } 3251 3252 /** 3253 * Returns a dynamically typesafe view of the specified sorted set. 3254 * Any attempt to insert an element of the wrong type will result in an 3255 * immediate {@link ClassCastException}. Assuming a sorted set 3256 * contains no incorrectly typed elements prior to the time a 3257 * dynamically typesafe view is generated, and that all subsequent 3258 * access to the sorted set takes place through the view, it is 3259 * <i>guaranteed</i> that the sorted set cannot contain an incorrectly 3260 * typed element. 3261 * 3262 * <p>A discussion of the use of dynamically typesafe views may be 3263 * found in the documentation for the {@link #checkedCollection 3264 * checkedCollection} method. 3265 * 3266 * <p>The returned sorted set will be serializable if the specified sorted 3267 * set is serializable. 3268 * 3269 * <p>Since {@code null} is considered to be a value of any reference 3270 * type, the returned sorted set permits insertion of null elements 3271 * whenever the backing sorted set does. 3272 * 3273 * @param <E> the class of the objects in the set 3274 * @param s the sorted set for which a dynamically typesafe view is to be 3275 * returned 3276 * @param type the type of element that {@code s} is permitted to hold 3277 * @return a dynamically typesafe view of the specified sorted set 3278 * @since 1.5 3279 */ 3280 public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s, 3281 Class<E> type) { 3282 return new CheckedSortedSet<>(s, type); 3283 } 3284 3285 /** 3286 * @serial include 3287 */ 3288 static class CheckedSortedSet<E> extends CheckedSet<E> 3289 implements SortedSet<E>, Serializable 3290 { 3291 private static final long serialVersionUID = 1599911165492914959L; 3292 3293 private final SortedSet<E> ss; 3294 3295 CheckedSortedSet(SortedSet<E> s, Class<E> type) { 3296 super(s, type); 3297 ss = s; 3298 } 3299 3300 public Comparator<? super E> comparator() { return ss.comparator(); } 3301 public E first() { return ss.first(); } 3302 public E last() { return ss.last(); } 3303 3304 public SortedSet<E> subSet(E fromElement, E toElement) { 3305 return checkedSortedSet(ss.subSet(fromElement,toElement), type); 3306 } 3307 public SortedSet<E> headSet(E toElement) { 3308 return checkedSortedSet(ss.headSet(toElement), type); 3309 } 3310 public SortedSet<E> tailSet(E fromElement) { 3311 return checkedSortedSet(ss.tailSet(fromElement), type); 3312 } 3313 } 3314 3315 /** 3316 * Returns a dynamically typesafe view of the specified navigable set. 3317 * Any attempt to insert an element of the wrong type will result in an 3318 * immediate {@link ClassCastException}. Assuming a navigable set 3319 * contains no incorrectly typed elements prior to the time a 3320 * dynamically typesafe view is generated, and that all subsequent 3321 * access to the navigable set takes place through the view, it is 3322 * <em>guaranteed</em> that the navigable set cannot contain an incorrectly 3323 * typed element. 3324 * 3325 * <p>A discussion of the use of dynamically typesafe views may be 3326 * found in the documentation for the {@link #checkedCollection 3327 * checkedCollection} method. 3328 * 3329 * <p>The returned navigable set will be serializable if the specified 3330 * navigable set is serializable. 3331 * 3332 * <p>Since {@code null} is considered to be a value of any reference 3333 * type, the returned navigable set permits insertion of null elements 3334 * whenever the backing sorted set does. 3335 * 3336 * @param <E> the class of the objects in the set 3337 * @param s the navigable set for which a dynamically typesafe view is to be 3338 * returned 3339 * @param type the type of element that {@code s} is permitted to hold 3340 * @return a dynamically typesafe view of the specified navigable set 3341 * @since 1.8 3342 */ 3343 public static <E> NavigableSet<E> checkedNavigableSet(NavigableSet<E> s, 3344 Class<E> type) { 3345 return new CheckedNavigableSet<>(s, type); 3346 } 3347 3348 /** 3349 * @serial include 3350 */ 3351 static class CheckedNavigableSet<E> extends CheckedSortedSet<E> 3352 implements NavigableSet<E>, Serializable 3353 { 3354 private static final long serialVersionUID = -5429120189805438922L; 3355 3356 private final NavigableSet<E> ns; 3357 3358 CheckedNavigableSet(NavigableSet<E> s, Class<E> type) { 3359 super(s, type); 3360 ns = s; 3361 } 3362 3363 public E lower(E e) { return ns.lower(e); } 3364 public E floor(E e) { return ns.floor(e); } 3365 public E ceiling(E e) { return ns.ceiling(e); } 3366 public E higher(E e) { return ns.higher(e); } 3367 public E pollFirst() { return ns.pollFirst(); } 3368 public E pollLast() {return ns.pollLast(); } 3369 public NavigableSet<E> descendingSet() 3370 { return checkedNavigableSet(ns.descendingSet(), type); } 3371 public Iterator<E> descendingIterator() 3372 {return checkedNavigableSet(ns.descendingSet(), type).iterator(); } 3373 3374 public NavigableSet<E> subSet(E fromElement, E toElement) { 3375 return checkedNavigableSet(ns.subSet(fromElement, true, toElement, false), type); 3376 } 3377 public NavigableSet<E> headSet(E toElement) { 3378 return checkedNavigableSet(ns.headSet(toElement, false), type); 3379 } 3380 public NavigableSet<E> tailSet(E fromElement) { 3381 return checkedNavigableSet(ns.tailSet(fromElement, true), type); 3382 } 3383 3384 public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) { 3385 return checkedNavigableSet(ns.subSet(fromElement, fromInclusive, toElement, toInclusive), type); 3386 } 3387 3388 public NavigableSet<E> headSet(E toElement, boolean inclusive) { 3389 return checkedNavigableSet(ns.headSet(toElement, inclusive), type); 3390 } 3391 3392 public NavigableSet<E> tailSet(E fromElement, boolean inclusive) { 3393 return checkedNavigableSet(ns.tailSet(fromElement, inclusive), type); 3394 } 3395 } 3396 3397 /** 3398 * Returns a dynamically typesafe view of the specified list. 3399 * Any attempt to insert an element of the wrong type will result in 3400 * an immediate {@link ClassCastException}. Assuming a list contains 3401 * no incorrectly typed elements prior to the time a dynamically typesafe 3402 * view is generated, and that all subsequent access to the list 3403 * takes place through the view, it is <i>guaranteed</i> that the 3404 * list cannot contain an incorrectly typed element. 3405 * 3406 * <p>A discussion of the use of dynamically typesafe views may be 3407 * found in the documentation for the {@link #checkedCollection 3408 * checkedCollection} method. 3409 * 3410 * <p>The returned list will be serializable if the specified list 3411 * is serializable. 3412 * 3413 * <p>Since {@code null} is considered to be a value of any reference 3414 * type, the returned list permits insertion of null elements whenever 3415 * the backing list does. 3416 * 3417 * @param <E> the class of the objects in the list 3418 * @param list the list for which a dynamically typesafe view is to be 3419 * returned 3420 * @param type the type of element that {@code list} is permitted to hold 3421 * @return a dynamically typesafe view of the specified list 3422 * @since 1.5 3423 */ 3424 public static <E> List<E> checkedList(List<E> list, Class<E> type) { 3425 return (list instanceof RandomAccess ? 3426 new CheckedRandomAccessList<>(list, type) : 3427 new CheckedList<>(list, type)); 3428 } 3429 3430 /** 3431 * @serial include 3432 */ 3433 static class CheckedList<E> 3434 extends CheckedCollection<E> 3435 implements List<E> 3436 { 3437 private static final long serialVersionUID = 65247728283967356L; 3438 final List<E> list; 3439 3440 CheckedList(List<E> list, Class<E> type) { 3441 super(list, type); 3442 this.list = list; 3443 } 3444 3445 public boolean equals(Object o) { return o == this || list.equals(o); } 3446 public int hashCode() { return list.hashCode(); } 3447 public E get(int index) { return list.get(index); } 3448 public E remove(int index) { return list.remove(index); } 3449 public int indexOf(Object o) { return list.indexOf(o); } 3450 public int lastIndexOf(Object o) { return list.lastIndexOf(o); } 3451 3452 public E set(int index, E element) { 3453 return list.set(index, typeCheck(element)); 3454 } 3455 3456 public void add(int index, E element) { 3457 list.add(index, typeCheck(element)); 3458 } 3459 3460 public boolean addAll(int index, Collection<? extends E> c) { 3461 return list.addAll(index, checkedCopyOf(c)); 3462 } 3463 public ListIterator<E> listIterator() { return listIterator(0); } 3464 3465 public ListIterator<E> listIterator(final int index) { 3466 final ListIterator<E> i = list.listIterator(index); 3467 3468 return new ListIterator<E>() { 3469 public boolean hasNext() { return i.hasNext(); } 3470 public E next() { return i.next(); } 3471 public boolean hasPrevious() { return i.hasPrevious(); } 3472 public E previous() { return i.previous(); } 3473 public int nextIndex() { return i.nextIndex(); } 3474 public int previousIndex() { return i.previousIndex(); } 3475 public void remove() { i.remove(); } 3476 3477 public void set(E e) { 3478 i.set(typeCheck(e)); 3479 } 3480 3481 public void add(E e) { 3482 i.add(typeCheck(e)); 3483 } 3484 3485 @Override 3486 public void forEachRemaining(Consumer<? super E> action) { 3487 i.forEachRemaining(action); 3488 } 3489 }; 3490 } 3491 3492 public List<E> subList(int fromIndex, int toIndex) { 3493 return new CheckedList<>(list.subList(fromIndex, toIndex), type); 3494 } 3495 3496 /** 3497 * {@inheritDoc} 3498 * 3499 * @throws ClassCastException if the class of an element returned by the 3500 * operator prevents it from being added to this collection. The 3501 * exception may be thrown after some elements of the list have 3502 * already been replaced. 3503 */ 3504 @Override 3505 public void replaceAll(UnaryOperator<E> operator) { 3506 Objects.requireNonNull(operator); 3507 list.replaceAll(e -> typeCheck(operator.apply(e))); 3508 } 3509 3510 @Override 3511 public void sort(Comparator<? super E> c) { 3512 list.sort(c); 3513 } 3514 } 3515 3516 /** 3517 * @serial include 3518 */ 3519 static class CheckedRandomAccessList<E> extends CheckedList<E> 3520 implements RandomAccess 3521 { 3522 private static final long serialVersionUID = 1638200125423088369L; 3523 3524 CheckedRandomAccessList(List<E> list, Class<E> type) { 3525 super(list, type); 3526 } 3527 3528 public List<E> subList(int fromIndex, int toIndex) { 3529 return new CheckedRandomAccessList<>( 3530 list.subList(fromIndex, toIndex), type); 3531 } 3532 } 3533 3534 /** 3535 * Returns a dynamically typesafe view of the specified map. 3536 * Any attempt to insert a mapping whose key or value have the wrong 3537 * type will result in an immediate {@link ClassCastException}. 