1 /* 2 * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.util; 27 import java.io.Serializable; 28 import java.io.ObjectOutputStream; 29 import java.io.IOException; 30 import java.lang.reflect.Array; 31 import java.util.function.BiConsumer; 32 import java.util.function.BiFunction; 33 import java.util.function.Consumer; 34 import java.util.function.Function; 35 import java.util.function.Predicate; 36 import java.util.function.UnaryOperator; 37 38 /** 39 * This class consists exclusively of static methods that operate on or return 40 * collections. It contains polymorphic algorithms that operate on 41 * collections, "wrappers", which return a new collection backed by a 42 * specified collection, and a few other odds and ends. 43 * 44 * <p>The methods of this class all throw a <tt>NullPointerException</tt> 45 * if the collections or class objects provided to them are null. 46 * 47 * <p>The documentation for the polymorphic algorithms contained in this class 48 * generally includes a brief description of the <i>implementation</i>. Such 49 * descriptions should be regarded as <i>implementation notes</i>, rather than 50 * parts of the <i>specification</i>. Implementors should feel free to 51 * substitute other algorithms, so long as the specification itself is adhered 52 * to. (For example, the algorithm used by <tt>sort</tt> does not have to be 53 * a mergesort, but it does have to be <i>stable</i>.) 54 * 55 * <p>The "destructive" algorithms contained in this class, that is, the 56 * algorithms that modify the collection on which they operate, are specified 57 * to throw <tt>UnsupportedOperationException</tt> if the collection does not 58 * support the appropriate mutation primitive(s), such as the <tt>set</tt> 59 * method. These algorithms may, but are not required to, throw this 60 * exception if an invocation would have no effect on the collection. For 61 * example, invoking the <tt>sort</tt> method on an unmodifiable list that is 62 * already sorted may or may not throw <tt>UnsupportedOperationException</tt>. 63 * 64 * <p>This class is a member of the 65 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 66 * Java Collections Framework</a>. 67 * 68 * @author Josh Bloch 69 * @author Neal Gafter 70 * @see Collection 71 * @see Set 72 * @see List 73 * @see Map 74 * @since 1.2 75 */ 76 77 public class Collections { 78 // Suppresses default constructor, ensuring non-instantiability. 79 private Collections() { 80 } 81 82 // Algorithms 83 84 /* 85 * Tuning parameters for algorithms - Many of the List algorithms have 86 * two implementations, one of which is appropriate for RandomAccess 87 * lists, the other for "sequential." Often, the random access variant 88 * yields better performance on small sequential access lists. The 89 * tuning parameters below determine the cutoff point for what constitutes 90 * a "small" sequential access list for each algorithm. The values below 91 * were empirically determined to work well for LinkedList. Hopefully 92 * they should be reasonable for other sequential access List 93 * implementations. Those doing performance work on this code would 94 * do well to validate the values of these parameters from time to time. 95 * (The first word of each tuning parameter name is the algorithm to which 96 * it applies.) 97 */ 98 private static final int BINARYSEARCH_THRESHOLD = 5000; 99 private static final int REVERSE_THRESHOLD = 18; 100 private static final int SHUFFLE_THRESHOLD = 5; 101 private static final int FILL_THRESHOLD = 25; 102 private static final int ROTATE_THRESHOLD = 100; 103 private static final int COPY_THRESHOLD = 10; 104 private static final int REPLACEALL_THRESHOLD = 11; 105 private static final int INDEXOFSUBLIST_THRESHOLD = 35; 106 107 /** 108 * Sorts the specified list into ascending order, according to the 109 * {@linkplain Comparable natural ordering} of its elements. 110 * All elements in the list must implement the {@link Comparable} 111 * interface. Furthermore, all elements in the list must be 112 * <i>mutually comparable</i> (that is, {@code e1.compareTo(e2)} 113 * must not throw a {@code ClassCastException} for any elements 114 * {@code e1} and {@code e2} in the list). 115 * 116 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will 117 * not be reordered as a result of the sort. 118 * 119 * <p>The specified list must be modifiable, but need not be resizable. 120 * 121 * <p>Implementation note: This implementation is a stable, adaptive, 122 * iterative mergesort that requires far fewer than n lg(n) comparisons 123 * when the input array is partially sorted, while offering the 124 * performance of a traditional mergesort when the input array is 125 * randomly ordered. If the input array is nearly sorted, the 126 * implementation requires approximately n comparisons. Temporary 127 * storage requirements vary from a small constant for nearly sorted 128 * input arrays to n/2 object references for randomly ordered input 129 * arrays. 130 * 131 * <p>The implementation takes equal advantage of ascending and 132 * descending order in its input array, and can take advantage of 133 * ascending and descending order in different parts of the same 134 * input array. It is well-suited to merging two or more sorted arrays: 135 * simply concatenate the arrays and sort the resulting array. 136 * 137 * <p>The implementation was adapted from Tim Peters's list sort for Python 138 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt"> 139 * TimSort</a>). It uses techiques from Peter McIlroy's "Optimistic 140 * Sorting and Information Theoretic Complexity", in Proceedings of the 141 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474, 142 * January 1993. 143 * 144 * <p>This implementation dumps the specified list into an array, sorts 145 * the array, and iterates over the list resetting each element 146 * from the corresponding position in the array. This avoids the 147 * n<sup>2</sup> log(n) performance that would result from attempting 148 * to sort a linked list in place. 149 * 150 * @param list the list to be sorted. 151 * @throws ClassCastException if the list contains elements that are not 152 * <i>mutually comparable</i> (for example, strings and integers). 153 * @throws UnsupportedOperationException if the specified list's 154 * list-iterator does not support the {@code set} operation. 155 * @throws IllegalArgumentException (optional) if the implementation 156 * detects that the natural ordering of the list elements is 157 * found to violate the {@link Comparable} contract 158 */ 159 @SuppressWarnings("unchecked") 160 public static <T extends Comparable<? super T>> void sort(List<T> list) { 161 Object[] a = list.toArray(); 162 Arrays.sort(a); 163 ListIterator<T> i = list.listIterator(); 164 for (int j=0; j<a.length; j++) { 165 i.next(); 166 i.set((T)a[j]); 167 } 168 } 169 170 /** 171 * Sorts the specified list according to the order induced by the 172 * specified comparator. All elements in the list must be <i>mutually 173 * comparable</i> using the specified comparator (that is, 174 * {@code c.compare(e1, e2)} must not throw a {@code ClassCastException} 175 * for any elements {@code e1} and {@code e2} in the list). 176 * 177 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will 178 * not be reordered as a result of the sort. 179 * 180 * <p>The specified list must be modifiable, but need not be resizable. 181 * 182 * <p>Implementation note: This implementation is a stable, adaptive, 183 * iterative mergesort that requires far fewer than n lg(n) comparisons 184 * when the input array is partially sorted, while offering the 185 * performance of a traditional mergesort when the input array is 186 * randomly ordered. If the input array is nearly sorted, the 187 * implementation requires approximately n comparisons. Temporary 188 * storage requirements vary from a small constant for nearly sorted 189 * input arrays to n/2 object references for randomly ordered input 190 * arrays. 191 * 192 * <p>The implementation takes equal advantage of ascending and 193 * descending order in its input array, and can take advantage of 194 * ascending and descending order in different parts of the same 195 * input array. It is well-suited to merging two or more sorted arrays: 196 * simply concatenate the arrays and sort the resulting array. 197 * 198 * <p>The implementation was adapted from Tim Peters's list sort for Python 199 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt"> 200 * TimSort</a>). It uses techiques from Peter McIlroy's "Optimistic 201 * Sorting and Information Theoretic Complexity", in Proceedings of the 202 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474, 203 * January 1993. 204 * 205 * <p>This implementation dumps the specified list into an array, sorts 206 * the array, and iterates over the list resetting each element 207 * from the corresponding position in the array. This avoids the 208 * n<sup>2</sup> log(n) performance that would result from attempting 209 * to sort a linked list in place. 210 * 211 * @param list the list to be sorted. 212 * @param c the comparator to determine the order of the list. A 213 * {@code null} value indicates that the elements' <i>natural 214 * ordering</i> should be used. 215 * @throws ClassCastException if the list contains elements that are not 216 * <i>mutually comparable</i> using the specified comparator. 217 * @throws UnsupportedOperationException if the specified list's 218 * list-iterator does not support the {@code set} operation. 219 * @throws IllegalArgumentException (optional) if the comparator is 220 * found to violate the {@link Comparator} contract 221 */ 222 @SuppressWarnings({"unchecked", "rawtypes"}) 223 public static <T> void sort(List<T> list, Comparator<? super T> c) { 224 Object[] a = list.toArray(); 225 Arrays.sort(a, (Comparator)c); 226 ListIterator<T> i = list.listIterator(); 227 for (int j=0; j<a.length; j++) { 228 i.next(); 229 i.set((T)a[j]); 230 } 231 } 232 233 234 /** 235 * Searches the specified list for the specified object using the binary 236 * search algorithm. The list must be sorted into ascending order 237 * according to the {@linkplain Comparable natural ordering} of its 238 * elements (as by the {@link #sort(List)} method) prior to making this 239 * call. If it is not sorted, the results are undefined. If the list 240 * contains multiple elements equal to the specified object, there is no 241 * guarantee which one will be found. 242 * 243 * <p>This method runs in log(n) time for a "random access" list (which 244 * provides near-constant-time positional access). If the specified list 245 * does not implement the {@link RandomAccess} interface and is large, 246 * this method will do an iterator-based binary search that performs 247 * O(n) link traversals and O(log n) element comparisons. 248 * 249 * @param list the list to be searched. 250 * @param key the key to be searched for. 251 * @return the index of the search key, if it is contained in the list; 252 * otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The 253 * <i>insertion point</i> is defined as the point at which the 254 * key would be inserted into the list: the index of the first 255 * element greater than the key, or <tt>list.size()</tt> if all 256 * elements in the list are less than the specified key. Note 257 * that this guarantees that the return value will be >= 0 if 258 * and only if the key is found. 259 * @throws ClassCastException if the list contains elements that are not 260 * <i>mutually comparable</i> (for example, strings and 261 * integers), or the search key is not mutually comparable 262 * with the elements of the list. 263 */ 264 public static <T> 265 int binarySearch(List<? extends Comparable<? super T>> list, T key) { 266 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD) 267 return Collections.indexedBinarySearch(list, key); 268 else 269 return Collections.iteratorBinarySearch(list, key); 270 } 271 272 private static <T> 273 int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key) { 274 int low = 0; 275 int high = list.size()-1; 276 277 while (low <= high) { 278 int mid = (low + high) >>> 1; 279 Comparable<? super T> midVal = list.get(mid); 280 int cmp = midVal.compareTo(key); 281 282 if (cmp < 0) 283 low = mid + 1; 284 else if (cmp > 0) 285 high = mid - 1; 286 else 287 return mid; // key found 288 } 289 return -(low + 1); // key not found 290 } 291 292 private static <T> 293 int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key) 294 { 295 int low = 0; 296 int high = list.size()-1; 297 ListIterator<? extends Comparable<? super T>> i = list.listIterator(); 298 299 while (low <= high) { 300 int mid = (low + high) >>> 1; 301 Comparable<? super T> midVal = get(i, mid); 302 int cmp = midVal.compareTo(key); 303 304 if (cmp < 0) 305 low = mid + 1; 306 else if (cmp > 0) 307 high = mid - 1; 308 else 309 return mid; // key found 310 } 311 return -(low + 1); // key not found 312 } 313 314 /** 315 * Gets the ith element from the given list by repositioning the specified 316 * list listIterator. 317 */ 318 private static <T> T get(ListIterator<? extends T> i, int index) { 319 T obj = null; 320 int pos = i.nextIndex(); 321 if (pos <= index) { 322 do { 323 obj = i.next(); 324 } while (pos++ < index); 325 } else { 326 do { 327 obj = i.previous(); 328 } while (--pos > index); 329 } 330 return obj; 331 } 332 333 /** 334 * Searches the specified list for the specified object using the binary 335 * search algorithm. The list must be sorted into ascending order 336 * according to the specified comparator (as by the 337 * {@link #sort(List, Comparator) sort(List, Comparator)} 338 * method), prior to making this call. If it is 339 * not sorted, the results are undefined. If the list contains multiple 340 * elements equal to the specified object, there is no guarantee which one 341 * will be found. 342 * 343 * <p>This method runs in log(n) time for a "random access" list (which 344 * provides near-constant-time positional access). If the specified list 345 * does not implement the {@link RandomAccess} interface and is large, 346 * this method will do an iterator-based binary search that performs 347 * O(n) link traversals and O(log n) element comparisons. 348 * 349 * @param list the list to be searched. 350 * @param key the key to be searched for. 351 * @param c the comparator by which the list is ordered. 352 * A <tt>null</tt> value indicates that the elements' 353 * {@linkplain Comparable natural ordering} should be used. 354 * @return the index of the search key, if it is contained in the list; 355 * otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The 356 * <i>insertion point</i> is defined as the point at which the 357 * key would be inserted into the list: the index of the first 358 * element greater than the key, or <tt>list.size()</tt> if all 359 * elements in the list are less than the specified key. Note 360 * that this guarantees that the return value will be >= 0 if 361 * and only if the key is found. 362 * @throws ClassCastException if the list contains elements that are not 363 * <i>mutually comparable</i> using the specified comparator, 364 * or the search key is not mutually comparable with the 365 * elements of the list using this comparator. 366 */ 367 @SuppressWarnings("unchecked") 368 public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) { 369 if (c==null) 370 return binarySearch((List<? extends Comparable<? super T>>) list, key); 371 372 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD) 373 return Collections.indexedBinarySearch(list, key, c); 374 else 375 return Collections.iteratorBinarySearch(list, key, c); 376 } 377 378 private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) { 379 int low = 0; 380 int high = l.size()-1; 381 382 while (low <= high) { 383 int mid = (low + high) >>> 1; 384 T midVal = l.get(mid); 385 int cmp = c.compare(midVal, key); 386 387 if (cmp < 0) 388 low = mid + 1; 389 else if (cmp > 0) 390 high = mid - 1; 391 else 392 return mid; // key found 393 } 394 return -(low + 1); // key not found 395 } 396 397 private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) { 398 int low = 0; 399 int high = l.size()-1; 400 ListIterator<? extends T> i = l.listIterator(); 401 402 while (low <= high) { 403 int mid = (low + high) >>> 1; 404 T midVal = get(i, mid); 405 int cmp = c.compare(midVal, key); 406 407 if (cmp < 0) 408 low = mid + 1; 409 else if (cmp > 0) 410 high = mid - 1; 411 else 412 return mid; // key found 413 } 414 return -(low + 1); // key not found 415 } 416 417 /** 418 * Reverses the order of the elements in the specified list.<p> 419 * 420 * This method runs in linear time. 421 * 422 * @param list the list whose elements are to be reversed. 423 * @throws UnsupportedOperationException if the specified list or 424 * its list-iterator does not support the <tt>set</tt> operation. 425 */ 426 @SuppressWarnings({"rawtypes", "unchecked"}) 427 public static void reverse(List<?> list) { 428 int size = list.size(); 429 if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) { 430 for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--) 431 swap(list, i, j); 432 } else { 433 // instead of using a raw type here, it's possible to capture 434 // the wildcard but it will require a call to a supplementary 435 // private method 436 ListIterator fwd = list.listIterator(); 437 ListIterator rev = list.listIterator(size); 438 for (int i=0, mid=list.size()>>1; i<mid; i++) { 439 Object tmp = fwd.next(); 440 fwd.set(rev.previous()); 441 rev.set(tmp); 442 } 443 } 444 } 445 446 /** 447 * Randomly permutes the specified list using a default source of 448 * randomness. All permutations occur with approximately equal 449 * likelihood. 450 * 451 * <p>The hedge "approximately" is used in the foregoing description because 452 * default source of randomness is only approximately an unbiased source 453 * of independently chosen bits. If it were a perfect source of randomly 454 * chosen bits, then the algorithm would choose permutations with perfect 455 * uniformity. 456 * 457 * <p>This implementation traverses the list backwards, from the last 458 * element up to the second, repeatedly swapping a randomly selected element 459 * into the "current position". Elements are randomly selected from the 460 * portion of the list that runs from the first element to the current 461 * position, inclusive. 462 * 463 * <p>This method runs in linear time. If the specified list does not 464 * implement the {@link RandomAccess} interface and is large, this 465 * implementation dumps the specified list into an array before shuffling 466 * it, and dumps the shuffled array back into the list. This avoids the 467 * quadratic behavior that would result from shuffling a "sequential 468 * access" list in place. 469 * 470 * @param list the list to be shuffled. 471 * @throws UnsupportedOperationException if the specified list or 472 * its list-iterator does not support the <tt>set</tt> operation. 473 */ 474 public static void shuffle(List<?> list) { 475 Random rnd = r; 476 if (rnd == null) 477 r = rnd = new Random(); // harmless race. 478 shuffle(list, rnd); 479 } 480 481 private static Random r; 482 483 /** 484 * Randomly permute the specified list using the specified source of 485 * randomness. All permutations occur with equal likelihood 486 * assuming that the source of randomness is fair.<p> 487 * 488 * This implementation traverses the list backwards, from the last element 489 * up to the second, repeatedly swapping a randomly selected element into 490 * the "current position". Elements are randomly selected from the 491 * portion of the list that runs from the first element to the current 492 * position, inclusive.