Collections.java revision 51b1b6997fd3f980076b8081f7f1165ccc2a4008
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 26package java.util; 27import java.io.Serializable; 28import java.io.ObjectOutputStream; 29import java.io.IOException; 30import java.lang.reflect.Array; 31 32/** 33 * This class consists exclusively of static methods that operate on or return 34 * collections. It contains polymorphic algorithms that operate on 35 * collections, "wrappers", which return a new collection backed by a 36 * specified collection, and a few other odds and ends. 37 * 38 * <p>The methods of this class all throw a <tt>NullPointerException</tt> 39 * if the collections or class objects provided to them are null. 40 * 41 * <p>The documentation for the polymorphic algorithms contained in this class 42 * generally includes a brief description of the <i>implementation</i>. Such 43 * descriptions should be regarded as <i>implementation notes</i>, rather than 44 * parts of the <i>specification</i>. Implementors should feel free to 45 * substitute other algorithms, so long as the specification itself is adhered 46 * to. (For example, the algorithm used by <tt>sort</tt> does not have to be 47 * a mergesort, but it does have to be <i>stable</i>.) 48 * 49 * <p>The "destructive" algorithms contained in this class, that is, the 50 * algorithms that modify the collection on which they operate, are specified 51 * to throw <tt>UnsupportedOperationException</tt> if the collection does not 52 * support the appropriate mutation primitive(s), such as the <tt>set</tt> 53 * method. These algorithms may, but are not required to, throw this 54 * exception if an invocation would have no effect on the collection. For 55 * example, invoking the <tt>sort</tt> method on an unmodifiable list that is 56 * already sorted may or may not throw <tt>UnsupportedOperationException</tt>. 57 * 58 * <p>This class is a member of the 59 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 60 * Java Collections Framework</a>. 61 * 62 * @author Josh Bloch 63 * @author Neal Gafter 64 * @see Collection 65 * @see Set 66 * @see List 67 * @see Map 68 * @since 1.2 69 */ 70 71public class Collections { 72 // Suppresses default constructor, ensuring non-instantiability. 73 private Collections() { 74 } 75 76 // Algorithms 77 78 /* 79 * Tuning parameters for algorithms - Many of the List algorithms have 80 * two implementations, one of which is appropriate for RandomAccess 81 * lists, the other for "sequential." Often, the random access variant 82 * yields better performance on small sequential access lists. The 83 * tuning parameters below determine the cutoff point for what constitutes 84 * a "small" sequential access list for each algorithm. The values below 85 * were empirically determined to work well for LinkedList. Hopefully 86 * they should be reasonable for other sequential access List 87 * implementations. Those doing performance work on this code would 88 * do well to validate the values of these parameters from time to time. 89 * (The first word of each tuning parameter name is the algorithm to which 90 * it applies.) 91 */ 92 private static final int BINARYSEARCH_THRESHOLD = 5000; 93 private static final int REVERSE_THRESHOLD = 18; 94 private static final int SHUFFLE_THRESHOLD = 5; 95 private static final int FILL_THRESHOLD = 25; 96 private static final int ROTATE_THRESHOLD = 100; 97 private static final int COPY_THRESHOLD = 10; 98 private static final int REPLACEALL_THRESHOLD = 11; 99 private static final int INDEXOFSUBLIST_THRESHOLD = 35; 100 101 /** 102 * Sorts the specified list into ascending order, according to the 103 * {@linkplain Comparable natural ordering} of its elements. 104 * All elements in the list must implement the {@link Comparable} 105 * interface. Furthermore, all elements in the list must be 106 * <i>mutually comparable</i> (that is, {@code e1.compareTo(e2)} 107 * must not throw a {@code ClassCastException} for any elements 108 * {@code e1} and {@code e2} in the list). 109 * 110 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will 111 * not be reordered as a result of the sort. 112 * 113 * <p>The specified list must be modifiable, but need not be resizable. 114 * 115 * <p>Implementation note: This implementation is a stable, adaptive, 116 * iterative mergesort that requires far fewer than n lg(n) comparisons 117 * when the input array is partially sorted, while offering the 118 * performance of a traditional mergesort when the input array is 119 * randomly ordered. If the input array is nearly sorted, the 120 * implementation requires approximately n comparisons. Temporary 121 * storage requirements vary from a small constant for nearly sorted 122 * input arrays to n/2 object references for randomly ordered input 123 * arrays. 