1 /* 2 * Copyright (C) 2014 The Android Open Source Project 3 * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved. 4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 5 * 6 * This code is free software; you can redistribute it and/or modify it 7 * under the terms of the GNU General Public License version 2 only, as 8 * published by the Free Software Foundation. Oracle designates this 9 * particular file as subject to the "Classpath" exception as provided 10 * by Oracle in the LICENSE file that accompanied this code. 11 * 12 * This code is distributed in the hope that it will be useful, but WITHOUT 13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 15 * version 2 for more details (a copy is included in the LICENSE file that 16 * accompanied this code). 17 * 18 * You should have received a copy of the GNU General Public License version 19 * 2 along with this work; if not, write to the Free Software Foundation, 20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 21 * 22 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 23 * or visit www.oracle.com if you need additional information or have any 24 * questions. 25 */ 26 27 package java.util; 28 import java.io.Serializable; 29 import java.io.ObjectOutputStream; 30 import java.io.IOException; 31 import java.io.ObjectOutputStream; 32 import java.io.Serializable; 33 import java.lang.reflect.Array; 34 import java.util.function.BiConsumer; 35 import java.util.function.BiFunction; 36 import java.util.function.Consumer; 37 import java.util.function.Function; 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 44 import dalvik.system.VMRuntime; 45 46 /** 47 * This class consists exclusively of static methods that operate on or return 48 * collections. It contains polymorphic algorithms that operate on 49 * collections, "wrappers", which return a new collection backed by a 50 * specified collection, and a few other odds and ends. 51 * 52 * <p>The methods of this class all throw a <tt>NullPointerException</tt> 53 * if the collections or class objects provided to them are null. 54 * 55 * <p>The documentation for the polymorphic algorithms contained in this class 56 * generally includes a brief description of the <i>implementation</i>. Such 57 * descriptions should be regarded as <i>implementation notes</i>, rather than 58 * parts of the <i>specification</i>. Implementors should feel free to 59 * substitute other algorithms, so long as the specification itself is adhered 60 * to. (For example, the algorithm used by <tt>sort</tt> does not have to be 61 * a mergesort, but it does have to be <i>stable</i>.) 62 * 63 * <p>The "destructive" algorithms contained in this class, that is, the 64 * algorithms that modify the collection on which they operate, are specified 65 * to throw <tt>UnsupportedOperationException</tt> if the collection does not 66 * support the appropriate mutation primitive(s), such as the <tt>set</tt> 67 * method. These algorithms may, but are not required to, throw this 68 * exception if an invocation would have no effect on the collection. For 69 * example, invoking the <tt>sort</tt> method on an unmodifiable list that is 70 * already sorted may or may not throw <tt>UnsupportedOperationException</tt>. 71 * 72 * <p>This class is a member of the 73 * <a href="{@docRoot}openjdk-redirect.html?v=8&path=/technotes/guides/collections/index.html"> 74 * Java Collections Framework</a>. 75 * 76 * @author Josh Bloch 77 * @author Neal Gafter 78 * @see Collection 79 * @see Set 80 * @see List 81 * @see Map 82 * @since 1.2 83 */ 84 85 public class Collections { 86 // Suppresses default constructor, ensuring non-instantiability. Collections()87 private Collections() { 88 } 89 90 // Algorithms 91 92 /* 93 * Tuning parameters for algorithms - Many of the List algorithms have 94 * two implementations, one of which is appropriate for RandomAccess 95 * lists, the other for "sequential." Often, the random access variant 96 * yields better performance on small sequential access lists. The 97 * tuning parameters below determine the cutoff point for what constitutes 98 * a "small" sequential access list for each algorithm. The values below 99 * were empirically determined to work well for LinkedList. Hopefully 100 * they should be reasonable for other sequential access List 101 * implementations. Those doing performance work on this code would 102 * do well to validate the values of these parameters from time to time. 103 * (The first word of each tuning parameter name is the algorithm to which 104 * it applies.) 105 */ 106 private static final int BINARYSEARCH_THRESHOLD = 5000; 107 private static final int REVERSE_THRESHOLD = 18; 108 private static final int SHUFFLE_THRESHOLD = 5; 109 private static final int FILL_THRESHOLD = 25; 110 private static final int ROTATE_THRESHOLD = 100; 111 private static final int COPY_THRESHOLD = 10; 112 private static final int REPLACEALL_THRESHOLD = 11; 113 private static final int INDEXOFSUBLIST_THRESHOLD = 35; 114 115 // Android-changed: Warn about Collections.sort() being built on top 116 // of List.sort() when it used to be the other way round in Nougat. 117 /** 118 * Sorts the specified list into ascending order, according to the 119 * {@linkplain Comparable natural ordering} of its elements. 120 * All elements in the list must implement the {@link Comparable} 121 * interface. Furthermore, all elements in the list must be 122 * <i>mutually comparable</i> (that is, {@code e1.compareTo(e2)} 123 * must not throw a {@code ClassCastException} for any elements 124 * {@code e1} and {@code e2} in the list). 125 * 126 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will 127 * not be reordered as a result of the sort. 128 * 129 * <p>The specified list must be modifiable, but need not be resizable. 130 * 131 * @implNote 132 * This implementation defers to the {@link List#sort(Comparator)} 133 * method using the specified list and a {@code null} comparator. 134 * Do not call this method from {@code List.sort()} since that can lead 135 * to infinite recursion. Apps targeting APIs {@code <= 25} observe 136 * backwards compatibility behavior where this method was implemented 137 * on top of {@link List#toArray()}, {@link ListIterator#next()} and 138 * {@link ListIterator#set(Object)}. 139 * 140 * @param <T> the class of the objects in the list 141 * @param list the list to be sorted. 142 * @throws ClassCastException if the list contains elements that are not 143 * <i>mutually comparable</i> (for example, strings and integers). 144 * @throws UnsupportedOperationException if the specified list's 145 * list-iterator does not support the {@code set} operation. 146 * @throws IllegalArgumentException (optional) if the implementation 147 * detects that the natural ordering of the list elements is 148 * found to violate the {@link Comparable} contract 149 * @see List#sort(Comparator) 150 */ 151 @SuppressWarnings("unchecked") sort(List<T> list)152 public static <T extends Comparable<? super T>> void sort(List<T> list) { 153 // Android-changed: Call sort(list, null) here to be consistent 154 // with that method's (Android-changed) behavior. 155 // list.sort(null); 156 sort(list, null); 157 } 158 159 // Android-changed: Warn about Collections.sort() being built on top 160 // of List.sort() when it used to be the other way round in Nougat. 161 /** 162 * Sorts the specified list according to the order induced by the 163 * specified comparator. All elements in the list must be <i>mutually 164 * comparable</i> using the specified comparator (that is, 165 * {@code c.compare(e1, e2)} must not throw a {@code ClassCastException} 166 * for any elements {@code e1} and {@code e2} in the list). 167 * 168 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will 169 * not be reordered as a result of the sort. 170 * 171 * <p>The specified list must be modifiable, but need not be resizable. 172 * 173 * @implNote 174 * This implementation defers to the {@link List#sort(Comparator)} 175 * method using the specified list and comparator. 176 * Do not call this method from {@code List.sort()} since that can lead 177 * to infinite recursion. Apps targeting APIs {@code <= 25} observe 178 * backwards compatibility behavior where this method was implemented 179 * on top of {@link List#toArray()}, {@link ListIterator#next()} and 180 * {@link ListIterator#set(Object)}. 181 * 182 * @param <T> the class of the objects in the list 183 * @param list the list to be sorted. 184 * @param c the comparator to determine the order of the list. A 185 * {@code null} value indicates that the elements' <i>natural 186 * ordering</i> should be used. 187 * @throws ClassCastException if the list contains elements that are not 188 * <i>mutually comparable</i> using the specified comparator. 189 * @throws UnsupportedOperationException if the specified list's 190 * list-iterator does not support the {@code set} operation. 191 * @throws IllegalArgumentException (optional) if the comparator is 192 * found to violate the {@link Comparator} contract 193 * @see List#sort(Comparator) 194 */ 195 @SuppressWarnings({"unchecked", "rawtypes"}) sort(List<T> list, Comparator<? super T> c)196 public static <T> void sort(List<T> list, Comparator<? super T> c) { 197 // BEGIN Android-changed: Compat behavior for apps targeting APIs <= 25. 198 // list.sort(c); 199 int targetSdkVersion = VMRuntime.getRuntime().getTargetSdkVersion(); 200 if (targetSdkVersion > 25) { 201 list.sort(c); 202 } else { 203 // Compatibility behavior for API <= 25. http://b/33482884 204 if (list.getClass() == ArrayList.class) { 205 Arrays.sort((T[]) ((ArrayList) list).elementData, 0, list.size(), c); 206 return; 207 } 208 209 Object[] a = list.toArray(); 210 Arrays.sort(a, (Comparator) c); 211 ListIterator<T> i = list.listIterator(); 212 for (int j = 0; j < a.length; j++) { 213 i.next(); 214 i.set((T) a[j]); 215 } 216 } 217 // END Android-changed: Compat behavior for apps targeting APIs <= 25. 218 } 219 220 221 /** 222 * Searches the specified list for the specified object using the binary 223 * search algorithm. The list must be sorted into ascending order 224 * according to the {@linkplain Comparable natural ordering} of its 225 * elements (as by the {@link #sort(List)} method) prior to making this 226 * call. If it is not sorted, the results are undefined. If the list 227 * contains multiple elements equal to the specified object, there is no 228 * guarantee which one will be found. 229 * 230 * <p>This method runs in log(n) time for a "random access" list (which 231 * provides near-constant-time positional access). If the specified list 232 * does not implement the {@link RandomAccess} interface and is large, 233 * this method will do an iterator-based binary search that performs 234 * O(n) link traversals and O(log n) element comparisons. 235 * 236 * @param <T> the class of the objects in the list 237 * @param list the list to be searched. 238 * @param key the key to be searched for. 239 * @return the index of the search key, if it is contained in the list; 240 * otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The 241 * <i>insertion point</i> is defined as the point at which the 242 * key would be inserted into the list: the index of the first 243 * element greater than the key, or <tt>list.size()</tt> if all 244 * elements in the list are less than the specified key. Note 245 * that this guarantees that the return value will be >= 0 if 246 * and only if the key is found. 247 * @throws ClassCastException if the list contains elements that are not 248 * <i>mutually comparable</i> (for example, strings and 249 * integers), or the search key is not mutually comparable 250 * with the elements of the list. 251 */ 252 public static <T> binarySearch(List<? extends Comparable<? super T>> list, T key)253 int binarySearch(List<? extends Comparable<? super T>> list, T key) { 254 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD) 255 return Collections.indexedBinarySearch(list, key); 256 else 257 return Collections.iteratorBinarySearch(list, key); 258 } 259 260 private static <T> indexedBinarySearch(List<? extends Comparable<? super T>> list, T key)261 int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key) { 262 int low = 0; 263 int high = list.size()-1; 264 265 while (low <= high) { 266 int mid = (low + high) >>> 1; 267 Comparable<? super T> midVal = list.get(mid); 268 int cmp = midVal.compareTo(key); 269 270 if (cmp < 0) 271 low = mid + 1; 272 else if (cmp > 0) 273 high = mid - 1; 274 else 275 return mid; // key found 276 } 277 return -(low + 1); // key not found 278 } 279 280 private static <T> iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key)281 int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key) 282 { 283 int low = 0; 284 int high = list.size()-1; 285 ListIterator<? extends Comparable<? super T>> i = list.listIterator(); 286 287 while (low <= high) { 288 int mid = (low + high) >>> 1; 289 Comparable<? super T> midVal = get(i, mid); 290 int cmp = midVal.compareTo(key); 291 292 if (cmp < 0) 293 low = mid + 1; 294 else if (cmp > 0) 295 high = mid - 1; 296 else 297 return mid; // key found 298 } 299 return -(low + 1); // key not found 300 } 301 302 /** 303 * Gets the ith element from the given list by repositioning the specified 304 * list listIterator. 305 */ get(ListIterator<? extends T> i, int index)306 private static <T> T get(ListIterator<? extends T> i, int index) { 307 T obj = null; 308 int pos = i.nextIndex(); 309 if (pos <= index) { 310 do { 311 obj = i.next(); 312 } while (pos++ < index); 313 } else { 314 do { 315 obj = i.previous(); 316 } while (--pos > index); 317 } 318 return obj; 319 } 320 321 /** 322 * Searches the specified list for the specified object using the binary 323 * search algorithm. The list must be sorted into ascending order 324 * according to the specified comparator (as by the 325 * {@link #sort(List, Comparator) sort(List, Comparator)} 326 * method), prior to making this call. If it is 327 * not sorted, the results are undefined. If the list contains multiple 328 * elements equal to the specified object, there is no guarantee which one 329 * will be found. 330 * 331 * <p>This method runs in log(n) time for a "random access" list (which 332 * provides near-constant-time positional access). If the specified list 333 * does not implement the {@link RandomAccess} interface and is large, 334 * this method will do an iterator-based binary search that performs 335 * O(n) link traversals and O(log n) element comparisons. 336 * 337 * @param <T> the class of the objects in the list 338 * @param list the list to be searched. 339 * @param key the key to be searched for. 340 * @param c the comparator by which the list is ordered. 341 * A <tt>null</tt> value indicates that the elements' 342 * {@linkplain Comparable natural ordering} should be used. 343 * @return the index of the search key, if it is contained in the list; 344 * otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The 345 * <i>insertion point</i> is defined as the point at which the 346 * key would be inserted into the list: the index of the first 347 * element greater than the key, or <tt>list.size()</tt> if all 348 * elements in the list are less than the specified key. Note 349 * that this guarantees that the return value will be >= 0 if 350 * and only if the key is found. 351 * @throws ClassCastException if the list contains elements that are not 352 * <i>mutually comparable</i> using the specified comparator, 353 * or the search key is not mutually comparable with the 354 * elements of the list using this comparator. 355 */ 356 @SuppressWarnings("unchecked") binarySearch(List<? extends T> list, T key, Comparator<? super T> c)357 public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) { 358 if (c==null) 359 return binarySearch((List<? extends Comparable<? super T>>) list, key); 360 361 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD) 362 return Collections.indexedBinarySearch(list, key, c); 363 else 364 return Collections.iteratorBinarySearch(list, key, c); 365 } 366 indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c)367 private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) { 368 int low = 0; 369 int high = l.size()-1; 370 371 while (low <= high) { 372 int mid = (low + high) >>> 1; 373 T midVal = l.get(mid); 374 int cmp = c.compare(midVal, key); 375 376 if (cmp < 0) 377 low = mid + 1; 378 else if (cmp > 0) 379 high = mid - 1; 380 else 381 return mid; // key found 382 } 383 return -(low + 1); // key not found 384 } 385 iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c)386 private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) { 387 int low = 0; 388 int high = l.size()-1; 389 ListIterator<? extends T> i = l.listIterator(); 390 391 while (low <= high) { 392 int mid = (low + high) >>> 1; 393 T midVal = get(i, mid); 394 int cmp = c.compare(midVal, key); 395 396 if (cmp < 0) 397 low = mid + 1; 398 else if (cmp > 0) 399 high = mid - 1; 400 else 401 return mid; // key found 402 } 403 return -(low + 1); // key not found 404 } 405 406 /** 407 * Reverses the order of the elements in the specified list.<p> 408 * 409 * This method runs in linear time. 410 * 411 * @param list the list whose elements are to be reversed. 412 * @throws UnsupportedOperationException if the specified list or 413 * its list-iterator does not support the <tt>set</tt> operation. 414 */ 415 @SuppressWarnings({"rawtypes", "unchecked"}) reverse(List<?> list)416 public static void reverse(List<?> list) { 417 int size = list.size(); 418 if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) { 419 for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--) 420 swap(list, i, j); 421 } else { 422 // instead of using a raw type here, it's possible to capture 423 // the wildcard but it will require a call to a supplementary 424 // private method 425 ListIterator fwd = list.listIterator(); 426 ListIterator rev = list.listIterator(size); 427 for (int i=0, mid=list.size()>>1; i<mid; i++) { 428 Object tmp = fwd.next(); 429 fwd.set(rev.previous()); 430 rev.set(tmp); 431 } 432 } 433 } 434 435 /** 436 * Randomly permutes the specified list using a default source of 437 * randomness. All permutations occur with approximately equal 438 * likelihood. 439 * 440 * <p>The hedge "approximately" is used in the foregoing description because 441 * default source of randomness is only approximately an unbiased source 442 * of independently chosen bits. If it were a perfect source of randomly 443 * chosen bits, then the algorithm would choose permutations with perfect 444 * uniformity. 445 * 446 * <p>This implementation traverses the list backwards, from the last 447 * element up to the second, repeatedly swapping a randomly selected element 448 * into the "current position". Elements are randomly selected from the 449 * portion of the list that runs from the first element to the current 450 * position, inclusive. 451 * 452 * <p>This method runs in linear time. If the specified list does not 453 * implement the {@link RandomAccess} interface and is large, this 454 * implementation dumps the specified list into an array before shuffling 455 * it, and dumps the shuffled array back into the list. This avoids the 456 * quadratic behavior that would result from shuffling a "sequential 457 * access" list in place. 458 * 459 * @param list the list to be shuffled. 460 * @throws UnsupportedOperationException if the specified list or 461 * its list-iterator does not support the <tt>set</tt> operation. 462 */ shuffle(List<?> list)463 public static void shuffle(List<?> list) { 464 Random rnd = r; 465 if (rnd == null) 466 r = rnd = new Random(); // harmless race. 467 shuffle(list, rnd); 468 } 469 470 private static Random r; 471 472 /** 473 * Randomly permute the specified list using the specified source of 474 * randomness. All permutations occur with equal likelihood 475 * assuming that the source of randomness is fair.<p> 476 * 477 * This implementation traverses the list backwards, from the last element 478 * up to the second, repeatedly swapping a randomly selected element into 479 * the "current position". Elements are randomly selected from the 480 * portion of the list that runs from the first element to the current 481 * position, inclusive.<p> 482 * 483 * This method runs in linear time. If the specified list does not 484 * implement the {@link RandomAccess} interface and is large, this 485 * implementation dumps the specified list into an array before shuffling 486 * it, and dumps the shuffled array back into the list. This avoids the 487 * quadratic behavior that would result from shuffling a "sequential 488 * access" list in place. 489 * 490 * @param list the list to be shuffled. 491 * @param rnd the source of randomness to use to shuffle the list. 492 * @throws UnsupportedOperationException if the specified list or its 493 * list-iterator does not support the <tt>set</tt> operation. 494 */ 495 @SuppressWarnings({"rawtypes", "unchecked"}) shuffle(List<?> list, Random rnd)496 public static void shuffle(List<?> list, Random rnd) { 497 int size = list.size(); 498 if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) { 499 for (int i=size; i>1; i--) 500 swap(list, i-1, rnd.nextInt(i)); 501 } else { 502 Object arr[] = list.toArray(); 503 504 // Shuffle array 505 for (int i=size; i>1; i--) 506 swap(arr, i-1, rnd.nextInt(i)); 507 508 // Dump array back into list 509 // instead of using a raw type here, it's possible to capture 510 // the wildcard but it will require a call to a supplementary 511 // private method 512 ListIterator it = list.listIterator(); 513 for (int i=0; i<arr.length; i++) { 514 it.next(); 515 it.set(arr[i]); 516 } 517 } 518 } 519 520 /** 521 * Swaps the elements at the specified positions in the specified list. 522 * (If the specified positions are equal, invoking this method leaves 523 * the list unchanged.) 524 * 525 * @param list The list in which to swap elements. 526 * @param i the index of one element to be swapped. 527 * @param j the index of the other element to be swapped. 528 * @throws IndexOutOfBoundsException if either <tt>i</tt> or <tt>j</tt> 529 * is out of range (i < 0 || i >= list.size() 530 * || j < 0 || j >= list.size()). 531 * @since 1.4 532 */ 533 @SuppressWarnings({"rawtypes", "unchecked"}) swap(List<?> list, int i, int j)534 public static void swap(List<?> list, int i, int j) { 535 // instead of using a raw type here, it's possible to capture 536 // the wildcard but it will require a call to a supplementary 537 // private method 538 final List l = list; 539 l.set(i, l.set(j, l.get(i))); 540 } 541 542 /** 543 * Swaps the two specified elements in the specified array. 544 */ swap(Object[] arr, int i, int j)545 private static void swap(Object[] arr, int i, int j) { 546 Object tmp = arr[i]; 547 arr[i] = arr[j]; 548 arr[j] = tmp; 549 } 550 551 /** 552 * Replaces all of the elements of the specified list with the specified 553 * element. <p> 554 * 555 * This method runs in linear time. 556 * 557 * @param <T> the class of the objects in the list 558 * @param list the list to be filled with the specified element. 559 * @param obj The element with which to fill the specified list. 560 * @throws UnsupportedOperationException if the specified list or its 561 * list-iterator does not support the <tt>set</tt> operation. 562 */ fill(List<? super T> list, T obj)563 public static <T> void fill(List<? super T> list, T obj) { 564 int size = list.size(); 565 566 if (size < FILL_THRESHOLD || list instanceof RandomAccess) { 567 for (int i=0; i<size; i++) 568 list.set(i, obj); 569 } else { 570 ListIterator<? super T> itr = list.listIterator(); 571 for (int i=0; i<size; i++) { 572 itr.next(); 573 itr.set(obj); 574 } 575 } 576 } 577 578 /** 579 * Copies all of the elements from one list into another. After the 580 * operation, the index of each copied element in the destination list 581 * will be identical to its index in the source list. The destination 582 * list must be at least as long as the source list. If it is longer, the 583 * remaining elements in the destination list are unaffected. <p> 584 * 585 * This method runs in linear time. 586 * 587 * @param <T> the class of the objects in the lists 588 * @param dest The destination list. 589 * @param src The source list. 590 * @throws IndexOutOfBoundsException if the destination list is too small 591 * to contain the entire source List. 592 * @throws UnsupportedOperationException if the destination list's 593 * list-iterator does not support the <tt>set</tt> operation. 594 */ copy(List<? super T> dest, List<? extends T> src)595 public static <T> void copy(List<? super T> dest, List<? extends T> src) { 596 int srcSize = src.size(); 597 if (srcSize > dest.size()) 598 throw new IndexOutOfBoundsException("Source does not fit in dest"); 599 600 if (srcSize < COPY_THRESHOLD || 601 (src instanceof RandomAccess && dest instanceof RandomAccess)) { 602 for (int i=0; i<srcSize; i++) 603 dest.set(i, src.get(i)); 604 } else { 605 ListIterator<? super T> di=dest.listIterator(); 606 ListIterator<? extends T> si=src.listIterator(); 607 for (int i=0; i<srcSize; i++) { 608 di.next(); 609 di.set(si.next()); 610 } 611 } 612 } 613 614 /** 615 * Returns the minimum element of the given collection, according to the 616 * <i>natural ordering</i> of its elements. All elements in the 617 * collection must implement the <tt>Comparable</tt> interface. 