3538 * Similarly, any attempt to modify the value currently associated with 3539 * a key will result in an immediate {@link ClassCastException}, 3540 * whether the modification is attempted directly through the map 3541 * itself, or through a {@link Map.Entry} instance obtained from the 3542 * map's {@link Map#entrySet() entry set} view. 3543 * 3544 * <p>Assuming a map contains no incorrectly typed keys or values 3545 * prior to the time a dynamically typesafe view is generated, and 3546 * that all subsequent access to the map takes place through the view 3547 * (or one of its collection views), it is <i>guaranteed</i> that the 3548 * map cannot contain an incorrectly typed key or value. 3549 * 3550 * <p>A discussion of the use of dynamically typesafe views may be 3551 * found in the documentation for the {@link #checkedCollection 3552 * checkedCollection} method. 3553 * 3554 * <p>The returned map will be serializable if the specified map is 3555 * serializable. 3556 * 3557 * <p>Since {@code null} is considered to be a value of any reference 3558 * type, the returned map permits insertion of null keys or values 3559 * whenever the backing map does. 3560 * 3561 * @param <K> the class of the map keys 3562 * @param <V> the class of the map values 3563 * @param m the map for which a dynamically typesafe view is to be 3564 * returned 3565 * @param keyType the type of key that {@code m} is permitted to hold 3566 * @param valueType the type of value that {@code m} is permitted to hold 3567 * @return a dynamically typesafe view of the specified map 3568 * @since 1.5 3569 */ 3570 public static <K, V> Map<K, V> checkedMap(Map<K, V> m, 3571 Class<K> keyType, 3572 Class<V> valueType) { 3573 return new CheckedMap<>(m, keyType, valueType); 3574 } 3575 3576 3577 /** 3578 * @serial include 3579 */ 3580 private static class CheckedMap<K,V> 3581 implements Map<K,V>, Serializable 3582 { 3583 private static final long serialVersionUID = 5742860141034234728L; 3584 3585 private final Map<K, V> m; 3586 final Class<K> keyType; 3587 final Class<V> valueType; 3588 3589 private void typeCheck(Object key, Object value) { 3590 if (key != null && !keyType.isInstance(key)) 3591 throw new ClassCastException(badKeyMsg(key)); 3592 3593 if (value != null && !valueType.isInstance(value)) 3594 throw new ClassCastException(badValueMsg(value)); 3595 } 3596 3597 private BiFunction<? super K, ? super V, ? extends V> typeCheck( 3598 BiFunction<? super K, ? super V, ? extends V> func) { 3599 Objects.requireNonNull(func); 3600 return (k, v) -> { 3601 V newValue = func.apply(k, v); 3602 typeCheck(k, newValue); 3603 return newValue; 3604 }; 3605 } 3606 3607 private String badKeyMsg(Object key) { 3608 return "Attempt to insert " + key.getClass() + 3609 " key into map with key type " + keyType; 3610 } 3611 3612 private String badValueMsg(Object value) { 3613 return "Attempt to insert " + value.getClass() + 3614 " value into map with value type " + valueType; 3615 } 3616 3617 CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) { 3618 this.m = Objects.requireNonNull(m); 3619 this.keyType = Objects.requireNonNull(keyType); 3620 this.valueType = Objects.requireNonNull(valueType); 3621 } 3622 3623 public int size() { return m.size(); } 3624 public boolean isEmpty() { return m.isEmpty(); } 3625 public boolean containsKey(Object key) { return m.containsKey(key); } 3626 public boolean containsValue(Object v) { return m.containsValue(v); } 3627 public V get(Object key) { return m.get(key); } 3628 public V remove(Object key) { return m.remove(key); } 3629 public void clear() { m.clear(); } 3630 public Set<K> keySet() { return m.keySet(); } 3631 public Collection<V> values() { return m.values(); } 3632 public boolean equals(Object o) { return o == this || m.equals(o); } 3633 public int hashCode() { return m.hashCode(); } 3634 public String toString() { return m.toString(); } 3635 3636 public V put(K key, V value) { 3637 typeCheck(key, value); 3638 return m.put(key, value); 3639 } 3640 3641 @SuppressWarnings("unchecked") 3642 public void putAll(Map<? extends K, ? extends V> t) { 3643 // Satisfy the following goals: 3644 // - good diagnostics in case of type mismatch 3645 // - all-or-nothing semantics 3646 // - protection from malicious t 3647 // - correct behavior if t is a concurrent map 3648 Object[] entries = t.entrySet().toArray(); 3649 List<Map.Entry<K,V>> checked = new ArrayList<>(entries.length); 3650 for (Object o : entries) { 3651 Map.Entry<?,?> e = (Map.Entry<?,?>) o; 3652 Object k = e.getKey(); 3653 Object v = e.getValue(); 3654 typeCheck(k, v); 3655 checked.add( 3656 new AbstractMap.SimpleImmutableEntry<>((K)k, (V)v)); 3657 } 3658 for (Map.Entry<K,V> e : checked) 3659 m.put(e.getKey(), e.getValue()); 3660 } 3661 3662 private transient Set<Map.Entry<K,V>> entrySet; 3663 3664 public Set<Map.Entry<K,V>> entrySet() { 3665 if (entrySet==null) 3666 entrySet = new CheckedEntrySet<>(m.entrySet(), valueType); 3667 return entrySet; 3668 } 3669 3670 // Override default methods in Map 3671 @Override 3672 public void forEach(BiConsumer<? super K, ? super V> action) { 3673 m.forEach(action); 3674 } 3675 3676 @Override 3677 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 3678 m.replaceAll(typeCheck(function)); 3679 } 3680 3681 @Override 3682 public V putIfAbsent(K key, V value) { 3683 typeCheck(key, value); 3684 return m.putIfAbsent(key, value); 3685 } 3686 3687 @Override 3688 public boolean remove(Object key, Object value) { 3689 return m.remove(key, value); 3690 } 3691 3692 @Override 3693 public boolean replace(K key, V oldValue, V newValue) { 3694 typeCheck(key, newValue); 3695 return m.replace(key, oldValue, newValue); 3696 } 3697 3698 @Override 3699 public V replace(K key, V value) { 3700 typeCheck(key, value); 3701 return m.replace(key, value); 3702 } 3703 3704 @Override 3705 public V computeIfAbsent(K key, 3706 Function<? super K, ? extends V> mappingFunction) { 3707 Objects.requireNonNull(mappingFunction); 3708 return m.computeIfAbsent(key, k -> { 3709 V value = mappingFunction.apply(k); 3710 typeCheck(k, value); 3711 return value; 3712 }); 3713 } 3714 3715 @Override 3716 public V computeIfPresent(K key, 3717 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 3718 return m.computeIfPresent(key, typeCheck(remappingFunction)); 3719 } 3720 3721 @Override 3722 public V compute(K key, 3723 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 3724 return m.compute(key, typeCheck(remappingFunction)); 3725 } 3726 3727 @Override 3728 public V merge(K key, V value, 3729 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 3730 Objects.requireNonNull(remappingFunction); 3731 return m.merge(key, value, (v1, v2) -> { 3732 V newValue = remappingFunction.apply(v1, v2); 3733 typeCheck(null, newValue); 3734 return newValue; 3735 }); 3736 } 3737 3738 /** 3739 * We need this class in addition to CheckedSet as Map.Entry permits 3740 * modification of the backing Map via the setValue operation. This 3741 * class is subtle: there are many possible attacks that must be 3742 * thwarted. 3743 * 3744 * @serial exclude 3745 */ 3746 static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> { 3747 private final Set<Map.Entry<K,V>> s; 3748 private final Class<V> valueType; 3749 3750 CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) { 3751 this.s = s; 3752 this.valueType = valueType; 3753 } 3754 3755 public int size() { return s.size(); } 3756 public boolean isEmpty() { return s.isEmpty(); } 3757 public String toString() { return s.toString(); } 3758 public int hashCode() { return s.hashCode(); } 3759 public void clear() { s.clear(); } 3760 3761 public boolean add(Map.Entry<K, V> e) { 3762 throw new UnsupportedOperationException(); 3763 } 3764 public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) { 3765 throw new UnsupportedOperationException(); 3766 } 3767 3768 public Iterator<Map.Entry<K,V>> iterator() { 3769 final Iterator<Map.Entry<K, V>> i = s.iterator(); 3770 3771 return new Iterator<Map.Entry<K,V>>() { 3772 public boolean hasNext() { return i.hasNext(); } 3773 public void remove() { i.remove(); } 3774 3775 public Map.Entry<K,V> next() { 3776 return checkedEntry(i.next(), valueType); 3777 } 3778 3779 public void forEachRemaining(Consumer<? super Entry<K, V>> action) { 3780 i.forEachRemaining( 3781 e -> action.accept(checkedEntry(e, valueType))); 3782 } 3783 }; 3784 } 3785 3786 @SuppressWarnings("unchecked") 3787 public Object[] toArray() { 3788 Object[] source = s.toArray(); 3789 3790 /* 3791 * Ensure that we don't get an ArrayStoreException even if 3792 * s.toArray returns an array of something other than Object 3793 */ 3794 Object[] dest = (source.getClass() == Object[].class) 3795 ? source 3796 : new Object[source.length]; 3797 3798 for (int i = 0; i < source.length; i++) 3799 dest[i] = checkedEntry((Map.Entry<K,V>)source[i], 3800 valueType); 3801 return dest; 3802 } 3803 3804 @SuppressWarnings("unchecked") 3805 public <T> T[] toArray(T[] a) { 3806 // We don't pass a to s.toArray, to avoid window of 3807 // vulnerability wherein an unscrupulous multithreaded client 3808 // could get his hands on raw (unwrapped) Entries from s. 3809 T[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0)); 3810 3811 for (int i=0; i<arr.length; i++) 3812 arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i], 3813 valueType); 3814 if (arr.length > a.length) 3815 return arr; 3816 3817 System.arraycopy(arr, 0, a, 0, arr.length); 3818 if (a.length > arr.length) 3819 a[arr.length] = null; 3820 return a; 3821 } 3822 3823 /** 3824 * This method is overridden to protect the backing set against 3825 * an object with a nefarious equals function that senses 3826 * that the equality-candidate is Map.Entry and calls its 3827 * setValue method. 3828 */ 3829 public boolean contains(Object o) { 3830 if (!