124 * 125 * <p>The implementation takes equal advantage of ascending and 126 * descending order in its input array, and can take advantage of 127 * ascending and descending order in different parts of the same 128 * input array. It is well-suited to merging two or more sorted arrays: 129 * simply concatenate the arrays and sort the resulting array. 130 * 131 * <p>The implementation was adapted from Tim Peters's list sort for Python 132 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt"> 133 * TimSort</a>). It uses techiques from Peter McIlroy's "Optimistic 134 * Sorting and Information Theoretic Complexity", in Proceedings of the 135 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474, 136 * January 1993. 137 * 138 * <p>This implementation dumps the specified list into an array, sorts 139 * the array, and iterates over the list resetting each element 140 * from the corresponding position in the array. This avoids the 141 * n<sup>2</sup> log(n) performance that would result from attempting 142 * to sort a linked list in place. 143 * 144 * @param list the list to be sorted. 145 * @throws ClassCastException if the list contains elements that are not 146 * <i>mutually comparable</i> (for example, strings and integers). 147 * @throws UnsupportedOperationException if the specified list's 148 * list-iterator does not support the {@code set} operation. 149 * @throws IllegalArgumentException (optional) if the implementation 150 * detects that the natural ordering of the list elements is 151 * found to violate the {@link Comparable} contract 152 */ 153 public static <T extends Comparable<? super T>> void sort(List<T> list) { 154 Object[] a = list.toArray(); 155 Arrays.sort(a); 156 ListIterator<T> i = list.listIterator(); 157 for (int j=0; j<a.length; j++) { 158 i.next(); 159 i.set((T)a[j]); 160 } 161 } 162 163 /** 164 * Sorts the specified list according to the order induced by the 165 * specified comparator. All elements in the list must be <i>mutually 166 * comparable</i> using the specified comparator (that is, 167 * {@code c.compare(e1, e2)} must not throw a {@code ClassCastException} 168 * for any elements {@code e1} and {@code e2} in the list). 169 * 170 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will 171 * not be reordered as a result of the sort. 172 * 173 * <p>The specified list must be modifiable, but need not be resizable. 174 * 175 * <p>Implementation note: This implementation is a stable, adaptive, 176 * iterative mergesort that requires far fewer than n lg(n) comparisons 177 * when the input array is partially sorted, while offering the 178 * performance of a traditional mergesort when the input array is 179 * randomly ordered. If the input array is nearly sorted, the 180 * implementation requires approximately n comparisons. Temporary 181 * storage requirements vary from a small constant for nearly sorted 182 * input arrays to n/2 object references for randomly ordered input 183 * arrays. 184 * 185 * <p>The implementation takes equal advantage of ascending and 186 * descending order in its input array, and can take advantage of 187 * ascending and descending order in different parts of the same 188 * input array. It is well-suited to merging two or more sorted arrays: 189 * simply concatenate the arrays and sort the resulting array. 190 * 191 * <p>The implementation was adapted from Tim Peters's list sort for Python 192 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt"> 193 * TimSort</a>). It uses techiques from Peter McIlroy's "Optimistic 194 * Sorting and Information Theoretic Complexity", in Proceedings of the 195 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474, 196 * January 1993. 197 * 198 * <p>This implementation dumps the specified list into an array, sorts 199 * the array, and iterates over the list resetting each element 200 * from the corresponding position in the array. This avoids the 201 * n<sup>2</sup> log(n) performance that would result from attempting 202 * to sort a linked list in place. 203 * 204 * @param list the list to be sorted. 205 * @param c the comparator to determine the order of the list. A 206 * {@code null} value indicates that the elements' <i>natural 207 * ordering</i> should be used. 208 * @throws ClassCastException if the list contains elements that are not 209 * <i>mutually comparable</i> using the specified comparator. 210 * @throws UnsupportedOperationException if the specified list's 211 * list-iterator does not support the {@code set} operation. 