<p> 493 * 494 * This method runs in linear time. If the specified list does not 495 * implement the {@link RandomAccess} interface and is large, this 496 * implementation dumps the specified list into an array before shuffling 497 * it, and dumps the shuffled array back into the list. This avoids the 498 * quadratic behavior that would result from shuffling a "sequential 499 * access" list in place. 500 * 501 * @param list the list to be shuffled. 502 * @param rnd the source of randomness to use to shuffle the list. 503 * @throws UnsupportedOperationException if the specified list or its 504 * list-iterator does not support the <tt>set</tt> operation. 505 */ 506 @SuppressWarnings({"rawtypes", "unchecked"}) 507 public static void shuffle(List<?> list, Random rnd) { 508 int size = list.size(); 509 if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) { 510 for (int i=size; i>1; i--) 511 swap(list, i-1, rnd.nextInt(i)); 512 } else { 513 Object arr[] = list.toArray(); 514 515 // Shuffle array 516 for (int i=size; i>1; i--) 517 swap(arr, i-1, rnd.nextInt(i)); 518 519 // Dump array back into list 520 // instead of using a raw type here, it's possible to capture 521 // the wildcard but it will require a call to a supplementary 522 // private method 523 ListIterator it = list.listIterator(); 524 for (int i=0; i<arr.length; i++) { 525 it.next(); 526 it.set(arr[i]); 527 } 528 } 529 } 530 531 /** 532 * Swaps the elements at the specified positions in the specified list. 533 * (If the specified positions are equal, invoking this method leaves 534 * the list unchanged.) 535 * 536 * @param list The list in which to swap elements. 537 * @param i the index of one element to be swapped. 538 * @param j the index of the other element to be swapped. 539 * @throws IndexOutOfBoundsException if either <tt>i</tt> or <tt>j</tt> 540 * is out of range (i < 0 || i >= list.size() 541 * || j < 0 || j >= list.size()). 542 * @since 1.4 543 */ 544 @SuppressWarnings({"rawtypes", "unchecked"}) 545 public static void swap(List<?> list, int i, int j) { 546 // instead of using a raw type here, it's possible to capture 547 // the wildcard but it will require a call to a supplementary 548 // private method 549 final List l = list; 550 l.set(i, l.set(j, l.get(i))); 551 } 552 553 /** 554 * Swaps the two specified elements in the specified array. 555 */ 556 private static void swap(Object[] arr, int i, int j) { 557 Object tmp = arr[i]; 558 arr[i] = arr[j]; 559 arr[j] = tmp; 560 } 561 562 /** 563 * Replaces all of the elements of the specified list with the specified 564 * element. <p> 565 * 566 * This method runs in linear time. 567 * 568 * @param list the list to be filled with the specified element. 569 * @param obj The element with which to fill the specified list. 570 * @throws UnsupportedOperationException if the specified list or its 571 * list-iterator does not support the <tt>set</tt> operation. 572 */ 573 public static <T> void fill(List<? super T> list, T obj) { 574 int size = list.size(); 575 576 if (size < FILL_THRESHOLD || list instanceof RandomAccess) { 577 for (int i=0; i<size; i++) 578 list.set(i, obj); 579 } else { 580 ListIterator<? super T> itr = list.listIterator(); 581 for (int i=0; i<size; i++) { 582 itr.next(); 583 itr.set(obj); 584 } 585 } 586 } 587 588 /** 589 * Copies all of the elements from one list into another. After the 590 * operation, the index of each copied element in the destination list 591 * will be identical to its index in the source list. The destination 592 * list must be at least as long as the source list. If it is longer, the 593 * remaining elements in the destination list are unaffected. <p> 594 * 595 * This method runs in linear time. 596 * 597 * @param dest The destination list. 598 * @param src The source list. 599 * @throws IndexOutOfBoundsException if the destination list is too small 600 * to contain the entire source List. 601 * @throws UnsupportedOperationException if the destination list's 602 * list-iterator does not support the <tt>set</tt> operation. 603 */ 604 public static <T> void copy(List<? super T> dest, List<? extends T> src) { 605 int srcSize = src.size(); 606 if (srcSize > dest.size()) 607 throw new IndexOutOfBoundsException("Source does not fit in dest"); 608 609 if (srcSize < COPY_THRESHOLD || 610 (src instanceof RandomAccess && dest instanceof RandomAccess)) { 611 for (int i=0; i<srcSize; i++) 612 dest.set(i, src.get(i)); 613 } else { 614 ListIterator<? super T> di=dest.listIterator(); 615 ListIterator<? extends T> si=src.listIterator(); 616 for (int i=0; i<srcSize; i++) { 617 di.next(); 618 di.set(si.next()); 619 } 620 } 621 } 622 623 /** 624 * Returns the minimum element of the given collection, according to the 625 * <i>natural ordering</i> of its elements. All elements in the 626 * collection must implement the <tt>Comparable</tt> interface. 627 * Furthermore, all elements in the collection must be <i>mutually 628 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a 629 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 630 * <tt>e2</tt> in the collection).<p> 631 * 632 * This method iterates over the entire collection, hence it requires 633 * time proportional to the size of the collection. 634 * 635 * @param coll the collection whose minimum element is to be determined. 636 * @return the minimum element of the given collection, according 637 * to the <i>natural ordering</i> of its elements. 638 * @throws ClassCastException if the collection contains elements that are 639 * not <i>mutually comparable</i> (for example, strings and 640 * integers). 641 * @throws NoSuchElementException if the collection is empty. 642 * @see Comparable 643 */ 644 public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) { 645 Iterator<? extends T> i = coll.iterator(); 646 T candidate = i.next(); 647 648 while (i.hasNext()) { 649 T next = i.next(); 650 if (next.compareTo(candidate) < 0) 651 candidate = next; 652 } 653 return candidate; 654 } 655 656 /** 657 * Returns the minimum element of the given collection, according to the 658 * order induced by the specified comparator. All elements in the 659 * collection must be <i>mutually comparable</i> by the specified 660 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a 661 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 662 * <tt>e2</tt> in the collection).<p> 663 * 664 * This method iterates over the entire collection, hence it requires 665 * time proportional to the size of the collection. 666 * 667 * @param coll the collection whose minimum element is to be determined. 668 * @param comp the comparator with which to determine the minimum element. 669 * A <tt>null</tt> value indicates that the elements' <i>natural 670 * ordering</i> should be used. 671 * @return the minimum element of the given collection, according 672 * to the specified comparator. 673 * @throws ClassCastException if the collection contains elements that are 674 * not <i>mutually comparable</i> using the specified comparator. 675 * @throws NoSuchElementException if the collection is empty. 676 * @see Comparable 677 */ 678 @SuppressWarnings({"unchecked", "rawtypes"}) 679 public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) { 680 if (comp==null) 681 return (T)min((Collection) coll); 682 683 Iterator<? extends T> i = coll.iterator(); 684 T candidate = i.next(); 685 686 while (i.hasNext()) { 687 T next = i.next(); 688 if (comp.compare(next, candidate) < 0) 689 candidate = next; 690 } 691 return candidate; 692 } 693 694 /** 695 * Returns the maximum element of the given collection, according to the 696 * <i>natural ordering</i> of its elements. All elements in the 697 * collection must implement the <tt>Comparable</tt> interface. 698 * Furthermore, all elements in the collection must be <i>mutually 699 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a 700 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 701 * <tt>e2</tt> in the collection).<p> 702 * 703 * This method iterates over the entire collection, hence it requires 704 * time proportional to the size of the collection. 705 * 706 * @param coll the collection whose maximum element is to be determined. 707 * @return the maximum element of the given collection, according 708 * to the <i>natural ordering</i> of its elements. 709 * @throws ClassCastException if the collection contains elements that are 710 * not <i>mutually comparable</i> (for example, strings and 711 * integers). 712 * @throws NoSuchElementException if the collection is empty. 713 * @see Comparable 714 */ 715 public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) { 716 Iterator<? extends T> i = coll.iterator(); 717 T candidate = i.next(); 718 719 while (i.hasNext()) { 720 T next = i.next(); 721 if (next.compareTo(candidate) > 0) 722 candidate = next; 723 } 724 return candidate; 725 } 726 727 /** 728 * Returns the maximum element of the given collection, according to the 729 * order induced by the specified comparator. All elements in the 730 * collection must be <i>mutually comparable</i> by the specified 731 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a 732 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 733 * <tt>e2</tt> in the collection).<p> 734 * 735 * This method iterates over the entire collection, hence it requires 736 * time proportional to the size of the collection. 737 * 738 * @param coll the collection whose maximum element is to be determined. 739 * @param comp the comparator with which to determine the maximum element. 740 * A <tt>null</tt> value indicates that the elements' <i>natural 741 * ordering</i> should be used. 742 * @return the maximum element of the given collection, according 743 * to the specified comparator. 744 * @throws ClassCastException if the collection contains elements that are 745 * not <i>mutually comparable</i> using the specified comparator. 746 * @throws NoSuchElementException if the collection is empty. 747 * @see Comparable 748 */ 749 @SuppressWarnings({"unchecked", "rawtypes"}) 750 public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) { 751 if (comp==null) 752 return (T)max((Collection) coll); 753 754 Iterator<? extends T> i = coll.iterator(); 755 T candidate = i.next(); 756 757 while (i.hasNext()) { 758 T next = i.next(); 759 if (comp.compare(next, candidate) > 0) 760 candidate = next; 761 } 762 return candidate; 763 } 764 765 /** 766 * Rotates the elements in the specified list by the specified distance. 767 * After calling this method, the element at index <tt>i</tt> will be 768 * the element previously at index <tt>(i - distance)</tt> mod 769 * <tt>list.size()</tt>, for all values of <tt>i</tt> between <tt>0</tt> 770 * and <tt>list.size()-1</tt>, inclusive. (This method has no effect on 771 * the size of the list.) 772 * 773 * <p>For example, suppose <tt>list</tt> comprises<tt> [t, a, n, k, s]</tt>. 774 * After invoking <tt>Collections.rotate(list, 1)</tt> (or 775 * <tt>Collections.rotate(list, -4)</tt>), <tt>list</tt> will comprise 776 * <tt>[s, t, a, n, k]</tt>. 777 * 778 * <p>Note that this method can usefully be applied to sublists to 779 * move one or more elements within a list while preserving the 780 * order of the remaining elements. For example, the following idiom 781 * moves the element at index <tt>j</tt> forward to position 782 * <tt>k</tt> (which must be greater than or equal to <tt>j</tt>): 783 * <pre> 784 * Collections.rotate(list.subList(j, k+1), -1); 785 * </pre> 786 * To make this concrete, suppose <tt>list</tt> comprises 787 * <tt>[a, b, c, d, e]</tt>. To move the element at index <tt>1</tt> 788 * (<tt>b</tt>) forward two positions, perform the following invocation: 789 * <pre> 790 * Collections.rotate(l.subList(1, 4), -1); 791 * </pre> 792 * The resulting list is <tt>[a, c, d, b, e]</tt>. 793 * 794 * <p>To move more than one element forward, increase the absolute value 795 * of the rotation distance. To move elements backward, use a positive 796 * shift distance. 797 * 798 * <p>If the specified list is small or implements the {@link 799 * RandomAccess} interface, this implementation exchanges the first 800 * element into the location it should go, and then repeatedly exchanges 801 * the displaced element into the location it should go until a displaced 802 * element is swapped into the first element. If necessary, the process 803 * is repeated on the second and successive elements, until the rotation 804 * is complete. If the specified list is large and doesn't implement the 805 * <tt>RandomAccess</tt> interface, this implementation breaks the 806 * list into two sublist views around index <tt>-distance mod size</tt>. 807 * Then the {@link #reverse(List)} method is invoked on each sublist view, 808 * and finally it is invoked on the entire list. For a more complete 809 * description of both algorithms, see Section 2.3 of Jon Bentley's 810 * <i>Programming Pearls</i> (Addison-Wesley, 1986). 811 * 812 * @param list the list to be rotated. 813 * @param distance the distance to rotate the list. There are no 814 * constraints on this value; it may be zero, negative, or 815 * greater than <tt>list.size()</tt>. 816 * @throws UnsupportedOperationException if the specified list or 817 * its list-iterator does not support the <tt>set</tt> operation. 818 * @since 1.4 819 */ 820 public static void rotate(List<?> list, int distance) { 821 if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD) 822 rotate1(list, distance); 823 else 824 rotate2(list, distance); 825 } 826 827 private static <T> void rotate1(List<T> list, int distance) { 828 int size = list.size(); 829 if (size == 0) 830 return; 831 distance = distance % size; 832 if (distance < 0) 833 distance += size; 834 if (distance == 0) 835 return; 836 837 for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) { 838 T displaced = list.get(cycleStart); 839 int i = cycleStart; 840 do { 841 i += distance; 842 if (i >= size) 843 i -= size; 844 displaced = list.set(i, displaced); 845 nMoved ++; 846 } while (i != cycleStart); 847 } 848 } 849 850 private static void rotate2(List<?> list, int distance) { 851 int size = list.size(); 852 if (size == 0) 853 return; 854 int mid = -distance % size; 855 if (mid < 0) 856 mid += size; 857 if (mid == 0) 858 return; 859 860 reverse(list.subList(0, mid)); 861 reverse(list.subList(mid, size)); 862 reverse(list); 863 } 864 865 /** 866 * Replaces all occurrences of one specified value in a list with another. 867 * More formally, replaces with <tt>newVal</tt> each element <tt>e</tt> 868 * in <tt>list</tt> such that 869 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>. 870 * (This method has no effect on the size of the list.) 871 * 872 * @param list the list in which replacement is to occur. 873 * @param oldVal the old value to be replaced. 874 * @param newVal the new value with which <tt>oldVal</tt> is to be 875 * replaced. 876 * @return <tt>true</tt> if <tt>list</tt> contained one or more elements 877 * <tt>e</tt> such that 878 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>. 879 * @throws UnsupportedOperationException if the specified list or 880 * its list-iterator does not support the <tt>set</tt> operation. 881 * @since 1.4 882 */ 883 public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) { 884 boolean result = false; 885 int size = list.size(); 886 if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) { 887 if (oldVal==null) { 888 for (int i=0; i<size; i++) { 889 if (list.get(i)==null) { 890 list.set(i, newVal); 891 result = true; 892 } 893 } 894 } else { 895 for (int i=0; i<size; i++) { 896 if (oldVal.equals(list.get(i))) { 897 list.set(i, newVal); 898 result = true; 899 } 900 } 901 } 902 } else { 903 ListIterator<T> itr=list.listIterator(); 904 if (oldVal==null) { 905 for (int i=0; i<size; i++) { 906 if (itr.next()==null) { 907 itr.set(newVal); 908 result = true; 909 } 910 } 911 } else { 912 for (int i=0; i<size; i++) { 913 if (oldVal.equals(itr.next())) { 914 itr.set(newVal); 915 result = true; 916 } 917 } 918 } 919 } 920 return result; 921 } 922 923 /** 924 * Returns the starting position of the first occurrence of the specified 925 * target list within the specified source list, or -1 if there is no 926 * such occurrence. More formally, returns the lowest index <tt>i</tt> 927 * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>, 928 * or -1 if there is no such index. (Returns -1 if 929 * <tt>target.size() > source.size()</tt>.) 930 * 931 * <p>This implementation uses the "brute force" technique of scanning 932 * over the source list, looking for a match with the target at each 933 * location in turn. 934 * 935 * @param source the list in which to search for the first occurrence 936 * of <tt>target</tt>. 937 * @param target the list to search for as a subList of <tt>source</tt>. 938 * @return the starting position of the first occurrence of the specified 939 * target list within the specified source list, or -1 if there 940 * is no such occurrence. 941 * @since 1.4 942 */ 943 public static int indexOfSubList(List<?> source, List<?> target) { 944 int sourceSize = source.size(); 945 int targetSize = target.size(); 946 int maxCandidate = sourceSize - targetSize; 947 948 if (sourceSize < INDEXOFSUBLIST_THRESHOLD || 949 (source instanceof RandomAccess&&target instanceof RandomAccess)) { 950 nextCand: 951 for (int candidate = 0; candidate <= maxCandidate; candidate++) { 952 for (int i=0, j=candidate; i<targetSize; i++, j++) 953 if (!eq(target.get(i), source.get(j))) 954 continue nextCand; // Element mismatch, try next cand 955 return candidate; // All elements of candidate matched target 956 } 957 } else { // Iterator version of above algorithm 958 ListIterator<?> si = source.listIterator(); 959 nextCand: 960 for (int candidate = 0; candidate <= maxCandidate; candidate++) { 961 ListIterator<?> ti = target.listIterator(); 962 for (int i=0; i<targetSize; i++) { 963 if (!eq(ti.next(), si.next())) { 964 // Back up source iterator to next candidate 965 for (int j=0; j<i; j++) 966 si.previous(); 967 continue nextCand; 968 } 969 } 970 return candidate; 971 } 972 } 973 return -1; // No candidate matched the target 974 } 975 976 /** 977 * Returns the starting position of the last occurrence of the specified 978 * target list within the specified source list, or -1 if there is no such 979 * occurrence. More formally, returns the highest index <tt>i</tt> 980 * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>, 981 * or -1 if there is no such index. (Returns -1 if 982 * <tt>target.size() > source.size()</tt>.) 983 * 984 * <p>This implementation uses the "brute force" technique of iterating 985 * over the source list, looking for a match with the target at each 986 * location in turn. 987 * 988 * @param source the list in which to search for the last occurrence 989 * of <tt>target</tt>. 990 * @param target the list to search for as a subList of <tt>source</tt>. 991 * @return the starting position of the last occurrence of the specified 992 * target list within the specified source list, or -1 if there 993 * is no such occurrence. 994 * @since 1.4 995 */ 996 public static int lastIndexOfSubList(List<?> source, List<?> target) { 997 int sourceSize = source.size(); 998 int targetSize = target.size(); 999 int maxCandidate = sourceSize - targetSize; 1000 1001 if (sourceSize < INDEXOFSUBLIST_THRESHOLD || 1002 source instanceof RandomAccess) { // Index access version 1003 nextCand: 1004 for (int candidate = maxCandidate; candidate >= 0; candidate--) { 1005 for (int i=0, j=candidate; i<targetSize; i++, j++) 1006 if (!eq(target.get(i), source.get(j))) 1007 continue nextCand; // Element mismatch, try next cand 1008 return candidate; // All elements of candidate matched target 1009 } 1010 } else { // Iterator version of above algorithm 1011 if (maxCandidate < 0) 1012 return -1; 1013 ListIterator<?> si = source.listIterator(maxCandidate); 1014 nextCand: 1015 for (int candidate = maxCandidate; candidate >= 0; candidate--) { 1016 ListIterator<?