Collections.java revision 60796efea3a74e02aea384b8eb56103ea21b880b
1/* 2 * Copyright (C) 2014 The Android Open Source Project 3 * Copyright (c) 1997, 2012, 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 }; 1087 } 1088 1089 public boolean add(E e) { 1090 throw new UnsupportedOperationException(); 1091 } 1092 public boolean remove(Object o) { 1093 throw new UnsupportedOperationException(); 1094 } 1095 1096 public boolean containsAll(Collection<?> coll) { 1097 return c.containsAll(coll); 1098 } 1099 public boolean addAll(Collection<? extends E> coll) { 1100 throw new UnsupportedOperationException(); 1101 } 1102 public boolean removeAll(Collection<?> coll) { 1103 throw new UnsupportedOperationException(); 1104 } 1105 public boolean retainAll(Collection<?> coll) { 1106 throw new UnsupportedOperationException(); 1107 } 1108 public void clear() { 1109 throw new UnsupportedOperationException(); 1110 } 1111 1112 // Override default methods in Collection 1113 @Override 1114 public void forEach(Consumer<? super E> action) { 1115 c.forEach(action); 1116 } 1117 } 1118 1119 /** 1120 * Returns an unmodifiable view of the specified set. This method allows 1121 * modules to provide users with "read-only" access to internal sets. 1122 * Query operations on the returned set "read through" to the specified 1123 * set, and attempts to modify the returned set, whether direct or via its 1124 * iterator, result in an <tt>UnsupportedOperationException</tt>.<p> 1125 * 1126 * The returned set will be serializable if the specified set 1127 * is serializable. 1128 * 1129 * @param s the set for which an unmodifiable view is to be returned. 1130 * @return an unmodifiable view of the specified set. 1131 */ 1132 public static <T> Set<T> unmodifiableSet(Set<? extends T> s) { 1133 return new UnmodifiableSet<>(s); 1134 } 1135 1136 /** 1137 * @serial include 1138 */ 1139 static class UnmodifiableSet<E> extends UnmodifiableCollection<E> 1140 implements Set<E>, Serializable { 1141 private static final long serialVersionUID = -9215047833775013803L; 1142 1143 UnmodifiableSet(Set<? extends E> s) {super(s);} 1144 public boolean equals(Object o) {return o == this || c.equals(o);} 1145 public int hashCode() {return c.hashCode();} 1146 } 1147 1148 /** 1149 * Returns an unmodifiable view of the specified sorted set. This method 1150 * allows modules to provide users with "read-only" access to internal 1151 * sorted sets. Query operations on the returned sorted set "read 1152 * through" to the specified sorted set. Attempts to modify the returned 1153 * sorted set, whether direct, via its iterator, or via its 1154 * <tt>subSet</tt>, <tt>headSet</tt>, or <tt>tailSet</tt> views, result in 1155 * an <tt>UnsupportedOperationException</tt>.<p> 1156 * 1157 * The returned sorted set will be serializable if the specified sorted set 1158 * is serializable. 1159 * 1160 * @param s the sorted set for which an unmodifiable view is to be 1161 * returned. 1162 * @return an unmodifiable view of the specified sorted set. 1163 */ 1164 public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) { 1165 return new UnmodifiableSortedSet<>(s); 1166 } 1167 1168 /** 1169 * @serial include 1170 */ 1171 static class UnmodifiableSortedSet<E> 1172 extends UnmodifiableSet<E> 1173 implements SortedSet<E>, Serializable { 1174 private static final long serialVersionUID = -4929149591599911165L; 1175 private final SortedSet<E> ss; 1176 1177 UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;} 1178 1179 public Comparator<? super E> comparator() {return ss.comparator();} 1180 1181 public SortedSet<E> subSet(E fromElement, E toElement) { 1182 return new UnmodifiableSortedSet<>(ss.subSet(fromElement,toElement)); 1183 } 1184 public SortedSet<E> headSet(E toElement) { 1185 return new UnmodifiableSortedSet<>(ss.headSet(toElement)); 1186 } 1187 public SortedSet<E> tailSet(E fromElement) { 1188 return new UnmodifiableSortedSet<>(ss.tailSet(fromElement)); 1189 } 1190 1191 public E first() {return ss.first();} 1192 public E last() {return ss.last();} 1193 } 1194 1195 /** 1196 * Returns an unmodifiable view of the specified list. This method allows 1197 * modules to provide users with "read-only" access to internal 1198 * lists. Query operations on the returned list "read through" to the 1199 * specified list, and attempts to modify the returned list, whether 1200 * direct or via its iterator, result in an 1201 * <tt>UnsupportedOperationException</tt>.<p> 1202 * 1203 * The returned list will be serializable if the specified list 1204 * is serializable. Similarly, the returned list will implement 1205 * {@link RandomAccess} if the specified list does. 1206 * 1207 * @param list the list for which an unmodifiable view is to be returned. 1208 * @return an unmodifiable view of the specified list. 1209 */ 1210 public static <T> List<T> unmodifiableList(List<? extends T> list) { 1211 return (list instanceof RandomAccess ? 1212 new UnmodifiableRandomAccessList<>(list) : 1213 new UnmodifiableList<>(list)); 1214 } 1215 1216 /** 1217 * @serial include 1218 */ 1219 static class UnmodifiableList<E> extends UnmodifiableCollection<E> 1220 implements List<E> { 1221 private static final long serialVersionUID = -283967356065247728L; 1222 final List<? extends E> list; 1223 1224 UnmodifiableList(List<? extends E> list) { 1225 super(list); 1226 this.list = list; 1227 } 1228 1229 public boolean equals(Object o) {return o == this || list.equals(o);} 1230 public int hashCode() {return list.hashCode();} 1231 1232 public E get(int index) {return list.get(index);} 1233 public E set(int index, E element) { 1234 throw new UnsupportedOperationException(); 1235 } 1236 public void add(int index, E element) { 1237 throw new UnsupportedOperationException(); 1238 } 1239 public E remove(int index) { 1240 throw new UnsupportedOperationException(); 1241 } 1242 public int indexOf(Object o) {return list.indexOf(o);} 1243 public int lastIndexOf(Object o) {return list.lastIndexOf(o);} 1244 public boolean addAll(int index, Collection<? extends E> c) { 1245 throw new UnsupportedOperationException(); 1246 } 1247 public ListIterator<E> listIterator() {return listIterator(0);} 1248 1249 public ListIterator<E> listIterator(final int index) { 1250 return new ListIterator<E>() { 1251 private final ListIterator<? extends E> i 1252 = list.listIterator(index); 1253 1254 public boolean hasNext() {return i.hasNext();} 1255 public E next() {return i.next();} 1256 public boolean hasPrevious() {return i.hasPrevious();} 1257 public E previous() {return i.previous();} 1258 public int nextIndex() {return i.nextIndex();} 1259 public int previousIndex() {return i.previousIndex();} 1260 1261 public void remove() { 1262 throw new UnsupportedOperationException(); 1263 } 1264 public void set(E e) { 1265 throw new UnsupportedOperationException(); 1266 } 1267 public void add(E e) { 1268 throw new UnsupportedOperationException(); 1269 } 1270 }; 1271 } 1272 1273 public List<E> subList(int fromIndex, int toIndex) { 1274 return new UnmodifiableList<>(list.subList(fromIndex, toIndex)); 1275 } 1276 1277 /** 1278 * UnmodifiableRandomAccessList instances are serialized as 1279 * UnmodifiableList instances to allow them to be deserialized 1280 * in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList). 1281 * This method inverts the transformation. As a beneficial 1282 * side-effect, it also grafts the RandomAccess marker onto 1283 * UnmodifiableList instances that were serialized in pre-1.4 JREs. 1284 * 1285 * Note: Unfortunately, UnmodifiableRandomAccessList instances 1286 * serialized in 1.4.1 and deserialized in 1.4 will become 1287 * UnmodifiableList instances, as this method was missing in 1.4. 1288 */ 1289 private Object readResolve() { 1290 return (list instanceof RandomAccess 1291 ? new UnmodifiableRandomAccessList<>(list) 1292 : this); 1293 } 1294 } 1295 1296 /** 1297 * @serial include 1298 */ 1299 static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E> 1300 implements RandomAccess 1301 { 1302 UnmodifiableRandomAccessList(List<? extends E> list) { 1303 super(list); 1304 } 1305 1306 public List<E> subList(int fromIndex, int toIndex) { 1307 return new UnmodifiableRandomAccessList<>( 1308 list.subList(fromIndex, toIndex)); 1309 } 1310 1311 private static final long serialVersionUID = -2542308836966382001L; 1312 1313 /** 1314 * Allows instances to be deserialized in pre-1.4 JREs (which do 1315 * not have UnmodifiableRandomAccessList). UnmodifiableList has 1316 * a readResolve method that inverts this transformation upon 1317 * deserialization. 1318 */ 1319 private Object writeReplace() { 1320 return new UnmodifiableList<>(list); 1321 } 1322 } 1323 1324 /** 1325 * Returns an unmodifiable view of the specified map. This method 1326 * allows modules to provide users with "read-only" access to internal 1327 * maps. Query operations on the returned map "read through" 1328 * to the specified map, and attempts to modify the returned 1329 * map, whether direct or via its collection views, result in an 1330 * <tt>UnsupportedOperationException</tt>.<p> 1331 * 1332 * The returned map will be serializable if the specified map 1333 * is serializable. 1334 * 1335 * @param m the map for which an unmodifiable view is to be returned. 1336 * @return an unmodifiable view of the specified map. 1337 */ 1338 public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) { 1339 return new UnmodifiableMap<>(m); 1340 } 1341 1342 /** 1343 * @serial include 1344 */ 1345 private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable { 1346 private static final long serialVersionUID = -1034234728574286014L; 1347 1348 private final Map<? extends K, ? extends V> m; 1349 1350 UnmodifiableMap(Map<? extends K, ? extends V> m) { 1351 if (m==null) 1352 throw new NullPointerException(); 1353 this.m = m; 1354 } 1355 1356 public int size() {return m.size();} 1357 public boolean isEmpty() {return m.isEmpty();} 1358 public boolean containsKey(Object key) {return m.containsKey(key);} 1359 public boolean containsValue(Object val) {return m.containsValue(val);} 1360 public V get(Object key) {return m.get(key);} 1361 1362 public V put(K key, V value) { 1363 throw new UnsupportedOperationException(); 1364 } 1365 public V remove(Object key) { 1366 throw new UnsupportedOperationException(); 1367 } 1368 public void putAll(Map<? extends K, ? extends V> m) { 1369 throw new UnsupportedOperationException(); 1370 } 1371 public void clear() { 1372 throw new UnsupportedOperationException(); 1373 } 1374 1375 private transient Set<K> keySet = null; 1376 private transient Set<Map.Entry<K,V>> entrySet = null; 1377 private transient Collection<V> values = null; 1378 1379 public Set<K> keySet() { 1380 if (keySet==null) 1381 keySet = unmodifiableSet(m.keySet()); 1382 return keySet; 1383 } 1384 1385 public Set<Map.Entry<K,V>> entrySet() { 1386 if (entrySet==null) 1387 entrySet = new UnmodifiableEntrySet<>(m.entrySet()); 1388 return entrySet; 1389 } 1390 1391 public Collection<V> values() { 1392 if (values==null) 1393 values = unmodifiableCollection(m.values()); 1394 return values; 1395 } 1396 1397 public boolean equals(Object o) {return o == this || m.equals(o);} 1398 public int hashCode() {return m.hashCode();} 1399 public String toString() {return m.toString();} 1400 1401 // Override default methods in Map 1402 @Override 1403 public void forEach(BiConsumer<? super K, ? super V> action) { 1404 m.forEach(action); 1405 } 1406 1407 /** 1408 * We need this class in addition to UnmodifiableSet as 1409 * Map.Entries themselves permit modification of the backing Map 1410 * via their setValue operation. This class is subtle: there are 1411 * many possible attacks that must be thwarted. 1412 * 1413 * @serial include 1414 */ 1415 static class UnmodifiableEntrySet<K,V> 1416 extends UnmodifiableSet<Map.Entry<K,V>> { 1417 private static final long serialVersionUID = 7854390611657943733L; 1418 1419 UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) { 1420 super((Set)s); 1421 } 1422 1423 static <K, V> Consumer<Map.Entry<K, V>> entryConsumer(Consumer<? super Entry<K, V>> action) { 1424 return e -> action.accept(new UnmodifiableEntry<>(e)); 1425 } 1426 1427 // Override default methods in Collection 1428 public void forEach(Consumer<? super Entry<K, V>> action) { 1429 Objects.requireNonNull(action); 1430 c.forEach(entryConsumer(action)); 1431 } 1432 1433 public Iterator<Map.Entry<K,V>> iterator() { 1434 return new Iterator<Map.Entry<K,V>>() { 1435 private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator(); 1436 1437 public boolean hasNext() { 1438 return i.hasNext(); 1439 } 1440 public Map.Entry<K,V> next() { 1441 return new UnmodifiableEntry<>(i.next()); 1442 } 1443 public void remove() { 1444 throw new UnsupportedOperationException(); 1445 } 1446 }; 1447 } 1448 1449 public Object[] toArray() { 1450 Object[] a = c.toArray(); 1451 for (int i=0; i<a.length; i++) 1452 a[i] = new UnmodifiableEntry<>((Map.Entry<K,V>)a[i]); 1453 return a; 1454 } 1455 1456 public <T> T[] toArray(T[] a) { 1457 // We don't pass a to c.toArray, to avoid window of 1458 // vulnerability wherein an unscrupulous multithreaded client 1459 // could get his hands on raw (unwrapped) Entries from c. 1460 Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0)); 1461 1462 for (int i=0; i<arr.length; i++) 1463 arr[i] = new UnmodifiableEntry<>((Map.Entry<K,V>)arr[i]); 1464 1465 if (arr.length > a.length) 1466 return (T[])arr; 1467 1468 System.arraycopy(arr, 0, a, 0, arr.length); 1469 if (a.length > arr.length) 1470 a[arr.length] = null; 1471 return a; 1472 } 1473 1474 /** 1475 * This method is overridden to protect the backing set against 1476 * an object with a nefarious equals function that senses 1477 * that the equality-candidate is Map.Entry and calls its 1478 * setValue method. 