618 * Furthermore, all elements in the collection must be <i>mutually 619 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a 620 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 621 * <tt>e2</tt> in the collection).<p> 622 * 623 * This method iterates over the entire collection, hence it requires 624 * time proportional to the size of the collection. 625 * 626 * @param <T> the class of the objects in the collection 627 * @param coll the collection whose minimum element is to be determined. 628 * @return the minimum element of the given collection, according 629 * to the <i>natural ordering</i> of its elements. 630 * @throws ClassCastException if the collection contains elements that are 631 * not <i>mutually comparable</i> (for example, strings and 632 * integers). 633 * @throws NoSuchElementException if the collection is empty. 634 * @see Comparable 635 */ min(Collection<? extends T> coll)636 public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) { 637 Iterator<? extends T> i = coll.iterator(); 638 T candidate = i.next(); 639 640 while (i.hasNext()) { 641 T next = i.next(); 642 if (next.compareTo(candidate) < 0) 643 candidate = next; 644 } 645 return candidate; 646 } 647 648 /** 649 * Returns the minimum element of the given collection, according to the 650 * order induced by the specified comparator. All elements in the 651 * collection must be <i>mutually comparable</i> by the specified 652 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a 653 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 654 * <tt>e2</tt> in the collection).<p> 655 * 656 * This method iterates over the entire collection, hence it requires 657 * time proportional to the size of the collection. 658 * 659 * @param <T> the class of the objects in the collection 660 * @param coll the collection whose minimum element is to be determined. 661 * @param comp the comparator with which to determine the minimum element. 662 * A <tt>null</tt> value indicates that the elements' <i>natural 663 * ordering</i> should be used. 664 * @return the minimum element of the given collection, according 665 * to the specified comparator. 666 * @throws ClassCastException if the collection contains elements that are 667 * not <i>mutually comparable</i> using the specified comparator. 668 * @throws NoSuchElementException if the collection is empty. 669 * @see Comparable 670 */ 671 @SuppressWarnings({"unchecked", "rawtypes"}) min(Collection<? extends T> coll, Comparator<? super T> comp)672 public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) { 673 if (comp==null) 674 return (T)min((Collection) coll); 675 676 Iterator<? extends T> i = coll.iterator(); 677 T candidate = i.next(); 678 679 while (i.hasNext()) { 680 T next = i.next(); 681 if (comp.compare(next, candidate) < 0) 682 candidate = next; 683 } 684 return candidate; 685 } 686 687 /** 688 * Returns the maximum element of the given collection, according to the 689 * <i>natural ordering</i> of its elements. All elements in the 690 * collection must implement the <tt>Comparable</tt> interface. 691 * Furthermore, all elements in the collection must be <i>mutually 692 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a 693 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 694 * <tt>e2</tt> in the collection).<p> 695 * 696 * This method iterates over the entire collection, hence it requires 697 * time proportional to the size of the collection. 698 * 699 * @param <T> the class of the objects in the collection 700 * @param coll the collection whose maximum element is to be determined. 701 * @return the maximum element of the given collection, according 702 * to the <i>natural ordering</i> of its elements. 703 * @throws ClassCastException if the collection contains elements that are 704 * not <i>mutually comparable</i> (for example, strings and 705 * integers). 706 * @throws NoSuchElementException if the collection is empty. 707 * @see Comparable 708 */ max(Collection<? extends T> coll)709 public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) { 710 Iterator<? extends T> i = coll.iterator(); 711 T candidate = i.next(); 712 713 while (i.hasNext()) { 714 T next = i.next(); 715 if (next.compareTo(candidate) > 0) 716 candidate = next; 717 } 718 return candidate; 719 } 720 721 /** 722 * Returns the maximum element of the given collection, according to the 723 * order induced by the specified comparator. All elements in the 724 * collection must be <i>mutually comparable</i> by the specified 725 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a 726 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 727 * <tt>e2</tt> in the collection).<p> 728 * 729 * This method iterates over the entire collection, hence it requires 730 * time proportional to the size of the collection. 731 * 732 * @param <T> the class of the objects in the collection 733 * @param coll the collection whose maximum element is to be determined. 734 * @param comp the comparator with which to determine the maximum element. 735 * A <tt>null</tt> value indicates that the elements' <i>natural 736 * ordering</i> should be used. 737 * @return the maximum element of the given collection, according 738 * to the specified comparator. 739 * @throws ClassCastException if the collection contains elements that are 740 * not <i>mutually comparable</i> using the specified comparator. 741 * @throws NoSuchElementException if the collection is empty. 742 * @see Comparable 743 */ 744 @SuppressWarnings({"unchecked", "rawtypes"}) max(Collection<? extends T> coll, Comparator<? super T> comp)745 public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) { 746 if (comp==null) 747 return (T)max((Collection) coll); 748 749 Iterator<? extends T> i = coll.iterator(); 750 T candidate = i.next(); 751 752 while (i.hasNext()) { 753 T next = i.next(); 754 if (comp.compare(next, candidate) > 0) 755 candidate = next; 756 } 757 return candidate; 758 } 759 760 /** 761 * Rotates the elements in the specified list by the specified distance. 762 * After calling this method, the element at index <tt>i</tt> will be 763 * the element previously at index <tt>(i - distance)</tt> mod 764 * <tt>list.size()</tt>, for all values of <tt>i</tt> between <tt>0</tt> 765 * and <tt>list.size()-1</tt>, inclusive. (This method has no effect on 766 * the size of the list.) 767 * 768 * <p>For example, suppose <tt>list</tt> comprises<tt> [t, a, n, k, s]</tt>. 769 * After invoking <tt>Collections.rotate(list, 1)</tt> (or 770 * <tt>Collections.rotate(list, -4)</tt>), <tt>list</tt> will comprise 771 * <tt>[s, t, a, n, k]</tt>. 772 * 773 * <p>Note that this method can usefully be applied to sublists to 774 * move one or more elements within a list while preserving the 775 * order of the remaining elements. For example, the following idiom 776 * moves the element at index <tt>j</tt> forward to position 777 * <tt>k</tt> (which must be greater than or equal to <tt>j</tt>): 778 * <pre> 779 * Collections.rotate(list.subList(j, k+1), -1); 780 * </pre> 781 * To make this concrete, suppose <tt>list</tt> comprises 782 * <tt>[a, b, c, d, e]</tt>. To move the element at index <tt>1</tt> 783 * (<tt>b</tt>) forward two positions, perform the following invocation: 784 * <pre> 785 * Collections.rotate(l.subList(1, 4), -1); 786 * </pre> 787 * The resulting list is <tt>[a, c, d, b, e]</tt>. 788 * 789 * <p>To move more than one element forward, increase the absolute value 790 * of the rotation distance. To move elements backward, use a positive 791 * shift distance. 792 * 793 * <p>If the specified list is small or implements the {@link 794 * RandomAccess} interface, this implementation exchanges the first 795 * element into the location it should go, and then repeatedly exchanges 796 * the displaced element into the location it should go until a displaced 797 * element is swapped into the first element. If necessary, the process 798 * is repeated on the second and successive elements, until the rotation 799 * is complete. If the specified list is large and doesn't implement the 800 * <tt>RandomAccess</tt> interface, this implementation breaks the 801 * list into two sublist views around index <tt>-distance mod size</tt>. 802 * Then the {@link #reverse(List)} method is invoked on each sublist view, 803 * and finally it is invoked on the entire list. For a more complete 804 * description of both algorithms, see Section 2.3 of Jon Bentley's 805 * <i>Programming Pearls</i> (Addison-Wesley, 1986). 806 * 807 * @param list the list to be rotated. 808 * @param distance the distance to rotate the list. There are no 809 * constraints on this value; it may be zero, negative, or 810 * greater than <tt>list.size()</tt>. 811 * @throws UnsupportedOperationException if the specified list or 812 * its list-iterator does not support the <tt>set</tt> operation. 813 * @since 1.4 814 */ rotate(List<?> list, int distance)815 public static void rotate(List<?> list, int distance) { 816 if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD) 817 rotate1(list, distance); 818 else 819 rotate2(list, distance); 820 } 821 rotate1(List<T> list, int distance)822 private static <T> void rotate1(List<T> list, int distance) { 823 int size = list.size(); 824 if (size == 0) 825 return; 826 distance = distance % size; 827 if (distance < 0) 828 distance += size; 829 if (distance == 0) 830 return; 831 832 for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) { 833 T displaced = list.get(cycleStart); 834 int i = cycleStart; 835 do { 836 i += distance; 837 if (i >= size) 838 i -= size; 839 displaced = list.set(i, displaced); 840 nMoved ++; 841 } while (i != cycleStart); 842 } 843 } 844 rotate2(List<?> list, int distance)845 private static void rotate2(List<?> list, int distance) { 846 int size = list.size(); 847 if (size == 0) 848 return; 849 int mid = -distance % size; 850 if (mid < 0) 851 mid += size; 852 if (mid == 0) 853 return; 854 855 reverse(list.subList(0, mid)); 856 reverse(list.subList(mid, size)); 857 reverse(list); 858 } 859 860 /** 861 * Replaces all occurrences of one specified value in a list with another. 862 * More formally, replaces with <tt>newVal</tt> each element <tt>e</tt> 863 * in <tt>list</tt> such that 864 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>. 865 * (This method has no effect on the size of the list.) 866 * 867 * @param <T> the class of the objects in the list 868 * @param list the list in which replacement is to occur. 869 * @param oldVal the old value to be replaced. 870 * @param newVal the new value with which <tt>oldVal</tt> is to be 871 * replaced. 872 * @return <tt>true</tt> if <tt>list</tt> contained one or more elements 873 * <tt>e</tt> such that 874 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>. 875 * @throws UnsupportedOperationException if the specified list or 876 * its list-iterator does not support the <tt>set</tt> operation. 877 * @since 1.4 878 */ replaceAll(List<T> list, T oldVal, T newVal)879 public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) { 880 boolean result = false; 881 int size = list.size(); 882 if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) { 883 if (oldVal==null) { 884 for (int i=0; i<size; i++) { 885 if (list.get(i)==null) { 886 list.set(i, newVal); 887 result = true; 888 } 889 } 890 } else { 891 for (int i=0; i<size; i++) { 892 if (oldVal.equals(list.get(i))) { 893 list.set(i, newVal); 894 result = true; 895 } 896 } 897 } 898 } else { 899 ListIterator<T> itr=list.listIterator(); 900 if (oldVal==null) { 901 for (int i=0; i<size; i++) { 902 if (itr.next()==null) { 903 itr.set(newVal); 904 result = true; 905 } 906 } 907 } else { 908 for (int i=0; i<size; i++) { 909 if (oldVal.equals(itr.next())) { 910 itr.set(newVal); 911 result = true; 912 } 913 } 914 } 915 } 916 return result; 917 } 918 919 /** 920 * Returns the starting position of the first occurrence of the specified 921 * target list within the specified source list, or -1 if there is no 922 * such occurrence. More formally, returns the lowest index <tt>i</tt> 923 * such that {@code source.subList(i, i+target.size()).equals(target)}, 924 * or -1 if there is no such index. (Returns -1 if 925 * {@code target.size() > source.size()}) 926 * 927 * <p>This implementation uses the "brute force" technique of scanning 928 * over the source list, looking for a match with the target at each 929 * location in turn. 930 * 931 * @param source the list in which to search for the first occurrence 932 * of <tt>target</tt>. 933 * @param target the list to search for as a subList of <tt>source</tt>. 934 * @return the starting position of the first occurrence of the specified 935 * target list within the specified source list, or -1 if there 936 * is no such occurrence. 937 * @since 1.4 938 */ indexOfSubList(List<?> source, List<?> target)939 public static int indexOfSubList(List<?> source, List<?> target) { 940 int sourceSize = source.size(); 941 int targetSize = target.size(); 942 int maxCandidate = sourceSize - targetSize; 943 944 if (sourceSize < INDEXOFSUBLIST_THRESHOLD || 945 (source instanceof RandomAccess&&target instanceof RandomAccess)) { 946 nextCand: 947 for (int candidate = 0; candidate <= maxCandidate; candidate++) { 948 for (int i=0, j=candidate; i<targetSize; i++, j++) 949 if (!eq(target.get(i), source.get(j))) 950 continue nextCand; // Element mismatch, try next cand 951 return candidate; // All elements of candidate matched target 952 } 953 } else { // Iterator version of above algorithm 954 ListIterator<?> si = source.listIterator(); 955 nextCand: 956 for (int candidate = 0; candidate <= maxCandidate; candidate++) { 957 ListIterator<?> ti = target.listIterator(); 958 for (int i=0; i<targetSize; i++) { 959 if (!eq(ti.next(), si.next())) { 960 // Back up source iterator to next candidate 961 for (int j=0; j<i; j++) 962 si.previous(); 963 continue nextCand; 964 } 965 } 966 return candidate; 967 } 968 } 969 return -1; // No candidate matched the target 970 } 971 972 /** 973 * Returns the starting position of the last occurrence of the specified 974 * target list within the specified source list, or -1 if there is no such 975 * occurrence. More formally, returns the highest index <tt>i</tt> 976 * such that {@code source.subList(i, i+target.size()).equals(target)}, 977 * or -1 if there is no such index. (Returns -1 if 978 * {@code target.size() > source.size()}) 979 * 980 * <p>This implementation uses the "brute force" technique of iterating 981 * over the source list, looking for a match with the target at each 982 * location in turn. 983 * 984 * @param source the list in which to search for the last occurrence 985 * of <tt>target</tt>. 986 * @param target the list to search for as a subList of <tt>source</tt>. 987 * @return the starting position of the last occurrence of the specified 988 * target list within the specified source list, or -1 if there 989 * is no such occurrence. 990 * @since 1.4 991 */ lastIndexOfSubList(List<?> source, List<?> target)992 public static int lastIndexOfSubList(List<?> source, List<?> target) { 993 int sourceSize = source.size(); 994 int targetSize = target.size(); 995 int maxCandidate = sourceSize - targetSize; 996 997 if (sourceSize < INDEXOFSUBLIST_THRESHOLD || 998 source instanceof RandomAccess) { // Index access version 999 nextCand: 1000 for (int candidate = maxCandidate; candidate >= 0; candidate--) { 1001 for (int i=0, j=candidate; i<targetSize; i++, j++) 1002 if (!eq(target.get(i), source.get(j))) 1003 continue nextCand; // Element mismatch, try next cand 1004 return candidate; // All elements of candidate matched target 1005 } 1006 } else { // Iterator version of above algorithm 1007 if (maxCandidate < 0) 1008 return -1; 1009 ListIterator<?> si = source.listIterator(maxCandidate); 1010 nextCand: 1011 for (int candidate = maxCandidate; candidate >= 0; candidate--) { 1012 ListIterator<?> ti = target.listIterator(); 1013 for (int i=0; i<targetSize; i++) { 1014 if (!eq(ti.next(), si.next())) { 1015 if (candidate != 0) { 1016 // Back up source iterator to next candidate 1017 for (int j=0; j<=i+1; j++) 1018 si.previous(); 1019 } 1020 continue nextCand; 1021 } 1022 } 1023 return candidate; 1024 } 1025 } 1026 return -1; // No candidate matched the target 1027 } 1028 1029 1030 // Unmodifiable Wrappers 1031 1032 /** 1033 * Returns an unmodifiable view of the specified collection. This method 1034 * allows modules to provide users with "read-only" access to internal 1035 * collections. Query operations on the returned collection "read through" 1036 * to the specified collection, and attempts to modify the returned 1037 * collection, whether direct or via its iterator, result in an 1038 * <tt>UnsupportedOperationException</tt>.<p> 1039 * 1040 * The returned collection does <i>not</i> pass the hashCode and equals 1041 * operations through to the backing collection, but relies on 1042 * <tt>Object</tt>'s <tt>equals</tt> and <tt>hashCode</tt> methods. This 1043 * is necessary to preserve the contracts of these operations in the case 1044 * that the backing collection is a set or a list.<p> 1045 * 1046 * The returned collection will be serializable if the specified collection 1047 * is serializable. 1048 * 1049 * @param <T> the class of the objects in the collection 1050 * @param c the collection for which an unmodifiable view is to be 1051 * returned. 1052 * @return an unmodifiable view of the specified collection. 1053 */ unmodifiableCollection(Collection<? extends T> c)1054 public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) { 1055 return new UnmodifiableCollection<>(c); 1056 } 1057 1058 /** 1059 * @serial include 1060 */ 1061 static class UnmodifiableCollection<E> implements Collection<E>, Serializable { 1062 private static final long serialVersionUID = 1820017752578914078L; 1063 1064 final Collection<? extends E> c; 1065 UnmodifiableCollection(Collection<? extends E> c)1066 UnmodifiableCollection(Collection<? extends E> c) { 1067 if (c==null) 1068 throw new NullPointerException(); 1069 this.c = c; 1070 } 1071 size()1072 public int size() {return c.size();} isEmpty()1073 public boolean isEmpty() {return c.isEmpty();} contains(Object o)1074 public boolean contains(Object o) {return c.contains(o);} toArray()1075 public Object[] toArray() {return c.toArray();} toArray(T[] a)1076 public <T> T[] toArray(T[] a) {return c.toArray(a);} toString()1077 public String toString() {return c.toString();} 1078 iterator()1079 public Iterator<E> iterator() { 1080 return new Iterator<E>() { 1081 private final Iterator<? extends E> i = c.iterator(); 1082 1083 public boolean hasNext() {return i.hasNext();} 1084 public E next() {return i.next();} 1085 public void remove() { 1086 throw new UnsupportedOperationException(); 1087 } 1088 @Override 1089 public void forEachRemaining(Consumer<? super E> action) { 1090 // Use backing collection version 1091 i.forEachRemaining(action); 1092 } 1093 }; 1094 } 1095 add(E e)1096 public boolean add(E e) { 1097 throw new UnsupportedOperationException(); 1098 } remove(Object o)1099 public boolean remove(Object o) { 1100 throw new UnsupportedOperationException(); 1101 } 1102 containsAll(Collection<?> coll)1103 public boolean containsAll(Collection<?> coll) { 1104 return c.containsAll(coll); 1105 } addAll(Collection<? extends E> coll)1106 public boolean addAll(Collection<? extends E> coll) { 1107 throw new UnsupportedOperationException(); 1108 } removeAll(Collection<?> coll)1109 public boolean removeAll(Collection<?> coll) { 1110 throw new UnsupportedOperationException(); 1111 } retainAll(Collection<?> coll)1112 public boolean retainAll(Collection<?> coll) { 1113 throw new UnsupportedOperationException(); 1114 } clear()1115 public void clear() { 1116 throw new UnsupportedOperationException(); 1117 } 1118 1119 // Override default methods in Collection 1120 @Override forEach(Consumer<? super E> action)1121 public void forEach(Consumer<? super E> action) { 1122 c.forEach(action); 1123 } 1124 @Override removeIf(Predicate<? super E> filter)1125 public boolean removeIf(Predicate<? super E> filter) { 1126 throw new UnsupportedOperationException(); 1127 } 1128 @SuppressWarnings("unchecked") 1129 @Override spliterator()1130 public Spliterator<E> spliterator() { 1131 return (Spliterator<E>)c.spliterator(); 1132 } 1133 @SuppressWarnings("unchecked") 1134 @Override stream()1135 public Stream<E> stream() { 1136 return (Stream<E>)c.stream(); 1137 } 1138 @SuppressWarnings("unchecked") 1139 @Override parallelStream()1140 public Stream<E> parallelStream() { 1141 return (Stream<E>)c.parallelStream(); 1142 } 1143 } 1144 1145 /** 1146 * Returns an unmodifiable view of the specified set. This method allows 1147 * modules to provide users with "read-only" access to internal sets. 1148 * Query operations on the returned set "read through" to the specified 1149 * set, and attempts to modify the returned set, whether direct or via its 1150 * iterator, result in an <tt>UnsupportedOperationException</tt>.<p> 1151 * 1152 * The returned set will be serializable if the specified set 1153 * is serializable. 1154 * 1155 * @param <T> the class of the objects in the set 1156 * @param s the set for which an unmodifiable view is to be returned. 1157 * @return an unmodifiable view of the specified set. 1158 */ unmodifiableSet(Set<? extends T> s)1159 public static <T> Set<T> unmodifiableSet(Set<? extends T> s) { 1160 return new UnmodifiableSet<>(s); 1161 } 1162 1163 /** 1164 * @serial include 1165 */ 1166 static class UnmodifiableSet<E> extends UnmodifiableCollection<E> 1167 implements Set<E>, Serializable { 1168 private static final long serialVersionUID = -9215047833775013803L; 1169 UnmodifiableSet(Set<? extends E> s)1170 UnmodifiableSet(Set<? extends E> s) {super(s);} equals(Object o)1171 public boolean equals(Object o) {return o == this || c.equals(o);} hashCode()1172 public int hashCode() {return c.hashCode();} 1173 } 1174 1175 /** 1176 * Returns an unmodifiable view of the specified sorted set. This method 1177 * allows modules to provide users with "read-only" access to internal 1178 * sorted sets. Query operations on the returned sorted set "read 1179 * through" to the specified sorted set. Attempts to modify the returned 1180 * sorted set, whether direct, via its iterator, or via its 1181 * <tt>subSet</tt>, <tt>headSet</tt>, or <tt>tailSet</tt> views, result in 1182 * an <tt>UnsupportedOperationException</tt>.<p> 1183 * 1184 * The returned sorted set will be serializable if the specified sorted set 1185 * is serializable. 1186 * 1187 * @param <T> the class of the objects in the set 1188 * @param s the sorted set for which an unmodifiable view is to be 1189 * returned. 1190 * @return an unmodifiable view of the specified sorted set. 1191 */ unmodifiableSortedSet(SortedSet<T> s)1192 public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) { 1193 return new UnmodifiableSortedSet<>(s); 1194 } 1195 1196 /** 1197 * @serial include 1198 */ 1199 static class UnmodifiableSortedSet<E> 1200 extends UnmodifiableSet<E> 1201 implements SortedSet<E>, Serializable { 1202 private static final long serialVersionUID = -4929149591599911165L; 1203 private final SortedSet<E> ss; 1204 UnmodifiableSortedSet(SortedSet<E> s)1205 UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;} 1206 comparator()1207 public Comparator<? super E> comparator() {return ss.comparator();} 1208 subSet(E fromElement, E toElement)1209 public SortedSet<E> subSet(E fromElement, E toElement) { 1210 return new UnmodifiableSortedSet<>(ss.subSet(fromElement,toElement)); 1211 } headSet(E toElement)1212 public SortedSet<E> headSet(E toElement) { 1213 return new UnmodifiableSortedSet<>(ss.headSet(toElement)); 1214 } tailSet(E fromElement)1215 public SortedSet<E> tailSet(E fromElement) { 1216 return new UnmodifiableSortedSet<>(ss.tailSet(fromElement)); 1217 } 1218 first()1219 public E first() {return ss.first();} last()1220 public E last() {return ss.last();} 1221 } 1222 1223 /** 1224 * Returns an unmodifiable view of the specified navigable set. This method 1225 * allows modules to provide users with "read-only" access to internal 1226 * navigable sets. Query operations on the returned navigable set "read 1227 * through" to the specified navigable set. Attempts to modify the returned 1228 * navigable set, whether direct, via its iterator, or via its 1229 * {@code subSet}, {@code headSet}, or {@code tailSet} views, result in 1230 * an {@code UnsupportedOperationException}.<p> 1231 * 1232 * The returned navigable set will be serializable if the specified 1233 * navigable set is serializable. 