(o instanceof Map.Entry)) 3831 return false; 3832 Map.Entry<?,?> e = (Map.Entry<?,?>) o; 3833 return s.contains( 3834 (e instanceof CheckedEntry) ? e : checkedEntry(e, valueType)); 3835 } 3836 3837 /** 3838 * The bulk collection methods are overridden to protect 3839 * against an unscrupulous collection whose contains(Object o) 3840 * method senses when o is a Map.Entry, and calls o.setValue. 3841 */ 3842 public boolean containsAll(Collection<?> c) { 3843 for (Object o : c) 3844 if (!contains(o)) // Invokes safe contains() above 3845 return false; 3846 return true; 3847 } 3848 3849 public boolean remove(Object o) { 3850 if (!(o instanceof Map.Entry)) 3851 return false; 3852 return s.remove(new AbstractMap.SimpleImmutableEntry 3853 <>((Map.Entry<?,?>)o)); 3854 } 3855 3856 public boolean removeAll(Collection<?> c) { 3857 return batchRemove(c, false); 3858 } 3859 public boolean retainAll(Collection<?> c) { 3860 return batchRemove(c, true); 3861 } 3862 private boolean batchRemove(Collection<?> c, boolean complement) { 3863 Objects.requireNonNull(c); 3864 boolean modified = false; 3865 Iterator<Map.Entry<K,V>> it = iterator(); 3866 while (it.hasNext()) { 3867 if (c.contains(it.next()) != complement) { 3868 it.remove(); 3869 modified = true; 3870 } 3871 } 3872 return modified; 3873 } 3874 3875 public boolean equals(Object o) { 3876 if (o == this) 3877 return true; 3878 if (!(o instanceof Set)) 3879 return false; 3880 Set<?> that = (Set<?>) o; 3881 return that.size() == s.size() 3882 && containsAll(that); // Invokes safe containsAll() above 3883 } 3884 3885 static <K,V,T> CheckedEntry<K,V,T> checkedEntry(Map.Entry<K,V> e, 3886 Class<T> valueType) { 3887 return new CheckedEntry<>(e, valueType); 3888 } 3889 3890 /** 3891 * This "wrapper class" serves two purposes: it prevents 3892 * the client from modifying the backing Map, by short-circuiting 3893 * the setValue method, and it protects the backing Map against 3894 * an ill-behaved Map.Entry that attempts to modify another 3895 * Map.Entry when asked to perform an equality check. 3896 */ 3897 private static class CheckedEntry<K,V,T> implements Map.Entry<K,V> { 3898 private final Map.Entry<K, V> e; 3899 private final Class<T> valueType; 3900 3901 CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) { 3902 this.e = Objects.requireNonNull(e); 3903 this.valueType = Objects.requireNonNull(valueType); 3904 } 3905 3906 public K getKey() { return e.getKey(); } 3907 public V getValue() { return e.getValue(); } 3908 public int hashCode() { return e.hashCode(); } 3909 public String toString() { return e.toString(); } 3910 3911 public V setValue(V value) { 3912 if (value != null && !valueType.isInstance(value)) 3913 throw new ClassCastException(badValueMsg(value)); 3914 return e.setValue(value); 3915 } 3916 3917 private String badValueMsg(Object value) { 3918 return "Attempt to insert " + value.getClass() + 3919 " value into map with value type " + valueType; 3920 } 3921 3922 public boolean equals(Object o) { 3923 if (o == this) 3924 return true; 3925 if (!(o instanceof Map.Entry)) 3926 return false; 3927 return e.equals(new AbstractMap.SimpleImmutableEntry 3928 <>((Map.Entry<?,?>)o)); 3929 } 3930 } 3931 } 3932 } 3933 3934 /** 3935 * Returns a dynamically typesafe view of the specified sorted map. 3936 * Any attempt to insert a mapping whose key or value have the wrong 3937 * type will result in an immediate {@link ClassCastException}. 3938 * Similarly, any attempt to modify the value currently associated with 3939 * a key will result in an immediate {@link ClassCastException}, 3940 * whether the modification is attempted directly through the map 3941 * itself, or through a {@link Map.Entry} instance obtained from the 3942 * map's {@link Map#entrySet() entry set} view. 3943 * 3944 * <p>Assuming a map contains no incorrectly typed keys or values 3945 * prior to the time a dynamically typesafe view is generated, and 3946 * that all subsequent access to the map takes place through the view 3947 * (or one of its collection views), it is <i>guaranteed</i> that the 3948 * map cannot contain an incorrectly typed key or value. 3949 * 3950 * <p>A discussion of the use of dynamically typesafe views may be 3951 * found in the documentation for the {@link #checkedCollection 3952 * checkedCollection} method. 3953 * 3954 * <p>The returned map will be serializable if the specified map is 3955 * serializable. 3956 * 3957 * <p>Since {@code null} is considered to be a value of any reference 3958 * type, the returned map permits insertion of null keys or values 3959 * whenever the backing map does. 3960 * 3961 * @param <K> the class of the map keys 3962 * @param <V> the class of the map values 3963 * @param m the map for which a dynamically typesafe view is to be 3964 * returned 3965 * @param keyType the type of key that {@code m} is permitted to hold 3966 * @param valueType the type of value that {@code m} is permitted to hold 3967 * @return a dynamically typesafe view of the specified map 3968 * @since 1.5 3969 */ 3970 public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m, 3971 Class<K> keyType, 3972 Class<V> valueType) { 3973 return new CheckedSortedMap<>(m, keyType, valueType); 3974 } 3975 3976 /** 3977 * @serial include 3978 */ 3979 static class CheckedSortedMap<K,V> extends CheckedMap<K,V> 3980 implements SortedMap<K,V>, Serializable 3981 { 3982 private static final long serialVersionUID = 1599671320688067438L; 3983 3984 private final SortedMap<K, V> sm; 3985 3986 CheckedSortedMap(SortedMap<K, V> m, 3987 Class<K> keyType, Class<V> valueType) { 3988 super(m, keyType, valueType); 3989 sm = m; 3990 } 3991 3992 public Comparator<? super K> comparator() { return sm.comparator(); } 3993 public K firstKey() { return sm.firstKey(); } 3994 public K lastKey() { return sm.lastKey(); } 3995 3996 public SortedMap<K,V> subMap(K fromKey, K toKey) { 3997 return checkedSortedMap(sm.subMap(fromKey, toKey), 3998 keyType, valueType); 3999 } 4000 public SortedMap<K,V> headMap(K toKey) { 4001 return checkedSortedMap(sm.headMap(toKey), keyType, valueType); 4002 } 4003 public SortedMap<K,V> tailMap(K fromKey) { 4004 return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType); 4005 } 4006 } 4007 4008 /** 4009 * Returns a dynamically typesafe view of the specified navigable map. 4010 * Any attempt to insert a mapping whose key or value have the wrong 4011 * type will result in an immediate {@link ClassCastException}. 4012 * Similarly, any attempt to modify the value currently associated with 4013 * a key will result in an immediate {@link ClassCastException}, 4014 * whether the modification is attempted directly through the map 4015 * itself, or through a {@link Map.Entry} instance obtained from the 4016 * map's {@link Map#entrySet() entry set} view. 4017 * 4018 * <p>Assuming a map contains no incorrectly typed keys or values 4019 * prior to the time a dynamically typesafe view is generated, and 4020 * that all subsequent access to the map takes place through the view 4021 * (or one of its collection views), it is <em>guaranteed</em> that the 4022 * map cannot contain an incorrectly typed key or value. 4023 * 4024 * <p>A discussion of the use of dynamically typesafe views may be 4025 * found in the documentation for the {@link #checkedCollection 4026 * checkedCollection} method. 4027 * 4028 * <p>The returned map will be serializable if the specified map is 4029 * serializable. 4030 * 4031 * <p>Since {@code null} is considered to be a value of any reference 4032 * type, the returned map permits insertion of null keys or values 4033 * whenever the backing map does. 4034 * 4035 * @param <K> type of map keys 4036 * @param <V> type of map values 4037 * @param m the map for which a dynamically typesafe view is to be 4038 * returned 4039 * @param keyType the type of key that {@code m} is permitted to hold 4040 * @param valueType the type of value that {@code m} is permitted to hold 4041 * @return a dynamically typesafe view of the specified map 4042 * @since 1.8 4043 */ 4044 public static <K,V> NavigableMap<K,V> checkedNavigableMap(NavigableMap<K, V> m, 4045 Class<K> keyType, 4046 Class<V> valueType) { 4047 return new CheckedNavigableMap<>(m, keyType, valueType); 4048 } 4049 4050 /** 4051 * @serial include 4052 */ 4053 static class CheckedNavigableMap<K,V> extends CheckedSortedMap<K,V> 4054 implements NavigableMap<K,V>, Serializable 4055 { 4056 private static final long serialVersionUID = -4852462692372534096L; 4057 4058 private final NavigableMap<K, V> nm; 4059 4060 CheckedNavigableMap(NavigableMap<K, V> m, 4061 Class<K> keyType, Class<V> valueType) { 4062 super(m, keyType, valueType); 4063 nm = m; 4064 } 4065 4066 public Comparator<? super K> comparator() { return nm.comparator(); } 4067 public K firstKey() { return nm.firstKey(); } 4068 public K lastKey() { return nm.lastKey(); } 4069 4070 public Entry<K, V> lowerEntry(K key) { 4071 Entry<K,V> lower = nm.lowerEntry(key); 4072 return (null != lower) 4073 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(lower, valueType) 4074 : null; 4075 } 4076 4077 public K lowerKey(K key) { return nm.lowerKey(key); } 4078 4079 public Entry<K, V> floorEntry(K key) { 4080 Entry<K,V> floor = nm.floorEntry(key); 4081 return (null != floor) 4082 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(floor, valueType) 4083 : null; 4084 } 4085 4086 public K floorKey(K key) { return nm.floorKey(key); } 4087 4088 public Entry<K, V> ceilingEntry(K key) { 4089 Entry<K,V> ceiling = nm.ceilingEntry(key); 4090 return (null != ceiling) 4091 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(ceiling, valueType) 4092 : null; 4093 } 4094 4095 public K ceilingKey(K key) { return nm.ceilingKey(key); } 4096 4097 public Entry<K, V> higherEntry(K key) { 4098 Entry<K,V> higher = nm.higherEntry(key); 4099 return (null != higher) 4100 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(higher, valueType) 4101 : null; 4102 } 4103 4104 public K higherKey(K key) { return nm.higherKey(key); } 4105 4106 public Entry<K, V> firstEntry() { 4107 Entry<K,V> first = nm.firstEntry(); 4108 return (null != first) 4109 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(first, valueType) 4110 : null; 4111 } 4112 4113 public Entry<K, V> lastEntry() { 4114 