212 * @throws IllegalArgumentException (optional) if the comparator is 213 * found to violate the {@link Comparator} contract 214 */ 215 public static <T> void sort(List<T> list, Comparator<? super T> c) { 216 Object[] a = list.toArray(); 217 Arrays.sort(a, (Comparator)c); 218 ListIterator i = list.listIterator(); 219 for (int j=0; j<a.length; j++) { 220 i.next(); 221 i.set(a[j]); 222 } 223 } 224 225 226 /** 227 * Searches the specified list for the specified object using the binary 228 * search algorithm. The list must be sorted into ascending order 229 * according to the {@linkplain Comparable natural ordering} of its 230 * elements (as by the {@link #sort(List)} method) prior to making this 231 * call. If it is not sorted, the results are undefined. If the list 232 * contains multiple elements equal to the specified object, there is no 233 * guarantee which one will be found. 234 * 235 * <p>This method runs in log(n) time for a "random access" list (which 236 * provides near-constant-time positional access). If the specified list 237 * does not implement the {@link RandomAccess} interface and is large, 238 * this method will do an iterator-based binary search that performs 239 * O(n) link traversals and O(log n) element comparisons. 240 * 241 * @param list the list to be searched. 242 * @param key the key to be searched for. 243 * @return the index of the search key, if it is contained in the list; 244 * otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The 245 * <i>insertion point</i> is defined as the point at which the 246 * key would be inserted into the list: the index of the first 247 * element greater than the key, or <tt>list.size()</tt> if all 248 * elements in the list are less than the specified key. Note 249 * that this guarantees that the return value will be >= 0 if 250 * and only if the key is found. 251 * @throws ClassCastException if the list contains elements that are not 252 * <i>mutually comparable</i> (for example, strings and 253 * integers), or the search key is not mutually comparable 254 * with the elements of the list. 255 */ 256 public static <T> 257 int binarySearch(List<? extends Comparable<? super T>> list, T key) { 258 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD) 259 return Collections.indexedBinarySearch(list, key); 260 else 261 return Collections.iteratorBinarySearch(list, key); 262 } 263 264 private static <T> 265 int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key) 266 { 267 int low = 0; 268 int high = list.size()-1; 269 270 while (low <= high) { 271 int mid = (low + high) >>> 1; 272 Comparable<? super T> midVal = list.get(mid); 273 int cmp = midVal.compareTo(key); 274 275 if (cmp < 0) 276 low = mid + 1; 277 else if (cmp > 0) 278 high = mid - 1; 279 else 280 return mid; // key found 281 } 282 return -(low + 1); // key not found 283 } 284 285 private static <T> 286 int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key) 287 { 288 int low = 0; 289 int high = list.size()-1; 290 ListIterator<? extends Comparable<? super T>> i = list.listIterator(); 291 292 while (low <= high) { 293 int mid = (low + high) >>> 1; 294 Comparable<? super T> midVal = get(i, mid); 295 int cmp = midVal.compareTo(key); 296 297 if (cmp < 0) 298 low = mid + 1; 299 else if (cmp > 0) 300 high = mid - 1; 301 else 302 return mid; // key found 303 } 304 return -(low + 1); // key not found 305 } 306 307 /** 308 * Gets the ith element from the given list by repositioning the specified 309 * list listIterator. 310 */ 311 private static <T> T get(ListIterator<? extends T> i, int index) { 312 T obj = null; 313 int pos = i.nextIndex(); 314 if (pos <= index) { 315 do { 316 obj = i.next(); 317 } while (pos++ < index); 318 } else { 319 do { 320 obj = i.previous(); 321 } while (--pos > index); 322 } 323 return obj; 324 } 325 326 /** 327 * Searches the specified list for the specified object using the binary 328 * search algorithm. The list must be sorted into ascending order 329 * according to the specified comparator (as by the 330 * {@link #sort(List, Comparator) sort(List, Comparator)} 331 * method), prior to making this call. If it is 332 * not sorted, the results are undefined. If the list contains multiple 333 * elements equal to the specified object, there is no guarantee which one 334 * will be found. 335 * 336 * <p>This method runs in log(n) time for a "random access" list (which 337 * provides near-constant-time positional access). If the specified list 338 * does not implement the {@link RandomAccess} interface and is large, 339 * this method will do an iterator-based binary search that performs 340 * O(n) link traversals and O(log n) element comparisons. 341 * 342 * @param list the list to be searched. 343 * @param key the key to be searched for. 344 * @param c the comparator by which the list is ordered. 