1234 * 1235 * @param <T> the class of the objects in the set 1236 * @param s the navigable set for which an unmodifiable view is to be 1237 * returned 1238 * @return an unmodifiable view of the specified navigable set 1239 * @since 1.8 1240 */ unmodifiableNavigableSet(NavigableSet<T> s)1241 public static <T> NavigableSet<T> unmodifiableNavigableSet(NavigableSet<T> s) { 1242 return new UnmodifiableNavigableSet<>(s); 1243 } 1244 1245 /** 1246 * Wraps a navigable set and disables all of the mutative operations. 1247 * 1248 * @param <E> type of elements 1249 * @serial include 1250 */ 1251 static class UnmodifiableNavigableSet<E> 1252 extends UnmodifiableSortedSet<E> 1253 implements NavigableSet<E>, Serializable { 1254 1255 private static final long serialVersionUID = -6027448201786391929L; 1256 1257 /** 1258 * A singleton empty unmodifiable navigable set used for 1259 * {@link #emptyNavigableSet()}. 1260 * 1261 * @param <E> type of elements, if there were any, and bounds 1262 */ 1263 private static class EmptyNavigableSet<E> extends UnmodifiableNavigableSet<E> 1264 implements Serializable { 1265 private static final long serialVersionUID = -6291252904449939134L; 1266 EmptyNavigableSet()1267 public EmptyNavigableSet() { 1268 super(new TreeSet<E>()); 1269 } 1270 readResolve()1271 private Object readResolve() { return EMPTY_NAVIGABLE_SET; } 1272 } 1273 1274 @SuppressWarnings("rawtypes") 1275 private static final NavigableSet<?> EMPTY_NAVIGABLE_SET = 1276 new EmptyNavigableSet<>(); 1277 1278 /** 1279 * The instance we are protecting. 1280 */ 1281 private final NavigableSet<E> ns; 1282 UnmodifiableNavigableSet(NavigableSet<E> s)1283 UnmodifiableNavigableSet(NavigableSet<E> s) {super(s); ns = s;} 1284 lower(E e)1285 public E lower(E e) { return ns.lower(e); } floor(E e)1286 public E floor(E e) { return ns.floor(e); } ceiling(E e)1287 public E ceiling(E e) { return ns.ceiling(e); } higher(E e)1288 public E higher(E e) { return ns.higher(e); } pollFirst()1289 public E pollFirst() { throw new UnsupportedOperationException(); } pollLast()1290 public E pollLast() { throw new UnsupportedOperationException(); } descendingSet()1291 public NavigableSet<E> descendingSet() 1292 { return new UnmodifiableNavigableSet<>(ns.descendingSet()); } descendingIterator()1293 public Iterator<E> descendingIterator() 1294 { return descendingSet().iterator(); } 1295 subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive)1296 public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) { 1297 return new UnmodifiableNavigableSet<>( 1298 ns.subSet(fromElement, fromInclusive, toElement, toInclusive)); 1299 } 1300 headSet(E toElement, boolean inclusive)1301 public NavigableSet<E> headSet(E toElement, boolean inclusive) { 1302 return new UnmodifiableNavigableSet<>( 1303 ns.headSet(toElement, inclusive)); 1304 } 1305 tailSet(E fromElement, boolean inclusive)1306 public NavigableSet<E> tailSet(E fromElement, boolean inclusive) { 1307 return new UnmodifiableNavigableSet<>( 1308 ns.tailSet(fromElement, inclusive)); 1309 } 1310 } 1311 1312 /** 1313 * Returns an unmodifiable view of the specified list. This method allows 1314 * modules to provide users with "read-only" access to internal 1315 * lists. Query operations on the returned list "read through" to the 1316 * specified list, and attempts to modify the returned list, whether 1317 * direct or via its iterator, result in an 1318 * <tt>UnsupportedOperationException</tt>.<p> 1319 * 1320 * The returned list will be serializable if the specified list 1321 * is serializable. Similarly, the returned list will implement 1322 * {@link RandomAccess} if the specified list does. 1323 * 1324 * @param <T> the class of the objects in the list 1325 * @param list the list for which an unmodifiable view is to be returned. 1326 * @return an unmodifiable view of the specified list. 1327 */ unmodifiableList(List<? extends T> list)1328 public static <T> List<T> unmodifiableList(List<? extends T> list) { 1329 return (list instanceof RandomAccess ? 1330 new UnmodifiableRandomAccessList<>(list) : 1331 new UnmodifiableList<>(list)); 1332 } 1333 1334 /** 1335 * @serial include 1336 */ 1337 static class UnmodifiableList<E> extends UnmodifiableCollection<E> 1338 implements List<E> { 1339 private static final long serialVersionUID = -283967356065247728L; 1340 1341 final List<? extends E> list; 1342 UnmodifiableList(List<? extends E> list)1343 UnmodifiableList(List<? extends E> list) { 1344 super(list); 1345 this.list = list; 1346 } 1347 equals(Object o)1348 public boolean equals(Object o) {return o == this || list.equals(o);} hashCode()1349 public int hashCode() {return list.hashCode();} 1350 get(int index)1351 public E get(int index) {return list.get(index);} set(int index, E element)1352 public E set(int index, E element) { 1353 throw new UnsupportedOperationException(); 1354 } add(int index, E element)1355 public void add(int index, E element) { 1356 throw new UnsupportedOperationException(); 1357 } remove(int index)1358 public E remove(int index) { 1359 throw new UnsupportedOperationException(); 1360 } indexOf(Object o)1361 public int indexOf(Object o) {return list.indexOf(o);} lastIndexOf(Object o)1362 public int lastIndexOf(Object o) {return list.lastIndexOf(o);} addAll(int index, Collection<? extends E> c)1363 public boolean addAll(int index, Collection<? extends E> c) { 1364 throw new UnsupportedOperationException(); 1365 } 1366 1367 @Override replaceAll(UnaryOperator<E> operator)1368 public void replaceAll(UnaryOperator<E> operator) { 1369 throw new UnsupportedOperationException(); 1370 } 1371 @Override sort(Comparator<? super E> c)1372 public void sort(Comparator<? super E> c) { 1373 throw new UnsupportedOperationException(); 1374 } 1375 listIterator()1376 public ListIterator<E> listIterator() {return listIterator(0);} 1377 listIterator(final int index)1378 public ListIterator<E> listIterator(final int index) { 1379 return new ListIterator<E>() { 1380 private final ListIterator<? extends E> i 1381 = list.listIterator(index); 1382 1383 public boolean hasNext() {return i.hasNext();} 1384 public E next() {return i.next();} 1385 public boolean hasPrevious() {return i.hasPrevious();} 1386 public E previous() {return i.previous();} 1387 public int nextIndex() {return i.nextIndex();} 1388 public int previousIndex() {return i.previousIndex();} 1389 1390 public void remove() { 1391 throw new UnsupportedOperationException(); 1392 } 1393 public void set(E e) { 1394 throw new UnsupportedOperationException(); 1395 } 1396 public void add(E e) { 1397 throw new UnsupportedOperationException(); 1398 } 1399 1400 @Override 1401 public void forEachRemaining(Consumer<? super E> action) { 1402 i.forEachRemaining(action); 1403 } 1404 }; 1405 } 1406 subList(int fromIndex, int toIndex)1407 public List<E> subList(int fromIndex, int toIndex) { 1408 return new UnmodifiableList<>(list.subList(fromIndex, toIndex)); 1409 } 1410 1411 /** 1412 * UnmodifiableRandomAccessList instances are serialized as 1413 * UnmodifiableList instances to allow them to be deserialized 1414 * in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList). 1415 * This method inverts the transformation. As a beneficial 1416 * side-effect, it also grafts the RandomAccess marker onto 1417 * UnmodifiableList instances that were serialized in pre-1.4 JREs. 1418 * 1419 * Note: Unfortunately, UnmodifiableRandomAccessList instances 1420 * serialized in 1.4.1 and deserialized in 1.4 will become 1421 * UnmodifiableList instances, as this method was missing in 1.4. 1422 */ readResolve()1423 private Object readResolve() { 1424 return (list instanceof RandomAccess 1425 ? new UnmodifiableRandomAccessList<>(list) 1426 : this); 1427 } 1428 } 1429 1430 /** 1431 * @serial include 1432 */ 1433 static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E> 1434 implements RandomAccess 1435 { 1436 UnmodifiableRandomAccessList(List<? extends E> list) { 1437 super(list); 1438 } 1439 1440 public List<E> subList(int fromIndex, int toIndex) { 1441 return new UnmodifiableRandomAccessList<>( 1442 list.subList(fromIndex, toIndex)); 1443 } 1444 1445 private static final long serialVersionUID = -2542308836966382001L; 1446 1447 /** 1448 * Allows instances to be deserialized in pre-1.4 JREs (which do 1449 * not have UnmodifiableRandomAccessList). UnmodifiableList has 1450 * a readResolve method that inverts this transformation upon 1451 * deserialization. 1452 */ 1453 private Object writeReplace() { 1454 return new UnmodifiableList<>(list); 1455 } 1456 } 1457 1458 /** 1459 * Returns an unmodifiable view of the specified map. This method 1460 * allows modules to provide users with "read-only" access to internal 1461 * maps. Query operations on the returned map "read through" 1462 * to the specified map, and attempts to modify the returned 1463 * map, whether direct or via its collection views, result in an 1464 * <tt>UnsupportedOperationException</tt>.<p> 1465 * 1466 * The returned map will be serializable if the specified map 1467 * is serializable. 1468 * 1469 * @param <K> the class of the map keys 1470 * @param <V> the class of the map values 1471 * @param m the map for which an unmodifiable view is to be returned. 1472 * @return an unmodifiable view of the specified map. 1473 */ 1474 public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) { 1475 return new UnmodifiableMap<>(m); 1476 } 1477 1478 /** 1479 * @serial include 1480 */ 1481 private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable { 1482 private static final long serialVersionUID = -1034234728574286014L; 1483 1484 private final Map<? extends K, ? extends V> m; 1485 1486 UnmodifiableMap(Map<? extends K, ? extends V> m) { 1487 if (m==null) 1488 throw new NullPointerException(); 1489 this.m = m; 1490 } 1491 1492 public int size() {return m.size();} 1493 public boolean isEmpty() {return m.isEmpty();} 1494 public boolean containsKey(Object key) {return m.containsKey(key);} 1495 public boolean containsValue(Object val) {return m.containsValue(val);} 1496 public V get(Object key) {return m.get(key);} 1497 1498 public V put(K key, V value) { 1499 throw new UnsupportedOperationException(); 1500 } 1501 public V remove(Object key) { 1502 throw new UnsupportedOperationException(); 1503 } 1504 public void putAll(Map<? extends K, ? extends V> m) { 1505 throw new UnsupportedOperationException(); 1506 } 1507 public void clear() { 1508 throw new UnsupportedOperationException(); 1509 } 1510 1511 private transient Set<K> keySet; 1512 private transient Set<Map.Entry<K,V>> entrySet; 1513 private transient Collection<V> values; 1514 1515 public Set<K> keySet() { 1516 if (keySet==null) 1517 keySet = unmodifiableSet(m.keySet()); 1518 return keySet; 1519 } 1520 1521 public Set<Map.Entry<K,V>> entrySet() { 1522 if (entrySet==null) 1523 entrySet = new UnmodifiableEntrySet<>(m.entrySet()); 1524 return entrySet; 1525 } 1526 1527 public Collection<V> values() { 1528 if (values==null) 1529 values = unmodifiableCollection(m.values()); 1530 return values; 1531 } 1532 1533 public boolean equals(Object o) {return o == this || m.equals(o);} 1534 public int hashCode() {return m.hashCode();} 1535 public String toString() {return m.toString();} 1536 1537 // Override default methods in Map 1538 @Override 1539 @SuppressWarnings("unchecked") 1540 public V getOrDefault(Object k, V defaultValue) { 1541 // Safe cast as we don't change the value 1542 return ((Map<K, V>)m).getOrDefault(k, defaultValue); 1543 } 1544 1545 @Override 1546 public void forEach(BiConsumer<? super K, ? super V> action) { 1547 m.forEach(action); 1548 } 1549 1550 @Override 1551 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 1552 throw new UnsupportedOperationException(); 1553 } 1554 1555 @Override 1556 public V putIfAbsent(K key, V value) { 1557 throw new UnsupportedOperationException(); 1558 } 1559 1560 @Override 1561 public boolean remove(Object key, Object value) { 1562 throw new UnsupportedOperationException(); 1563 } 1564 1565 @Override 1566 public boolean replace(K key, V oldValue, V newValue) { 1567 throw new UnsupportedOperationException(); 1568 } 1569 1570 @Override 1571 public V replace(K key, V value) { 1572 throw new UnsupportedOperationException(); 1573 } 1574 1575 @Override 1576 public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) { 1577 throw new UnsupportedOperationException(); 1578 } 1579 1580 @Override 1581 public V computeIfPresent(K key, 1582 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 1583 throw new UnsupportedOperationException(); 1584 } 1585 1586 @Override 1587 public V compute(K key, 1588 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 1589 throw new UnsupportedOperationException(); 1590 } 1591 1592 @Override 1593 public V merge(K key, V value, 1594 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 1595 throw new UnsupportedOperationException(); 1596 } 1597 1598 /** 1599 * We need this class in addition to UnmodifiableSet as 1600 * Map.Entries themselves permit modification of the backing Map 1601 * via their setValue operation. This class is subtle: there are 1602 * many possible attacks that must be thwarted. 1603 * 1604 * @serial include 1605 */ 1606 static class UnmodifiableEntrySet<K,V> 1607 extends UnmodifiableSet<Map.Entry<K,V>> { 1608 private static final long serialVersionUID = 7854390611657943733L; 1609 1610 @SuppressWarnings({"unchecked", "rawtypes"}) 1611 UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) { 1612 // Need to cast to raw in order to work around a limitation in the type system 1613 super((Set)s); 1614 } 1615 1616 static <K, V> Consumer<Map.Entry<K, V>> entryConsumer(Consumer<? super Entry<K, V>> action) { 1617 return e -> action.accept(new UnmodifiableEntry<>(e)); 1618 } 1619 1620 public void forEach(Consumer<? super Entry<K, V>> action) { 1621 Objects.requireNonNull(action); 1622 c.forEach(entryConsumer(action)); 1623 } 1624 1625 static final class UnmodifiableEntrySetSpliterator<K, V> 1626 implements Spliterator<Entry<K,V>> { 1627 final Spliterator<Map.Entry<K, V>> s; 1628 1629 UnmodifiableEntrySetSpliterator(Spliterator<Entry<K, V>> s) { 1630 this.s = s; 1631 } 1632 1633 @Override 1634 public boolean tryAdvance(Consumer<? super Entry<K, V>> action) { 1635 Objects.requireNonNull(action); 1636 return s.tryAdvance(entryConsumer(action)); 1637 } 1638 1639 @Override 1640 public void forEachRemaining(Consumer<? super Entry<K, V>> action) { 1641 Objects.requireNonNull(action); 1642 s.forEachRemaining(entryConsumer(action)); 1643 } 1644 1645 @Override 1646 public Spliterator<Entry<K, V>> trySplit() { 1647 Spliterator<Entry<K, V>> split = s.trySplit(); 1648 return split == null 1649 ? null 1650 : new UnmodifiableEntrySetSpliterator<>(split); 1651 } 1652 1653 @Override 1654 public long estimateSize() { 1655 return s.estimateSize(); 1656 } 1657 1658 @Override 1659 public long getExactSizeIfKnown() { 1660 return s.getExactSizeIfKnown(); 1661 } 1662 1663 @Override 1664 public int characteristics() { 1665 return s.characteristics(); 1666 } 1667 1668 @Override 1669 public boolean hasCharacteristics(int characteristics) { 1670 return s.hasCharacteristics(characteristics); 1671 } 1672 1673 @Override 1674 public Comparator<? super Entry<K, V>> getComparator() { 1675 return s.getComparator(); 1676 } 1677 } 1678 1679 @SuppressWarnings("unchecked") 1680 public Spliterator<Entry<K,V>> spliterator() { 1681 return new UnmodifiableEntrySetSpliterator<>( 1682 (Spliterator<Map.Entry<K, V>>) c.spliterator()); 1683 } 1684 1685 @Override 1686 public Stream<Entry<K,V>> stream() { 1687 return StreamSupport.stream(spliterator(), false); 1688 } 1689 1690 @Override 1691 public Stream<Entry<K,V>> parallelStream() { 1692 return StreamSupport.stream(spliterator(), true); 1693 } 1694 1695 public Iterator<Map.Entry<K,V>> iterator() { 1696 return new Iterator<Map.Entry<K,V>>() { 1697 private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator(); 1698 1699 public boolean hasNext() { 1700 return i.hasNext(); 1701 } 1702 public Map.Entry<K,V> next() { 1703 return new UnmodifiableEntry<>(i.next()); 1704 } 1705 public void remove() { 1706 throw new UnsupportedOperationException(); 1707 } 1708 // Android-note: This seems pretty inconsistent. Unlike other subclasses, we aren't 1709 // delegating to the subclass iterator here. Seems like an oversight. 1710 }; 1711 } 1712 1713 @SuppressWarnings("unchecked") 1714 public Object[] toArray() { 1715 Object[] a = c.toArray(); 1716 for (int i=0; i<a.length; i++) 1717 a[i] = new UnmodifiableEntry<>((Map.Entry<? extends K, ? extends V>)a[i]); 1718 return a; 1719 } 1720 1721 @SuppressWarnings("unchecked") 1722 public <T> T[] toArray(T[] a) { 1723 // We don't pass a to c.toArray, to avoid window of 1724 // vulnerability wherein an unscrupulous multithreaded client 1725 // could get his hands on raw (unwrapped) Entries from c. 1726 Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0)); 1727 1728 for (int i=0; i<arr.length; i++) 1729 arr[i] = new UnmodifiableEntry<>((Map.Entry<? extends K, ? extends V>)arr[i]); 1730 1731 if (arr.length > a.length) 1732 return (T[])arr; 1733 1734 System.arraycopy(arr, 0, a, 0, arr.length); 1735 if (a.length > arr.length) 1736 a[arr.length] = null; 1737 return a; 1738 } 1739 1740 /** 1741 * This method is overridden to protect the backing set against 1742 * an object with a nefarious equals function that senses 1743 * that the equality-candidate is Map.Entry and calls its 1744 * setValue method. 1745 */ 1746 public boolean contains(Object o) { 1747 if (!(o instanceof Map.Entry)) 1748 return false; 1749 return c.contains( 1750 new UnmodifiableEntry<>((Map.Entry<?,?>) o)); 1751 } 1752 1753 /** 1754 * The next two methods are overridden to protect against 1755 * an unscrupulous List whose contains(Object o) method senses 1756 * when o is a Map.Entry, and calls o.setValue. 1757 */ 1758 public boolean containsAll(Collection<?> coll) { 1759 for (Object e : coll) { 1760 if (!contains(e)) // Invokes safe contains() above 1761 return false; 1762 } 1763 return true; 1764 } 1765 public boolean equals(Object o) { 1766 if (o == this) 1767 return true; 1768 1769 if (!(o instanceof Set)) 1770 return false; 1771 Set<?> s = (Set<?>) o; 1772 if (s.size() != c.size()) 1773 return false; 1774 return containsAll(s); // Invokes safe containsAll() above 1775 } 1776 1777 /** 1778 * This "wrapper class" serves two purposes: it prevents 1779 * the client from modifying the backing Map, by short-circuiting 1780 * the setValue method, and it protects the backing Map against 1781 * an ill-behaved Map.Entry that attempts to modify another 1782 * Map Entry when asked to perform an equality check. 1783 */ 1784 private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> { 1785 private Map.Entry<? extends K, ? extends V> e; 1786 1787 UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) 1788 {this.e = Objects.requireNonNull(e);} 1789 1790 public K getKey() {return e.getKey();} 1791 public V getValue() {return e.getValue();} 1792 public V setValue(V value) { 1793 throw new UnsupportedOperationException(); 1794 } 1795 public int hashCode() {return e.hashCode();} 1796 public boolean equals(Object o) { 1797 if (this == o) 1798 return true; 1799 if (!(o instanceof Map.Entry)) 1800 return false; 1801 Map.Entry<?,?> t = (Map.Entry<?,?>)o; 1802 return eq(e.getKey(), t.getKey()) && 1803 eq(e.getValue(), t.getValue()); 1804 } 1805 public String toString() {return e.toString();} 1806 } 1807 } 1808 } 1809 1810 /** 1811 * Returns an unmodifiable view of the specified sorted map. This method 1812 * allows modules to provide users with "read-only" access to internal 1813 * sorted maps. Query operations on the returned sorted map "read through" 1814 * to the specified sorted map. Attempts to modify the returned 1815 * sorted map, whether direct, via its collection views, or via its 1816 * <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in 1817 * an <tt>UnsupportedOperationException</tt>.<p> 1818 * 1819 * The returned sorted map will be serializable if the specified sorted map 1820 * is serializable. 1821 * 1822 * @param <K> the class of the map keys 1823 * @param <V> the class of the map values 1824 * @param m the sorted map for which an unmodifiable view is to be 1825 * returned. 1826 * @return an unmodifiable view of the specified sorted map. 1827 */ 1828 public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) { 1829 return new UnmodifiableSortedMap<>(m); 1830 } 1831 1832 /** 1833 * @serial include 1834 */ 1835 static class UnmodifiableSortedMap<K,V> 1836 extends UnmodifiableMap<K,V> 1837 implements SortedMap<K,V>, Serializable { 1838 private static final long serialVersionUID = -8806743815996713206L; 1839 1840 private final SortedMap<K, ? extends V> sm; 1841 1842 UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m; } 1843 public Comparator<? super K> comparator() { return sm.comparator(); } 1844 public SortedMap<K,V> subMap(K fromKey, K toKey) 1845 { return new UnmodifiableSortedMap<>(sm.subMap(fromKey, toKey)); } 1846 public SortedMap<K,V> headMap(K toKey) 1847 { return new UnmodifiableSortedMap<>(sm.headMap(toKey)); } 1848 public SortedMap<K,V> tailMap(K fromKey) 1849 { return new UnmodifiableSortedMap<>(sm.tailMap(fromKey)); } 1850 public K firstKey() { return sm.firstKey(); } 1851 public K lastKey() { return sm.lastKey(); } 1852 } 1853 1854 /** 1855 * Returns an unmodifiable view of the specified navigable map. This method 1856 * allows modules to provide users with "read-only" access to internal 1857 * navigable maps. Query operations on the returned navigable map "read 1858 * through" to the specified navigable map. Attempts to modify the returned 1859 * navigable map, whether direct, via its collection views, or via its 1860 * {@code subMap}, {@code headMap}, or {@code tailMap} views, result in 1861 * an {@code UnsupportedOperationException}.<p> 1862 * 1863 * The returned navigable map will be serializable if the specified 1864 * navigable map is serializable. 1865 * 1866 * @param <K> the class of the map keys 1867 * @param <V> the class of the map values 1868 * @param m the navigable map for which an unmodifiable view is to be 1869 * returned 1870 * @return an unmodifiable view of the specified navigable map 1871 * @since 1.8 1872 */ 1873 public static <K,V> NavigableMap<K,V> unmodifiableNavigableMap(NavigableMap<K, ? extends V> m) { 1874 return new UnmodifiableNavigableMap<>(m); 1875 } 1876 1877 /** 1878 * @serial include 1879 */ 1880 static class UnmodifiableNavigableMap<K,V> 1881 extends UnmodifiableSortedMap<K,V> 1882 implements NavigableMap<K,V>, Serializable { 1883 private static final long serialVersionUID = -4858195264774772197L; 1884 1885 /** 1886 * A class for the {@link EMPTY_NAVIGABLE_MAP} which needs readResolve 1887 * to preserve singleton property. 1888 * 1889 * @param <K> type of keys, if there were any, and of bounds 1890 * @param <V> type of values, if there were any 1891 */ 1892 private static class EmptyNavigableMap<K,V> extends UnmodifiableNavigableMap<K,V> 1893 implements Serializable { 1894 1895 private static final long serialVersionUID = -2239321462712562324L; 1896 1897 EmptyNavigableMap() { super(new TreeMap<K,V>()); } 1898 1899 @Override 1900 public NavigableSet<K> navigableKeySet() 1901 { return emptyNavigableSet(); } 1902 1903 private Object readResolve() { return EMPTY_NAVIGABLE_MAP; } 1904 } 1905 1906 /** 1907 * Singleton for {@link emptyNavigableMap()} which is also immutable. 1908 */ 1909 private static final EmptyNavigableMap<?,?> EMPTY_NAVIGABLE_MAP = 1910 new EmptyNavigableMap<>(); 1911 1912 /** 1913 * The instance we wrap and protect. 