1479 */ 1480 public boolean contains(Object o) { 1481 if (!(o instanceof Map.Entry)) 1482 return false; 1483 return c.contains( 1484 new UnmodifiableEntry<>((Map.Entry<?,?>) o)); 1485 } 1486 1487 /** 1488 * The next two methods are overridden to protect against 1489 * an unscrupulous List whose contains(Object o) method senses 1490 * when o is a Map.Entry, and calls o.setValue. 1491 */ 1492 public boolean containsAll(Collection<?> coll) { 1493 for (Object e : coll) { 1494 if (!contains(e)) // Invokes safe contains() above 1495 return false; 1496 } 1497 return true; 1498 } 1499 public boolean equals(Object o) { 1500 if (o == this) 1501 return true; 1502 1503 if (!(o instanceof Set)) 1504 return false; 1505 Set s = (Set) o; 1506 if (s.size() != c.size()) 1507 return false; 1508 return containsAll(s); // Invokes safe containsAll() above 1509 } 1510 1511 /** 1512 * This "wrapper class" serves two purposes: it prevents 1513 * the client from modifying the backing Map, by short-circuiting 1514 * the setValue method, and it protects the backing Map against 1515 * an ill-behaved Map.Entry that attempts to modify another 1516 * Map Entry when asked to perform an equality check. 1517 */ 1518 private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> { 1519 private Map.Entry<? extends K, ? extends V> e; 1520 1521 UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) {this.e = e;} 1522 1523 public K getKey() {return e.getKey();} 1524 public V getValue() {return e.getValue();} 1525 public V setValue(V value) { 1526 throw new UnsupportedOperationException(); 1527 } 1528 public int hashCode() {return e.hashCode();} 1529 public boolean equals(Object o) { 1530 if (this == o) 1531 return true; 1532 if (!(o instanceof Map.Entry)) 1533 return false; 1534 Map.Entry t = (Map.Entry)o; 1535 return eq(e.getKey(), t.getKey()) && 1536 eq(e.getValue(), t.getValue()); 1537 } 1538 public String toString() {return e.toString();} 1539 } 1540 } 1541 } 1542 1543 /** 1544 * Returns an unmodifiable view of the specified sorted map. This method 1545 * allows modules to provide users with "read-only" access to internal 1546 * sorted maps. Query operations on the returned sorted map "read through" 1547 * to the specified sorted map. Attempts to modify the returned 1548 * sorted map, whether direct, via its collection views, or via its 1549 * <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in 1550 * an <tt>UnsupportedOperationException</tt>.<p> 1551 * 1552 * The returned sorted map will be serializable if the specified sorted map 1553 * is serializable. 1554 * 1555 * @param m the sorted map for which an unmodifiable view is to be 1556 * returned. 1557 * @return an unmodifiable view of the specified sorted map. 1558 */ 1559 public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) { 1560 return new UnmodifiableSortedMap<>(m); 1561 } 1562 1563 /** 1564 * @serial include 1565 */ 1566 static class UnmodifiableSortedMap<K,V> 1567 extends UnmodifiableMap<K,V> 1568 implements SortedMap<K,V>, Serializable { 1569 private static final long serialVersionUID = -8806743815996713206L; 1570 1571 private final SortedMap<K, ? extends V> sm; 1572 1573 UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m;} 1574 1575 public Comparator<? super K> comparator() {return sm.comparator();} 1576 1577 public SortedMap<K,V> subMap(K fromKey, K toKey) { 1578 return new UnmodifiableSortedMap<>(sm.subMap(fromKey, toKey)); 1579 } 1580 public SortedMap<K,V> headMap(K toKey) { 1581 return new UnmodifiableSortedMap<>(sm.headMap(toKey)); 1582 } 1583 public SortedMap<K,V> tailMap(K fromKey) { 1584 return new UnmodifiableSortedMap<>(sm.tailMap(fromKey)); 1585 } 1586 1587 public K firstKey() {return sm.firstKey();} 1588 public K lastKey() {return sm.lastKey();} 1589 } 1590 1591 1592 // Synch Wrappers 1593 1594 /** 1595 * Returns a synchronized (thread-safe) collection backed by the specified 1596 * collection. In order to guarantee serial access, it is critical that 1597 * <strong>all</strong> access to the backing collection is accomplished 1598 * through the returned collection.<p> 1599 * 1600 * It is imperative that the user manually synchronize on the returned 1601 * collection when iterating over it: 1602 * <pre> 1603 * Collection c = Collections.synchronizedCollection(myCollection); 1604 * ... 1605 * synchronized (c) { 1606 * Iterator i = c.iterator(); // Must be in the synchronized block 1607 * while (i.hasNext()) 1608 * foo(i.next()); 1609 * } 1610 * </pre> 1611 * Failure to follow this advice may result in non-deterministic behavior. 1612 * 1613 * <p>The returned collection does <i>not</i> pass the <tt>hashCode</tt> 1614 * and <tt>equals</tt> operations through to the backing collection, but 1615 * relies on <tt>Object</tt>'s equals and hashCode methods. This is 1616 * necessary to preserve the contracts of these operations in the case 1617 * that the backing collection is a set or a list.<p> 1618 * 1619 * The returned collection will be serializable if the specified collection 1620 * is serializable. 1621 * 1622 * @param c the collection to be "wrapped" in a synchronized collection. 1623 * @return a synchronized view of the specified collection. 1624 */ 1625 public static <T> Collection<T> synchronizedCollection(Collection<T> c) { 1626 return new SynchronizedCollection<>(c); 1627 } 1628 1629 static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) { 1630 return new SynchronizedCollection<>(c, mutex); 1631 } 1632 1633 /** 1634 * @serial include 1635 */ 1636 static class SynchronizedCollection<E> implements Collection<E>, Serializable { 1637 private static final long serialVersionUID = 3053995032091335093L; 1638 1639 final Collection<E> c; // Backing Collection 1640 final Object mutex; // Object on which to synchronize 1641 1642 SynchronizedCollection(Collection<E> c) { 1643 if (c==null) 1644 throw new NullPointerException(); 1645 this.c = c; 1646 mutex = this; 1647 } 1648 SynchronizedCollection(Collection<E> c, Object mutex) { 1649 this.c = c; 1650 this.mutex = mutex; 1651 } 1652 1653 public int size() { 1654 synchronized (mutex) {return c.size();} 1655 } 1656 public boolean isEmpty() { 1657 synchronized (mutex) {return c.isEmpty();} 1658 } 1659 public boolean contains(Object o) { 1660 synchronized (mutex) {return c.contains(o);} 1661 } 1662 public Object[] toArray() { 1663 synchronized (mutex) {return c.toArray();} 1664 } 1665 public <T> T[] toArray(T[] a) { 1666 synchronized (mutex) {return c.toArray(a);} 1667 } 1668 1669 public Iterator<E> iterator() { 1670 return c.iterator(); // Must be manually synched by user! 1671 } 1672 1673 public boolean add(E e) { 1674 synchronized (mutex) {return c.add(e);} 1675 } 1676 public boolean remove(Object o) { 1677 synchronized (mutex) {return c.remove(o);} 1678 } 1679 1680 public boolean containsAll(Collection<?> coll) { 1681 synchronized (mutex) {return c.containsAll(coll);} 1682 } 1683 public boolean addAll(Collection<? extends E> coll) { 1684 synchronized (mutex) {return c.addAll(coll);} 1685 } 1686 public boolean removeAll(Collection<?> coll) { 1687 synchronized (mutex) {return c.removeAll(coll);} 1688 } 1689 public boolean retainAll(Collection<?> coll) { 1690 synchronized (mutex) {return c.retainAll(coll);} 1691 } 1692 public void clear() { 1693 synchronized (mutex) {c.clear();} 1694 } 1695 public String toString() { 1696 synchronized (mutex) {return c.toString();} 1697 } 1698 1699 // Override default methods in Collection 1700 @Override 1701 public void forEach(Consumer<? super E> consumer) { 1702 synchronized (mutex) {c.forEach(consumer);} 1703 } 1704 1705 private void writeObject(ObjectOutputStream s) throws IOException { 1706 synchronized (mutex) {s.defaultWriteObject();} 1707 } 1708 } 1709 1710 /** 1711 * Returns a synchronized (thread-safe) set backed by the specified 1712 * set. In order to guarantee serial access, it is critical that 1713 * <strong>all</strong> access to the backing set is accomplished 1714 * through the returned set.<p> 1715 * 1716 * It is imperative that the user manually synchronize on the returned 1717 * set when iterating over it: 1718 * <pre> 1719 * Set s = Collections.synchronizedSet(new HashSet()); 1720 * ... 1721 * synchronized (s) { 1722 * Iterator i = s.iterator(); // Must be in the synchronized block 1723 * while (i.hasNext()) 1724 * foo(i.next()); 1725 * } 1726 * </pre> 1727 * Failure to follow this advice may result in non-deterministic behavior. 1728 * 1729 * <p>The returned set will be serializable if the specified set is 1730 * serializable. 1731 * 1732 * @param s the set to be "wrapped" in a synchronized set. 1733 * @return a synchronized view of the specified set. 1734 */ 1735 public static <T> Set<T> synchronizedSet(Set<T> s) { 1736 return new SynchronizedSet<>(s); 1737 } 1738 1739 static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) { 1740 return new SynchronizedSet<>(s, mutex); 1741 } 1742 1743 /** 1744 * @serial include 1745 */ 1746 static class SynchronizedSet<E> 1747 extends SynchronizedCollection<E> 1748 implements Set<E> { 1749 private static final long serialVersionUID = 487447009682186044L; 1750 1751 SynchronizedSet(Set<E> s) { 1752 super(s); 1753 } 1754 SynchronizedSet(Set<E> s, Object mutex) { 1755 super(s, mutex); 1756 } 1757 1758 public boolean equals(Object o) { 1759 if (this == o) 1760 return true; 1761 synchronized (mutex) {return c.equals(o);} 1762 } 1763 public int hashCode() { 1764 synchronized (mutex) {return c.hashCode();} 1765 } 1766 } 1767 1768 /** 1769 * Returns a synchronized (thread-safe) sorted set backed by the specified 1770 * sorted set. In order to guarantee serial access, it is critical that 1771 * <strong>all</strong> access to the backing sorted set is accomplished 1772 * through the returned sorted set (or its views).<p> 1773 * 1774 * It is imperative that the user manually synchronize on the returned 1775 * sorted set when iterating over it or any of its <tt>subSet</tt>, 1776 * <tt>headSet</tt>, or <tt>tailSet</tt> views. 1777 * <pre> 1778 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet()); 1779 * ... 1780 * synchronized (s) { 1781 * Iterator i = s.iterator(); // Must be in the synchronized block 1782 * while (i.hasNext()) 1783 * foo(i.next()); 1784 * } 1785 * </pre> 1786 * or: 1787 * <pre> 1788 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet()); 1789 * SortedSet s2 = s.headSet(foo); 1790 * ... 1791 * synchronized (s) { // Note: s, not s2!!! 1792 * Iterator i = s2.iterator(); // Must be in the synchronized block 1793 * while (i.hasNext()) 1794 * foo(i.next()); 1795 * } 1796 * </pre> 1797 * Failure to follow this advice may result in non-deterministic behavior. 1798 * 1799 * <p>The returned sorted set will be serializable if the specified 1800 * sorted set is serializable. 1801 * 1802 * @param s the sorted set to be "wrapped" in a synchronized sorted set. 1803 * @return a synchronized view of the specified sorted set. 1804 */ 1805 public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) { 1806 return new SynchronizedSortedSet<>(s); 1807 } 1808 1809 /** 1810 * @serial include 1811 */ 1812 static class SynchronizedSortedSet<E> 1813 extends SynchronizedSet<E> 1814 implements SortedSet<E> 1815 { 1816 private static final long serialVersionUID = 8695801310862127406L; 1817 1818 private final SortedSet<E> ss; 1819 1820 SynchronizedSortedSet(SortedSet<E> s) { 1821 super(s); 1822 ss = s; 1823 } 1824 SynchronizedSortedSet(SortedSet<E> s, Object mutex) { 1825 super(s, mutex); 1826 ss = s; 1827 } 1828 1829 public Comparator<? super E> comparator() { 1830 synchronized (mutex) {return ss.comparator();} 1831 } 1832 1833 public SortedSet<E> subSet(E fromElement, E toElement) { 1834 synchronized (mutex) { 1835 return new SynchronizedSortedSet<>( 1836 ss.subSet(fromElement, toElement), mutex); 1837 } 1838 } 1839 public SortedSet<E> headSet(E toElement) { 1840 synchronized (mutex) { 1841 return new SynchronizedSortedSet<>(ss.headSet(toElement), mutex); 1842 } 1843 } 1844 public SortedSet<E> tailSet(E fromElement) { 1845 synchronized (mutex) { 1846 return new SynchronizedSortedSet<>(ss.tailSet(fromElement),mutex); 1847 } 1848 } 1849 1850 public E first() { 1851 synchronized (mutex) {return ss.first();} 1852 } 1853 public E last() { 1854 synchronized (mutex) {return ss.last();} 1855 } 1856 } 1857 1858 /** 1859 * Returns a synchronized (thread-safe) list backed by the specified 1860 * list. In order to guarantee serial access, it is critical that 1861 * <strong>all</strong> access to the backing list is accomplished 1862 * through the returned list.