Entry<K,V> last = nm.lastEntry(); 4115 return (null != last) 4116 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(last, valueType) 4117 : null; 4118 } 4119 4120 public Entry<K, V> pollFirstEntry() { 4121 Entry<K,V> entry = nm.pollFirstEntry(); 4122 return (null == entry) 4123 ? null 4124 : new CheckedMap.CheckedEntrySet.CheckedEntry<>(entry, valueType); 4125 } 4126 4127 public Entry<K, V> pollLastEntry() { 4128 Entry<K,V> entry = nm.pollLastEntry(); 4129 return (null == entry) 4130 ? null 4131 : new CheckedMap.CheckedEntrySet.CheckedEntry<>(entry, valueType); 4132 } 4133 4134 public NavigableMap<K, V> descendingMap() { 4135 return checkedNavigableMap(nm.descendingMap(), keyType, valueType); 4136 } 4137 4138 public NavigableSet<K> keySet() { 4139 return navigableKeySet(); 4140 } 4141 4142 public NavigableSet<K> navigableKeySet() { 4143 return checkedNavigableSet(nm.navigableKeySet(), keyType); 4144 } 4145 4146 public NavigableSet<K> descendingKeySet() { 4147 return checkedNavigableSet(nm.descendingKeySet(), keyType); 4148 } 4149 4150 @Override 4151 public NavigableMap<K,V> subMap(K fromKey, K toKey) { 4152 return checkedNavigableMap(nm.subMap(fromKey, true, toKey, false), 4153 keyType, valueType); 4154 } 4155 4156 @Override 4157 public NavigableMap<K,V> headMap(K toKey) { 4158 return checkedNavigableMap(nm.headMap(toKey, false), keyType, valueType); 4159 } 4160 4161 @Override 4162 public NavigableMap<K,V> tailMap(K fromKey) { 4163 return checkedNavigableMap(nm.tailMap(fromKey, true), keyType, valueType); 4164 } 4165 4166 public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) { 4167 return checkedNavigableMap(nm.subMap(fromKey, fromInclusive, toKey, toInclusive), keyType, valueType); 4168 } 4169 4170 public NavigableMap<K, V> headMap(K toKey, boolean inclusive) { 4171 return checkedNavigableMap(nm.headMap(toKey, inclusive), keyType, valueType); 4172 } 4173 4174 public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) { 4175 return checkedNavigableMap(nm.tailMap(fromKey, inclusive), keyType, valueType); 4176 } 4177 } 4178 4179 // Empty collections 4180 4181 /** 4182 * Returns an iterator that has no elements. More precisely, 4183 * 4184 * <ul> 4185 * <li>{@link Iterator#hasNext hasNext} always returns {@code 4186 * false}.</li> 4187 * <li>{@link Iterator#next next} always throws {@link 4188 * NoSuchElementException}.</li> 4189 * <li>{@link Iterator#remove remove} always throws {@link 4190 * IllegalStateException}.</li> 4191 * </ul> 4192 * 4193 * <p>Implementations of this method are permitted, but not 4194 * required, to return the same object from multiple invocations. 4195 * 4196 * @param <T> type of elements, if there were any, in the iterator 4197 * @return an empty iterator 4198 * @since 1.7 4199 */ 4200 @SuppressWarnings("unchecked") 4201 public static <T> Iterator<T> emptyIterator() { 4202 return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR; 4203 } 4204 4205 private static class EmptyIterator<E> implements Iterator<E> { 4206 static final EmptyIterator<Object> EMPTY_ITERATOR 4207 = new EmptyIterator<>(); 4208 4209 public boolean hasNext() { return false; } 4210 public E next() { throw new NoSuchElementException(); } 4211 public void remove() { throw new IllegalStateException(); } 4212 @Override 4213 public void forEachRemaining(Consumer<? super E> action) { 4214 Objects.requireNonNull(action); 4215 } 4216 } 4217 4218 /** 4219 * Returns a list iterator that has no elements. More precisely, 4220 * 4221 * <ul> 4222 * <li>{@link Iterator#hasNext hasNext} and {@link 4223 * ListIterator#hasPrevious hasPrevious} always return {@code 4224 * false}.</li> 4225 * <li>{@link Iterator#next next} and {@link ListIterator#previous 4226 * previous} always throw {@link NoSuchElementException}.</li> 4227 * <li>{@link Iterator#remove remove} and {@link ListIterator#set 4228 * set} always throw {@link IllegalStateException}.</li> 4229 * <li>{@link ListIterator#add add} always throws {@link 4230 * UnsupportedOperationException}.</li> 4231 * <li>{@link ListIterator#nextIndex nextIndex} always returns 4232 * {@code 0}.</li> 4233 * <li>{@link ListIterator#previousIndex previousIndex} always 4234 * returns {@code -1}.</li> 4235 * </ul> 4236 * 4237 * <p>Implementations of this method are permitted, but not 4238 * required, to return the same object from multiple invocations. 4239 * 4240 * @param <T> type of elements, if there were any, in the iterator 4241 * @return an empty list iterator 4242 * @since 1.7 4243 */ 4244 @SuppressWarnings("unchecked") 4245 public static <T> ListIterator<T> emptyListIterator() { 4246 return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR; 4247 } 4248 4249 private static class EmptyListIterator<E> 4250 extends EmptyIterator<E> 4251 implements ListIterator<E> 4252 { 4253 static final EmptyListIterator<Object> EMPTY_ITERATOR 4254 = new EmptyListIterator<>(); 4255 4256 public boolean hasPrevious() { return false; } 4257 public E previous() { throw new NoSuchElementException(); } 4258 public int nextIndex() { return 0; } 4259 public int previousIndex() { return -1; } 4260 public void set(E e) { throw new IllegalStateException(); } 4261 public void add(E e) { throw new UnsupportedOperationException(); } 4262 } 4263 4264 /** 4265 * Returns an enumeration that has no elements. More precisely, 4266 * 4267 * <ul> 4268 * <li>{@link Enumeration#hasMoreElements hasMoreElements} always 4269 * returns {@code false}.</li> 4270 * <li> {@link Enumeration#nextElement nextElement} always throws 4271 * {@link NoSuchElementException}.</li> 4272 * </ul> 4273 * 4274 * <p>Implementations of this method are permitted, but not 4275 * required, to return the same object from multiple invocations. 4276 * 4277 * @param <T> the class of the objects in the enumeration 4278 * @return an empty enumeration 4279 * @since 1.7 4280 */ 4281 @SuppressWarnings("unchecked") 4282 public static <T> Enumeration<T> emptyEnumeration() { 4283 return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION; 4284 } 4285 4286 private static class EmptyEnumeration<E> implements Enumeration<E> { 4287 static final EmptyEnumeration<Object> EMPTY_ENUMERATION 4288 = new EmptyEnumeration<>(); 4289 4290 public boolean hasMoreElements() { return false; } 4291 public E nextElement() { throw new NoSuchElementException(); } 4292 public Iterator<E> asIterator() { return emptyIterator(); } 4293 } 4294 4295 /** 4296 * The empty set (immutable). This set is serializable. 4297 * 4298 * @see #emptySet() 4299 */ 4300 @SuppressWarnings("rawtypes") 4301 public static final Set EMPTY_SET = new EmptySet<>(); 4302 4303 /** 4304 * Returns an empty set (immutable). This set is serializable. 4305 * Unlike the like-named field, this method is parameterized. 4306 * 4307 * <p>This example illustrates the type-safe way to obtain an empty set: 4308 * <pre> 4309 * Set<String> s = Collections.emptySet(); 4310 * </pre> 4311 * @implNote Implementations of this method need not create a separate 4312 * {@code Set} object for each call. Using this method is likely to have 4313 * comparable cost to using the like-named field. (Unlike this method, the 4314 * field does not provide type safety.) 4315 * 4316 * @param <T> the class of the objects in the set 4317 * @return the empty set 4318 * 4319 * @see #EMPTY_SET 4320 * @since 1.5 4321 */ 4322 @SuppressWarnings("unchecked") 4323 public static final <T> Set<T> emptySet() { 4324 return (Set<T>) EMPTY_SET; 4325 } 4326 4327 /** 4328 * @serial include 4329 */ 4330 private static class EmptySet<E> 4331 extends AbstractSet<E> 4332 implements Serializable 4333 { 4334 private static final long serialVersionUID = 1582296315990362920L; 4335 4336 public Iterator<E> iterator() { return emptyIterator(); } 4337 4338 public int size() {return 0;} 4339 public boolean isEmpty() {return true;} 4340 public void clear() {} 4341 4342 public boolean contains(Object obj) {return false;} 4343 public boolean containsAll(Collection<?> c) { return c.isEmpty(); } 4344 4345 public Object[] toArray() { return new Object[0]; } 4346 4347 public <T> T[] toArray(T[] a) { 4348 if (a.length > 0) 4349 a[0] = null; 4350 return a; 4351 } 4352 4353 // Override default methods in Collection 4354 @Override 4355 public void forEach(Consumer<? super E> action) { 4356 Objects.requireNonNull(action); 4357 } 4358 @Override 4359 public boolean removeIf(Predicate<? super E> filter) { 4360 Objects.requireNonNull(filter); 4361 return false; 4362 } 4363 @Override 4364 public Spliterator<E> spliterator() { return Spliterators.emptySpliterator(); } 4365 4366 // Preserves singleton property 4367 private Object readResolve() { 4368 return EMPTY_SET; 4369 } 4370 4371 @Override 4372 public int hashCode() { 4373 return 0; 4374 } 4375 } 4376 4377 /** 4378 * Returns an empty sorted set (immutable). This set is serializable. 4379 * 4380 * <p>This example illustrates the type-safe way to obtain an empty 4381 * sorted set: 4382 * <pre> {@code 4383 * SortedSet<String> s = Collections.emptySortedSet(); 4384 * }</pre> 4385 * 4386 * @implNote Implementations of this method need not create a separate 4387 * {@code SortedSet} object for each call. 4388 * 4389 * @param <E> type of elements, if there were any, in the set 4390 * @return the empty sorted set 4391 * @since 1.8 4392 */ 4393 @SuppressWarnings("unchecked") 4394 public static <E> SortedSet<E> emptySortedSet() { 4395 return (SortedSet<E>) UnmodifiableNavigableSet.EMPTY_NAVIGABLE_SET; 4396 } 4397 4398 /** 4399 * Returns an empty navigable set (immutable). This set is serializable. 4400 * 4401 * <p>This example illustrates the type-safe way to obtain an empty 4402 * navigable set: 4403 * <pre> {@code 4404 * NavigableSet<String> s = Collections.emptyNavigableSet(); 4405 * }</pre> 4406 * 4407 * @implNote Implementations of this method need not 4408 * create a separate {@code NavigableSet} object for each call. 4409 * 4410 * @param <E> type of elements, if there were any, in the set 4411 * @return the empty navigable set 4412 * @since 1.8 4413 */ 4414 @SuppressWarnings("unchecked") 4415 public static <E> NavigableSet<E> emptyNavigableSet() { 4416 return (NavigableSet<E>) UnmodifiableNavigableSet.EMPTY_NAVIGABLE_SET; 4417 } 4418 4419 /** 4420 * The empty list (immutable). This list is serializable. 