1914 */ 1915 private final NavigableMap<K, ? extends V> nm; 1916 1917 UnmodifiableNavigableMap(NavigableMap<K, ? extends V> m) 1918 {super(m); nm = m;} 1919 1920 public K lowerKey(K key) { return nm.lowerKey(key); } 1921 public K floorKey(K key) { return nm.floorKey(key); } 1922 public K ceilingKey(K key) { return nm.ceilingKey(key); } 1923 public K higherKey(K key) { return nm.higherKey(key); } 1924 1925 @SuppressWarnings("unchecked") 1926 public Entry<K, V> lowerEntry(K key) { 1927 Entry<K,V> lower = (Entry<K, V>) nm.lowerEntry(key); 1928 return (null != lower) 1929 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(lower) 1930 : null; 1931 } 1932 1933 @SuppressWarnings("unchecked") 1934 public Entry<K, V> floorEntry(K key) { 1935 Entry<K,V> floor = (Entry<K, V>) nm.floorEntry(key); 1936 return (null != floor) 1937 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(floor) 1938 : null; 1939 } 1940 1941 @SuppressWarnings("unchecked") 1942 public Entry<K, V> ceilingEntry(K key) { 1943 Entry<K,V> ceiling = (Entry<K, V>) nm.ceilingEntry(key); 1944 return (null != ceiling) 1945 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(ceiling) 1946 : null; 1947 } 1948 1949 1950 @SuppressWarnings("unchecked") 1951 public Entry<K, V> higherEntry(K key) { 1952 Entry<K,V> higher = (Entry<K, V>) nm.higherEntry(key); 1953 return (null != higher) 1954 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(higher) 1955 : null; 1956 } 1957 1958 @SuppressWarnings("unchecked") 1959 public Entry<K, V> firstEntry() { 1960 Entry<K,V> first = (Entry<K, V>) nm.firstEntry(); 1961 return (null != first) 1962 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(first) 1963 : null; 1964 } 1965 1966 @SuppressWarnings("unchecked") 1967 public Entry<K, V> lastEntry() { 1968 Entry<K,V> last = (Entry<K, V>) nm.lastEntry(); 1969 return (null != last) 1970 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(last) 1971 : null; 1972 } 1973 1974 public Entry<K, V> pollFirstEntry() 1975 { throw new UnsupportedOperationException(); } 1976 public Entry<K, V> pollLastEntry() 1977 { throw new UnsupportedOperationException(); } 1978 public NavigableMap<K, V> descendingMap() 1979 { return unmodifiableNavigableMap(nm.descendingMap()); } 1980 public NavigableSet<K> navigableKeySet() 1981 { return unmodifiableNavigableSet(nm.navigableKeySet()); } 1982 public NavigableSet<K> descendingKeySet() 1983 { return unmodifiableNavigableSet(nm.descendingKeySet()); } 1984 1985 public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) { 1986 return unmodifiableNavigableMap( 1987 nm.subMap(fromKey, fromInclusive, toKey, toInclusive)); 1988 } 1989 1990 public NavigableMap<K, V> headMap(K toKey, boolean inclusive) 1991 { return unmodifiableNavigableMap(nm.headMap(toKey, inclusive)); } 1992 public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) 1993 { return unmodifiableNavigableMap(nm.tailMap(fromKey, inclusive)); } 1994 } 1995 1996 // Synch Wrappers 1997 1998 /** 1999 * Returns a synchronized (thread-safe) collection backed by the specified 2000 * collection. In order to guarantee serial access, it is critical that 2001 * <strong>all</strong> access to the backing collection is accomplished 2002 * through the returned collection.<p> 2003 * 2004 * It is imperative that the user manually synchronize on the returned 2005 * collection when traversing it via {@link Iterator}, {@link Spliterator} 2006 * or {@link Stream}: 2007 * <pre> 2008 * Collection c = Collections.synchronizedCollection(myCollection); 2009 * ... 2010 * synchronized (c) { 2011 * Iterator i = c.iterator(); // Must be in the synchronized block 2012 * while (i.hasNext()) 2013 * foo(i.next()); 2014 * } 2015 * </pre> 2016 * Failure to follow this advice may result in non-deterministic behavior. 2017 * 2018 * <p>The returned collection does <i>not</i> pass the {@code hashCode} 2019 * and {@code equals} operations through to the backing collection, but 2020 * relies on {@code Object}'s equals and hashCode methods. This is 2021 * necessary to preserve the contracts of these operations in the case 2022 * that the backing collection is a set or a list.<p> 2023 * 2024 * The returned collection will be serializable if the specified collection 2025 * is serializable. 2026 * 2027 * @param <T> the class of the objects in the collection 2028 * @param c the collection to be "wrapped" in a synchronized collection. 2029 * @return a synchronized view of the specified collection. 2030 */ 2031 public static <T> Collection<T> synchronizedCollection(Collection<T> c) { 2032 return new SynchronizedCollection<>(c); 2033 } 2034 2035 static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) { 2036 return new SynchronizedCollection<>(c, mutex); 2037 } 2038 2039 /** 2040 * @serial include 2041 */ 2042 static class SynchronizedCollection<E> implements Collection<E>, Serializable { 2043 private static final long serialVersionUID = 3053995032091335093L; 2044 2045 final Collection<E> c; // Backing Collection 2046 final Object mutex; // Object on which to synchronize 2047 2048 SynchronizedCollection(Collection<E> c) { 2049 this.c = Objects.requireNonNull(c); 2050 mutex = this; 2051 } 2052 2053 SynchronizedCollection(Collection<E> c, Object mutex) { 2054 this.c = Objects.requireNonNull(c); 2055 this.mutex = Objects.requireNonNull(mutex); 2056 } 2057 2058 public int size() { 2059 synchronized (mutex) {return c.size();} 2060 } 2061 public boolean isEmpty() { 2062 synchronized (mutex) {return c.isEmpty();} 2063 } 2064 public boolean contains(Object o) { 2065 synchronized (mutex) {return c.contains(o);} 2066 } 2067 public Object[] toArray() { 2068 synchronized (mutex) {return c.toArray();} 2069 } 2070 public <T> T[] toArray(T[] a) { 2071 synchronized (mutex) {return c.toArray(a);} 2072 } 2073 2074 public Iterator<E> iterator() { 2075 return c.iterator(); // Must be manually synched by user! 2076 } 2077 2078 public boolean add(E e) { 2079 synchronized (mutex) {return c.add(e);} 2080 } 2081 public boolean remove(Object o) { 2082 synchronized (mutex) {return c.remove(o);} 2083 } 2084 2085 public boolean containsAll(Collection<?> coll) { 2086 synchronized (mutex) {return c.containsAll(coll);} 2087 } 2088 public boolean addAll(Collection<? extends E> coll) { 2089 synchronized (mutex) {return c.addAll(coll);} 2090 } 2091 public boolean removeAll(Collection<?> coll) { 2092 synchronized (mutex) {return c.removeAll(coll);} 2093 } 2094 public boolean retainAll(Collection<?> coll) { 2095 synchronized (mutex) {return c.retainAll(coll);} 2096 } 2097 public void clear() { 2098 synchronized (mutex) {c.clear();} 2099 } 2100 public String toString() { 2101 synchronized (mutex) {return c.toString();} 2102 } 2103 // Override default methods in Collection 2104 @Override 2105 public void forEach(Consumer<? super E> consumer) { 2106 synchronized (mutex) {c.forEach(consumer);} 2107 } 2108 @Override 2109 public boolean removeIf(Predicate<? super E> filter) { 2110 synchronized (mutex) {return c.removeIf(filter);} 2111 } 2112 @Override 2113 public Spliterator<E> spliterator() { 2114 return c.spliterator(); // Must be manually synched by user! 2115 } 2116 @Override 2117 public Stream<E> stream() { 2118 return c.stream(); // Must be manually synched by user! 2119 } 2120 @Override 2121 public Stream<E> parallelStream() { 2122 return c.parallelStream(); // Must be manually synched by user! 2123 } 2124 private void writeObject(ObjectOutputStream s) throws IOException { 2125 synchronized (mutex) {s.defaultWriteObject();} 2126 } 2127 } 2128 2129 /** 2130 * Returns a synchronized (thread-safe) set backed by the specified 2131 * set. In order to guarantee serial access, it is critical that 2132 * <strong>all</strong> access to the backing set is accomplished 2133 * through the returned set.<p> 2134 * 2135 * It is imperative that the user manually synchronize on the returned 2136 * set when iterating over it: 2137 * <pre> 2138 * Set s = Collections.synchronizedSet(new HashSet()); 2139 * ... 2140 * synchronized (s) { 2141 * Iterator i = s.iterator(); // Must be in the synchronized block 2142 * while (i.hasNext()) 2143 * foo(i.next()); 2144 * } 2145 * </pre> 2146 * Failure to follow this advice may result in non-deterministic behavior. 2147 * 2148 * <p>The returned set will be serializable if the specified set is 2149 * serializable. 2150 * 2151 * @param <T> the class of the objects in the set 2152 * @param s the set to be "wrapped" in a synchronized set. 2153 * @return a synchronized view of the specified set. 2154 */ 2155 public static <T> Set<T> synchronizedSet(Set<T> s) { 2156 return new SynchronizedSet<>(s); 2157 } 2158 2159 static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) { 2160 return new SynchronizedSet<>(s, mutex); 2161 } 2162 2163 /** 2164 * @serial include 2165 */ 2166 static class SynchronizedSet<E> 2167 extends SynchronizedCollection<E> 2168 implements Set<E> { 2169 private static final long serialVersionUID = 487447009682186044L; 2170 2171 SynchronizedSet(Set<E> s) { 2172 super(s); 2173 } 2174 SynchronizedSet(Set<E> s, Object mutex) { 2175 super(s, mutex); 2176 } 2177 2178 public boolean equals(Object o) { 2179 if (this == o) 2180 return true; 2181 synchronized (mutex) {return c.equals(o);} 2182 } 2183 public int hashCode() { 2184 synchronized (mutex) {return c.hashCode();} 2185 } 2186 } 2187 2188 /** 2189 * Returns a synchronized (thread-safe) sorted set backed by the specified 2190 * sorted set. In order to guarantee serial access, it is critical that 2191 * <strong>all</strong> access to the backing sorted set is accomplished 2192 * through the returned sorted set (or its views).<p> 2193 * 2194 * It is imperative that the user manually synchronize on the returned 2195 * sorted set when iterating over it or any of its <tt>subSet</tt>, 2196 * <tt>headSet</tt>, or <tt>tailSet</tt> views. 2197 * <pre> 2198 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet()); 2199 * ... 2200 * synchronized (s) { 2201 * Iterator i = s.iterator(); // Must be in the synchronized block 2202 * while (i.hasNext()) 2203 * foo(i.next()); 2204 * } 2205 * </pre> 2206 * or: 2207 * <pre> 2208 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet()); 2209 * SortedSet s2 = s.headSet(foo); 2210 * ... 2211 * synchronized (s) { // Note: s, not s2!!! 2212 * Iterator i = s2.iterator(); // Must be in the synchronized block 2213 * while (i.hasNext()) 2214 * foo(i.next()); 2215 * } 2216 * </pre> 2217 * Failure to follow this advice may result in non-deterministic behavior. 2218 * 2219 * <p>The returned sorted set will be serializable if the specified 2220 * sorted set is serializable. 2221 * 2222 * @param <T> the class of the objects in the set 2223 * @param s the sorted set to be "wrapped" in a synchronized sorted set. 2224 * @return a synchronized view of the specified sorted set. 2225 */ 2226 public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) { 2227 return new SynchronizedSortedSet<>(s); 2228 } 2229 2230 /** 2231 * @serial include 2232 */ 2233 static class SynchronizedSortedSet<E> 2234 extends SynchronizedSet<E> 2235 implements SortedSet<E> 2236 { 2237 private static final long serialVersionUID = 8695801310862127406L; 2238 2239 private final SortedSet<E> ss; 2240 2241 SynchronizedSortedSet(SortedSet<E> s) { 2242 super(s); 2243 ss = s; 2244 } 2245 SynchronizedSortedSet(SortedSet<E> s, Object mutex) { 2246 super(s, mutex); 2247 ss = s; 2248 } 2249 2250 public Comparator<? super E> comparator() { 2251 synchronized (mutex) {return ss.comparator();} 2252 } 2253 2254 public SortedSet<E> subSet(E fromElement, E toElement) { 2255 synchronized (mutex) { 2256 return new SynchronizedSortedSet<>( 2257 ss.subSet(fromElement, toElement), mutex); 2258 } 2259 } 2260 public SortedSet<E> headSet(E toElement) { 2261 synchronized (mutex) { 2262 return new SynchronizedSortedSet<>(ss.headSet(toElement), mutex); 2263 } 2264 } 2265 public SortedSet<E> tailSet(E fromElement) { 2266 synchronized (mutex) { 2267 return new SynchronizedSortedSet<>(ss.tailSet(fromElement),mutex); 2268 } 2269 } 2270 2271 public E first() { 2272 synchronized (mutex) {return ss.first();} 2273 } 2274 public E last() { 2275 synchronized (mutex) {return ss.last();} 2276 } 2277 } 2278 2279 /** 2280 * Returns a synchronized (thread-safe) navigable set backed by the 2281 * specified navigable set. In order to guarantee serial access, it is 2282 * critical that <strong>all</strong> access to the backing navigable set is 2283 * accomplished through the returned navigable set (or its views).<p> 2284 * 2285 * It is imperative that the user manually synchronize on the returned 2286 * navigable set when iterating over it or any of its {@code subSet}, 2287 * {@code headSet}, or {@code tailSet} views. 2288 * <pre> 2289 * NavigableSet s = Collections.synchronizedNavigableSet(new TreeSet()); 2290 * ... 2291 * synchronized (s) { 2292 * Iterator i = s.iterator(); // Must be in the synchronized block 2293 * while (i.hasNext()) 2294 * foo(i.next()); 2295 * } 2296 * </pre> 2297 * or: 2298 * <pre> 2299 * NavigableSet s = Collections.synchronizedNavigableSet(new TreeSet()); 2300 * NavigableSet s2 = s.headSet(foo, true); 2301 * ... 2302 * synchronized (s) { // Note: s, not s2!!! 2303 * Iterator i = s2.iterator(); // Must be in the synchronized block 2304 * while (i.hasNext()) 2305 * foo(i.next()); 2306 * } 2307 * </pre> 2308 * Failure to follow this advice may result in non-deterministic behavior. 2309 * 2310 * <p>The returned navigable set will be serializable if the specified 2311 * navigable set is serializable. 2312 * 2313 * @param <T> the class of the objects in the set 2314 * @param s the navigable set to be "wrapped" in a synchronized navigable 2315 * set 2316 * @return a synchronized view of the specified navigable set 2317 * @since 1.8 2318 */ 2319 public static <T> NavigableSet<T> synchronizedNavigableSet(NavigableSet<T> s) { 2320 return new SynchronizedNavigableSet<>(s); 2321 } 2322 2323 /** 2324 * @serial include 2325 */ 2326 static class SynchronizedNavigableSet<E> 2327 extends SynchronizedSortedSet<E> 2328 implements NavigableSet<E> 2329 { 2330 private static final long serialVersionUID = -5505529816273629798L; 2331 2332 private final NavigableSet<E> ns; 2333 2334 SynchronizedNavigableSet(NavigableSet<E> s) { 2335 super(s); 2336 ns = s; 2337 } 2338 2339 SynchronizedNavigableSet(NavigableSet<E> s, Object mutex) { 2340 super(s, mutex); 2341 ns = s; 2342 } 2343 public E lower(E e) { synchronized (mutex) {return ns.lower(e);} } 2344 public E floor(E e) { synchronized (mutex) {return ns.floor(e);} } 2345 public E ceiling(E e) { synchronized (mutex) {return ns.ceiling(e);} } 2346 public E higher(E e) { synchronized (mutex) {return ns.higher(e);} } 2347 public E pollFirst() { synchronized (mutex) {return ns.pollFirst();} } 2348 public E pollLast() { synchronized (mutex) {return ns.pollLast();} } 2349 2350 public NavigableSet<E> descendingSet() { 2351 synchronized (mutex) { 2352 return new SynchronizedNavigableSet<>(ns.descendingSet(), mutex); 2353 } 2354 } 2355 2356 public Iterator<E> descendingIterator() 2357 { synchronized (mutex) { return descendingSet().iterator(); } } 2358 2359 public NavigableSet<E> subSet(E fromElement, E toElement) { 2360 synchronized (mutex) { 2361 return new SynchronizedNavigableSet<>(ns.subSet(fromElement, true, toElement, false), mutex); 2362 } 2363 } 2364 public NavigableSet<E> headSet(E toElement) { 2365 synchronized (mutex) { 2366 return new SynchronizedNavigableSet<>(ns.headSet(toElement, false), mutex); 2367 } 2368 } 2369 public NavigableSet<E> tailSet(E fromElement) { 2370 synchronized (mutex) { 2371 return new SynchronizedNavigableSet<>(ns.tailSet(fromElement, true), mutex); 2372 } 2373 } 2374 2375 public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) { 2376 synchronized (mutex) { 2377 return new SynchronizedNavigableSet<>(ns.subSet(fromElement, fromInclusive, toElement, toInclusive), mutex); 2378 } 2379 } 2380 2381 public NavigableSet<E> headSet(E toElement, boolean inclusive) { 2382 synchronized (mutex) { 2383 return new SynchronizedNavigableSet<>(ns.headSet(toElement, inclusive), mutex); 2384 } 2385 } 2386 2387 public NavigableSet<E> tailSet(E fromElement, boolean inclusive) { 2388 synchronized (mutex) { 2389 return new SynchronizedNavigableSet<>(ns.tailSet(fromElement, inclusive), mutex); 2390 } 2391 } 2392 } 2393 2394 /** 2395 * Returns a synchronized (thread-safe) list backed by the specified 2396 * list. In order to guarantee serial access, it is critical that 2397 * <strong>all</strong> access to the backing list is accomplished 2398 * through the returned list.<p> 2399 * 2400 * It is imperative that the user manually synchronize on the returned 2401 * list when iterating over it: 2402 * <pre> 2403 * List list = Collections.synchronizedList(new ArrayList()); 2404 * ... 2405 * synchronized (list) { 2406 * Iterator i = list.iterator(); // Must be in synchronized block 2407 * while (i.hasNext()) 2408 * foo(i.next()); 2409 * } 2410 * </pre> 2411 * Failure to follow this advice may result in non-deterministic behavior. 2412 * 2413 * <p>The returned list will be serializable if the specified list is 2414 * serializable. 2415 * 2416 * @param <T> the class of the objects in the list 2417 * @param list the list to be "wrapped" in a synchronized list. 2418 * @return a synchronized view of the specified list. 2419 */ 2420 public static <T> List<T> synchronizedList(List<T> list) { 2421 return (list instanceof RandomAccess ? 2422 new SynchronizedRandomAccessList<>(list) : 2423 new SynchronizedList<>(list)); 2424 } 2425 2426 static <T> List<T> synchronizedList(List<T> list, Object mutex) { 2427 return (list instanceof RandomAccess ? 2428 new SynchronizedRandomAccessList<>(list, mutex) : 2429 new SynchronizedList<>(list, mutex)); 2430 } 2431 2432 /** 2433 * @serial include 2434 */ 2435 static class SynchronizedList<E> 2436 extends SynchronizedCollection<E> 2437 implements List<E> { 2438 private static final long serialVersionUID = -7754090372962971524L; 2439 2440 final List<E> list; 2441 2442 SynchronizedList(List<E> list) { 2443 super(list); 2444 this.list = list; 2445 } 2446 SynchronizedList(List<E> list, Object mutex) { 2447 super(list, mutex); 2448 this.list = list; 2449 } 2450 2451 public boolean equals(Object o) { 2452 if (this == o) 2453 return true; 2454 synchronized (mutex) {return list.equals(o);} 2455 } 2456 public int hashCode() { 2457 synchronized (mutex) {return list.hashCode();} 2458 } 2459 2460 public E get(int index) { 2461 synchronized (mutex) {return list.get(index);} 2462 } 2463 public E set(int index, E element) { 2464 synchronized (mutex) {return list.set(index, element);} 2465 } 2466 public void add(int index, E element) { 2467 synchronized (mutex) {list.add(index, element);} 2468 } 2469 public E remove(int index) { 2470 synchronized (mutex) {return list.remove(index);} 2471 } 2472 2473 public int indexOf(Object o) { 2474 synchronized (mutex) {return list.indexOf(o);} 2475 } 2476 public int lastIndexOf(Object o) { 2477 synchronized (mutex) {return list.lastIndexOf(o);} 2478 } 2479 2480 public boolean addAll(int index, Collection<? extends E> c) { 2481 synchronized (mutex) {return list.addAll(index, c);} 2482 } 2483 2484 public ListIterator<E> listIterator() { 2485 return list.listIterator(); // Must be manually synched by user 2486 } 2487 2488 public ListIterator<E> listIterator(int index) { 2489 return list.listIterator(index); // Must be manually synched by user 2490 } 2491 2492 public List<E> subList(int fromIndex, int toIndex) { 2493 synchronized (mutex) { 2494 return new SynchronizedList<>(list.subList(fromIndex, toIndex), 2495 mutex); 2496 } 2497 } 2498 2499 @Override 2500 public void replaceAll(UnaryOperator<E> operator) { 2501 synchronized (mutex) {list.replaceAll(operator);} 2502 } 2503 @Override 2504 public void sort(Comparator<? super E> c) { 2505 synchronized (mutex) {list.sort(c);} 2506 } 2507 2508 /** 2509 * SynchronizedRandomAccessList instances are serialized as 2510 * SynchronizedList instances to allow them to be deserialized 2511 * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList). 2512 * This method inverts the transformation. As a beneficial 2513 * side-effect, it also grafts the RandomAccess marker onto 2514 * SynchronizedList instances that were serialized in pre-1.4 JREs. 2515 * 2516 * Note: Unfortunately, SynchronizedRandomAccessList instances 2517 * serialized in 1.4.1 and deserialized in 1.4 will become 2518 * SynchronizedList instances, as this method was missing in 1.4. 2519 */ 2520 private Object readResolve() { 2521 return (list instanceof RandomAccess 2522 ? new SynchronizedRandomAccessList<>(list) 2523 : this); 2524 } 2525 } 2526 2527 /** 2528 * @serial include 2529 */ 2530 static class SynchronizedRandomAccessList<E> 2531 extends SynchronizedList<E> 2532 implements RandomAccess { 2533 2534 SynchronizedRandomAccessList(List<E> list) { 2535 super(list); 2536 } 2537 2538 SynchronizedRandomAccessList(List<E> list, Object mutex) { 2539 super(list, mutex); 2540 } 2541 2542 public List<E> subList(int fromIndex, int toIndex) { 2543 synchronized (mutex) { 2544 return new SynchronizedRandomAccessList<>( 2545 list.subList(fromIndex, toIndex), mutex); 2546 } 2547 } 2548 2549 private static final long serialVersionUID = 1530674583602358482L; 2550 2551 /** 2552 * Allows instances to be deserialized in pre-1.4 JREs (which do 2553 * not have SynchronizedRandomAccessList). SynchronizedList has 2554 * a readResolve method that inverts this transformation upon 2555 * deserialization. 2556 */ 2557 private Object writeReplace() { 2558 return new SynchronizedList<>(list); 2559 } 2560 } 2561 2562 /** 2563 * Returns a synchronized (thread-safe) map backed by the specified 2564 * map. In order to guarantee serial access, it is critical that 2565 * <strong>all</strong> access to the backing map is accomplished 2566 * through the returned map.<p> 2567 * 2568 * It is imperative that the user manually synchronize on the returned 2569 * map when iterating over any of its collection views: 2570 * <pre> 2571 * Map m = Collections.synchronizedMap(new HashMap()); 2572 * ... 2573 * Set s = m.keySet(); // Needn't be in synchronized block 2574 * ... 2575 * synchronized (m) { // Synchronizing on m, not s! 2576 * Iterator i = s.iterator(); // Must be in synchronized block 2577 * while (i.hasNext()) 2578 * foo(i.next()); 2579 * } 2580 * </pre> 2581 * Failure to follow this advice may result in non-deterministic behavior. 2582 * 2583 * <p>The returned map will be serializable if the specified map is 2584 * serializable. 2585 * 2586 * @param <K> the class of the map keys 2587 * @param <V> the class of the map values 2588 * @param m the map to be "wrapped" in a synchronized map. 2589 * @return a synchronized view of the specified map. 2590 */ 2591 public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) { 2592 return new SynchronizedMap<>(m); 2593 } 2594 2595 /** 2596 * @serial include 2597 */ 2598 private static class SynchronizedMap<K,V> 2599 implements Map<K,V>, Serializable { 2600 private static final long serialVersionUID = 1978198479659022715L; 2601 2602 private final Map<K,V> m; // Backing Map 2603 final Object mutex; // Object on which to synchronize 2604 2605 SynchronizedMap(Map<K,V> m) { 2606 this.m = Objects.requireNonNull(m); 2607 mutex = this; 2608 } 2609 2610 SynchronizedMap(Map<K,V> m, Object mutex) { 2611 this.m = m; 2612 this.mutex = mutex; 2613 } 2614 2615 public int size() { 2616 synchronized (mutex) {return m.size();} 2617 } 2618 public boolean isEmpty() { 2619 synchronized (mutex) {return m.isEmpty();} 2620 } 2621 public boolean containsKey(Object key) { 2622 synchronized (mutex) {return m.containsKey(key);} 2623 } 2624 public boolean containsValue(Object value) { 2625 synchronized (mutex) {return m.containsValue(value);} 2626 } 2627 public V get(Object key) { 2628 synchronized (mutex) {return m.get(key);} 2629 } 2630 2631 public V put(K key, V value) { 2632 synchronized (mutex) {return m.put(key, value);} 2633 } 2634 public V remove(Object key) { 2635 synchronized (mutex) {return m.remove(key);} 2636 } 2637 public void putAll(Map<? extends K, ? extends V> map) { 2638 synchronized (mutex) {m.putAll(map);} 2639 } 2640 public void clear() { 2641 synchronized (mutex) {m.clear();} 2642 } 2643 2644 private transient Set<K> keySet; 2645 private transient Set<Map.Entry<K,V>> entrySet; 2646 private transient Collection<V> values; 2647 2648 public Set<K> keySet() { 2649 synchronized (mutex) { 2650 if (keySet==null) 2651 keySet = new SynchronizedSet<>(m.keySet(), mutex); 2652 return keySet; 2653 } 2654 } 2655 2656 public Set<Map.Entry<K,V>> entrySet() { 2657 synchronized (mutex) { 2658 if (entrySet==null) 2659 entrySet = new SynchronizedSet<>(m.entrySet(), mutex); 2660 return entrySet; 2661 } 2662 } 2663 2664 public Collection<V> values() { 2665 synchronized (mutex) { 2666 if (values==null) 2667 values = new SynchronizedCollection<>(m.values(), mutex); 2668 return values; 2669 } 2670 } 2671 2672 public boolean equals(Object o) { 2673 if (this == o) 2674 return true; 2675 synchronized (mutex) {return m.equals(o);} 2676 } 2677 public int hashCode() { 2678 synchronized (mutex) {return m.hashCode();} 2679 } 2680 public String toString() { 2681 synchronized (mutex) {return m.toString();} 2682 } 2683 2684 // Override default methods in Map 2685 @Override 2686 public V getOrDefault(Object k, V defaultValue) { 2687 synchronized (mutex) {return m.getOrDefault(k, defaultValue);} 2688 } 2689 @Override 2690 public void forEach(BiConsumer<? super K, ? super V> action) { 2691 synchronized (mutex) {m.forEach(action);} 2692 } 2693 @Override 2694 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 2695 synchronized (mutex) {m.replaceAll(function);} 2696 } 2697 @Override 2698 public V putIfAbsent(K key, V value) { 2699 synchronized (mutex) {return m.putIfAbsent(key, value);} 2700 } 2701 @Override 2702 public boolean remove(Object key, Object value) { 2703 synchronized (mutex) {return m.remove(key, value);} 2704 } 2705 @Override 2706 public boolean replace(K key, V oldValue, V newValue) { 2707 synchronized (mutex) {return m.replace(key, oldValue, newValue);} 2708 } 2709 @Override 2710 public V replace(K key, V value) { 2711 synchronized (mutex) {return m.replace(key, value);} 2712 } 2713 @Override 2714 public V computeIfAbsent(K key, 2715 Function<? super K, ? extends V> mappingFunction) { 2716 synchronized (mutex) {return m.computeIfAbsent(key, mappingFunction);} 2717 } 2718 @Override 2719 public V computeIfPresent(K key, 2720 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 2721 synchronized (mutex) {return m.computeIfPresent(key, remappingFunction);} 2722 } 2723 @Override 2724 public V compute(K key, 2725 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 2726 synchronized (mutex) {return m.compute(key, remappingFunction);} 2727 } 2728 @Override 2729 public V merge(K key, V value, 2730 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 2731 synchronized (mutex) {return m.merge(key, value, remappingFunction);} 2732 } 2733 2734 private void writeObject(ObjectOutputStream s) throws IOException { 2735 synchronized (mutex) {s.defaultWriteObject();} 2736 } 2737 } 2738 2739 /** 2740 * Returns a synchronized (thread-safe) sorted map backed by the specified 2741 * sorted map. In order to guarantee serial access, it is critical that 2742 * <strong>all</strong> access to the backing sorted map is accomplished 2743 * through the returned sorted map (or its views).