Collections.java revision a8da445cdc91374ed0e105686feefd7e8ed79dc1
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 27package java.util; 28 29import java.io.IOException; 30import java.io.ObjectOutputStream; 31import java.io.Serializable; 32import java.lang.reflect.Array; 33import java.util.function.BiConsumer; 34import java.util.function.Consumer; 35 36 37/** 38 * This class consists exclusively of static methods that operate on or return 39 * collections. It contains polymorphic algorithms that operate on 40 * collections, "wrappers", which return a new collection backed by a 41 * specified collection, and a few other odds and ends. 42 * 43 * <p>The methods of this class all throw a <tt>NullPointerException</tt> 44 * if the collections or class objects provided to them are null. 45 * 46 * <p>The documentation for the polymorphic algorithms contained in this class 47 * generally includes a brief description of the <i>implementation</i>. Such 48 * descriptions should be regarded as <i>implementation notes</i>, rather than 49 * parts of the <i>specification</i>. Implementors should feel free to 50 * substitute other algorithms, so long as the specification itself is adhered 51 * to. (For example, the algorithm used by <tt>sort</tt> does not have to be 52 * a mergesort, but it does have to be <i>stable</i>.) 53 * 54 * <p>The "destructive" algorithms contained in this class, that is, the 55 * algorithms that modify the collection on which they operate, are specified 56 * to throw <tt>UnsupportedOperationException</tt> if the collection does not 57 * support the appropriate mutation primitive(s), such as the <tt>set</tt> 58 * method. These algorithms may, but are not required to, throw this 59 * exception if an invocation would have no effect on the collection. For 60 * example, invoking the <tt>sort</tt> method on an unmodifiable list that is 61 * already sorted may or may not throw <tt>UnsupportedOperationException</tt>. 62 * 63 * <p>This class is a member of the 64 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 65 * Java Collections Framework</a>. 66 * 67 * @author Josh Bloch 68 * @author Neal Gafter 69 * @see Collection 70 * @see Set 71 * @see List 72 * @see Map 73 * @since 1.2 74 */ 75 76public class Collections { 77 // Suppresses default constructor, ensuring non-instantiability. 78 private Collections() { 79 } 80 81 // Algorithms 82 83 /* 84 * Tuning parameters for algorithms - Many of the List algorithms have 85 * two implementations, one of which is appropriate for RandomAccess 86 * lists, the other for "sequential." Often, the random access variant 87 * yields better performance on small sequential access lists. The 88 * tuning parameters below determine the cutoff point for what constitutes 89 * a "small" sequential access list for each algorithm. The values below 90 * were empirically determined to work well for LinkedList. Hopefully 91 * they should be reasonable for other sequential access List 92 * implementations. Those doing performance work on this code would 93 * do well to validate the values of these parameters from time to time. 94 * (The first word of each tuning parameter name is the algorithm to which 95 * it applies.) 96 */ 97 private static final int BINARYSEARCH_THRESHOLD = 5000; 98 private static final int REVERSE_THRESHOLD = 18; 99 private static final int SHUFFLE_THRESHOLD = 5; 100 private static final int FILL_THRESHOLD = 25; 101 private static final int ROTATE_THRESHOLD = 100; 102 private static final int COPY_THRESHOLD = 10; 103 private static final int REPLACEALL_THRESHOLD = 11; 104 private static final int INDEXOFSUBLIST_THRESHOLD = 35; 105 106 /** 107 * Sorts the specified list into ascending order, according to the 108 * {@linkplain Comparable natural ordering} of its elements. 109 * All elements in the list must implement the {@link Comparable} 110 * interface. Furthermore, all elements in the list must be 111 * <i>mutually comparable</i> (that is, {@code e1.compareTo(e2)} 112 * must not throw a {@code ClassCastException} for any elements 113 * {@code e1} and {@code e2} in the list). 114 * 115 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will 116 * not be reordered as a result of the sort. 117 * 118 * <p>The specified list must be modifiable, but need not be resizable. 119 * 120 * <p>Implementation note: This implementation is a stable, adaptive, 121 * iterative mergesort that requires far fewer than n lg(n) comparisons 122 * when the input array is partially sorted, while offering the 123 * performance of a traditional mergesort when the input array is 124 * randomly ordered. If the input array is nearly sorted, the 125 * implementation requires approximately n comparisons. Temporary 126 * storage requirements vary from a small constant for nearly sorted 127 * input arrays to n/2 object references for randomly ordered input 128 * arrays. 129 * 130 * <p>The implementation takes equal advantage of ascending and 131 * descending order in its input array, and can take advantage of 132 * ascending and descending order in different parts of the same 133 * input array. It is well-suited to merging two or more sorted arrays: 134 * simply concatenate the arrays and sort the resulting array. 135 * 136 * <p>The implementation was adapted from Tim Peters's list sort for Python 137 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt"> 138 * TimSort</a>). It uses techiques from Peter McIlroy's "Optimistic 139 * Sorting and Information Theoretic Complexity", in Proceedings of the 140 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474, 141 * January 1993. 142 * 143 * <p>This implementation dumps the specified list into an array, sorts 144 * the array, and iterates over the list resetting each element 145 * from the corresponding position in the array. This avoids the 146 * n<sup>2</sup> log(n) performance that would result from attempting 147 * to sort a linked list in place. 148 * 149 * @param list the list to be sorted. 150 * @throws ClassCastException if the list contains elements that are not 151 * <i>mutually comparable</i> (for example, strings and integers). 152 * @throws UnsupportedOperationException if the specified list's 153 * list-iterator does not support the {@code set} operation. 154 * @throws IllegalArgumentException (optional) if the implementation 155 * detects that the natural ordering of the list elements is 156 * found to violate the {@link Comparable} contract 157 */ 158 public static <T extends Comparable<? super T>> void sort(List<T> list) { 159 if (list.getClass() == ArrayList.class) { 160 Arrays.sort(((ArrayList) list).elementData, 0, list.size()); 161 return; 162 } 163 164 Object[] a = list.toArray(); 165 Arrays.sort(a); 166 ListIterator<T> i = list.listIterator(); 167 for (int j=0; j<a.length; j++) { 168 i.next(); 169 i.set((T)a[j]); 170 } 171 } 172 173 /** 174 * Sorts the specified list according to the order induced by the 175 * specified comparator. All elements in the list must be <i>mutually 176 * comparable</i> using the specified comparator (that is, 177 * {@code c.compare(e1, e2)} must not throw a {@code ClassCastException} 178 * for any elements {@code e1} and {@code e2} in the list). 179 * 180 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will 181 * not be reordered as a result of the sort. 182 * 183 * <p>The specified list must be modifiable, but need not be resizable. 184 * 185 * <p>Implementation note: This implementation is a stable, adaptive, 186 * iterative mergesort that requires far fewer than n lg(n) comparisons 187 * when the input array is partially sorted, while offering the 188 * performance of a traditional mergesort when the input array is 189 * randomly ordered. If the input array is nearly sorted, the 190 * implementation requires approximately n comparisons. Temporary 191 * storage requirements vary from a small constant for nearly sorted 192 * input arrays to n/2 object references for randomly ordered input 193 * arrays. 194 * 195 * <p>The implementation takes equal advantage of ascending and 196 * descending order in its input array, and can take advantage of 197 * ascending and descending order in different parts of the same 198 * input array. It is well-suited to merging two or more sorted arrays: 199 * simply concatenate the arrays and sort the resulting array. 200 * 201 * <p>The implementation was adapted from Tim Peters's list sort for Python 202 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt"> 203 * TimSort</a>). It uses techiques from Peter McIlroy's "Optimistic 204 * Sorting and Information Theoretic Complexity", in Proceedings of the 205 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474, 206 * January 1993. 207 * 208 * <p>This implementation dumps the specified list into an array, sorts 209 * the array, and iterates over the list resetting each element 210 * from the corresponding position in the array. This avoids the 211 * n<sup>2</sup> log(n) performance that would result from attempting 212 * to sort a linked list in place. 213 * 214 * @param list the list to be sorted. 215 * @param c the comparator to determine the order of the list. A 216 * {@code null} value indicates that the elements' <i>natural 217 * ordering</i> should be used. 218 * @throws ClassCastException if the list contains elements that are not 219 * <i>mutually comparable</i> using the specified comparator. 220 * @throws UnsupportedOperationException if the specified list's 221 * list-iterator does not support the {@code set} operation. 222 * @throws IllegalArgumentException (optional) if the comparator is 223 * found to violate the {@link Comparator} contract 224 */ 225 public static <T> void sort(List<T> list, Comparator<? super T> c) { 226 if (list.getClass() == ArrayList.class) { 227 Arrays.sort(((ArrayList) list).elementData, 0, list.size(), (Comparator) c); 228 return; 229 } 230 231 Object[] a = list.toArray(); 232 Arrays.sort(a, (Comparator)c); 233 ListIterator i = list.listIterator(); 234 for (int j=0; j<a.length; j++) { 235 i.next(); 236 i.set(a[j]); 237 } 238 } 239 240 241 /** 242 * Searches the specified list for the specified object using the binary 243 * search algorithm. The list must be sorted into ascending order 244 * according to the {@linkplain Comparable natural ordering} of its 245 * elements (as by the {@link #sort(List)} method) prior to making this 246 * call. If it is not sorted, the results are undefined. If the list 247 * contains multiple elements equal to the specified object, there is no 248 * guarantee which one will be found. 249 * 250 * <p>This method runs in log(n) time for a "random access" list (which 251 * provides near-constant-time positional access). If the specified list 252 * does not implement the {@link RandomAccess} interface and is large, 253 * this method will do an iterator-based binary search that performs 254 * O(n) link traversals and O(log n) element comparisons. 255 * 256 * @param list the list to be searched. 257 * @param key the key to be searched for. 258 * @return the index of the search key, if it is contained in the list; 259 * otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The 260 * <i>insertion point</i> is defined as the point at which the 261 * key would be inserted into the list: the index of the first 262 * element greater than the key, or <tt>list.size()</tt> if all 263 * elements in the list are less than the specified key. Note 264 * that this guarantees that the return value will be >= 0 if 265 * and only if the key is found. 266 * @throws ClassCastException if the list contains elements that are not 267 * <i>mutually comparable</i> (for example, strings and 268 * integers), or the search key is not mutually comparable 269 * with the elements of the list. 270 */ 271 public static <T> 272 int binarySearch(List<? extends Comparable<? super T>> list, T key) { 273 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD) 274 return Collections.indexedBinarySearch(list, key); 275 else 276 return Collections.iteratorBinarySearch(list, key); 277 } 278 279 private static <T> 280 int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key) 281 { 282 int low = 0; 283 int high = list.size()-1; 284 285 while (low <= high) { 286 int mid = (low + high) >>> 1; 287 Comparable<? super T> midVal = list.get(mid); 288 int cmp = midVal.compareTo(key); 289 290 if (cmp < 0) 291 low = mid + 1; 292 else if (cmp > 0) 293 high = mid - 1; 294 else 295 return mid; // key found 296 } 297 return -(low + 1); // key not found 298 } 299 300 private static <T> 301 int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key) 302 { 303 int low = 0; 304 int high = list.size()-1; 305 ListIterator<? extends Comparable<? super T>> i = list.listIterator(); 306 307 while (low <= high) { 308 int mid = (low + high) >>> 1; 309 Comparable<? super T> midVal = get(i, mid); 310 int cmp = midVal.compareTo(key); 311 312 if (cmp < 0) 313 low = mid + 1; 314 else if (cmp > 0) 315 high = mid - 1; 316 else 317 return mid; // key found 318 } 319 return -(low + 1); // key not found 320 } 321 322 /** 323 * Gets the ith element from the given list by repositioning the specified 324 * list listIterator. 325 */ 326 private static <T> T get(ListIterator<? extends T> i, int index) { 327 T obj = null; 328 int pos = i.nextIndex(); 329 if (pos <= index) { 330 do { 331 obj = i.next(); 332 } while (pos++ < index); 333 } else { 334 do { 335 obj = i.previous(); 336 } while (--pos > index); 337 } 338 return obj; 339 } 340 341 /** 342 * Searches the specified list for the specified object using the binary 343 * search algorithm. The list must be sorted into ascending order 344 * according to the specified comparator (as by the 345 * {@link #sort(List, Comparator) sort(List, Comparator)} 346 * method), prior to making this call. If it is 347 * not sorted, the results are undefined. If the list contains multiple 348 * elements equal to the specified object, there is no guarantee which one 349 * will be found. 350 * 351 * <p>This method runs in log(n) time for a "random access" list (which 352 * provides near-constant-time positional access). If the specified list 353 * does not implement the {@link RandomAccess} interface and is large, 354 * this method will do an iterator-based binary search that performs 355 * O(n) link traversals and O(log n) element comparisons. 356 * 357 * @param list the list to be searched. 358 * @param key the key to be searched for. 359 * @param c the comparator by which the list is ordered. 360 * A <tt>null</tt> value indicates that the elements' 361 * {@linkplain Comparable natural ordering} should be used. 362 * @return the index of the search key, if it is contained in the list; 363 * otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The 364 * <i>insertion point</i> is defined as the point at which the 365 * key would be inserted into the list: the index of the first 366 * element greater than the key, or <tt>list.size()</tt> if all 367 * elements in the list are less than the specified key. Note 368 * that this guarantees that the return value will be >= 0 if 369 * and only if the key is found. 370 * @throws ClassCastException if the list contains elements that are not 371 * <i>mutually comparable</i> using the specified comparator, 372 * or the search key is not mutually comparable with the 373 * elements of the list using this comparator. 374 */ 375 public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) { 376 if (c==null) 377 return binarySearch((List) list, key); 378 379 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD) 380 return Collections.indexedBinarySearch(list, key, c); 381 else 382 return Collections.iteratorBinarySearch(list, key, c); 383 } 384 385 private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) { 386 int low = 0; 387 int high = l.size()-1; 388 389 while (low <= high) { 390 int mid = (low + high) >>> 1; 391 T midVal = l.get(mid); 392 int cmp = c.compare(midVal, key); 393 394 if (cmp < 0) 395 low = mid + 1; 396 else if (cmp > 0) 397 high = mid - 1; 398 else 399 return mid; // key found 400 } 401 return -(low + 1); // key not found 402 } 403 404 private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) { 405 int low = 0; 406 int high = l.size()-1; 407 ListIterator<? extends T> i = l.listIterator(); 408 409 while (low <= high) { 410 int mid = (low + high) >>> 1; 411 T midVal = get(i, mid); 412 int cmp = c.compare(midVal, key); 413 414 if (cmp < 0) 415 low = mid + 1; 416 else if (cmp > 0) 417 high = mid - 1; 418 else 419 return mid; // key found 420 } 421 return -(low + 1); // key not found 422 } 423 424 private interface SelfComparable extends Comparable<SelfComparable> {} 425 426 427 /** 428 * Reverses the order of the elements in the specified list.<p> 429 * 430 * This method runs in linear time. 431 * 432 * @param list the list whose elements are to be reversed. 433 * @throws UnsupportedOperationException if the specified list or 434 * its list-iterator does not support the <tt>set</tt> operation. 435 */ 436 public static void reverse(List<?> list) { 437 int size = list.size(); 438 if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) { 439 for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--) 440 swap(list, i, j); 441 } else { 442 ListIterator fwd = list.listIterator(); 443 ListIterator rev = list.listIterator(size); 444 for (int i=0, mid=list.size()>>1; i<mid; i++) { 445 Object tmp = fwd.next(); 446 fwd.set(rev.previous()); 447 rev.set(tmp); 448 } 449 } 450 } 451 452 /** 453 * Randomly permutes the specified list using a default source of 454 * randomness. All permutations occur with approximately equal 455 * likelihood.