4421 * 4422 * @see #emptyList() 4423 */ 4424 @SuppressWarnings("rawtypes") 4425 public static final List EMPTY_LIST = new EmptyList<>(); 4426 4427 /** 4428 * Returns an empty list (immutable). This list is serializable. 4429 * 4430 * <p>This example illustrates the type-safe way to obtain an empty list: 4431 * <pre> 4432 * List<String> s = Collections.emptyList(); 4433 * </pre> 4434 * 4435 * @implNote 4436 * Implementations of this method need not create a separate {@code List} 4437 * object for each call. Using this method is likely to have comparable 4438 * cost to using the like-named field. (Unlike this method, the field does 4439 * not provide type safety.) 4440 * 4441 * @param <T> type of elements, if there were any, in the list 4442 * @return an empty immutable list 4443 * 4444 * @see #EMPTY_LIST 4445 * @since 1.5 4446 */ 4447 @SuppressWarnings("unchecked") 4448 public static final <T> List<T> emptyList() { 4449 return (List<T>) EMPTY_LIST; 4450 } 4451 4452 /** 4453 * @serial include 4454 */ 4455 private static class EmptyList<E> 4456 extends AbstractList<E> 4457 implements RandomAccess, Serializable { 4458 private static final long serialVersionUID = 8842843931221139166L; 4459 4460 public Iterator<E> iterator() { 4461 return emptyIterator(); 4462 } 4463 public ListIterator<E> listIterator() { 4464 return emptyListIterator(); 4465 } 4466 4467 public int size() {return 0;} 4468 public boolean isEmpty() {return true;} 4469 public void clear() {} 4470 4471 public boolean contains(Object obj) {return false;} 4472 public boolean containsAll(Collection<?> c) { return c.isEmpty(); } 4473 4474 public Object[] toArray() { return new Object[0]; } 4475 4476 public <T> T[] toArray(T[] a) { 4477 if (a.length > 0) 4478 a[0] = null; 4479 return a; 4480 } 4481 4482 public E get(int index) { 4483 throw new IndexOutOfBoundsException("Index: "+index); 4484 } 4485 4486 public boolean equals(Object o) { 4487 return (o instanceof List) && ((List<?>)o).isEmpty(); 4488 } 4489 4490 public int hashCode() { return 1; } 4491 4492 @Override 4493 public boolean removeIf(Predicate<? super E> filter) { 4494 Objects.requireNonNull(filter); 4495 return false; 4496 } 4497 @Override 4498 public void replaceAll(UnaryOperator<E> operator) { 4499 Objects.requireNonNull(operator); 4500 } 4501 @Override 4502 public void sort(Comparator<? super E> c) { 4503 } 4504 4505 // Override default methods in Collection 4506 @Override 4507 public void forEach(Consumer<? super E> action) { 4508 Objects.requireNonNull(action); 4509 } 4510 4511 @Override 4512 public Spliterator<E> spliterator() { return Spliterators.emptySpliterator(); } 4513 4514 // Preserves singleton property 4515 private Object readResolve() { 4516 return EMPTY_LIST; 4517 } 4518 } 4519 4520 /** 4521 * The empty map (immutable). This map is serializable. 4522 * 4523 * @see #emptyMap() 4524 * @since 1.3 4525 */ 4526 @SuppressWarnings("rawtypes") 4527 public static final Map EMPTY_MAP = new EmptyMap<>(); 4528 4529 /** 4530 * Returns an empty map (immutable). This map is serializable. 4531 * 4532 * <p>This example illustrates the type-safe way to obtain an empty map: 4533 * <pre> 4534 * Map<String, Date> s = Collections.emptyMap(); 4535 * </pre> 4536 * @implNote Implementations of this method need not create a separate 4537 * {@code Map} object for each call. Using this method is likely to have 4538 * comparable cost to using the like-named field. (Unlike this method, the 4539 * field does not provide type safety.) 4540 * 4541 * @param <K> the class of the map keys 4542 * @param <V> the class of the map values 4543 * @return an empty map 4544 * @see #EMPTY_MAP 4545 * @since 1.5 4546 */ 4547 @SuppressWarnings("unchecked") 4548 public static final <K,V> Map<K,V> emptyMap() { 4549 return (Map<K,V>) EMPTY_MAP; 4550 } 4551 4552 /** 4553 * Returns an empty sorted map (immutable). This map is serializable. 4554 * 4555 * <p>This example illustrates the type-safe way to obtain an empty map: 4556 * <pre> {@code 4557 * SortedMap<String, Date> s = Collections.emptySortedMap(); 4558 * }</pre> 4559 * 4560 * @implNote Implementations of this method need not create a separate 4561 * {@code SortedMap} object for each call. 4562 * 4563 * @param <K> the class of the map keys 4564 * @param <V> the class of the map values 4565 * @return an empty sorted map 4566 * @since 1.8 4567 */ 4568 @SuppressWarnings("unchecked") 4569 public static final <K,V> SortedMap<K,V> emptySortedMap() { 4570 return (SortedMap<K,V>) UnmodifiableNavigableMap.EMPTY_NAVIGABLE_MAP; 4571 } 4572 4573 /** 4574 * Returns an empty navigable map (immutable). This map is serializable. 4575 * 4576 * <p>This example illustrates the type-safe way to obtain an empty map: 4577 * <pre> {@code 4578 * NavigableMap<String, Date> s = Collections.emptyNavigableMap(); 4579 * }</pre> 4580 * 4581 * @implNote Implementations of this method need not create a separate 4582 * {@code NavigableMap} object for each call. 4583 * 4584 * @param <K> the class of the map keys 4585 * @param <V> the class of the map values 4586 * @return an empty navigable map 4587 * @since 1.8 4588 */ 4589 @SuppressWarnings("unchecked") 4590 public static final <K,V> NavigableMap<K,V> emptyNavigableMap() { 4591 return (NavigableMap<K,V>) UnmodifiableNavigableMap.EMPTY_NAVIGABLE_MAP; 4592 } 4593 4594 /** 4595 * @serial include 4596 */ 4597 private static class EmptyMap<K,V> 4598 extends AbstractMap<K,V> 4599 implements Serializable 4600 { 4601 private static final long serialVersionUID = 6428348081105594320L; 4602 4603 public int size() {return 0;} 4604 public boolean isEmpty() {return true;} 4605 public void clear() {} 4606 public boolean containsKey(Object key) {return false;} 4607 public boolean containsValue(Object value) {return false;} 4608 public V get(Object key) {return null;} 4609 public Set<K> keySet() {return emptySet();} 4610 public Collection<V> values() {return emptySet();} 4611 public Set<Map.Entry<K,V>> entrySet() {return emptySet();} 4612 4613 public boolean equals(Object o) { 4614 return (o instanceof Map) && ((Map<?,?>)o).isEmpty(); 4615 } 4616 4617 public int hashCode() {return 0;} 4618 4619 // Override default methods in Map 4620 @Override 4621 @SuppressWarnings("unchecked") 4622 public V getOrDefault(Object k, V defaultValue) { 4623 return defaultValue; 4624 } 4625 4626 @Override 4627 public void forEach(BiConsumer<? super K, ? super V> action) { 4628 Objects.requireNonNull(action); 4629 } 4630 4631 @Override 4632 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 4633 Objects.requireNonNull(function); 4634 } 4635 4636 @Override 4637 public V putIfAbsent(K key, V value) { 4638 throw new UnsupportedOperationException(); 4639 } 4640 4641 @Override 4642 public boolean remove(Object key, Object value) { 4643 throw new UnsupportedOperationException(); 4644 } 4645 4646 @Override 4647 public boolean replace(K key, V oldValue, V newValue) { 4648 throw new UnsupportedOperationException(); 4649 } 4650 4651 @Override 4652 public V replace(K key, V value) { 4653 throw new UnsupportedOperationException(); 4654 } 4655 4656 @Override 4657 public V computeIfAbsent(K key, 4658 Function<? super K, ? extends V> mappingFunction) { 4659 throw new UnsupportedOperationException(); 4660 } 4661 4662 @Override 4663 public V computeIfPresent(K key, 4664 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 4665 throw new UnsupportedOperationException(); 4666 } 4667 4668 @Override 4669 public V compute(K key, 4670 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 4671 throw new UnsupportedOperationException(); 4672 } 4673 4674 @Override 4675 public V merge(K key, V value, 4676 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 4677 throw new UnsupportedOperationException(); 4678 } 4679 4680 // Preserves singleton property 4681 private Object readResolve() { 4682 return EMPTY_MAP; 4683 } 4684 } 4685 4686 // Singleton collections 4687 4688 /** 4689 * Returns an immutable set containing only the specified object. 4690 * The returned set is serializable. 4691 * 4692 * @param <T> the class of the objects in the set 4693 * @param o the sole object to be stored in the returned set. 4694 * @return an immutable set containing only the specified object. 4695 */ 4696 public static <T> Set<T> singleton(T o) { 4697 return new SingletonSet<>(o); 4698 } 4699 4700 static <E> Iterator<E> singletonIterator(final E e) { 4701 return new Iterator<E>() { 4702 private boolean hasNext = true; 4703 public boolean hasNext() { 4704 return hasNext; 4705 } 4706 public E next() { 4707 if (hasNext) { 4708 hasNext = false; 4709 return e; 4710 } 4711 throw new NoSuchElementException(); 4712 } 4713 public void remove() { 4714 throw new UnsupportedOperationException(); 4715 } 4716 @Override 4717 public void forEachRemaining(Consumer<? super E> action) { 4718 Objects.requireNonNull(action); 4719 if (hasNext) { 4720 hasNext = false; 4721 action.accept(e); 4722 } 4723 } 4724 }; 4725 } 4726 4727 /** 4728 * Creates a {@code Spliterator} with only the specified element 4729 * 4730 * @param <T> Type of elements 4731 * @return A singleton {@code Spliterator} 4732 */ 4733 static <T> Spliterator<T> singletonSpliterator(final T element) { 4734 return new Spliterator<T>() { 4735 long est = 1; 4736 4737 @Override 4738 public Spliterator<T> trySplit() { 4739 return null; 4740 } 4741 4742 @Override 4743 public boolean tryAdvance(Consumer<? super T> consumer) { 4744 Objects.requireNonNull(consumer); 4745 if (est > 0) { 4746 est--; 4747 consumer.accept(element); 4748 return true; 4749 } 4750 return false; 4751 } 4752 4753 @Override 4754 public void forEachRemaining(Consumer<? super T> consumer) { 4755 tryAdvance(consumer); 4756 } 4757 4758 @Override 4759 public long estimateSize() { 4760 return est; 4761 } 4762 4763 @Override 4764 public int characteristics() { 4765 int value = (element != null) ? Spliterator.NONNULL : 0; 4766 4767 return value | Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.IMMUTABLE | 4768 Spliterator.DISTINCT | Spliterator.ORDERED; 4769 } 4770 }; 4771 } 4772 4773 /** 4774 * @serial include 4775 */ 4776 private static class SingletonSet<E> 4777 extends AbstractSet<E> 4778 implements Serializable 4779 { 4780 private static final long serialVersionUID = 3193687207550431679L; 4781 4782 private final E element; 4783 4784 SingletonSet(E e) {element = e;} 4785 4786 public Iterator<E> iterator() { 4787 return singletonIterator(element); 4788 } 4789 4790 public int size() {return 1;} 4791 4792 public boolean contains(Object o) {return eq(o, element);} 4793 4794 // Override default methods for Collection 4795 @Override 4796 public void forEach(Consumer<? super E> action) { 4797 action.accept(element); 4798 } 4799 @Override 4800 public Spliterator<E> spliterator() { 4801 return singletonSpliterator(element); 4802 } 4803 @Override 4804 public boolean removeIf(Predicate<? super E> filter) { 4805 throw new UnsupportedOperationException(); 4806 } 4807 @Override 4808 public int hashCode() { 4809 return Objects.hashCode(element); 4810 } 4811 } 4812 4813 /** 4814 * Returns an immutable list containing only the specified object. 