<p> 2744 * 2745 * It is imperative that the user manually synchronize on the returned 2746 * sorted map when iterating over any of its collection views, or the 2747 * collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or 2748 * <tt>tailMap</tt> views. 2749 * <pre> 2750 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap()); 2751 * ... 2752 * Set s = m.keySet(); // Needn't be in synchronized block 2753 * ... 2754 * synchronized (m) { // Synchronizing on m, not s! 2755 * Iterator i = s.iterator(); // Must be in synchronized block 2756 * while (i.hasNext()) 2757 * foo(i.next()); 2758 * } 2759 * </pre> 2760 * or: 2761 * <pre> 2762 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap()); 2763 * SortedMap m2 = m.subMap(foo, bar); 2764 * ... 2765 * Set s2 = m2.keySet(); // Needn't be in synchronized block 2766 * ... 2767 * synchronized (m) { // Synchronizing on m, not m2 or s2! 2768 * Iterator i = s.iterator(); // Must be in synchronized block 2769 * while (i.hasNext()) 2770 * foo(i.next()); 2771 * } 2772 * </pre> 2773 * Failure to follow this advice may result in non-deterministic behavior. 2774 * 2775 * <p>The returned sorted map will be serializable if the specified 2776 * sorted map is serializable. 2777 * 2778 * @param <K> the class of the map keys 2779 * @param <V> the class of the map values 2780 * @param m the sorted map to be "wrapped" in a synchronized sorted map. 2781 * @return a synchronized view of the specified sorted map. 2782 */ 2783 public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) { 2784 return new SynchronizedSortedMap<>(m); 2785 } 2786 2787 /** 2788 * @serial include 2789 */ 2790 static class SynchronizedSortedMap<K,V> 2791 extends SynchronizedMap<K,V> 2792 implements SortedMap<K,V> 2793 { 2794 private static final long serialVersionUID = -8798146769416483793L; 2795 2796 private final SortedMap<K,V> sm; 2797 2798 SynchronizedSortedMap(SortedMap<K,V> m) { 2799 super(m); 2800 sm = m; 2801 } 2802 SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) { 2803 super(m, mutex); 2804 sm = m; 2805 } 2806 2807 public Comparator<? super K> comparator() { 2808 synchronized (mutex) {return sm.comparator();} 2809 } 2810 2811 public SortedMap<K,V> subMap(K fromKey, K toKey) { 2812 synchronized (mutex) { 2813 return new SynchronizedSortedMap<>( 2814 sm.subMap(fromKey, toKey), mutex); 2815 } 2816 } 2817 public SortedMap<K,V> headMap(K toKey) { 2818 synchronized (mutex) { 2819 return new SynchronizedSortedMap<>(sm.headMap(toKey), mutex); 2820 } 2821 } 2822 public SortedMap<K,V> tailMap(K fromKey) { 2823 synchronized (mutex) { 2824 return new SynchronizedSortedMap<>(sm.tailMap(fromKey),mutex); 2825 } 2826 } 2827 2828 public K firstKey() { 2829 synchronized (mutex) {return sm.firstKey();} 2830 } 2831 public K lastKey() { 2832 synchronized (mutex) {return sm.lastKey();} 2833 } 2834 } 2835 2836 /** 2837 * Returns a synchronized (thread-safe) navigable map backed by the 2838 * specified navigable map. In order to guarantee serial access, it is 2839 * critical that <strong>all</strong> access to the backing navigable map is 2840 * accomplished through the returned navigable map (or its views).<p> 2841 * 2842 * It is imperative that the user manually synchronize on the returned 2843 * navigable map when iterating over any of its collection views, or the 2844 * collections views of any of its {@code subMap}, {@code headMap} or 2845 * {@code tailMap} views. 2846 * <pre> 2847 * NavigableMap m = Collections.synchronizedNavigableMap(new TreeMap()); 2848 * ... 2849 * Set s = m.keySet(); // Needn't be in synchronized block 2850 * ... 2851 * synchronized (m) { // Synchronizing on m, not s! 2852 * Iterator i = s.iterator(); // Must be in synchronized block 2853 * while (i.hasNext()) 2854 * foo(i.next()); 2855 * } 2856 * </pre> 2857 * or: 2858 * <pre> 2859 * NavigableMap m = Collections.synchronizedNavigableMap(new TreeMap()); 2860 * NavigableMap m2 = m.subMap(foo, true, bar, false); 2861 * ... 2862 * Set s2 = m2.keySet(); // Needn't be in synchronized block 2863 * ... 2864 * synchronized (m) { // Synchronizing on m, not m2 or s2! 2865 * Iterator i = s.iterator(); // Must be in synchronized block 2866 * while (i.hasNext()) 2867 * foo(i.next()); 2868 * } 2869 * </pre> 2870 * Failure to follow this advice may result in non-deterministic behavior. 2871 * 2872 * <p>The returned navigable map will be serializable if the specified 2873 * navigable map is serializable. 2874 * 2875 * @param <K> the class of the map keys 2876 * @param <V> the class of the map values 2877 * @param m the navigable map to be "wrapped" in a synchronized navigable 2878 * map 2879 * @return a synchronized view of the specified navigable map. 2880 * @since 1.8 2881 */ 2882 public static <K,V> NavigableMap<K,V> synchronizedNavigableMap(NavigableMap<K,V> m) { 2883 return new SynchronizedNavigableMap<>(m); 2884 } 2885 2886 /** 2887 * A synchronized NavigableMap. 2888 * 2889 * @serial include 2890 */ 2891 static class SynchronizedNavigableMap<K,V> 2892 extends SynchronizedSortedMap<K,V> 2893 implements NavigableMap<K,V> 2894 { 2895 private static final long serialVersionUID = 699392247599746807L; 2896 2897 private final NavigableMap<K,V> nm; 2898 2899 SynchronizedNavigableMap(NavigableMap<K,V> m) { 2900 super(m); 2901 nm = m; 2902 } 2903 SynchronizedNavigableMap(NavigableMap<K,V> m, Object mutex) { 2904 super(m, mutex); 2905 nm = m; 2906 } 2907 2908 public Entry<K, V> lowerEntry(K key) 2909 { synchronized (mutex) { return nm.lowerEntry(key); } } 2910 public K lowerKey(K key) 2911 { synchronized (mutex) { return nm.lowerKey(key); } } 2912 public Entry<K, V> floorEntry(K key) 2913 { synchronized (mutex) { return nm.floorEntry(key); } } 2914 public K floorKey(K key) 2915 { synchronized (mutex) { return nm.floorKey(key); } } 2916 public Entry<K, V> ceilingEntry(K key) 2917 { synchronized (mutex) { return nm.ceilingEntry(key); } } 2918 public K ceilingKey(K key) 2919 { synchronized (mutex) { return nm.ceilingKey(key); } } 2920 public Entry<K, V> higherEntry(K key) 2921 { synchronized (mutex) { return nm.higherEntry(key); } } 2922 public K higherKey(K key) 2923 { synchronized (mutex) { return nm.higherKey(key); } } 2924 public Entry<K, V> firstEntry() 2925 { synchronized (mutex) { return nm.firstEntry(); } } 2926 public Entry<K, V> lastEntry() 2927 { synchronized (mutex) { return nm.lastEntry(); } } 2928 public Entry<K, V> pollFirstEntry() 2929 { synchronized (mutex) { return nm.pollFirstEntry(); } } 2930 public Entry<K, V> pollLastEntry() 2931 { synchronized (mutex) { return nm.pollLastEntry(); } } 2932 2933 public NavigableMap<K, V> descendingMap() { 2934 synchronized (mutex) { 2935 return 2936 new SynchronizedNavigableMap<>(nm.descendingMap(), mutex); 2937 } 2938 } 2939 2940 public NavigableSet<K> keySet() { 2941 return navigableKeySet(); 2942 } 2943 2944 public NavigableSet<K> navigableKeySet() { 2945 synchronized (mutex) { 2946 return new SynchronizedNavigableSet<>(nm.navigableKeySet(), mutex); 2947 } 2948 } 2949 2950 public NavigableSet<K> descendingKeySet() { 2951 synchronized (mutex) { 2952 return new SynchronizedNavigableSet<>(nm.descendingKeySet(), mutex); 2953 } 2954 } 2955 2956 2957 public SortedMap<K,V> subMap(K fromKey, K toKey) { 2958 synchronized (mutex) { 2959 return new SynchronizedNavigableMap<>( 2960 nm.subMap(fromKey, true, toKey, false), mutex); 2961 } 2962 } 2963 public SortedMap<K,V> headMap(K toKey) { 2964 synchronized (mutex) { 2965 return new SynchronizedNavigableMap<>(nm.headMap(toKey, false), mutex); 2966 } 2967 } 2968 public SortedMap<K,V> tailMap(K fromKey) { 2969 synchronized (mutex) { 2970 return new SynchronizedNavigableMap<>(nm.tailMap(fromKey, true),mutex); 2971 } 2972 } 2973 2974 public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) { 2975 synchronized (mutex) { 2976 return new SynchronizedNavigableMap<>( 2977 nm.subMap(fromKey, fromInclusive, toKey, toInclusive), mutex); 2978 } 2979 } 2980 2981 public NavigableMap<K, V> headMap(K toKey, boolean inclusive) { 2982 synchronized (mutex) { 2983 return new SynchronizedNavigableMap<>( 2984 nm.headMap(toKey, inclusive), mutex); 2985 } 2986 } 2987 2988 public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) { 2989 synchronized (mutex) { 2990 return new SynchronizedNavigableMap<>( 2991 nm.tailMap(fromKey, inclusive), mutex); 2992 } 2993 } 2994 } 2995 2996 // Dynamically typesafe collection wrappers 2997 2998 /** 2999 * Returns a dynamically typesafe view of the specified collection. 3000 * Any attempt to insert an element of the wrong type will result in an 3001 * immediate {@link ClassCastException}. Assuming a collection 3002 * contains no incorrectly typed elements prior to the time a 3003 * dynamically typesafe view is generated, and that all subsequent 3004 * access to the collection takes place through the view, it is 3005 * <i>guaranteed</i> that the collection cannot contain an incorrectly 3006 * typed element. 3007 * 3008 * <p>The generics mechanism in the language provides compile-time 3009 * (static) type checking, but it is possible to defeat this mechanism 3010 * with unchecked casts. Usually this is not a problem, as the compiler 3011 * issues warnings on all such unchecked operations. There are, however, 3012 * times when static type checking alone is not sufficient. For example, 3013 * suppose a collection is passed to a third-party library and it is 3014 * imperative that the library code not corrupt the collection by 3015 * inserting an element of the wrong type. 3016 * 3017 * <p>Another use of dynamically typesafe views is debugging. Suppose a 3018 * program fails with a {@code ClassCastException}, indicating that an 3019 * incorrectly typed element was put into a parameterized collection. 3020 * Unfortunately, the exception can occur at any time after the erroneous 3021 * element is inserted, so it typically provides little or no information 3022 * as to the real source of the problem. If the problem is reproducible, 3023 * one can quickly determine its source by temporarily modifying the 3024 * program to wrap the collection with a dynamically typesafe view. 3025 * For example, this declaration: 3026 * <pre> {@code 3027 * Collection<String> c = new HashSet<>(); 3028 * }</pre> 3029 * may be replaced temporarily by this one: 3030 * <pre> {@code 3031 * Collection<String> c = Collections.checkedCollection( 3032 * new HashSet<>(), String.class); 3033 * }</pre> 3034 * Running the program again will cause it to fail at the point where 3035 * an incorrectly typed element is inserted into the collection, clearly 3036 * identifying the source of the problem. Once the problem is fixed, the 3037 * modified declaration may be reverted back to the original. 3038 * 3039 * <p>The returned collection does <i>not</i> pass the hashCode and equals 3040 * operations through to the backing collection, but relies on 3041 * {@code Object}'s {@code equals} and {@code hashCode} methods. This 3042 * is necessary to preserve the contracts of these operations in the case 3043 * that the backing collection is a set or a list. 3044 * 3045 * <p>The returned collection will be serializable if the specified 3046 * collection is serializable. 3047 * 3048 * <p>Since {@code null} is considered to be a value of any reference 3049 * type, the returned collection permits insertion of null elements 3050 * whenever the backing collection does. 3051 * 3052 * @param <E> the class of the objects in the collection 3053 * @param c the collection for which a dynamically typesafe view is to be 3054 * returned 3055 * @param type the type of element that {@code c} is permitted to hold 3056 * @return a dynamically typesafe view of the specified collection 3057 * @since 1.5 3058 */ 3059 public static <E> Collection<E> checkedCollection(Collection<E> c, 3060 Class<E> type) { 3061 return new CheckedCollection<>(c, type); 3062 } 3063 3064 @SuppressWarnings("unchecked") 3065 static <T> T[] zeroLengthArray(Class<T> type) { 3066 return (T[]) Array.newInstance(type, 0); 3067 } 3068 3069 /** 3070 * @serial include 3071 */ 3072 static class CheckedCollection<E> implements Collection<E>, Serializable { 3073 private static final long serialVersionUID = 1578914078182001775L; 3074 3075 final Collection<E> c; 3076 final Class<E> type; 3077 3078 @SuppressWarnings("unchecked") 3079 E typeCheck(Object o) { 3080 if (o != null && !type.isInstance(o)) 3081 throw new ClassCastException(badElementMsg(o)); 3082 return (E) o; 3083 } 3084 3085 private String badElementMsg(Object o) { 3086 return "Attempt to insert " + o.getClass() + 3087 " element into collection with element type " + type; 3088 } 3089 3090 CheckedCollection(Collection<E> c, Class<E> type) { 3091 this.c = Objects.requireNonNull(c, "c"); 3092 this.type = Objects.requireNonNull(type, "type"); 3093 } 3094 3095 public int size() { return c.size(); } 3096 public boolean isEmpty() { return c.isEmpty(); } 3097 public boolean contains(Object o) { return c.contains(o); } 3098 public Object[] toArray() { return c.toArray(); } 3099 public <T> T[] toArray(T[] a) { return c.toArray(a); } 3100 public String toString() { return c.toString(); } 3101 public boolean remove(Object o) { return c.remove(o); } 3102 public void clear() { c.clear(); } 3103 3104 public boolean containsAll(Collection<?> coll) { 3105 return c.containsAll(coll); 3106 } 3107 public boolean removeAll(Collection<?> coll) { 3108 return c.removeAll(coll); 3109 } 3110 public boolean retainAll(Collection<?> coll) { 3111 return c.retainAll(coll); 3112 } 3113 3114 public Iterator<E> iterator() { 3115 // JDK-6363904 - unwrapped iterator could be typecast to 3116 // ListIterator with unsafe set() 3117 final Iterator<E> it = c.iterator(); 3118 return new Iterator<E>() { 3119 public boolean hasNext() { return it.hasNext(); } 3120 public E next() { return it.next(); } 3121 public void remove() { it.remove(); }}; 3122 // Android-note: Should we delegate to it for forEachRemaining ? 3123 } 3124 3125 public boolean add(E e) { return c.add(typeCheck(e)); } 3126 3127 private E[] zeroLengthElementArray; // Lazily initialized 3128 3129 private E[] zeroLengthElementArray() { 3130 return zeroLengthElementArray != null ? zeroLengthElementArray : 3131 (zeroLengthElementArray = zeroLengthArray(type)); 3132 } 3133 3134 @SuppressWarnings("unchecked") 3135 Collection<E> checkedCopyOf(Collection<? extends E> coll) { 3136 Object[] a; 3137 try { 3138 E[] z = zeroLengthElementArray(); 3139 a = coll.toArray(z); 3140 // Defend against coll violating the toArray contract 3141 if (a.getClass() != z.getClass()) 3142 a = Arrays.copyOf(a, a.length, z.getClass()); 3143 } catch (ArrayStoreException ignore) { 3144 // To get better and consistent diagnostics, 3145 // we call typeCheck explicitly on each element. 3146 // We call clone() to defend against coll retaining a 3147 // reference to the returned array and storing a bad 3148 // element into it after it has been type checked. 3149 a = coll.toArray().clone(); 3150 for (Object o : a) 3151 typeCheck(o); 3152 } 3153 // A slight abuse of the type system, but safe here. 3154 return (Collection<E>) Arrays.asList(a); 3155 } 3156 3157 public boolean addAll(Collection<? extends E> coll) { 3158 // Doing things this way insulates us from concurrent changes 3159 // in the contents of coll and provides all-or-nothing 3160 // semantics (which we wouldn't get if we type-checked each 3161 // element as we added it) 3162 return c.addAll(checkedCopyOf(coll)); 3163 } 3164 3165 // Override default methods in Collection 3166 @Override 3167 public void forEach(Consumer<? super E> action) {c.forEach(action);} 3168 @Override 3169 public boolean removeIf(Predicate<? super E> filter) { 3170 return c.removeIf(filter); 3171 } 3172 @Override 3173 public Spliterator<E> spliterator() {return c.spliterator();} 3174 @Override 3175 public Stream<E> stream() {return c.stream();} 3176 @Override 3177 public Stream<E> parallelStream() {return c.parallelStream();} 3178 } 3179 3180 /** 3181 * Returns a dynamically typesafe view of the specified queue. 3182 * Any attempt to insert an element of the wrong type will result in 3183 * an immediate {@link ClassCastException}. Assuming a queue contains 3184 * no incorrectly typed elements prior to the time a dynamically typesafe 3185 * view is generated, and that all subsequent access to the queue 3186 * takes place through the view, it is <i>guaranteed</i> that the 3187 * queue cannot contain an incorrectly typed element. 3188 * 3189 * <p>A discussion of the use of dynamically typesafe views may be 3190 * found in the documentation for the {@link #checkedCollection 3191 * checkedCollection} method. 3192 * 3193 * <p>The returned queue will be serializable if the specified queue 3194 * is serializable. 3195 * 3196 * <p>Since {@code null} is considered to be a value of any reference 3197 * type, the returned queue permits insertion of {@code null} elements 3198 * whenever the backing queue does. 3199 * 3200 * @param <E> the class of the objects in the queue 3201 * @param queue the queue for which a dynamically typesafe view is to be 3202 * returned 3203 * @param type the type of element that {@code queue} is permitted to hold 3204 * @return a dynamically typesafe view of the specified queue 3205 * @since 1.8 3206 */ 3207 public static <E> Queue<E> checkedQueue(Queue<E> queue, Class<E> type) { 3208 return new CheckedQueue<>(queue, type); 3209 } 3210 3211 /** 3212 * @serial include 3213 */ 3214 static class CheckedQueue<E> 3215 extends CheckedCollection<E> 3216 implements Queue<E>, Serializable 3217 { 3218 private static final long serialVersionUID = 1433151992604707767L; 3219 final Queue<E> queue; 3220 3221 CheckedQueue(Queue<E> queue, Class<E> elementType) { 3222 super(queue, elementType); 3223 this.queue = queue; 3224 } 3225 3226 public E element() {return queue.element();} 3227 public boolean equals(Object o) {return o == this || c.equals(o);} 3228 public int hashCode() {return c.hashCode();} 3229 public E peek() {return queue.peek();} 3230 public E poll() {return queue.poll();} 3231 public E remove() {return queue.remove();} 3232 public boolean offer(E e) {return queue.offer(typeCheck(e));} 3233 } 3234 3235 /** 3236 * Returns a dynamically typesafe view of the specified set. 3237 * Any attempt to insert an element of the wrong type will result in 3238 * an immediate {@link ClassCastException}. Assuming a set contains 3239 * no incorrectly typed elements prior to the time a dynamically typesafe 3240 * view is generated, and that all subsequent access to the set 3241 * takes place through the view, it is <i>guaranteed</i> that the 3242 * set cannot contain an incorrectly typed element. 3243 * 3244 * <p>A discussion of the use of dynamically typesafe views may be 3245 * found in the documentation for the {@link #checkedCollection 3246 * checkedCollection} method. 3247 * 3248 * <p>The returned set will be serializable if the specified set is 3249 * serializable. 3250 * 3251 * <p>Since {@code null} is considered to be a value of any reference 3252 * type, the returned set permits insertion of null elements whenever 3253 * the backing set does. 3254 * 3255 * @param <E> the class of the objects in the set 3256 * @param s the set for which a dynamically typesafe view is to be 3257 * returned 3258 * @param type the type of element that {@code s} is permitted to hold 3259 * @return a dynamically typesafe view of the specified set 3260 * @since 1.5 3261 */ 3262 public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) { 3263 return new CheckedSet<>(s, type); 3264 } 3265 3266 /** 3267 * @serial include 3268 */ 3269 static class CheckedSet<E> extends CheckedCollection<E> 3270 implements Set<E>, Serializable 3271 { 3272 private static final long serialVersionUID = 4694047833775013803L; 3273 3274 CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); } 3275 3276 public boolean equals(Object o) { return o == this || c.equals(o); } 3277 public int hashCode() { return c.hashCode(); } 3278 } 3279 3280 /** 3281 * Returns a dynamically typesafe view of the specified sorted set. 3282 * Any attempt to insert an element of the wrong type will result in an 3283 * immediate {@link ClassCastException}. Assuming a sorted set 3284 * contains no incorrectly typed elements prior to the time a 3285 * dynamically typesafe view is generated, and that all subsequent 3286 * access to the sorted set takes place through the view, it is 3287 * <i>guaranteed</i> that the sorted set cannot contain an incorrectly 3288 * typed element. 3289 * 3290 * <p>A discussion of the use of dynamically typesafe views may be 3291 * found in the documentation for the {@link #checkedCollection 3292 * checkedCollection} method. 3293 * 3294 * <p>The returned sorted set will be serializable if the specified sorted 3295 * set is serializable. 3296 * 3297 * <p>Since {@code null} is considered to be a value of any reference 3298 * type, the returned sorted set permits insertion of null elements 3299 * whenever the backing sorted set does. 3300 * 3301 * @param <E> the class of the objects in the set 3302 * @param s the sorted set for which a dynamically typesafe view is to be 3303 * returned 3304 * @param type the type of element that {@code s} is permitted to hold 3305 * @return a dynamically typesafe view of the specified sorted set 3306 * @since 1.5 3307 */ 3308 public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s, 3309 Class<E> type) { 3310 return new CheckedSortedSet<>(s, type); 3311 } 3312 3313 /** 3314 * @serial include 3315 */ 3316 static class CheckedSortedSet<E> extends CheckedSet<E> 3317 implements SortedSet<E>, Serializable 3318 { 3319 private static final long serialVersionUID = 1599911165492914959L; 3320 3321 private final SortedSet<E> ss; 3322 3323 CheckedSortedSet(SortedSet<E> s, Class<E> type) { 3324 super(s, type); 3325 ss = s; 3326 } 3327 3328 public Comparator<? super E> comparator() { return ss.comparator(); } 3329 public E first() { return ss.first(); } 3330 public E last() { return ss.last(); } 3331 3332 public SortedSet<E> subSet(E fromElement, E toElement) { 3333 return checkedSortedSet(ss.subSet(fromElement,toElement), type); 3334 } 3335 public SortedSet<E> headSet(E toElement) { 3336 return checkedSortedSet(ss.headSet(toElement), type); 3337 } 3338 public SortedSet<E> tailSet(E fromElement) { 3339 return checkedSortedSet(ss.tailSet(fromElement), type); 3340 } 3341 } 3342 3343 /** 3344 * Returns a dynamically typesafe view of the specified navigable set. 3345 * Any attempt to insert an element of the wrong type will result in an 3346 * immediate {@link ClassCastException}. Assuming a navigable set 3347 * contains no incorrectly typed elements prior to the time a 3348 * dynamically typesafe view is generated, and that all subsequent 3349 * access to the navigable set takes place through the view, it is 3350 * <em>guaranteed</em> that the navigable set cannot contain an incorrectly 3351 * typed element. 3352 * 3353 * <p>A discussion of the use of dynamically typesafe views may be 3354 * found in the documentation for the {@link #checkedCollection 3355 * checkedCollection} method. 3356 * 3357 * <p>The returned navigable set will be serializable if the specified 3358 * navigable set is serializable. 