> ti = target.listIterator(); 1017 for (int i=0; i<targetSize; i++) { 1018 if (!eq(ti.next(), si.next())) { 1019 if (candidate != 0) { 1020 // Back up source iterator to next candidate 1021 for (int j=0; j<=i+1; j++) 1022 si.previous(); 1023 } 1024 continue nextCand; 1025 } 1026 } 1027 return candidate; 1028 } 1029 } 1030 return -1; // No candidate matched the target 1031 } 1032 1033 1034 // Unmodifiable Wrappers 1035 1036 /** 1037 * Returns an unmodifiable view of the specified collection. This method 1038 * allows modules to provide users with "read-only" access to internal 1039 * collections. Query operations on the returned collection "read through" 1040 * to the specified collection, and attempts to modify the returned 1041 * collection, whether direct or via its iterator, result in an 1042 * <tt>UnsupportedOperationException</tt>.<p> 1043 * 1044 * The returned collection does <i>not</i> pass the hashCode and equals 1045 * operations through to the backing collection, but relies on 1046 * <tt>Object</tt>'s <tt>equals</tt> and <tt>hashCode</tt> methods. This 1047 * is necessary to preserve the contracts of these operations in the case 1048 * that the backing collection is a set or a list.<p> 1049 * 1050 * The returned collection will be serializable if the specified collection 1051 * is serializable. 1052 * 1053 * @param c the collection for which an unmodifiable view is to be 1054 * returned. 1055 * @return an unmodifiable view of the specified collection. 1056 */ 1057 public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) { 1058 return new UnmodifiableCollection<>(c); 1059 } 1060 1061 /** 1062 * @serial include 1063 */ 1064 static class UnmodifiableCollection<E> implements Collection<E>, Serializable { 1065 private static final long serialVersionUID = 1820017752578914078L; 1066 1067 final Collection<? extends E> c; 1068 1069 UnmodifiableCollection(Collection<? extends E> c) { 1070 if (c==null) 1071 throw new NullPointerException(); 1072 this.c = c; 1073 } 1074 1075 public int size() {return c.size();} 1076 public boolean isEmpty() {return c.isEmpty();} 1077 public boolean contains(Object o) {return c.contains(o);} 1078 public Object[] toArray() {return c.toArray();} 1079 public <T> T[] toArray(T[] a) {return c.toArray(a);} 1080 public String toString() {return c.toString();} 1081 1082 public Iterator<E> iterator() { 1083 return new Iterator<E>() { 1084 private final Iterator<? extends E> i = c.iterator(); 1085 1086 public boolean hasNext() {return i.hasNext();} 1087 public E next() {return i.next();} 1088 public void remove() { 1089 throw new UnsupportedOperationException(); 1090 } 1091 }; 1092 } 1093 1094 public boolean add(E e) { 1095 throw new UnsupportedOperationException(); 1096 } 1097 public boolean remove(Object o) { 1098 throw new UnsupportedOperationException(); 1099 } 1100 1101 public boolean containsAll(Collection<?> coll) { 1102 return c.containsAll(coll); 1103 } 1104 public boolean addAll(Collection<? extends E> coll) { 1105 throw new UnsupportedOperationException(); 1106 } 1107 public boolean removeAll(Collection<?> coll) { 1108 throw new UnsupportedOperationException(); 1109 } 1110 public boolean retainAll(Collection<?> coll) { 1111 throw new UnsupportedOperationException(); 1112 } 1113 public void clear() { 1114 throw new UnsupportedOperationException(); 1115 } 1116 1117 @Override 1118 public void forEach(Consumer<? super E> action) { 1119 c.forEach(action); 1120 } 1121 @Override 1122 public boolean removeIf(Predicate<? super E> filter) { 1123 throw new UnsupportedOperationException(); 1124 } 1125 } 1126 1127 /** 1128 * Returns an unmodifiable view of the specified set. This method allows 1129 * modules to provide users with "read-only" access to internal sets. 1130 * Query operations on the returned set "read through" to the specified 1131 * set, and attempts to modify the returned set, whether direct or via its 1132 * iterator, result in an <tt>UnsupportedOperationException</tt>.<p> 1133 * 1134 * The returned set will be serializable if the specified set 1135 * is serializable. 1136 * 1137 * @param s the set for which an unmodifiable view is to be returned. 1138 * @return an unmodifiable view of the specified set. 1139 */ 1140 public static <T> Set<T> unmodifiableSet(Set<? extends T> s) { 1141 return new UnmodifiableSet<>(s); 1142 } 1143 1144 /** 1145 * @serial include 1146 */ 1147 static class UnmodifiableSet<E> extends UnmodifiableCollection<E> 1148 implements Set<E>, Serializable { 1149 private static final long serialVersionUID = -9215047833775013803L; 1150 1151 UnmodifiableSet(Set<? extends E> s) {super(s);} 1152 public boolean equals(Object o) {return o == this || c.equals(o);} 1153 public int hashCode() {return c.hashCode();} 1154 } 1155 1156 /** 1157 * Returns an unmodifiable view of the specified sorted set. This method 1158 * allows modules to provide users with "read-only" access to internal 1159 * sorted sets. Query operations on the returned sorted set "read 1160 * through" to the specified sorted set. Attempts to modify the returned 1161 * sorted set, whether direct, via its iterator, or via its 1162 * <tt>subSet</tt>, <tt>headSet</tt>, or <tt>tailSet</tt> views, result in 1163 * an <tt>UnsupportedOperationException</tt>.<p> 1164 * 1165 * The returned sorted set will be serializable if the specified sorted set 1166 * is serializable. 1167 * 1168 * @param s the sorted set for which an unmodifiable view is to be 1169 * returned. 1170 * @return an unmodifiable view of the specified sorted set. 1171 */ 1172 public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) { 1173 return new UnmodifiableSortedSet<>(s); 1174 } 1175 1176 /** 1177 * @serial include 1178 */ 1179 static class UnmodifiableSortedSet<E> 1180 extends UnmodifiableSet<E> 1181 implements SortedSet<E>, Serializable { 1182 private static final long serialVersionUID = -4929149591599911165L; 1183 private final SortedSet<E> ss; 1184 1185 UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;} 1186 1187 public Comparator<? super E> comparator() {return ss.comparator();} 1188 1189 public SortedSet<E> subSet(E fromElement, E toElement) { 1190 return new UnmodifiableSortedSet<>(ss.subSet(fromElement,toElement)); 1191 } 1192 public SortedSet<E> headSet(E toElement) { 1193 return new UnmodifiableSortedSet<>(ss.headSet(toElement)); 1194 } 1195 public SortedSet<E> tailSet(E fromElement) { 1196 return new UnmodifiableSortedSet<>(ss.tailSet(fromElement)); 1197 } 1198 1199 public E first() {return ss.first();} 1200 public E last() {return ss.last();} 1201 } 1202 1203 /** 1204 * Returns an unmodifiable view of the specified list. This method allows 1205 * modules to provide users with "read-only" access to internal 1206 * lists. Query operations on the returned list "read through" to the 1207 * specified list, and attempts to modify the returned list, whether 1208 * direct or via its iterator, result in an 1209 * <tt>UnsupportedOperationException</tt>.<p> 1210 * 1211 * The returned list will be serializable if the specified list 1212 * is serializable. Similarly, the returned list will implement 1213 * {@link RandomAccess} if the specified list does. 1214 * 1215 * @param list the list for which an unmodifiable view is to be returned. 1216 * @return an unmodifiable view of the specified list. 1217 */ 1218 public static <T> List<T> unmodifiableList(List<? extends T> list) { 1219 return (list instanceof RandomAccess ? 1220 new UnmodifiableRandomAccessList<>(list) : 1221 new UnmodifiableList<>(list)); 1222 } 1223 1224 /** 1225 * @serial include 1226 */ 1227 static class UnmodifiableList<E> extends UnmodifiableCollection<E> 1228 implements List<E> { 1229 private static final long serialVersionUID = -283967356065247728L; 1230 final List<? extends E> list; 1231 1232 UnmodifiableList(List<? extends E> list) { 1233 super(list); 1234 this.list = list; 1235 } 1236 1237 public boolean equals(Object o) {return o == this || list.equals(o);} 1238 public int hashCode() {return list.hashCode();} 1239 1240 public E get(int index) {return list.get(index);} 1241 public E set(int index, E element) { 1242 throw new UnsupportedOperationException(); 1243 } 1244 public void add(int index, E element) { 1245 throw new UnsupportedOperationException(); 1246 } 1247 public E remove(int index) { 1248 throw new UnsupportedOperationException(); 1249 } 1250 public int indexOf(Object o) {return list.indexOf(o);} 1251 public int lastIndexOf(Object o) {return list.lastIndexOf(o);} 1252 public boolean addAll(int index, Collection<? extends E> c) { 1253 throw new UnsupportedOperationException(); 1254 } 1255 1256 @Override 1257 public void replaceAll(UnaryOperator<E> operator) { 1258 throw new UnsupportedOperationException(); 1259 } 1260 @Override 1261 public void sort(Comparator<? super E> c) { 1262 throw new UnsupportedOperationException(); 1263 } 1264 1265 public ListIterator<E> listIterator() {return listIterator(0);} 1266 1267 public ListIterator<E> listIterator(final int index) { 1268 return new ListIterator<E>() { 1269 private final ListIterator<? extends E> i 1270 = list.listIterator(index); 1271 1272 public boolean hasNext() {return i.hasNext();} 1273 public E next() {return i.next();} 1274 public boolean hasPrevious() {return i.hasPrevious();} 1275 public E previous() {return i.previous();} 1276 public int nextIndex() {return i.nextIndex();} 1277 public int previousIndex() {return i.previousIndex();} 1278 1279 public void remove() { 1280 throw new UnsupportedOperationException(); 1281 } 1282 public void set(E e) { 1283 throw new UnsupportedOperationException(); 1284 } 1285 public void add(E e) { 1286 throw new UnsupportedOperationException(); 1287 } 1288 }; 1289 } 1290 1291 public List<E> subList(int fromIndex, int toIndex) { 1292 return new UnmodifiableList<>(list.subList(fromIndex, toIndex)); 1293 } 1294 1295 /** 1296 * UnmodifiableRandomAccessList instances are serialized as 1297 * UnmodifiableList instances to allow them to be deserialized 1298 * in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList). 1299 * This method inverts the transformation. As a beneficial 1300 * side-effect, it also grafts the RandomAccess marker onto 1301 * UnmodifiableList instances that were serialized in pre-1.4 JREs. 1302 * 1303 * Note: Unfortunately, UnmodifiableRandomAccessList instances 1304 * serialized in 1.4.1 and deserialized in 1.4 will become 1305 * UnmodifiableList instances, as this method was missing in 1.4. 1306 */ 1307 private Object readResolve() { 1308 return (list instanceof RandomAccess 1309 ? new UnmodifiableRandomAccessList<>(list) 1310 : this); 1311 } 1312 } 1313 1314 /** 1315 * @serial include 1316 */ 1317 static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E> 1318 implements RandomAccess 1319 { 1320 UnmodifiableRandomAccessList(List<? extends E> list) { 1321 super(list); 1322 } 1323 1324 public List<E> subList(int fromIndex, int toIndex) { 1325 return new UnmodifiableRandomAccessList<>( 1326 list.subList(fromIndex, toIndex)); 1327 } 1328 1329 private static final long serialVersionUID = -2542308836966382001L; 1330 1331 /** 1332 * Allows instances to be deserialized in pre-1.4 JREs (which do 1333 * not have UnmodifiableRandomAccessList). UnmodifiableList has 1334 * a readResolve method that inverts this transformation upon 1335 * deserialization. 1336 */ 1337 private Object writeReplace() { 1338 return new UnmodifiableList<>(list); 1339 } 1340 } 1341 1342 /** 1343 * Returns an unmodifiable view of the specified map. This method 1344 * allows modules to provide users with "read-only" access to internal 1345 * maps. Query operations on the returned map "read through" 1346 * to the specified map, and attempts to modify the returned 1347 * map, whether direct or via its collection views, result in an 1348 * <tt>UnsupportedOperationException</tt>.<p> 1349 * 1350 * The returned map will be serializable if the specified map 1351 * is serializable. 1352 * 1353 * @param m the map for which an unmodifiable view is to be returned. 1354 * @return an unmodifiable view of the specified map. 1355 */ 1356 public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) { 1357 return new UnmodifiableMap<>(m); 1358 } 1359 1360 /** 1361 * @serial include 1362 */ 1363 private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable { 1364 private static final long serialVersionUID = -1034234728574286014L; 1365 1366 private final Map<? extends K, ? extends V> m; 1367 1368 UnmodifiableMap(Map<? extends K, ? extends V> m) { 1369 if (m==null) 1370 throw new NullPointerException(); 1371 this.m = m; 1372 } 1373 1374 public int size() {return m.size();} 1375 public boolean isEmpty() {return m.isEmpty();} 1376 public boolean containsKey(Object key) {return m.containsKey(key);} 1377 public boolean containsValue(Object val) {return m.containsValue(val);} 1378 public V get(Object key) {return m.get(key);} 1379 1380 public V put(K key, V value) { 1381 throw new UnsupportedOperationException(); 1382 } 1383 public V remove(Object key) { 1384 throw new UnsupportedOperationException(); 1385 } 1386 public void putAll(Map<? extends K, ? extends V> m) { 1387 throw new UnsupportedOperationException(); 1388 } 1389 public void clear() { 1390 throw new UnsupportedOperationException(); 1391 } 1392 1393 private transient Set<K> keySet = null; 1394 private transient Set<Map.Entry<K,V>> entrySet = null; 1395 private transient Collection<V> values = null; 1396 1397 public Set<K> keySet() { 1398 if (keySet==null) 1399 keySet = unmodifiableSet(m.keySet()); 1400 return keySet; 1401 } 1402 1403 public Set<Map.Entry<K,V>> entrySet() { 1404 if (entrySet==null) 1405 entrySet = new UnmodifiableEntrySet<>(m.entrySet()); 1406 return entrySet; 1407 } 1408 1409 public Collection<V> values() { 1410 if (values==null) 1411 values = unmodifiableCollection(m.values()); 1412 return values; 1413 } 1414 1415 public boolean equals(Object o) {return o == this || m.equals(o);} 1416 public int hashCode() {return m.hashCode();} 1417 public String toString() {return m.toString();} 1418 1419 // Override default methods in Map 1420 @Override 1421 @SuppressWarnings("unchecked") 1422 public V getOrDefault(Object k, V defaultValue) { 1423 // Safe cast as we don't change the value 1424 return ((Map<K, V>)m).getOrDefault(k, defaultValue); 1425 } 1426 1427 @Override 1428 public void forEach(BiConsumer<? super K, ? super V> action) { 1429 m.forEach(action); 1430 } 1431 1432 @Override 1433 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 1434 throw new UnsupportedOperationException(); 1435 } 1436 1437 @Override 1438 public V putIfAbsent(K key, V value) { 1439 throw new UnsupportedOperationException(); 1440 } 1441 1442 @Override 1443 public boolean remove(Object key, Object value) { 1444 throw new UnsupportedOperationException(); 1445 } 1446 1447 @Override 1448 public boolean replace(K key, V oldValue, V newValue) { 1449 throw new UnsupportedOperationException(); 1450 } 1451 1452 @Override 1453 public V replace(K key, V value) { 1454 throw new UnsupportedOperationException(); 1455 } 1456 1457 @Override 1458 public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) { 1459 throw new UnsupportedOperationException(); 1460 } 1461 1462 @Override 1463 public V computeIfPresent(K key, 1464 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 1465 throw new UnsupportedOperationException(); 1466 } 1467 1468 @Override 1469 public V compute(K key, 1470 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 1471 throw new UnsupportedOperationException(); 1472 } 1473 1474 @Override 1475 public V merge(K key, V value, 1476 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 1477 throw new UnsupportedOperationException(); 1478 } 1479 1480 /** 1481 * We need this class in addition to UnmodifiableSet as 1482 * Map.Entries themselves permit modification of the backing Map 1483 * via their setValue operation. This class is subtle: there are 1484 * many possible attacks that must be thwarted. 1485 * 1486 * @serial include 1487 */ 1488 static class UnmodifiableEntrySet<K,V> 1489 extends UnmodifiableSet<Map.Entry<K,V>> { 1490 private static final long serialVersionUID = 7854390611657943733L; 1491 1492 @SuppressWarnings({"unchecked", "rawtypes"}) 1493 UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) { 1494 // Need to cast to raw in order to work around a limitation in the type system 1495 super((Set)s); 1496 } 1497 public Iterator<Map.Entry<K,V>> iterator() { 1498 return new Iterator<Map.Entry<K,V>>() { 1499 private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator(); 1500 1501 public boolean hasNext() { 1502 return i.hasNext(); 1503 } 1504 public Map.Entry<K,V> next() { 1505 return new UnmodifiableEntry<>(i.next()); 1506 } 1507 public void remove() { 1508 throw new UnsupportedOperationException(); 1509 } 1510 }; 1511 } 1512 1513 @SuppressWarnings("unchecked") 1514 public Object[] toArray() { 1515 Object[] a = c.toArray(); 1516 for (int i=0; i<a.length; i++) 1517 a[i] = new UnmodifiableEntry<>((Map.Entry<? extends K, ? extends V>)a[i]); 1518 return a; 1519 } 1520 1521 @SuppressWarnings("unchecked") 1522 public <T> T[] toArray(T[] a) { 1523 // We don't pass a to c.toArray, to avoid window of 1524 // vulnerability wherein an unscrupulous multithreaded client 1525 // could get his hands on raw (unwrapped) Entries from c. 1526 Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0)); 1527 1528 for (int i=0; i<arr.length; i++) 1529 arr[i] = new UnmodifiableEntry<>((Map.Entry<? extends K, ? extends V>)arr[i]); 1530 1531 if (arr.length > a.length) 1532 return (T[])arr; 1533 1534 System.arraycopy(arr, 0, a, 0, arr.length); 1535 if (a.length > arr.length) 1536 a[arr.length] = null; 1537 return a; 1538 } 1539 1540 /** 1541 * This method is overridden to protect the backing set against 1542 * an object with a nefarious equals function that senses 1543 * that the equality-candidate is Map.Entry and calls its 1544 * setValue method. 1545 */ 1546 public boolean contains(Object o) { 1547 if (!(o instanceof Map.Entry)) 1548 return false; 1549 return c.contains( 1550 new UnmodifiableEntry<>((Map.Entry<?,?>) o)); 1551 } 1552 1553 /** 1554 * The next two methods are overridden to protect against 1555 * an unscrupulous List whose contains(Object o) method senses 1556 * when o is a Map.Entry, and calls o.setValue. 1557 */ 1558 public boolean containsAll(Collection<?> coll) { 1559 for (Object e : coll) { 1560 if (!contains(e)) // Invokes safe contains() above 1561 return false; 1562 } 1563 return true; 1564 } 1565 public boolean equals(Object o) { 1566 if (o == this) 1567 return true; 1568 1569 if (!(o instanceof Set)) 1570 return false; 1571 Set<?> s = (Set<?>) o; 1572 if (s.size() != c.size()) 1573 return false; 1574 return containsAll(s); // Invokes safe containsAll() above 1575 } 1576 1577 /** 1578 * This "wrapper class" serves two purposes: it prevents 1579 * the client from modifying the backing Map, by short-circuiting 1580 * the setValue method, and it protects the backing Map against 1581 * an ill-behaved Map.Entry that attempts to modify another 1582 * Map Entry when asked to perform an equality check. 1583 */ 1584 private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> { 1585 private Map.Entry<? extends K, ? extends V> e; 1586 1587 UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) {this.e = e;} 1588 1589 public K getKey() {return e.getKey();} 1590 public V getValue() {return e.getValue();} 1591 public V setValue(V value) { 1592 throw new UnsupportedOperationException(); 1593 } 1594 public int hashCode() {return e.hashCode();} 1595 public boolean equals(Object o) { 1596 if (this == o) 1597 return true; 1598 if (!(o instanceof Map.Entry)) 1599 return false; 1600 Map.Entry<?,?> t = (Map.Entry<?,?