<p> 1863 * 1864 * It is imperative that the user manually synchronize on the returned 1865 * list when iterating over it: 1866 * <pre> 1867 * List list = Collections.synchronizedList(new ArrayList()); 1868 * ... 1869 * synchronized (list) { 1870 * Iterator i = list.iterator(); // Must be in synchronized block 1871 * while (i.hasNext()) 1872 * foo(i.next()); 1873 * } 1874 * </pre> 1875 * Failure to follow this advice may result in non-deterministic behavior. 1876 * 1877 * <p>The returned list will be serializable if the specified list is 1878 * serializable. 1879 * 1880 * @param list the list to be "wrapped" in a synchronized list. 1881 * @return a synchronized view of the specified list. 1882 */ 1883 public static <T> List<T> synchronizedList(List<T> list) { 1884 return (list instanceof RandomAccess ? 1885 new SynchronizedRandomAccessList<>(list) : 1886 new SynchronizedList<>(list)); 1887 } 1888 1889 static <T> List<T> synchronizedList(List<T> list, Object mutex) { 1890 return (list instanceof RandomAccess ? 1891 new SynchronizedRandomAccessList<>(list, mutex) : 1892 new SynchronizedList<>(list, mutex)); 1893 } 1894 1895 /** 1896 * @serial include 1897 */ 1898 static class SynchronizedList<E> 1899 extends SynchronizedCollection<E> 1900 implements List<E> { 1901 private static final long serialVersionUID = -7754090372962971524L; 1902 1903 final List<E> list; 1904 1905 SynchronizedList(List<E> list) { 1906 super(list); 1907 this.list = list; 1908 } 1909 SynchronizedList(List<E> list, Object mutex) { 1910 super(list, mutex); 1911 this.list = list; 1912 } 1913 1914 public boolean equals(Object o) { 1915 if (this == o) 1916 return true; 1917 synchronized (mutex) {return list.equals(o);} 1918 } 1919 public int hashCode() { 1920 synchronized (mutex) {return list.hashCode();} 1921 } 1922 1923 public E get(int index) { 1924 synchronized (mutex) {return list.get(index);} 1925 } 1926 public E set(int index, E element) { 1927 synchronized (mutex) {return list.set(index, element);} 1928 } 1929 public void add(int index, E element) { 1930 synchronized (mutex) {list.add(index, element);} 1931 } 1932 public E remove(int index) { 1933 synchronized (mutex) {return list.remove(index);} 1934 } 1935 1936 public int indexOf(Object o) { 1937 synchronized (mutex) {return list.indexOf(o);} 1938 } 1939 public int lastIndexOf(Object o) { 1940 synchronized (mutex) {return list.lastIndexOf(o);} 1941 } 1942 1943 public boolean addAll(int index, Collection<? extends E> c) { 1944 synchronized (mutex) {return list.addAll(index, c);} 1945 } 1946 1947 public ListIterator<E> listIterator() { 1948 return list.listIterator(); // Must be manually synched by user 1949 } 1950 1951 public ListIterator<E> listIterator(int index) { 1952 return list.listIterator(index); // Must be manually synched by user 1953 } 1954 1955 public List<E> subList(int fromIndex, int toIndex) { 1956 synchronized (mutex) { 1957 return new SynchronizedList<>(list.subList(fromIndex, toIndex), 1958 mutex); 1959 } 1960 } 1961 1962 /** 1963 * SynchronizedRandomAccessList instances are serialized as 1964 * SynchronizedList instances to allow them to be deserialized 1965 * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList). 1966 * This method inverts the transformation. As a beneficial 1967 * side-effect, it also grafts the RandomAccess marker onto 1968 * SynchronizedList instances that were serialized in pre-1.4 JREs. 1969 * 1970 * Note: Unfortunately, SynchronizedRandomAccessList instances 1971 * serialized in 1.4.1 and deserialized in 1.4 will become 1972 * SynchronizedList instances, as this method was missing in 1.4. 1973 */ 1974 private Object readResolve() { 1975 return (list instanceof RandomAccess 1976 ? new SynchronizedRandomAccessList<>(list) 1977 : this); 1978 } 1979 } 1980 1981 /** 1982 * @serial include 1983 */ 1984 static class SynchronizedRandomAccessList<E> 1985 extends SynchronizedList<E> 1986 implements RandomAccess { 1987 1988 SynchronizedRandomAccessList(List<E> list) { 1989 super(list); 1990 } 1991 1992 SynchronizedRandomAccessList(List<E> list, Object mutex) { 1993 super(list, mutex); 1994 } 1995 1996 public List<E> subList(int fromIndex, int toIndex) { 1997 synchronized (mutex) { 1998 return new SynchronizedRandomAccessList<>( 1999 list.subList(fromIndex, toIndex), mutex); 2000 } 2001 } 2002 2003 private static final long serialVersionUID = 1530674583602358482L; 2004 2005 /** 2006 * Allows instances to be deserialized in pre-1.4 JREs (which do 2007 * not have SynchronizedRandomAccessList). SynchronizedList has 2008 * a readResolve method that inverts this transformation upon 2009 * deserialization. 2010 */ 2011 private Object writeReplace() { 2012 return new SynchronizedList<>(list); 2013 } 2014 } 2015 2016 /** 2017 * Returns a synchronized (thread-safe) map backed by the specified 2018 * map. In order to guarantee serial access, it is critical that 2019 * <strong>all</strong> access to the backing map is accomplished 2020 * through the returned map.<p> 2021 * 2022 * It is imperative that the user manually synchronize on the returned 2023 * map when iterating over any of its collection views: 2024 * <pre> 2025 * Map m = Collections.synchronizedMap(new HashMap()); 2026 * ... 2027 * Set s = m.keySet(); // Needn't be in synchronized block 2028 * ... 2029 * synchronized (m) { // Synchronizing on m, not s! 2030 * Iterator i = s.iterator(); // Must be in synchronized block 2031 * while (i.hasNext()) 2032 * foo(i.next()); 2033 * } 2034 * </pre> 2035 * Failure to follow this advice may result in non-deterministic behavior. 2036 * 2037 * <p>The returned map will be serializable if the specified map is 2038 * serializable. 2039 * 2040 * @param m the map to be "wrapped" in a synchronized map. 2041 * @return a synchronized view of the specified map. 2042 */ 2043 public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) { 2044 return new SynchronizedMap<>(m); 2045 } 2046 2047 /** 2048 * @serial include 2049 */ 2050 private static class SynchronizedMap<K,V> 2051 implements Map<K,V>, Serializable { 2052 private static final long serialVersionUID = 1978198479659022715L; 2053 2054 private final Map<K,V> m; // Backing Map 2055 final Object mutex; // Object on which to synchronize 2056 2057 SynchronizedMap(Map<K,V> m) { 2058 if (m==null) 2059 throw new NullPointerException(); 2060 this.m = m; 2061 mutex = this; 2062 } 2063 2064 SynchronizedMap(Map<K,V> m, Object mutex) { 2065 this.m = m; 2066 this.mutex = mutex; 2067 } 2068 2069 public int size() { 2070 synchronized (mutex) {return m.size();} 2071 } 2072 public boolean isEmpty() { 2073 synchronized (mutex) {return m.isEmpty();} 2074 } 2075 public boolean containsKey(Object key) { 2076 synchronized (mutex) {return m.containsKey(key);} 2077 } 2078 public boolean containsValue(Object value) { 2079 synchronized (mutex) {return m.containsValue(value);} 2080 } 2081 public V get(Object key) { 2082 synchronized (mutex) {return m.get(key);} 2083 } 2084 2085 public V put(K key, V value) { 2086 synchronized (mutex) {return m.put(key, value);} 2087 } 2088 public V remove(Object key) { 2089 synchronized (mutex) {return m.remove(key);} 2090 } 2091 public void putAll(Map<? extends K, ? extends V> map) { 2092 synchronized (mutex) {m.putAll(map);} 2093 } 2094 public void clear() { 2095 synchronized (mutex) {m.clear();} 2096 } 2097 2098 private transient Set<K> keySet = null; 2099 private transient Set<Map.Entry<K,V>> entrySet = null; 2100 private transient Collection<V> values = null; 2101 2102 public Set<K> keySet() { 2103 synchronized (mutex) { 2104 if (keySet==null) 2105 keySet = new SynchronizedSet<>(m.keySet(), mutex); 2106 return keySet; 2107 } 2108 } 2109 2110 public Set<Map.Entry<K,V>> entrySet() { 2111 synchronized (mutex) { 2112 if (entrySet==null) 2113 entrySet = new SynchronizedSet<>(m.entrySet(), mutex); 2114 return entrySet; 2115 } 2116 } 2117 2118 public Collection<V> values() { 2119 synchronized (mutex) { 2120 if (values==null) 2121 values = new SynchronizedCollection<>(m.values(), mutex); 2122 return values; 2123 } 2124 } 2125 2126 public boolean equals(Object o) { 2127 if (this == o) 2128 return true; 2129 synchronized (mutex) {return m.equals(o);} 2130 } 2131 public int hashCode() { 2132 synchronized (mutex) {return m.hashCode();} 2133 } 2134 public String toString() { 2135 synchronized (mutex) {return m.toString();} 2136 } 2137 // Override default methods in Map 2138 @Override 2139 public void forEach(BiConsumer<? super K, ? super V> action) { 2140 synchronized (mutex) {m.forEach(action);} 2141 } 2142 2143 private void writeObject(ObjectOutputStream s) throws IOException { 2144 synchronized (mutex) {s.defaultWriteObject();} 2145 } 2146 } 2147 2148 /** 2149 * Returns a synchronized (thread-safe) sorted map backed by the specified 2150 * sorted map. In order to guarantee serial access, it is critical that 2151 * <strong>all</strong> access to the backing sorted map is accomplished 2152 * through the returned sorted map (or its views).<p> 2153 * 2154 * It is imperative that the user manually synchronize on the returned 2155 * sorted map when iterating over any of its collection views, or the 2156 * collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or 2157 * <tt>tailMap</tt> views. 2158 * <pre> 2159 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap()); 2160 * ... 2161 * Set s = m.keySet(); // Needn't be in synchronized block 2162 * ... 2163 * synchronized (m) { // Synchronizing on m, not s! 2164 * Iterator i = s.iterator(); // Must be in synchronized block 2165 * while (i.hasNext()) 2166 * foo(i.next()); 2167 * } 2168 * </pre> 2169 * or: 2170 * <pre> 2171 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap()); 2172 * SortedMap m2 = m.subMap(foo, bar); 2173 * ... 2174 * Set s2 = m2.keySet(); // Needn't be in synchronized block 2175 * ... 2176 * synchronized (m) { // Synchronizing on m, not m2 or s2! 2177 * Iterator i = s.iterator(); // Must be in synchronized block 2178 * while (i.hasNext()) 2179 * foo(i.next()); 2180 * } 2181 * </pre> 2182 * Failure to follow this advice may result in non-deterministic behavior. 2183 * 2184 * <p>The returned sorted map will be serializable if the specified 2185 * sorted map is serializable. 2186 * 2187 * @param m the sorted map to be "wrapped" in a synchronized sorted map. 2188 * @return a synchronized view of the specified sorted map. 2189 */ 2190 public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) { 2191 return new SynchronizedSortedMap<>(m); 2192 } 2193 2194 2195 /** 2196 * @serial include 2197 */ 2198 static class SynchronizedSortedMap<K,V> 2199 extends SynchronizedMap<K,V> 2200 implements SortedMap<K,V> 2201 { 2202 private static final long serialVersionUID = -8798146769416483793L; 2203 2204 private final SortedMap<K,V> sm; 2205 2206 SynchronizedSortedMap(SortedMap<K,V> m) { 2207 super(m); 2208 sm = m; 2209 } 2210 SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) { 2211 super(m, mutex); 2212 sm = m; 2213 } 2214 2215 public Comparator<? super K> comparator() { 2216 synchronized (mutex) {return sm.comparator();} 2217 } 2218 2219 public SortedMap<K,V> subMap(K fromKey, K toKey) { 2220 synchronized (mutex) { 2221 return new SynchronizedSortedMap<>( 2222 sm.subMap(fromKey, toKey), mutex); 2223 } 2224 } 2225 public SortedMap<K,V> headMap(K toKey) { 2226 synchronized (mutex) { 2227 return new SynchronizedSortedMap<>(sm.headMap(toKey), mutex); 2228 } 2229 } 2230 public SortedMap<K,V> tailMap(K fromKey) { 2231 synchronized (mutex) { 2232 return new SynchronizedSortedMap<>(sm.tailMap(fromKey),mutex); 2233 } 2234 } 2235 2236 public K firstKey() { 2237 synchronized (mutex) {return sm.firstKey();} 2238 } 2239 public K lastKey() { 2240 synchronized (mutex) {return sm.lastKey();} 2241 } 2242 } 2243 2244 // Dynamically typesafe collection wrappers 2245 2246 /** 2247 * Returns a dynamically typesafe view of the specified collection. 