4815 * The returned list is serializable. 4816 * 4817 * @param <T> the class of the objects in the list 4818 * @param o the sole object to be stored in the returned list. 4819 * @return an immutable list containing only the specified object. 4820 * @since 1.3 4821 */ 4822 public static <T> List<T> singletonList(T o) { 4823 return new SingletonList<>(o); 4824 } 4825 4826 /** 4827 * @serial include 4828 */ 4829 private static class SingletonList<E> 4830 extends AbstractList<E> 4831 implements RandomAccess, Serializable { 4832 4833 private static final long serialVersionUID = 3093736618740652951L; 4834 4835 private final E element; 4836 4837 SingletonList(E obj) {element = obj;} 4838 4839 public Iterator<E> iterator() { 4840 return singletonIterator(element); 4841 } 4842 4843 public int size() {return 1;} 4844 4845 public boolean contains(Object obj) {return eq(obj, element);} 4846 4847 public E get(int index) { 4848 if (index != 0) 4849 throw new IndexOutOfBoundsException("Index: "+index+", Size: 1"); 4850 return element; 4851 } 4852 4853 // Override default methods for Collection 4854 @Override 4855 public void forEach(Consumer<? super E> action) { 4856 action.accept(element); 4857 } 4858 @Override 4859 public boolean removeIf(Predicate<? super E> filter) { 4860 throw new UnsupportedOperationException(); 4861 } 4862 @Override 4863 public void replaceAll(UnaryOperator<E> operator) { 4864 throw new UnsupportedOperationException(); 4865 } 4866 @Override 4867 public void sort(Comparator<? super E> c) { 4868 } 4869 @Override 4870 public Spliterator<E> spliterator() { 4871 return singletonSpliterator(element); 4872 } 4873 @Override 4874 public int hashCode() { 4875 return 31 + Objects.hashCode(element); 4876 } 4877 } 4878 4879 /** 4880 * Returns an immutable map, mapping only the specified key to the 4881 * specified value. The returned map is serializable. 4882 * 4883 * @param <K> the class of the map keys 4884 * @param <V> the class of the map values 4885 * @param key the sole key to be stored in the returned map. 4886 * @param value the value to which the returned map maps {@code key}. 4887 * @return an immutable map containing only the specified key-value 4888 * mapping. 4889 * @since 1.3 4890 */ 4891 public static <K,V> Map<K,V> singletonMap(K key, V value) { 4892 return new SingletonMap<>(key, value); 4893 } 4894 4895 /** 4896 * @serial include 4897 */ 4898 private static class SingletonMap<K,V> 4899 extends AbstractMap<K,V> 4900 implements Serializable { 4901 private static final long serialVersionUID = -6979724477215052911L; 4902 4903 private final K k; 4904 private final V v; 4905 4906 SingletonMap(K key, V value) { 4907 k = key; 4908 v = value; 4909 } 4910 4911 public int size() {return 1;} 4912 public boolean isEmpty() {return false;} 4913 public boolean containsKey(Object key) {return eq(key, k);} 4914 public boolean containsValue(Object value) {return eq(value, v);} 4915 public V get(Object key) {return (eq(key, k) ? v : null);} 4916 4917 private transient Set<K> keySet; 4918 private transient Set<Map.Entry<K,V>> entrySet; 4919 private transient Collection<V> values; 4920 4921 public Set<K> keySet() { 4922 if (keySet==null) 4923 keySet = singleton(k); 4924 return keySet; 4925 } 4926 4927 public Set<Map.Entry<K,V>> entrySet() { 4928 if (entrySet==null) 4929 entrySet = Collections.<Map.Entry<K,V>>singleton( 4930 new SimpleImmutableEntry<>(k, v)); 4931 return entrySet; 4932 } 4933 4934 public Collection<V> values() { 4935 if (values==null) 4936 values = singleton(v); 4937 return values; 4938 } 4939 4940 // Override default methods in Map 4941 @Override 4942 public V getOrDefault(Object key, V defaultValue) { 4943 return eq(key, k) ? v : defaultValue; 4944 } 4945 4946 @Override 4947 public void forEach(BiConsumer<? super K, ? super V> action) { 4948 action.accept(k, v); 4949 } 4950 4951 @Override 4952 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 4953 throw new UnsupportedOperationException(); 4954 } 4955 4956 @Override 4957 public V putIfAbsent(K key, V value) { 4958 throw new UnsupportedOperationException(); 4959 } 4960 4961 @Override 4962 public boolean remove(Object key, Object value) { 4963 throw new UnsupportedOperationException(); 4964 } 4965 4966 @Override 4967 public boolean replace(K key, V oldValue, V newValue) { 4968 throw new UnsupportedOperationException(); 4969 } 4970 4971 @Override 4972 public V replace(K key, V value) { 4973 throw new UnsupportedOperationException(); 4974 } 4975 4976 @Override 4977 public V computeIfAbsent(K key, 4978 Function<? super K, ? extends V> mappingFunction) { 4979 throw new UnsupportedOperationException(); 4980 } 4981 4982 @Override 4983 public V computeIfPresent(K key, 4984 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 4985 throw new UnsupportedOperationException(); 4986 } 4987 4988 @Override 4989 public V compute(K key, 4990 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 4991 throw new UnsupportedOperationException(); 4992 } 4993 4994 @Override 4995 public V merge(K key, V value, 4996 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 4997 throw new UnsupportedOperationException(); 4998 } 4999 5000 @Override 5001 public int hashCode() { 5002 return Objects.hashCode(k) ^ Objects.hashCode(v); 5003 } 5004 } 5005 5006 // Miscellaneous 5007 5008 /** 5009 * Returns an immutable list consisting of {@code n} copies of the 5010 * specified object. The newly allocated data object is tiny (it contains 5011 * a single reference to the data object). This method is useful in 5012 * combination with the {@code List.addAll} method to grow lists. 5013 * The returned list is serializable. 5014 * 5015 * @param <T> the class of the object to copy and of the objects 5016 * in the returned list. 5017 * @param n the number of elements in the returned list. 5018 * @param o the element to appear repeatedly in the returned list. 5019 * @return an immutable list consisting of {@code n} copies of the 5020 * specified object. 5021 * @throws IllegalArgumentException if {@code n < 0} 5022 * @see List#addAll(Collection) 5023 * @see List#addAll(int, Collection) 5024 */ 5025 public static <T> List<T> nCopies(int n, T o) { 5026 if (n < 0) 5027 throw new IllegalArgumentException("List length = " + n); 5028 return new CopiesList<>(n, o); 5029 } 5030 5031 /** 5032 * @serial include 5033 */ 5034 private static class CopiesList<E> 5035 extends AbstractList<E> 5036 implements RandomAccess, Serializable 5037 { 5038 private static final long serialVersionUID = 2739099268398711800L; 5039 5040 final int n; 5041 final E element; 5042 5043 CopiesList(int n, E e) { 5044 assert n >= 0; 5045 this.n = n; 5046 element = e; 5047 } 5048 5049 public int size() { 5050 return n; 5051 } 5052 5053 public boolean contains(Object obj) { 5054 return n != 0 && eq(obj, element); 5055 } 5056 5057 public int indexOf(Object o) { 5058 return contains(o) ? 0 : -1; 5059 } 5060 5061 public int lastIndexOf(Object o) { 5062 return contains(o) ? n - 1 : -1; 5063 } 5064 5065 public E get(int index) { 5066 if (index < 0 || index >= n) 5067 throw new IndexOutOfBoundsException("Index: "+index+ 5068 ", Size: "+n); 5069 return element; 5070 } 5071 5072 public Object[] toArray() { 5073 final Object[] a = new Object[n]; 5074 if (element != null) 5075 Arrays.fill(a, 0, n, element); 5076 return a; 5077 } 5078 5079 @SuppressWarnings("unchecked") 5080 public <T> T[] toArray(T[] a) { 5081 final int n = this.n; 5082 if (a.length < n) { 5083 a = (T[])java.lang.reflect.Array 5084 .newInstance(a.getClass().getComponentType(), n); 5085 if (element != null) 5086 Arrays.fill(a, 0, n, element); 5087 } else { 5088 Arrays.fill(a, 0, n, element); 5089 if (a.length > n) 5090 a[n] = null; 5091 } 5092 return a; 5093 } 5094 5095 public List<E> subList(int fromIndex, int toIndex) { 5096 if (fromIndex < 0) 5097 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex); 5098 if (toIndex > n) 5099 throw new IndexOutOfBoundsException("toIndex = " + toIndex); 5100 if (fromIndex > toIndex) 5101 throw new IllegalArgumentException("fromIndex(" + fromIndex + 5102 ") > toIndex(" + toIndex + ")"); 5103 return new CopiesList<>(toIndex - fromIndex, element); 5104 } 5105 5106 @Override 5107 public int hashCode() { 5108 if (n == 0) return 1; 5109 // hashCode of n repeating elements is 31^n + elementHash * Sum(31^k, k = 0..n-1) 5110 // this implementation completes in O(log(n)) steps taking advantage of 5111 // 31^(2*n) = (31^n)^2 and Sum(31^k, k = 0..(2*n-1)) = Sum(31^k, k = 0..n-1) * (31^n + 1) 5112 int pow = 31; 5113 int sum = 1; 5114 for (int i = Integer.numberOfLeadingZeros(n) + 1; i < Integer.SIZE; i++) { 5115 sum *= pow + 1; 5116 pow *= pow; 5117 if ((n << i) < 0) { 5118 pow *= 31; 5119 sum = sum * 31 + 1; 5120 } 5121 } 5122 return pow + sum * (element == null ? 0 : element.hashCode()); 5123 } 5124 5125 @Override 5126 public boolean equals(Object o) { 5127 if (o == this) 5128 return true; 5129 if (o instanceof CopiesList) { 5130 CopiesList<?> other = (CopiesList<?>) o; 5131 return n == other.n && (n == 0 || eq(element, other.element)); 5132 } 5133 if (!(o instanceof List)) 5134 return false; 5135 5136 int remaining = n; 5137 E e = element; 5138 Iterator<?> itr = ((List<?