>)o; 1601 return eq(e.getKey(), t.getKey()) && 1602 eq(e.getValue(), t.getValue()); 1603 } 1604 public String toString() {return e.toString();} 1605 } 1606 } 1607 } 1608 1609 /** 1610 * Returns an unmodifiable view of the specified sorted map. This method 1611 * allows modules to provide users with "read-only" access to internal 1612 * sorted maps. Query operations on the returned sorted map "read through" 1613 * to the specified sorted map. Attempts to modify the returned 1614 * sorted map, whether direct, via its collection views, or via its 1615 * <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in 1616 * an <tt>UnsupportedOperationException</tt>.<p> 1617 * 1618 * The returned sorted map will be serializable if the specified sorted map 1619 * is serializable. 1620 * 1621 * @param m the sorted map for which an unmodifiable view is to be 1622 * returned. 1623 * @return an unmodifiable view of the specified sorted map. 1624 */ 1625 public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) { 1626 return new UnmodifiableSortedMap<>(m); 1627 } 1628 1629 /** 1630 * @serial include 1631 */ 1632 static class UnmodifiableSortedMap<K,V> 1633 extends UnmodifiableMap<K,V> 1634 implements SortedMap<K,V>, Serializable { 1635 private static final long serialVersionUID = -8806743815996713206L; 1636 1637 private final SortedMap<K, ? extends V> sm; 1638 1639 UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m;} 1640 1641 public Comparator<? super K> comparator() {return sm.comparator();} 1642 1643 public SortedMap<K,V> subMap(K fromKey, K toKey) { 1644 return new UnmodifiableSortedMap<>(sm.subMap(fromKey, toKey)); 1645 } 1646 public SortedMap<K,V> headMap(K toKey) { 1647 return new UnmodifiableSortedMap<>(sm.headMap(toKey)); 1648 } 1649 public SortedMap<K,V> tailMap(K fromKey) { 1650 return new UnmodifiableSortedMap<>(sm.tailMap(fromKey)); 1651 } 1652 1653 public K firstKey() {return sm.firstKey();} 1654 public K lastKey() {return sm.lastKey();} 1655 } 1656 1657 1658 // Synch Wrappers 1659 1660 /** 1661 * Returns a synchronized (thread-safe) collection backed by the specified 1662 * collection. In order to guarantee serial access, it is critical that 1663 * <strong>all</strong> access to the backing collection is accomplished 1664 * through the returned collection.<p> 1665 * 1666 * It is imperative that the user manually synchronize on the returned 1667 * collection when iterating over it: 1668 * <pre> 1669 * Collection c = Collections.synchronizedCollection(myCollection); 1670 * ... 1671 * synchronized (c) { 1672 * Iterator i = c.iterator(); // Must be in the synchronized block 1673 * while (i.hasNext()) 1674 * foo(i.next()); 1675 * } 1676 * </pre> 1677 * Failure to follow this advice may result in non-deterministic behavior. 1678 * 1679 * <p>The returned collection does <i>not</i> pass the {@code hashCode} 1680 * and {@code equals} operations through to the backing collection, but 1681 * relies on {@code Object}'s equals and hashCode methods. This is 1682 * necessary to preserve the contracts of these operations in the case 1683 * that the backing collection is a set or a list.<p> 1684 * 1685 * The returned collection will be serializable if the specified collection 1686 * is serializable. 1687 * 1688 * @param c the collection to be "wrapped" in a synchronized collection. 1689 * @return a synchronized view of the specified collection. 1690 */ 1691 public static <T> Collection<T> synchronizedCollection(Collection<T> c) { 1692 return new SynchronizedCollection<>(c); 1693 } 1694 1695 static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) { 1696 return new SynchronizedCollection<>(c, mutex); 1697 } 1698 1699 /** 1700 * @serial include 1701 */ 1702 static class SynchronizedCollection<E> implements Collection<E>, Serializable { 1703 private static final long serialVersionUID = 3053995032091335093L; 1704 1705 final Collection<E> c; // Backing Collection 1706 final Object mutex; // Object on which to synchronize 1707 1708 SynchronizedCollection(Collection<E> c) { 1709 if (c==null) 1710 throw new NullPointerException(); 1711 this.c = c; 1712 mutex = this; 1713 } 1714 SynchronizedCollection(Collection<E> c, Object mutex) { 1715 this.c = c; 1716 this.mutex = mutex; 1717 } 1718 1719 public int size() { 1720 synchronized (mutex) {return c.size();} 1721 } 1722 public boolean isEmpty() { 1723 synchronized (mutex) {return c.isEmpty();} 1724 } 1725 public boolean contains(Object o) { 1726 synchronized (mutex) {return c.contains(o);} 1727 } 1728 public Object[] toArray() { 1729 synchronized (mutex) {return c.toArray();} 1730 } 1731 public <T> T[] toArray(T[] a) { 1732 synchronized (mutex) {return c.toArray(a);} 1733 } 1734 1735 public Iterator<E> iterator() { 1736 return c.iterator(); // Must be manually synched by user! 1737 } 1738 1739 public boolean add(E e) { 1740 synchronized (mutex) {return c.add(e);} 1741 } 1742 public boolean remove(Object o) { 1743 synchronized (mutex) {return c.remove(o);} 1744 } 1745 1746 public boolean containsAll(Collection<?> coll) { 1747 synchronized (mutex) {return c.containsAll(coll);} 1748 } 1749 public boolean addAll(Collection<? extends E> coll) { 1750 synchronized (mutex) {return c.addAll(coll);} 1751 } 1752 public boolean removeAll(Collection<?> coll) { 1753 synchronized (mutex) {return c.removeAll(coll);} 1754 } 1755 public boolean retainAll(Collection<?> coll) { 1756 synchronized (mutex) {return c.retainAll(coll);} 1757 } 1758 public void clear() { 1759 synchronized (mutex) {c.clear();} 1760 } 1761 public String toString() { 1762 synchronized (mutex) {return c.toString();} 1763 } 1764 private void writeObject(ObjectOutputStream s) throws IOException { 1765 synchronized (mutex) {s.defaultWriteObject();} 1766 } 1767 1768 @Override 1769 public void forEach(Consumer<? super E> action) { 1770 synchronized (mutex) {c.forEach(action);} 1771 } 1772 @Override 1773 public boolean removeIf(Predicate<? super E> filter) { 1774 synchronized (mutex) {return c.removeIf(filter);} 1775 } 1776 } 1777 1778 /** 1779 * Returns a synchronized (thread-safe) set backed by the specified 1780 * set. In order to guarantee serial access, it is critical that 1781 * <strong>all</strong> access to the backing set is accomplished 1782 * through the returned set.<p> 1783 * 1784 * It is imperative that the user manually synchronize on the returned 1785 * set when iterating over it: 1786 * <pre> 1787 * Set s = Collections.synchronizedSet(new HashSet()); 1788 * ... 1789 * synchronized (s) { 1790 * Iterator i = s.iterator(); // Must be in the synchronized block 1791 * while (i.hasNext()) 1792 * foo(i.next()); 1793 * } 1794 * </pre> 1795 * Failure to follow this advice may result in non-deterministic behavior. 1796 * 1797 * <p>The returned set will be serializable if the specified set is 1798 * serializable. 1799 * 1800 * @param s the set to be "wrapped" in a synchronized set. 1801 * @return a synchronized view of the specified set. 1802 */ 1803 public static <T> Set<T> synchronizedSet(Set<T> s) { 1804 return new SynchronizedSet<>(s); 1805 } 1806 1807 static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) { 1808 return new SynchronizedSet<>(s, mutex); 1809 } 1810 1811 /** 1812 * @serial include 1813 */ 1814 static class SynchronizedSet<E> 1815 extends SynchronizedCollection<E> 1816 implements Set<E> { 1817 private static final long serialVersionUID = 487447009682186044L; 1818 1819 SynchronizedSet(Set<E> s) { 1820 super(s); 1821 } 1822 SynchronizedSet(Set<E> s, Object mutex) { 1823 super(s, mutex); 1824 } 1825 1826 public boolean equals(Object o) { 1827 if (this == o) 1828 return true; 1829 synchronized (mutex) {return c.equals(o);} 1830 } 1831 public int hashCode() { 1832 synchronized (mutex) {return c.hashCode();} 1833 } 1834 } 1835 1836 /** 1837 * Returns a synchronized (thread-safe) sorted set backed by the specified 1838 * sorted set. In order to guarantee serial access, it is critical that 1839 * <strong>all</strong> access to the backing sorted set is accomplished 1840 * through the returned sorted set (or its views).<p> 1841 * 1842 * It is imperative that the user manually synchronize on the returned 1843 * sorted set when iterating over it or any of its <tt>subSet</tt>, 1844 * <tt>headSet</tt>, or <tt>tailSet</tt> views. 1845 * <pre> 1846 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet()); 1847 * ... 1848 * synchronized (s) { 1849 * Iterator i = s.iterator(); // Must be in the synchronized block 1850 * while (i.hasNext()) 1851 * foo(i.next()); 1852 * } 1853 * </pre> 1854 * or: 1855 * <pre> 1856 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet()); 1857 * SortedSet s2 = s.headSet(foo); 1858 * ... 1859 * synchronized (s) { // Note: s, not s2!!! 1860 * Iterator i = s2.iterator(); // Must be in the synchronized block 1861 * while (i.hasNext()) 1862 * foo(i.next()); 1863 * } 1864 * </pre> 1865 * Failure to follow this advice may result in non-deterministic behavior. 1866 * 1867 * <p>The returned sorted set will be serializable if the specified 1868 * sorted set is serializable. 1869 * 1870 * @param s the sorted set to be "wrapped" in a synchronized sorted set. 1871 * @return a synchronized view of the specified sorted set. 1872 */ 1873 public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) { 1874 return new SynchronizedSortedSet<>(s); 1875 } 1876 1877 /** 1878 * @serial include 1879 */ 1880 static class SynchronizedSortedSet<E> 1881 extends SynchronizedSet<E> 1882 implements SortedSet<E> 1883 { 1884 private static final long serialVersionUID = 8695801310862127406L; 1885 1886 private final SortedSet<E> ss; 1887 1888 SynchronizedSortedSet(SortedSet<E> s) { 1889 super(s); 1890 ss = s; 1891 } 1892 SynchronizedSortedSet(SortedSet<E> s, Object mutex) { 1893 super(s, mutex); 1894 ss = s; 1895 } 1896 1897 public Comparator<? super E> comparator() { 1898 synchronized (mutex) {return ss.comparator();} 1899 } 1900 1901 public SortedSet<E> subSet(E fromElement, E toElement) { 1902 synchronized (mutex) { 1903 return new SynchronizedSortedSet<>( 1904 ss.subSet(fromElement, toElement), mutex); 1905 } 1906 } 1907 public SortedSet<E> headSet(E toElement) { 1908 synchronized (mutex) { 1909 return new SynchronizedSortedSet<>(ss.headSet(toElement), mutex); 1910 } 1911 } 1912 public SortedSet<E> tailSet(E fromElement) { 1913 synchronized (mutex) { 1914 return new SynchronizedSortedSet<>(ss.tailSet(fromElement),mutex); 1915 } 1916 } 1917 1918 public E first() { 1919 synchronized (mutex) {return ss.first();} 1920 } 1921 public E last() { 1922 synchronized (mutex) {return ss.last();} 1923 } 1924 } 1925 1926 /** 1927 * Returns a synchronized (thread-safe) list backed by the specified 1928 * list. In order to guarantee serial access, it is critical that 1929 * <strong>all</strong> access to the backing list is accomplished 1930 * through the returned list.<p> 1931 * 1932 * It is imperative that the user manually synchronize on the returned 1933 * list when iterating over it: 1934 * <pre> 1935 * List list = Collections.synchronizedList(new ArrayList()); 1936 * ... 1937 * synchronized (list) { 1938 * Iterator i = list.iterator(); // Must be in synchronized block 1939 * while (i.hasNext()) 1940 * foo(i.next()); 1941 * } 1942 * </pre> 1943 * Failure to follow this advice may result in non-deterministic behavior. 1944 * 1945 * <p>The returned list will be serializable if the specified list is 1946 * serializable. 1947 * 1948 * @param list the list to be "wrapped" in a synchronized list. 1949 * @return a synchronized view of the specified list. 1950 */ 1951 public static <T> List<T> synchronizedList(List<T> list) { 1952 return (list instanceof RandomAccess ? 1953 new SynchronizedRandomAccessList<>(list) : 1954 new SynchronizedList<>(list)); 1955 } 1956 1957 static <T> List<T> synchronizedList(List<T> list, Object mutex) { 1958 return (list instanceof RandomAccess ? 1959 new SynchronizedRandomAccessList<>(list, mutex) : 1960 new SynchronizedList<>(list, mutex)); 1961 } 1962 1963 /** 1964 * @serial include 1965 */ 1966 static class SynchronizedList<E> 1967 extends SynchronizedCollection<E> 1968 implements List<E> { 1969 private static final long serialVersionUID = -7754090372962971524L; 1970 1971 final List<E> list; 1972 1973 SynchronizedList(List<E> list) { 1974 super(list); 1975 this.list = list; 1976 } 1977 SynchronizedList(List<E> list, Object mutex) { 1978 super(list, mutex); 1979 this.list = list; 1980 } 1981 1982 public boolean equals(Object o) { 1983 if (this == o) 1984 return true; 1985 synchronized (mutex) {return list.equals(o);} 1986 } 1987 public int hashCode() { 1988 synchronized (mutex) {return list.hashCode();} 1989 } 1990 1991 public E get(int index) { 1992 synchronized (mutex) {return list.get(index);} 1993 } 1994 public E set(int index, E element) { 1995 synchronized (mutex) {return list.set(index, element);} 1996 } 1997 public void add(int index, E element) { 1998 synchronized (mutex) {list.add(index, element);} 1999 } 2000 public E remove(int index) { 2001 synchronized (mutex) {return list.remove(index);} 2002 } 2003 2004 public int indexOf(Object o) { 2005 synchronized (mutex) {return list.indexOf(o);} 2006 } 2007 public int lastIndexOf(Object o) { 2008 synchronized (mutex) {return list.lastIndexOf(o);} 2009 } 2010 2011 public boolean addAll(int index, Collection<? extends E> c) { 2012 synchronized (mutex) {return list.addAll(index, c);} 2013 } 2014 2015 public ListIterator<E> listIterator() { 2016 return list.listIterator(); // Must be manually synched by user 2017 } 2018 2019 public ListIterator<E> listIterator(int index) { 2020 return list.listIterator(index); // Must be manually synched by user 2021 } 2022 2023 public List<E> subList(int fromIndex, int toIndex) { 2024 synchronized (mutex) { 2025 return new SynchronizedList<>(list.subList(fromIndex, toIndex), 2026 mutex); 2027 } 2028 } 2029 2030 @Override 2031 public void replaceAll(UnaryOperator<E> operator) { 2032 synchronized (mutex) {list.replaceAll(operator);} 2033 } 2034 @Override 2035 public void sort(Comparator<? super E> c) { 2036 synchronized (mutex) {list.sort(c);} 2037 } 2038 2039 /** 2040 * SynchronizedRandomAccessList instances are serialized as 2041 * SynchronizedList instances to allow them to be deserialized 2042 * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList). 2043 * This method inverts the transformation. As a beneficial 2044 * side-effect, it also grafts the RandomAccess marker onto 2045 * SynchronizedList instances that were serialized in pre-1.4 JREs. 2046 * 2047 * Note: Unfortunately, SynchronizedRandomAccessList instances 2048 * serialized in 1.4.1 and deserialized in 1.4 will become 2049 * SynchronizedList instances, as this method was missing in 1.4. 2050 */ 2051 private Object readResolve() { 2052 return (list instanceof RandomAccess 2053 ? new SynchronizedRandomAccessList<>(list) 2054 : this); 2055 } 2056 } 2057 2058 /** 2059 * @serial include 2060 */ 2061 static class SynchronizedRandomAccessList<E> 2062 extends SynchronizedList<E> 2063 implements RandomAccess { 2064 2065 SynchronizedRandomAccessList(List<E> list) { 2066 super(list); 2067 } 2068 2069 SynchronizedRandomAccessList(List<E> list, Object mutex) { 2070 super(list, mutex); 2071 } 2072 2073 public List<E> subList(int fromIndex, int toIndex) { 2074 synchronized (mutex) { 2075 return new SynchronizedRandomAccessList<>( 2076 list.subList(fromIndex, toIndex), mutex); 2077 } 2078 } 2079 2080 private static final long serialVersionUID = 1530674583602358482L; 2081 2082 /** 2083 * Allows instances to be deserialized in pre-1.4 JREs (which do 2084 * not have SynchronizedRandomAccessList). SynchronizedList has 2085 * a readResolve method that inverts this transformation upon 2086 * deserialization. 2087 */ 2088 private Object writeReplace() { 2089 return new SynchronizedList<>(list); 2090 } 2091 } 2092 2093 /** 2094 * Returns a synchronized (thread-safe) map backed by the specified 2095 * map. In order to guarantee serial access, it is critical that 2096 * <strong>all</strong> access to the backing map is accomplished 2097 * through the returned map.<p> 2098 * 2099 * It is imperative that the user manually synchronize on the returned 2100 * map when iterating over any of its collection views: 2101 * <pre> 2102 * Map m = Collections.synchronizedMap(new HashMap()); 2103 * ... 2104 * Set s = m.keySet(); // Needn't be in synchronized block 2105 * ... 2106 * synchronized (m) { // Synchronizing on m, not s! 2107 * Iterator i = s.iterator(); // Must be in synchronized block 2108 * while (i.hasNext()) 2109 * foo(i.next()); 2110 * } 2111 * </pre> 2112 * Failure to follow this advice may result in non-deterministic behavior. 2113 * 2114 * <p>The returned map will be serializable if the specified map is 2115 * serializable. 2116 * 2117 * @param m the map to be "wrapped" in a synchronized map. 2118 * @return a synchronized view of the specified map. 2119 */ 2120 public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) { 2121 return new SynchronizedMap<>(m); 2122 } 2123 2124 /** 2125 * @serial include 2126 */ 2127 private static class SynchronizedMap<K,V> 2128 implements Map<K,V>, Serializable { 2129 private static final long serialVersionUID = 1978198479659022715L; 2130 2131 private final Map<K,V> m; // Backing Map 2132 final Object mutex; // Object on which to synchronize 2133 2134 SynchronizedMap(Map<K,V> m) { 2135 if (m==null) 2136 throw new NullPointerException(); 2137 this.m = m; 2138 mutex = this; 2139 } 2140 2141 SynchronizedMap(Map<K,V> m, Object mutex) { 2142 this.m = m; 2143 this.mutex = mutex; 2144 } 2145 2146 public int size() { 2147 synchronized (mutex) {return m.size();} 2148 } 2149 public boolean isEmpty() { 2150 synchronized (mutex) {return m.isEmpty();} 2151 } 2152 public boolean containsKey(Object key) { 2153 synchronized (mutex) {return m.containsKey(key);} 2154 } 2155 public boolean containsValue(Object value) { 2156 synchronized (mutex) {return m.containsValue(value);} 2157 } 2158 public V get(Object key) { 2159 synchronized (mutex) {return m.get(key);} 2160 } 2161 2162 public V put(K key, V value) { 2163 synchronized (mutex) {return m.put(key, value);} 2164 } 2165 public V remove(Object key) { 2166 synchronized (mutex) {return m.remove(key);} 2167 } 2168 public void putAll(Map<? extends K, ? extends V> map) { 2169 synchronized (mutex) {m.putAll(map);} 2170 } 2171 public void clear() { 2172 synchronized (mutex) {m.clear();} 2173 } 2174 2175 private transient Set<K> keySet = null; 2176 private transient Set<Map.Entry<K,V>> entrySet = null; 2177 private transient Collection<V> values = null; 2178 2179 public Set<K> keySet() { 2180 synchronized (mutex) { 2181 if (keySet==null) 2182 keySet = new SynchronizedSet<>(m.keySet(), mutex); 2183 return keySet; 2184 } 2185 } 2186 2187 public Set<Map.Entry<K,V>> entrySet() { 2188 synchronized (mutex) { 2189 if (entrySet==null) 2190 entrySet = new SynchronizedSet<>(m.entrySet(), mutex); 2191 return entrySet; 2192 } 2193 } 2194 2195 public Collection<V> values() { 2196 synchronized (mutex) { 2197 if (values==null) 2198 values = new SynchronizedCollection<>(m.values(), mutex); 2199 return values; 2200 } 2201 } 2202 2203 public boolean equals(Object o) { 2204 if (this == o) 2205 return true; 2206 synchronized (mutex) {return m.equals(o);} 2207 } 2208 public int hashCode() { 2209 synchronized (mutex) {return m.hashCode();} 2210 } 2211 public String toString() { 2212 synchronized (mutex) {return m.toString();} 2213 } 2214 2215 // Override default methods in Map 2216 @Override 2217 public V getOrDefault(Object k, V defaultValue) { 2218 synchronized (mutex) {return m.getOrDefault(k, defaultValue);} 2219 } 2220 @Override 2221 public void forEach(BiConsumer<? super K, ? super V> action) { 2222 synchronized (mutex) {m.forEach(action);} 2223 } 2224 @Override 2225 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 2226 synchronized (mutex) {m.replaceAll(function);} 2227 } 2228 @Override 2229 public V putIfAbsent(K key, V value) { 2230 synchronized (mutex) {return m.putIfAbsent(key, value);} 2231 } 2232 @Override 2233 public boolean remove(Object key, Object value) { 2234 synchronized (mutex) {return m.remove(key, value);} 2235 } 2236 @Override 2237 public boolean replace(K key, V oldValue, V newValue) { 2238 synchronized (mutex) {return m.replace(key, oldValue, newValue);} 2239 } 2240 @Override 2241 public V replace(K key, V value) { 2242 synchronized (mutex) {return m.replace(key, value);} 2243 } 2244 @Override 2245 public V computeIfAbsent(K key, 2246 Function<? super K, ? extends V> mappingFunction) { 2247 synchronized (mutex) {return m.computeIfAbsent(key, mappingFunction);} 2248 } 2249 @Override 2250 public V computeIfPresent(K key, 2251 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 2252 synchronized (mutex) {return m.computeIfPresent(key, remappingFunction);} 2253 } 2254 @Override 2255 public V compute(K key, 2256 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 2257 synchronized (mutex) {return m.compute(key, remappingFunction);} 2258 } 2259 @Override 2260 public V merge(K key, V value, 2261 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 2262 synchronized (mutex) {return m.merge(key, value, remappingFunction);} 2263 } 2264 2265 private void writeObject(ObjectOutputStream s) throws IOException { 2266 synchronized (mutex) {s.defaultWriteObject();} 2267 } 2268 } 2269 2270 /** 2271 * Returns a synchronized (thread-safe) sorted map backed by the specified 2272 * sorted map. In order to guarantee serial access, it is critical that 2273 * <strong>all</strong> access to the backing sorted map is accomplished 2274 * through the returned sorted map (or its views).