<p> 456 * 457 * The hedge "approximately" is used in the foregoing description because 458 * default source of randomness is only approximately an unbiased source 459 * of independently chosen bits. If it were a perfect source of randomly 460 * chosen bits, then the algorithm would choose permutations with perfect 461 * uniformity.<p> 462 * 463 * This implementation traverses the list backwards, from the last element 464 * up to the second, repeatedly swapping a randomly selected element into 465 * the "current position". Elements are randomly selected from the 466 * portion of the list that runs from the first element to the current 467 * position, inclusive.<p> 468 * 469 * This method runs in linear time. If the specified list does not 470 * implement the {@link RandomAccess} interface and is large, this 471 * implementation dumps the specified list into an array before shuffling 472 * it, and dumps the shuffled array back into the list. This avoids the 473 * quadratic behavior that would result from shuffling a "sequential 474 * access" list in place. 475 * 476 * @param list the list to be shuffled. 477 * @throws UnsupportedOperationException if the specified list or 478 * its list-iterator does not support the <tt>set</tt> operation. 479 */ 480 public static void shuffle(List<?> list) { 481 Random rnd = r; 482 if (rnd == null) 483 r = rnd = new Random(); 484 shuffle(list, rnd); 485 } 486 private static Random r; 487 488 /** 489 * Randomly permute the specified list using the specified source of 490 * randomness. All permutations occur with equal likelihood 491 * assuming that the source of randomness is fair.<p> 492 * 493 * This implementation traverses the list backwards, from the last element 494 * up to the second, repeatedly swapping a randomly selected element into 495 * the "current position". Elements are randomly selected from the 496 * portion of the list that runs from the first element to the current 497 * position, inclusive.<p> 498 * 499 * This method runs in linear time. If the specified list does not 500 * implement the {@link RandomAccess} interface and is large, this 501 * implementation dumps the specified list into an array before shuffling 502 * it, and dumps the shuffled array back into the list. This avoids the 503 * quadratic behavior that would result from shuffling a "sequential 504 * access" list in place. 505 * 506 * @param list the list to be shuffled. 507 * @param rnd the source of randomness to use to shuffle the list. 508 * @throws UnsupportedOperationException if the specified list or its 509 * list-iterator does not support the <tt>set</tt> operation. 510 */ 511 public static void shuffle(List<?> list, Random rnd) { 512 int size = list.size(); 513 if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) { 514 for (int i=size; i>1; i--) 515 swap(list, i-1, rnd.nextInt(i)); 516 } else { 517 Object arr[] = list.toArray(); 518 519 // Shuffle array 520 for (int i=size; i>1; i--) 521 swap(arr, i-1, rnd.nextInt(i)); 522 523 // Dump array back into list 524 ListIterator it = list.listIterator(); 525 for (int i=0; i<arr.length; i++) { 526 it.next(); 527 it.set(arr[i]); 528 } 529 } 530 } 531 532 /** 533 * Swaps the elements at the specified positions in the specified list. 534 * (If the specified positions are equal, invoking this method leaves 535 * the list unchanged.) 536 * 537 * @param list The list in which to swap elements. 538 * @param i the index of one element to be swapped. 539 * @param j the index of the other element to be swapped. 540 * @throws IndexOutOfBoundsException if either <tt>i</tt> or <tt>j</tt> 541 * is out of range (i < 0 || i >= list.size() 542 * || j < 0 || j >= list.size()). 543 * @since 1.4 544 */ 545 public static void swap(List<?> list, int i, int j) { 546 final List l = list; 547 l.set(i, l.set(j, l.get(i))); 548 } 549 550 /** 551 * Swaps the two specified elements in the specified array. 552 */ 553 private static void swap(Object[] arr, int i, int j) { 554 Object tmp = arr[i]; 555 arr[i] = arr[j]; 556 arr[j] = tmp; 557 } 558 559 /** 560 * Replaces all of the elements of the specified list with the specified 561 * element. <p> 562 * 563 * This method runs in linear time. 564 * 565 * @param list the list to be filled with the specified element. 566 * @param obj The element with which to fill the specified list. 567 * @throws UnsupportedOperationException if the specified list or its 568 * list-iterator does not support the <tt>set</tt> operation. 569 */ 570 public static <T> void fill(List<? super T> list, T obj) { 571 int size = list.size(); 572 573 if (size < FILL_THRESHOLD || list instanceof RandomAccess) { 574 for (int i=0; i<size; i++) 575 list.set(i, obj); 576 } else { 577 ListIterator<? super T> itr = list.listIterator(); 578 for (int i=0; i<size; i++) { 579 itr.next(); 580 itr.set(obj); 581 } 582 } 583 } 584 585 /** 586 * Copies all of the elements from one list into another. After the 587 * operation, the index of each copied element in the destination list 588 * will be identical to its index in the source list. The destination 589 * list must be at least as long as the source list. If it is longer, the 590 * remaining elements in the destination list are unaffected. <p> 591 * 592 * This method runs in linear time. 593 * 594 * @param dest The destination list. 595 * @param src The source list. 596 * @throws IndexOutOfBoundsException if the destination list is too small 597 * to contain the entire source List. 598 * @throws UnsupportedOperationException if the destination list's 599 * list-iterator does not support the <tt>set</tt> operation. 600 */ 601 public static <T> void copy(List<? super T> dest, List<? extends T> src) { 602 int srcSize = src.size(); 603 if (srcSize > dest.size()) 604 throw new IndexOutOfBoundsException("Source does not fit in dest"); 605 606 if (srcSize < COPY_THRESHOLD || 607 (src instanceof RandomAccess && dest instanceof RandomAccess)) { 608 for (int i=0; i<srcSize; i++) 609 dest.set(i, src.get(i)); 610 } else { 611 ListIterator<? super T> di=dest.listIterator(); 612 ListIterator<? extends T> si=src.listIterator(); 613 for (int i=0; i<srcSize; i++) { 614 di.next(); 615 di.set(si.next()); 616 } 617 } 618 } 619 620 /** 621 * Returns the minimum element of the given collection, according to the 622 * <i>natural ordering</i> of its elements. All elements in the 623 * collection must implement the <tt>Comparable</tt> interface. 624 * Furthermore, all elements in the collection must be <i>mutually 625 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a 626 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 627 * <tt>e2</tt> in the collection).<p> 628 * 629 * This method iterates over the entire collection, hence it requires 630 * time proportional to the size of the collection. 631 * 632 * @param coll the collection whose minimum element is to be determined. 633 * @return the minimum element of the given collection, according 634 * to the <i>natural ordering</i> of its elements. 635 * @throws ClassCastException if the collection contains elements that are 636 * not <i>mutually comparable</i> (for example, strings and 637 * integers). 638 * @throws NoSuchElementException if the collection is empty. 639 * @see Comparable 640 */ 641 public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) { 642 Iterator<? extends T> i = coll.iterator(); 643 T candidate = i.next(); 644 645 while (i.hasNext()) { 646 T next = i.next(); 647 if (next.compareTo(candidate) < 0) 648 candidate = next; 649 } 650 return candidate; 651 } 652 653 /** 654 * Returns the minimum element of the given collection, according to the 655 * order induced by the specified comparator. All elements in the 656 * collection must be <i>mutually comparable</i> by the specified 657 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a 658 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 659 * <tt>e2</tt> in the collection).<p> 660 * 661 * This method iterates over the entire collection, hence it requires 662 * time proportional to the size of the collection. 663 * 664 * @param coll the collection whose minimum element is to be determined. 665 * @param comp the comparator with which to determine the minimum element. 666 * A <tt>null</tt> value indicates that the elements' <i>natural 667 * ordering</i> should be used. 668 * @return the minimum element of the given collection, according 669 * to the specified comparator. 670 * @throws ClassCastException if the collection contains elements that are 671 * not <i>mutually comparable</i> using the specified comparator. 672 * @throws NoSuchElementException if the collection is empty. 673 * @see Comparable 674 */ 675 public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) { 676 if (comp==null) 677 return (T)min((Collection<SelfComparable>) (Collection) coll); 678 679 Iterator<? extends T> i = coll.iterator(); 680 T candidate = i.next(); 681 682 while (i.hasNext()) { 683 T next = i.next(); 684 if (comp.compare(next, candidate) < 0) 685 candidate = next; 686 } 687 return candidate; 688 } 689 690 /** 691 * Returns the maximum element of the given collection, according to the 692 * <i>natural ordering</i> of its elements. All elements in the 693 * collection must implement the <tt>Comparable</tt> interface. 694 * Furthermore, all elements in the collection must be <i>mutually 695 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a 696 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 697 * <tt>e2</tt> in the collection).<p> 698 * 699 * This method iterates over the entire collection, hence it requires 700 * time proportional to the size of the collection. 701 * 702 * @param coll the collection whose maximum element is to be determined. 703 * @return the maximum element of the given collection, according 704 * to the <i>natural ordering</i> of its elements. 705 * @throws ClassCastException if the collection contains elements that are 706 * not <i>mutually comparable</i> (for example, strings and 707 * integers). 708 * @throws NoSuchElementException if the collection is empty. 709 * @see Comparable 710 */ 711 public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) { 712 Iterator<? extends T> i = coll.iterator(); 713 T candidate = i.next(); 714 715 while (i.hasNext()) { 716 T next = i.next(); 717 if (next.compareTo(candidate) > 0) 718 candidate = next; 719 } 720 return candidate; 721 } 722 723 /** 724 * Returns the maximum element of the given collection, according to the 725 * order induced by the specified comparator. All elements in the 726 * collection must be <i>mutually comparable</i> by the specified 727 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a 728 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 729 * <tt>e2</tt> in the collection).<p> 730 * 731 * This method iterates over the entire collection, hence it requires 732 * time proportional to the size of the collection. 733 * 734 * @param coll the collection whose maximum element is to be determined. 735 * @param comp the comparator with which to determine the maximum element. 736 * A <tt>null</tt> value indicates that the elements' <i>natural 737 * ordering</i> should be used. 738 * @return the maximum element of the given collection, according 739 * to the specified comparator. 740 * @throws ClassCastException if the collection contains elements that are 741 * not <i>mutually comparable</i> using the specified comparator. 742 * @throws NoSuchElementException if the collection is empty. 743 * @see Comparable 744 */ 745 public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) { 746 if (comp==null) 747 return (T)max((Collection<SelfComparable>) (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 */ 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 } 821 822 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 } 844 845 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 list the list in which replacement is to occur. 868 * @param oldVal the old value to be replaced. 869 * @param newVal the new value with which <tt>oldVal</tt> is to be 870 * replaced. 871 * @return <tt>true</tt> if <tt>list</tt> contained one or more elements 872 * <tt>e</tt> such that 873 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>. 874 * @throws UnsupportedOperationException if the specified list or 875 * its list-iterator does not support the <tt>set</tt> operation. 876 * @since 1.4 877 */ 878 public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) { 879 boolean result = false; 880 int size = list.size(); 881 if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) { 882 if (oldVal==null) { 883 for (int i=0; i<size; i++) { 884 if (list.get(i)==null) { 885 list.set(i, newVal); 886 result = true; 887 } 888 } 889 } else { 890 for (int i=0; i<size; i++) { 891 if (oldVal.equals(list.get(i))) { 892 list.set(i, newVal); 893 result = true; 894 } 895 } 896 } 897 } else { 898 ListIterator<T> itr=list.listIterator(); 899 if (oldVal==null) { 900 for (int i=0; i<size; i++) { 901 if (itr.next()==null) { 902 itr.set(newVal); 903 result = true; 904 } 905 } 906 } else { 907 for (int i=0; i<size; i++) { 908 if (oldVal.equals(itr.next())) { 909 itr.set(newVal); 910 result = true; 911 } 912 } 913 } 914 } 915 return result; 916 } 917 918 /** 919 * Returns the starting position of the first occurrence of the specified 920 * target list within the specified source list, or -1 if there is no 921 * such occurrence. More formally, returns the lowest index <tt>i</tt> 922 * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>, 923 * or -1 if there is no such index. (Returns -1 if 924 * <tt>target.size() > source.size()</tt>.) 925 * 926 * <p>This implementation uses the "brute force" technique of scanning 927 * over the source list, looking for a match with the target at each 928 * location in turn. 929 * 930 * @param source the list in which to search for the first occurrence 931 * of <tt>target</tt>. 932 * @param target the list to search for as a subList of <tt>source</tt>. 933 * @return the starting position of the first occurrence of the specified 934 * target list within the specified source list, or -1 if there 935 * is no such occurrence. 936 * @since 1.4 937 */ 938 public static int indexOfSubList(List<?> source, List<?> target) { 939 int sourceSize = source.size(); 940 int targetSize = target.size(); 941 int maxCandidate = sourceSize - targetSize; 942 943 if (sourceSize < INDEXOFSUBLIST_THRESHOLD || 944 (source instanceof RandomAccess&&target instanceof RandomAccess)) { 945 nextCand: 946 for (int candidate = 0; candidate <= maxCandidate; candidate++) { 947 for (int i=0, j=candidate; i<targetSize; i++, j++) 948 if (!eq(target.get(i), source.get(j))) 949 continue nextCand; // Element mismatch, try next cand 950 return candidate; // All elements of candidate matched target 951 } 952 } else { // Iterator version of above algorithm 953 ListIterator<?> si = source.listIterator(); 954 nextCand: 955 for (int candidate = 0; candidate <= maxCandidate; candidate++) { 956 ListIterator<?> ti = target.listIterator(); 957 for (int i=0; i<targetSize; i++) { 958 if (!eq(ti.next(), si.next())) { 959 // Back up source iterator to next candidate 960 for (int j=0; j<i; j++) 961 si.previous(); 962 continue nextCand; 963 } 964 } 965 return candidate; 966 } 967 } 968 return -1; // No candidate matched the target 969 } 970 971 /** 972 * Returns the starting position of the last occurrence of the specified 973 * target list within the specified source list, or -1 if there is no such 974 * occurrence. More formally, returns the highest index <tt>i</tt> 975 * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>, 976 * or -1 if there is no such index. (Returns -1 if 977 * <tt>target.size() > source.size()</tt>.) 978 * 979 * <p>This implementation uses the "brute force" technique of iterating 980 * over the source list, looking for a match with the target at each 981 * location in turn. 982 * 983 * @param source the list in which to search for the last occurrence 984 * of <tt>target</tt>. 985 * @param target the list to search for as a subList of <tt>source</tt>. 986 * @return the starting position of the last occurrence of the specified 987 * target list within the specified source list, or -1 if there 988 * is no such occurrence. 989 * @since 1.4 990 */ 991 public static int lastIndexOfSubList(List<?> source, List<?> target) { 992 int sourceSize = source.size(); 993 int targetSize = target.size(); 994 int maxCandidate = sourceSize - targetSize; 995 996 if (sourceSize < INDEXOFSUBLIST_THRESHOLD || 997 source instanceof RandomAccess) { // Index access version 998 nextCand: 999 for (int candidate = maxCandidate; candidate >= 0; candidate--) { 1000 for (int i=0, j=candidate; i<targetSize; i++, j++) 1001 if (!eq(target.get(i), source.get(j))) 1002 continue nextCand; // Element mismatch, try next cand 1003 return candidate; // All elements of candidate matched target 1004 } 1005 } else { // Iterator version of above algorithm 1006 if (maxCandidate < 0) 1007 return -1; 1008 ListIterator<?> si = source.listIterator(maxCandidate); 1009 nextCand: 1010 for (int candidate = maxCandidate; candidate >= 0; candidate--) { 1011 ListIterator<?