3359 * 3360 * <p>Since {@code null} is considered to be a value of any reference 3361 * type, the returned navigable set permits insertion of null elements 3362 * whenever the backing sorted set does. 3363 * 3364 * @param <E> the class of the objects in the set 3365 * @param s the navigable set for which a dynamically typesafe view is to be 3366 * returned 3367 * @param type the type of element that {@code s} is permitted to hold 3368 * @return a dynamically typesafe view of the specified navigable set 3369 * @since 1.8 3370 */ 3371 public static <E> NavigableSet<E> checkedNavigableSet(NavigableSet<E> s, 3372 Class<E> type) { 3373 return new CheckedNavigableSet<>(s, type); 3374 } 3375 3376 /** 3377 * @serial include 3378 */ 3379 static class CheckedNavigableSet<E> extends CheckedSortedSet<E> 3380 implements NavigableSet<E>, Serializable 3381 { 3382 private static final long serialVersionUID = -5429120189805438922L; 3383 3384 private final NavigableSet<E> ns; 3385 3386 CheckedNavigableSet(NavigableSet<E> s, Class<E> type) { 3387 super(s, type); 3388 ns = s; 3389 } 3390 3391 public E lower(E e) { return ns.lower(e); } 3392 public E floor(E e) { return ns.floor(e); } 3393 public E ceiling(E e) { return ns.ceiling(e); } 3394 public E higher(E e) { return ns.higher(e); } 3395 public E pollFirst() { return ns.pollFirst(); } 3396 public E pollLast() {return ns.pollLast(); } 3397 public NavigableSet<E> descendingSet() 3398 { return checkedNavigableSet(ns.descendingSet(), type); } 3399 public Iterator<E> descendingIterator() 3400 {return checkedNavigableSet(ns.descendingSet(), type).iterator(); } 3401 3402 public NavigableSet<E> subSet(E fromElement, E toElement) { 3403 return checkedNavigableSet(ns.subSet(fromElement, true, toElement, false), type); 3404 } 3405 public NavigableSet<E> headSet(E toElement) { 3406 return checkedNavigableSet(ns.headSet(toElement, false), type); 3407 } 3408 public NavigableSet<E> tailSet(E fromElement) { 3409 return checkedNavigableSet(ns.tailSet(fromElement, true), type); 3410 } 3411 3412 public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) { 3413 return checkedNavigableSet(ns.subSet(fromElement, fromInclusive, toElement, toInclusive), type); 3414 } 3415 3416 public NavigableSet<E> headSet(E toElement, boolean inclusive) { 3417 return checkedNavigableSet(ns.headSet(toElement, inclusive), type); 3418 } 3419 3420 public NavigableSet<E> tailSet(E fromElement, boolean inclusive) { 3421 return checkedNavigableSet(ns.tailSet(fromElement, inclusive), type); 3422 } 3423 } 3424 3425 /** 3426 * Returns a dynamically typesafe view of the specified list. 3427 * Any attempt to insert an element of the wrong type will result in 3428 * an immediate {@link ClassCastException}. Assuming a list contains 3429 * no incorrectly typed elements prior to the time a dynamically typesafe 3430 * view is generated, and that all subsequent access to the list 3431 * takes place through the view, it is <i>guaranteed</i> that the 3432 * list cannot contain an incorrectly typed element. 3433 * 3434 * <p>A discussion of the use of dynamically typesafe views may be 3435 * found in the documentation for the {@link #checkedCollection 3436 * checkedCollection} method. 3437 * 3438 * <p>The returned list will be serializable if the specified list 3439 * is serializable. 3440 * 3441 * <p>Since {@code null} is considered to be a value of any reference 3442 * type, the returned list permits insertion of null elements whenever 3443 * the backing list does. 3444 * 3445 * @param <E> the class of the objects in the list 3446 * @param list the list for which a dynamically typesafe view is to be 3447 * returned 3448 * @param type the type of element that {@code list} is permitted to hold 3449 * @return a dynamically typesafe view of the specified list 3450 * @since 1.5 3451 */ 3452 public static <E> List<E> checkedList(List<E> list, Class<E> type) { 3453 return (list instanceof RandomAccess ? 3454 new CheckedRandomAccessList<>(list, type) : 3455 new CheckedList<>(list, type)); 3456 } 3457 3458 /** 3459 * @serial include 3460 */ 3461 static class CheckedList<E> 3462 extends CheckedCollection<E> 3463 implements List<E> 3464 { 3465 private static final long serialVersionUID = 65247728283967356L; 3466 final List<E> list; 3467 3468 CheckedList(List<E> list, Class<E> type) { 3469 super(list, type); 3470 this.list = list; 3471 } 3472 3473 public boolean equals(Object o) { return o == this || list.equals(o); } 3474 public int hashCode() { return list.hashCode(); } 3475 public E get(int index) { return list.get(index); } 3476 public E remove(int index) { return list.remove(index); } 3477 public int indexOf(Object o) { return list.indexOf(o); } 3478 public int lastIndexOf(Object o) { return list.lastIndexOf(o); } 3479 3480 public E set(int index, E element) { 3481 return list.set(index, typeCheck(element)); 3482 } 3483 3484 public void add(int index, E element) { 3485 list.add(index, typeCheck(element)); 3486 } 3487 3488 public boolean addAll(int index, Collection<? extends E> c) { 3489 return list.addAll(index, checkedCopyOf(c)); 3490 } 3491 public ListIterator<E> listIterator() { return listIterator(0); } 3492 3493 public ListIterator<E> listIterator(final int index) { 3494 final ListIterator<E> i = list.listIterator(index); 3495 3496 return new ListIterator<E>() { 3497 public boolean hasNext() { return i.hasNext(); } 3498 public E next() { return i.next(); } 3499 public boolean hasPrevious() { return i.hasPrevious(); } 3500 public E previous() { return i.previous(); } 3501 public int nextIndex() { return i.nextIndex(); } 3502 public int previousIndex() { return i.previousIndex(); } 3503 public void remove() { i.remove(); } 3504 3505 public void set(E e) { 3506 i.set(typeCheck(e)); 3507 } 3508 3509 public void add(E e) { 3510 i.add(typeCheck(e)); 3511 } 3512 3513 @Override 3514 public void forEachRemaining(Consumer<? super E> action) { 3515 i.forEachRemaining(action); 3516 } 3517 }; 3518 } 3519 3520 public List<E> subList(int fromIndex, int toIndex) { 3521 return new CheckedList<>(list.subList(fromIndex, toIndex), type); 3522 } 3523 3524 /** 3525 * {@inheritDoc} 3526 * 3527 * @throws ClassCastException if the class of an element returned by the 3528 * operator prevents it from being added to this collection. The 3529 * exception may be thrown after some elements of the list have 3530 * already been replaced. 3531 */ 3532 @Override 3533 public void replaceAll(UnaryOperator<E> operator) { 3534 Objects.requireNonNull(operator); 3535 list.replaceAll(e -> typeCheck(operator.apply(e))); 3536 } 3537 3538 @Override 3539 public void sort(Comparator<? super E> c) { 3540 list.sort(c); 3541 } 3542 } 3543 3544 /** 3545 * @serial include 3546 */ 3547 static class CheckedRandomAccessList<E> extends CheckedList<E> 3548 implements RandomAccess 3549 { 3550 private static final long serialVersionUID = 1638200125423088369L; 3551 3552 CheckedRandomAccessList(List<E> list, Class<E> type) { 3553 super(list, type); 3554 } 3555 3556 public List<E> subList(int fromIndex, int toIndex) { 3557 return new CheckedRandomAccessList<>( 3558 list.subList(fromIndex, toIndex), type); 3559 } 3560 } 3561 3562 /** 3563 * Returns a dynamically typesafe view of the specified map. 3564 * Any attempt to insert a mapping whose key or value have the wrong 3565 * type will result in an immediate {@link ClassCastException}. 3566 * Similarly, any attempt to modify the value currently associated with 3567 * a key will result in an immediate {@link ClassCastException}, 3568 * whether the modification is attempted directly through the map 3569 * itself, or through a {@link Map.Entry} instance obtained from the 3570 * map's {@link Map#entrySet() entry set} view. 3571 * 3572 * <p>Assuming a map contains no incorrectly typed keys or values 3573 * prior to the time a dynamically typesafe view is generated, and 3574 * that all subsequent access to the map takes place through the view 3575 * (or one of its collection views), it is <i>guaranteed</i> that the 3576 * map cannot contain an incorrectly typed key or value. 3577 * 3578 * <p>A discussion of the use of dynamically typesafe views may be 3579 * found in the documentation for the {@link #checkedCollection 3580 * checkedCollection} method. 3581 * 3582 * <p>The returned map will be serializable if the specified map is 3583 * serializable. 3584 * 3585 * <p>Since {@code null} is considered to be a value of any reference 3586 * type, the returned map permits insertion of null keys or values 3587 * whenever the backing map does. 3588 * 3589 * @param <K> the class of the map keys 3590 * @param <V> the class of the map values 3591 * @param m the map for which a dynamically typesafe view is to be 3592 * returned 3593 * @param keyType the type of key that {@code m} is permitted to hold 3594 * @param valueType the type of value that {@code m} is permitted to hold 3595 * @return a dynamically typesafe view of the specified map 3596 * @since 1.5 3597 */ 3598 public static <K, V> Map<K, V> checkedMap(Map<K, V> m, 3599 Class<K> keyType, 3600 Class<V> valueType) { 3601 return new CheckedMap<>(m, keyType, valueType); 3602 } 3603 3604 3605 /** 3606 * @serial include 3607 */ 3608 private static class CheckedMap<K,V> 3609 implements Map<K,V>, Serializable 3610 { 3611 private static final long serialVersionUID = 5742860141034234728L; 3612 3613 private final Map<K, V> m; 3614 final Class<K> keyType; 3615 final Class<V> valueType; 3616 3617 private void typeCheck(Object key, Object value) { 3618 if (key != null && !keyType.isInstance(key)) 3619 throw new ClassCastException(badKeyMsg(key)); 3620 3621 if (value != null && !valueType.isInstance(value)) 3622 throw new ClassCastException(badValueMsg(value)); 3623 } 3624 3625 private BiFunction<? super K, ? super V, ? extends V> typeCheck( 3626 BiFunction<? super K, ? super V, ? extends V> func) { 3627 Objects.requireNonNull(func); 3628 return (k, v) -> { 3629 V newValue = func.apply(k, v); 3630 typeCheck(k, newValue); 3631 return newValue; 3632 }; 3633 } 3634 3635 private String badKeyMsg(Object key) { 3636 return "Attempt to insert " + key.getClass() + 3637 " key into map with key type " + keyType; 3638 } 3639 3640 private String badValueMsg(Object value) { 3641 return "Attempt to insert " + value.getClass() + 3642 " value into map with value type " + valueType; 3643 } 3644 3645 CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) { 3646 this.m = Objects.requireNonNull(m); 3647 this.keyType = Objects.requireNonNull(keyType); 3648 this.valueType = Objects.requireNonNull(valueType); 3649 } 3650 3651 public int size() { return m.size(); } 3652 public boolean isEmpty() { return m.isEmpty(); } 3653 public boolean containsKey(Object key) { return m.containsKey(key); } 3654 public boolean containsValue(Object v) { return m.containsValue(v); } 3655 public V get(Object key) { return m.get(key); } 3656 public V remove(Object key) { return m.remove(key); } 3657 public void clear() { m.clear(); } 3658 public Set<K> keySet() { return m.keySet(); } 3659 public Collection<V> values() { return m.values(); } 3660 public boolean equals(Object o) { return o == this || m.equals(o); } 3661 public int hashCode() { return m.hashCode(); } 3662 public String toString() { return m.toString(); } 3663 3664 public V put(K key, V value) { 3665 typeCheck(key, value); 3666 return m.put(key, value); 3667 } 3668 3669 @SuppressWarnings("unchecked") 3670 public void putAll(Map<? extends K, ? extends V> t) { 3671 // Satisfy the following goals: 3672 // - good diagnostics in case of type mismatch 3673 // - all-or-nothing semantics 3674 // - protection from malicious t 3675 // - correct behavior if t is a concurrent map 3676 Object[] entries = t.entrySet().toArray(); 3677 List<Map.Entry<K,V>> checked = new ArrayList<>(entries.length); 3678 for (Object o : entries) { 3679 Map.Entry<?,?> e = (Map.Entry<?,?>) o; 3680 Object k = e.getKey(); 3681 Object v = e.getValue(); 3682 typeCheck(k, v); 3683 checked.add( 3684 new AbstractMap.SimpleImmutableEntry<>((K)k, (V)v)); 3685 } 3686 for (Map.Entry<K,V> e : checked) 3687 m.put(e.getKey(), e.getValue()); 3688 } 3689 3690 private transient Set<Map.Entry<K,V>> entrySet; 3691 3692 public Set<Map.Entry<K,V>> entrySet() { 3693 if (entrySet==null) 3694 entrySet = new CheckedEntrySet<>(m.entrySet(), valueType); 3695 return entrySet; 3696 } 3697 3698 // Override default methods in Map 3699 @Override 3700 public void forEach(BiConsumer<? super K, ? super V> action) { 3701 m.forEach(action); 3702 } 3703 3704 @Override 3705 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 3706 m.replaceAll(typeCheck(function)); 3707 } 3708 3709 @Override 3710 public V putIfAbsent(K key, V value) { 3711 typeCheck(key, value); 3712 return m.putIfAbsent(key, value); 3713 } 3714 3715 @Override 3716 public boolean remove(Object key, Object value) { 3717 return m.remove(key, value); 3718 } 3719 3720 @Override 3721 public boolean replace(K key, V oldValue, V newValue) { 3722 typeCheck(key, newValue); 3723 return m.replace(key, oldValue, newValue); 3724 } 3725 3726 @Override 3727 public V replace(K key, V value) { 3728 typeCheck(key, value); 3729 return m.replace(key, value); 3730 } 3731 3732 @Override 3733 public V computeIfAbsent(K key, 3734 Function<? super K, ? extends V> mappingFunction) { 3735 Objects.requireNonNull(mappingFunction); 3736 return m.computeIfAbsent(key, k -> { 3737 V value = mappingFunction.apply(k); 3738 typeCheck(k, value); 3739 return value; 3740 }); 3741 } 3742 3743 @Override 3744 public V computeIfPresent(K key, 3745 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 3746 return m.computeIfPresent(key, typeCheck(remappingFunction)); 3747 } 3748 3749 @Override 3750 public V compute(K key, 3751 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 3752 return m.compute(key, typeCheck(remappingFunction)); 3753 } 3754 3755 @Override 3756 public V merge(K key, V value, 3757 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 3758 Objects.requireNonNull(remappingFunction); 3759 return m.merge(key, value, (v1, v2) -> { 3760 V newValue = remappingFunction.apply(v1, v2); 3761 typeCheck(null, newValue); 3762 return newValue; 3763 }); 3764 } 3765 3766 /** 3767 * We need this class in addition to CheckedSet as Map.Entry permits 3768 * modification of the backing Map via the setValue operation. This 3769 * class is subtle: there are many possible attacks that must be 3770 * thwarted. 3771 * 3772 * @serial exclude 3773 */ 3774 static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> { 3775 private final Set<Map.Entry<K,V>> s; 3776 private final Class<V> valueType; 3777 3778 CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) { 3779 this.s = s; 3780 this.valueType = valueType; 3781 } 3782 3783 public int size() { return s.size(); } 3784 public boolean isEmpty() { return s.isEmpty(); } 3785 public String toString() { return s.toString(); } 3786 public int hashCode() { return s.hashCode(); } 3787 public void clear() { s.clear(); } 3788 3789 public boolean add(Map.Entry<K, V> e) { 3790 throw new UnsupportedOperationException(); 3791 } 3792 public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) { 3793 throw new UnsupportedOperationException(); 3794 } 3795 3796 public Iterator<Map.Entry<K,V>> iterator() { 3797 final Iterator<Map.Entry<K, V>> i = s.iterator(); 3798 final Class<V> valueType = this.valueType; 3799 3800 return new Iterator<Map.Entry<K,V>>() { 3801 public boolean hasNext() { return i.hasNext(); } 3802 public void remove() { i.remove(); } 3803 3804 public Map.Entry<K,V> next() { 3805 return checkedEntry(i.next(), valueType); 3806 } 3807 // Android-note: forEachRemaining is missing checks. 3808 }; 3809 } 3810 3811 @SuppressWarnings("unchecked") 3812 public Object[] toArray() { 3813 Object[] source = s.toArray(); 3814 3815 /* 3816 * Ensure that we don't get an ArrayStoreException even if 3817 * s.toArray returns an array of something other than Object 3818 */ 3819 Object[] dest = (CheckedEntry.class.isInstance( 3820 source.getClass().getComponentType()) ? source : 3821 new Object[source.length]); 3822 3823 for (int i = 0; i < source.length; i++) 3824 dest[i] = checkedEntry((Map.Entry<K,V>)source[i], 3825 valueType); 3826 return dest; 3827 } 3828 3829 @SuppressWarnings("unchecked") 3830 public <T> T[] toArray(T[] a) { 3831 // We don't pass a to s.toArray, to avoid window of 3832 // vulnerability wherein an unscrupulous multithreaded client 3833 // could get his hands on raw (unwrapped) Entries from s. 3834 T[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0)); 3835 3836 for (int i=0; i<arr.length; i++) 3837 arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i], 3838 valueType); 3839 if (arr.length > a.length) 3840 return arr; 3841 3842 System.arraycopy(arr, 0, a, 0, arr.length); 3843 if (a.length > arr.length) 3844 a[arr.length] = null; 3845 return a; 3846 } 3847 3848 /** 3849 * This method is overridden to protect the backing set against 3850 * an object with a nefarious equals function that senses 3851 * that the equality-candidate is Map.Entry and calls its 3852 * setValue method. 3853 */ 3854 public boolean contains(Object o) { 3855 if (!(o instanceof Map.Entry)) 3856 return false; 3857 Map.Entry<?,?> e = (Map.Entry<?,?>) o; 3858 return s.contains( 3859 (e instanceof CheckedEntry) ? e : checkedEntry(e, valueType)); 3860 } 3861 3862 /** 3863 * The bulk collection methods are overridden to protect 3864 * against an unscrupulous collection whose contains(Object o) 3865 * method senses when o is a Map.Entry, and calls o.setValue. 3866 */ 3867 public boolean containsAll(Collection<?> c) { 3868 for (Object o : c) 3869 if (!contains(o)) // Invokes safe contains() above 3870 return false; 3871 return true; 3872 } 3873 3874 public boolean remove(Object o) { 3875 if (!(o instanceof Map.Entry)) 3876 return false; 3877 return s.remove(new AbstractMap.SimpleImmutableEntry 3878 <>((Map.Entry<?,?>)o)); 3879 } 3880 3881 public boolean removeAll(Collection<?> c) { 3882 return batchRemove(c, false); 3883 } 3884 public boolean retainAll(Collection<?> c) { 3885 return batchRemove(c, true); 3886 } 3887 private boolean batchRemove(Collection<?> c, boolean complement) { 3888 Objects.requireNonNull(c); 3889 boolean modified = false; 3890 Iterator<Map.Entry<K,V>> it = iterator(); 3891 while (it.hasNext()) { 3892 if (c.contains(it.next()) != complement) { 3893 it.remove(); 3894 modified = true; 3895 } 3896 } 3897 return modified; 3898 } 3899 3900 public boolean equals(Object o) { 3901 if (o == this) 3902 return true; 3903 if (!(o instanceof Set)) 3904 return false; 3905 Set<?> that = (Set<?>) o; 3906 return that.size() == s.size() 3907 && containsAll(that); // Invokes safe containsAll() above 3908 } 3909 3910 static <K,V,T> CheckedEntry<K,V,T> checkedEntry(Map.Entry<K,V> e, 3911 Class<T> valueType) { 3912 return new CheckedEntry<>(e, valueType); 3913 } 3914 3915 /** 3916 * This "wrapper class" serves two purposes: it prevents 3917 * the client from modifying the backing Map, by short-circuiting 3918 * the setValue method, and it protects the backing Map against 3919 * an ill-behaved Map.Entry that attempts to modify another 3920 * Map.Entry when asked to perform an equality check. 3921 */ 3922 private static class CheckedEntry<K,V,T> implements Map.Entry<K,V> { 3923 private final Map.Entry<K, V> e; 3924 private final Class<T> valueType; 3925 3926 CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) { 3927 this.e = Objects.requireNonNull(e); 3928 this.valueType = Objects.requireNonNull(valueType); 3929 } 3930 3931 public K getKey() { return e.getKey(); } 3932 public V getValue() { return e.getValue(); } 3933 public int hashCode() { return e.hashCode(); } 3934 public String toString() { return e.toString(); } 3935 3936 public V setValue(V value) { 3937 if (value != null && !valueType.isInstance(value)) 3938 throw new ClassCastException(badValueMsg(value)); 3939 return e.setValue(value); 3940 } 3941 3942 private String badValueMsg(Object value) { 3943 return "Attempt to insert " + value.getClass() + 3944 " value into map with value type " + valueType; 3945 } 3946 3947 public boolean equals(Object o) { 3948 if (o == this) 3949 return true; 3950 if (!(o instanceof Map.Entry)) 3951 return false; 3952 return e.equals(new AbstractMap.SimpleImmutableEntry 3953 <>((Map.Entry<?,?>)o)); 3954 } 3955 } 3956 } 3957 } 3958 3959 /** 3960 * Returns a dynamically typesafe view of the specified sorted map. 3961 * Any attempt to insert a mapping whose key or value have the wrong 3962 * type will result in an immediate {@link ClassCastException}. 3963 * Similarly, any attempt to modify the value currently associated with 3964 * a key will result in an immediate {@link ClassCastException}, 3965 * whether the modification is attempted directly through the map 3966 * itself, or through a {@link Map.Entry} instance obtained from the 3967 * map's {@link Map#entrySet() entry set} view. 3968 * 3969 * <p>Assuming a map contains no incorrectly typed keys or values 3970 * prior to the time a dynamically typesafe view is generated, and 3971 * that all subsequent access to the map takes place through the view 3972 * (or one of its collection views), it is <i>guaranteed</i> that the 3973 * map cannot contain an incorrectly typed key or value. 3974 * 3975 * <p>A discussion of the use of dynamically typesafe views may be 3976 * found in the documentation for the {@link #checkedCollection 3977 * checkedCollection} method. 3978 * 3979 * <p>The returned map will be serializable if the specified map is 3980 * serializable. 3981 * 3982 * <p>Since {@code null} is considered to be a value of any reference 3983 * type, the returned map permits insertion of null keys or values 3984 * whenever the backing map does. 3985 * 3986 * @param <K> the class of the map keys 3987 * @param <V> the class of the map values 3988 * @param m the map for which a dynamically typesafe view is to be 3989 * returned 3990 * @param keyType the type of key that {@code m} is permitted to hold 3991 * @param valueType the type of value that {@code m} is permitted to hold 3992 * @return a dynamically typesafe view of the specified map 3993 * @since 1.5 3994 */ 3995 public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m, 3996 Class<K> keyType, 3997 Class<V> valueType) { 3998 return new CheckedSortedMap<>(m, keyType, valueType); 3999 } 4000 4001 /** 4002 * @serial include 4003 */ 4004 static class CheckedSortedMap<K,V> extends CheckedMap<K,V> 4005 implements SortedMap<K,V>, Serializable 4006 { 4007 private static final long serialVersionUID = 1599671320688067438L; 4008 4009 private final SortedMap<K, V> sm; 4010 4011 CheckedSortedMap(SortedMap<K, V> m, 4012 Class<K> keyType, Class<V> valueType) { 4013 super(m, keyType, valueType); 4014 sm = m; 4015 } 4016 4017 public Comparator<? super K> comparator() { return sm.comparator(); } 4018 public K firstKey() { return sm.firstKey(); } 4019 public K lastKey() { return sm.lastKey(); } 4020 4021 public SortedMap<K,V> subMap(K fromKey, K toKey) { 4022 return checkedSortedMap(sm.subMap(fromKey, toKey), 4023 keyType, valueType); 4024 } 4025 public SortedMap<K,V> headMap(K toKey) { 4026 return checkedSortedMap(sm.headMap(toKey), keyType, valueType); 4027 } 4028 public SortedMap<K,V> tailMap(K fromKey) { 4029 return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType); 4030 } 4031 } 4032 4033 /** 4034 * Returns a dynamically typesafe view of the specified navigable map. 4035 * Any attempt to insert a mapping whose key or value have the wrong 4036 * type will result in an immediate {@link ClassCastException}. 4037 * Similarly, any attempt to modify the value currently associated with 4038 * a key will result in an immediate {@link ClassCastException}, 4039 * whether the modification is attempted directly through the map 4040 * itself, or through a {@link Map.Entry} instance obtained from the 4041 * map's {@link Map#entrySet() entry set} view. 4042 * 4043 * <p>Assuming a map contains no incorrectly typed keys or values 4044 * prior to the time a dynamically typesafe view is generated, and 4045 * that all subsequent access to the map takes place through the view 4046 * (or one of its collection views), it is <em>guaranteed</em> that the 4047 * map cannot contain an incorrectly typed key or value. 4048 * 4049 * <p>A discussion of the use of dynamically typesafe views may be 4050 * found in the documentation for the {@link #checkedCollection 4051 * checkedCollection} method. 4052 * 4053 * <p>The returned map will be serializable if the specified map is 4054 * serializable. 