2248 * Any attempt to insert an element of the wrong type will result in an 2249 * immediate {@link ClassCastException}. Assuming a collection 2250 * contains no incorrectly typed elements prior to the time a 2251 * dynamically typesafe view is generated, and that all subsequent 2252 * access to the collection takes place through the view, it is 2253 * <i>guaranteed</i> that the collection cannot contain an incorrectly 2254 * typed element. 2255 * 2256 * <p>The generics mechanism in the language provides compile-time 2257 * (static) type checking, but it is possible to defeat this mechanism 2258 * with unchecked casts. Usually this is not a problem, as the compiler 2259 * issues warnings on all such unchecked operations. There are, however, 2260 * times when static type checking alone is not sufficient. For example, 2261 * suppose a collection is passed to a third-party library and it is 2262 * imperative that the library code not corrupt the collection by 2263 * inserting an element of the wrong type. 2264 * 2265 * <p>Another use of dynamically typesafe views is debugging. Suppose a 2266 * program fails with a {@code ClassCastException}, indicating that an 2267 * incorrectly typed element was put into a parameterized collection. 2268 * Unfortunately, the exception can occur at any time after the erroneous 2269 * element is inserted, so it typically provides little or no information 2270 * as to the real source of the problem. If the problem is reproducible, 2271 * one can quickly determine its source by temporarily modifying the 2272 * program to wrap the collection with a dynamically typesafe view. 2273 * For example, this declaration: 2274 * <pre> {@code 2275 * Collection<String> c = new HashSet<String>(); 2276 * }</pre> 2277 * may be replaced temporarily by this one: 2278 * <pre> {@code 2279 * Collection<String> c = Collections.checkedCollection( 2280 * new HashSet<String>(), String.class); 2281 * }</pre> 2282 * Running the program again will cause it to fail at the point where 2283 * an incorrectly typed element is inserted into the collection, clearly 2284 * identifying the source of the problem. Once the problem is fixed, the 2285 * modified declaration may be reverted back to the original. 2286 * 2287 * <p>The returned collection does <i>not</i> pass the hashCode and equals 2288 * operations through to the backing collection, but relies on 2289 * {@code Object}'s {@code equals} and {@code hashCode} methods. This 2290 * is necessary to preserve the contracts of these operations in the case 2291 * that the backing collection is a set or a list. 2292 * 2293 * <p>The returned collection will be serializable if the specified 2294 * collection is serializable. 2295 * 2296 * <p>Since {@code null} is considered to be a value of any reference 2297 * type, the returned collection permits insertion of null elements 2298 * whenever the backing collection does. 2299 * 2300 * @param c the collection for which a dynamically typesafe view is to be 2301 * returned 2302 * @param type the type of element that {@code c} is permitted to hold 2303 * @return a dynamically typesafe view of the specified collection 2304 * @since 1.5 2305 */ 2306 public static <E> Collection<E> checkedCollection(Collection<E> c, 2307 Class<E> type) { 2308 return new CheckedCollection<>(c, type); 2309 } 2310 2311 @SuppressWarnings("unchecked") 2312 static <T> T[] zeroLengthArray(Class<T> type) { 2313 return (T[]) Array.newInstance(type, 0); 2314 } 2315 2316 /** 2317 * @serial include 2318 */ 2319 static class CheckedCollection<E> implements Collection<E>, Serializable { 2320 private static final long serialVersionUID = 1578914078182001775L; 2321 2322 final Collection<E> c; 2323 final Class<E> type; 2324 2325 void typeCheck(Object o) { 2326 if (o != null && !type.isInstance(o)) 2327 throw new ClassCastException(badElementMsg(o)); 2328 } 2329 2330 private String badElementMsg(Object o) { 2331 return "Attempt to insert " + o.getClass() + 2332 " element into collection with element type " + type; 2333 } 2334 2335 CheckedCollection(Collection<E> c, Class<E> type) { 2336 if (c==null || type == null) 2337 throw new NullPointerException(); 2338 this.c = c; 2339 this.type = type; 2340 } 2341 2342 public int size() { return c.size(); } 2343 public boolean isEmpty() { return c.isEmpty(); } 2344 public boolean contains(Object o) { return c.contains(o); } 2345 public Object[] toArray() { return c.toArray(); } 2346 public <T> T[] toArray(T[] a) { return c.toArray(a); } 2347 public String toString() { return c.toString(); } 2348 public boolean remove(Object o) { return c.remove(o); } 2349 public void clear() { c.clear(); } 2350 2351 public boolean containsAll(Collection<?> coll) { 2352 return c.containsAll(coll); 2353 } 2354 public boolean removeAll(Collection<?> coll) { 2355 return c.removeAll(coll); 2356 } 2357 public boolean retainAll(Collection<?> coll) { 2358 return c.retainAll(coll); 2359 } 2360 2361 public Iterator<E> iterator() { 2362 final Iterator<E> it = c.iterator(); 2363 return new Iterator<E>() { 2364 public boolean hasNext() { return it.hasNext(); } 2365 public E next() { return it.next(); } 2366 public void remove() { it.remove(); }}; 2367 } 2368 2369 public boolean add(E e) { 2370 typeCheck(e); 2371 return c.add(e); 2372 } 2373 2374 private E[] zeroLengthElementArray = null; // Lazily initialized 2375 2376 private E[] zeroLengthElementArray() { 2377 return zeroLengthElementArray != null ? zeroLengthElementArray : 2378 (zeroLengthElementArray = zeroLengthArray(type)); 2379 } 2380 2381 @SuppressWarnings("unchecked") 2382 Collection<E> checkedCopyOf(Collection<? extends E> coll) { 2383 Object[] a = null; 2384 try { 2385 E[] z = zeroLengthElementArray(); 2386 a = coll.toArray(z); 2387 // Defend against coll violating the toArray contract 2388 if (a.getClass() != z.getClass()) 2389 a = Arrays.copyOf(a, a.length, z.getClass()); 2390 } catch (ArrayStoreException ignore) { 2391 // To get better and consistent diagnostics, 2392 // we call typeCheck explicitly on each element. 2393 // We call clone() to defend against coll retaining a 2394 // reference to the returned array and storing a bad 2395 // element into it after it has been type checked. 2396 a = coll.toArray().clone(); 2397 for (Object o : a) 2398 typeCheck(o); 2399 } 2400 // A slight abuse of the type system, but safe here. 2401 return (Collection<E>) Arrays.asList(a); 2402 } 2403 2404 public boolean addAll(Collection<? extends E> coll) { 2405 // Doing things this way insulates us from concurrent changes 2406 // in the contents of coll and provides all-or-nothing 2407 // semantics (which we wouldn't get if we type-checked each 2408 // element as we added it) 2409 return c.addAll(checkedCopyOf(coll)); 2410 } 2411 2412 // Override default methods in Collection 2413 @Override 2414 public void forEach(Consumer<? super E> action) {c.forEach(action);} 2415 } 2416 2417 /** 2418 * Returns a dynamically typesafe view of the specified set. 2419 * Any attempt to insert an element of the wrong type will result in 2420 * an immediate {@link ClassCastException}. Assuming a set contains 2421 * no incorrectly typed elements prior to the time a dynamically typesafe 2422 * view is generated, and that all subsequent access to the set 2423 * takes place through the view, it is <i>guaranteed</i> that the 2424 * set cannot contain an incorrectly typed element. 2425 * 2426 * <p>A discussion of the use of dynamically typesafe views may be 2427 * found in the documentation for the {@link #checkedCollection 2428 * checkedCollection} method. 2429 * 2430 * <p>The returned set will be serializable if the specified set is 2431 * serializable. 2432 * 2433 * <p>Since {@code null} is considered to be a value of any reference 2434 * type, the returned set permits insertion of null elements whenever 2435 * the backing set does. 2436 * 2437 * @param s the set for which a dynamically typesafe view is to be 2438 * returned 2439 * @param type the type of element that {@code s} is permitted to hold 2440 * @return a dynamically typesafe view of the specified set 2441 * @since 1.5 2442 */ 2443 public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) { 2444 return new CheckedSet<>(s, type); 2445 } 2446 2447 /** 2448 * @serial include 2449 */ 2450 static class CheckedSet<E> extends CheckedCollection<E> 2451 implements Set<E>, Serializable 2452 { 2453 private static final long serialVersionUID = 4694047833775013803L; 2454 2455 CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); } 2456 2457 public boolean equals(Object o) { return o == this || c.equals(o); } 2458 public int hashCode() { return c.hashCode(); } 2459 } 2460 2461 /** 2462 * Returns a dynamically typesafe view of the specified sorted set. 2463 * Any attempt to insert an element of the wrong type will result in an 2464 * immediate {@link ClassCastException}. Assuming a sorted set 2465 * contains no incorrectly typed elements prior to the time a 2466 * dynamically typesafe view is generated, and that all subsequent 2467 * access to the sorted set takes place through the view, it is 2468 * <i>guaranteed</i> that the sorted set cannot contain an incorrectly 2469 * typed element. 2470 * 2471 * <p>A discussion of the use of dynamically typesafe views may be 2472 * found in the documentation for the {@link #checkedCollection 2473 * checkedCollection} method. 2474 * 2475 * <p>The returned sorted set will be serializable if the specified sorted 2476 * set is serializable. 2477 * 2478 * <p>Since {@code null} is considered to be a value of any reference 2479 * type, the returned sorted set permits insertion of null elements 2480 * whenever the backing sorted set does. 2481 * 2482 * @param s the sorted set for which a dynamically typesafe view is to be 2483 * returned 2484 * @param type the type of element that {@code s} is permitted to hold 2485 * @return a dynamically typesafe view of the specified sorted set 2486 * @since 1.5 2487 */ 2488 public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s, 2489 Class<E> type) { 2490 return new CheckedSortedSet<>(s, type); 2491 } 2492 2493 /** 2494 * @serial include 2495 */ 2496 static class CheckedSortedSet<E> extends CheckedSet<E> 2497 implements SortedSet<E>, Serializable 2498 { 2499 private static final long serialVersionUID = 1599911165492914959L; 2500 private final SortedSet<E> ss; 2501 2502 CheckedSortedSet(SortedSet<E> s, Class<E> type) { 2503 super(s, type); 2504 ss = s; 2505 } 2506 2507 public Comparator<? super E> comparator() { return ss.comparator(); } 2508 public E first() { return ss.first(); } 2509 public E last() { return ss.last(); } 2510 2511 public SortedSet<E> subSet(E fromElement, E toElement) { 2512 return checkedSortedSet(ss.subSet(fromElement,toElement), type); 2513 } 2514 public SortedSet<E> headSet(E toElement) { 2515 return checkedSortedSet(ss.headSet(toElement), type); 2516 } 2517 public SortedSet<E> tailSet(E fromElement) { 2518 return checkedSortedSet(ss.tailSet(fromElement), type); 2519 } 2520 } 2521 2522 /** 2523 * Returns a dynamically typesafe view of the specified list. 2524 * Any attempt to insert an element of the wrong type will result in 2525 * an immediate {@link ClassCastException}. Assuming a list contains 2526 * no incorrectly typed elements prior to the time a dynamically typesafe 2527 * view is generated, and that all subsequent access to the list 2528 * takes place through the view, it is <i>guaranteed</i> that the 2529 * list cannot contain an incorrectly typed element. 2530 * 2531 * <p>A discussion of the use of dynamically typesafe views may be 2532 * found in the documentation for the {@link #checkedCollection 2533 * checkedCollection} method. 2534 * 2535 * <p>The returned list will be serializable if the specified list 2536 * is serializable. 2537 * 2538 * <p>Since {@code null} is considered to be a value of any reference 2539 * type, the returned list permits insertion of null elements whenever 2540 * the backing list does. 2541 * 2542 * @param list the list for which a dynamically typesafe view is to be 2543 * returned 2544 * @param type the type of element that {@code list} is permitted to hold 2545 * @return a dynamically typesafe view of the specified list 2546 * @since 1.5 2547 */ 2548 public static <E> List<E> checkedList(List<E> list, Class<E> type) { 2549 return (list instanceof RandomAccess ? 