<p> 2275 * 2276 * It is imperative that the user manually synchronize on the returned 2277 * sorted map when iterating over any of its collection views, or the 2278 * collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or 2279 * <tt>tailMap</tt> views. 2280 * <pre> 2281 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap()); 2282 * ... 2283 * Set s = m.keySet(); // Needn't be in synchronized block 2284 * ... 2285 * synchronized (m) { // Synchronizing on m, not s! 2286 * Iterator i = s.iterator(); // Must be in synchronized block 2287 * while (i.hasNext()) 2288 * foo(i.next()); 2289 * } 2290 * </pre> 2291 * or: 2292 * <pre> 2293 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap()); 2294 * SortedMap m2 = m.subMap(foo, bar); 2295 * ... 2296 * Set s2 = m2.keySet(); // Needn't be in synchronized block 2297 * ... 2298 * synchronized (m) { // Synchronizing on m, not m2 or s2! 2299 * Iterator i = s.iterator(); // Must be in synchronized block 2300 * while (i.hasNext()) 2301 * foo(i.next()); 2302 * } 2303 * </pre> 2304 * Failure to follow this advice may result in non-deterministic behavior. 2305 * 2306 * <p>The returned sorted map will be serializable if the specified 2307 * sorted map is serializable. 2308 * 2309 * @param m the sorted map to be "wrapped" in a synchronized sorted map. 2310 * @return a synchronized view of the specified sorted map. 2311 */ 2312 public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) { 2313 return new SynchronizedSortedMap<>(m); 2314 } 2315 2316 2317 /** 2318 * @serial include 2319 */ 2320 static class SynchronizedSortedMap<K,V> 2321 extends SynchronizedMap<K,V> 2322 implements SortedMap<K,V> 2323 { 2324 private static final long serialVersionUID = -8798146769416483793L; 2325 2326 private final SortedMap<K,V> sm; 2327 2328 SynchronizedSortedMap(SortedMap<K,V> m) { 2329 super(m); 2330 sm = m; 2331 } 2332 SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) { 2333 super(m, mutex); 2334 sm = m; 2335 } 2336 2337 public Comparator<? super K> comparator() { 2338 synchronized (mutex) {return sm.comparator();} 2339 } 2340 2341 public SortedMap<K,V> subMap(K fromKey, K toKey) { 2342 synchronized (mutex) { 2343 return new SynchronizedSortedMap<>( 2344 sm.subMap(fromKey, toKey), mutex); 2345 } 2346 } 2347 public SortedMap<K,V> headMap(K toKey) { 2348 synchronized (mutex) { 2349 return new SynchronizedSortedMap<>(sm.headMap(toKey), mutex); 2350 } 2351 } 2352 public SortedMap<K,V> tailMap(K fromKey) { 2353 synchronized (mutex) { 2354 return new SynchronizedSortedMap<>(sm.tailMap(fromKey),mutex); 2355 } 2356 } 2357 2358 public K firstKey() { 2359 synchronized (mutex) {return sm.firstKey();} 2360 } 2361 public K lastKey() { 2362 synchronized (mutex) {return sm.lastKey();} 2363 } 2364 } 2365 2366 // Dynamically typesafe collection wrappers 2367 2368 /** 2369 * Returns a dynamically typesafe view of the specified collection. 2370 * Any attempt to insert an element of the wrong type will result in an 2371 * immediate {@link ClassCastException}. Assuming a collection 2372 * contains no incorrectly typed elements prior to the time a 2373 * dynamically typesafe view is generated, and that all subsequent 2374 * access to the collection takes place through the view, it is 2375 * <i>guaranteed</i> that the collection cannot contain an incorrectly 2376 * typed element. 2377 * 2378 * <p>The generics mechanism in the language provides compile-time 2379 * (static) type checking, but it is possible to defeat this mechanism 2380 * with unchecked casts. Usually this is not a problem, as the compiler 2381 * issues warnings on all such unchecked operations. There are, however, 2382 * times when static type checking alone is not sufficient. For example, 2383 * suppose a collection is passed to a third-party library and it is 2384 * imperative that the library code not corrupt the collection by 2385 * inserting an element of the wrong type. 2386 * 2387 * <p>Another use of dynamically typesafe views is debugging. Suppose a 2388 * program fails with a {@code ClassCastException}, indicating that an 2389 * incorrectly typed element was put into a parameterized collection. 2390 * Unfortunately, the exception can occur at any time after the erroneous 2391 * element is inserted, so it typically provides little or no information 2392 * as to the real source of the problem. If the problem is reproducible, 2393 * one can quickly determine its source by temporarily modifying the 2394 * program to wrap the collection with a dynamically typesafe view. 2395 * For example, this declaration: 2396 * <pre> {@code 2397 * Collection<String> c = new HashSet<String>(); 2398 * }</pre> 2399 * may be replaced temporarily by this one: 2400 * <pre> {@code 2401 * Collection<String> c = Collections.checkedCollection( 2402 * new HashSet<String>(), String.class); 2403 * }</pre> 2404 * Running the program again will cause it to fail at the point where 2405 * an incorrectly typed element is inserted into the collection, clearly 2406 * identifying the source of the problem. Once the problem is fixed, the 2407 * modified declaration may be reverted back to the original. 2408 * 2409 * <p>The returned collection does <i>not</i> pass the hashCode and equals 2410 * operations through to the backing collection, but relies on 2411 * {@code Object}'s {@code equals} and {@code hashCode} methods. This 2412 * is necessary to preserve the contracts of these operations in the case 2413 * that the backing collection is a set or a list. 2414 * 2415 * <p>The returned collection will be serializable if the specified 2416 * collection is serializable. 2417 * 2418 * <p>Since {@code null} is considered to be a value of any reference 2419 * type, the returned collection permits insertion of null elements 2420 * whenever the backing collection does. 2421 * 2422 * @param c the collection for which a dynamically typesafe view is to be 2423 * returned 2424 * @param type the type of element that {@code c} is permitted to hold 2425 * @return a dynamically typesafe view of the specified collection 2426 * @since 1.5 2427 */ 2428 public static <E> Collection<E> checkedCollection(Collection<E> c, 2429 Class<E> type) { 2430 return new CheckedCollection<>(c, type); 2431 } 2432 2433 @SuppressWarnings("unchecked") 2434 static <T> T[] zeroLengthArray(Class<T> type) { 2435 return (T[]) Array.newInstance(type, 0); 2436 } 2437 2438 /** 2439 * @serial include 2440 */ 2441 static class CheckedCollection<E> implements Collection<E>, Serializable { 2442 private static final long serialVersionUID = 1578914078182001775L; 2443 2444 final Collection<E> c; 2445 final Class<E> type; 2446 2447 void typeCheck(Object o) { 2448 if (o != null && !type.isInstance(o)) 2449 throw new ClassCastException(badElementMsg(o)); 2450 } 2451 2452 private String badElementMsg(Object o) { 2453 return "Attempt to insert " + o.getClass() + 2454 " element into collection with element type " + type; 2455 } 2456 2457 CheckedCollection(Collection<E> c, Class<E> type) { 2458 if (c==null || type == null) 2459 throw new NullPointerException(); 2460 this.c = c; 2461 this.type = type; 2462 } 2463 2464 public int size() { return c.size(); } 2465 public boolean isEmpty() { return c.isEmpty(); } 2466 public boolean contains(Object o) { return c.contains(o); } 2467 public Object[] toArray() { return c.toArray(); } 2468 public <T> T[] toArray(T[] a) { return c.toArray(a); } 2469 public String toString() { return c.toString(); } 2470 public boolean remove(Object o) { return c.remove(o); } 2471 public void clear() { c.clear(); } 2472 2473 public boolean containsAll(Collection<?> coll) { 2474 return c.containsAll(coll); 2475 } 2476 public boolean removeAll(Collection<?> coll) { 2477 return c.removeAll(coll); 2478 } 2479 public boolean retainAll(Collection<?> coll) { 2480 return c.retainAll(coll); 2481 } 2482 2483 public Iterator<E> iterator() { 2484 // JDK-6363904 - unwrapped iterator could be typecast to 2485 // ListIterator with unsafe set() 2486 final Iterator<E> it = c.iterator(); 2487 return new Iterator<E>() { 2488 public boolean hasNext() { return it.hasNext(); } 2489 public E next() { return it.next(); } 2490 public void remove() { it.remove(); }}; 2491 } 2492 2493 public boolean add(E e) { 2494 typeCheck(e); 2495 return c.add(e); 2496 } 2497 2498 private E[] zeroLengthElementArray = null; // Lazily initialized 2499 2500 private E[] zeroLengthElementArray() { 2501 return zeroLengthElementArray != null ? zeroLengthElementArray : 2502 (zeroLengthElementArray = zeroLengthArray(type)); 2503 } 2504 2505 @SuppressWarnings("unchecked") 2506 Collection<E> checkedCopyOf(Collection<? extends E> coll) { 2507 Object[] a = null; 2508 try { 2509 E[] z = zeroLengthElementArray(); 2510 a = coll.toArray(z); 2511 // Defend against coll violating the toArray contract 2512 if (a.getClass() != z.getClass()) 2513 a = Arrays.copyOf(a, a.length, z.getClass()); 2514 } catch (ArrayStoreException ignore) { 2515 // To get better and consistent diagnostics, 2516 // we call typeCheck explicitly on each element. 2517 // We call clone() to defend against coll retaining a 2518 // reference to the returned array and storing a bad 2519 // element into it after it has been type checked. 2520 a = coll.toArray().clone(); 2521 for (Object o : a) 2522 typeCheck(o); 2523 } 2524 // A slight abuse of the type system, but safe here. 2525 return (Collection<E>) Arrays.asList(a); 2526 } 2527 2528 public boolean addAll(Collection<? extends E> coll) { 2529 // Doing things this way insulates us from concurrent changes 2530 // in the contents of coll and provides all-or-nothing 2531 // semantics (which we wouldn't get if we type-checked each 2532 // element as we added it) 2533 return c.addAll(checkedCopyOf(coll)); 2534 } 2535 2536 @Override 2537 public void forEach(Consumer<? super E> action) { 2538 c.forEach(action); 2539 } 2540 @Override 2541 public boolean removeIf(Predicate<? super E> filter) { 2542 return c.removeIf(filter); 2543 } 2544 } 2545 2546 /** 2547 * Returns a dynamically typesafe view of the specified queue. 2548 * Any attempt to insert an element of the wrong type will result in 2549 * an immediate {@link ClassCastException}. Assuming a queue contains 2550 * no incorrectly typed elements prior to the time a dynamically typesafe 2551 * view is generated, and that all subsequent access to the queue 2552 * takes place through the view, it is <i>guaranteed</i> that the 2553 * queue cannot contain an incorrectly typed element. 2554 * 2555 * <p>A discussion of the use of dynamically typesafe views may be 2556 * found in the documentation for the {@link #checkedCollection 2557 * checkedCollection} method. 2558 * 2559 * <p>The returned queue will be serializable if the specified queue 2560 * is serializable. 2561 * 2562 * <p>Since {@code null} is considered to be a value of any reference 2563 * type, the returned queue permits insertion of {@code null} elements 2564 * whenever the backing queue does. 2565 * 2566 * @param queue the queue for which a dynamically typesafe view is to be 2567 * returned 2568 * @param type the type of element that {@code queue} is permitted to hold 2569 * @return a dynamically typesafe view of the specified queue 2570 * @since 1.8 2571 */ 2572 public static <E> Queue<E> checkedQueue(Queue<E> queue, Class<E> type) { 2573 return new CheckedQueue<>(queue, type); 2574 } 2575 2576 /** 2577 * @serial include 2578 */ 2579 static class CheckedQueue<E> 2580 extends CheckedCollection<E> 2581 implements Queue<E>, Serializable 2582 { 2583 private static final long serialVersionUID = 1433151992604707767L; 2584 final Queue<E> queue; 2585 2586 CheckedQueue(Queue<E> queue, Class<E> elementType) { 2587 super(queue, elementType); 2588 this.queue = queue; 2589 } 2590 2591 public E element() {return queue.element();} 2592 public boolean equals(Object o) {return o == this || c.equals(o);} 2593 public int hashCode() {return c.hashCode();} 2594 public E peek() {return queue.peek();} 2595 public E poll() {return queue.poll();} 2596 public E remove() {return queue.remove();} 2597 2598 public boolean offer(E e) { 2599 typeCheck(e); 2600 return add(e); 2601 } 2602 } 2603 2604 /** 2605 * Returns a dynamically typesafe view of the specified set. 2606 * Any attempt to insert an element of the wrong type will result in 2607 * an immediate {@link ClassCastException}. Assuming a set contains 2608 * no incorrectly typed elements prior to the time a dynamically typesafe 2609 * view is generated, and that all subsequent access to the set 2610 * takes place through the view, it is <i>guaranteed</i> that the 2611 * set cannot contain an incorrectly typed element. 2612 * 2613 * <p>A discussion of the use of dynamically typesafe views may be 2614 * found in the documentation for the {@link #checkedCollection 2615 * checkedCollection} method. 2616 * 2617 * <p>The returned set will be serializable if the specified set is 2618 * serializable. 2619 * 2620 * <p>Since {@code null} is considered to be a value of any reference 2621 * type, the returned set permits insertion of null elements whenever 2622 * the backing set does. 2623 * 2624 * @param s the set for which a dynamically typesafe view is to be 2625 * returned 2626 * @param type the type of element that {@code s} is permitted to hold 2627 * @return a dynamically typesafe view of the specified set 2628 * @since 1.5 2629 */ 2630 public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) { 2631 return new CheckedSet<>(s, type); 2632 } 2633 2634 /** 2635 * @serial include 2636 */ 2637 static class CheckedSet<E> extends CheckedCollection<E> 2638 implements Set<E>, Serializable 2639 { 2640 private static final long serialVersionUID = 4694047833775013803L; 2641 2642 CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); } 2643 2644 public boolean equals(Object o) { return o == this || c.equals(o); } 2645 public int hashCode() { return c.hashCode(); } 2646 } 2647 2648 /** 2649 * Returns a dynamically typesafe view of the specified sorted set. 2650 * Any attempt to insert an element of the wrong type will result in an 2651 * immediate {@link ClassCastException}. Assuming a sorted set 2652 * contains no incorrectly typed elements prior to the time a 2653 * dynamically typesafe view is generated, and that all subsequent 2654 * access to the sorted set takes place through the view, it is 2655 * <i>guaranteed</i> that the sorted set cannot contain an incorrectly 2656 * typed element. 2657 * 2658 * <p>A discussion of the use of dynamically typesafe views may be 2659 * found in the documentation for the {@link #checkedCollection 2660 * checkedCollection} method. 2661 * 2662 * <p>The returned sorted set will be serializable if the specified sorted 2663 * set is serializable. 2664 * 2665 * <p>Since {@code null} is considered to be a value of any reference 2666 * type, the returned sorted set permits insertion of null elements 2667 * whenever the backing sorted set does. 2668 * 2669 * @param s the sorted set for which a dynamically typesafe view is to be 2670 * returned 2671 * @param type the type of element that {@code s} is permitted to hold 2672 * @return a dynamically typesafe view of the specified sorted set 2673 * @since 1.5 2674 */ 2675 public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s, 2676 Class<E> type) { 2677 return new CheckedSortedSet<>(s, type); 2678 } 2679 2680 /** 2681 * @serial include 2682 */ 2683 static class CheckedSortedSet<E> extends CheckedSet<E> 2684 implements SortedSet<E>, Serializable 2685 { 2686 private static final long serialVersionUID = 1599911165492914959L; 2687 private final SortedSet<E> ss; 2688 2689 CheckedSortedSet(SortedSet<E> s, Class<E> type) { 2690 super(s, type); 2691 ss = s; 2692 } 2693 2694 public Comparator<? super E> comparator() { return ss.comparator(); } 2695 public E first() { return ss.first(); } 2696 public E last() { return ss.last(); } 2697 2698 public SortedSet<E> subSet(E fromElement, E toElement) { 2699 return checkedSortedSet(ss.subSet(fromElement,toElement), type); 2700 } 2701 public SortedSet<E> headSet(E toElement) { 2702 return checkedSortedSet(ss.headSet(toElement), type); 2703 } 2704 public SortedSet<E> tailSet(E fromElement) { 2705 return checkedSortedSet(ss.tailSet(fromElement), type); 2706 } 2707 } 2708 2709 /** 2710 * Returns a dynamically typesafe view of the specified list. 2711 * Any attempt to insert an element of the wrong type will result in 2712 * an immediate {@link ClassCastException}. Assuming a list contains 2713 * no incorrectly typed elements prior to the time a dynamically typesafe 2714 * view is generated, and that all subsequent access to the list 2715 * takes place through the view, it is <i>guaranteed</i> that the 2716 * list cannot contain an incorrectly typed element. 2717 * 2718 * <p>A discussion of the use of dynamically typesafe views may be 2719 * found in the documentation for the {@link #checkedCollection 2720 * checkedCollection} method. 2721 * 2722 * <p>The returned list will be serializable if the specified list 2723 * is serializable. 2724 * 2725 * <p>Since {@code null} is considered to be a value of any reference 2726 * type, the returned list permits insertion of null elements whenever 2727 * the backing list does. 2728 * 2729 * @param list the list for which a dynamically typesafe view is to be 2730 * returned 2731 * @param type the type of element that {@code list} is permitted to hold 2732 * @return a dynamically typesafe view of the specified list 2733 * @since 1.5 2734 */ 2735 public static <E> List<E> checkedList(List<E> list, Class<E> type) { 2736 return (list instanceof RandomAccess ? 