> ti = target.listIterator(); 1012 for (int i=0; i<targetSize; i++) { 1013 if (!eq(ti.next(), si.next())) { 1014 if (candidate != 0) { 1015 // Back up source iterator to next candidate 1016 for (int j=0; j<=i+1; j++) 1017 si.previous(); 1018 } 1019 continue nextCand; 1020 } 1021 } 1022 return candidate; 1023 } 1024 } 1025 return -1; // No candidate matched the target 1026 } 1027 1028 1029 // Unmodifiable Wrappers 1030 1031 /** 1032 * Returns an unmodifiable view of the specified collection. This method 1033 * allows modules to provide users with "read-only" access to internal 1034 * collections. Query operations on the returned collection "read through" 1035 * to the specified collection, and attempts to modify the returned 1036 * collection, whether direct or via its iterator, result in an 1037 * <tt>UnsupportedOperationException</tt>.<p> 1038 * 1039 * The returned collection does <i>not</i> pass the hashCode and equals 1040 * operations through to the backing collection, but relies on 1041 * <tt>Object</tt>'s <tt>equals</tt> and <tt>hashCode</tt> methods. This 1042 * is necessary to preserve the contracts of these operations in the case 1043 * that the backing collection is a set or a list.<p> 1044 * 1045 * The returned collection will be serializable if the specified collection 1046 * is serializable. 1047 * 1048 * @param c the collection for which an unmodifiable view is to be 1049 * returned. 1050 * @return an unmodifiable view of the specified collection. 1051 */ 1052 public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) { 1053 return new UnmodifiableCollection<>(c); 1054 } 1055 1056 /** 1057 * @serial include 1058 */ 1059 static class UnmodifiableCollection<E> implements Collection<E>, Serializable { 1060 private static final long serialVersionUID = 1820017752578914078L; 1061 1062 final Collection<? extends E> c; 1063 1064 UnmodifiableCollection(Collection<? extends E> c) { 1065 if (c==null) 1066 throw new NullPointerException(); 1067 this.c = c; 1068 } 1069 1070 public int size() {return c.size();} 1071 public boolean isEmpty() {return c.isEmpty();} 1072 public boolean contains(Object o) {return c.contains(o);} 1073 public Object[] toArray() {return c.toArray();} 1074 public <T> T[] toArray(T[] a) {return c.toArray(a);} 1075 public String toString() {return c.toString();} 1076 1077 public Iterator<E> iterator() { 1078 return new Iterator<E>() { 1079 private final Iterator<? extends E> i = c.iterator(); 1080 1081 public boolean hasNext() {return i.hasNext();} 1082 public E next() {return i.next();} 1083 public void remove() { 1084 throw new UnsupportedOperationException(); 1085 } 1086 @Override 1087 public void forEachRemaining(Consumer<? super E> action) { 1088 // Use backing collection version 1089 i.forEachRemaining(action); 1090 } 1091 }; 1092 } 1093 1094 public boolean add(E e) { 1095 throw new UnsupportedOperationException(); 1096 } 1097 public boolean remove(Object o) { 1098 throw new UnsupportedOperationException(); 1099 } 1100 1101 public boolean containsAll(Collection<?> coll) { 1102 return c.containsAll(coll); 1103 } 1104 public boolean addAll(Collection<? extends E> coll) { 1105 throw new UnsupportedOperationException(); 1106 } 1107 public boolean removeAll(Collection<?> coll) { 1108 throw new UnsupportedOperationException(); 1109 } 1110 public boolean retainAll(Collection<?> coll) { 1111 throw new UnsupportedOperationException(); 1112 } 1113 public void clear() { 1114 throw new UnsupportedOperationException(); 1115 } 1116 1117 // Override default methods in Collection 1118 @Override 1119 public void forEach(Consumer<? super E> action) { 1120 c.forEach(action); 1121 } 1122 } 1123 1124 /** 1125 * Returns an unmodifiable view of the specified set. This method allows 1126 * modules to provide users with "read-only" access to internal sets. 1127 * Query operations on the returned set "read through" to the specified 1128 * set, and attempts to modify the returned set, whether direct or via its 1129 * iterator, result in an <tt>UnsupportedOperationException</tt>.<p> 1130 * 1131 * The returned set will be serializable if the specified set 1132 * is serializable. 1133 * 1134 * @param s the set for which an unmodifiable view is to be returned. 1135 * @return an unmodifiable view of the specified set. 1136 */ 1137 public static <T> Set<T> unmodifiableSet(Set<? extends T> s) { 1138 return new UnmodifiableSet<>(s); 1139 } 1140 1141 /** 1142 * @serial include 1143 */ 1144 static class UnmodifiableSet<E> extends UnmodifiableCollection<E> 1145 implements Set<E>, Serializable { 1146 private static final long serialVersionUID = -9215047833775013803L; 1147 1148 UnmodifiableSet(Set<? extends E> s) {super(s);} 1149 public boolean equals(Object o) {return o == this || c.equals(o);} 1150 public int hashCode() {return c.hashCode();} 1151 } 1152 1153 /** 1154 * Returns an unmodifiable view of the specified sorted set. This method 1155 * allows modules to provide users with "read-only" access to internal 1156 * sorted sets. Query operations on the returned sorted set "read 1157 * through" to the specified sorted set. Attempts to modify the returned 1158 * sorted set, whether direct, via its iterator, or via its 1159 * <tt>subSet</tt>, <tt>headSet</tt>, or <tt>tailSet</tt> views, result in 1160 * an <tt>UnsupportedOperationException</tt>.<p> 1161 * 1162 * The returned sorted set will be serializable if the specified sorted set 1163 * is serializable. 1164 * 1165 * @param s the sorted set for which an unmodifiable view is to be 1166 * returned. 1167 * @return an unmodifiable view of the specified sorted set. 1168 */ 1169 public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) { 1170 return new UnmodifiableSortedSet<>(s); 1171 } 1172 1173 /** 1174 * @serial include 1175 */ 1176 static class UnmodifiableSortedSet<E> 1177 extends UnmodifiableSet<E> 1178 implements SortedSet<E>, Serializable { 1179 private static final long serialVersionUID = -4929149591599911165L; 1180 private final SortedSet<E> ss; 1181 1182 UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;} 1183 1184 public Comparator<? super E> comparator() {return ss.comparator();} 1185 1186 public SortedSet<E> subSet(E fromElement, E toElement) { 1187 return new UnmodifiableSortedSet<>(ss.subSet(fromElement,toElement)); 1188 } 1189 public SortedSet<E> headSet(E toElement) { 1190 return new UnmodifiableSortedSet<>(ss.headSet(toElement)); 1191 } 1192 public SortedSet<E> tailSet(E fromElement) { 1193 return new UnmodifiableSortedSet<>(ss.tailSet(fromElement)); 1194 } 1195 1196 public E first() {return ss.first();} 1197 public E last() {return ss.last();} 1198 } 1199 1200 /** 1201 * Returns an unmodifiable view of the specified list. This method allows 1202 * modules to provide users with "read-only" access to internal 1203 * lists. Query operations on the returned list "read through" to the 1204 * specified list, and attempts to modify the returned list, whether 1205 * direct or via its iterator, result in an 1206 * <tt>UnsupportedOperationException</tt>.<p> 1207 * 1208 * The returned list will be serializable if the specified list 1209 * is serializable. Similarly, the returned list will implement 1210 * {@link RandomAccess} if the specified list does. 1211 * 1212 * @param list the list for which an unmodifiable view is to be returned. 1213 * @return an unmodifiable view of the specified list. 1214 */ 1215 public static <T> List<T> unmodifiableList(List<? extends T> list) { 1216 return (list instanceof RandomAccess ? 1217 new UnmodifiableRandomAccessList<>(list) : 1218 new UnmodifiableList<>(list)); 1219 } 1220 1221 /** 1222 * @serial include 1223 */ 1224 static class UnmodifiableList<E> extends UnmodifiableCollection<E> 1225 implements List<E> { 1226 private static final long serialVersionUID = -283967356065247728L; 1227 final List<? extends E> list; 1228 1229 UnmodifiableList(List<? extends E> list) { 1230 super(list); 1231 this.list = list; 1232 } 1233 1234 public boolean equals(Object o) {return o == this || list.equals(o);} 1235 public int hashCode() {return list.hashCode();} 1236 1237 public E get(int index) {return list.get(index);} 1238 public E set(int index, E element) { 1239 throw new UnsupportedOperationException(); 1240 } 1241 public void add(int index, E element) { 1242 throw new UnsupportedOperationException(); 1243 } 1244 public E remove(int index) { 1245 throw new UnsupportedOperationException(); 1246 } 1247 public int indexOf(Object o) {return list.indexOf(o);} 1248 public int lastIndexOf(Object o) {return list.lastIndexOf(o);} 1249 public boolean addAll(int index, Collection<? extends E> c) { 1250 throw new UnsupportedOperationException(); 1251 } 1252 public ListIterator<E> listIterator() {return listIterator(0);} 1253 1254 public ListIterator<E> listIterator(final int index) { 1255 return new ListIterator<E>() { 1256 private final ListIterator<? extends E> i 1257 = list.listIterator(index); 1258 1259 public boolean hasNext() {return i.hasNext();} 1260 public E next() {return i.next();} 1261 public boolean hasPrevious() {return i.hasPrevious();} 1262 public E previous() {return i.previous();} 1263 public int nextIndex() {return i.nextIndex();} 1264 public int previousIndex() {return i.previousIndex();} 1265 1266 public void remove() { 1267 throw new UnsupportedOperationException(); 1268 } 1269 public void set(E e) { 1270 throw new UnsupportedOperationException(); 1271 } 1272 public void add(E e) { 1273 throw new UnsupportedOperationException(); 1274 } 1275 1276 @Override 1277 public void forEachRemaining(Consumer<? super E> action) { 1278 i.forEachRemaining(action); 1279 } 1280 }; 1281 } 1282 1283 public List<E> subList(int fromIndex, int toIndex) { 1284 return new UnmodifiableList<>(list.subList(fromIndex, toIndex)); 1285 } 1286 1287 /** 1288 * UnmodifiableRandomAccessList instances are serialized as 1289 * UnmodifiableList instances to allow them to be deserialized 1290 * in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList). 1291 * This method inverts the transformation. As a beneficial 1292 * side-effect, it also grafts the RandomAccess marker onto 1293 * UnmodifiableList instances that were serialized in pre-1.4 JREs. 1294 * 1295 * Note: Unfortunately, UnmodifiableRandomAccessList instances 1296 * serialized in 1.4.1 and deserialized in 1.4 will become 1297 * UnmodifiableList instances, as this method was missing in 1.4. 1298 */ 1299 private Object readResolve() { 1300 return (list instanceof RandomAccess 1301 ? new UnmodifiableRandomAccessList<>(list) 1302 : this); 1303 } 1304 } 1305 1306 /** 1307 * @serial include 1308 */ 1309 static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E> 1310 implements RandomAccess 1311 { 1312 UnmodifiableRandomAccessList(List<? extends E> list) { 1313 super(list); 1314 } 1315 1316 public List<E> subList(int fromIndex, int toIndex) { 1317 return new UnmodifiableRandomAccessList<>( 1318 list.subList(fromIndex, toIndex)); 1319 } 1320 1321 private static final long serialVersionUID = -2542308836966382001L; 1322 1323 /** 1324 * Allows instances to be deserialized in pre-1.4 JREs (which do 1325 * not have UnmodifiableRandomAccessList). UnmodifiableList has 1326 * a readResolve method that inverts this transformation upon 1327 * deserialization. 1328 */ 1329 private Object writeReplace() { 1330 return new UnmodifiableList<>(list); 1331 } 1332 } 1333 1334 /** 1335 * Returns an unmodifiable view of the specified map. This method 1336 * allows modules to provide users with "read-only" access to internal 1337 * maps. Query operations on the returned map "read through" 1338 * to the specified map, and attempts to modify the returned 1339 * map, whether direct or via its collection views, result in an 1340 * <tt>UnsupportedOperationException</tt>.<p> 1341 * 1342 * The returned map will be serializable if the specified map 1343 * is serializable. 1344 * 1345 * @param m the map for which an unmodifiable view is to be returned. 1346 * @return an unmodifiable view of the specified map. 1347 */ 1348 public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) { 1349 return new UnmodifiableMap<>(m); 1350 } 1351 1352 /** 1353 * @serial include 1354 */ 1355 private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable { 1356 private static final long serialVersionUID = -1034234728574286014L; 1357 1358 private final Map<? extends K, ? extends V> m; 1359 1360 UnmodifiableMap(Map<? extends K, ? extends V> m) { 1361 if (m==null) 1362 throw new NullPointerException(); 1363 this.m = m; 1364 } 1365 1366 public int size() {return m.size();} 1367 public boolean isEmpty() {return m.isEmpty();} 1368 public boolean containsKey(Object key) {return m.containsKey(key);} 1369 public boolean containsValue(Object val) {return m.containsValue(val);} 1370 public V get(Object key) {return m.get(key);} 1371 1372 public V put(K key, V value) { 1373 throw new UnsupportedOperationException(); 1374 } 1375 public V remove(Object key) { 1376 throw new UnsupportedOperationException(); 1377 } 1378 public void putAll(Map<? extends K, ? extends V> m) { 1379 throw new UnsupportedOperationException(); 1380 } 1381 public void clear() { 1382 throw new UnsupportedOperationException(); 1383 } 1384 1385 private transient Set<K> keySet = null; 1386 private transient Set<Map.Entry<K,V>> entrySet = null; 1387 private transient Collection<V> values = null; 1388 1389 public Set<K> keySet() { 1390 if (keySet==null) 1391 keySet = unmodifiableSet(m.keySet()); 1392 return keySet; 1393 } 1394 1395 public Set<Map.Entry<K,V>> entrySet() { 1396 if (entrySet==null) 1397 entrySet = new UnmodifiableEntrySet<>(m.entrySet()); 1398 return entrySet; 1399 } 1400 1401 public Collection<V> values() { 1402 if (values==null) 1403 values = unmodifiableCollection(m.values()); 1404 return values; 1405 } 1406 1407 public boolean equals(Object o) {return o == this || m.equals(o);} 1408 public int hashCode() {return m.hashCode();} 1409 public String toString() {return m.toString();} 1410 1411 // Override default methods in Map 1412 @Override 1413 public void forEach(BiConsumer<? super K, ? super V> action) { 1414 m.forEach(action); 1415 } 1416 1417 /** 1418 * We need this class in addition to UnmodifiableSet as 1419 * Map.Entries themselves permit modification of the backing Map 1420 * via their setValue operation. This class is subtle: there are 1421 * many possible attacks that must be thwarted. 1422 * 1423 * @serial include 1424 */ 1425 static class UnmodifiableEntrySet<K,V> 1426 extends UnmodifiableSet<Map.Entry<K,V>> { 1427 private static final long serialVersionUID = 7854390611657943733L; 1428 1429 UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) { 1430 super((Set)s); 1431 } 1432 1433 static <K, V> Consumer<Map.Entry<K, V>> entryConsumer(Consumer<? super Entry<K, V>> action) { 1434 return e -> action.accept(new UnmodifiableEntry<>(e)); 1435 } 1436 1437 // Override default methods in Collection 1438 public void forEach(Consumer<? super Entry<K, V>> action) { 1439 Objects.requireNonNull(action); 1440 c.forEach(entryConsumer(action)); 1441 } 1442 1443 public Iterator<Map.Entry<K,V>> iterator() { 1444 return new Iterator<Map.Entry<K,V>>() { 1445 private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator(); 1446 1447 public boolean hasNext() { 1448 return i.hasNext(); 1449 } 1450 public Map.Entry<K,V> next() { 1451 return new UnmodifiableEntry<>(i.next()); 1452 } 1453 public void remove() { 1454 throw new UnsupportedOperationException(); 1455 } 1456 // Android-note: This seems pretty inconsistent. Unlike other subclasses, we aren't 1457 // delegating to the subclass iterator here. Seems like an oversight. 1458 }; 1459 } 1460 1461 public Object[] toArray() { 1462 Object[] a = c.toArray(); 1463 for (int i=0; i<a.length; i++) 1464 a[i] = new UnmodifiableEntry<>((Map.Entry<K,V>)a[i]); 1465 return a; 1466 } 1467 1468 public <T> T[] toArray(T[] a) { 1469 // We don't pass a to c.toArray, to avoid window of 1470 // vulnerability wherein an unscrupulous multithreaded client 1471 // could get his hands on raw (unwrapped) Entries from c. 1472 Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0)); 1473 1474 for (int i=0; i<arr.length; i++) 1475 arr[i] = new UnmodifiableEntry<>((Map.Entry<K,V>)arr[i]); 1476 1477 if (arr.length > a.length) 1478 return (T[])arr; 1479 1480 System.arraycopy(arr, 0, a, 0, arr.length); 1481 if (a.length > arr.length) 1482 a[arr.length] = null; 1483 return a; 1484 } 1485 1486 /** 1487 * This method is overridden to protect the backing set against 1488 * an object with a nefarious equals function that senses 1489 * that the equality-candidate is Map.Entry and calls its 1490 * setValue method. 1491 */ 1492 public boolean contains(Object o) { 1493 if (!(o instanceof Map.Entry)) 1494 return false; 1495 return c.contains( 1496 new UnmodifiableEntry<>((Map.Entry<?,?>) o)); 1497 } 1498 1499 /** 1500 * The next two methods are overridden to protect against 1501 * an unscrupulous List whose contains(Object o) method senses 1502 * when o is a Map.Entry, and calls o.setValue. 1503 */ 1504 public boolean containsAll(Collection<?> coll) { 1505 for (Object e : coll) { 1506 if (!contains(e)) // Invokes safe contains() above 1507 return false; 1508 } 1509 return true; 1510 } 1511 public boolean equals(Object o) { 1512 if (o == this) 1513 return true; 1514 1515 if (!(o instanceof Set)) 1516 return false; 1517 Set s = (Set) o; 1518 if (s.size() != c.size()) 1519 return false; 1520 return containsAll(s); // Invokes safe containsAll() above 1521 } 1522 1523 /** 1524 * This "wrapper class" serves two purposes: it prevents 1525 * the client from modifying the backing Map, by short-circuiting 1526 * the setValue method, and it protects the backing Map against 1527 * an ill-behaved Map.Entry that attempts to modify another 1528 * Map Entry when asked to perform an equality check. 