2550 new CheckedRandomAccessList<>(list, type) : 2551 new CheckedList<>(list, type)); 2552 } 2553 2554 /** 2555 * @serial include 2556 */ 2557 static class CheckedList<E> 2558 extends CheckedCollection<E> 2559 implements List<E> 2560 { 2561 private static final long serialVersionUID = 65247728283967356L; 2562 final List<E> list; 2563 2564 CheckedList(List<E> list, Class<E> type) { 2565 super(list, type); 2566 this.list = list; 2567 } 2568 2569 public boolean equals(Object o) { return o == this || list.equals(o); } 2570 public int hashCode() { return list.hashCode(); } 2571 public E get(int index) { return list.get(index); } 2572 public E remove(int index) { return list.remove(index); } 2573 public int indexOf(Object o) { return list.indexOf(o); } 2574 public int lastIndexOf(Object o) { return list.lastIndexOf(o); } 2575 2576 public E set(int index, E element) { 2577 typeCheck(element); 2578 return list.set(index, element); 2579 } 2580 2581 public void add(int index, E element) { 2582 typeCheck(element); 2583 list.add(index, element); 2584 } 2585 2586 public boolean addAll(int index, Collection<? extends E> c) { 2587 return list.addAll(index, checkedCopyOf(c)); 2588 } 2589 public ListIterator<E> listIterator() { return listIterator(0); } 2590 2591 public ListIterator<E> listIterator(final int index) { 2592 final ListIterator<E> i = list.listIterator(index); 2593 2594 return new ListIterator<E>() { 2595 public boolean hasNext() { return i.hasNext(); } 2596 public E next() { return i.next(); } 2597 public boolean hasPrevious() { return i.hasPrevious(); } 2598 public E previous() { return i.previous(); } 2599 public int nextIndex() { return i.nextIndex(); } 2600 public int previousIndex() { return i.previousIndex(); } 2601 public void remove() { i.remove(); } 2602 2603 public void set(E e) { 2604 typeCheck(e); 2605 i.set(e); 2606 } 2607 2608 public void add(E e) { 2609 typeCheck(e); 2610 i.add(e); 2611 } 2612 }; 2613 } 2614 2615 public List<E> subList(int fromIndex, int toIndex) { 2616 return new CheckedList<>(list.subList(fromIndex, toIndex), type); 2617 } 2618 } 2619 2620 /** 2621 * @serial include 2622 */ 2623 static class CheckedRandomAccessList<E> extends CheckedList<E> 2624 implements RandomAccess 2625 { 2626 private static final long serialVersionUID = 1638200125423088369L; 2627 2628 CheckedRandomAccessList(List<E> list, Class<E> type) { 2629 super(list, type); 2630 } 2631 2632 public List<E> subList(int fromIndex, int toIndex) { 2633 return new CheckedRandomAccessList<>( 2634 list.subList(fromIndex, toIndex), type); 2635 } 2636 } 2637 2638 /** 2639 * Returns a dynamically typesafe view of the specified map. 2640 * Any attempt to insert a mapping whose key or value have the wrong 2641 * type will result in an immediate {@link ClassCastException}. 2642 * Similarly, any attempt to modify the value currently associated with 2643 * a key will result in an immediate {@link ClassCastException}, 2644 * whether the modification is attempted directly through the map 2645 * itself, or through a {@link Map.Entry} instance obtained from the 2646 * map's {@link Map#entrySet() entry set} view. 2647 * 2648 * <p>Assuming a map contains no incorrectly typed keys or values 2649 * prior to the time a dynamically typesafe view is generated, and 2650 * that all subsequent access to the map takes place through the view 2651 * (or one of its collection views), it is <i>guaranteed</i> that the 2652 * map cannot contain an incorrectly typed key or value. 2653 * 2654 * <p>A discussion of the use of dynamically typesafe views may be 2655 * found in the documentation for the {@link #checkedCollection 2656 * checkedCollection} method. 2657 * 2658 * <p>The returned map will be serializable if the specified map is 2659 * serializable. 2660 * 2661 * <p>Since {@code null} is considered to be a value of any reference 2662 * type, the returned map permits insertion of null keys or values 2663 * whenever the backing map does. 2664 * 2665 * @param m the map for which a dynamically typesafe view is to be 2666 * returned 2667 * @param keyType the type of key that {@code m} is permitted to hold 2668 * @param valueType the type of value that {@code m} is permitted to hold 2669 * @return a dynamically typesafe view of the specified map 2670 * @since 1.5 2671 */ 2672 public static <K, V> Map<K, V> checkedMap(Map<K, V> m, 2673 Class<K> keyType, 2674 Class<V> valueType) { 2675 return new CheckedMap<>(m, keyType, valueType); 2676 } 2677 2678 2679 /** 2680 * @serial include 2681 */ 2682 private static class CheckedMap<K,V> 2683 implements Map<K,V>, Serializable 2684 { 2685 private static final long serialVersionUID = 5742860141034234728L; 2686 2687 private final Map<K, V> m; 2688 final Class<K> keyType; 2689 final Class<V> valueType; 2690 2691 private void typeCheck(Object key, Object value) { 2692 if (key != null && !keyType.isInstance(key)) 2693 throw new ClassCastException(badKeyMsg(key)); 2694 2695 if (value != null && !valueType.isInstance(value)) 2696 throw new ClassCastException(badValueMsg(value)); 2697 } 2698 2699 private String badKeyMsg(Object key) { 2700 return "Attempt to insert " + key.getClass() + 2701 " key into map with key type " + keyType; 2702 } 2703 2704 private String badValueMsg(Object value) { 2705 return "Attempt to insert " + value.getClass() + 2706 " value into map with value type " + valueType; 2707 } 2708 2709 CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) { 2710 if (m == null || keyType == null || valueType == null) 2711 throw new NullPointerException(); 2712 this.m = m; 2713 this.keyType = keyType; 2714 this.valueType = valueType; 2715 } 2716 2717 public int size() { return m.size(); } 2718 public boolean isEmpty() { return m.isEmpty(); } 2719 public boolean containsKey(Object key) { return m.containsKey(key); } 2720 public boolean containsValue(Object v) { return m.containsValue(v); } 2721 public V get(Object key) { return m.get(key); } 2722 public V remove(Object key) { return m.remove(key); } 2723 public void clear() { m.clear(); } 2724 public Set<K> keySet() { return m.keySet(); } 2725 public Collection<V> values() { return m.values(); } 2726 public boolean equals(Object o) { return o == this || m.equals(o); } 2727 public int hashCode() { return m.hashCode(); } 2728 public String toString() { return m.toString(); } 2729 2730 public V put(K key, V value) { 2731 typeCheck(key, value); 2732 return m.put(key, value); 2733 } 2734 2735 @SuppressWarnings("unchecked") 2736 public void putAll(Map<? extends K, ? extends V> t) { 2737 // Satisfy the following goals: 2738 // - good diagnostics in case of type mismatch 2739 // - all-or-nothing semantics 2740 // - protection from malicious t 2741 // - correct behavior if t is a concurrent map 2742 Object[] entries = t.entrySet().toArray(); 2743 List<Map.Entry<K,V>> checked = new ArrayList<>(entries.length); 2744 for (Object o : entries) { 2745 Map.Entry<?,?> e = (Map.Entry<?,?>) o; 2746 Object k = e.getKey(); 2747 Object v = e.getValue(); 2748 typeCheck(k, v); 2749 checked.add( 2750 new AbstractMap.SimpleImmutableEntry<>((K) k, (V) v)); 2751 } 2752 for (Map.Entry<K,V> e : checked) 2753 m.put(e.getKey(), e.getValue()); 2754 } 2755 2756 private transient Set<Map.Entry<K,V>> entrySet = null; 2757 2758 public Set<Map.Entry<K,V>> entrySet() { 2759 if (entrySet==null) 2760 entrySet = new CheckedEntrySet<>(m.entrySet(), valueType); 2761 return entrySet; 2762 } 2763 2764 // Override default methods in Map 2765 @Override 2766 public void forEach(BiConsumer<? super K, ? super V> action) { 2767 m.forEach(action); 2768 } 2769 2770 /** 2771 * We need this class in addition to CheckedSet as Map.Entry permits 2772 * modification of the backing Map via the setValue operation. This 2773 * class is subtle: there are many possible attacks that must be 2774 * thwarted. 2775 * 2776 * @serial exclude 2777 */ 2778 static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> { 2779 private final Set<Map.Entry<K,V>> s; 2780 private final Class<V> valueType; 2781 2782 CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) { 2783 this.s = s; 2784 this.valueType = valueType; 2785 } 2786 2787 public int size() { return s.size(); } 2788 public boolean isEmpty() { return s.isEmpty(); } 2789 public String toString() { return s.toString(); } 2790 public int hashCode() { return s.hashCode(); } 2791 public void clear() { s.clear(); } 2792 2793 public boolean add(Map.Entry<K, V> e) { 2794 throw new UnsupportedOperationException(); 2795 } 2796 public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) { 2797 throw new UnsupportedOperationException(); 2798 } 2799 2800 public Iterator<Map.Entry<K,V>> iterator() { 2801 final Iterator<Map.Entry<K, V>> i = s.iterator(); 2802 final Class<V> valueType = this.valueType; 2803 2804 return new Iterator<Map.Entry<K,V>>() { 2805 public boolean hasNext() { return i.hasNext(); } 2806 public void remove() { i.remove(); } 2807 2808 public Map.Entry<K,V> next() { 2809 return checkedEntry(i.next(), valueType); 2810 } 2811 }; 2812 } 2813 2814 @SuppressWarnings("unchecked") 2815 public Object[] toArray() { 2816 Object[] source = s.toArray(); 2817 2818 /* 2819 * Ensure that we don't get an ArrayStoreException even if 2820 * s.toArray returns an array of something other than Object 2821 */ 2822 Object[] dest = (CheckedEntry.class.isInstance( 2823 source.getClass().getComponentType()) ? source : 2824 new Object[source.length]); 2825 2826 for (int i = 0; i < source.length; i++) 2827 dest[i] = checkedEntry((Map.Entry<K,V>)source[i], 2828 valueType); 2829 return dest; 2830 } 2831 2832 @SuppressWarnings("unchecked") 2833 public <T> T[] toArray(T[] a) { 2834 // We don't pass a to s.toArray, to avoid window of 2835 // vulnerability wherein an unscrupulous multithreaded client 2836 // could get his hands on raw (unwrapped) Entries from s. 2837 T[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0)); 2838 2839 for (int i=0; i<arr.length; i++) 2840 arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i], 2841 valueType); 2842 if (arr.length > a.length) 2843 return arr; 2844 2845 System.arraycopy(arr, 0, a, 0, arr.length); 2846 if (a.length > arr.length) 2847 a[arr.length] = null; 2848 return a; 2849 } 2850 2851 /** 2852 * This method is overridden to protect the backing set against 2853 * an object with a nefarious equals function that senses 2854 * that the equality-candidate is Map.Entry and calls its 2855 * setValue method. 2856 */ 2857 public boolean contains(Object o) { 2858 if (!(o instanceof Map.Entry)) 2859 return false; 2860 Map.Entry<?,?> e = (Map.Entry<?,?>) o; 2861 return s.contains( 2862 (e instanceof CheckedEntry) ? e : checkedEntry(e, valueType)); 2863 } 2864 2865 /** 2866 * The bulk collection methods are overridden to protect 2867 * against an unscrupulous collection whose contains(Object o) 2868 * method senses when o is a Map.Entry, and calls o.setValue. 2869 */ 2870 public boolean containsAll(Collection<?> c) { 2871 for (Object o : c) 2872 if (!contains(o)) // Invokes safe contains() above 2873 return false; 2874 return true; 2875 } 2876 2877 public boolean remove(Object o) { 2878 if (!(o instanceof Map.Entry)) 2879 return false; 2880 return s.remove(new AbstractMap.SimpleImmutableEntry 2881 <>((Map.Entry<?,?>)o)); 2882 } 2883 2884 public boolean removeAll(Collection<?> c) { 2885 return batchRemove(c, false); 2886 } 2887 public boolean retainAll(Collection<?> c) { 2888 return batchRemove(c, true); 2889 } 2890 private boolean batchRemove(Collection<?> c, boolean complement) { 2891 boolean modified = false; 2892 Iterator<Map.Entry<K,V>> it = iterator(); 2893 while (it.hasNext()) { 2894 if (c.contains(it.next()) != complement) { 2895 it.remove(); 2896 modified = true; 2897 } 2898 } 2899 return modified; 2900 } 2901 2902 public boolean equals(Object o) { 2903 if (o == this) 2904 return true; 2905 if (!(o instanceof Set)) 2906 return false; 2907 Set<?> that = (Set<?>) o; 2908 return that.size() == s.size() 2909 && containsAll(that); // Invokes safe containsAll() above 2910 } 2911 2912 static <K,V,T> CheckedEntry<K,V,T> checkedEntry(Map.Entry<K,V> e, 2913 Class<T> valueType) { 2914 return new CheckedEntry<>(e, valueType); 2915 } 2916 2917 /** 2918 * This "wrapper class" serves two purposes: it prevents 2919 * the client from modifying the backing Map, by short-circuiting 2920 * the setValue method, and it protects the backing Map against 2921 * an ill-behaved Map.Entry that attempts to modify another 2922 * Map.Entry when asked to perform an equality check. 2923 */ 2924 private static class CheckedEntry<K,V,T> implements Map.Entry<K,V> { 2925 private final Map.Entry<K, V> e; 2926 private final Class<T> valueType; 2927 2928 CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) { 2929 this.e = e; 2930 this.valueType = valueType; 2931 } 2932 2933 public K getKey() { return e.getKey(); } 2934 public V getValue() { return e.getValue(); } 2935 public int hashCode() { return e.hashCode(); } 2936 public String toString() { return e.toString(); } 2937 2938 public V setValue(V value) { 2939 if (value != null && !valueType.isInstance(value)) 2940 throw new ClassCastException(badValueMsg(value)); 2941 return e.setValue(value); 2942 } 2943 2944 private String badValueMsg(Object value) { 2945 return "Attempt to insert " + value.getClass() + 2946 " value into map with value type " + valueType; 2947 } 2948 2949 public boolean equals(Object o) { 2950 if (o == this) 2951 return true; 2952 if (!