2737 new CheckedRandomAccessList<>(list, type) : 2738 new CheckedList<>(list, type)); 2739 } 2740 2741 /** 2742 * @serial include 2743 */ 2744 static class CheckedList<E> 2745 extends CheckedCollection<E> 2746 implements List<E> 2747 { 2748 private static final long serialVersionUID = 65247728283967356L; 2749 final List<E> list; 2750 2751 CheckedList(List<E> list, Class<E> type) { 2752 super(list, type); 2753 this.list = list; 2754 } 2755 2756 public boolean equals(Object o) { return o == this || list.equals(o); } 2757 public int hashCode() { return list.hashCode(); } 2758 public E get(int index) { return list.get(index); } 2759 public E remove(int index) { return list.remove(index); } 2760 public int indexOf(Object o) { return list.indexOf(o); } 2761 public int lastIndexOf(Object o) { return list.lastIndexOf(o); } 2762 2763 public E set(int index, E element) { 2764 typeCheck(element); 2765 return list.set(index, element); 2766 } 2767 2768 public void add(int index, E element) { 2769 typeCheck(element); 2770 list.add(index, element); 2771 } 2772 2773 public boolean addAll(int index, Collection<? extends E> c) { 2774 return list.addAll(index, checkedCopyOf(c)); 2775 } 2776 public ListIterator<E> listIterator() { return listIterator(0); } 2777 2778 public ListIterator<E> listIterator(final int index) { 2779 final ListIterator<E> i = list.listIterator(index); 2780 2781 return new ListIterator<E>() { 2782 public boolean hasNext() { return i.hasNext(); } 2783 public E next() { return i.next(); } 2784 public boolean hasPrevious() { return i.hasPrevious(); } 2785 public E previous() { return i.previous(); } 2786 public int nextIndex() { return i.nextIndex(); } 2787 public int previousIndex() { return i.previousIndex(); } 2788 public void remove() { i.remove(); } 2789 2790 public void set(E e) { 2791 typeCheck(e); 2792 i.set(e); 2793 } 2794 2795 public void add(E e) { 2796 typeCheck(e); 2797 i.add(e); 2798 } 2799 }; 2800 } 2801 2802 public List<E> subList(int fromIndex, int toIndex) { 2803 return new CheckedList<>(list.subList(fromIndex, toIndex), type); 2804 } 2805 2806 @Override 2807 public void replaceAll(UnaryOperator<E> operator) { 2808 list.replaceAll(operator); 2809 } 2810 @Override 2811 public void sort(Comparator<? super E> c) { 2812 list.sort(c); 2813 } 2814 } 2815 2816 /** 2817 * @serial include 2818 */ 2819 static class CheckedRandomAccessList<E> extends CheckedList<E> 2820 implements RandomAccess 2821 { 2822 private static final long serialVersionUID = 1638200125423088369L; 2823 2824 CheckedRandomAccessList(List<E> list, Class<E> type) { 2825 super(list, type); 2826 } 2827 2828 public List<E> subList(int fromIndex, int toIndex) { 2829 return new CheckedRandomAccessList<>( 2830 list.subList(fromIndex, toIndex), type); 2831 } 2832 } 2833 2834 /** 2835 * Returns a dynamically typesafe view of the specified map. 2836 * Any attempt to insert a mapping whose key or value have the wrong 2837 * type will result in an immediate {@link ClassCastException}. 2838 * Similarly, any attempt to modify the value currently associated with 2839 * a key will result in an immediate {@link ClassCastException}, 2840 * whether the modification is attempted directly through the map 2841 * itself, or through a {@link Map.Entry} instance obtained from the 2842 * map's {@link Map#entrySet() entry set} view. 2843 * 2844 * <p>Assuming a map contains no incorrectly typed keys or values 2845 * prior to the time a dynamically typesafe view is generated, and 2846 * that all subsequent access to the map takes place through the view 2847 * (or one of its collection views), it is <i>guaranteed</i> that the 2848 * map cannot contain an incorrectly typed key or value. 2849 * 2850 * <p>A discussion of the use of dynamically typesafe views may be 2851 * found in the documentation for the {@link #checkedCollection 2852 * checkedCollection} method. 2853 * 2854 * <p>The returned map will be serializable if the specified map is 2855 * serializable. 2856 * 2857 * <p>Since {@code null} is considered to be a value of any reference 2858 * type, the returned map permits insertion of null keys or values 2859 * whenever the backing map does. 2860 * 2861 * @param m the map for which a dynamically typesafe view is to be 2862 * returned 2863 * @param keyType the type of key that {@code m} is permitted to hold 2864 * @param valueType the type of value that {@code m} is permitted to hold 2865 * @return a dynamically typesafe view of the specified map 2866 * @since 1.5 2867 */ 2868 public static <K, V> Map<K, V> checkedMap(Map<K, V> m, 2869 Class<K> keyType, 2870 Class<V> valueType) { 2871 return new CheckedMap<>(m, keyType, valueType); 2872 } 2873 2874 2875 /** 2876 * @serial include 2877 */ 2878 private static class CheckedMap<K,V> 2879 implements Map<K,V>, Serializable 2880 { 2881 private static final long serialVersionUID = 5742860141034234728L; 2882 2883 private final Map<K, V> m; 2884 final Class<K> keyType; 2885 final Class<V> valueType; 2886 2887 private void typeCheck(Object key, Object value) { 2888 if (key != null && !keyType.isInstance(key)) 2889 throw new ClassCastException(badKeyMsg(key)); 2890 2891 if (value != null && !valueType.isInstance(value)) 2892 throw new ClassCastException(badValueMsg(value)); 2893 } 2894 2895 private BiFunction<? super K, ? super V, ? extends V> typeCheck( 2896 BiFunction<? super K, ? super V, ? extends V> func) { 2897 Objects.requireNonNull(func); 2898 return (k, v) -> { 2899 V newValue = func.apply(k, v); 2900 typeCheck(k, newValue); 2901 return newValue; 2902 }; 2903 } 2904 2905 private String badKeyMsg(Object key) { 2906 return "Attempt to insert " + key.getClass() + 2907 " key into map with key type " + keyType; 2908 } 2909 2910 private String badValueMsg(Object value) { 2911 return "Attempt to insert " + value.getClass() + 2912 " value into map with value type " + valueType; 2913 } 2914 2915 CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) { 2916 if (m == null || keyType == null || valueType == null) 2917 throw new NullPointerException(); 2918 this.m = m; 2919 this.keyType = keyType; 2920 this.valueType = valueType; 2921 } 2922 2923 public int size() { return m.size(); } 2924 public boolean isEmpty() { return m.isEmpty(); } 2925 public boolean containsKey(Object key) { return m.containsKey(key); } 2926 public boolean containsValue(Object v) { return m.containsValue(v); } 2927 public V get(Object key) { return m.get(key); } 2928 public V remove(Object key) { return m.remove(key); } 2929 public void clear() { m.clear(); } 2930 public Set<K> keySet() { return m.keySet(); } 2931 public Collection<V> values() { return m.values(); } 2932 public boolean equals(Object o) { return o == this || m.equals(o); } 2933 public int hashCode() { return m.hashCode(); } 2934 public String toString() { return m.toString(); } 2935 2936 public V put(K key, V value) { 2937 typeCheck(key, value); 2938 return m.put(key, value); 2939 } 2940 2941 @SuppressWarnings("unchecked") 2942 public void putAll(Map<? extends K, ? extends V> t) { 2943 // Satisfy the following goals: 2944 // - good diagnostics in case of type mismatch 2945 // - all-or-nothing semantics 2946 // - protection from malicious t 2947 // - correct behavior if t is a concurrent map 2948 Object[] entries = t.entrySet().toArray(); 2949 List<Map.Entry<K,V>> checked = new ArrayList<>(entries.length); 2950 for (Object o : entries) { 2951 Map.Entry<?,?> e = (Map.Entry<?,?>) o; 2952 Object k = e.getKey(); 2953 Object v = e.getValue(); 2954 typeCheck(k, v); 2955 checked.add( 2956 new AbstractMap.SimpleImmutableEntry<>((K)k, (V)v)); 2957 } 2958 for (Map.Entry<K,V> e : checked) 2959 m.put(e.getKey(), e.getValue()); 2960 } 2961 2962 private transient Set<Map.Entry<K,V>> entrySet = null; 2963 2964 public Set<Map.Entry<K,V>> entrySet() { 2965 if (entrySet==null) 2966 entrySet = new CheckedEntrySet<>(m.entrySet(), valueType); 2967 return entrySet; 2968 } 2969 2970 // Override default methods in Map 2971 @Override 2972 public void forEach(BiConsumer<? super K, ? super V> action) { 2973 m.forEach(action); 2974 } 2975 2976 @Override 2977 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 2978 m.replaceAll(typeCheck(function)); 2979 } 2980 2981 @Override 2982 public V putIfAbsent(K key, V value) { 2983 typeCheck(key, value); 2984 return m.putIfAbsent(key, value); 2985 } 2986 2987 @Override 2988 public boolean remove(Object key, Object value) { 2989 return m.remove(key, value); 2990 } 2991 2992 @Override 2993 public boolean replace(K key, V oldValue, V newValue) { 2994 typeCheck(key, newValue); 2995 return m.replace(key, oldValue, newValue); 2996 } 2997 2998 @Override 2999 public V replace(K key, V value) { 3000 typeCheck(key, value); 3001 return m.replace(key, value); 3002 } 3003 3004 @Override 3005 public V computeIfAbsent(K key, 3006 Function<? super K, ? extends V> mappingFunction) { 3007 Objects.requireNonNull(mappingFunction); 3008 return m.computeIfAbsent(key, k -> { 3009 V value = mappingFunction.apply(k); 3010 typeCheck(k, value); 3011 return value; 3012 }); 3013 } 3014 3015 @Override 3016 public V computeIfPresent(K key, 3017 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 3018 return m.computeIfPresent(key, typeCheck(remappingFunction)); 3019 } 3020 3021 @Override 3022 public V compute(K key, 3023 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 3024 return m.compute(key, typeCheck(remappingFunction)); 3025 } 3026 3027 @Override 3028 public V merge(K key, V value, 3029 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 3030 Objects.requireNonNull(remappingFunction); 3031 return m.merge(key, value, (v1, v2) -> { 3032 V newValue = remappingFunction.apply(v1, v2); 3033 typeCheck(null, newValue); 3034 return newValue; 3035 }); 3036 } 3037 3038 /** 3039 * We need this class in addition to CheckedSet as Map.Entry permits 3040 * modification of the backing Map via the setValue operation. This 3041 * class is subtle: there are many possible attacks that must be 3042 * thwarted. 3043 * 3044 * @serial exclude 3045 */ 3046 static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> { 3047 private final Set<Map.Entry<K,V>> s; 3048 private final Class<V> valueType; 3049 3050 CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) { 3051 this.s = s; 3052 this.valueType = valueType; 3053 } 3054 3055 public int size() { return s.size(); } 3056 public boolean isEmpty() { return s.isEmpty(); } 3057 public String toString() { return s.toString(); } 3058 public int hashCode() { return s.hashCode(); } 3059 public void clear() { s.clear(); } 3060 3061 public boolean add(Map.Entry<K, V> e) { 3062 throw new UnsupportedOperationException(); 3063 } 3064 public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) { 3065 throw new UnsupportedOperationException(); 3066 } 3067 3068 public Iterator<Map.Entry<K,V>> iterator() { 3069 final Iterator<Map.Entry<K, V>> i = s.iterator(); 3070 final Class<V> valueType = this.valueType; 3071 3072 return new Iterator<Map.Entry<K,V>>() { 3073 public boolean hasNext() { return i.hasNext(); } 3074 public void remove() { i.remove(); } 3075 3076 public Map.Entry<K,V> next() { 3077 return checkedEntry(i.next(), valueType); 3078 } 3079 }; 3080 } 3081 3082 @SuppressWarnings("unchecked") 3083 public Object[] toArray() { 3084 Object[] source = s.toArray(); 3085 3086 /* 3087 * Ensure that we don't get an ArrayStoreException even if 3088 * s.toArray returns an array of something other than Object 3089 */ 3090 Object[] dest = (CheckedEntry.class.isInstance( 3091 source.getClass().getComponentType()) ? source : 3092 new Object[source.length]); 3093 3094 for (int i = 0; i < source.length; i++) 3095 dest[i] = checkedEntry((Map.Entry<K,V>)source[i], 3096 valueType); 3097 return dest; 3098 } 3099 3100 @SuppressWarnings("unchecked") 3101 public <T> T[] toArray(T[] a) { 3102 // We don't pass a to s.toArray, to avoid window of 3103 // vulnerability wherein an unscrupulous multithreaded client 3104 // could get his hands on raw (unwrapped) Entries from s. 3105 T[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0)); 3106 3107 for (int i=0; i<arr.length; i++) 3108 arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i], 3109 valueType); 3110 if (arr.length > a.length) 3111 return arr; 3112 3113 System.arraycopy(arr, 0, a, 0, arr.length); 3114 if (a.length > arr.length) 3115 a[arr.length] = null; 3116 return a; 3117 } 3118 3119 /** 3120 * This method is overridden to protect the backing set against 3121 * an object with a nefarious equals function that senses 3122 * that the equality-candidate is Map.Entry and calls its 3123 * setValue method. 3124 */ 3125 public boolean contains(Object o) { 3126 if (!(o instanceof Map.Entry)) 3127 return false; 3128 Map.Entry<?,?> e = (Map.Entry<?,?>) o; 3129 return s.contains( 3130 (e instanceof CheckedEntry) ? e : checkedEntry(e, valueType)); 3131 } 3132 3133 /** 3134 * The bulk collection methods are overridden to protect 3135 * against an unscrupulous collection whose contains(Object o) 3136 * method senses when o is a Map.Entry, and calls o.setValue. 3137 */ 3138 public boolean containsAll(Collection<?> c) { 3139 for (Object o : c) 3140 if (!contains(o)) // Invokes safe contains() above 3141 return false; 3142 return true; 3143 } 3144 3145 public boolean remove(Object o) { 3146 if (!(o instanceof Map.Entry)) 3147 return false; 3148 return s.remove(new AbstractMap.SimpleImmutableEntry 3149 <>((Map.Entry<?,?>)o)); 3150 } 3151 3152 public boolean removeAll(Collection<?> c) { 3153 return batchRemove(c, false); 3154 } 3155 public boolean retainAll(Collection<?> c) { 3156 return batchRemove(c, true); 3157 } 3158 private boolean batchRemove(Collection<?> c, boolean complement) { 3159 boolean modified = false; 3160 Iterator<Map.Entry<K,V>> it = iterator(); 3161 while (it.hasNext()) { 3162 if (c.contains(it.next()) != complement) { 3163 it.remove(); 3164 modified = true; 3165 } 3166 } 3167 return modified; 3168 } 3169 3170 public boolean equals(Object o) { 3171 if (o == this) 3172 return true; 3173 if (!(o instanceof Set)) 3174 return false; 3175 Set<?> that = (Set<?>) o; 3176 return that.size() == s.size() 3177 && containsAll(that); // Invokes safe containsAll() above 3178 } 3179 3180 static <K,V,T> CheckedEntry<K,V,T> checkedEntry(Map.Entry<K,V> e, 3181 Class<T> valueType) { 3182 return new CheckedEntry<>(e, valueType); 3183 } 3184 3185 /** 3186 * This "wrapper class" serves two purposes: it prevents 3187 * the client from modifying the backing Map, by short-circuiting 3188 * the setValue method, and it protects the backing Map against 3189 * an ill-behaved Map.Entry that attempts to modify another 3190 * Map.Entry when asked to perform an equality check. 3191 */ 3192 private static class CheckedEntry<K,V,T> implements Map.Entry<K,V> { 3193 private final Map.Entry<K, V> e; 3194 private final Class<T> valueType; 3195 3196 CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) { 3197 this.e = e; 3198 this.valueType = valueType; 3199 } 3200 3201 public K getKey() { return e.getKey(); } 3202 public V getValue() { return e.getValue(); } 3203 public int hashCode() { return e.hashCode(); } 3204 public String toString() { return e.toString(); } 3205 3206 public V setValue(V value) { 3207 if (value != null && !valueType.isInstance(value)) 3208 throw new ClassCastException(badValueMsg(value)); 3209 return e.setValue(value); 3210 } 3211 3212 private String badValueMsg(Object value) { 3213 return "Attempt to insert " + value.getClass() + 3214 " value into map with value type " + valueType; 3215 } 3216 3217 public boolean equals(Object o) { 3218 if (o == this) 3219 return true; 3220 if (!(o instanceof Map.Entry)) 3221 return false; 3222 return e.equals(new AbstractMap.SimpleImmutableEntry 3223 <>((Map.Entry<?,?>)o)); 3224 } 3225 } 3226 } 3227 } 3228 3229 /** 3230 * Returns a dynamically typesafe view of the specified sorted map. 3231 * Any attempt to insert a mapping whose key or value have the wrong 3232 * type will result in an immediate {@link ClassCastException}. 3233 * Similarly, any attempt to modify the value currently associated with 3234 * a key will result in an immediate {@link ClassCastException}, 3235 * whether the modification is attempted directly through the map 3236 * itself, or through a {@link Map.Entry} instance obtained from the 3237 * map's {@link Map#entrySet() entry set} view. 3238 * 3239 * <p>Assuming a map contains no incorrectly typed keys or values 3240 * prior to the time a dynamically typesafe view is generated, and 3241 * that all subsequent access to the map takes place through the view 3242 * (or one of its collection views), it is <i>guaranteed</i> that the 3243 * map cannot contain an incorrectly typed key or value. 3244 * 3245 * <p>A discussion of the use of dynamically typesafe views may be 3246 * found in the documentation for the {@link #checkedCollection 3247 * checkedCollection} method. 3248 * 3249 * <p>The returned map will be serializable if the specified map is 3250 * serializable. 3251 * 3252 * <p>Since {@code null} is considered to be a value of any reference 3253 * type, the returned map permits insertion of null keys or values 3254 * whenever the backing map does. 3255 * 3256 * @param m the map for which a dynamically typesafe view is to be 3257 * returned 3258 * @param keyType the type of key that {@code m} is permitted to hold 3259 * @param valueType the type of value that {@code m} is permitted to hold 3260 * @return a dynamically typesafe view of the specified map 3261 * @since 1.5 3262 */ 3263 public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m, 3264 Class<K> keyType, 3265 Class<V> valueType) { 3266 return new CheckedSortedMap<>(m, keyType, valueType); 3267 } 3268 3269 /** 3270 * @serial include 3271 */ 3272 static class CheckedSortedMap<K,V> extends CheckedMap<K,V> 3273 implements SortedMap<K,V>, Serializable 3274 { 3275 private static final long serialVersionUID = 1599671320688067438L; 3276 3277 private final SortedMap<K, V> sm; 3278 3279 CheckedSortedMap(SortedMap<K, V> m, 3280 Class<K> keyType, Class<V> valueType) { 3281 super(m, keyType, valueType); 3282 sm = m; 3283 } 3284 3285 public Comparator<? super K> comparator() { return sm.comparator(); } 3286 public K firstKey() { return sm.firstKey(); } 3287 public K lastKey() { return sm.lastKey(); } 3288 3289 public SortedMap<K,V> subMap(K fromKey, K toKey) { 3290 return checkedSortedMap(sm.subMap(fromKey, toKey), 3291 keyType, valueType); 3292 } 3293 public SortedMap<K,V> headMap(K toKey) { 3294 return checkedSortedMap(sm.headMap(toKey), keyType, valueType); 3295 } 3296 public SortedMap<K,V> tailMap(K fromKey) { 3297 return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType); 3298 } 3299 } 3300 3301 // Empty collections 3302 3303 /** 3304 * Returns an iterator that has no elements. More precisely, 3305 * 3306 * <ul compact> 3307 * 3308 * <li>{@link Iterator#hasNext hasNext} always returns {@code 3309 * false}. 3310 * 3311 * <li>{@link Iterator#next next} always throws {@link 3312 * NoSuchElementException}. 3313 * 3314 * <li>{@link Iterator#remove remove} always throws {@link 3315 * IllegalStateException}. 3316 * 3317 * </ul> 3318 * 3319 * <p>Implementations of this method are permitted, but not 3320 * required, to return the same object from multiple invocations. 3321 * 3322 * @return an empty iterator 3323 * @since 1.7 3324 */ 3325 @SuppressWarnings("unchecked") 3326 public static <T> Iterator<T> emptyIterator() { 3327 return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR; 3328 } 3329 3330 private static class EmptyIterator<E> implements Iterator<E> { 3331 static final EmptyIterator<Object> EMPTY_ITERATOR 3332 = new EmptyIterator<>(); 3333 3334 public boolean hasNext() { return false; } 3335 public E next() { throw new NoSuchElementException(); } 3336 public void remove() { throw new IllegalStateException(); } 3337 } 3338 3339 /** 3340 * Returns a list iterator that has no elements. More precisely, 3341 * 3342 * <ul compact> 3343 * 3344 * <li>{@link Iterator#hasNext hasNext} and {@link 3345 * ListIterator#hasPrevious hasPrevious} always return {@code 3346 * false}. 3347 * 3348 * <li>{@link Iterator#next next} and {@link ListIterator#previous 3349 * previous} always throw {@link NoSuchElementException}. 3350 * 3351 * <li>{@link Iterator#remove remove} and {@link ListIterator#set 3352 * set} always throw {@link IllegalStateException}. 3353 * 3354 * <li>{@link ListIterator#add add} always throws {@link 3355 * UnsupportedOperationException}. 3356 * 3357 * <li>{@link ListIterator#nextIndex nextIndex} always returns 3358 * {@code 0} . 3359 * 3360 * <li>{@link ListIterator#previousIndex previousIndex} always 3361 * returns {@code -1}. 3362 * 3363 * </ul> 3364 * 3365 * <p>Implementations of this method are permitted, but not 3366 * required, to return the same object from multiple invocations. 