1529 */ 1530 private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> { 1531 private Map.Entry<? extends K, ? extends V> e; 1532 1533 UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) {this.e = e;} 1534 1535 public K getKey() {return e.getKey();} 1536 public V getValue() {return e.getValue();} 1537 public V setValue(V value) { 1538 throw new UnsupportedOperationException(); 1539 } 1540 public int hashCode() {return e.hashCode();} 1541 public boolean equals(Object o) { 1542 if (this == o) 1543 return true; 1544 if (!(o instanceof Map.Entry)) 1545 return false; 1546 Map.Entry t = (Map.Entry)o; 1547 return eq(e.getKey(), t.getKey()) && 1548 eq(e.getValue(), t.getValue()); 1549 } 1550 public String toString() {return e.toString();} 1551 } 1552 } 1553 } 1554 1555 /** 1556 * Returns an unmodifiable view of the specified sorted map. This method 1557 * allows modules to provide users with "read-only" access to internal 1558 * sorted maps. Query operations on the returned sorted map "read through" 1559 * to the specified sorted map. Attempts to modify the returned 1560 * sorted map, whether direct, via its collection views, or via its 1561 * <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in 1562 * an <tt>UnsupportedOperationException</tt>.<p> 1563 * 1564 * The returned sorted map will be serializable if the specified sorted map 1565 * is serializable. 1566 * 1567 * @param m the sorted map for which an unmodifiable view is to be 1568 * returned. 1569 * @return an unmodifiable view of the specified sorted map. 1570 */ 1571 public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) { 1572 return new UnmodifiableSortedMap<>(m); 1573 } 1574 1575 /** 1576 * @serial include 1577 */ 1578 static class UnmodifiableSortedMap<K,V> 1579 extends UnmodifiableMap<K,V> 1580 implements SortedMap<K,V>, Serializable { 1581 private static final long serialVersionUID = -8806743815996713206L; 1582 1583 private final SortedMap<K, ? extends V> sm; 1584 1585 UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m;} 1586 1587 public Comparator<? super K> comparator() {return sm.comparator();} 1588 1589 public SortedMap<K,V> subMap(K fromKey, K toKey) { 1590 return new UnmodifiableSortedMap<>(sm.subMap(fromKey, toKey)); 1591 } 1592 public SortedMap<K,V> headMap(K toKey) { 1593 return new UnmodifiableSortedMap<>(sm.headMap(toKey)); 1594 } 1595 public SortedMap<K,V> tailMap(K fromKey) { 1596 return new UnmodifiableSortedMap<>(sm.tailMap(fromKey)); 1597 } 1598 1599 public K firstKey() {return sm.firstKey();} 1600 public K lastKey() {return sm.lastKey();} 1601 } 1602 1603 1604 // Synch Wrappers 1605 1606 /** 1607 * Returns a synchronized (thread-safe) collection backed by the specified 1608 * collection. In order to guarantee serial access, it is critical that 1609 * <strong>all</strong> access to the backing collection is accomplished 1610 * through the returned collection.<p> 1611 * 1612 * It is imperative that the user manually synchronize on the returned 1613 * collection when iterating over it: 1614 * <pre> 1615 * Collection c = Collections.synchronizedCollection(myCollection); 1616 * ... 1617 * synchronized (c) { 1618 * Iterator i = c.iterator(); // Must be in the synchronized block 1619 * while (i.hasNext()) 1620 * foo(i.next()); 1621 * } 1622 * </pre> 1623 * Failure to follow this advice may result in non-deterministic behavior. 1624 * 1625 * <p>The returned collection does <i>not</i> pass the <tt>hashCode</tt> 1626 * and <tt>equals</tt> operations through to the backing collection, but 1627 * relies on <tt>Object</tt>'s equals and hashCode methods. This is 1628 * necessary to preserve the contracts of these operations in the case 1629 * that the backing collection is a set or a list.<p> 1630 * 1631 * The returned collection will be serializable if the specified collection 1632 * is serializable. 1633 * 1634 * @param c the collection to be "wrapped" in a synchronized collection. 1635 * @return a synchronized view of the specified collection. 1636 */ 1637 public static <T> Collection<T> synchronizedCollection(Collection<T> c) { 1638 return new SynchronizedCollection<>(c); 1639 } 1640 1641 static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) { 1642 return new SynchronizedCollection<>(c, mutex); 1643 } 1644 1645 /** 1646 * @serial include 1647 */ 1648 static class SynchronizedCollection<E> implements Collection<E>, Serializable { 1649 private static final long serialVersionUID = 3053995032091335093L; 1650 1651 final Collection<E> c; // Backing Collection 1652 final Object mutex; // Object on which to synchronize 1653 1654 SynchronizedCollection(Collection<E> c) { 1655 if (c==null) 1656 throw new NullPointerException(); 1657 this.c = c; 1658 mutex = this; 1659 } 1660 SynchronizedCollection(Collection<E> c, Object mutex) { 1661 this.c = c; 1662 this.mutex = mutex; 1663 } 1664 1665 public int size() { 1666 synchronized (mutex) {return c.size();} 1667 } 1668 public boolean isEmpty() { 1669 synchronized (mutex) {return c.isEmpty();} 1670 } 1671 public boolean contains(Object o) { 1672 synchronized (mutex) {return c.contains(o);} 1673 } 1674 public Object[] toArray() { 1675 synchronized (mutex) {return c.toArray();} 1676 } 1677 public <T> T[] toArray(T[] a) { 1678 synchronized (mutex) {return c.toArray(a);} 1679 } 1680 1681 public Iterator<E> iterator() { 1682 return c.iterator(); // Must be manually synched by user! 1683 } 1684 1685 public boolean add(E e) { 1686 synchronized (mutex) {return c.add(e);} 1687 } 1688 public boolean remove(Object o) { 1689 synchronized (mutex) {return c.remove(o);} 1690 } 1691 1692 public boolean containsAll(Collection<?> coll) { 1693 synchronized (mutex) {return c.containsAll(coll);} 1694 } 1695 public boolean addAll(Collection<? extends E> coll) { 1696 synchronized (mutex) {return c.addAll(coll);} 1697 } 1698 public boolean removeAll(Collection<?> coll) { 1699 synchronized (mutex) {return c.removeAll(coll);} 1700 } 1701 public boolean retainAll(Collection<?> coll) { 1702 synchronized (mutex) {return c.retainAll(coll);} 1703 } 1704 public void clear() { 1705 synchronized (mutex) {c.clear();} 1706 } 1707 public String toString() { 1708 synchronized (mutex) {return c.toString();} 1709 } 1710 1711 // Override default methods in Collection 1712 @Override 1713 public void forEach(Consumer<? super E> consumer) { 1714 synchronized (mutex) {c.forEach(consumer);} 1715 } 1716 1717 private void writeObject(ObjectOutputStream s) throws IOException { 1718 synchronized (mutex) {s.defaultWriteObject();} 1719 } 1720 } 1721 1722 /** 1723 * Returns a synchronized (thread-safe) set backed by the specified 1724 * set. In order to guarantee serial access, it is critical that 1725 * <strong>all</strong> access to the backing set is accomplished 1726 * through the returned set.<p> 1727 * 1728 * It is imperative that the user manually synchronize on the returned 1729 * set when iterating over it: 1730 * <pre> 1731 * Set s = Collections.synchronizedSet(new HashSet()); 1732 * ... 1733 * synchronized (s) { 1734 * Iterator i = s.iterator(); // Must be in the synchronized block 1735 * while (i.hasNext()) 1736 * foo(i.next()); 1737 * } 1738 * </pre> 1739 * Failure to follow this advice may result in non-deterministic behavior. 1740 * 1741 * <p>The returned set will be serializable if the specified set is 1742 * serializable. 1743 * 1744 * @param s the set to be "wrapped" in a synchronized set. 1745 * @return a synchronized view of the specified set. 1746 */ 1747 public static <T> Set<T> synchronizedSet(Set<T> s) { 1748 return new SynchronizedSet<>(s); 1749 } 1750 1751 static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) { 1752 return new SynchronizedSet<>(s, mutex); 1753 } 1754 1755 /** 1756 * @serial include 1757 */ 1758 static class SynchronizedSet<E> 1759 extends SynchronizedCollection<E> 1760 implements Set<E> { 1761 private static final long serialVersionUID = 487447009682186044L; 1762 1763 SynchronizedSet(Set<E> s) { 1764 super(s); 1765 } 1766 SynchronizedSet(Set<E> s, Object mutex) { 1767 super(s, mutex); 1768 } 1769 1770 public boolean equals(Object o) { 1771 if (this == o) 1772 return true; 1773 synchronized (mutex) {return c.equals(o);} 1774 } 1775 public int hashCode() { 1776 synchronized (mutex) {return c.hashCode();} 1777 } 1778 } 1779 1780 /** 1781 * Returns a synchronized (thread-safe) sorted set backed by the specified 1782 * sorted set. In order to guarantee serial access, it is critical that 1783 * <strong>all</strong> access to the backing sorted set is accomplished 1784 * through the returned sorted set (or its views).<p> 1785 * 1786 * It is imperative that the user manually synchronize on the returned 1787 * sorted set when iterating over it or any of its <tt>subSet</tt>, 1788 * <tt>headSet</tt>, or <tt>tailSet</tt> views. 1789 * <pre> 1790 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet()); 1791 * ... 1792 * synchronized (s) { 1793 * Iterator i = s.iterator(); // Must be in the synchronized block 1794 * while (i.hasNext()) 1795 * foo(i.next()); 1796 * } 1797 * </pre> 1798 * or: 1799 * <pre> 1800 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet()); 1801 * SortedSet s2 = s.headSet(foo); 1802 * ... 1803 * synchronized (s) { // Note: s, not s2!!! 1804 * Iterator i = s2.iterator(); // Must be in the synchronized block 1805 * while (i.hasNext()) 1806 * foo(i.next()); 1807 * } 1808 * </pre> 1809 * Failure to follow this advice may result in non-deterministic behavior. 1810 * 1811 * <p>The returned sorted set will be serializable if the specified 1812 * sorted set is serializable. 1813 * 1814 * @param s the sorted set to be "wrapped" in a synchronized sorted set. 1815 * @return a synchronized view of the specified sorted set. 1816 */ 1817 public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) { 1818 return new SynchronizedSortedSet<>(s); 1819 } 1820 1821 /** 1822 * @serial include 1823 */ 1824 static class SynchronizedSortedSet<E> 1825 extends SynchronizedSet<E> 1826 implements SortedSet<E> 1827 { 1828 private static final long serialVersionUID = 8695801310862127406L; 1829 1830 private final SortedSet<E> ss; 1831 1832 SynchronizedSortedSet(SortedSet<E> s) { 1833 super(s); 1834 ss = s; 1835 } 1836 SynchronizedSortedSet(SortedSet<E> s, Object mutex) { 1837 super(s, mutex); 1838 ss = s; 1839 } 1840 1841 public Comparator<? super E> comparator() { 1842 synchronized (mutex) {return ss.comparator();} 1843 } 1844 1845 public SortedSet<E> subSet(E fromElement, E toElement) { 1846 synchronized (mutex) { 1847 return new SynchronizedSortedSet<>( 1848 ss.subSet(fromElement, toElement), mutex); 1849 } 1850 } 1851 public SortedSet<E> headSet(E toElement) { 1852 synchronized (mutex) { 1853 return new SynchronizedSortedSet<>(ss.headSet(toElement), mutex); 1854 } 1855 } 1856 public SortedSet<E> tailSet(E fromElement) { 1857 synchronized (mutex) { 1858 return new SynchronizedSortedSet<>(ss.tailSet(fromElement),mutex); 1859 } 1860 } 1861 1862 public E first() { 1863 synchronized (mutex) {return ss.first();} 1864 } 1865 public E last() { 1866 synchronized (mutex) {return ss.last();} 1867 } 1868 } 1869 1870 /** 1871 * Returns a synchronized (thread-safe) list backed by the specified 1872 * list. In order to guarantee serial access, it is critical that 1873 * <strong>all</strong> access to the backing list is accomplished 1874 * through the returned list.<p> 1875 * 1876 * It is imperative that the user manually synchronize on the returned 1877 * list when iterating over it: 1878 * <pre> 1879 * List list = Collections.synchronizedList(new ArrayList()); 1880 * ... 1881 * synchronized (list) { 1882 * Iterator i = list.iterator(); // Must be in synchronized block 1883 * while (i.hasNext()) 1884 * foo(i.next()); 1885 * } 1886 * </pre> 1887 * Failure to follow this advice may result in non-deterministic behavior. 1888 * 1889 * <p>The returned list will be serializable if the specified list is 1890 * serializable. 1891 * 1892 * @param list the list to be "wrapped" in a synchronized list. 1893 * @return a synchronized view of the specified list. 1894 */ 1895 public static <T> List<T> synchronizedList(List<T> list) { 1896 return (list instanceof RandomAccess ? 1897 new SynchronizedRandomAccessList<>(list) : 1898 new SynchronizedList<>(list)); 1899 } 1900 1901 static <T> List<T> synchronizedList(List<T> list, Object mutex) { 1902 return (list instanceof RandomAccess ? 1903 new SynchronizedRandomAccessList<>(list, mutex) : 1904 new SynchronizedList<>(list, mutex)); 1905 } 1906 1907 /** 1908 * @serial include 1909 */ 1910 static class SynchronizedList<E> 1911 extends SynchronizedCollection<E> 1912 implements List<E> { 1913 private static final long serialVersionUID = -7754090372962971524L; 1914 1915 final List<E> list; 1916 1917 SynchronizedList(List<E> list) { 1918 super(list); 1919 this.list = list; 1920 } 1921 SynchronizedList(List<E> list, Object mutex) { 1922 super(list, mutex); 1923 this.list = list; 1924 } 1925 1926 public boolean equals(Object o) { 1927 if (this == o) 1928 return true; 1929 synchronized (mutex) {return list.equals(o);} 1930 } 1931 public int hashCode() { 1932 synchronized (mutex) {return list.hashCode();} 1933 } 1934 1935 public E get(int index) { 1936 synchronized (mutex) {return list.get(index);} 1937 } 1938 public E set(int index, E element) { 1939 synchronized (mutex) {return list.set(index, element);} 1940 } 1941 public void add(int index, E element) { 1942 synchronized (mutex) {list.add(index, element);} 1943 } 1944 public E remove(int index) { 1945 synchronized (mutex) {return list.remove(index);} 1946 } 1947 1948 public int indexOf(Object o) { 1949 synchronized (mutex) {return list.indexOf(o);} 1950 } 1951 public int lastIndexOf(Object o) { 1952 synchronized (mutex) {return list.lastIndexOf(o);} 1953 } 1954 1955 public boolean addAll(int index, Collection<? extends E> c) { 1956 synchronized (mutex) {return list.addAll(index, c);} 1957 } 1958 1959 public ListIterator<E> listIterator() { 1960 return list.listIterator(); // Must be manually synched by user 1961 } 1962 1963 public ListIterator<E> listIterator(int index) { 1964 return list.listIterator(index); // Must be manually synched by user 1965 } 1966 1967 public List<E> subList(int fromIndex, int toIndex) { 1968 synchronized (mutex) { 1969 return new SynchronizedList<>(list.subList(fromIndex, toIndex), 1970 mutex); 1971 } 1972 } 1973 1974 /** 1975 * SynchronizedRandomAccessList instances are serialized as 1976 * SynchronizedList instances to allow them to be deserialized 1977 * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList). 1978 * This method inverts the transformation. As a beneficial 1979 * side-effect, it also grafts the RandomAccess marker onto 1980 * SynchronizedList instances that were serialized in pre-1.4 JREs. 1981 * 1982 * Note: Unfortunately, SynchronizedRandomAccessList instances 1983 * serialized in 1.4.1 and deserialized in 1.4 will become 1984 * SynchronizedList instances, as this method was missing in 1.4. 1985 */ 1986 private Object readResolve() { 1987 return (list instanceof RandomAccess 1988 ? new SynchronizedRandomAccessList<>(list) 1989 : this); 1990 } 1991 } 1992 1993 /** 1994 * @serial include 1995 */ 1996 static class SynchronizedRandomAccessList<E> 1997 extends SynchronizedList<E> 1998 implements RandomAccess { 1999 2000 SynchronizedRandomAccessList(List<E> list) { 2001 super(list); 2002 } 2003 2004 SynchronizedRandomAccessList(List<E> list, Object mutex) { 2005 super(list, mutex); 2006 } 2007 2008 public List<E> subList(int fromIndex, int toIndex) { 2009 synchronized (mutex) { 2010 return new SynchronizedRandomAccessList<>( 2011 list.subList(fromIndex, toIndex), mutex); 2012 } 2013 } 2014 2015 private static final long serialVersionUID = 1530674583602358482L; 2016 2017 /** 2018 * Allows instances to be deserialized in pre-1.4 JREs (which do 2019 * not have SynchronizedRandomAccessList). SynchronizedList has 2020 * a readResolve method that inverts this transformation upon 2021 * deserialization. 2022 */ 2023 private Object writeReplace() { 2024 return new SynchronizedList<>(list); 2025 } 2026 } 2027 2028 /** 2029 * Returns a synchronized (thread-safe) map backed by the specified 2030 * map. In order to guarantee serial access, it is critical that 2031 * <strong>all</strong> access to the backing map is accomplished 2032 * through the returned map.<p> 2033 * 2034 * It is imperative that the user manually synchronize on the returned 2035 * map when iterating over any of its collection views: 2036 * <pre> 2037 * Map m = Collections.synchronizedMap(new HashMap()); 2038 * ... 2039 * Set s = m.keySet(); // Needn't be in synchronized block 2040 * ... 2041 * synchronized (m) { // Synchronizing on m, not s! 2042 * Iterator i = s.iterator(); // Must be in synchronized block 2043 * while (i.hasNext()) 2044 * foo(i.next()); 2045 * } 2046 * </pre> 2047 * Failure to follow this advice may result in non-deterministic behavior. 2048 * 2049 * <p>The returned map will be serializable if the specified map is 2050 * serializable. 