4055 * 4056 * <p>Since {@code null} is considered to be a value of any reference 4057 * type, the returned map permits insertion of null keys or values 4058 * whenever the backing map does. 4059 * 4060 * @param <K> type of map keys 4061 * @param <V> type of map values 4062 * @param m the map for which a dynamically typesafe view is to be 4063 * returned 4064 * @param keyType the type of key that {@code m} is permitted to hold 4065 * @param valueType the type of value that {@code m} is permitted to hold 4066 * @return a dynamically typesafe view of the specified map 4067 * @since 1.8 4068 */ 4069 public static <K,V> NavigableMap<K,V> checkedNavigableMap(NavigableMap<K, V> m, 4070 Class<K> keyType, 4071 Class<V> valueType) { 4072 return new CheckedNavigableMap<>(m, keyType, valueType); 4073 } 4074 4075 /** 4076 * @serial include 4077 */ 4078 static class CheckedNavigableMap<K,V> extends CheckedSortedMap<K,V> 4079 implements NavigableMap<K,V>, Serializable 4080 { 4081 private static final long serialVersionUID = -4852462692372534096L; 4082 4083 private final NavigableMap<K, V> nm; 4084 4085 CheckedNavigableMap(NavigableMap<K, V> m, 4086 Class<K> keyType, Class<V> valueType) { 4087 super(m, keyType, valueType); 4088 nm = m; 4089 } 4090 4091 public Comparator<? super K> comparator() { return nm.comparator(); } 4092 public K firstKey() { return nm.firstKey(); } 4093 public K lastKey() { return nm.lastKey(); } 4094 4095 public Entry<K, V> lowerEntry(K key) { 4096 Entry<K,V> lower = nm.lowerEntry(key); 4097 return (null != lower) 4098 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(lower, valueType) 4099 : null; 4100 } 4101 4102 public K lowerKey(K key) { return nm.lowerKey(key); } 4103 4104 public Entry<K, V> floorEntry(K key) { 4105 Entry<K,V> floor = nm.floorEntry(key); 4106 return (null != floor) 4107 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(floor, valueType) 4108 : null; 4109 } 4110 4111 public K floorKey(K key) { return nm.floorKey(key); } 4112 4113 public Entry<K, V> ceilingEntry(K key) { 4114 Entry<K,V> ceiling = nm.ceilingEntry(key); 4115 return (null != ceiling) 4116 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(ceiling, valueType) 4117 : null; 4118 } 4119 4120 public K ceilingKey(K key) { return nm.ceilingKey(key); } 4121 4122 public Entry<K, V> higherEntry(K key) { 4123 Entry<K,V> higher = nm.higherEntry(key); 4124 return (null != higher) 4125 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(higher, valueType) 4126 : null; 4127 } 4128 4129 public K higherKey(K key) { return nm.higherKey(key); } 4130 4131 public Entry<K, V> firstEntry() { 4132 Entry<K,V> first = nm.firstEntry(); 4133 return (null != first) 4134 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(first, valueType) 4135 : null; 4136 } 4137 4138 public Entry<K, V> lastEntry() { 4139 Entry<K,V> last = nm.lastEntry(); 4140 return (null != last) 4141 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(last, valueType) 4142 : null; 4143 } 4144 4145 public Entry<K, V> pollFirstEntry() { 4146 Entry<K,V> entry = nm.pollFirstEntry(); 4147 return (null == entry) 4148 ? null 4149 : new CheckedMap.CheckedEntrySet.CheckedEntry<>(entry, valueType); 4150 } 4151 4152 public Entry<K, V> pollLastEntry() { 4153 Entry<K,V> entry = nm.pollLastEntry(); 4154 return (null == entry) 4155 ? null 4156 : new CheckedMap.CheckedEntrySet.CheckedEntry<>(entry, valueType); 4157 } 4158 4159 public NavigableMap<K, V> descendingMap() { 4160 return checkedNavigableMap(nm.descendingMap(), keyType, valueType); 4161 } 4162 4163 public NavigableSet<K> keySet() { 4164 return navigableKeySet(); 4165 } 4166 4167 public NavigableSet<K> navigableKeySet() { 4168 return checkedNavigableSet(nm.navigableKeySet(), keyType); 4169 } 4170 4171 public NavigableSet<K> descendingKeySet() { 4172 return checkedNavigableSet(nm.descendingKeySet(), keyType); 4173 } 4174 4175 @Override 4176 public NavigableMap<K,V> subMap(K fromKey, K toKey) { 4177 return checkedNavigableMap(nm.subMap(fromKey, true, toKey, false), 4178 keyType, valueType); 4179 } 4180 4181 @Override 4182 public NavigableMap<K,V> headMap(K toKey) { 4183 return checkedNavigableMap(nm.headMap(toKey, false), keyType, valueType); 4184 } 4185 4186 @Override 4187 public NavigableMap<K,V> tailMap(K fromKey) { 4188 return checkedNavigableMap(nm.tailMap(fromKey, true), keyType, valueType); 4189 } 4190 4191 public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) { 4192 return checkedNavigableMap(nm.subMap(fromKey, fromInclusive, toKey, toInclusive), keyType, valueType); 4193 } 4194 4195 public NavigableMap<K, V> headMap(K toKey, boolean inclusive) { 4196 return checkedNavigableMap(nm.headMap(toKey, inclusive), keyType, valueType); 4197 } 4198 4199 public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) { 4200 return checkedNavigableMap(nm.tailMap(fromKey, inclusive), keyType, valueType); 4201 } 4202 } 4203 4204 // Empty collections 4205 4206 /** 4207 * Returns an iterator that has no elements. More precisely, 4208 * 4209 * <ul> 4210 * <li>{@link Iterator#hasNext hasNext} always returns {@code 4211 * false}.</li> 4212 * <li>{@link Iterator#next next} always throws {@link 4213 * NoSuchElementException}.</li> 4214 * <li>{@link Iterator#remove remove} always throws {@link 4215 * IllegalStateException}.</li> 4216 * </ul> 4217 * 4218 * <p>Implementations of this method are permitted, but not 4219 * required, to return the same object from multiple invocations. 4220 * 4221 * @param <T> type of elements, if there were any, in the iterator 4222 * @return an empty iterator 4223 * @since 1.7 4224 */ 4225 @SuppressWarnings("unchecked") 4226 public static <T> Iterator<T> emptyIterator() { 4227 return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR; 4228 } 4229 4230 private static class EmptyIterator<E> implements Iterator<E> { 4231 static final EmptyIterator<Object> EMPTY_ITERATOR 4232 = new EmptyIterator<>(); 4233 4234 public boolean hasNext() { return false; } 4235 public E next() { throw new NoSuchElementException(); } 4236 public void remove() { throw new IllegalStateException(); } 4237 @Override 4238 public void forEachRemaining(Consumer<? super E> action) { 4239 Objects.requireNonNull(action); 4240 } 4241 } 4242 4243 /** 4244 * Returns a list iterator that has no elements. More precisely, 4245 * 4246 * <ul> 4247 * <li>{@link Iterator#hasNext hasNext} and {@link 4248 * ListIterator#hasPrevious hasPrevious} always return {@code 4249 * false}.</li> 4250 * <li>{@link Iterator#next next} and {@link ListIterator#previous 4251 * previous} always throw {@link NoSuchElementException}.</li> 4252 * <li>{@link Iterator#remove remove} and {@link ListIterator#set 4253 * set} always throw {@link IllegalStateException}.</li> 4254 * <li>{@link ListIterator#add add} always throws {@link 4255 * UnsupportedOperationException}.</li> 4256 * <li>{@link ListIterator#nextIndex nextIndex} always returns 4257 * {@code 0}.</li> 4258 * <li>{@link ListIterator#previousIndex previousIndex} always 4259 * returns {@code -1}.</li> 4260 * </ul> 4261 * 4262 * <p>Implementations of this method are permitted, but not 4263 * required, to return the same object from multiple invocations. 4264 * 4265 * @param <T> type of elements, if there were any, in the iterator 4266 * @return an empty list iterator 4267 * @since 1.7 4268 */ 4269 @SuppressWarnings("unchecked") 4270 public static <T> ListIterator<T> emptyListIterator() { 4271 return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR; 4272 } 4273 4274 private static class EmptyListIterator<E> 4275 extends EmptyIterator<E> 4276 implements ListIterator<E> 4277 { 4278 static final EmptyListIterator<Object> EMPTY_ITERATOR 4279 = new EmptyListIterator<>(); 4280 4281 public boolean hasPrevious() { return false; } 4282 public E previous() { throw new NoSuchElementException(); } 4283 public int nextIndex() { return 0; } 4284 public int previousIndex() { return -1; } 4285 public void set(E e) { throw new IllegalStateException(); } 4286 public void add(E e) { throw new UnsupportedOperationException(); } 4287 } 4288 4289 /** 4290 * Returns an enumeration that has no elements. More precisely, 4291 * 4292 * <ul> 4293 * <li>{@link Enumeration#hasMoreElements hasMoreElements} always 4294 * returns {@code false}.</li> 4295 * <li> {@link Enumeration#nextElement nextElement} always throws 4296 * {@link NoSuchElementException}.</li> 4297 * </ul> 4298 * 4299 * <p>Implementations of this method are permitted, but not 4300 * required, to return the same object from multiple invocations. 4301 * 4302 * @param <T> the class of the objects in the enumeration 4303 * @return an empty enumeration 4304 * @since 1.7 4305 */ 4306 @SuppressWarnings("unchecked") 4307 public static <T> Enumeration<T> emptyEnumeration() { 4308 return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION; 4309 } 4310 4311 private static class EmptyEnumeration<E> implements Enumeration<E> { 4312 static final EmptyEnumeration<Object> EMPTY_ENUMERATION 4313 = new EmptyEnumeration<>(); 4314 4315 public boolean hasMoreElements() { return false; } 4316 public E nextElement() { throw new NoSuchElementException(); } 4317 } 4318 4319 /** 4320 * The empty set (immutable). This set is serializable. 4321 * 4322 * @see #emptySet() 4323 */ 4324 @SuppressWarnings("rawtypes") 4325 public static final Set EMPTY_SET = new EmptySet<>(); 4326 4327 /** 4328 * Returns an empty set (immutable). This set is serializable. 4329 * Unlike the like-named field, this method is parameterized. 4330 * 4331 * <p>This example illustrates the type-safe way to obtain an empty set: 4332 * <pre> 4333 * Set<String> s = Collections.emptySet(); 4334 * </pre> 4335 * @implNote Implementations of this method need not create a separate 4336 * {@code Set} object for each call. Using this method is likely to have 4337 * comparable cost to using the like-named field. (Unlike this method, the 4338 * field does not provide type safety.) 4339 * 4340 * @param <T> the class of the objects in the set 4341 * @return the empty set 4342 * 4343 * @see #EMPTY_SET 4344 * @since 1.5 4345 */ 4346 @SuppressWarnings("unchecked") 4347 public static final <T> Set<T> emptySet() { 4348 return (Set<T>) EMPTY_SET; 4349 } 4350 4351 /** 4352 * @serial include 4353 */ 4354 private static class EmptySet<E> 4355 extends AbstractSet<E> 4356 implements Serializable 4357 { 4358 private static final long serialVersionUID = 1582296315990362920L; 4359 4360 public Iterator<E> iterator() { return emptyIterator(); } 4361 4362 public int size() {return 0;} 4363 public boolean isEmpty() {return true;} 4364 4365 public boolean contains(Object obj) {return false;} 4366 public boolean containsAll(Collection<?> c) { return c.isEmpty(); } 4367 4368 public Object[] toArray() { return new Object[0]; } 4369 4370 public <T> T[] toArray(T[] a) { 4371 if (a.length > 0) 4372 a[0] = null; 4373 return a; 4374 } 4375 4376 // Override default methods in Collection 4377 @Override 4378 public void forEach(Consumer<? super E> action) { 4379 Objects.requireNonNull(action); 4380 } 4381 @Override 4382 public boolean removeIf(Predicate<? super E> filter) { 4383 Objects.requireNonNull(filter); 4384 return false; 4385 } 4386 @Override 4387 public Spliterator<E> spliterator() { return Spliterators.emptySpliterator(); } 4388 4389 // Preserves singleton property 4390 private Object readResolve() { 4391 return EMPTY_SET; 4392 } 4393 } 4394 4395 /** 4396 * Returns an empty sorted set (immutable). This set is serializable. 4397 * 4398 * <p>This example illustrates the type-safe way to obtain an empty 4399 * sorted set: 4400 * <pre> {@code 4401 * SortedSet<String> s = Collections.emptySortedSet(); 4402 * }</pre> 4403 * 4404 * @implNote Implementations of this method need not create a separate 4405 * {@code SortedSet} object for each call. 4406 * 4407 * @param <E> type of elements, if there were any, in the set 4408 * @return the empty sorted set 4409 * @since 1.8 4410 */ 4411 @SuppressWarnings("unchecked") 4412 public static <E> SortedSet<E> emptySortedSet() { 4413 return (SortedSet<E>) UnmodifiableNavigableSet.EMPTY_NAVIGABLE_SET; 4414 } 4415 4416 /** 4417 * Returns an empty navigable set (immutable). This set is serializable. 4418 * 4419 * <p>This example illustrates the type-safe way to obtain an empty 4420 * navigable set: 4421 * <pre> {@code 4422 * NavigableSet<String> s = Collections.emptyNavigableSet(); 4423 * }</pre> 4424 * 4425 * @implNote Implementations of this method need not 4426 * create a separate {@code NavigableSet} object for each call. 4427 * 4428 * @param <E> type of elements, if there were any, in the set 4429 * @return the empty navigable set 4430 * @since 1.8 4431 */ 4432 @SuppressWarnings("unchecked") 4433 public static <E> NavigableSet<E> emptyNavigableSet() { 4434 return (NavigableSet<E>) UnmodifiableNavigableSet.EMPTY_NAVIGABLE_SET; 4435 } 4436 4437 /** 4438 * The empty list (immutable). This list is serializable. 4439 * 4440 * @see #emptyList() 4441 */ 4442 @SuppressWarnings("rawtypes") 4443 public static final List EMPTY_LIST = new EmptyList<>(); 4444 4445 /** 4446 * Returns an empty list (immutable). This list is serializable. 4447 * 4448 * <p>This example illustrates the type-safe way to obtain an empty list: 4449 * <pre> 4450 * List<String> s = Collections.emptyList(); 4451 * </pre> 4452 * 4453 * @implNote 4454 * Implementations of this method need not create a separate <tt>List</tt> 4455 * object for each call. Using this method is likely to have comparable 4456 * cost to using the like-named field. (Unlike this method, the field does 4457 * not provide type safety.) 4458 * 4459 * @param <T> type of elements, if there were any, in the list 4460 * @return an empty immutable list 4461 * 4462 * @see #EMPTY_LIST 4463 * @since 1.5 4464 */ 4465 @SuppressWarnings("unchecked") 4466 public static final <T> List<T> emptyList() { 4467 return (List<T>) EMPTY_LIST; 4468 } 4469 4470 /** 4471 * @serial include 4472 */ 4473 private static class EmptyList<E> 4474 extends AbstractList<E> 4475 implements RandomAccess, Serializable { 4476 private static final long serialVersionUID = 8842843931221139166L; 4477 4478 public Iterator<E> iterator() { 4479 return emptyIterator(); 4480 } 4481 public ListIterator<E> listIterator() { 4482 return emptyListIterator(); 4483 } 4484 4485 public int size() {return 0;} 4486 public boolean isEmpty() {return true;} 4487 4488 public boolean contains(Object obj) {return false;} 4489 public boolean containsAll(Collection<?> c) { return c.isEmpty(); } 4490 4491 public Object[] toArray() { return new Object[0]; } 4492 4493 public <T> T[] toArray(T[] a) { 4494 if (a.length > 0) 4495 a[0] = null; 4496 return a; 4497 } 4498 4499 public E get(int index) { 4500 throw new IndexOutOfBoundsException("Index: "+index); 4501 } 4502 4503 public boolean equals(Object o) { 4504 return (o instanceof List) && ((List<?>)o).isEmpty(); 4505 } 4506 4507 public int hashCode() { return 1; } 4508 4509 @Override 4510 public boolean removeIf(Predicate<? super E> filter) { 4511 Objects.requireNonNull(filter); 4512 return false; 4513 } 4514 @Override 4515 public void replaceAll(UnaryOperator<E> operator) { 4516 Objects.requireNonNull(operator); 4517 } 4518 @Override 4519 public void sort(Comparator<? super E> c) { 4520 } 4521 4522 // Override default methods in Collection 4523 @Override 4524 public void forEach(Consumer<? super E> action) { 4525 Objects.requireNonNull(action); 4526 } 4527 4528 @Override 4529 public Spliterator<E> spliterator() { return Spliterators.emptySpliterator(); } 4530 4531 // Preserves singleton property 4532 private Object readResolve() { 4533 return EMPTY_LIST; 4534 } 4535 } 4536 4537 /** 4538 * The empty map (immutable). This map is serializable. 4539 * 4540 * @see #emptyMap() 4541 * @since 1.3 4542 */ 4543 @SuppressWarnings("rawtypes") 4544 public static final Map EMPTY_MAP = new EmptyMap<>(); 4545 4546 /** 4547 * Returns an empty map (immutable). This map is serializable. 4548 * 4549 * <p>This example illustrates the type-safe way to obtain an empty map: 4550 * <pre> 4551 * Map<String, Date> s = Collections.emptyMap(); 4552 * </pre> 4553 * @implNote Implementations of this method need not create a separate 4554 * {@code Map} object for each call. Using this method is likely to have 4555 * comparable cost to using the like-named field. (Unlike this method, the 4556 * field does not provide type safety.) 4557 * 4558 * @param <K> the class of the map keys 4559 * @param <V> the class of the map values 4560 * @return an empty map 4561 * @see #EMPTY_MAP 4562 * @since 1.5 4563 */ 4564 @SuppressWarnings("unchecked") 4565 public static final <K,V> Map<K,V> emptyMap() { 4566 return (Map<K,V>) EMPTY_MAP; 4567 } 4568 4569 /** 4570 * Returns an empty sorted map (immutable). This map is serializable. 4571 * 4572 * <p>This example illustrates the type-safe way to obtain an empty map: 4573 * <pre> {@code 4574 * SortedMap<String, Date> s = Collections.emptySortedMap(); 4575 * }</pre> 4576 * 4577 * @implNote Implementations of this method need not create a separate 4578 * {@code SortedMap} object for each call. 4579 * 4580 * @param <K> the class of the map keys 4581 * @param <V> the class of the map values 4582 * @return an empty sorted map 4583 * @since 1.8 4584 */ 4585 @SuppressWarnings("unchecked") 4586 public static final <K,V> SortedMap<K,V> emptySortedMap() { 4587 return (SortedMap<K,V>) UnmodifiableNavigableMap.EMPTY_NAVIGABLE_MAP; 4588 } 4589 4590 /** 4591 * Returns an empty navigable map (immutable). This map is serializable. 4592 * 4593 * <p>This example illustrates the type-safe way to obtain an empty map: 4594 * <pre> {@code 4595 * NavigableMap<String, Date> s = Collections.emptyNavigableMap(); 4596 * }</pre> 4597 * 4598 * @implNote Implementations of this method need not create a separate 4599 * {@code NavigableMap} object for each call. 4600 * 4601 * @param <K> the class of the map keys 4602 * @param <V> the class of the map values 4603 * @return an empty navigable map 4604 * @since 1.8 4605 */ 4606 @SuppressWarnings("unchecked") 4607 public static final <K,V> NavigableMap<K,V> emptyNavigableMap() { 4608 return (NavigableMap<K,V>) UnmodifiableNavigableMap.EMPTY_NAVIGABLE_MAP; 4609 } 4610 4611 /** 4612 * @serial include 4613 */ 4614 private static class EmptyMap<K,V> 4615 extends AbstractMap<K,V> 4616 implements Serializable 4617 { 4618 private static final long serialVersionUID = 6428348081105594320L; 4619 4620 public int size() {return 0;} 4621 public boolean isEmpty() {return true;} 4622 public boolean containsKey(Object key) {return false;} 4623 public boolean containsValue(Object value) {return false;} 4624 public V get(Object key) {return null;} 4625 public Set<K> keySet() {return emptySet();} 4626 public Collection<V> values() {return emptySet();} 4627 public Set<Map.Entry<K,V>> entrySet() {return emptySet();} 4628 4629 public boolean equals(Object o) { 4630 return (o instanceof Map) && ((Map<?,?>)o).isEmpty(); 4631 } 4632 4633 public int hashCode() {return 0;} 4634 4635 // Override default methods in Map 4636 @Override 4637 @SuppressWarnings("unchecked") 4638 public V getOrDefault(Object k, V defaultValue) { 4639 return defaultValue; 4640 } 4641 4642 @Override 4643 public void forEach(BiConsumer<? super K, ? super V> action) { 4644 Objects.requireNonNull(action); 4645 } 4646 4647 @Override 4648 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 4649 Objects.requireNonNull(function); 4650 } 4651 4652 @Override 4653 public V putIfAbsent(K key, V value) { 4654 throw new UnsupportedOperationException(); 4655 } 4656 4657 @Override 4658 public boolean remove(Object key, Object value) { 4659 throw new UnsupportedOperationException(); 4660 } 4661 4662 @Override 4663 public boolean replace(K key, V oldValue, V newValue) { 4664 throw new UnsupportedOperationException(); 4665 } 4666 4667 @Override 4668 public V replace(K key, V value) { 4669 throw new UnsupportedOperationException(); 4670 } 4671 4672 @Override 4673 public V computeIfAbsent(K key, 4674 Function<? super K, ? extends V> mappingFunction) { 4675 throw new UnsupportedOperationException(); 4676 } 4677 4678 @Override 4679 public V computeIfPresent(K key, 4680 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 4681 throw new UnsupportedOperationException(); 4682 } 4683 4684 @Override 4685 public V compute(K key, 4686 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 4687 throw new UnsupportedOperationException(); 4688 } 4689 4690 @Override 4691 public V merge(K key, V value, 4692 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 4693 throw new UnsupportedOperationException(); 4694 } 4695 4696 // Preserves singleton property 4697 private Object readResolve() { 4698 return EMPTY_MAP; 4699 } 4700 } 4701 4702 // Singleton collections 4703 4704 /** 4705 * Returns an immutable set containing only the specified object. 4706 * The returned set is serializable. 4707 * 4708 * @param <T> the class of the objects in the set 4709 * @param o the sole object to be stored in the returned set. 4710 * @return an immutable set containing only the specified object. 4711 */ 4712 public static <T> Set<T> singleton(T o) { 4713 return new SingletonSet<>(o); 4714 } 4715 4716 static <E> Iterator<E> singletonIterator(final E e) { 4717 return new Iterator<E>() { 4718 private boolean hasNext = true; 4719 public boolean hasNext() { 4720 return hasNext; 4721 } 4722 public E next() { 4723 if (hasNext) { 4724 hasNext = false; 4725 return e; 4726 } 4727 throw new NoSuchElementException(); 4728 } 4729 public void remove() { 4730 throw new UnsupportedOperationException(); 4731 } 4732 @Override 4733 public void forEachRemaining(Consumer<? super E> action) { 4734 Objects.requireNonNull(action); 4735 if (hasNext) { 4736 action.accept(e); 4737 hasNext = false; 4738 } 4739 } 4740 }; 4741 } 4742 4743 /** 4744 * Creates a {@code Spliterator} with only the specified element 4745 * 4746 * @param <T> Type of elements 4747 * @return A singleton {@code Spliterator} 4748 */ 4749 static <T> Spliterator<T> singletonSpliterator(final T element) { 4750 return new Spliterator<T>() { 4751 long est = 1; 4752 4753 @Override 4754 public Spliterator<T> trySplit() { 4755 return null; 4756 } 4757 4758 @Override 4759 public boolean tryAdvance(Consumer<? super T> consumer) { 4760 Objects.requireNonNull(consumer); 4761 if (est > 0) { 4762 est--; 4763 consumer.accept(element); 4764 return true; 4765 } 4766 return false; 4767 } 4768 4769 @Override 4770 public void forEachRemaining(Consumer<? super T> consumer) { 4771 tryAdvance(consumer); 4772 } 4773 4774 @Override 4775 public long estimateSize() { 4776 return est; 4777 } 4778 4779 @Override 4780 public int characteristics() { 4781 int value = (element != null) ? Spliterator.NONNULL : 0; 4782 4783 return value | Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.IMMUTABLE | 4784 Spliterator.DISTINCT | Spliterator.ORDERED; 4785 } 4786 }; 4787 } 4788 4789 /** 4790 * @serial include 4791 */ 4792 private static class SingletonSet<E> 4793 extends AbstractSet<E> 4794 implements Serializable 4795 { 4796 private static final long serialVersionUID = 3193687207550431679L; 4797 4798 private final E element; 4799 4800 SingletonSet(E e) {element = e;} 4801 4802 public Iterator<E> iterator() { 4803 return singletonIterator(element); 4804 } 4805 4806 public int size() {return 1;} 4807 4808 public boolean contains(Object o) {return eq(o, element);} 4809 4810 // Override default methods for Collection 4811 @Override 4812 public void forEach(Consumer<? super E> action) { 4813 action.accept(element); 4814 } 4815 @Override 4816 public Spliterator<E> spliterator() { 4817 return singletonSpliterator(element); 4818 } 4819 @Override 4820 public boolean removeIf(Predicate<? super E> filter) { 4821 throw new UnsupportedOperationException(); 4822 } 4823 } 4824 4825 /** 4826 * Returns an immutable list containing only the specified object. 4827 * The returned list is serializable. 4828 * 4829 * @param <T> the class of the objects in the list 4830 * @param o the sole object to be stored in the returned list. 4831 * @return an immutable list containing only the specified object. 4832 * @since 1.3 4833 */ 4834 public static <T> List<T> singletonList(T o) { 4835 return new SingletonList<>(o); 4836 } 4837 4838 /** 4839 * @serial include 4840 */ 4841 private static class SingletonList<E> 4842 extends AbstractList<E> 4843 implements RandomAccess, Serializable { 4844 4845 private static final long serialVersionUID = 3093736618740652951L; 4846 4847 private final E element; 4848 4849 SingletonList(E obj) {element = obj;} 4850 4851 public Iterator<E> iterator() { 4852 return singletonIterator(element); 4853 } 4854 4855 public int size() {return 1;} 4856 4857 public boolean contains(Object obj) {return eq(obj, element);} 4858 4859 public E get(int index) { 4860 if (index != 0) 4861 throw new IndexOutOfBoundsException("Index: "+index+", Size: 1"); 4862 return element; 4863 } 4864 4865 // Override default methods for Collection 4866 @Override 4867 public void forEach(Consumer<? super E> action) { 4868 action.accept(element); 4869 } 4870 @Override 4871 public boolean removeIf(Predicate<? super E> filter) { 4872 throw new UnsupportedOperationException(); 4873 } 4874 @Override 4875 public void replaceAll(UnaryOperator<E> operator) { 4876 throw new UnsupportedOperationException(); 4877 } 4878 @Override 4879 public void sort(Comparator<? super E> c) { 4880 } 4881 @Override 4882 public Spliterator<E> spliterator() { 4883 return singletonSpliterator(element); 4884 } 4885 } 4886 4887 /** 4888 * Returns an immutable map, mapping only the specified key to the 4889 * specified value. The returned map is serializable. 4890 * 4891 * @param <K> the class of the map keys 4892 * @param <V> the class of the map values 4893 * @param key the sole key to be stored in the returned map. 4894 * @param value the value to which the returned map maps <tt>key</tt>. 4895 * @return an immutable map containing only the specified key-value 4896 * mapping. 