3367 * 3368 * @return an empty list iterator 3369 * @since 1.7 3370 */ 3371 @SuppressWarnings("unchecked") 3372 public static <T> ListIterator<T> emptyListIterator() { 3373 return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR; 3374 } 3375 3376 private static class EmptyListIterator<E> 3377 extends EmptyIterator<E> 3378 implements ListIterator<E> 3379 { 3380 static final EmptyListIterator<Object> EMPTY_ITERATOR 3381 = new EmptyListIterator<>(); 3382 3383 public boolean hasPrevious() { return false; } 3384 public E previous() { throw new NoSuchElementException(); } 3385 public int nextIndex() { return 0; } 3386 public int previousIndex() { return -1; } 3387 public void set(E e) { throw new IllegalStateException(); } 3388 public void add(E e) { throw new UnsupportedOperationException(); } 3389 } 3390 3391 /** 3392 * Returns an enumeration that has no elements. More precisely, 3393 * 3394 * <ul compact> 3395 * 3396 * <li>{@link Enumeration#hasMoreElements hasMoreElements} always 3397 * returns {@code false}. 3398 * 3399 * <li> {@link Enumeration#nextElement nextElement} always throws 3400 * {@link NoSuchElementException}. 3401 * 3402 * </ul> 3403 * 3404 * <p>Implementations of this method are permitted, but not 3405 * required, to return the same object from multiple invocations. 3406 * 3407 * @return an empty enumeration 3408 * @since 1.7 3409 */ 3410 @SuppressWarnings("unchecked") 3411 public static <T> Enumeration<T> emptyEnumeration() { 3412 return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION; 3413 } 3414 3415 private static class EmptyEnumeration<E> implements Enumeration<E> { 3416 static final EmptyEnumeration<Object> EMPTY_ENUMERATION 3417 = new EmptyEnumeration<>(); 3418 3419 public boolean hasMoreElements() { return false; } 3420 public E nextElement() { throw new NoSuchElementException(); } 3421 } 3422 3423 /** 3424 * The empty set (immutable). This set is serializable. 3425 * 3426 * @see #emptySet() 3427 */ 3428 @SuppressWarnings("rawtypes") 3429 public static final Set EMPTY_SET = new EmptySet<>(); 3430 3431 /** 3432 * Returns the empty set (immutable). This set is serializable. 3433 * Unlike the like-named field, this method is parameterized. 3434 * 3435 * <p>This example illustrates the type-safe way to obtain an empty set: 3436 * <pre> 3437 * Set<String> s = Collections.emptySet(); 3438 * </pre> 3439 * Implementation note: Implementations of this method need not 3440 * create a separate <tt>Set</tt> object for each call. Using this 3441 * method is likely to have comparable cost to using the like-named 3442 * field. (Unlike this method, the field does not provide type safety.) 3443 * 3444 * @see #EMPTY_SET 3445 * @since 1.5 3446 */ 3447 @SuppressWarnings("unchecked") 3448 public static final <T> Set<T> emptySet() { 3449 return (Set<T>) EMPTY_SET; 3450 } 3451 3452 /** 3453 * @serial include 3454 */ 3455 private static class EmptySet<E> 3456 extends AbstractSet<E> 3457 implements Serializable 3458 { 3459 private static final long serialVersionUID = 1582296315990362920L; 3460 3461 public Iterator<E> iterator() { return emptyIterator(); } 3462 3463 public int size() {return 0;} 3464 public boolean isEmpty() {return true;} 3465 3466 public boolean contains(Object obj) {return false;} 3467 public boolean containsAll(Collection<?> c) { return c.isEmpty(); } 3468 3469 public Object[] toArray() { return new Object[0]; } 3470 3471 public <T> T[] toArray(T[] a) { 3472 if (a.length > 0) 3473 a[0] = null; 3474 return a; 3475 } 3476 3477 @Override 3478 public void forEach(Consumer<? super E> action) { 3479 Objects.requireNonNull(action); 3480 } 3481 @Override 3482 public boolean removeIf(Predicate<? super E> filter) { 3483 Objects.requireNonNull(filter); 3484 return false; 3485 } 3486 3487 // Preserves singleton property 3488 private Object readResolve() { 3489 return EMPTY_SET; 3490 } 3491 } 3492 3493 /** 3494 * Returns the empty sorted set (immutable). This set is serializable. 3495 * 3496 * <p>This example illustrates the type-safe way to obtain an empty sorted 3497 * set: 3498 * <pre> 3499 * SortedSet<String> s = Collections.emptySortedSet(); 3500 * </pre> 3501 * Implementation note: Implementations of this method need not 3502 * create a separate <tt>SortedSet</tt> object for each call. 3503 * 3504 * @since 1.8 3505 */ 3506 @SuppressWarnings("unchecked") 3507 public static final <E> SortedSet<E> emptySortedSet() { 3508 return (SortedSet<E>) new EmptySortedSet<>(); 3509 } 3510 3511 /** 3512 * @serial include 3513 */ 3514 private static class EmptySortedSet<E> 3515 extends AbstractSet<E> 3516 implements SortedSet<E>, Serializable 3517 { 3518 private static final long serialVersionUID = 6316515401502265487L; 3519 public Iterator<E> iterator() { return emptyIterator(); } 3520 public int size() {return 0;} 3521 public boolean isEmpty() {return true;} 3522 public boolean contains(Object obj) {return false;} 3523 public boolean containsAll(Collection<?> c) { return c.isEmpty(); } 3524 public Object[] toArray() { return new Object[0]; } 3525 3526 public <E> E[] toArray(E[] a) { 3527 if (a.length > 0) 3528 a[0] = null; 3529 return a; 3530 } 3531 3532 // Preserves singleton property 3533 private Object readResolve() { 3534 return new EmptySortedSet<>(); 3535 } 3536 3537 @Override 3538 public Comparator<? super E> comparator() { 3539 return null; 3540 } 3541 3542 @Override 3543 @SuppressWarnings("unchecked") 3544 public SortedSet<E> subSet(Object fromElement, Object toElement) { 3545 Objects.requireNonNull(fromElement); 3546 Objects.requireNonNull(toElement); 3547 3548 if (!(fromElement instanceof Comparable) || 3549 !(toElement instanceof Comparable)) 3550 { 3551 throw new ClassCastException(); 3552 } 3553 3554 if ((((Comparable)fromElement).compareTo(toElement) >= 0) || 3555 (((Comparable)toElement).compareTo(fromElement) < 0)) 3556 { 3557 throw new IllegalArgumentException(); 3558 } 3559 3560 return emptySortedSet(); 3561 } 3562 3563 @Override 3564 public SortedSet<E> headSet(Object toElement) { 3565 Objects.requireNonNull(toElement); 3566 3567 if (!(toElement instanceof Comparable)) { 3568 throw new ClassCastException(); 3569 } 3570 3571 return emptySortedSet(); 3572 } 3573 3574 @Override 3575 public SortedSet<E> tailSet(Object fromElement) { 3576 Objects.requireNonNull(fromElement); 3577 3578 if (!(fromElement instanceof Comparable)) { 3579 throw new ClassCastException(); 3580 } 3581 3582 return emptySortedSet(); 3583 } 3584 3585 @Override 3586 public E first() { 3587 throw new NoSuchElementException(); 3588 } 3589 3590 @Override 3591 public E last() { 3592 throw new NoSuchElementException(); 3593 } 3594 3595 @Override 3596 public void forEach(Consumer<? super E> action) { 3597 Objects.requireNonNull(action); 3598 } 3599 @Override 3600 public boolean removeIf(Predicate<? super E> filter) { 3601 Objects.requireNonNull(filter); 3602 return false; 3603 } 3604 } 3605 3606 /** 3607 * The empty list (immutable). This list is serializable. 3608 * 3609 * @see #emptyList() 3610 */ 3611 @SuppressWarnings("rawtypes") 3612 public static final List EMPTY_LIST = new EmptyList<>(); 3613 3614 /** 3615 * Returns the empty list (immutable). This list is serializable. 3616 * 3617 * <p>This example illustrates the type-safe way to obtain an empty list: 3618 * <pre> 3619 * List<String> s = Collections.emptyList(); 3620 * </pre> 3621 * Implementation note: Implementations of this method need not 3622 * create a separate <tt>List</tt> object for each call. Using this 3623 * method is likely to have comparable cost to using the like-named 3624 * field. (Unlike this method, the field does not provide type safety.) 3625 * 3626 * @see #EMPTY_LIST 3627 * @since 1.5 3628 */ 3629 @SuppressWarnings("unchecked") 3630 public static final <T> List<T> emptyList() { 3631 return (List<T>) EMPTY_LIST; 3632 } 3633 3634 /** 3635 * @serial include 3636 */ 3637 private static class EmptyList<E> 3638 extends AbstractList<E> 3639 implements RandomAccess, Serializable { 3640 private static final long serialVersionUID = 8842843931221139166L; 3641 3642 public Iterator<E> iterator() { 3643 return emptyIterator(); 3644 } 3645 public ListIterator<E> listIterator() { 3646 return emptyListIterator(); 3647 } 3648 3649 public int size() {return 0;} 3650 public boolean isEmpty() {return true;} 3651 3652 public boolean contains(Object obj) {return false;} 3653 public boolean containsAll(Collection<?> c) { return c.isEmpty(); } 3654 3655 public Object[] toArray() { return new Object[0]; } 3656 3657 public <T> T[] toArray(T[] a) { 3658 if (a.length > 0) 3659 a[0] = null; 3660 return a; 3661 } 3662 3663 public E get(int index) { 3664 throw new IndexOutOfBoundsException("Index: "+index); 3665 } 3666 3667 public boolean equals(Object o) { 3668 return (o instanceof List) && ((List<?>)o).isEmpty(); 3669 } 3670 3671 public int hashCode() { return 1; } 3672 3673 @Override 3674 public void forEach(Consumer<? super E> action) { 3675 Objects.requireNonNull(action); 3676 } 3677 @Override 3678 public boolean removeIf(Predicate<? super E> filter) { 3679 Objects.requireNonNull(filter); 3680 return false; 3681 } 3682 @Override 3683 public void replaceAll(UnaryOperator<E> operator) { 3684 Objects.requireNonNull(operator); 3685 } 3686 @Override 3687 public void sort(Comparator<? super E> c) { 3688 Objects.requireNonNull(c); 3689 } 3690 3691 // Preserves singleton property 3692 private Object readResolve() { 3693 return EMPTY_LIST; 3694 } 3695 } 3696 3697 /** 3698 * The empty map (immutable). This map is serializable. 3699 * 3700 * @see #emptyMap() 3701 * @since 1.3 3702 */ 3703 @SuppressWarnings("rawtypes") 3704 public static final Map EMPTY_MAP = new EmptyMap<>(); 3705 3706 /** 3707 * Returns the empty map (immutable). This map is serializable. 3708 * 3709 * <p>This example illustrates the type-safe way to obtain an empty set: 3710 * <pre> 3711 * Map<String, Date> s = Collections.emptyMap(); 3712 * </pre> 3713 * Implementation note: Implementations of this method need not 3714 * create a separate <tt>Map</tt> object for each call. Using this 3715 * method is likely to have comparable cost to using the like-named 3716 * field. (Unlike this method, the field does not provide type safety.) 3717 * 3718 * @see #EMPTY_MAP 3719 * @since 1.5 3720 */ 3721 @SuppressWarnings("unchecked") 3722 public static final <K,V> Map<K,V> emptyMap() { 3723 return (Map<K,V>) EMPTY_MAP; 3724 } 3725 3726 /** 3727 * @serial include 3728 */ 3729 private static class EmptyMap<K,V> 3730 extends AbstractMap<K,V> 3731 implements Serializable 3732 { 3733 private static final long serialVersionUID = 6428348081105594320L; 3734 3735 public int size() {return 0;} 3736 public boolean isEmpty() {return true;} 3737 public boolean containsKey(Object key) {return false;} 3738 public boolean containsValue(Object value) {return false;} 3739 public V get(Object key) {return null;} 3740 public Set<K> keySet() {return emptySet();} 3741 public Collection<V> values() {return emptySet();} 3742 public Set<Map.Entry<K,V>> entrySet() {return emptySet();} 3743 3744 public boolean equals(Object o) { 3745 return (o instanceof Map) && ((Map<?,?>)o).isEmpty(); 3746 } 3747 3748 public int hashCode() {return 0;} 3749 3750 // Override default methods in Map 3751 @Override 3752 @SuppressWarnings("unchecked") 3753 public V getOrDefault(Object k, V defaultValue) { 3754 return defaultValue; 3755 } 3756 3757 @Override 3758 public void forEach(BiConsumer<? super K, ? super V> action) { 3759 Objects.requireNonNull(action); 3760 } 3761 3762 @Override 3763 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 3764 Objects.requireNonNull(function); 3765 } 3766 3767 @Override 3768 public V putIfAbsent(K key, V value) { 3769 throw new UnsupportedOperationException(); 3770 } 3771 3772 @Override 3773 public boolean remove(Object key, Object value) { 3774 throw new UnsupportedOperationException(); 3775 } 3776 3777 @Override 3778 public boolean replace(K key, V oldValue, V newValue) { 3779 throw new UnsupportedOperationException(); 3780 } 3781 3782 @Override 3783 public V replace(K key, V value) { 3784 throw new UnsupportedOperationException(); 3785 } 3786 3787 @Override 3788 public V computeIfAbsent(K key, 3789 Function<? super K, ? extends V> mappingFunction) { 3790 throw new UnsupportedOperationException(); 3791 } 3792 3793 @Override 3794 public V computeIfPresent(K key, 3795 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 3796 throw new UnsupportedOperationException(); 3797 } 3798 3799 @Override 3800 public V compute(K key, 3801 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 3802 throw new UnsupportedOperationException(); 3803 } 3804 3805 @Override 3806 public V merge(K key, V value, 3807 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 3808 throw new UnsupportedOperationException(); 3809 } 3810 3811 // Preserves singleton property 3812 private Object readResolve() { 3813 return EMPTY_MAP; 3814 } 3815 } 3816 3817 // Singleton collections 3818 3819 /** 3820 * Returns an immutable set containing only the specified object. 3821 * The returned set is serializable. 3822 * 3823 * @param o the sole object to be stored in the returned set. 3824 * @return an immutable set containing only the specified object. 3825 */ 3826 public static <T> Set<T> singleton(T o) { 3827 return new SingletonSet<>(o); 3828 } 3829 3830 static <E> Iterator<E> singletonIterator(final E e) { 3831 return new Iterator<E>() { 3832 private boolean hasNext = true; 3833 public boolean hasNext() { 3834 return hasNext; 3835 } 3836 public E next() { 3837 if (hasNext) { 3838 hasNext = false; 3839 return e; 3840 } 3841 throw new NoSuchElementException(); 3842 } 3843 public void remove() { 3844 throw new UnsupportedOperationException(); 3845 } 3846 }; 3847 } 3848 3849 /** 3850 * @serial include 3851 */ 3852 private static class SingletonSet<E> 3853 extends AbstractSet<E> 3854 implements Serializable 3855 { 3856 private static final long serialVersionUID = 3193687207550431679L; 3857 3858 private final E element; 3859 3860 SingletonSet(E e) {element = e;} 3861 3862 public Iterator<E> iterator() { 3863 return singletonIterator(element); 3864 } 3865 3866 public int size() {return 1;} 3867 3868 public boolean contains(Object o) {return eq(o, element);} 3869 3870 @Override 3871 public void forEach(Consumer<? super E> action) { 3872 action.accept(element); 3873 } 3874 @Override 3875 public boolean removeIf(Predicate<? super E> filter) { 3876 throw new UnsupportedOperationException(); 3877 } 3878 } 3879 3880 /** 3881 * Returns an immutable list containing only the specified object. 3882 * The returned list is serializable. 3883 * 3884 * @param o the sole object to be stored in the returned list. 3885 * @return an immutable list containing only the specified object. 3886 * @since 1.3 3887 */ 3888 public static <T> List<T> singletonList(T o) { 3889 return new SingletonList<>(o); 3890 } 3891 3892 /** 3893 * @serial include 3894 */ 3895 private static class SingletonList<E> 3896 extends AbstractList<E> 3897 implements RandomAccess, Serializable { 3898 3899 private static final long serialVersionUID = 3093736618740652951L; 3900 3901 private final E element; 3902 3903 SingletonList(E obj) {element = obj;} 3904 3905 public Iterator<E> iterator() { 3906 return singletonIterator(element); 3907 } 3908 3909 public int size() {return 1;} 3910 3911 public boolean contains(Object obj) {return eq(obj, element);} 3912 3913 public E get(int index) { 3914 if (index != 0) 3915 throw new IndexOutOfBoundsException("Index: "+index+", Size: 1"); 3916 return element; 3917 } 3918 3919 @Override 3920 public void forEach(Consumer<? super E> action) { 3921 action.accept(element); 3922 } 3923 @Override 3924 public boolean removeIf(Predicate<? super E> filter) { 3925 throw new UnsupportedOperationException(); 3926 } 3927 @Override 3928 public void replaceAll(UnaryOperator<E> operator) { 3929 throw new UnsupportedOperationException(); 3930 } 3931 @Override 3932 public void sort(Comparator<? super E> c) { 3933 } 3934 } 3935 3936 /** 3937 * Returns an immutable map, mapping only the specified key to the 3938 * specified value. The returned map is serializable. 3939 * 3940 * @param key the sole key to be stored in the returned map. 3941 * @param value the value to which the returned map maps <tt>key</tt>. 3942 * @return an immutable map containing only the specified key-value 3943 * mapping. 3944 * @since 1.3 3945 */ 3946 public static <K,V> Map<K,V> singletonMap(K key, V value) { 3947 return new SingletonMap<>(key, value); 3948 } 3949 3950 /** 3951 * @serial include 3952 */ 3953 private static class SingletonMap<K,V> 3954 extends AbstractMap<K,V> 3955 implements Serializable { 3956 private static final long serialVersionUID = -6979724477215052911L; 3957 3958 private final K k; 3959 private final V v; 3960 3961 SingletonMap(K key, V value) { 3962 k = key; 3963 v = value; 3964 } 3965 3966 public int size() {return 1;} 3967 3968 public boolean isEmpty() {return false;} 3969 3970 public boolean containsKey(Object key) {return eq(key, k);} 3971 3972 public boolean containsValue(Object value) {return eq(value, v);} 3973 3974 public V get(Object key) {return (eq(key, k) ? v : null);} 3975 3976 private transient Set<K> keySet = null; 3977 private transient Set<Map.Entry<K,V>> entrySet = null; 3978 private transient Collection<V> values = null; 3979 3980 public Set<K> keySet() { 3981 if (keySet==null) 3982 keySet = singleton(k); 3983 return keySet; 3984 } 3985 3986 public Set<Map.Entry<K,V>> entrySet() { 3987 if (entrySet==null) 3988 entrySet = Collections.<Map.Entry<K,V>>singleton( 3989 new SimpleImmutableEntry<>(k, v)); 3990 return entrySet; 3991 } 3992 3993 public Collection<V> values() { 3994 if (values==null) 3995 values = singleton(v); 3996 return values; 3997 } 3998 3999 // Override default methods in Map 4000 @Override 4001 public V getOrDefault(Object key, V defaultValue) { 4002 return eq(key, k) ? v : defaultValue; 4003 } 4004 4005 @Override 4006 public void forEach(BiConsumer<? super K, ? super V> action) { 4007 action.accept(k, v); 4008 } 4009 4010 @Override 4011 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 4012 throw new UnsupportedOperationException(); 4013 } 4014 4015 @Override 4016 public V putIfAbsent(K key, V value) { 4017 throw new UnsupportedOperationException(); 4018 } 4019 4020 @Override 4021 public boolean remove(Object key, Object value) { 4022 throw new UnsupportedOperationException(); 4023 } 4024 4025 @Override 4026 public boolean replace(K key, V oldValue, V newValue) { 4027 throw new UnsupportedOperationException(); 4028 } 4029 4030 @Override 4031 public V replace(K key, V value) { 4032 throw new UnsupportedOperationException(); 4033 } 4034 4035 @Override 4036 public V computeIfAbsent(K key, 4037 Function<? super K, ? extends V> mappingFunction) { 4038 throw new UnsupportedOperationException(); 4039 } 4040 4041 @Override 4042 public V computeIfPresent(K key, 4043 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 4044 throw new UnsupportedOperationException(); 4045 } 4046 4047 @Override 4048 public V compute(K key, 4049 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 4050 throw new UnsupportedOperationException(); 4051 } 4052 4053 @Override 4054 public V merge(K key, V value, 4055 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 4056 throw new UnsupportedOperationException(); 4057 } 4058 } 4059 4060 // Miscellaneous 4061 4062 /** 4063 * Returns an immutable list consisting of <tt>n</tt> copies of the 4064 * specified object. The newly allocated data object is tiny (it contains 4065 * a single reference to the data object). This method is useful in 4066 * combination with the <tt>List.addAll</tt> method to grow lists. 4067 * The returned list is serializable. 