2051 * 2052 * @param m the map to be "wrapped" in a synchronized map. 2053 * @return a synchronized view of the specified map. 2054 */ 2055 public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) { 2056 return new SynchronizedMap<>(m); 2057 } 2058 2059 /** 2060 * @serial include 2061 */ 2062 private static class SynchronizedMap<K,V> 2063 implements Map<K,V>, Serializable { 2064 private static final long serialVersionUID = 1978198479659022715L; 2065 2066 private final Map<K,V> m; // Backing Map 2067 final Object mutex; // Object on which to synchronize 2068 2069 SynchronizedMap(Map<K,V> m) { 2070 if (m==null) 2071 throw new NullPointerException(); 2072 this.m = m; 2073 mutex = this; 2074 } 2075 2076 SynchronizedMap(Map<K,V> m, Object mutex) { 2077 this.m = m; 2078 this.mutex = mutex; 2079 } 2080 2081 public int size() { 2082 synchronized (mutex) {return m.size();} 2083 } 2084 public boolean isEmpty() { 2085 synchronized (mutex) {return m.isEmpty();} 2086 } 2087 public boolean containsKey(Object key) { 2088 synchronized (mutex) {return m.containsKey(key);} 2089 } 2090 public boolean containsValue(Object value) { 2091 synchronized (mutex) {return m.containsValue(value);} 2092 } 2093 public V get(Object key) { 2094 synchronized (mutex) {return m.get(key);} 2095 } 2096 2097 public V put(K key, V value) { 2098 synchronized (mutex) {return m.put(key, value);} 2099 } 2100 public V remove(Object key) { 2101 synchronized (mutex) {return m.remove(key);} 2102 } 2103 public void putAll(Map<? extends K, ? extends V> map) { 2104 synchronized (mutex) {m.putAll(map);} 2105 } 2106 public void clear() { 2107 synchronized (mutex) {m.clear();} 2108 } 2109 2110 private transient Set<K> keySet = null; 2111 private transient Set<Map.Entry<K,V>> entrySet = null; 2112 private transient Collection<V> values = null; 2113 2114 public Set<K> keySet() { 2115 synchronized (mutex) { 2116 if (keySet==null) 2117 keySet = new SynchronizedSet<>(m.keySet(), mutex); 2118 return keySet; 2119 } 2120 } 2121 2122 public Set<Map.Entry<K,V>> entrySet() { 2123 synchronized (mutex) { 2124 if (entrySet==null) 2125 entrySet = new SynchronizedSet<>(m.entrySet(), mutex); 2126 return entrySet; 2127 } 2128 } 2129 2130 public Collection<V> values() { 2131 synchronized (mutex) { 2132 if (values==null) 2133 values = new SynchronizedCollection<>(m.values(), mutex); 2134 return values; 2135 } 2136 } 2137 2138 public boolean equals(Object o) { 2139 if (this == o) 2140 return true; 2141 synchronized (mutex) {return m.equals(o);} 2142 } 2143 public int hashCode() { 2144 synchronized (mutex) {return m.hashCode();} 2145 } 2146 public String toString() { 2147 synchronized (mutex) {return m.toString();} 2148 } 2149 // Override default methods in Map 2150 @Override 2151 public void forEach(BiConsumer<? super K, ? super V> action) { 2152 synchronized (mutex) {m.forEach(action);} 2153 } 2154 2155 private void writeObject(ObjectOutputStream s) throws IOException { 2156 synchronized (mutex) {s.defaultWriteObject();} 2157 } 2158 } 2159 2160 /** 2161 * Returns a synchronized (thread-safe) sorted map backed by the specified 2162 * sorted map. In order to guarantee serial access, it is critical that 2163 * <strong>all</strong> access to the backing sorted map is accomplished 2164 * through the returned sorted map (or its views).<p> 2165 * 2166 * It is imperative that the user manually synchronize on the returned 2167 * sorted map when iterating over any of its collection views, or the 2168 * collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or 2169 * <tt>tailMap</tt> views. 2170 * <pre> 2171 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap()); 2172 * ... 2173 * Set s = m.keySet(); // Needn't be in synchronized block 2174 * ... 2175 * synchronized (m) { // Synchronizing on m, not s! 2176 * Iterator i = s.iterator(); // Must be in synchronized block 2177 * while (i.hasNext()) 2178 * foo(i.next()); 2179 * } 2180 * </pre> 2181 * or: 2182 * <pre> 2183 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap()); 2184 * SortedMap m2 = m.subMap(foo, bar); 2185 * ... 2186 * Set s2 = m2.keySet(); // Needn't be in synchronized block 2187 * ... 2188 * synchronized (m) { // Synchronizing on m, not m2 or s2! 2189 * Iterator i = s.iterator(); // Must be in synchronized block 2190 * while (i.hasNext()) 2191 * foo(i.next()); 2192 * } 2193 * </pre> 2194 * Failure to follow this advice may result in non-deterministic behavior. 2195 * 2196 * <p>The returned sorted map will be serializable if the specified 2197 * sorted map is serializable. 2198 * 2199 * @param m the sorted map to be "wrapped" in a synchronized sorted map. 2200 * @return a synchronized view of the specified sorted map. 2201 */ 2202 public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) { 2203 return new SynchronizedSortedMap<>(m); 2204 } 2205 2206 2207 /** 2208 * @serial include 2209 */ 2210 static class SynchronizedSortedMap<K,V> 2211 extends SynchronizedMap<K,V> 2212 implements SortedMap<K,V> 2213 { 2214 private static final long serialVersionUID = -8798146769416483793L; 2215 2216 private final SortedMap<K,V> sm; 2217 2218 SynchronizedSortedMap(SortedMap<K,V> m) { 2219 super(m); 2220 sm = m; 2221 } 2222 SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) { 2223 super(m, mutex); 2224 sm = m; 2225 } 2226 2227 public Comparator<? super K> comparator() { 2228 synchronized (mutex) {return sm.comparator();} 2229 } 2230 2231 public SortedMap<K,V> subMap(K fromKey, K toKey) { 2232 synchronized (mutex) { 2233 return new SynchronizedSortedMap<>( 2234 sm.subMap(fromKey, toKey), mutex); 2235 } 2236 } 2237 public SortedMap<K,V> headMap(K toKey) { 2238 synchronized (mutex) { 2239 return new SynchronizedSortedMap<>(sm.headMap(toKey), mutex); 2240 } 2241 } 2242 public SortedMap<K,V> tailMap(K fromKey) { 2243 synchronized (mutex) { 2244 return new SynchronizedSortedMap<>(sm.tailMap(fromKey),mutex); 2245 } 2246 } 2247 2248 public K firstKey() { 2249 synchronized (mutex) {return sm.firstKey();} 2250 } 2251 public K lastKey() { 2252 synchronized (mutex) {return sm.lastKey();} 2253 } 2254 } 2255 2256 // Dynamically typesafe collection wrappers 2257 2258 /** 2259 * Returns a dynamically typesafe view of the specified collection. 2260 * Any attempt to insert an element of the wrong type will result in an 2261 * immediate {@link ClassCastException}. Assuming a collection 2262 * contains no incorrectly typed elements prior to the time a 2263 * dynamically typesafe view is generated, and that all subsequent 2264 * access to the collection takes place through the view, it is 2265 * <i>guaranteed</i> that the collection cannot contain an incorrectly 2266 * typed element. 2267 * 2268 * <p>The generics mechanism in the language provides compile-time 2269 * (static) type checking, but it is possible to defeat this mechanism 2270 * with unchecked casts. Usually this is not a problem, as the compiler 2271 * issues warnings on all such unchecked operations. There are, however, 2272 * times when static type checking alone is not sufficient. For example, 2273 * suppose a collection is passed to a third-party library and it is 2274 * imperative that the library code not corrupt the collection by 2275 * inserting an element of the wrong type. 2276 * 2277 * <p>Another use of dynamically typesafe views is debugging. Suppose a 2278 * program fails with a {@code ClassCastException}, indicating that an 2279 * incorrectly typed element was put into a parameterized collection. 2280 * Unfortunately, the exception can occur at any time after the erroneous 2281 * element is inserted, so it typically provides little or no information 2282 * as to the real source of the problem. If the problem is reproducible, 2283 * one can quickly determine its source by temporarily modifying the 2284 * program to wrap the collection with a dynamically typesafe view. 2285 * For example, this declaration: 2286 * <pre> {@code 2287 * Collection<String> c = new HashSet<String>(); 2288 * }</pre> 2289 * may be replaced temporarily by this one: 2290 * <pre> {@code 2291 * Collection<String> c = Collections.checkedCollection( 2292 * new HashSet<String>(), String.class); 2293 * }</pre> 2294 * Running the program again will cause it to fail at the point where 2295 * an incorrectly typed element is inserted into the collection, clearly 2296 * identifying the source of the problem. Once the problem is fixed, the 2297 * modified declaration may be reverted back to the original. 2298 * 2299 * <p>The returned collection does <i>not</i> pass the hashCode and equals 2300 * operations through to the backing collection, but relies on 2301 * {@code Object}'s {@code equals} and {@code hashCode} methods. This 2302 * is necessary to preserve the contracts of these operations in the case 2303 * that the backing collection is a set or a list. 2304 * 2305 * <p>The returned collection will be serializable if the specified 2306 * collection is serializable. 2307 * 2308 * <p>Since {@code null} is considered to be a value of any reference 2309 * type, the returned collection permits insertion of null elements 2310 * whenever the backing collection does. 2311 * 2312 * @param c the collection for which a dynamically typesafe view is to be 2313 * returned 2314 * @param type the type of element that {@code c} is permitted to hold 2315 * @return a dynamically typesafe view of the specified collection 2316 * @since 1.5 2317 */ 2318 public static <E> Collection<E> checkedCollection(Collection<E> c, 2319 Class<E> type) { 2320 return new CheckedCollection<>(c, type); 2321 } 2322 2323 @SuppressWarnings("unchecked") 2324 static <T> T[] zeroLengthArray(Class<T> type) { 2325 return (T[]) Array.newInstance(type, 0); 2326 } 2327 2328 /** 2329 * @serial include 2330 */ 2331 static class CheckedCollection<E> implements Collection<E>, Serializable { 2332 private static final long serialVersionUID = 1578914078182001775L; 2333 2334 final Collection<E> c; 2335 final Class<E> type; 2336 2337 void typeCheck(Object o) { 2338 if (o != null && !type.isInstance(o)) 2339 throw new ClassCastException(badElementMsg(o)); 2340 } 2341 2342 private String badElementMsg(Object o) { 2343 return "Attempt to insert " + o.getClass() + 2344 " element into collection with element type " + type; 2345 } 2346 2347 CheckedCollection(Collection<E> c, Class<E> type) { 2348 if (c==null || type == null) 2349 throw new NullPointerException(); 2350 this.c = c; 2351 this.type = type; 2352 } 2353 2354 public int size() { return c.size(); } 2355 public boolean isEmpty() { return c.isEmpty(); } 2356 public boolean contains(Object o) { return c.contains(o); } 2357 public Object[] toArray() { return c.toArray(); } 2358 public <T> T[] toArray(T[] a) { return c.toArray(a); } 2359 public String toString() { return c.toString(); } 2360 public boolean remove(Object o) { return c.remove(o); } 2361 public void clear() { c.clear(); } 2362 2363 public boolean containsAll(Collection<?> coll) { 2364 return c.containsAll(coll); 2365 } 2366 public boolean removeAll(Collection<?> coll) { 2367 return c.removeAll(coll); 2368 } 2369 public boolean retainAll(Collection<?> coll) { 2370 return c.retainAll(coll); 2371 } 2372 2373 public Iterator<E> iterator() { 2374 final Iterator<E> it = c.iterator(); 2375 return new Iterator<E>() { 2376 public boolean hasNext() { return it.hasNext(); } 2377 public E next() { return it.next(); } 2378 public void remove() { it.remove(); }}; 2379 // Android-note: Should we delegate to it for forEachRemaining ? 2380 } 2381 2382 public boolean add(E e) { 2383 typeCheck(e); 2384 return c.add(e); 2385 } 2386 2387 private E[] zeroLengthElementArray = null; // Lazily initialized 2388 2389 private E[] zeroLengthElementArray() { 2390 return zeroLengthElementArray != null ? zeroLengthElementArray : 2391 (zeroLengthElementArray = zeroLengthArray(type)); 2392 } 2393 2394 @SuppressWarnings("unchecked") 2395 Collection<E> checkedCopyOf(Collection<? extends E> coll) { 2396 Object[] a = null; 2397 try { 2398 E[] z = zeroLengthElementArray(); 2399 a = coll.toArray(z); 2400 // Defend against coll violating the toArray contract 2401 if (a.getClass() != z.getClass()) 2402 a = Arrays.copyOf(a, a.length, z.getClass()); 2403 } catch (ArrayStoreException ignore) { 2404 // To get better and consistent diagnostics, 2405 // we call typeCheck explicitly on each element. 2406 // We call clone() to defend against coll retaining a 2407 // reference to the returned array and storing a bad 2408 // element into it after it has been type checked. 2409 a = coll.toArray().clone(); 2410 for (Object o : a) 2411 typeCheck(o); 2412 } 2413 // A slight abuse of the type system, but safe here. 2414 return (Collection<E>) Arrays.asList(a); 2415 } 2416 2417 public boolean addAll(Collection<? extends E> coll) { 2418 // Doing things this way insulates us from concurrent changes 2419 // in the contents of coll and provides all-or-nothing 2420 // semantics (which we wouldn't get if we type-checked each 2421 // element as we added it) 2422 return c.addAll(checkedCopyOf(coll)); 2423 } 2424 2425 // Override default methods in Collection 2426 @Override 2427 public void forEach(Consumer<? super E> action) {c.forEach(action);} 2428 } 2429 2430 /** 2431 * Returns a dynamically typesafe view of the specified set. 2432 * Any attempt to insert an element of the wrong type will result in 2433 * an immediate {@link ClassCastException}. Assuming a set contains 2434 * no incorrectly typed elements prior to the time a dynamically typesafe 2435 * view is generated, and that all subsequent access to the set 2436 * takes place through the view, it is <i>guaranteed</i> that the 2437 * set cannot contain an incorrectly typed element. 2438 * 2439 * <p>A discussion of the use of dynamically typesafe views may be 2440 * found in the documentation for the {@link #checkedCollection 2441 * checkedCollection} method. 2442 * 2443 * <p>The returned set will be serializable if the specified set is 2444 * serializable. 2445 * 2446 * <p>Since {@code null} is considered to be a value of any reference 2447 * type, the returned set permits insertion of null elements whenever 2448 * the backing set does. 2449 * 2450 * @param s the set for which a dynamically typesafe view is to be 2451 * returned 2452 * @param type the type of element that {@code s} is permitted to hold 2453 * @return a dynamically typesafe view of the specified set 2454 * @since 1.5 2455 */ 2456 public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) { 2457 return new CheckedSet<>(s, type); 2458 } 2459 2460 /** 2461 * @serial include 2462 */ 2463 static class CheckedSet<E> extends CheckedCollection<E> 2464 implements Set<E>, Serializable 2465 { 2466 private static final long serialVersionUID = 4694047833775013803L; 2467 2468 CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); } 2469 2470 public boolean equals(Object o) { return o == this || c.equals(o); } 2471 public int hashCode() { return c.hashCode(); } 2472 } 2473 2474 /** 2475 * Returns a dynamically typesafe view of the specified sorted set. 2476 * Any attempt to insert an element of the wrong type will result in an 2477 * immediate {@link ClassCastException}. Assuming a sorted set 2478 * contains no incorrectly typed elements prior to the time a 2479 * dynamically typesafe view is generated, and that all subsequent 2480 * access to the sorted set takes place through the view, it is 2481 * <i>guaranteed</i> that the sorted set cannot contain an incorrectly 2482 * typed element. 2483 * 2484 * <p>A discussion of the use of dynamically typesafe views may be 2485 * found in the documentation for the {@link #checkedCollection 2486 * checkedCollection} method. 2487 * 2488 * <p>The returned sorted set will be serializable if the specified sorted 2489 * set is serializable. 2490 * 2491 * <p>Since {@code null} is considered to be a value of any reference 2492 * type, the returned sorted set permits insertion of null elements 2493 * whenever the backing sorted set does. 2494 * 2495 * @param s the sorted set for which a dynamically typesafe view is to be 2496 * returned 2497 * @param type the type of element that {@code s} is permitted to hold 2498 * @return a dynamically typesafe view of the specified sorted set 2499 * @since 1.5 2500 */ 2501 public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s, 2502 Class<E> type) { 2503 return new CheckedSortedSet<>(s, type); 2504 } 2505 2506 /** 2507 * @serial include 2508 */ 2509 static class CheckedSortedSet<E> extends CheckedSet<E> 2510 implements SortedSet<E>, Serializable 2511 { 2512 private static final long serialVersionUID = 1599911165492914959L; 2513 private final SortedSet<E> ss; 2514 2515 CheckedSortedSet(SortedSet<E> s, Class<E> type) { 2516 super(s, type); 2517 ss = s; 2518 } 2519 2520 public Comparator<? super E> comparator() { return ss.comparator(); } 2521 public E first() { return ss.first(); } 2522 public E last() { return ss.last(); } 2523 2524 public SortedSet<E> subSet(E fromElement, E toElement) { 2525 return checkedSortedSet(ss.subSet(fromElement,toElement), type); 2526 } 2527 public SortedSet<E> headSet(E toElement) { 2528 return checkedSortedSet(ss.headSet(toElement), type); 2529 } 2530 public SortedSet<E> tailSet(E fromElement) { 2531 return checkedSortedSet(ss.tailSet(fromElement), type); 2532 } 2533 } 2534 2535 /** 2536 * Returns a dynamically typesafe view of the specified list. 2537 * Any attempt to insert an element of the wrong type will result in 2538 * an immediate {@link ClassCastException}. Assuming a list contains 2539 * no incorrectly typed elements prior to the time a dynamically typesafe 2540 * view is generated, and that all subsequent access to the list 2541 * takes place through the view, it is <i>guaranteed</i> that the 2542 * list cannot contain an incorrectly typed element. 2543 * 2544 * <p>A discussion of the use of dynamically typesafe views may be 2545 * found in the documentation for the {@link #checkedCollection 2546 * checkedCollection} method. 2547 * 2548 * <p>The returned list will be serializable if the specified list 2549 * is serializable. 