(o instanceof Map.Entry)) 2953 return false; 2954 return e.equals(new AbstractMap.SimpleImmutableEntry 2955 <>((Map.Entry<?,?>)o)); 2956 } 2957 } 2958 } 2959 } 2960 2961 /** 2962 * Returns a dynamically typesafe view of the specified sorted map. 2963 * Any attempt to insert a mapping whose key or value have the wrong 2964 * type will result in an immediate {@link ClassCastException}. 2965 * Similarly, any attempt to modify the value currently associated with 2966 * a key will result in an immediate {@link ClassCastException}, 2967 * whether the modification is attempted directly through the map 2968 * itself, or through a {@link Map.Entry} instance obtained from the 2969 * map's {@link Map#entrySet() entry set} view. 2970 * 2971 * <p>Assuming a map contains no incorrectly typed keys or values 2972 * prior to the time a dynamically typesafe view is generated, and 2973 * that all subsequent access to the map takes place through the view 2974 * (or one of its collection views), it is <i>guaranteed</i> that the 2975 * map cannot contain an incorrectly typed key or value. 2976 * 2977 * <p>A discussion of the use of dynamically typesafe views may be 2978 * found in the documentation for the {@link #checkedCollection 2979 * checkedCollection} method. 2980 * 2981 * <p>The returned map will be serializable if the specified map is 2982 * serializable. 2983 * 2984 * <p>Since {@code null} is considered to be a value of any reference 2985 * type, the returned map permits insertion of null keys or values 2986 * whenever the backing map does. 2987 * 2988 * @param m the map for which a dynamically typesafe view is to be 2989 * returned 2990 * @param keyType the type of key that {@code m} is permitted to hold 2991 * @param valueType the type of value that {@code m} is permitted to hold 2992 * @return a dynamically typesafe view of the specified map 2993 * @since 1.5 2994 */ 2995 public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m, 2996 Class<K> keyType, 2997 Class<V> valueType) { 2998 return new CheckedSortedMap<>(m, keyType, valueType); 2999 } 3000 3001 /** 3002 * @serial include 3003 */ 3004 static class CheckedSortedMap<K,V> extends CheckedMap<K,V> 3005 implements SortedMap<K,V>, Serializable 3006 { 3007 private static final long serialVersionUID = 1599671320688067438L; 3008 3009 private final SortedMap<K, V> sm; 3010 3011 CheckedSortedMap(SortedMap<K, V> m, 3012 Class<K> keyType, Class<V> valueType) { 3013 super(m, keyType, valueType); 3014 sm = m; 3015 } 3016 3017 public Comparator<? super K> comparator() { return sm.comparator(); } 3018 public K firstKey() { return sm.firstKey(); } 3019 public K lastKey() { return sm.lastKey(); } 3020 3021 public SortedMap<K,V> subMap(K fromKey, K toKey) { 3022 return checkedSortedMap(sm.subMap(fromKey, toKey), 3023 keyType, valueType); 3024 } 3025 public SortedMap<K,V> headMap(K toKey) { 3026 return checkedSortedMap(sm.headMap(toKey), keyType, valueType); 3027 } 3028 public SortedMap<K,V> tailMap(K fromKey) { 3029 return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType); 3030 } 3031 } 3032 3033 // Empty collections 3034 3035 /** 3036 * Returns an iterator that has no elements. More precisely, 3037 * 3038 * <ul compact> 3039 * 3040 * <li>{@link Iterator#hasNext hasNext} always returns {@code 3041 * false}. 3042 * 3043 * <li>{@link Iterator#next next} always throws {@link 3044 * NoSuchElementException}. 3045 * 3046 * <li>{@link Iterator#remove remove} always throws {@link 3047 * IllegalStateException}. 3048 * 3049 * </ul> 3050 * 3051 * <p>Implementations of this method are permitted, but not 3052 * required, to return the same object from multiple invocations. 3053 * 3054 * @return an empty iterator 3055 * @since 1.7 3056 */ 3057 @SuppressWarnings("unchecked") 3058 public static <T> Iterator<T> emptyIterator() { 3059 return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR; 3060 } 3061 3062 private static class EmptyIterator<E> implements Iterator<E> { 3063 static final EmptyIterator<Object> EMPTY_ITERATOR 3064 = new EmptyIterator<>(); 3065 3066 public boolean hasNext() { return false; } 3067 public E next() { throw new NoSuchElementException(); } 3068 public void remove() { throw new IllegalStateException(); } 3069 } 3070 3071 /** 3072 * Returns a list iterator that has no elements. More precisely, 3073 * 3074 * <ul compact> 3075 * 3076 * <li>{@link Iterator#hasNext hasNext} and {@link 3077 * ListIterator#hasPrevious hasPrevious} always return {@code 3078 * false}. 3079 * 3080 * <li>{@link Iterator#next next} and {@link ListIterator#previous 3081 * previous} always throw {@link NoSuchElementException}. 3082 * 3083 * <li>{@link Iterator#remove remove} and {@link ListIterator#set 3084 * set} always throw {@link IllegalStateException}. 3085 * 3086 * <li>{@link ListIterator#add add} always throws {@link 3087 * UnsupportedOperationException}. 3088 * 3089 * <li>{@link ListIterator#nextIndex nextIndex} always returns 3090 * {@code 0} . 3091 * 3092 * <li>{@link ListIterator#previousIndex previousIndex} always 3093 * returns {@code -1}. 3094 * 3095 * </ul> 3096 * 3097 * <p>Implementations of this method are permitted, but not 3098 * required, to return the same object from multiple invocations. 3099 * 3100 * @return an empty list iterator 3101 * @since 1.7 3102 */ 3103 @SuppressWarnings("unchecked") 3104 public static <T> ListIterator<T> emptyListIterator() { 3105 return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR; 3106 } 3107 3108 private static class EmptyListIterator<E> 3109 extends EmptyIterator<E> 3110 implements ListIterator<E> 3111 { 3112 static final EmptyListIterator<Object> EMPTY_ITERATOR 3113 = new EmptyListIterator<>(); 3114 3115 public boolean hasPrevious() { return false; } 3116 public E previous() { throw new NoSuchElementException(); } 3117 public int nextIndex() { return 0; } 3118 public int previousIndex() { return -1; } 3119 public void set(E e) { throw new IllegalStateException(); } 3120 public void add(E e) { throw new UnsupportedOperationException(); } 3121 } 3122 3123 /** 3124 * Returns an enumeration that has no elements. More precisely, 3125 * 3126 * <ul compact> 3127 * 3128 * <li>{@link Enumeration#hasMoreElements hasMoreElements} always 3129 * returns {@code false}. 3130 * 3131 * <li> {@link Enumeration#nextElement nextElement} always throws 3132 * {@link NoSuchElementException}. 3133 * 3134 * </ul> 3135 * 3136 * <p>Implementations of this method are permitted, but not 3137 * required, to return the same object from multiple invocations. 3138 * 3139 * @return an empty enumeration 3140 * @since 1.7 3141 */ 3142 @SuppressWarnings("unchecked") 3143 public static <T> Enumeration<T> emptyEnumeration() { 3144 return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION; 3145 } 3146 3147 private static class EmptyEnumeration<E> implements Enumeration<E> { 3148 static final EmptyEnumeration<Object> EMPTY_ENUMERATION 3149 = new EmptyEnumeration<>(); 3150 3151 public boolean hasMoreElements() { return false; } 3152 public E nextElement() { throw new NoSuchElementException(); } 3153 } 3154 3155 /** 3156 * The empty set (immutable). This set is serializable. 3157 * 3158 * @see #emptySet() 3159 */ 3160 @SuppressWarnings("unchecked") 3161 public static final Set EMPTY_SET = new EmptySet<>(); 3162 3163 /** 3164 * Returns the empty set (immutable). This set is serializable. 3165 * Unlike the like-named field, this method is parameterized. 3166 * 3167 * <p>This example illustrates the type-safe way to obtain an empty set: 3168 * <pre> 3169 * Set<String> s = Collections.emptySet(); 3170 * </pre> 3171 * Implementation note: Implementations of this method need not 3172 * create a separate <tt>Set</tt> object for each call. Using this 3173 * method is likely to have comparable cost to using the like-named 3174 * field. (Unlike this method, the field does not provide type safety.) 3175 * 3176 * @see #EMPTY_SET 3177 * @since 1.5 3178 */ 3179 @SuppressWarnings("unchecked") 3180 public static final <T> Set<T> emptySet() { 3181 return (Set<T>) EMPTY_SET; 3182 } 3183 3184 /** 3185 * @serial include 3186 */ 3187 private static class EmptySet<E> 3188 extends AbstractSet<E> 3189 implements Serializable 3190 { 3191 private static final long serialVersionUID = 1582296315990362920L; 3192 3193 public Iterator<E> iterator() { return emptyIterator(); } 3194 3195 public int size() {return 0;} 3196 public boolean isEmpty() {return true;} 3197 3198 public boolean contains(Object obj) {return false;} 3199 public boolean containsAll(Collection<?> c) { return c.isEmpty(); } 3200 3201 public Object[] toArray() { return new Object[0]; } 3202 3203 public <T> T[] toArray(T[] a) { 3204 if (a.length > 0) 3205 a[0] = null; 3206 return a; 3207 } 3208 3209 // Preserves singleton property 3210 private Object readResolve() { 3211 return EMPTY_SET; 3212 } 3213 3214 // Override default methods in Collection 3215 @Override 3216 public void forEach(Consumer<? super E> action) { 3217 Objects.requireNonNull(action); 3218 } 3219 } 3220 3221 /** 3222 * The empty list (immutable). This list is serializable. 3223 * 3224 * @see #emptyList() 3225 */ 3226 @SuppressWarnings("unchecked") 3227 public static final List EMPTY_LIST = new EmptyList<>(); 3228 3229 /** 3230 * Returns the empty list (immutable). This list is serializable. 3231 * 3232 * <p>This example illustrates the type-safe way to obtain an empty list: 3233 * <pre> 3234 * List<String> s = Collections.emptyList(); 3235 * </pre> 3236 * Implementation note: Implementations of this method need not 3237 * create a separate <tt>List</tt> object for each call. Using this 3238 * method is likely to have comparable cost to using the like-named 3239 * field. (Unlike this method, the field does not provide type safety.) 3240 * 3241 * @see #EMPTY_LIST 3242 * @since 1.5 3243 */ 3244 @SuppressWarnings("unchecked") 3245 public static final <T> List<T> emptyList() { 3246 return (List<T>) EMPTY_LIST; 3247 } 3248 3249 /** 3250 * @serial include 3251 */ 3252 private static class EmptyList<E> 3253 extends AbstractList<E> 3254 implements RandomAccess, Serializable { 3255 private static final long serialVersionUID = 8842843931221139166L; 3256 3257 public Iterator<E> iterator() { 3258 return emptyIterator(); 3259 } 3260 public ListIterator<E> listIterator() { 3261 return emptyListIterator(); 3262 } 3263 3264 public int size() {return 0;} 3265 public boolean isEmpty() {return true;} 3266 3267 public boolean contains(Object obj) {return false;} 3268 public boolean containsAll(Collection<?> c) { return c.isEmpty(); } 3269 3270 public Object[] toArray() { return new Object[0]; } 3271 3272 public <T> T[] toArray(T[] a) { 3273 if (a.length > 0) 3274 a[0] = null; 3275 return a; 3276 } 3277 3278 public E get(int index) { 3279 throw new IndexOutOfBoundsException("Index: "+index); 3280 } 3281 3282 public boolean equals(Object o) { 3283 return (o instanceof List) && ((List<?>)o).isEmpty(); 3284 } 3285 3286 public int hashCode() { return 1; } 3287 3288 // Preserves singleton property 3289 private Object readResolve() { 3290 return EMPTY_LIST; 3291 } 3292 3293 // Override default methods in Collection 3294 @Override 3295 public void forEach(Consumer<? super E> action) { 3296 Objects.requireNonNull(action); 3297 } 3298 } 3299 3300 /** 3301 * The empty map (immutable). This map is serializable. 3302 * 3303 * @see #emptyMap() 3304 * @since 1.3 3305 */ 3306 @SuppressWarnings("unchecked") 3307 public static final Map EMPTY_MAP = new EmptyMap<>(); 3308 3309 /** 3310 * Returns the empty map (immutable). This map is serializable. 3311 * 3312 * <p>This example illustrates the type-safe way to obtain an empty set: 3313 * <pre> 3314 * Map<String, Date> s = Collections.emptyMap(); 3315 * </pre> 3316 * Implementation note: Implementations of this method need not 3317 * create a separate <tt>Map</tt> object for each call. Using this 3318 * method is likely to have comparable cost to using the like-named 3319 * field. (Unlike this method, the field does not provide type safety.) 3320 * 3321 * @see #EMPTY_MAP 3322 * @since 1.5 3323 */ 3324 @SuppressWarnings("unchecked") 3325 public static final <K,V> Map<K,V> emptyMap() { 3326 return (Map<K,V>) EMPTY_MAP; 3327 } 3328 3329 /** 3330 * @serial include 3331 */ 3332 private static class EmptyMap<K,V> 3333 extends AbstractMap<K,V> 3334 implements Serializable 3335 { 3336 private static final long serialVersionUID = 6428348081105594320L; 3337 3338 public int size() {return 0;} 3339 public boolean isEmpty() {return true;} 3340 public boolean containsKey(Object key) {return false;} 3341 public boolean containsValue(Object value) {return false;} 3342 public V get(Object key) {return null;} 3343 public Set<K> keySet() {return emptySet();} 3344 public Collection<V> values() {return emptySet();} 3345 public Set<Map.Entry<K,V>> entrySet() {return emptySet();} 3346 3347 public boolean equals(Object o) { 3348 return (o instanceof Map) && ((Map<?,?