>) o).iterator(); 5139 if (e == null) { 5140 while (itr.hasNext() && remaining-- > 0) { 5141 if (itr.next() != null) 5142 return false; 5143 } 5144 } else { 5145 while (itr.hasNext() && remaining-- > 0) { 5146 if (!e.equals(itr.next())) 5147 return false; 5148 } 5149 } 5150 return remaining == 0 && !itr.hasNext(); 5151 } 5152 5153 // Override default methods in Collection 5154 @Override 5155 public Stream<E> stream() { 5156 return IntStream.range(0, n).mapToObj(i -> element); 5157 } 5158 5159 @Override 5160 public Stream<E> parallelStream() { 5161 return IntStream.range(0, n).parallel().mapToObj(i -> element); 5162 } 5163 5164 @Override 5165 public Spliterator<E> spliterator() { 5166 return stream().spliterator(); 5167 } 5168 5169 private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException { 5170 ois.defaultReadObject(); 5171 SharedSecrets.getJavaObjectInputStreamAccess().checkArray(ois, Object[].class, n); 5172 } 5173 } 5174 5175 /** 5176 * Returns a comparator that imposes the reverse of the <em>natural 5177 * ordering</em> on a collection of objects that implement the 5178 * {@code Comparable} interface. (The natural ordering is the ordering 5179 * imposed by the objects' own {@code compareTo} method.) This enables a 5180 * simple idiom for sorting (or maintaining) collections (or arrays) of 5181 * objects that implement the {@code Comparable} interface in 5182 * reverse-natural-order. For example, suppose {@code a} is an array of 5183 * strings. Then: <pre> 5184 * Arrays.sort(a, Collections.reverseOrder()); 5185 * </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p> 5186 * 5187 * The returned comparator is serializable. 5188 * 5189 * @param <T> the class of the objects compared by the comparator 5190 * @return A comparator that imposes the reverse of the <i>natural 5191 * ordering</i> on a collection of objects that implement 5192 * the {@code Comparable} interface. 5193 * @see Comparable 5194 */ 5195 @SuppressWarnings("unchecked") 5196 public static <T> Comparator<T> reverseOrder() { 5197 return (Comparator<T>) ReverseComparator.REVERSE_ORDER; 5198 } 5199 5200 /** 5201 * @serial include 5202 */ 5203 private static class ReverseComparator 5204 implements Comparator<Comparable<Object>>, Serializable { 5205 5206 private static final long serialVersionUID = 7207038068494060240L; 5207 5208 static final ReverseComparator REVERSE_ORDER 5209 = new ReverseComparator(); 5210 5211 public int compare(Comparable<Object> c1, Comparable<Object> c2) { 5212 return c2.compareTo(c1); 5213 } 5214 5215 private Object readResolve() { return Collections.reverseOrder(); } 5216 5217 @Override 5218 public Comparator<Comparable<Object>> reversed() { 5219 return Comparator.naturalOrder(); 5220 } 5221 } 5222 5223 /** 5224 * Returns a comparator that imposes the reverse ordering of the specified 5225 * comparator. If the specified comparator is {@code null}, this method is 5226 * equivalent to {@link #reverseOrder()} (in other words, it returns a 5227 * comparator that imposes the reverse of the <em>natural ordering</em> on 5228 * a collection of objects that implement the Comparable interface). 5229 * 5230 * <p>The returned comparator is serializable (assuming the specified 5231 * comparator is also serializable or {@code null}). 5232 * 5233 * @param <T> the class of the objects compared by the comparator 5234 * @param cmp a comparator who's ordering is to be reversed by the returned 5235 * comparator or {@code null} 5236 * @return A comparator that imposes the reverse ordering of the 5237 * specified comparator. 5238 * @since 1.5 5239 */ 5240 @SuppressWarnings("unchecked") 5241 public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) { 5242 if (cmp == null) { 5243 return (Comparator<T>) ReverseComparator.REVERSE_ORDER; 5244 } else if (cmp == ReverseComparator.REVERSE_ORDER) { 5245 return (Comparator<T>) Comparators.NaturalOrderComparator.INSTANCE; 5246 } else if (cmp == Comparators.NaturalOrderComparator.INSTANCE) { 5247 return (Comparator<T>) ReverseComparator.REVERSE_ORDER; 5248 } else if (cmp instanceof ReverseComparator2) { 5249 return ((ReverseComparator2<T>) cmp).cmp; 5250 } else { 5251 return new ReverseComparator2<>(cmp); 5252 } 5253 } 5254 5255 /** 5256 * @serial include 5257 */ 5258 private static class ReverseComparator2<T> implements Comparator<T>, 5259 Serializable 5260 { 5261 private static final long serialVersionUID = 4374092139857L; 5262 5263 /** 5264 * The comparator specified in the static factory. This will never 5265 * be null, as the static factory returns a ReverseComparator 5266 * instance if its argument is null. 5267 * 5268 * @serial 5269 */ 5270 final Comparator<T> cmp; 5271 5272 ReverseComparator2(Comparator<T> cmp) { 5273 assert cmp != null; 5274 this.cmp = cmp; 5275 } 5276 5277 public int compare(T t1, T t2) { 5278 return cmp.compare(t2, t1); 5279 } 5280 5281 public boolean equals(Object o) { 5282 return (o == this) || 5283 (o instanceof ReverseComparator2 && 5284 cmp.equals(((ReverseComparator2)o).cmp)); 5285 } 5286 5287 public int hashCode() { 5288 return cmp.hashCode() ^ Integer.MIN_VALUE; 5289 } 5290 5291 @Override 5292 public Comparator<T> reversed() { 5293 return cmp; 5294 } 5295 } 5296 5297 /** 5298 * Returns an enumeration over the specified collection. This provides 5299 * interoperability with legacy APIs that require an enumeration 5300 * as input. 5301 * 5302 * <p>The iterator returned from a call to {@link Enumeration#asIterator()} 5303 * does not support removal of elements from the specified collection. This 5304 * is necessary to avoid unintentionally increasing the capabilities of the 5305 * returned enumeration. 5306 * 5307 * @param <T> the class of the objects in the collection 5308 * @param c the collection for which an enumeration is to be returned. 5309 * @return an enumeration over the specified collection. 5310 * @see Enumeration 5311 */ 5312 public static <T> Enumeration<T> enumeration(final Collection<T> c) { 5313 return new Enumeration<T>() { 5314 private final Iterator<T> i = c.iterator(); 5315 5316 public boolean hasMoreElements() { 5317 return i.hasNext(); 5318 } 5319 5320 public T nextElement() { 5321 return i.next(); 5322 } 5323 }; 5324 } 5325 5326 /** 5327 * Returns an array list containing the elements returned by the 5328 * specified enumeration in the order they are returned by the 5329 * enumeration. This method provides interoperability between 5330 * legacy APIs that return enumerations and new APIs that require 5331 * collections. 5332 * 5333 * @param <T> the class of the objects returned by the enumeration 5334 * @param e enumeration providing elements for the returned 5335 * array list 5336 * @return an array list containing the elements returned 5337 * by the specified enumeration. 5338 * @since 1.4 5339 * @see Enumeration 5340 * @see ArrayList 5341 */ 5342 public static <T> ArrayList<T> list(Enumeration<T> e) { 5343 ArrayList<T> l = new ArrayList<>(); 5344 while (e.hasMoreElements()) 5345 l.add(e.nextElement()); 5346 return l; 5347 } 5348 5349 /** 5350 * Returns true if the specified arguments are equal, or both null. 5351 * 5352 * NB: Do not replace with Object.equals until JDK-8015417 is resolved. 5353 */ 5354 static boolean eq(Object o1, Object o2) { 5355 return o1==null ? o2==null : o1.equals(o2); 5356 } 5357 5358 /** 5359 * Returns the number of elements in the specified collection equal to the 5360 * specified object. More formally, returns the number of elements 5361 * {@code e} in the collection such that 5362 * {@code Objects.equals(o, e)}. 5363 * 5364 * @param c the collection in which to determine the frequency 5365 * of {@code o} 5366 * @param o the object whose frequency is to be determined 5367 * @return the number of elements in {@code c} equal to {@code o} 5368 * @throws NullPointerException if {@code c} is null 5369 * @since 1.5 5370 */ 5371 public static int frequency(Collection<?> c, Object o) { 5372 int result = 0; 5373 if (o == null) { 5374 for (Object e : c) 5375 if (e == null) 5376 result++; 5377 } else { 5378 for (Object e : c) 5379 if (o.equals(e)) 5380 result++; 5381 } 5382 return result; 5383 } 5384 5385 /** 5386 * Returns {@code true} if the two specified collections have no 5387 * elements in common. 5388 * 5389 * <p>Care must be exercised if this method is used on collections that 5390 * do not comply with the general contract for {@code Collection}. 5391 * Implementations may elect to iterate over either collection and test 5392 * for containment in the other collection (or to perform any equivalent 5393 * computation). If either collection uses a nonstandard equality test 5394 * (as does a {@link SortedSet} whose ordering is not <em>compatible with 5395 * equals</em>, or the key set of an {@link IdentityHashMap}), both 5396 * collections must use the same nonstandard equality test, or the 5397 * result of this method is undefined. 5398 * 5399 * <p>Care must also be exercised when using collections that have 5400 * restrictions on the elements that they may contain. Collection 5401 * implementations are allowed to throw exceptions for any operation 5402 * involving elements they deem ineligible. For absolute safety the 5403 * specified collections should contain only elements which are 5404 * eligible elements for both collections. 5405 * 5406 * <p>Note that it is permissible to pass the same collection in both 5407 * parameters, in which case the method will return {@code true} if and 5408 * only if the collection is empty. 5409 * 5410 * @param c1 a collection 5411 * @param c2 a collection 5412 * @return {@code true} if the two specified collections have no 5413 * elements in common. 5414 * @throws NullPointerException if either collection is {@code null}. 5415 * @throws NullPointerException if one collection contains a {@code null} 5416 * element and {@code null} is not an eligible element for the other collection. 5417 * (<a href="Collection.html#optional-restrictions">optional</a>) 5418 * @throws ClassCastException if one collection contains an element that is 5419 * of a type which is ineligible for the other collection. 5420 * (<a href="Collection.html#optional-restrictions">optional</a>) 5421 * @since 1.5 5422 */ 5423 public static boolean disjoint(Collection<?> c1, Collection<?> c2) { 5424 // The collection to be used for contains(). Preference is given to 5425 // the collection who's contains() has lower O() complexity. 