2550 * 2551 * <p>Since {@code null} is considered to be a value of any reference 2552 * type, the returned list permits insertion of null elements whenever 2553 * the backing list does. 2554 * 2555 * @param list the list for which a dynamically typesafe view is to be 2556 * returned 2557 * @param type the type of element that {@code list} is permitted to hold 2558 * @return a dynamically typesafe view of the specified list 2559 * @since 1.5 2560 */ 2561 public static <E> List<E> checkedList(List<E> list, Class<E> type) { 2562 return (list instanceof RandomAccess ? 2563 new CheckedRandomAccessList<>(list, type) : 2564 new CheckedList<>(list, type)); 2565 } 2566 2567 /** 2568 * @serial include 2569 */ 2570 static class CheckedList<E> 2571 extends CheckedCollection<E> 2572 implements List<E> 2573 { 2574 private static final long serialVersionUID = 65247728283967356L; 2575 final List<E> list; 2576 2577 CheckedList(List<E> list, Class<E> type) { 2578 super(list, type); 2579 this.list = list; 2580 } 2581 2582 public boolean equals(Object o) { return o == this || list.equals(o); } 2583 public int hashCode() { return list.hashCode(); } 2584 public E get(int index) { return list.get(index); } 2585 public E remove(int index) { return list.remove(index); } 2586 public int indexOf(Object o) { return list.indexOf(o); } 2587 public int lastIndexOf(Object o) { return list.lastIndexOf(o); } 2588 2589 public E set(int index, E element) { 2590 typeCheck(element); 2591 return list.set(index, element); 2592 } 2593 2594 public void add(int index, E element) { 2595 typeCheck(element); 2596 list.add(index, element); 2597 } 2598 2599 public boolean addAll(int index, Collection<? extends E> c) { 2600 return list.addAll(index, checkedCopyOf(c)); 2601 } 2602 public ListIterator<E> listIterator() { return listIterator(0); } 2603 2604 public ListIterator<E> listIterator(final int index) { 2605 final ListIterator<E> i = list.listIterator(index); 2606 2607 return new ListIterator<E>() { 2608 public boolean hasNext() { return i.hasNext(); } 2609 public E next() { return i.next(); } 2610 public boolean hasPrevious() { return i.hasPrevious(); } 2611 public E previous() { return i.previous(); } 2612 public int nextIndex() { return i.nextIndex(); } 2613 public int previousIndex() { return i.previousIndex(); } 2614 public void remove() { i.remove(); } 2615 2616 public void set(E e) { 2617 typeCheck(e); 2618 i.set(e); 2619 } 2620 2621 public void add(E e) { 2622 typeCheck(e); 2623 i.add(e); 2624 } 2625 2626 @Override 2627 public void forEachRemaining(Consumer<? super E> action) { 2628 i.forEachRemaining(action); 2629 } 2630 }; 2631 } 2632 2633 public List<E> subList(int fromIndex, int toIndex) { 2634 return new CheckedList<>(list.subList(fromIndex, toIndex), type); 2635 } 2636 } 2637 2638 /** 2639 * @serial include 2640 */ 2641 static class CheckedRandomAccessList<E> extends CheckedList<E> 2642 implements RandomAccess 2643 { 2644 private static final long serialVersionUID = 1638200125423088369L; 2645 2646 CheckedRandomAccessList(List<E> list, Class<E> type) { 2647 super(list, type); 2648 } 2649 2650 public List<E> subList(int fromIndex, int toIndex) { 2651 return new CheckedRandomAccessList<>( 2652 list.subList(fromIndex, toIndex), type); 2653 } 2654 } 2655 2656 /** 2657 * Returns a dynamically typesafe view of the specified map. 2658 * Any attempt to insert a mapping whose key or value have the wrong 2659 * type will result in an immediate {@link ClassCastException}. 2660 * Similarly, any attempt to modify the value currently associated with 2661 * a key will result in an immediate {@link ClassCastException}, 2662 * whether the modification is attempted directly through the map 2663 * itself, or through a {@link Map.Entry} instance obtained from the 2664 * map's {@link Map#entrySet() entry set} view. 2665 * 2666 * <p>Assuming a map contains no incorrectly typed keys or values 2667 * prior to the time a dynamically typesafe view is generated, and 2668 * that all subsequent access to the map takes place through the view 2669 * (or one of its collection views), it is <i>guaranteed</i> that the 2670 * map cannot contain an incorrectly typed key or value. 2671 * 2672 * <p>A discussion of the use of dynamically typesafe views may be 2673 * found in the documentation for the {@link #checkedCollection 2674 * checkedCollection} method. 2675 * 2676 * <p>The returned map will be serializable if the specified map is 2677 * serializable. 2678 * 2679 * <p>Since {@code null} is considered to be a value of any reference 2680 * type, the returned map permits insertion of null keys or values 2681 * whenever the backing map does. 2682 * 2683 * @param m the map for which a dynamically typesafe view is to be 2684 * returned 2685 * @param keyType the type of key that {@code m} is permitted to hold 2686 * @param valueType the type of value that {@code m} is permitted to hold 2687 * @return a dynamically typesafe view of the specified map 2688 * @since 1.5 2689 */ 2690 public static <K, V> Map<K, V> checkedMap(Map<K, V> m, 2691 Class<K> keyType, 2692 Class<V> valueType) { 2693 return new CheckedMap<>(m, keyType, valueType); 2694 } 2695 2696 2697 /** 2698 * @serial include 2699 */ 2700 private static class CheckedMap<K,V> 2701 implements Map<K,V>, Serializable 2702 { 2703 private static final long serialVersionUID = 5742860141034234728L; 2704 2705 private final Map<K, V> m; 2706 final Class<K> keyType; 2707 final Class<V> valueType; 2708 2709 private void typeCheck(Object key, Object value) { 2710 if (key != null && !keyType.isInstance(key)) 2711 throw new ClassCastException(badKeyMsg(key)); 2712 2713 if (value != null && !valueType.isInstance(value)) 2714 throw new ClassCastException(badValueMsg(value)); 2715 } 2716 2717 private String badKeyMsg(Object key) { 2718 return "Attempt to insert " + key.getClass() + 2719 " key into map with key type " + keyType; 2720 } 2721 2722 private String badValueMsg(Object value) { 2723 return "Attempt to insert " + value.getClass() + 2724 " value into map with value type " + valueType; 2725 } 2726 2727 CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) { 2728 if (m == null || keyType == null || valueType == null) 2729 throw new NullPointerException(); 2730 this.m = m; 2731 this.keyType = keyType; 2732 this.valueType = valueType; 2733 } 2734 2735 public int size() { return m.size(); } 2736 public boolean isEmpty() { return m.isEmpty(); } 2737 public boolean containsKey(Object key) { return m.containsKey(key); } 2738 public boolean containsValue(Object v) { return m.containsValue(v); } 2739 public V get(Object key) { return m.get(key); } 2740 public V remove(Object key) { return m.remove(key); } 2741 public void clear() { m.clear(); } 2742 public Set<K> keySet() { return m.keySet(); } 2743 public Collection<V> values() { return m.values(); } 2744 public boolean equals(Object o) { return o == this || m.equals(o); } 2745 public int hashCode() { return m.hashCode(); } 2746 public String toString() { return m.toString(); } 2747 2748 public V put(K key, V value) { 2749 typeCheck(key, value); 2750 return m.put(key, value); 2751 } 2752 2753 @SuppressWarnings("unchecked") 2754 public void putAll(Map<? extends K, ? extends V> t) { 2755 // Satisfy the following goals: 2756 // - good diagnostics in case of type mismatch 2757 // - all-or-nothing semantics 2758 // - protection from malicious t 2759 // - correct behavior if t is a concurrent map 2760 Object[] entries = t.entrySet().toArray(); 2761 List<Map.Entry<K,V>> checked = new ArrayList<>(entries.length); 2762 for (Object o : entries) { 2763 Map.Entry<?,?> e = (Map.Entry<?,?>) o; 2764 Object k = e.getKey(); 2765 Object v = e.getValue(); 2766 typeCheck(k, v); 2767 checked.add( 2768 new AbstractMap.SimpleImmutableEntry<>((K) k, (V) v)); 2769 } 2770 for (Map.Entry<K,V> e : checked) 2771 m.put(e.getKey(), e.getValue()); 2772 } 2773 2774 private transient Set<Map.Entry<K,V>> entrySet = null; 2775 2776 public Set<Map.Entry<K,V>> entrySet() { 2777 if (entrySet==null) 2778 entrySet = new CheckedEntrySet<>(m.entrySet(), valueType); 2779 return entrySet; 2780 } 2781 2782 // Override default methods in Map 2783 @Override 2784 public void forEach(BiConsumer<? super K, ? super V> action) { 2785 m.forEach(action); 2786 } 2787 2788 /** 2789 * We need this class in addition to CheckedSet as Map.Entry permits 2790 * modification of the backing Map via the setValue operation. This 2791 * class is subtle: there are many possible attacks that must be 2792 * thwarted. 2793 * 2794 * @serial exclude 2795 */ 2796 static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> { 2797 private final Set<Map.Entry<K,V>> s; 2798 private final Class<V> valueType; 2799 2800 CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) { 2801 this.s = s; 2802 this.valueType = valueType; 2803 } 2804 2805 public int size() { return s.size(); } 2806 public boolean isEmpty() { return s.isEmpty(); } 2807 public String toString() { return s.toString(); } 2808 public int hashCode() { return s.hashCode(); } 2809 public void clear() { s.clear(); } 2810 2811 public boolean add(Map.Entry<K, V> e) { 2812 throw new UnsupportedOperationException(); 2813 } 2814 public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) { 2815 throw new UnsupportedOperationException(); 2816 } 2817 2818 public Iterator<Map.Entry<K,V>> iterator() { 2819 final Iterator<Map.Entry<K, V>> i = s.iterator(); 2820 final Class<V> valueType = this.valueType; 2821 2822 return new Iterator<Map.Entry<K,V>>() { 2823 public boolean hasNext() { return i.hasNext(); } 2824 public void remove() { i.remove(); } 2825 2826 public Map.Entry<K,V> next() { 2827 return checkedEntry(i.next(), valueType); 2828 } 2829 // Android-note: forEachRemaining is missing checks. 2830 }; 2831 } 2832 2833 @SuppressWarnings("unchecked") 2834 public Object[] toArray() { 2835 Object[] source = s.toArray(); 2836 2837 /* 2838 * Ensure that we don't get an ArrayStoreException even if 2839 * s.toArray returns an array of something other than Object 2840 */ 2841 Object[] dest = (CheckedEntry.class.isInstance( 2842 source.getClass().getComponentType()) ? source : 2843 new Object[source.length]); 2844 2845 for (int i = 0; i < source.length; i++) 2846 dest[i] = checkedEntry((Map.Entry<K,V>)source[i], 2847 valueType); 2848 return dest; 2849 } 2850 2851 @SuppressWarnings("unchecked") 2852 public <T> T[] toArray(T[] a) { 2853 // We don't pass a to s.toArray, to avoid window of 2854 // vulnerability wherein an unscrupulous multithreaded client 2855 // could get his hands on raw (unwrapped) Entries from s. 2856 T[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0)); 2857 2858 for (int i=0; i<arr.length; i++) 2859 arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i], 2860 valueType); 2861 if (arr.length > a.length) 2862 return arr; 2863 2864 System.arraycopy(arr, 0, a, 0, arr.length); 2865 if (a.length > arr.length) 2866 a[arr.length] = null; 2867 return a; 2868 } 2869 2870 /** 2871 * This method is overridden to protect the backing set against 2872 * an object with a nefarious equals function that senses 2873 * that the equality-candidate is Map.Entry and calls its 2874 * setValue method. 2875 */ 2876 public boolean contains(Object o) { 2877 if (!(o instanceof Map.Entry)) 2878 return false; 2879 Map.Entry<?,?> e = (Map.Entry<?,?>) o; 2880 return s.contains( 2881 (e instanceof CheckedEntry) ? e : checkedEntry(e, valueType)); 2882 } 2883 2884 /** 2885 * The bulk collection methods are overridden to protect 2886 * against an unscrupulous collection whose contains(Object o) 2887 * method senses when o is a Map.Entry, and calls o.setValue. 2888 */ 2889 public boolean containsAll(Collection<?> c) { 2890 for (Object o : c) 2891 if (!contains(o)) // Invokes safe contains() above 2892 return false; 2893 return true; 2894 } 2895 2896 public boolean remove(Object o) { 2897 if (!(o instanceof Map.Entry)) 2898 return false; 2899 return s.remove(new AbstractMap.SimpleImmutableEntry 2900 <>((Map.Entry<?,?>)o)); 2901 } 2902 2903 public boolean removeAll(Collection<?> c) { 2904 return batchRemove(c, false); 2905 } 2906 public boolean retainAll(Collection<?> c) { 2907 return batchRemove(c, true); 2908 } 2909 private boolean batchRemove(Collection<?> c, boolean complement) { 2910 boolean modified = false; 2911 Iterator<Map.Entry<K,V>> it = iterator(); 2912 while (it.hasNext()) { 2913 if (c.contains(it.next()) != complement) { 2914 it.remove(); 2915 modified = true; 2916 } 2917 } 2918 return modified; 2919 } 2920 2921 public boolean equals(Object o) { 2922 if (o == this) 2923 return true; 2924 if (!(o instanceof Set)) 2925 return false; 2926 Set<?> that = (Set<?>) o; 2927 return that.size() == s.size() 2928 && containsAll(that); // Invokes safe containsAll() above 2929 } 2930 2931 static <K,V,T> CheckedEntry<K,V,T> checkedEntry(Map.Entry<K,V> e, 2932 Class<T> valueType) { 2933 return new CheckedEntry<>(e, valueType); 2934 } 2935 2936 /** 2937 * This "wrapper class" serves two purposes: it prevents 2938 * the client from modifying the backing Map, by short-circuiting 2939 * the setValue method, and it protects the backing Map against 2940 * an ill-behaved Map.Entry that attempts to modify another 2941 * Map.Entry when asked to perform an equality check. 2942 */ 2943 private static class CheckedEntry<K,V,T> implements Map.Entry<K,V> { 2944 private final Map.Entry<K, V> e; 2945 private final Class<T> valueType; 2946 2947 CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) { 2948 this.e = e; 2949 this.valueType = valueType; 2950 } 2951 2952 public K getKey() { return e.getKey(); } 2953 public V getValue() { return e.getValue(); } 2954 public int hashCode() { return e.hashCode(); } 2955 public String toString() { return e.toString(); } 2956 2957 public V setValue(V value) { 2958 if (value != null && !valueType.isInstance(value)) 2959 throw new ClassCastException(badValueMsg(value)); 2960 return e.setValue(value); 2961 } 2962 2963 private String badValueMsg(Object value) { 2964 return "Attempt to insert " + value.getClass() + 2965 " value into map with value type " + valueType; 2966 } 2967 2968 public boolean equals(Object o) { 2969 if (o == this) 2970 return true; 2971 if (!(o instanceof Map.Entry)) 2972 return false; 2973 return e.equals(new AbstractMap.SimpleImmutableEntry 2974 <>((Map.Entry<?,?>)o)); 2975 } 2976 } 2977 } 2978 } 2979 2980 /** 2981 * Returns a dynamically typesafe view of the specified sorted map. 2982 * Any attempt to insert a mapping whose key or value have the wrong 2983 * type will result in an immediate {@link ClassCastException}. 2984 * Similarly, any attempt to modify the value currently associated with 2985 * a key will result in an immediate {@link ClassCastException}, 2986 * whether the modification is attempted directly through the map 2987 * itself, or through a {@link Map.Entry} instance obtained from the 2988 * map's {@link Map#entrySet() entry set} view. 2989 * 2990 * <p>Assuming a map contains no incorrectly typed keys or values 2991 * prior to the time a dynamically typesafe view is generated, and 2992 * that all subsequent access to the map takes place through the view 2993 * (or one of its collection views), it is <i>guaranteed</i> that the 2994 * map cannot contain an incorrectly typed key or value. 2995 * 2996 * <p>A discussion of the use of dynamically typesafe views may be 2997 * found in the documentation for the {@link #checkedCollection 2998 * checkedCollection} method. 2999 * 3000 * <p>The returned map will be serializable if the specified map is 3001 * serializable. 3002 * 3003 * <p>Since {@code null} is considered to be a value of any reference 3004 * type, the returned map permits insertion of null keys or values 3005 * whenever the backing map does. 3006 * 3007 * @param m the map for which a dynamically typesafe view is to be 3008 * returned 3009 * @param keyType the type of key that {@code m} is permitted to hold 3010 * @param valueType the type of value that {@code m} is permitted to hold 3011 * @return a dynamically typesafe view of the specified map 3012 * @since 1.5 3013 */ 3014 public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m, 3015 Class<K> keyType, 3016 Class<V> valueType) { 3017 return new CheckedSortedMap<>(m, keyType, valueType); 3018 } 3019 3020 /** 3021 * @serial include 3022 */ 3023 static class CheckedSortedMap<K,V> extends CheckedMap<K,V> 3024 implements SortedMap<K,V>, Serializable 3025 { 3026 private static final long serialVersionUID = 1599671320688067438L; 3027 3028 private final SortedMap<K, V> sm; 3029 3030 CheckedSortedMap(SortedMap<K, V> m, 3031 Class<K> keyType, Class<V> valueType) { 3032 super(m, keyType, valueType); 3033 sm = m; 3034 } 3035 3036 public Comparator<? super K> comparator() { return sm.comparator(); } 3037 public K firstKey() { return sm.firstKey(); } 3038 public K lastKey() { return sm.lastKey(); } 3039 3040 public SortedMap<K,V> subMap(K fromKey, K toKey) { 3041 return checkedSortedMap(sm.subMap(fromKey, toKey), 3042 keyType, valueType); 3043 } 3044 public SortedMap<K,V> headMap(K toKey) { 3045 return checkedSortedMap(sm.headMap(toKey), keyType, valueType); 3046 } 3047 public SortedMap<K,V> tailMap(K fromKey) { 3048 return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType); 3049 } 3050 } 3051 3052 // Empty collections 3053 3054 /** 3055 * Returns an iterator that has no elements. More precisely, 3056 * 3057 * <ul compact> 3058 * 3059 * <li>{@link Iterator#hasNext hasNext} always returns {@code 3060 * false}. 3061 * 3062 * <li>{@link Iterator#next next} always throws {@link 3063 * NoSuchElementException}. 3064 * 3065 * <li>{@link Iterator#remove remove} always throws {@link 3066 * IllegalStateException}. 