>)o).isEmpty(); 3349 } 3350 3351 public int hashCode() {return 0;} 3352 3353 // Preserves singleton property 3354 private Object readResolve() { 3355 return EMPTY_MAP; 3356 } 3357 3358 // Override default methods in Map 3359 @Override 3360 public void forEach(BiConsumer<? super K, ? super V> action) { 3361 Objects.requireNonNull(action); 3362 } 3363 } 3364 3365 // Singleton collections 3366 3367 /** 3368 * Returns an immutable set containing only the specified object. 3369 * The returned set is serializable. 3370 * 3371 * @param o the sole object to be stored in the returned set. 3372 * @return an immutable set containing only the specified object. 3373 */ 3374 public static <E> Set<E> singleton(E o) { 3375 return new SingletonSet<>(o); 3376 } 3377 3378 static <E> Iterator<E> singletonIterator(final E e) { 3379 return new Iterator<E>() { 3380 private boolean hasNext = true; 3381 public boolean hasNext() { 3382 return hasNext; 3383 } 3384 public E next() { 3385 if (hasNext) { 3386 hasNext = false; 3387 return e; 3388 } 3389 throw new NoSuchElementException(); 3390 } 3391 public void remove() { 3392 throw new UnsupportedOperationException(); 3393 } 3394 }; 3395 } 3396 3397 /** 3398 * @serial include 3399 */ 3400 private static class SingletonSet<E> 3401 extends AbstractSet<E> 3402 implements Serializable 3403 { 3404 private static final long serialVersionUID = 3193687207550431679L; 3405 3406 private final E element; 3407 3408 SingletonSet(E e) {element = e;} 3409 3410 public Iterator<E> iterator() { 3411 return singletonIterator(element); 3412 } 3413 3414 public int size() {return 1;} 3415 3416 public boolean contains(Object o) {return eq(o, element);} 3417 3418 // Override default methods for Collection 3419 @Override 3420 public void forEach(Consumer<? super E> action) { 3421 action.accept(element); 3422 } 3423 } 3424 3425 /** 3426 * Returns an immutable list containing only the specified object. 3427 * The returned list is serializable. 3428 * 3429 * @param o the sole object to be stored in the returned list. 3430 * @return an immutable list containing only the specified object. 3431 * @since 1.3 3432 */ 3433 public static <E> List<E> singletonList(E o) { 3434 return new SingletonList<>(o); 3435 } 3436 3437 /** 3438 * @serial include 3439 */ 3440 private static class SingletonList<E> 3441 extends AbstractList<E> 3442 implements RandomAccess, Serializable { 3443 3444 private static final long serialVersionUID = 3093736618740652951L; 3445 3446 private final E element; 3447 3448 SingletonList(E obj) {element = obj;} 3449 3450 public Iterator<E> iterator() { 3451 return singletonIterator(element); 3452 } 3453 3454 public int size() {return 1;} 3455 3456 public boolean contains(Object obj) {return eq(obj, element);} 3457 3458 public E get(int index) { 3459 if (index != 0) 3460 throw new IndexOutOfBoundsException("Index: "+index+", Size: 1"); 3461 return element; 3462 } 3463 3464 // Override default methods for Collection 3465 @Override 3466 public void forEach(Consumer<? super E> action) { 3467 action.accept(element); 3468 } 3469 } 3470 3471 /** 3472 * Returns an immutable map, mapping only the specified key to the 3473 * specified value. The returned map is serializable. 3474 * 3475 * @param key the sole key to be stored in the returned map. 3476 * @param value the value to which the returned map maps <tt>key</tt>. 3477 * @return an immutable map containing only the specified key-value 3478 * mapping. 3479 * @since 1.3 3480 */ 3481 public static <K,V> Map<K,V> singletonMap(K key, V value) { 3482 return new SingletonMap<>(key, value); 3483 } 3484 3485 /** 3486 * @serial include 3487 */ 3488 private static class SingletonMap<K,V> 3489 extends AbstractMap<K,V> 3490 implements Serializable { 3491 private static final long serialVersionUID = -6979724477215052911L; 3492 3493 private final K k; 3494 private final V v; 3495 3496 SingletonMap(K key, V value) { 3497 k = key; 3498 v = value; 3499 } 3500 3501 public int size() {return 1;} 3502 3503 public boolean isEmpty() {return false;} 3504 3505 public boolean containsKey(Object key) {return eq(key, k);} 3506 3507 public boolean containsValue(Object value) {return eq(value, v);} 3508 3509 public V get(Object key) {return (eq(key, k) ? v : null);} 3510 3511 private transient Set<K> keySet = null; 3512 private transient Set<Map.Entry<K,V>> entrySet = null; 3513 private transient Collection<V> values = null; 3514 3515 public Set<K> keySet() { 3516 if (keySet==null) 3517 keySet = singleton(k); 3518 return keySet; 3519 } 3520 3521 public Set<Map.Entry<K,V>> entrySet() { 3522 if (entrySet==null) 3523 entrySet = Collections.<Map.Entry<K,V>>singleton( 3524 new SimpleImmutableEntry<>(k, v)); 3525 return entrySet; 3526 } 3527 3528 public Collection<V> values() { 3529 if (values==null) 3530 values = singleton(v); 3531 return values; 3532 } 3533 3534 // Override default methods in Map 3535 @Override 3536 public void forEach(BiConsumer<? super K, ? super V> action) { 3537 action.accept(k, v); 3538 } 3539 3540 } 3541 3542 // Miscellaneous 3543 3544 /** 3545 * Returns an immutable list consisting of <tt>n</tt> copies of the 3546 * specified object. The newly allocated data object is tiny (it contains 3547 * a single reference to the data object). This method is useful in 3548 * combination with the <tt>List.addAll</tt> method to grow lists. 3549 * The returned list is serializable. 3550 * 3551 * @param n the number of elements in the returned list. 3552 * @param o the element to appear repeatedly in the returned list. 3553 * @return an immutable list consisting of <tt>n</tt> copies of the 3554 * specified object. 3555 * @throws IllegalArgumentException if {@code n < 0} 3556 * @see List#addAll(Collection) 3557 * @see List#addAll(int, Collection) 3558 */ 3559 public static <T> List<T> nCopies(int n, T o) { 3560 if (n < 0) 3561 throw new IllegalArgumentException("List length = " + n); 3562 return new CopiesList<>(n, o); 3563 } 3564 3565 /** 3566 * @serial include 3567 */ 3568 private static class CopiesList<E> 3569 extends AbstractList<E> 3570 implements RandomAccess, Serializable 3571 { 3572 private static final long serialVersionUID = 2739099268398711800L; 3573 3574 final int n; 3575 final E element; 3576 3577 CopiesList(int n, E e) { 3578 assert n >= 0; 3579 this.n = n; 3580 element = e; 3581 } 3582 3583 public int size() { 3584 return n; 3585 } 3586 3587 public boolean contains(Object obj) { 3588 return n != 0 && eq(obj, element); 3589 } 3590 3591 public int indexOf(Object o) { 3592 return contains(o) ? 0 : -1; 3593 } 3594 3595 public int lastIndexOf(Object o) { 3596 return contains(o) ? n - 1 : -1; 3597 } 3598 3599 public E get(int index) { 3600 if (index < 0 || index >= n) 3601 throw new IndexOutOfBoundsException("Index: "+index+ 3602 ", Size: "+n); 3603 return element; 3604 } 3605 3606 public Object[] toArray() { 3607 final Object[] a = new Object[n]; 3608 if (element != null) 3609 Arrays.fill(a, 0, n, element); 3610 return a; 3611 } 3612 3613 public <T> T[] toArray(T[] a) { 3614 final int n = this.n; 3615 if (a.length < n) { 3616 a = (T[])java.lang.reflect.Array 3617 .newInstance(a.getClass().getComponentType(), n); 3618 if (element != null) 3619 Arrays.fill(a, 0, n, element); 3620 } else { 3621 Arrays.fill(a, 0, n, element); 3622 if (a.length > n) 3623 a[n] = null; 3624 } 3625 return a; 3626 } 3627 3628 public List<E> subList(int fromIndex, int toIndex) { 3629 if (fromIndex < 0) 3630 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex); 3631 if (toIndex > n) 3632 throw new IndexOutOfBoundsException("toIndex = " + toIndex); 3633 if (fromIndex > toIndex) 3634 throw new IllegalArgumentException("fromIndex(" + fromIndex + 3635 ") > toIndex(" + toIndex + ")"); 3636 return new CopiesList<>(toIndex - fromIndex, element); 3637 } 3638 } 3639 3640 /** 3641 * Returns a comparator that imposes the reverse of the <em>natural 3642 * ordering</em> on a collection of objects that implement the 3643 * {@code Comparable} interface. (The natural ordering is the ordering 3644 * imposed by the objects' own {@code compareTo} method.) This enables a 3645 * simple idiom for sorting (or maintaining) collections (or arrays) of 3646 * objects that implement the {@code Comparable} interface in 3647 * reverse-natural-order. For example, suppose {@code a} is an array of 3648 * strings. Then: <pre> 3649 * Arrays.sort(a, Collections.reverseOrder()); 3650 * </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p> 3651 * 3652 * The returned comparator is serializable. 3653 * 3654 * @return A comparator that imposes the reverse of the <i>natural 3655 * ordering</i> on a collection of objects that implement 3656 * the <tt>Comparable</tt> interface. 3657 * @see Comparable 3658 */ 3659 public static <T> Comparator<T> reverseOrder() { 3660 return (Comparator<T>) ReverseComparator.REVERSE_ORDER; 3661 } 3662 3663 /** 3664 * @serial include 3665 */ 3666 private static class ReverseComparator 3667 implements Comparator<Comparable<Object>>, Serializable { 3668 3669 private static final long serialVersionUID = 7207038068494060240L; 3670 3671 static final ReverseComparator REVERSE_ORDER 3672 = new ReverseComparator(); 3673 3674 public int compare(Comparable<Object> c1, Comparable<Object> c2) { 3675 return c2.compareTo(c1); 3676 } 3677 3678 private Object readResolve() { return reverseOrder(); } 3679 } 3680 3681 /** 3682 * Returns a comparator that imposes the reverse ordering of the specified 3683 * comparator. If the specified comparator is {@code null}, this method is 3684 * equivalent to {@link #reverseOrder()} (in other words, it returns a 3685 * comparator that imposes the reverse of the <em>natural ordering</em> on 3686 * a collection of objects that implement the Comparable interface). 3687 * 3688 * <p>The returned comparator is serializable (assuming the specified 3689 * comparator is also serializable or {@code null}). 3690 * 3691 * @param cmp a comparator who's ordering is to be reversed by the returned 3692 * comparator or {@code null} 3693 * @return A comparator that imposes the reverse ordering of the 3694 * specified comparator. 3695 * @since 1.5 3696 */ 3697 public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) { 3698 if (cmp == null) 3699 return reverseOrder(); 3700 3701 if (cmp instanceof ReverseComparator2) 3702 return ((ReverseComparator2<T>)cmp).cmp; 3703 3704 return new ReverseComparator2<>(cmp); 3705 } 3706 3707 /** 3708 * @serial include 3709 */ 3710 private static class ReverseComparator2<T> implements Comparator<T>, 3711 Serializable 3712 { 3713 private static final long serialVersionUID = 4374092139857L; 3714 3715 /** 3716 * The comparator specified in the static factory. This will never 3717 * be null, as the static factory returns a ReverseComparator 3718 * instance if its argument is null. 3719 * 3720 * @serial 3721 */ 3722 final Comparator<T> cmp; 3723 3724 ReverseComparator2(Comparator<T> cmp) { 3725 assert cmp != null; 3726 this.cmp = cmp; 3727 } 3728 3729 public int compare(T t1, T t2) { 3730 return cmp.compare(t2, t1); 3731 } 3732 3733 public boolean equals(Object o) { 3734 return (o == this) || 3735 (o instanceof ReverseComparator2 && 3736 cmp.equals(((ReverseComparator2)o).cmp)); 3737 } 3738 3739 public int hashCode() { 3740 return cmp.hashCode() ^ Integer.MIN_VALUE; 3741 } 3742 } 3743 3744 /** 3745 * Returns an enumeration over the specified collection. This provides 3746 * interoperability with legacy APIs that require an enumeration 3747 * as input. 3748 * 3749 * @param c the collection for which an enumeration is to be returned. 3750 * @return an enumeration over the specified collection. 3751 * @see Enumeration 3752 */ 3753 public static <T> Enumeration<T> enumeration(final Collection<T> c) { 3754 return new Enumeration<T>() { 3755 private final Iterator<T> i = c.iterator(); 3756 3757 public boolean hasMoreElements() { 3758 return i.hasNext(); 3759 } 3760 3761 public T nextElement() { 3762 return i.next(); 3763 } 3764 }; 3765 } 3766 3767 /** 3768 * Returns an array list containing the elements returned by the 3769 * specified enumeration in the order they are returned by the 3770 * enumeration. This method provides interoperability between 3771 * legacy APIs that return enumerations and new APIs that require 3772 * collections. 3773 * 3774 * @param e enumeration providing elements for the returned 3775 * array list 3776 * @return an array list containing the elements returned 3777 * by the specified enumeration. 