4897 * @since 1.3 4898 */ 4899 public static <K,V> Map<K,V> singletonMap(K key, V value) { 4900 return new SingletonMap<>(key, value); 4901 } 4902 4903 /** 4904 * @serial include 4905 */ 4906 private static class SingletonMap<K,V> 4907 extends AbstractMap<K,V> 4908 implements Serializable { 4909 private static final long serialVersionUID = -6979724477215052911L; 4910 4911 private final K k; 4912 private final V v; 4913 4914 SingletonMap(K key, V value) { 4915 k = key; 4916 v = value; 4917 } 4918 4919 public int size() {return 1;} 4920 public boolean isEmpty() {return false;} 4921 public boolean containsKey(Object key) {return eq(key, k);} 4922 public boolean containsValue(Object value) {return eq(value, v);} 4923 public V get(Object key) {return (eq(key, k) ? v : null);} 4924 4925 private transient Set<K> keySet; 4926 private transient Set<Map.Entry<K,V>> entrySet; 4927 private transient Collection<V> values; 4928 4929 public Set<K> keySet() { 4930 if (keySet==null) 4931 keySet = singleton(k); 4932 return keySet; 4933 } 4934 4935 public Set<Map.Entry<K,V>> entrySet() { 4936 if (entrySet==null) 4937 entrySet = Collections.<Map.Entry<K,V>>singleton( 4938 new SimpleImmutableEntry<>(k, v)); 4939 return entrySet; 4940 } 4941 4942 public Collection<V> values() { 4943 if (values==null) 4944 values = singleton(v); 4945 return values; 4946 } 4947 4948 // Override default methods in Map 4949 @Override 4950 public V getOrDefault(Object key, V defaultValue) { 4951 return eq(key, k) ? v : defaultValue; 4952 } 4953 4954 @Override 4955 public void forEach(BiConsumer<? super K, ? super V> action) { 4956 action.accept(k, v); 4957 } 4958 4959 @Override 4960 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 4961 throw new UnsupportedOperationException(); 4962 } 4963 4964 @Override 4965 public V putIfAbsent(K key, V value) { 4966 throw new UnsupportedOperationException(); 4967 } 4968 4969 @Override 4970 public boolean remove(Object key, Object value) { 4971 throw new UnsupportedOperationException(); 4972 } 4973 4974 @Override 4975 public boolean replace(K key, V oldValue, V newValue) { 4976 throw new UnsupportedOperationException(); 4977 } 4978 4979 @Override 4980 public V replace(K key, V value) { 4981 throw new UnsupportedOperationException(); 4982 } 4983 4984 @Override 4985 public V computeIfAbsent(K key, 4986 Function<? super K, ? extends V> mappingFunction) { 4987 throw new UnsupportedOperationException(); 4988 } 4989 4990 @Override 4991 public V computeIfPresent(K key, 4992 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 4993 throw new UnsupportedOperationException(); 4994 } 4995 4996 @Override 4997 public V compute(K key, 4998 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 4999 throw new UnsupportedOperationException(); 5000 } 5001 5002 @Override 5003 public V merge(K key, V value, 5004 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 5005 throw new UnsupportedOperationException(); 5006 } 5007 } 5008 5009 // Miscellaneous 5010 5011 /** 5012 * Returns an immutable list consisting of <tt>n</tt> copies of the 5013 * specified object. The newly allocated data object is tiny (it contains 5014 * a single reference to the data object). This method is useful in 5015 * combination with the <tt>List.addAll</tt> method to grow lists. 5016 * The returned list is serializable. 5017 * 5018 * @param <T> the class of the object to copy and of the objects 5019 * in the returned list. 5020 * @param n the number of elements in the returned list. 5021 * @param o the element to appear repeatedly in the returned list. 5022 * @return an immutable list consisting of <tt>n</tt> copies of the 5023 * specified object. 5024 * @throws IllegalArgumentException if {@code n < 0} 5025 * @see List#addAll(Collection) 5026 * @see List#addAll(int, Collection) 5027 */ 5028 public static <T> List<T> nCopies(int n, T o) { 5029 if (n < 0) 5030 throw new IllegalArgumentException("List length = " + n); 5031 return new CopiesList<>(n, o); 5032 } 5033 5034 /** 5035 * @serial include 5036 */ 5037 private static class CopiesList<E> 5038 extends AbstractList<E> 5039 implements RandomAccess, Serializable 5040 { 5041 private static final long serialVersionUID = 2739099268398711800L; 5042 5043 final int n; 5044 final E element; 5045 5046 CopiesList(int n, E e) { 5047 assert n >= 0; 5048 this.n = n; 5049 element = e; 5050 } 5051 5052 public int size() { 5053 return n; 5054 } 5055 5056 public boolean contains(Object obj) { 5057 return n != 0 && eq(obj, element); 5058 } 5059 5060 public int indexOf(Object o) { 5061 return contains(o) ? 0 : -1; 5062 } 5063 5064 public int lastIndexOf(Object o) { 5065 return contains(o) ? n - 1 : -1; 5066 } 5067 5068 public E get(int index) { 5069 if (index < 0 || index >= n) 5070 throw new IndexOutOfBoundsException("Index: "+index+ 5071 ", Size: "+n); 5072 return element; 5073 } 5074 5075 public Object[] toArray() { 5076 final Object[] a = new Object[n]; 5077 if (element != null) 5078 Arrays.fill(a, 0, n, element); 5079 return a; 5080 } 5081 5082 @SuppressWarnings("unchecked") 5083 public <T> T[] toArray(T[] a) { 5084 final int n = this.n; 5085 if (a.length < n) { 5086 a = (T[])java.lang.reflect.Array 5087 .newInstance(a.getClass().getComponentType(), n); 5088 if (element != null) 5089 Arrays.fill(a, 0, n, element); 5090 } else { 5091 Arrays.fill(a, 0, n, element); 5092 if (a.length > n) 5093 a[n] = null; 5094 } 5095 return a; 5096 } 5097 5098 public List<E> subList(int fromIndex, int toIndex) { 5099 if (fromIndex < 0) 5100 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex); 5101 if (toIndex > n) 5102 throw new IndexOutOfBoundsException("toIndex = " + toIndex); 5103 if (fromIndex > toIndex) 5104 throw new IllegalArgumentException("fromIndex(" + fromIndex + 5105 ") > toIndex(" + toIndex + ")"); 5106 return new CopiesList<>(toIndex - fromIndex, element); 5107 } 5108 5109 // Override default methods in Collection 5110 @Override 5111 public Stream<E> stream() { 5112 return IntStream.range(0, n).mapToObj(i -> element); 5113 } 5114 5115 @Override 5116 public Stream<E> parallelStream() { 5117 return IntStream.range(0, n).parallel().mapToObj(i -> element); 5118 } 5119 5120 @Override 5121 public Spliterator<E> spliterator() { 5122 return stream().spliterator(); 5123 } 5124 } 5125 5126 /** 5127 * Returns a comparator that imposes the reverse of the <em>natural 5128 * ordering</em> on a collection of objects that implement the 5129 * {@code Comparable} interface. (The natural ordering is the ordering 5130 * imposed by the objects' own {@code compareTo} method.) This enables a 5131 * simple idiom for sorting (or maintaining) collections (or arrays) of 5132 * objects that implement the {@code Comparable} interface in 5133 * reverse-natural-order. For example, suppose {@code a} is an array of 5134 * strings. Then: <pre> 5135 * Arrays.sort(a, Collections.reverseOrder()); 5136 * </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p> 5137 * 5138 * The returned comparator is serializable. 5139 * 5140 * @param <T> the class of the objects compared by the comparator 5141 * @return A comparator that imposes the reverse of the <i>natural 5142 * ordering</i> on a collection of objects that implement 5143 * the <tt>Comparable</tt> interface. 5144 * @see Comparable 5145 */ 5146 @SuppressWarnings("unchecked") 5147 public static <T> Comparator<T> reverseOrder() { 5148 return (Comparator<T>) ReverseComparator.REVERSE_ORDER; 5149 } 5150 5151 /** 5152 * @serial include 5153 */ 5154 private static class ReverseComparator 5155 implements Comparator<Comparable<Object>>, Serializable { 5156 5157 private static final long serialVersionUID = 7207038068494060240L; 5158 5159 static final ReverseComparator REVERSE_ORDER 5160 = new ReverseComparator(); 5161 5162 public int compare(Comparable<Object> c1, Comparable<Object> c2) { 5163 return c2.compareTo(c1); 5164 } 5165 5166 private Object readResolve() { return Collections.reverseOrder(); } 5167 5168 @Override 5169 public Comparator<Comparable<Object>> reversed() { 5170 return Comparator.naturalOrder(); 5171 } 5172 } 5173 5174 /** 5175 * Returns a comparator that imposes the reverse ordering of the specified 5176 * comparator. If the specified comparator is {@code null}, this method is 5177 * equivalent to {@link #reverseOrder()} (in other words, it returns a 5178 * comparator that imposes the reverse of the <em>natural ordering</em> on 5179 * a collection of objects that implement the Comparable interface). 5180 * 5181 * <p>The returned comparator is serializable (assuming the specified 5182 * comparator is also serializable or {@code null}). 5183 * 5184 * @param <T> the class of the objects compared by the comparator 5185 * @param cmp a comparator who's ordering is to be reversed by the returned 5186 * comparator or {@code null} 5187 * @return A comparator that imposes the reverse ordering of the 5188 * specified comparator. 5189 * @since 1.5 5190 */ 5191 public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) { 5192 if (cmp == null) 5193 return reverseOrder(); 5194 5195 if (cmp instanceof ReverseComparator2) 5196 return ((ReverseComparator2<T>)cmp).cmp; 5197 5198 return new ReverseComparator2<>(cmp); 5199 } 5200 5201 /** 5202 * @serial include 5203 */ 5204 private static class ReverseComparator2<T> implements Comparator<T>, 5205 Serializable 5206 { 5207 private static final long serialVersionUID = 4374092139857L; 5208 5209 /** 5210 * The comparator specified in the static factory. This will never 5211 * be null, as the static factory returns a ReverseComparator 5212 * instance if its argument is null. 5213 * 5214 * @serial 5215 */ 5216 final Comparator<T> cmp; 5217 5218 ReverseComparator2(Comparator<T> cmp) { 5219 assert cmp != null; 5220 this.cmp = cmp; 5221 } 5222 5223 public int compare(T t1, T t2) { 5224 return cmp.compare(t2, t1); 5225 } 5226 5227 public boolean equals(Object o) { 5228 return (o == this) || 5229 (o instanceof ReverseComparator2 && 5230 cmp.equals(((ReverseComparator2)o).cmp)); 5231 } 5232 5233 public int hashCode() { 5234 return cmp.hashCode() ^ Integer.MIN_VALUE; 5235 } 5236 5237 @Override 5238 public Comparator<T> reversed() { 5239 return cmp; 5240 } 5241 } 5242 5243 /** 5244 * Returns an enumeration over the specified collection. This provides 5245 * interoperability with legacy APIs that require an enumeration 5246 * as input. 5247 * 5248 * @param <T> the class of the objects in the collection 5249 * @param c the collection for which an enumeration is to be returned. 5250 * @return an enumeration over the specified collection. 5251 * @see Enumeration 5252 */ 5253 public static <T> Enumeration<T> enumeration(final Collection<T> c) { 5254 return new Enumeration<T>() { 5255 private final Iterator<T> i = c.iterator(); 5256 5257 public boolean hasMoreElements() { 5258 return i.hasNext(); 5259 } 5260 5261 public T nextElement() { 5262 return i.next(); 5263 } 5264 }; 5265 } 5266 5267 /** 5268 * Returns an array list containing the elements returned by the 5269 * specified enumeration in the order they are returned by the 5270 * enumeration. This method provides interoperability between 5271 * legacy APIs that return enumerations and new APIs that require 5272 * collections. 5273 * 5274 * @param <T> the class of the objects returned by the enumeration 5275 * @param e enumeration providing elements for the returned 5276 * array list 5277 * @return an array list containing the elements returned 5278 * by the specified enumeration. 5279 * @since 1.4 5280 * @see Enumeration 5281 * @see ArrayList 5282 */ 5283 public static <T> ArrayList<T> list(Enumeration<T> e) { 5284 ArrayList<T> l = new ArrayList<>(); 5285 while (e.hasMoreElements()) 5286 l.add(e.nextElement()); 5287 return l; 5288 } 5289 5290 /** 5291 * Returns true if the specified arguments are equal, or both null. 5292 * 5293 * NB: Do not replace with Object.equals until JDK-8015417 is resolved. 5294 */ 5295 static boolean eq(Object o1, Object o2) { 5296 return o1==null ? o2==null : o1.equals(o2); 5297 } 5298 5299 /** 5300 * Returns the number of elements in the specified collection equal to the 5301 * specified object. More formally, returns the number of elements 5302 * <tt>e</tt> in the collection such that 5303 * <tt>(o == null ? e == null : o.equals(e))</tt>. 5304 * 5305 * @param c the collection in which to determine the frequency 5306 * of <tt>o</tt> 5307 * @param o the object whose frequency is to be determined 5308 * @return the number of elements in {@code c} equal to {@code o} 5309 * @throws NullPointerException if <tt>c</tt> is null 5310 * @since 1.5 5311 */ 5312 public static int frequency(Collection<?> c, Object o) { 5313 int result = 0; 5314 if (o == null) { 5315 for (Object e : c) 5316 if (e == null) 5317 result++; 5318 } else { 5319 for (Object e : c) 5320 if (o.equals(e)) 5321 result++; 5322 } 5323 return result; 5324 } 5325 5326 /** 5327 * Returns {@code true} if the two specified collections have no 5328 * elements in common. 5329 * 5330 * <p>Care must be exercised if this method is used on collections that 5331 * do not comply with the general contract for {@code Collection}. 5332 * Implementations may elect to iterate over either collection and test 5333 * for containment in the other collection (or to perform any equivalent 5334 * computation). If either collection uses a nonstandard equality test 5335 * (as does a {@link SortedSet} whose ordering is not <em>compatible with 5336 * equals</em>, or the key set of an {@link IdentityHashMap}), both 5337 * collections must use the same nonstandard equality test, or the 5338 * result of this method is undefined. 5339 * 5340 * <p>Care must also be exercised when using collections that have 5341 * restrictions on the elements that they may contain. Collection 5342 * implementations are allowed to throw exceptions for any operation 5343 * involving elements they deem ineligible. For absolute safety the 5344 * specified collections should contain only elements which are 5345 * eligible elements for both collections. 5346 * 5347 * <p>Note that it is permissible to pass the same collection in both 5348 * parameters, in which case the method will return {@code true} if and 5349 * only if the collection is empty. 5350 * 5351 * @param c1 a collection 5352 * @param c2 a collection 5353 * @return {@code true} if the two specified collections have no 5354 * elements in common. 5355 * @throws NullPointerException if either collection is {@code null}. 5356 * @throws NullPointerException if one collection contains a {@code null} 5357 * element and {@code null} is not an eligible element for the other collection. 5358 * (<a href="Collection.html#optional-restrictions">optional</a>) 5359 * @throws ClassCastException if one collection contains an element that is 5360 * of a type which is ineligible for the other collection. 5361 * (<a href="Collection.html#optional-restrictions">optional</a>) 5362 * @since 1.5 5363 */ 5364 public static boolean disjoint(Collection<?> c1, Collection<?> c2) { 5365 // The collection to be used for contains(). Preference is given to 5366 // the collection who's contains() has lower O() complexity. 5367 Collection<?> contains = c2; 5368 // The collection to be iterated. If the collections' contains() impl 5369 // are of different O() complexity, the collection with slower 5370 // contains() will be used for iteration. For collections who's 5371 // contains() are of the same complexity then best performance is 5372 // achieved by iterating the smaller collection. 5373 Collection<?> iterate = c1; 5374 5375 // Performance optimization cases. The heuristics: 5376 // 1. Generally iterate over c1. 5377 // 2. If c1 is a Set then iterate over c2. 5378 // 3. If either collection is empty then result is always true. 5379 // 4. Iterate over the smaller Collection. 5380 if (c1 instanceof Set) { 5381 // Use c1 for contains as a Set's contains() is expected to perform 5382 // better than O(N/2) 5383 iterate = c2; 5384 contains = c1; 5385 } else if (!(c2 instanceof Set)) { 5386 // Both are mere Collections. Iterate over smaller collection. 5387 // Example: If c1 contains 3 elements and c2 contains 50 elements and 5388 // assuming contains() requires ceiling(N/2) comparisons then 5389 // checking for all c1 elements in c2 would require 75 comparisons 5390 // (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring 5391 // 100 comparisons (50 * ceiling(3/2)). 5392 int c1size = c1.size(); 5393 int c2size = c2.size(); 5394 if (c1size == 0 || c2size == 0) { 5395 // At least one collection is empty. Nothing will match. 5396 return true; 5397 } 5398 5399 if (c1size > c2size) { 5400 iterate = c2; 5401 contains = c1; 5402 } 5403 } 5404 5405 for (Object e : iterate) { 5406 if (contains.contains(e)) { 5407 // Found a common element. Collections are not disjoint. 5408 return false; 5409 } 5410 } 5411 5412 // No common elements were found. 5413 return true; 5414 } 5415 5416 /** 5417 * Adds all of the specified elements to the specified collection. 5418 * Elements to be added may be specified individually or as an array. 5419 * The behavior of this convenience method is identical to that of 5420 * <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely 5421 * to run significantly faster under most implementations. 5422 * 5423 * <p>When elements are specified individually, this method provides a 5424 * convenient way to add a few elements to an existing collection: 5425 * <pre> 5426 * Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon"); 5427 * </pre> 5428 * 5429 * @param <T> the class of the elements to add and of the collection 5430 * @param c the collection into which <tt>elements</tt> are to be inserted 5431 * @param elements the elements to insert into <tt>c</tt> 5432 * @return <tt>true</tt> if the collection changed as a result of the call 5433 * @throws UnsupportedOperationException if <tt>c</tt> does not support 5434 * the <tt>add</tt> operation 5435 * @throws NullPointerException if <tt>elements</tt> contains one or more 5436 * null values and <tt>c</tt> does not permit null elements, or 5437 * if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt> 5438 * @throws IllegalArgumentException if some property of a value in 5439 * <tt>elements</tt> prevents it from being added to <tt>c</tt> 5440 * @see Collection#addAll(Collection) 5441 * @since 1.5 5442 */ 5443 @SafeVarargs 5444 public static <T> boolean addAll(Collection<? super T> c, T... elements) { 5445 boolean result = false; 5446 for (T element : elements) 5447 result |= c.add(element); 5448 return result; 5449 } 5450 5451 /** 5452 * Returns a set backed by the specified map. The resulting set displays 5453 * the same ordering, concurrency, and performance characteristics as the 5454 * backing map. In essence, this factory method provides a {@link Set} 5455 * implementation corresponding to any {@link Map} implementation. There 5456 * is no need to use this method on a {@link Map} implementation that 5457 * already has a corresponding {@link Set} implementation (such as {@link 5458 * HashMap} or {@link TreeMap}). 5459 * 5460 * <p>Each method invocation on the set returned by this method results in 5461 * exactly one method invocation on the backing map or its <tt>keySet</tt> 5462 * view, with one exception. The <tt>addAll</tt> method is implemented 5463 * as a sequence of <tt>put</tt> invocations on the backing map. 5464 * 5465 * <p>The specified map must be empty at the time this method is invoked, 5466 * and should not be accessed directly after this method returns. These 5467 * conditions are ensured if the map is created empty, passed directly 5468 * to this method, and no reference to the map is retained, as illustrated 5469 * in the following code fragment: 5470 * <pre> 5471 * Set<Object> weakHashSet = Collections.newSetFromMap( 5472 * new WeakHashMap<Object, Boolean>()); 5473 * </pre> 5474 * 5475 * @param <E> the class of the map keys and of the objects in the 5476 * returned set 5477 * @param map the backing map 5478 * @return the set backed by the map 5479 * @throws IllegalArgumentException if <tt>map</tt> is not empty 5480 * @since 1.6 5481 */ 5482 public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) { 5483 return new SetFromMap<>(map); 5484 } 5485 5486 /** 5487 * @serial include 5488 */ 5489 private static class SetFromMap<E> extends AbstractSet<E> 5490 implements Set<E>, Serializable 5491 { 5492 private final Map<E, Boolean> m; // The backing map 5493 private transient Set<E> s; // Its keySet 5494 5495 SetFromMap(Map<E, Boolean> map) { 5496 if (!map.isEmpty()) 5497 throw new IllegalArgumentException("Map is non-empty"); 5498 m = map; 5499 s = map.keySet(); 5500 } 5501 5502 public void clear() { m.clear(); } 5503 public int size() { return m.size(); } 5504 public boolean isEmpty() { return m.isEmpty(); } 5505 public boolean contains(Object o) { return m.containsKey(o); } 5506 public boolean remove(Object o) { return m.remove(o) != null; } 5507 public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; } 5508 public Iterator<E> iterator() { return s.iterator(); } 5509 public Object[] toArray() { return s.toArray(); } 5510 public <T> T[] toArray(T[] a) { return s.toArray(a); } 5511 public String toString() { return s.toString(); } 5512 public int hashCode() { return s.hashCode(); } 5513 public boolean equals(Object o) { return o == this || s.equals(o); } 5514 public boolean containsAll(Collection<?> c) {return s.containsAll(c);} 5515 public boolean removeAll(Collection<?> c) {return s.removeAll(c);} 5516 public boolean retainAll(Collection<?> c) {return s.retainAll(c);} 5517 // addAll is the only inherited implementation 5518 5519 // Override default methods in Collection 5520 @Override 5521 public void forEach(Consumer<? super E> action) { 5522 s.forEach(action); 5523 } 5524 @Override 5525 public boolean removeIf(Predicate<? super E> filter) { 5526 return s.removeIf(filter); 5527 } 5528 5529 @Override 5530 public Spliterator<E> spliterator() {return s.spliterator();} 5531 @Override 5532 public Stream<E> stream() {return s.stream();} 5533 @Override 5534 public Stream<E> parallelStream() {return s.parallelStream();} 5535 5536 private static final long serialVersionUID = 2454657854757543876L; 5537 5538 private void readObject(java.io.ObjectInputStream stream) 5539 throws IOException, ClassNotFoundException 5540 { 5541 stream.defaultReadObject(); 5542 s = m.keySet(); 5543 } 5544 } 5545 5546 /** 5547 * Returns a view of a {@link Deque} as a Last-in-first-out (Lifo) 5548 * {@link Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>, 5549 * <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This 5550 * view can be useful when you would like to use a method 5551 * requiring a <tt>Queue</tt> but you need Lifo ordering. 5552 * 5553 * <p>Each method invocation on the queue returned by this method 5554 * results in exactly one method invocation on the backing deque, with 5555 * one exception. The {@link Queue#addAll addAll} method is 5556 * implemented as a sequence of {@link Deque#addFirst addFirst} 5557 * invocations on the backing deque. 5558 * 5559 * @param <T> the class of the objects in the deque 5560 * @param deque the deque 5561 * @return the queue 5562 * @since 1.6 5563 */ 5564 public static <T> Queue<T> asLifoQueue(Deque<T> deque) { 5565 return new AsLIFOQueue<>(deque); 5566 } 5567 5568 /** 5569 * @serial include 5570 */ 5571 static class AsLIFOQueue<E> extends AbstractQueue<E> 5572 implements Queue<E>, Serializable { 5573 private static final long serialVersionUID = 1802017725587941708L; 5574 private final Deque<E> q; 5575 AsLIFOQueue(Deque<E> q) { this.q = q; } 5576 public boolean add(E e) { q.addFirst(e); return true; } 5577 public boolean offer(E e) { return q.offerFirst(e); } 5578 public E poll() { return q.pollFirst(); } 5579 public E remove() { return q.removeFirst(); } 5580 public E peek() { return q.peekFirst(); } 5581 public E element() { return q.getFirst(); } 5582 public void clear() { q.clear(); } 5583 public int size() { return q.size(); } 5584 public boolean isEmpty() { return q.isEmpty(); } 5585 public boolean contains(Object o) { return q.contains(o); } 5586 public boolean remove(Object o) { return q.remove(o); } 5587 public Iterator<E> iterator() { return q.iterator(); } 5588 public Object[] toArray() { return q.toArray(); } 5589 public <T> T[] toArray(T[] a) { return q.toArray(a); } 5590 public String toString() { return q.toString(); } 5591 public boolean containsAll(Collection<?> c) {return q.containsAll(c);} 5592 public boolean removeAll(Collection<?> c) {return q.removeAll(c);} 5593 public boolean retainAll(Collection<?> c) {return q.retainAll(c);} 5594 // We use inherited addAll; forwarding addAll would be wrong 5595 5596 // Override default methods in Collection 5597 @Override 5598 public void forEach(Consumer<? super E> action) {q.forEach(action);} 5599 @Override 5600 public boolean removeIf(Predicate<? super E> filter) { 5601 return q.removeIf(filter); 5602 } 5603 @Override 5604 public Spliterator<E> spliterator() {return q.spliterator();} 5605 @Override 5606 public Stream<E> stream() {return q.stream();} 5607 @Override 5608 public Stream<E> parallelStream() {return q.parallelStream();} 5609 } 5610 } 5611