3067 * 3068 * </ul> 3069 * 3070 * <p>Implementations of this method are permitted, but not 3071 * required, to return the same object from multiple invocations. 3072 * 3073 * @return an empty iterator 3074 * @since 1.7 3075 */ 3076 @SuppressWarnings("unchecked") 3077 public static <T> Iterator<T> emptyIterator() { 3078 return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR; 3079 } 3080 3081 private static class EmptyIterator<E> implements Iterator<E> { 3082 static final EmptyIterator<Object> EMPTY_ITERATOR 3083 = new EmptyIterator<>(); 3084 3085 public boolean hasNext() { return false; } 3086 public E next() { throw new NoSuchElementException(); } 3087 public void remove() { throw new IllegalStateException(); } 3088 @Override 3089 public void forEachRemaining(Consumer<? super E> action) { 3090 Objects.requireNonNull(action); 3091 } 3092 } 3093 3094 /** 3095 * Returns a list iterator that has no elements. More precisely, 3096 * 3097 * <ul compact> 3098 * 3099 * <li>{@link Iterator#hasNext hasNext} and {@link 3100 * ListIterator#hasPrevious hasPrevious} always return {@code 3101 * false}. 3102 * 3103 * <li>{@link Iterator#next next} and {@link ListIterator#previous 3104 * previous} always throw {@link NoSuchElementException}. 3105 * 3106 * <li>{@link Iterator#remove remove} and {@link ListIterator#set 3107 * set} always throw {@link IllegalStateException}. 3108 * 3109 * <li>{@link ListIterator#add add} always throws {@link 3110 * UnsupportedOperationException}. 3111 * 3112 * <li>{@link ListIterator#nextIndex nextIndex} always returns 3113 * {@code 0} . 3114 * 3115 * <li>{@link ListIterator#previousIndex previousIndex} always 3116 * returns {@code -1}. 3117 * 3118 * </ul> 3119 * 3120 * <p>Implementations of this method are permitted, but not 3121 * required, to return the same object from multiple invocations. 3122 * 3123 * @return an empty list iterator 3124 * @since 1.7 3125 */ 3126 @SuppressWarnings("unchecked") 3127 public static <T> ListIterator<T> emptyListIterator() { 3128 return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR; 3129 } 3130 3131 private static class EmptyListIterator<E> 3132 extends EmptyIterator<E> 3133 implements ListIterator<E> 3134 { 3135 static final EmptyListIterator<Object> EMPTY_ITERATOR 3136 = new EmptyListIterator<>(); 3137 3138 public boolean hasPrevious() { return false; } 3139 public E previous() { throw new NoSuchElementException(); } 3140 public int nextIndex() { return 0; } 3141 public int previousIndex() { return -1; } 3142 public void set(E e) { throw new IllegalStateException(); } 3143 public void add(E e) { throw new UnsupportedOperationException(); } 3144 } 3145 3146 /** 3147 * Returns an enumeration that has no elements. More precisely, 3148 * 3149 * <ul compact> 3150 * 3151 * <li>{@link Enumeration#hasMoreElements hasMoreElements} always 3152 * returns {@code false}. 3153 * 3154 * <li> {@link Enumeration#nextElement nextElement} always throws 3155 * {@link NoSuchElementException}. 3156 * 3157 * </ul> 3158 * 3159 * <p>Implementations of this method are permitted, but not 3160 * required, to return the same object from multiple invocations. 3161 * 3162 * @return an empty enumeration 3163 * @since 1.7 3164 */ 3165 @SuppressWarnings("unchecked") 3166 public static <T> Enumeration<T> emptyEnumeration() { 3167 return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION; 3168 } 3169 3170 private static class EmptyEnumeration<E> implements Enumeration<E> { 3171 static final EmptyEnumeration<Object> EMPTY_ENUMERATION 3172 = new EmptyEnumeration<>(); 3173 3174 public boolean hasMoreElements() { return false; } 3175 public E nextElement() { throw new NoSuchElementException(); } 3176 } 3177 3178 /** 3179 * The empty set (immutable). This set is serializable. 3180 * 3181 * @see #emptySet() 3182 */ 3183 @SuppressWarnings("unchecked") 3184 public static final Set EMPTY_SET = new EmptySet<>(); 3185 3186 /** 3187 * Returns the empty set (immutable). This set is serializable. 3188 * Unlike the like-named field, this method is parameterized. 3189 * 3190 * <p>This example illustrates the type-safe way to obtain an empty set: 3191 * <pre> 3192 * Set<String> s = Collections.emptySet(); 3193 * </pre> 3194 * Implementation note: Implementations of this method need not 3195 * create a separate <tt>Set</tt> object for each call. Using this 3196 * method is likely to have comparable cost to using the like-named 3197 * field. (Unlike this method, the field does not provide type safety.) 3198 * 3199 * @see #EMPTY_SET 3200 * @since 1.5 3201 */ 3202 @SuppressWarnings("unchecked") 3203 public static final <T> Set<T> emptySet() { 3204 return (Set<T>) EMPTY_SET; 3205 } 3206 3207 /** 3208 * @serial include 3209 */ 3210 private static class EmptySet<E> 3211 extends AbstractSet<E> 3212 implements Serializable 3213 { 3214 private static final long serialVersionUID = 1582296315990362920L; 3215 3216 public Iterator<E> iterator() { return emptyIterator(); } 3217 3218 public int size() {return 0;} 3219 public boolean isEmpty() {return true;} 3220 3221 public boolean contains(Object obj) {return false;} 3222 public boolean containsAll(Collection<?> c) { return c.isEmpty(); } 3223 3224 public Object[] toArray() { return new Object[0]; } 3225 3226 public <T> T[] toArray(T[] a) { 3227 if (a.length > 0) 3228 a[0] = null; 3229 return a; 3230 } 3231 3232 // Preserves singleton property 3233 private Object readResolve() { 3234 return EMPTY_SET; 3235 } 3236 3237 // Override default methods in Collection 3238 @Override 3239 public void forEach(Consumer<? super E> action) { 3240 Objects.requireNonNull(action); 3241 } 3242 } 3243 3244 /** 3245 * The empty list (immutable). This list is serializable. 3246 * 3247 * @see #emptyList() 3248 */ 3249 @SuppressWarnings("unchecked") 3250 public static final List EMPTY_LIST = new EmptyList<>(); 3251 3252 /** 3253 * Returns the empty list (immutable). This list is serializable. 3254 * 3255 * <p>This example illustrates the type-safe way to obtain an empty list: 3256 * <pre> 3257 * List<String> s = Collections.emptyList(); 3258 * </pre> 3259 * Implementation note: Implementations of this method need not 3260 * create a separate <tt>List</tt> object for each call. Using this 3261 * method is likely to have comparable cost to using the like-named 3262 * field. (Unlike this method, the field does not provide type safety.) 3263 * 3264 * @see #EMPTY_LIST 3265 * @since 1.5 3266 */ 3267 @SuppressWarnings("unchecked") 3268 public static final <T> List<T> emptyList() { 3269 return (List<T>) EMPTY_LIST; 3270 } 3271 3272 /** 3273 * @serial include 3274 */ 3275 private static class EmptyList<E> 3276 extends AbstractList<E> 3277 implements RandomAccess, Serializable { 3278 private static final long serialVersionUID = 8842843931221139166L; 3279 3280 public Iterator<E> iterator() { 3281 return emptyIterator(); 3282 } 3283 public ListIterator<E> listIterator() { 3284 return emptyListIterator(); 3285 } 3286 3287 public int size() {return 0;} 3288 public boolean isEmpty() {return true;} 3289 3290 public boolean contains(Object obj) {return false;} 3291 public boolean containsAll(Collection<?> c) { return c.isEmpty(); } 3292 3293 public Object[] toArray() { return new Object[0]; } 3294 3295 public <T> T[] toArray(T[] a) { 3296 if (a.length > 0) 3297 a[0] = null; 3298 return a; 3299 } 3300 3301 public E get(int index) { 3302 throw new IndexOutOfBoundsException("Index: "+index); 3303 } 3304 3305 public boolean equals(Object o) { 3306 return (o instanceof List) && ((List<?>)o).isEmpty(); 3307 } 3308 3309 public int hashCode() { return 1; } 3310 3311 // Preserves singleton property 3312 private Object readResolve() { 3313 return EMPTY_LIST; 3314 } 3315 3316 // Override default methods in Collection 3317 @Override 3318 public void forEach(Consumer<? super E> action) { 3319 Objects.requireNonNull(action); 3320 } 3321 } 3322 3323 /** 3324 * The empty map (immutable). This map is serializable. 3325 * 3326 * @see #emptyMap() 3327 * @since 1.3 3328 */ 3329 @SuppressWarnings("unchecked") 3330 public static final Map EMPTY_MAP = new EmptyMap<>(); 3331 3332 /** 3333 * Returns the empty map (immutable). This map is serializable. 3334 * 3335 * <p>This example illustrates the type-safe way to obtain an empty set: 3336 * <pre> 3337 * Map<String, Date> s = Collections.emptyMap(); 3338 * </pre> 3339 * Implementation note: Implementations of this method need not 3340 * create a separate <tt>Map</tt> object for each call. Using this 3341 * method is likely to have comparable cost to using the like-named 3342 * field. (Unlike this method, the field does not provide type safety.) 3343 * 3344 * @see #EMPTY_MAP 3345 * @since 1.5 3346 */ 3347 @SuppressWarnings("unchecked") 3348 public static final <K,V> Map<K,V> emptyMap() { 3349 return (Map<K,V>) EMPTY_MAP; 3350 } 3351 3352 /** 3353 * @serial include 3354 */ 3355 private static class EmptyMap<K,V> 3356 extends AbstractMap<K,V> 3357 implements Serializable 3358 { 3359 private static final long serialVersionUID = 6428348081105594320L; 3360 3361 public int size() {return 0;} 3362 public boolean isEmpty() {return true;} 3363 public boolean containsKey(Object key) {return false;} 3364 public boolean containsValue(Object value) {return false;} 3365 public V get(Object key) {return null;} 3366 public Set<K> keySet() {return emptySet();} 3367 public Collection<V> values() {return emptySet();} 3368 public Set<Map.Entry<K,V>> entrySet() {return emptySet();} 3369 3370 public boolean equals(Object o) { 3371 return (o instanceof Map) && ((Map<?,?>)o).isEmpty(); 3372 } 3373 3374 public int hashCode() {return 0;} 3375 3376 // Preserves singleton property 3377 private Object readResolve() { 3378 return EMPTY_MAP; 3379 } 3380 3381 // Override default methods in Map 3382 @Override 3383 public void forEach(BiConsumer<? super K, ? super V> action) { 3384 Objects.requireNonNull(action); 3385 } 3386 } 3387 3388 // Singleton collections 3389 3390 /** 3391 * Returns an immutable set containing only the specified object. 3392 * The returned set is serializable. 3393 * 3394 * @param o the sole object to be stored in the returned set. 3395 * @return an immutable set containing only the specified object. 3396 */ 3397 public static <E> Set<E> singleton(E o) { 3398 return new SingletonSet<>(o); 3399 } 3400 3401 static <E> Iterator<E> singletonIterator(final E e) { 3402 return new Iterator<E>() { 3403 private boolean hasNext = true; 3404 public boolean hasNext() { 3405 return hasNext; 3406 } 3407 public E next() { 3408 if (hasNext) { 3409 hasNext = false; 3410 return e; 3411 } 3412 throw new NoSuchElementException(); 3413 } 3414 public void remove() { 3415 throw new UnsupportedOperationException(); 3416 } 3417 @Override 3418 public void forEachRemaining(Consumer<? super E> action) { 3419 Objects.requireNonNull(action); 3420 if (hasNext) { 3421 action.accept(e); 3422 hasNext = false; 3423 } 3424 } 3425 }; 3426 } 3427 3428 /** 3429 * @serial include 3430 */ 3431 private static class SingletonSet<E> 3432 extends AbstractSet<E> 3433 implements Serializable 3434 { 3435 private static final long serialVersionUID = 3193687207550431679L; 3436 3437 private final E element; 3438 3439 SingletonSet(E e) {element = e;} 3440 3441 public Iterator<E> iterator() { 3442 return singletonIterator(element); 3443 } 3444 3445 public int size() {return 1;} 3446 3447 public boolean contains(Object o) {return eq(o, element);} 3448 3449 // Override default methods for Collection 3450 @Override 3451 public void forEach(Consumer<? super E> action) { 3452 action.accept(element); 3453 } 3454 } 3455 3456 /** 3457 * Returns an immutable list containing only the specified object. 3458 * The returned list is serializable. 3459 * 3460 * @param o the sole object to be stored in the returned list. 3461 * @return an immutable list containing only the specified object. 3462 * @since 1.3 3463 */ 3464 public static <E> List<E> singletonList(E o) { 3465 return new SingletonList<>(o); 3466 } 3467 3468 /** 3469 * @serial include 3470 */ 3471 private static class SingletonList<E> 3472 extends AbstractList<E> 3473 implements RandomAccess, Serializable { 3474 3475 private static final long serialVersionUID = 3093736618740652951L; 3476 3477 private final E element; 3478 3479 SingletonList(E obj) {element = obj;} 3480 3481 public Iterator<E> iterator() { 3482 return singletonIterator(element); 3483 } 3484 3485 public int size() {return 1;} 3486 3487 public boolean contains(Object obj) {return eq(obj, element);} 3488 3489 public E get(int index) { 3490 if (index != 0) 3491 throw new IndexOutOfBoundsException("Index: "+index+", Size: 1"); 3492 return element; 3493 } 3494 3495 // Override default methods for Collection 3496 @Override 3497 public void forEach(Consumer<? super E> action) { 3498 action.accept(element); 3499 } 3500 } 3501 3502 /** 3503 * Returns an immutable map, mapping only the specified key to the 3504 * specified value. The returned map is serializable. 3505 * 3506 * @param key the sole key to be stored in the returned map. 3507 * @param value the value to which the returned map maps <tt>key</tt>. 3508 * @return an immutable map containing only the specified key-value 3509 * mapping. 3510 * @since 1.3 3511 */ 3512 public static <K,V> Map<K,V> singletonMap(K key, V value) { 3513 return new SingletonMap<>(key, value); 3514 } 3515 3516 /** 3517 * @serial include 3518 */ 3519 private static class SingletonMap<K,V> 3520 extends AbstractMap<K,V> 3521 implements Serializable { 3522 private static final long serialVersionUID = -6979724477215052911L; 3523 3524 private final K k; 3525 private final V v; 3526 3527 SingletonMap(K key, V value) { 3528 k = key; 3529 v = value; 3530 } 3531 3532 public int size() {return 1;} 3533 3534 public boolean isEmpty() {return false;} 3535 3536 public boolean containsKey(Object key) {return eq(key, k);} 3537 3538 public boolean containsValue(Object value) {return eq(value, v);} 3539 3540 public V get(Object key) {return (eq(key, k) ? v : null);} 3541 3542 private transient Set<K> keySet = null; 3543 private transient Set<Map.Entry<K,V>> entrySet = null; 3544 private transient Collection<V> values = null; 3545 3546 public Set<K> keySet() { 3547 if (keySet==null) 3548 keySet = singleton(k); 3549 return keySet; 3550 } 3551 3552 public Set<Map.Entry<K,V>> entrySet() { 3553 if (entrySet==null) 3554 entrySet = Collections.<Map.Entry<K,V>>singleton( 3555 new SimpleImmutableEntry<>(k, v)); 3556 return entrySet; 3557 } 3558 3559 public Collection<V> values() { 3560 if (values==null) 3561 values = singleton(v); 3562 return values; 3563 } 3564 3565 // Override default methods in Map 3566 @Override 3567 public void forEach(BiConsumer<? super K, ? super V> action) { 3568 action.accept(k, v); 3569 } 3570 3571 } 3572 3573 // Miscellaneous 3574 3575 /** 3576 * Returns an immutable list consisting of <tt>n</tt> copies of the 3577 * specified object. The newly allocated data object is tiny (it contains 3578 * a single reference to the data object). This method is useful in 3579 * combination with the <tt>List.addAll</tt> method to grow lists. 3580 * The returned list is serializable. 3581 * 3582 * @param n the number of elements in the returned list. 3583 * @param o the element to appear repeatedly in the returned list. 3584 * @return an immutable list consisting of <tt>n</tt> copies of the 3585 * specified object. 3586 * @throws IllegalArgumentException if {@code n < 0} 3587 * @see List#addAll(Collection) 3588 * @see List#addAll(int, Collection) 3589 */ 3590 public static <T> List<T> nCopies(int n, T o) { 3591 if (n < 0) 3592 throw new IllegalArgumentException("List length = " + n); 3593 return new CopiesList<>(n, o); 3594 } 3595 3596 /** 3597 * @serial include 3598 */ 3599 private static class CopiesList<E> 3600 extends AbstractList<E> 3601 implements RandomAccess, Serializable 3602 { 3603 private static final long serialVersionUID = 2739099268398711800L; 3604 3605 final int n; 3606 final E element; 3607 3608 CopiesList(int n, E e) { 3609 assert n >= 0; 3610 this.n = n; 3611 element = e; 3612 } 3613 3614 public int size() { 3615 return n; 3616 } 3617 3618 public boolean contains(Object obj) { 3619 return n != 0 && eq(obj, element); 3620 } 3621 3622 public int indexOf(Object o) { 3623 return contains(o) ? 0 : -1; 3624 } 3625 3626 public int lastIndexOf(Object o) { 3627 return contains(o) ? n - 1 : -1; 3628 } 3629 3630 public E get(int index) { 3631 if (index < 0 || index >= n) 3632 throw new IndexOutOfBoundsException("Index: "+index+ 3633 ", Size: "+n); 3634 return element; 3635 } 3636 3637 public Object[] toArray() { 3638 final Object[] a = new Object[n]; 3639 if (element != null) 3640 Arrays.fill(a, 0, n, element); 3641 return a; 3642 } 3643 3644 public <T> T[] toArray(T[] a) { 3645 final int n = this.n; 3646 if (a.length < n) { 3647 a = (T[])java.lang.reflect.Array 3648 .newInstance(a.getClass().getComponentType(), n); 3649 if (element != null) 3650 Arrays.fill(a, 0, n, element); 3651 } else { 3652 Arrays.fill(a, 0, n, element); 3653 if (a.length > n) 3654 a[n] = null; 3655 } 3656 return a; 3657 } 3658 3659 public List<E> subList(int fromIndex, int toIndex) { 3660 if (fromIndex < 0) 3661 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex); 3662 if (toIndex > n) 3663 throw new IndexOutOfBoundsException("toIndex = " + toIndex); 3664 if (fromIndex > toIndex) 3665 throw new IllegalArgumentException("fromIndex(" + fromIndex + 3666 ") > toIndex(" + toIndex + ")"); 3667 return new CopiesList<>(toIndex - fromIndex, element); 3668 } 3669 } 3670 3671 /** 3672 * Returns a comparator that imposes the reverse of the <em>natural 3673 * ordering</em> on a collection of objects that implement the 3674 * {@code Comparable} interface. (The natural ordering is the ordering 3675 * imposed by the objects' own {@code compareTo} method.) This enables a 3676 * simple idiom for sorting (or maintaining) collections (or arrays) of 3677 * objects that implement the {@code Comparable} interface in 3678 * reverse-natural-order. For example, suppose {@code a} is an array of 3679 * strings. Then: <pre> 3680 * Arrays.sort(a, Collections.reverseOrder()); 3681 * </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p> 3682 * 3683 * The returned comparator is serializable. 