345 * A <tt>null</tt> value indicates that the elements' 346 * {@linkplain Comparable natural ordering} should be used. 347 * @return the index of the search key, if it is contained in the list; 348 * otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The 349 * <i>insertion point</i> is defined as the point at which the 350 * key would be inserted into the list: the index of the first 351 * element greater than the key, or <tt>list.size()</tt> if all 352 * elements in the list are less than the specified key. Note 353 * that this guarantees that the return value will be >= 0 if 354 * and only if the key is found. 355 * @throws ClassCastException if the list contains elements that are not 356 * <i>mutually comparable</i> using the specified comparator, 357 * or the search key is not mutually comparable with the 358 * elements of the list using this comparator. 359 */ 360 public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) { 361 if (c==null) 362 return binarySearch((List) list, key); 363 364 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD) 365 return Collections.indexedBinarySearch(list, key, c); 366 else 367 return Collections.iteratorBinarySearch(list, key, c); 368 } 369 370 private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) { 371 int low = 0; 372 int high = l.size()-1; 373 374 while (low <= high) { 375 int mid = (low + high) >>> 1; 376 T midVal = l.get(mid); 377 int cmp = c.compare(midVal, key); 378 379 if (cmp < 0) 380 low = mid + 1; 381 else if (cmp > 0) 382 high = mid - 1; 383 else 384 return mid; // key found 385 } 386 return -(low + 1); // key not found 387 } 388 389 private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) { 390 int low = 0; 391 int high = l.size()-1; 392 ListIterator<? extends T> i = l.listIterator(); 393 394 while (low <= high) { 395 int mid = (low + high) >>> 1; 396 T midVal = get(i, mid); 397 int cmp = c.compare(midVal, key); 398 399 if (cmp < 0) 400 low = mid + 1; 401 else if (cmp > 0) 402 high = mid - 1; 403 else 404 return mid; // key found 405 } 406 return -(low + 1); // key not found 407 } 408 409 private interface SelfComparable extends Comparable<SelfComparable> {} 410 411 412 /** 413 * Reverses the order of the elements in the specified list.<p> 414 * 415 * This method runs in linear time. 416 * 417 * @param list the list whose elements are to be reversed. 418 * @throws UnsupportedOperationException if the specified list or 419 * its list-iterator does not support the <tt>set</tt> operation. 420 */ 421 public static void reverse(List<?> list) { 422 int size = list.size(); 423 if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) { 424 for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--) 425 swap(list, i, j); 426 } else { 427 ListIterator fwd = list.listIterator(); 428 ListIterator rev = list.listIterator(size); 429 for (int i=0, mid=list.size()>>1; i<mid; i++) { 430 Object tmp = fwd.next(); 431 fwd.set(rev.previous()); 432 rev.set(tmp); 433 } 434 } 435 } 436 437 /** 438 * Randomly permutes the specified list using a default source of 439 * randomness. All permutations occur with approximately equal 440 * likelihood.<p> 441 * 442 * The hedge "approximately" is used in the foregoing description because 443 * default source of randomness is only approximately an unbiased source 444 * of independently chosen bits. If it were a perfect source of randomly 445 * chosen bits, then the algorithm would choose permutations with perfect 446 * uniformity.<p> 447 * 448 * This implementation traverses the list backwards, from the last element 449 * up to the second, repeatedly swapping a randomly selected element into 450 * the "current position". Elements are randomly selected from the 451 * portion of the list that runs from the first element to the current 452 * position, inclusive.<p> 453 * 454 * This method runs in linear time. If the specified list does not 455 * implement the {@link RandomAccess} interface and is large, this 456 * implementation dumps the specified list into an array before shuffling 457 * it, and dumps the shuffled array back into the list. This avoids the 458 * quadratic behavior that would result from shuffling a "sequential 459 * access" list in place. 460 * 461 * @param list the list to be shuffled. 462 * @throws UnsupportedOperationException if the specified list or 463 * its list-iterator does not support the <tt>set</tt> operation. 464 */ 465 public static void shuffle(List<?> list) { 466 Random rnd = r; 467 if (rnd == null) 468 r = rnd = new Random(); 469 shuffle(list, rnd); 470 } 471 private static Random r; 472 473 /** 474 * Randomly permute the specified list using the specified source of 475 * randomness. All permutations occur with equal likelihood 476 * assuming that the source of randomness is fair.<p> 477 * 478 * This implementation traverses the list backwards, from the last element 479 * up to the second, repeatedly swapping a randomly selected element into 480 * the "current position". Elements are randomly selected from the 481 * portion of the list that runs from the first element to the current 482 * position, inclusive.