4068 * 4069 * @param n the number of elements in the returned list. 4070 * @param o the element to appear repeatedly in the returned list. 4071 * @return an immutable list consisting of <tt>n</tt> copies of the 4072 * specified object. 4073 * @throws IllegalArgumentException if {@code n < 0} 4074 * @see List#addAll(Collection) 4075 * @see List#addAll(int, Collection) 4076 */ 4077 public static <T> List<T> nCopies(int n, T o) { 4078 if (n < 0) 4079 throw new IllegalArgumentException("List length = " + n); 4080 return new CopiesList<>(n, o); 4081 } 4082 4083 /** 4084 * @serial include 4085 */ 4086 private static class CopiesList<E> 4087 extends AbstractList<E> 4088 implements RandomAccess, Serializable 4089 { 4090 private static final long serialVersionUID = 2739099268398711800L; 4091 4092 final int n; 4093 final E element; 4094 4095 CopiesList(int n, E e) { 4096 assert n >= 0; 4097 this.n = n; 4098 element = e; 4099 } 4100 4101 public int size() { 4102 return n; 4103 } 4104 4105 public boolean contains(Object obj) { 4106 return n != 0 && eq(obj, element); 4107 } 4108 4109 public int indexOf(Object o) { 4110 return contains(o) ? 0 : -1; 4111 } 4112 4113 public int lastIndexOf(Object o) { 4114 return contains(o) ? n - 1 : -1; 4115 } 4116 4117 public E get(int index) { 4118 if (index < 0 || index >= n) 4119 throw new IndexOutOfBoundsException("Index: "+index+ 4120 ", Size: "+n); 4121 return element; 4122 } 4123 4124 public Object[] toArray() { 4125 final Object[] a = new Object[n]; 4126 if (element != null) 4127 Arrays.fill(a, 0, n, element); 4128 return a; 4129 } 4130 4131 @SuppressWarnings("unchecked") 4132 public <T> T[] toArray(T[] a) { 4133 final int n = this.n; 4134 if (a.length < n) { 4135 a = (T[])java.lang.reflect.Array 4136 .newInstance(a.getClass().getComponentType(), n); 4137 if (element != null) 4138 Arrays.fill(a, 0, n, element); 4139 } else { 4140 Arrays.fill(a, 0, n, element); 4141 if (a.length > n) 4142 a[n] = null; 4143 } 4144 return a; 4145 } 4146 4147 public List<E> subList(int fromIndex, int toIndex) { 4148 if (fromIndex < 0) 4149 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex); 4150 if (toIndex > n) 4151 throw new IndexOutOfBoundsException("toIndex = " + toIndex); 4152 if (fromIndex > toIndex) 4153 throw new IllegalArgumentException("fromIndex(" + fromIndex + 4154 ") > toIndex(" + toIndex + ")"); 4155 return new CopiesList<>(toIndex - fromIndex, element); 4156 } 4157 } 4158 4159 /** 4160 * Returns a comparator that imposes the reverse of the <em>natural 4161 * ordering</em> on a collection of objects that implement the 4162 * {@code Comparable} interface. (The natural ordering is the ordering 4163 * imposed by the objects' own {@code compareTo} method.) This enables a 4164 * simple idiom for sorting (or maintaining) collections (or arrays) of 4165 * objects that implement the {@code Comparable} interface in 4166 * reverse-natural-order. For example, suppose {@code a} is an array of 4167 * strings. Then: <pre> 4168 * Arrays.sort(a, Collections.reverseOrder()); 4169 * </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p> 4170 * 4171 * The returned comparator is serializable. 4172 * 4173 * @return A comparator that imposes the reverse of the <i>natural 4174 * ordering</i> on a collection of objects that implement 4175 * the <tt>Comparable</tt> interface. 4176 * @see Comparable 4177 */ 4178 @SuppressWarnings("unchecked") 4179 public static <T> Comparator<T> reverseOrder() { 4180 return (Comparator<T>) ReverseComparator.REVERSE_ORDER; 4181 } 4182 4183 /** 4184 * @serial include 4185 */ 4186 private static class ReverseComparator 4187 implements Comparator<Comparable<Object>>, Serializable { 4188 4189 private static final long serialVersionUID = 7207038068494060240L; 4190 4191 static final ReverseComparator REVERSE_ORDER 4192 = new ReverseComparator(); 4193 4194 public int compare(Comparable<Object> c1, Comparable<Object> c2) { 4195 return c2.compareTo(c1); 4196 } 4197 4198 private Object readResolve() { return Collections.reverseOrder(); } 4199 } 4200 4201 /** 4202 * Returns a comparator that imposes the reverse ordering of the specified 4203 * comparator. If the specified comparator is {@code null}, this method is 4204 * equivalent to {@link #reverseOrder()} (in other words, it returns a 4205 * comparator that imposes the reverse of the <em>natural ordering</em> on 4206 * a collection of objects that implement the Comparable interface). 4207 * 4208 * <p>The returned comparator is serializable (assuming the specified 4209 * comparator is also serializable or {@code null}). 4210 * 4211 * @param cmp a comparator who's ordering is to be reversed by the returned 4212 * comparator or {@code null} 4213 * @return A comparator that imposes the reverse ordering of the 4214 * specified comparator. 4215 * @since 1.5 4216 */ 4217 public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) { 4218 if (cmp == null) 4219 return reverseOrder(); 4220 4221 if (cmp instanceof ReverseComparator2) 4222 return ((ReverseComparator2<T>)cmp).cmp; 4223 4224 return new ReverseComparator2<>(cmp); 4225 } 4226 4227 /** 4228 * @serial include 4229 */ 4230 private static class ReverseComparator2<T> implements Comparator<T>, 4231 Serializable 4232 { 4233 private static final long serialVersionUID = 4374092139857L; 4234 4235 /** 4236 * The comparator specified in the static factory. This will never 4237 * be null, as the static factory returns a ReverseComparator 4238 * instance if its argument is null. 4239 * 4240 * @serial 4241 */ 4242 final Comparator<T> cmp; 4243 4244 ReverseComparator2(Comparator<T> cmp) { 4245 assert cmp != null; 4246 this.cmp = cmp; 4247 } 4248 4249 public int compare(T t1, T t2) { 4250 return cmp.compare(t2, t1); 4251 } 4252 4253 public boolean equals(Object o) { 4254 return (o == this) || 4255 (o instanceof ReverseComparator2 && 4256 cmp.equals(((ReverseComparator2)o).cmp)); 4257 } 4258 4259 public int hashCode() { 4260 return cmp.hashCode() ^ Integer.MIN_VALUE; 4261 } 4262 } 4263 4264 /** 4265 * Returns an enumeration over the specified collection. This provides 4266 * interoperability with legacy APIs that require an enumeration 4267 * as input. 4268 * 4269 * @param c the collection for which an enumeration is to be returned. 4270 * @return an enumeration over the specified collection. 4271 * @see Enumeration 4272 */ 4273 public static <T> Enumeration<T> enumeration(final Collection<T> c) { 4274 return new Enumeration<T>() { 4275 private final Iterator<T> i = c.iterator(); 4276 4277 public boolean hasMoreElements() { 4278 return i.hasNext(); 4279 } 4280 4281 public T nextElement() { 4282 return i.next(); 4283 } 4284 }; 4285 } 4286 4287 /** 4288 * Returns an array list containing the elements returned by the 4289 * specified enumeration in the order they are returned by the 4290 * enumeration. This method provides interoperability between 4291 * legacy APIs that return enumerations and new APIs that require 4292 * collections. 4293 * 4294 * @param e enumeration providing elements for the returned 4295 * array list 4296 * @return an array list containing the elements returned 4297 * by the specified enumeration. 4298 * @since 1.4 4299 * @see Enumeration 4300 * @see ArrayList 4301 */ 4302 public static <T> ArrayList<T> list(Enumeration<T> e) { 4303 ArrayList<T> l = new ArrayList<>(); 4304 while (e.hasMoreElements()) 4305 l.add(e.nextElement()); 4306 return l; 4307 } 4308 4309 /** 4310 * Returns true if the specified arguments are equal, or both null. 4311 */ 4312 static boolean eq(Object o1, Object o2) { 4313 return o1==null ? o2==null : o1.equals(o2); 4314 } 4315 4316 /** 4317 * Returns the number of elements in the specified collection equal to the 4318 * specified object. More formally, returns the number of elements 4319 * <tt>e</tt> in the collection such that 4320 * <tt>(o == null ? e == null : o.equals(e))</tt>. 4321 * 4322 * @param c the collection in which to determine the frequency 4323 * of <tt>o</tt> 4324 * @param o the object whose frequency is to be determined 4325 * @throws NullPointerException if <tt>c</tt> is null 4326 * @since 1.5 4327 */ 4328 public static int frequency(Collection<?> c, Object o) { 4329 int result = 0; 4330 if (o == null) { 4331 for (Object e : c) 4332 if (e == null) 4333 result++; 4334 } else { 4335 for (Object e : c) 4336 if (o.equals(e)) 4337 result++; 4338 } 4339 return result; 4340 } 4341 4342 /** 4343 * Returns {@code true} if the two specified collections have no 4344 * elements in common. 4345 * 4346 * <p>Care must be exercised if this method is used on collections that 4347 * do not comply with the general contract for {@code Collection}. 4348 * Implementations may elect to iterate over either collection and test 4349 * for containment in the other collection (or to perform any equivalent 4350 * computation). If either collection uses a nonstandard equality test 4351 * (as does a {@link SortedSet} whose ordering is not <em>compatible with 4352 * equals</em>, or the key set of an {@link IdentityHashMap}), both 4353 * collections must use the same nonstandard equality test, or the 4354 * result of this method is undefined. 4355 * 4356 * <p>Care must also be exercised when using collections that have 4357 * restrictions on the elements that they may contain. Collection 4358 * implementations are allowed to throw exceptions for any operation 4359 * involving elements they deem ineligible. For absolute safety the 4360 * specified collections should contain only elements which are 4361 * eligible elements for both collections. 4362 * 4363 * <p>Note that it is permissible to pass the same collection in both 4364 * parameters, in which case the method will return {@code true} if and 4365 * only if the collection is empty. 4366 * 4367 * @param c1 a collection 4368 * @param c2 a collection 4369 * @return {@code true} if the two specified collections have no 4370 * elements in common. 4371 * @throws NullPointerException if either collection is {@code null}. 4372 * @throws NullPointerException if one collection contains a {@code null} 4373 * element and {@code null} is not an eligible element for the other collection. 4374 * (<a href="Collection.html#optional-restrictions">optional</a>) 4375 * @throws ClassCastException if one collection contains an element that is 4376 * of a type which is ineligible for the other collection. 4377 * (<a href="Collection.html#optional-restrictions">optional</a>) 4378 * @since 1.5 4379 */ 4380 public static boolean disjoint(Collection<?> c1, Collection<?> c2) { 4381 // The collection to be used for contains(). Preference is given to 4382 // the collection who's contains() has lower O() complexity. 4383 Collection<?> contains = c2; 4384 // The collection to be iterated. If the collections' contains() impl 4385 // are of different O() complexity, the collection with slower 4386 // contains() will be used for iteration. For collections who's 4387 // contains() are of the same complexity then best performance is 4388 // achieved by iterating the smaller collection. 4389 Collection<?> iterate = c1; 4390 4391 // Performance optimization cases. The heuristics: 4392 // 1. Generally iterate over c1. 4393 // 2. If c1 is a Set then iterate over c2. 4394 // 3. If either collection is empty then result is always true. 4395 // 4. Iterate over the smaller Collection. 4396 if (c1 instanceof Set) { 4397 // Use c1 for contains as a Set's contains() is expected to perform 4398 // better than O(N/2) 4399 iterate = c2; 4400 contains = c1; 4401 } else if (!(c2 instanceof Set)) { 4402 // Both are mere Collections. Iterate over smaller collection. 4403 // Example: If c1 contains 3 elements and c2 contains 50 elements and 4404 // assuming contains() requires ceiling(N/2) comparisons then 4405 // checking for all c1 elements in c2 would require 75 comparisons 4406 // (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring 4407 // 100 comparisons (50 * ceiling(3/2)). 4408 int c1size = c1.size(); 4409 int c2size = c2.size(); 4410 if (c1size == 0 || c2size == 0) { 4411 // At least one collection is empty. Nothing will match. 4412 return true; 4413 } 4414 4415 if (c1size > c2size) { 4416 iterate = c2; 4417 contains = c1; 4418 } 4419 } 4420 4421 for (Object e : iterate) { 4422 if (contains.contains(e)) { 4423 // Found a common element. Collections are not disjoint. 4424 return false; 4425 } 4426 } 4427 4428 // No common elements were found. 4429 return true; 4430 } 4431 4432 /** 4433 * Adds all of the specified elements to the specified collection. 4434 * Elements to be added may be specified individually or as an array. 4435 * The behavior of this convenience method is identical to that of 4436 * <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely 4437 * to run significantly faster under most implementations. 4438 * 4439 * <p>When elements are specified individually, this method provides a 4440 * convenient way to add a few elements to an existing collection: 4441 * <pre> 4442 * Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon"); 4443 * </pre> 4444 * 4445 * @param c the collection into which <tt>elements</tt> are to be inserted 4446 * @param elements the elements to insert into <tt>c</tt> 4447 * @return <tt>true</tt> if the collection changed as a result of the call 4448 * @throws UnsupportedOperationException if <tt>c</tt> does not support 4449 * the <tt>add</tt> operation 4450 * @throws NullPointerException if <tt>elements</tt> contains one or more 4451 * null values and <tt>c</tt> does not permit null elements, or 4452 * if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt> 4453 * @throws IllegalArgumentException if some property of a value in 4454 * <tt>elements</tt> prevents it from being added to <tt>c</tt> 4455 * @see Collection#addAll(Collection) 4456 * @since 1.5 4457 */ 4458 @SafeVarargs 4459 public static <T> boolean addAll(Collection<? super T> c, T... elements) { 4460 boolean result = false; 4461 for (T element : elements) 4462 result |= c.add(element); 4463 return result; 4464 } 4465 4466 /** 4467 * Returns a set backed by the specified map. The resulting set displays 4468 * the same ordering, concurrency, and performance characteristics as the 4469 * backing map. In essence, this factory method provides a {@link Set} 4470 * implementation corresponding to any {@link Map} implementation. There 4471 * is no need to use this method on a {@link Map} implementation that 4472 * already has a corresponding {@link Set} implementation (such as {@link 4473 * HashMap} or {@link TreeMap}). 4474 * 4475 * <p>Each method invocation on the set returned by this method results in 4476 * exactly one method invocation on the backing map or its <tt>keySet</tt> 4477 * view, with one exception. The <tt>addAll</tt> method is implemented 4478 * as a sequence of <tt>put</tt> invocations on the backing map. 4479 * 4480 * <p>The specified map must be empty at the time this method is invoked, 4481 * and should not be accessed directly after this method returns. These 4482 * conditions are ensured if the map is created empty, passed directly 4483 * to this method, and no reference to the map is retained, as illustrated 4484 * in the following code fragment: 4485 * <pre> 4486 * Set<Object> weakHashSet = Collections.newSetFromMap( 4487 * new WeakHashMap<Object, Boolean>()); 4488 * </pre> 4489 * 4490 * @param map the backing map 4491 * @return the set backed by the map 4492 * @throws IllegalArgumentException if <tt>map</tt> is not empty 4493 * @since 1.6 4494 */ 4495 public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) { 4496 return new SetFromMap<>(map); 4497 } 4498 4499 /** 4500 * @serial include 4501 */ 4502 private static class SetFromMap<E> extends AbstractSet<E> 4503 implements Set<E>, Serializable 4504 { 4505 private final Map<E, Boolean> m; // The backing map 4506 private transient Set<E> s; // Its keySet 4507 4508 SetFromMap(Map<E, Boolean> map) { 4509 if (!map.isEmpty()) 4510 throw new IllegalArgumentException("Map is non-empty"); 4511 m = map; 4512 s = map.keySet(); 4513 } 4514 4515 public void clear() { m.clear(); } 4516 public int size() { return m.size(); } 4517 public boolean isEmpty() { return m.isEmpty(); } 4518 public boolean contains(Object o) { return m.containsKey(o); } 4519 public boolean remove(Object o) { return m.remove(o) != null; } 4520 public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; } 4521 public Iterator<E> iterator() { return s.iterator(); } 4522 public Object[] toArray() { return s.toArray(); } 4523 public <T> T[] toArray(T[] a) { return s.toArray(a); } 4524 public String toString() { return s.toString(); } 4525 public int hashCode() { return s.hashCode(); } 4526 public boolean equals(Object o) { return o == this || s.equals(o); } 4527 public boolean containsAll(Collection<?> c) {return s.containsAll(c);} 4528 public boolean removeAll(Collection<?> c) {return s.removeAll(c);} 4529 public boolean retainAll(Collection<?> c) {return s.retainAll(c);} 4530 // addAll is the only inherited implementation 4531 4532 @Override 4533 public void forEach(Consumer<? super E> action) { 4534 s.forEach(action); 4535 } 4536 @Override 4537 public boolean removeIf(Predicate<? super E> filter) { 4538 return s.removeIf(filter); 4539 } 4540 4541 private static final long serialVersionUID = 2454657854757543876L; 4542 4543 private void readObject(java.io.ObjectInputStream stream) 4544 throws IOException, ClassNotFoundException 4545 { 4546 stream.defaultReadObject(); 4547 s = m.keySet(); 4548 } 4549 } 4550 4551 /** 4552 * Returns a view of a {@link Deque} as a Last-in-first-out (Lifo) 4553 * {@link Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>, 4554 * <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This 4555 * view can be useful when you would like to use a method 4556 * requiring a <tt>Queue</tt> but you need Lifo ordering. 4557 * 4558 * <p>Each method invocation on the queue returned by this method 4559 * results in exactly one method invocation on the backing deque, with 4560 * one exception. The {@link Queue#addAll addAll} method is 4561 * implemented as a sequence of {@link Deque#addFirst addFirst} 4562 * invocations on the backing deque. 4563 * 4564 * @param deque the deque 4565 * @return the queue 4566 * @since 1.6 4567 */ 4568 public static <T> Queue<T> asLifoQueue(Deque<T> deque) { 4569 return new AsLIFOQueue<>(deque); 4570 } 4571 4572 /** 4573 * @serial include 4574 */ 4575 static class AsLIFOQueue<E> extends AbstractQueue<E> 4576 implements Queue<E>, Serializable { 4577 private static final long serialVersionUID = 1802017725587941708L; 4578 private final Deque<E> q; 4579 AsLIFOQueue(Deque<E> q) { this.q = q; } 4580 public boolean add(E e) { q.addFirst(e); return true; } 4581 public boolean offer(E e) { return q.offerFirst(e); } 4582 public E poll() { return q.pollFirst(); } 4583 public E remove() { return q.removeFirst(); } 4584 public E peek() { return q.peekFirst(); } 4585 public E element() { return q.getFirst(); } 4586 public void clear() { q.clear(); } 4587 public int size() { return q.size(); } 4588 public boolean isEmpty() { return q.isEmpty(); } 4589 public boolean contains(Object o) { return q.contains(o); } 4590 public boolean remove(Object o) { return q.remove(o); } 4591 public Iterator<E> iterator() { return q.iterator(); } 4592 public Object[] toArray() { return q.toArray(); } 4593 public <T> T[] toArray(T[] a) { return q.toArray(a); } 4594 public String toString() { return q.toString(); } 4595 public boolean containsAll(Collection<?> c) {return q.containsAll(c);} 4596 public boolean removeAll(Collection<?> c) {return q.removeAll(c);} 4597 public boolean retainAll(Collection<?> c) {return q.retainAll(c);} 4598 // We use inherited addAll; forwarding addAll would be wrong 4599 4600 @Override 4601 public void forEach(Consumer<? super E> action) { 4602 q.forEach(action); 4603 } 4604 @Override 4605 public boolean removeIf(Predicate<? super E> filter) { 4606 return q.removeIf(filter); 4607 } 4608 } 4609 }