3684 * 3685 * @return A comparator that imposes the reverse of the <i>natural 3686 * ordering</i> on a collection of objects that implement 3687 * the <tt>Comparable</tt> interface. 3688 * @see Comparable 3689 */ 3690 public static <T> Comparator<T> reverseOrder() { 3691 return (Comparator<T>) ReverseComparator.REVERSE_ORDER; 3692 } 3693 3694 /** 3695 * @serial include 3696 */ 3697 private static class ReverseComparator 3698 implements Comparator<Comparable<Object>>, Serializable { 3699 3700 private static final long serialVersionUID = 7207038068494060240L; 3701 3702 static final ReverseComparator REVERSE_ORDER 3703 = new ReverseComparator(); 3704 3705 public int compare(Comparable<Object> c1, Comparable<Object> c2) { 3706 return c2.compareTo(c1); 3707 } 3708 3709 private Object readResolve() { return reverseOrder(); } 3710 3711 @Override 3712 public Comparator<Comparable<Object>> reversed() { 3713 return Comparator.naturalOrder(); 3714 } 3715 } 3716 3717 /** 3718 * Returns a comparator that imposes the reverse ordering of the specified 3719 * comparator. If the specified comparator is {@code null}, this method is 3720 * equivalent to {@link #reverseOrder()} (in other words, it returns a 3721 * comparator that imposes the reverse of the <em>natural ordering</em> on 3722 * a collection of objects that implement the Comparable interface). 3723 * 3724 * <p>The returned comparator is serializable (assuming the specified 3725 * comparator is also serializable or {@code null}). 3726 * 3727 * @param cmp a comparator who's ordering is to be reversed by the returned 3728 * comparator or {@code null} 3729 * @return A comparator that imposes the reverse ordering of the 3730 * specified comparator. 3731 * @since 1.5 3732 */ 3733 public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) { 3734 if (cmp == null) 3735 return reverseOrder(); 3736 3737 if (cmp instanceof ReverseComparator2) 3738 return ((ReverseComparator2<T>)cmp).cmp; 3739 3740 return new ReverseComparator2<>(cmp); 3741 } 3742 3743 /** 3744 * @serial include 3745 */ 3746 private static class ReverseComparator2<T> implements Comparator<T>, 3747 Serializable 3748 { 3749 private static final long serialVersionUID = 4374092139857L; 3750 3751 /** 3752 * The comparator specified in the static factory. This will never 3753 * be null, as the static factory returns a ReverseComparator 3754 * instance if its argument is null. 3755 * 3756 * @serial 3757 */ 3758 final Comparator<T> cmp; 3759 3760 ReverseComparator2(Comparator<T> cmp) { 3761 assert cmp != null; 3762 this.cmp = cmp; 3763 } 3764 3765 public int compare(T t1, T t2) { 3766 return cmp.compare(t2, t1); 3767 } 3768 3769 public boolean equals(Object o) { 3770 return (o == this) || 3771 (o instanceof ReverseComparator2 && 3772 cmp.equals(((ReverseComparator2)o).cmp)); 3773 } 3774 3775 public int hashCode() { 3776 return cmp.hashCode() ^ Integer.MIN_VALUE; 3777 } 3778 3779 @Override 3780 public Comparator<T> reversed() { 3781 return cmp; 3782 } 3783 } 3784 3785 /** 3786 * Returns an enumeration over the specified collection. This provides 3787 * interoperability with legacy APIs that require an enumeration 3788 * as input. 3789 * 3790 * @param c the collection for which an enumeration is to be returned. 3791 * @return an enumeration over the specified collection. 3792 * @see Enumeration 3793 */ 3794 public static <T> Enumeration<T> enumeration(final Collection<T> c) { 3795 return new Enumeration<T>() { 3796 private final Iterator<T> i = c.iterator(); 3797 3798 public boolean hasMoreElements() { 3799 return i.hasNext(); 3800 } 3801 3802 public T nextElement() { 3803 return i.next(); 3804 } 3805 }; 3806 } 3807 3808 /** 3809 * Returns an array list containing the elements returned by the 3810 * specified enumeration in the order they are returned by the 3811 * enumeration. This method provides interoperability between 3812 * legacy APIs that return enumerations and new APIs that require 3813 * collections. 3814 * 3815 * @param e enumeration providing elements for the returned 3816 * array list 3817 * @return an array list containing the elements returned 3818 * by the specified enumeration. 3819 * @since 1.4 3820 * @see Enumeration 3821 * @see ArrayList 3822 */ 3823 public static <T> ArrayList<T> list(Enumeration<T> e) { 3824 ArrayList<T> l = new ArrayList<>(); 3825 while (e.hasMoreElements()) 3826 l.add(e.nextElement()); 3827 return l; 3828 } 3829 3830 /** 3831 * Returns true if the specified arguments are equal, or both null. 3832 */ 3833 static boolean eq(Object o1, Object o2) { 3834 return o1==null ? o2==null : o1.equals(o2); 3835 } 3836 3837 /** 3838 * Returns the number of elements in the specified collection equal to the 3839 * specified object. More formally, returns the number of elements 3840 * <tt>e</tt> in the collection such that 3841 * <tt>(o == null ? e == null : o.equals(e))</tt>. 3842 * 3843 * @param c the collection in which to determine the frequency 3844 * of <tt>o</tt> 3845 * @param o the object whose frequency is to be determined 3846 * @throws NullPointerException if <tt>c</tt> is null 3847 * @since 1.5 3848 */ 3849 public static int frequency(Collection<?> c, Object o) { 3850 int result = 0; 3851 if (o == null) { 3852 for (Object e : c) 3853 if (e == null) 3854 result++; 3855 } else { 3856 for (Object e : c) 3857 if (o.equals(e)) 3858 result++; 3859 } 3860 return result; 3861 } 3862 3863 /** 3864 * Returns {@code true} if the two specified collections have no 3865 * elements in common. 3866 * 3867 * <p>Care must be exercised if this method is used on collections that 3868 * do not comply with the general contract for {@code Collection}. 3869 * Implementations may elect to iterate over either collection and test 3870 * for containment in the other collection (or to perform any equivalent 3871 * computation). If either collection uses a nonstandard equality test 3872 * (as does a {@link SortedSet} whose ordering is not <em>compatible with 3873 * equals</em>, or the key set of an {@link IdentityHashMap}), both 3874 * collections must use the same nonstandard equality test, or the 3875 * result of this method is undefined. 3876 * 3877 * <p>Care must also be exercised when using collections that have 3878 * restrictions on the elements that they may contain. Collection 3879 * implementations are allowed to throw exceptions for any operation 3880 * involving elements they deem ineligible. For absolute safety the 3881 * specified collections should contain only elements which are 3882 * eligible elements for both collections. 3883 * 3884 * <p>Note that it is permissible to pass the same collection in both 3885 * parameters, in which case the method will return {@code true} if and 3886 * only if the collection is empty. 3887 * 3888 * @param c1 a collection 3889 * @param c2 a collection 3890 * @return {@code true} if the two specified collections have no 3891 * elements in common. 3892 * @throws NullPointerException if either collection is {@code null}. 3893 * @throws NullPointerException if one collection contains a {@code null} 3894 * element and {@code null} is not an eligible element for the other collection. 3895 * (<a href="Collection.html#optional-restrictions">optional</a>) 3896 * @throws ClassCastException if one collection contains an element that is 3897 * of a type which is ineligible for the other collection. 3898 * (<a href="Collection.html#optional-restrictions">optional</a>) 3899 * @since 1.5 3900 */ 3901 public static boolean disjoint(Collection<?> c1, Collection<?> c2) { 3902 // The collection to be used for contains(). Preference is given to 3903 // the collection who's contains() has lower O() complexity. 3904 Collection<?> contains = c2; 3905 // The collection to be iterated. If the collections' contains() impl 3906 // are of different O() complexity, the collection with slower 3907 // contains() will be used for iteration. For collections who's 3908 // contains() are of the same complexity then best performance is 3909 // achieved by iterating the smaller collection. 3910 Collection<?> iterate = c1; 3911 3912 // Performance optimization cases. The heuristics: 3913 // 1. Generally iterate over c1. 3914 // 2. If c1 is a Set then iterate over c2. 3915 // 3. If either collection is empty then result is always true. 3916 // 4. Iterate over the smaller Collection. 3917 if (c1 instanceof Set) { 3918 // Use c1 for contains as a Set's contains() is expected to perform 3919 // better than O(N/2) 3920 iterate = c2; 3921 contains = c1; 3922 } else if (!(c2 instanceof Set)) { 3923 // Both are mere Collections. Iterate over smaller collection. 3924 // Example: If c1 contains 3 elements and c2 contains 50 elements and 3925 // assuming contains() requires ceiling(N/2) comparisons then 3926 // checking for all c1 elements in c2 would require 75 comparisons 3927 // (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring 3928 // 100 comparisons (50 * ceiling(3/2)). 3929 int c1size = c1.size(); 3930 int c2size = c2.size(); 3931 if (c1size == 0 || c2size == 0) { 3932 // At least one collection is empty. Nothing will match. 3933 return true; 3934 } 3935 3936 if (c1size > c2size) { 3937 iterate = c2; 3938 contains = c1; 3939 } 3940 } 3941 3942 for (Object e : iterate) { 3943 if (contains.contains(e)) { 3944 // Found a common element. Collections are not disjoint. 3945 return false; 3946 } 3947 } 3948 3949 // No common elements were found. 3950 return true; 3951 } 3952 3953 /** 3954 * Adds all of the specified elements to the specified collection. 3955 * Elements to be added may be specified individually or as an array. 3956 * The behavior of this convenience method is identical to that of 3957 * <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely 3958 * to run significantly faster under most implementations. 3959 * 3960 * <p>When elements are specified individually, this method provides a 3961 * convenient way to add a few elements to an existing collection: 3962 * <pre> 3963 * Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon"); 3964 * </pre> 3965 * 3966 * @param c the collection into which <tt>elements</tt> are to be inserted 3967 * @param elements the elements to insert into <tt>c</tt> 3968 * @return <tt>true</tt> if the collection changed as a result of the call 3969 * @throws UnsupportedOperationException if <tt>c</tt> does not support 3970 * the <tt>add</tt> operation 3971 * @throws NullPointerException if <tt>elements</tt> contains one or more 3972 * null values and <tt>c</tt> does not permit null elements, or 3973 * if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt> 3974 * @throws IllegalArgumentException if some property of a value in 3975 * <tt>elements</tt> prevents it from being added to <tt>c</tt> 3976 * @see Collection#addAll(Collection) 3977 * @since 1.5 3978 */ 3979 @SafeVarargs 3980 public static <T> boolean addAll(Collection<? super T> c, T... elements) { 3981 boolean result = false; 3982 for (T element : elements) 3983 result |= c.add(element); 3984 return result; 3985 } 3986 3987 /** 3988 * Returns a set backed by the specified map. The resulting set displays 3989 * the same ordering, concurrency, and performance characteristics as the 3990 * backing map. In essence, this factory method provides a {@link Set} 3991 * implementation corresponding to any {@link Map} implementation. There 3992 * is no need to use this method on a {@link Map} implementation that 3993 * already has a corresponding {@link Set} implementation (such as {@link 3994 * HashMap} or {@link TreeMap}). 3995 * 3996 * <p>Each method invocation on the set returned by this method results in 3997 * exactly one method invocation on the backing map or its <tt>keySet</tt> 3998 * view, with one exception. The <tt>addAll</tt> method is implemented 3999 * as a sequence of <tt>put</tt> invocations on the backing map. 4000 * 4001 * <p>The specified map must be empty at the time this method is invoked, 4002 * and should not be accessed directly after this method returns. These 4003 * conditions are ensured if the map is created empty, passed directly 4004 * to this method, and no reference to the map is retained, as illustrated 4005 * in the following code fragment: 4006 * <pre> 4007 * Set<Object> weakHashSet = Collections.newSetFromMap( 4008 * new WeakHashMap<Object, Boolean>()); 4009 * </pre> 4010 * 4011 * @param map the backing map 4012 * @return the set backed by the map 4013 * @throws IllegalArgumentException if <tt>map</tt> is not empty 4014 * @since 1.6 4015 */ 4016 public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) { 4017 return new SetFromMap<>(map); 4018 } 4019 4020 /** 4021 * @serial include 4022 */ 4023 private static class SetFromMap<E> extends AbstractSet<E> 4024 implements Set<E>, Serializable 4025 { 4026 private final Map<E, Boolean> m; // The backing map 4027 private transient Set<E> s; // Its keySet 4028 4029 SetFromMap(Map<E, Boolean> map) { 4030 if (!map.isEmpty()) 4031 throw new IllegalArgumentException("Map is non-empty"); 4032 m = map; 4033 s = map.keySet(); 4034 } 4035 4036 public void clear() { m.clear(); } 4037 public int size() { return m.size(); } 4038 public boolean isEmpty() { return m.isEmpty(); } 4039 public boolean contains(Object o) { return m.containsKey(o); } 4040 public boolean remove(Object o) { return m.remove(o) != null; } 4041 public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; } 4042 public Iterator<E> iterator() { return s.iterator(); } 4043 public Object[] toArray() { return s.toArray(); } 4044 public <T> T[] toArray(T[] a) { return s.toArray(a); } 4045 public String toString() { return s.toString(); } 4046 public int hashCode() { return s.hashCode(); } 4047 public boolean equals(Object o) { return o == this || s.equals(o); } 4048 public boolean containsAll(Collection<?> c) {return s.containsAll(c);} 4049 public boolean removeAll(Collection<?> c) {return s.removeAll(c);} 4050 public boolean retainAll(Collection<?> c) {return s.retainAll(c);} 4051 // addAll is the only inherited implementation 4052 4053 private static final long serialVersionUID = 2454657854757543876L; 4054 4055 // Override default methods in Collection 4056 @Override 4057 public void forEach(Consumer<? super E> action) { 4058 s.forEach(action); 4059 } 4060 4061 private void readObject(java.io.ObjectInputStream stream) 4062 throws IOException, ClassNotFoundException 4063 { 4064 stream.defaultReadObject(); 4065 s = m.keySet(); 4066 } 4067 } 4068 4069 /** 4070 * Returns a view of a {@link Deque} as a Last-in-first-out (Lifo) 4071 * {@link Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>, 4072 * <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This 4073 * view can be useful when you would like to use a method 4074 * requiring a <tt>Queue</tt> but you need Lifo ordering. 4075 * 4076 * <p>Each method invocation on the queue returned by this method 4077 * results in exactly one method invocation on the backing deque, with 4078 * one exception. The {@link Queue#addAll addAll} method is 4079 * implemented as a sequence of {@link Deque#addFirst addFirst} 4080 * invocations on the backing deque. 4081 * 4082 * @param deque the deque 4083 * @return the queue 4084 * @since 1.6 4085 */ 4086 public static <T> Queue<T> asLifoQueue(Deque<T> deque) { 4087 return new AsLIFOQueue<>(deque); 4088 } 4089 4090 /** 4091 * @serial include 4092 */ 4093 static class AsLIFOQueue<E> extends AbstractQueue<E> 4094 implements Queue<E>, Serializable { 4095 private static final long serialVersionUID = 1802017725587941708L; 4096 private final Deque<E> q; 4097 AsLIFOQueue(Deque<E> q) { this.q = q; } 4098 public boolean add(E e) { q.addFirst(e); return true; } 4099 public boolean offer(E e) { return q.offerFirst(e); } 4100 public E poll() { return q.pollFirst(); } 4101 public E remove() { return q.removeFirst(); } 4102 public E peek() { return q.peekFirst(); } 4103 public E element() { return q.getFirst(); } 4104 public void clear() { q.clear(); } 4105 public int size() { return q.size(); } 4106 public boolean isEmpty() { return q.isEmpty(); } 4107 public boolean contains(Object o) { return q.contains(o); } 4108 public boolean remove(Object o) { return q.remove(o); } 4109 public Iterator<E> iterator() { return q.iterator(); } 4110 public Object[] toArray() { return q.toArray(); } 4111 public <T> T[] toArray(T[] a) { return q.toArray(a); } 4112 public String toString() { return q.toString(); } 4113 public boolean containsAll(Collection<?> c) {return q.containsAll(c);} 4114 public boolean removeAll(Collection<?> c) {return q.removeAll(c);} 4115 public boolean retainAll(Collection<?> c) {return q.retainAll(c);} 4116 // We use inherited addAll; forwarding addAll would be wrong 4117 4118 // Override default methods in Collection 4119 @Override 4120 public void forEach(Consumer<? super E> action) {q.forEach(action);} 4121 } 4122} 4123