3778 * @since 1.4 3779 * @see Enumeration 3780 * @see ArrayList 3781 */ 3782 public static <T> ArrayList<T> list(Enumeration<T> e) { 3783 ArrayList<T> l = new ArrayList<>(); 3784 while (e.hasMoreElements()) 3785 l.add(e.nextElement()); 3786 return l; 3787 } 3788 3789 /** 3790 * Returns true if the specified arguments are equal, or both null. 3791 */ 3792 static boolean eq(Object o1, Object o2) { 3793 return o1==null ? o2==null : o1.equals(o2); 3794 } 3795 3796 /** 3797 * Returns the number of elements in the specified collection equal to the 3798 * specified object. More formally, returns the number of elements 3799 * <tt>e</tt> in the collection such that 3800 * <tt>(o == null ? e == null : o.equals(e))</tt>. 3801 * 3802 * @param c the collection in which to determine the frequency 3803 * of <tt>o</tt> 3804 * @param o the object whose frequency is to be determined 3805 * @throws NullPointerException if <tt>c</tt> is null 3806 * @since 1.5 3807 */ 3808 public static int frequency(Collection<?> c, Object o) { 3809 int result = 0; 3810 if (o == null) { 3811 for (Object e : c) 3812 if (e == null) 3813 result++; 3814 } else { 3815 for (Object e : c) 3816 if (o.equals(e)) 3817 result++; 3818 } 3819 return result; 3820 } 3821 3822 /** 3823 * Returns {@code true} if the two specified collections have no 3824 * elements in common. 3825 * 3826 * <p>Care must be exercised if this method is used on collections that 3827 * do not comply with the general contract for {@code Collection}. 3828 * Implementations may elect to iterate over either collection and test 3829 * for containment in the other collection (or to perform any equivalent 3830 * computation). If either collection uses a nonstandard equality test 3831 * (as does a {@link SortedSet} whose ordering is not <em>compatible with 3832 * equals</em>, or the key set of an {@link IdentityHashMap}), both 3833 * collections must use the same nonstandard equality test, or the 3834 * result of this method is undefined. 3835 * 3836 * <p>Care must also be exercised when using collections that have 3837 * restrictions on the elements that they may contain. Collection 3838 * implementations are allowed to throw exceptions for any operation 3839 * involving elements they deem ineligible. For absolute safety the 3840 * specified collections should contain only elements which are 3841 * eligible elements for both collections. 3842 * 3843 * <p>Note that it is permissible to pass the same collection in both 3844 * parameters, in which case the method will return {@code true} if and 3845 * only if the collection is empty. 3846 * 3847 * @param c1 a collection 3848 * @param c2 a collection 3849 * @return {@code true} if the two specified collections have no 3850 * elements in common. 3851 * @throws NullPointerException if either collection is {@code null}. 3852 * @throws NullPointerException if one collection contains a {@code null} 3853 * element and {@code null} is not an eligible element for the other collection. 3854 * (<a href="Collection.html#optional-restrictions">optional</a>) 3855 * @throws ClassCastException if one collection contains an element that is 3856 * of a type which is ineligible for the other collection. 3857 * (<a href="Collection.html#optional-restrictions">optional</a>) 3858 * @since 1.5 3859 */ 3860 public static boolean disjoint(Collection<?> c1, Collection<?> c2) { 3861 // The collection to be used for contains(). Preference is given to 3862 // the collection who's contains() has lower O() complexity. 3863 Collection<?> contains = c2; 3864 // The collection to be iterated. If the collections' contains() impl 3865 // are of different O() complexity, the collection with slower 3866 // contains() will be used for iteration. For collections who's 3867 // contains() are of the same complexity then best performance is 3868 // achieved by iterating the smaller collection. 3869 Collection<?> iterate = c1; 3870 3871 // Performance optimization cases. The heuristics: 3872 // 1. Generally iterate over c1. 3873 // 2. If c1 is a Set then iterate over c2. 3874 // 3. If either collection is empty then result is always true. 3875 // 4. Iterate over the smaller Collection. 3876 if (c1 instanceof Set) { 3877 // Use c1 for contains as a Set's contains() is expected to perform 3878 // better than O(N/2) 3879 iterate = c2; 3880 contains = c1; 3881 } else if (!(c2 instanceof Set)) { 3882 // Both are mere Collections. Iterate over smaller collection. 3883 // Example: If c1 contains 3 elements and c2 contains 50 elements and 3884 // assuming contains() requires ceiling(N/2) comparisons then 3885 // checking for all c1 elements in c2 would require 75 comparisons 3886 // (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring 3887 // 100 comparisons (50 * ceiling(3/2)). 3888 int c1size = c1.size(); 3889 int c2size = c2.size(); 3890 if (c1size == 0 || c2size == 0) { 3891 // At least one collection is empty. Nothing will match. 3892 return true; 3893 } 3894 3895 if (c1size > c2size) { 3896 iterate = c2; 3897 contains = c1; 3898 } 3899 } 3900 3901 for (Object e : iterate) { 3902 if (contains.contains(e)) { 3903 // Found a common element. Collections are not disjoint. 3904 return false; 3905 } 3906 } 3907 3908 // No common elements were found. 3909 return true; 3910 } 3911 3912 /** 3913 * Adds all of the specified elements to the specified collection. 3914 * Elements to be added may be specified individually or as an array. 3915 * The behavior of this convenience method is identical to that of 3916 * <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely 3917 * to run significantly faster under most implementations. 3918 * 3919 * <p>When elements are specified individually, this method provides a 3920 * convenient way to add a few elements to an existing collection: 3921 * <pre> 3922 * Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon"); 3923 * </pre> 3924 * 3925 * @param c the collection into which <tt>elements</tt> are to be inserted 3926 * @param elements the elements to insert into <tt>c</tt> 3927 * @return <tt>true</tt> if the collection changed as a result of the call 3928 * @throws UnsupportedOperationException if <tt>c</tt> does not support 3929 * the <tt>add</tt> operation 3930 * @throws NullPointerException if <tt>elements</tt> contains one or more 3931 * null values and <tt>c</tt> does not permit null elements, or 3932 * if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt> 3933 * @throws IllegalArgumentException if some property of a value in 3934 * <tt>elements</tt> prevents it from being added to <tt>c</tt> 3935 * @see Collection#addAll(Collection) 3936 * @since 1.5 3937 */ 3938 @SafeVarargs 3939 public static <T> boolean addAll(Collection<? super T> c, T... elements) { 3940 boolean result = false; 3941 for (T element : elements) 3942 result |= c.add(element); 3943 return result; 3944 } 3945 3946 /** 3947 * Returns a set backed by the specified map. The resulting set displays 3948 * the same ordering, concurrency, and performance characteristics as the 3949 * backing map. In essence, this factory method provides a {@link Set} 3950 * implementation corresponding to any {@link Map} implementation. There 3951 * is no need to use this method on a {@link Map} implementation that 3952 * already has a corresponding {@link Set} implementation (such as {@link 3953 * HashMap} or {@link TreeMap}). 3954 * 3955 * <p>Each method invocation on the set returned by this method results in 3956 * exactly one method invocation on the backing map or its <tt>keySet</tt> 3957 * view, with one exception. The <tt>addAll</tt> method is implemented 3958 * as a sequence of <tt>put</tt> invocations on the backing map. 3959 * 3960 * <p>The specified map must be empty at the time this method is invoked, 3961 * and should not be accessed directly after this method returns. These 3962 * conditions are ensured if the map is created empty, passed directly 3963 * to this method, and no reference to the map is retained, as illustrated 3964 * in the following code fragment: 3965 * <pre> 3966 * Set<Object> weakHashSet = Collections.newSetFromMap( 3967 * new WeakHashMap<Object, Boolean>()); 3968 * </pre> 3969 * 3970 * @param map the backing map 3971 * @return the set backed by the map 3972 * @throws IllegalArgumentException if <tt>map</tt> is not empty 3973 * @since 1.6 3974 */ 3975 public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) { 3976 return new SetFromMap<>(map); 3977 } 3978 3979 /** 3980 * @serial include 3981 */ 3982 private static class SetFromMap<E> extends AbstractSet<E> 3983 implements Set<E>, Serializable 3984 { 3985 private final Map<E, Boolean> m; // The backing map 3986 private transient Set<E> s; // Its keySet 3987 3988 SetFromMap(Map<E, Boolean> map) { 3989 if (!map.isEmpty()) 3990 throw new IllegalArgumentException("Map is non-empty"); 3991 m = map; 3992 s = map.keySet(); 3993 } 3994 3995 public void clear() { m.clear(); } 3996 public int size() { return m.size(); } 3997 public boolean isEmpty() { return m.isEmpty(); } 3998 public boolean contains(Object o) { return m.containsKey(o); } 3999 public boolean remove(Object o) { return m.remove(o) != null; } 4000 public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; } 4001 public Iterator<E> iterator() { return s.iterator(); } 4002 public Object[] toArray() { return s.toArray(); } 4003 public <T> T[] toArray(T[] a) { return s.toArray(a); } 4004 public String toString() { return s.toString(); } 4005 public int hashCode() { return s.hashCode(); } 4006 public boolean equals(Object o) { return o == this || s.equals(o); } 4007 public boolean containsAll(Collection<?> c) {return s.containsAll(c);} 4008 public boolean removeAll(Collection<?> c) {return s.removeAll(c);} 4009 public boolean retainAll(Collection<?> c) {return s.retainAll(c);} 4010 // addAll is the only inherited implementation 4011 4012 private static final long serialVersionUID = 2454657854757543876L; 4013 4014 // Override default methods in Collection 4015 @Override 4016 public void forEach(Consumer<? super E> action) { 4017 s.forEach(action); 4018 } 4019 4020 private void readObject(java.io.ObjectInputStream stream) 4021 throws IOException, ClassNotFoundException 4022 { 4023 stream.defaultReadObject(); 4024 s = m.keySet(); 4025 } 4026 } 4027 4028 /** 4029 * Returns a view of a {@link Deque} as a Last-in-first-out (Lifo) 4030 * {@link Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>, 4031 * <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This 4032 * view can be useful when you would like to use a method 4033 * requiring a <tt>Queue</tt> but you need Lifo ordering. 4034 * 4035 * <p>Each method invocation on the queue returned by this method 4036 * results in exactly one method invocation on the backing deque, with 4037 * one exception. The {@link Queue#addAll addAll} method is 4038 * implemented as a sequence of {@link Deque#addFirst addFirst} 4039 * invocations on the backing deque. 4040 * 4041 * @param deque the deque 4042 * @return the queue 4043 * @since 1.6 4044 */ 4045 public static <T> Queue<T> asLifoQueue(Deque<T> deque) { 4046 return new AsLIFOQueue<>(deque); 4047 } 4048 4049 /** 4050 * @serial include 4051 */ 4052 static class AsLIFOQueue<E> extends AbstractQueue<E> 4053 implements Queue<E>, Serializable { 4054 private static final long serialVersionUID = 1802017725587941708L; 4055 private final Deque<E> q; 4056 AsLIFOQueue(Deque<E> q) { this.q = q; } 4057 public boolean add(E e) { q.addFirst(e); return true; } 4058 public boolean offer(E e) { return q.offerFirst(e); } 4059 public E poll() { return q.pollFirst(); } 4060 public E remove() { return q.removeFirst(); } 4061 public E peek() { return q.peekFirst(); } 4062 public E element() { return q.getFirst(); } 4063 public void clear() { q.clear(); } 4064 public int size() { return q.size(); } 4065 public boolean isEmpty() { return q.isEmpty(); } 4066 public boolean contains(Object o) { return q.contains(o); } 4067 public boolean remove(Object o) { return q.remove(o); } 4068 public Iterator<E> iterator() { return q.iterator(); } 4069 public Object[] toArray() { return q.toArray(); } 4070 public <T> T[] toArray(T[] a) { return q.toArray(a); } 4071 public String toString() { return q.toString(); } 4072 public boolean containsAll(Collection<?> c) {return q.containsAll(c);} 4073 public boolean removeAll(Collection<?> c) {return q.removeAll(c);} 4074 public boolean retainAll(Collection<?> c) {return q.retainAll(c);} 4075 // We use inherited addAll; forwarding addAll would be wrong 4076 4077 // Override default methods in Collection 4078 @Override 4079 public void forEach(Consumer<? super E> action) {q.forEach(action);} 4080 } 4081} 4082