5426 Collection<?> contains = c2; 5427 // The collection to be iterated. If the collections' contains() impl 5428 // are of different O() complexity, the collection with slower 5429 // contains() will be used for iteration. For collections who's 5430 // contains() are of the same complexity then best performance is 5431 // achieved by iterating the smaller collection. 5432 Collection<?> iterate = c1; 5433 5434 // Performance optimization cases. The heuristics: 5435 // 1. Generally iterate over c1. 5436 // 2. If c1 is a Set then iterate over c2. 5437 // 3. If either collection is empty then result is always true. 5438 // 4. Iterate over the smaller Collection. 5439 if (c1 instanceof Set) { 5440 // Use c1 for contains as a Set's contains() is expected to perform 5441 // better than O(N/2) 5442 iterate = c2; 5443 contains = c1; 5444 } else if (!(c2 instanceof Set)) { 5445 // Both are mere Collections. Iterate over smaller collection. 5446 // Example: If c1 contains 3 elements and c2 contains 50 elements and 5447 // assuming contains() requires ceiling(N/2) comparisons then 5448 // checking for all c1 elements in c2 would require 75 comparisons 5449 // (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring 5450 // 100 comparisons (50 * ceiling(3/2)). 5451 int c1size = c1.size(); 5452 int c2size = c2.size(); 5453 if (c1size == 0 || c2size == 0) { 5454 // At least one collection is empty. Nothing will match. 5455 return true; 5456 } 5457 5458 if (c1size > c2size) { 5459 iterate = c2; 5460 contains = c1; 5461 } 5462 } 5463 5464 for (Object e : iterate) { 5465 if (contains.contains(e)) { 5466 // Found a common element. Collections are not disjoint. 5467 return false; 5468 } 5469 } 5470 5471 // No common elements were found. 5472 return true; 5473 } 5474 5475 /** 5476 * Adds all of the specified elements to the specified collection. 5477 * Elements to be added may be specified individually or as an array. 5478 * The behavior of this convenience method is identical to that of 5479 * {@code c.addAll(Arrays.asList(elements))}, but this method is likely 5480 * to run significantly faster under most implementations. 5481 * 5482 * <p>When elements are specified individually, this method provides a 5483 * convenient way to add a few elements to an existing collection: 5484 * <pre> 5485 * Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon"); 5486 * </pre> 5487 * 5488 * @param <T> the class of the elements to add and of the collection 5489 * @param c the collection into which {@code elements} are to be inserted 5490 * @param elements the elements to insert into {@code c} 5491 * @return {@code true} if the collection changed as a result of the call 5492 * @throws UnsupportedOperationException if {@code c} does not support 5493 * the {@code add} operation 5494 * @throws NullPointerException if {@code elements} contains one or more 5495 * null values and {@code c} does not permit null elements, or 5496 * if {@code c} or {@code elements} are {@code null} 5497 * @throws IllegalArgumentException if some property of a value in 5498 * {@code elements} prevents it from being added to {@code c} 5499 * @see Collection#addAll(Collection) 5500 * @since 1.5 5501 */ 5502 @SafeVarargs 5503 public static <T> boolean addAll(Collection<? super T> c, T... elements) { 5504 boolean result = false; 5505 for (T element : elements) 5506 result |= c.add(element); 5507 return result; 5508 } 5509 5510 /** 5511 * Returns a set backed by the specified map. The resulting set displays 5512 * the same ordering, concurrency, and performance characteristics as the 5513 * backing map. In essence, this factory method provides a {@link Set} 5514 * implementation corresponding to any {@link Map} implementation. There 5515 * is no need to use this method on a {@link Map} implementation that 5516 * already has a corresponding {@link Set} implementation (such as {@link 5517 * HashMap} or {@link TreeMap}). 5518 * 5519 * <p>Each method invocation on the set returned by this method results in 5520 * exactly one method invocation on the backing map or its {@code keySet} 5521 * view, with one exception. The {@code addAll} method is implemented 5522 * as a sequence of {@code put} invocations on the backing map. 5523 * 5524 * <p>The specified map must be empty at the time this method is invoked, 5525 * and should not be accessed directly after this method returns. These 5526 * conditions are ensured if the map is created empty, passed directly 5527 * to this method, and no reference to the map is retained, as illustrated 5528 * in the following code fragment: 5529 * <pre> 5530 * Set<Object> weakHashSet = Collections.newSetFromMap( 5531 * new WeakHashMap<Object, Boolean>()); 5532 * </pre> 5533 * 5534 * @param <E> the class of the map keys and of the objects in the 5535 * returned set 5536 * @param map the backing map 5537 * @return the set backed by the map 5538 * @throws IllegalArgumentException if {@code map} is not empty 5539 * @since 1.6 5540 */ 5541 public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) { 5542 return new SetFromMap<>(map); 5543 } 5544 5545 /** 5546 * @serial include 5547 */ 5548 private static class SetFromMap<E> extends AbstractSet<E> 5549 implements Set<E>, Serializable 5550 { 5551 private final Map<E, Boolean> m; // The backing map 5552 private transient Set<E> s; // Its keySet 5553 5554 SetFromMap(Map<E, Boolean> map) { 5555 if (!map.isEmpty()) 5556 throw new IllegalArgumentException("Map is non-empty"); 5557 m = map; 5558 s = map.keySet(); 5559 } 5560 5561 public void clear() { m.clear(); } 5562 public int size() { return m.size(); } 5563 public boolean isEmpty() { return m.isEmpty(); } 5564 public boolean contains(Object o) { return m.containsKey(o); } 5565 public boolean remove(Object o) { return m.remove(o) != null; } 5566 public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; } 5567 public Iterator<E> iterator() { return s.iterator(); } 5568 public Object[] toArray() { return s.toArray(); } 5569 public <T> T[] toArray(T[] a) { return s.toArray(a); } 5570 public String toString() { return s.toString(); } 5571 public int hashCode() { return s.hashCode(); } 5572 public boolean equals(Object o) { return o == this || s.equals(o); } 5573 public boolean containsAll(Collection<?> c) {return s.containsAll(c);} 5574 public boolean removeAll(Collection<?> c) {return s.removeAll(c);} 5575 public boolean retainAll(Collection<?> c) {return s.retainAll(c);} 5576 // addAll is the only inherited implementation 5577 5578 // Override default methods in Collection 5579 @Override 5580 public void forEach(Consumer<? super E> action) { 5581 s.forEach(action); 5582 } 5583 @Override 5584 public boolean removeIf(Predicate<? super E> filter) { 5585 return s.removeIf(filter); 5586 } 5587 5588 @Override 5589 public Spliterator<E> spliterator() {return s.spliterator();} 5590 @Override 5591 public Stream<E> stream() {return s.stream();} 5592 @Override 5593 public Stream<E> parallelStream() {return s.parallelStream();} 5594 5595 private static final long serialVersionUID = 2454657854757543876L; 5596 5597 private void readObject(java.io.ObjectInputStream stream) 5598 throws IOException, ClassNotFoundException 5599 { 5600 stream.defaultReadObject(); 5601 s = m.keySet(); 5602 } 5603 } 5604 5605 /** 5606 * Returns a view of a {@link Deque} as a Last-in-first-out (Lifo) 5607 * {@link Queue}. Method {@code add} is mapped to {@code push}, 5608 * {@code remove} is mapped to {@code pop} and so on. This 5609 * view can be useful when you would like to use a method 5610 * requiring a {@code Queue} but you need Lifo ordering. 5611 * 5612 * <p>Each method invocation on the queue returned by this method 5613 * results in exactly one method invocation on the backing deque, with 5614 * one exception. The {@link Queue#addAll addAll} method is 5615 * implemented as a sequence of {@link Deque#addFirst addFirst} 5616 * invocations on the backing deque. 5617 * 5618 * @param <T> the class of the objects in the deque 5619 * @param deque the deque 5620 * @return the queue 5621 * @since 1.6 5622 */ 5623 public static <T> Queue<T> asLifoQueue(Deque<T> deque) { 5624 return new AsLIFOQueue<>(Objects.requireNonNull(deque)); 5625 } 5626 5627 /** 5628 * @serial include 5629 */ 5630 static class AsLIFOQueue<E> extends AbstractQueue<E> 5631 implements Queue<E>, Serializable { 5632 private static final long serialVersionUID = 1802017725587941708L; 5633 private final Deque<E> q; 5634 AsLIFOQueue(Deque<E> q) { this.q = q; } 5635 public boolean add(E e) { q.addFirst(e); return true; } 5636 public boolean offer(E e) { return q.offerFirst(e); } 5637 public E poll() { return q.pollFirst(); } 5638 public E remove() { return q.removeFirst(); } 5639 public E peek() { return q.peekFirst(); } 5640 public E element() { return q.getFirst(); } 5641 public void clear() { q.clear(); } 5642 public int size() { return q.size(); } 5643 public boolean isEmpty() { return q.isEmpty(); } 5644 public boolean contains(Object o) { return q.contains(o); } 5645 public boolean remove(Object o) { return q.remove(o); } 5646 public Iterator<E> iterator() { return q.iterator(); } 5647 public Object[] toArray() { return q.toArray(); } 5648 public <T> T[] toArray(T[] a) { return q.toArray(a); } 5649 public <T> T[] toArray(IntFunction<T[]> f) { return q.toArray(f); } 5650 public String toString() { return q.toString(); } 5651 public boolean containsAll(Collection<?> c) { return q.containsAll(c); } 5652 public boolean removeAll(Collection<?> c) { return q.removeAll(c); } 5653 public boolean retainAll(Collection<?> c) { return q.retainAll(c); } 5654 // We use inherited addAll; forwarding addAll would be wrong 5655 5656 // Override default methods in Collection 5657 @Override 5658 public void forEach(Consumer<? super E> action) {q.forEach(action);} 5659 @Override 5660 public boolean removeIf(Predicate<? super E> filter) { 5661 return q.removeIf(filter); 5662 } 5663 @Override 5664 public Spliterator<E> spliterator() {return q.spliterator();} 5665 @Override 5666 public Stream<E> stream() {return q.stream();} 5667 @Override 5668 public Stream<E> parallelStream() {return q.parallelStream();} 5669 } 5670 }