<p> 483 * 484 * This method runs in linear time. If the specified list does not 485 * implement the {@link RandomAccess} interface and is large, this 486 * implementation dumps the specified list into an array before shuffling 487 * it, and dumps the shuffled array back into the list. This avoids the 488 * quadratic behavior that would result from shuffling a "sequential 489 * access" list in place. 490 * 491 * @param list the list to be shuffled. 492 * @param rnd the source of randomness to use to shuffle the list. 493 * @throws UnsupportedOperationException if the specified list or its 494 * list-iterator does not support the <tt>set</tt> operation. 495 */ 496 public static void shuffle(List<?> list, Random rnd) { 497 int size = list.size(); 498 if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) { 499 for (int i=size; i>1; i--) 500 swap(list, i-1, rnd.nextInt(i)); 501 } else { 502 Object arr[] = list.toArray(); 503 504 // Shuffle array 505 for (int i=size; i>1; i--) 506 swap(arr, i-1, rnd.nextInt(i)); 507 508 // Dump array back into list 509 ListIterator it = list.listIterator(); 510 for (int i=0; i<arr.length; i++) { 511 it.next(); 512 it.set(arr[i]); 513 } 514 } 515 } 516 517 /** 518 * Swaps the elements at the specified positions in the specified list. 519 * (If the specified positions are equal, invoking this method leaves 520 * the list unchanged.) 521 * 522 * @param list The list in which to swap elements. 523 * @param i the index of one element to be swapped. 524 * @param j the index of the other element to be swapped. 525 * @throws IndexOutOfBoundsException if either <tt>i</tt> or <tt>j</tt> 526 * is out of range (i < 0 || i >= list.size() 527 * || j < 0 || j >= list.size()). 528 * @since 1.4 529 */ 530 public static void swap(List<?> list, int i, int j) { 531 final List l = list; 532 l.set(i, l.set(j, l.get(i))); 533 } 534 535 /** 536 * Swaps the two specified elements in the specified array. 537 */ 538 private static void swap(Object[] arr, int i, int j) { 539 Object tmp = arr[i]; 540 arr[i] = arr[j]; 541 arr[j] = tmp; 542 } 543 544 /** 545 * Replaces all of the elements of the specified list with the specified 546 * element. <p> 547 * 548 * This method runs in linear time. 549 * 550 * @param list the list to be filled with the specified element. 551 * @param obj The element with which to fill the specified list. 552 * @throws UnsupportedOperationException if the specified list or its 553 * list-iterator does not support the <tt>set</tt> operation. 554 */ 555 public static <T> void fill(List<? super T> list, T obj) { 556 int size = list.size(); 557 558 if (size < FILL_THRESHOLD || list instanceof RandomAccess) { 559 for (int i=0; i<size; i++) 560 list.set(i, obj); 561 } else { 562 ListIterator<? super T> itr = list.listIterator(); 563 for (int i=0; i<size; i++) { 564 itr.next(); 565 itr.set(obj); 566 } 567 } 568 } 569 570 /** 571 * Copies all of the elements from one list into another. After the 572 * operation, the index of each copied element in the destination list 573 * will be identical to its index in the source list. The destination 574 * list must be at least as long as the source list. If it is longer, the 575 * remaining elements in the destination list are unaffected. <p> 576 * 577 * This method runs in linear time. 578 * 579 * @param dest The destination list. 580 * @param src The source list. 581 * @throws IndexOutOfBoundsException if the destination list is too small 582 * to contain the entire source List. 583 * @throws UnsupportedOperationException if the destination list's 584 * list-iterator does not support the <tt>set</tt> operation. 585 */ 586 public static <T> void copy(List<? super T> dest, List<? extends T> src) { 587 int srcSize = src.size(); 588 if (srcSize > dest.size()) 589 throw new IndexOutOfBoundsException("Source does not fit in dest"); 590 591 if (srcSize < COPY_THRESHOLD || 592 (src instanceof RandomAccess && dest instanceof RandomAccess)) { 593 for (int i=0; i<srcSize; i++) 594 dest.set(i, src.get(i)); 595 } else { 596 ListIterator<? super T> di=dest.listIterator(); 597 ListIterator<? extends T> si=src.listIterator(); 598 for (int i=0; i<srcSize; i++) { 599 di.next(); 600 di.set(si.next()); 601 } 602 } 603 } 604 605 /** 606 * Returns the minimum element of the given collection, according to the 607 * <i>natural ordering</i> of its elements. All elements in the 608 * collection must implement the <tt>Comparable</tt> interface. 609 * Furthermore, all elements in the collection must be <i>mutually 610 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a 611 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 612 * <tt>e2</tt> in the collection).<p> 613 * 614 * This method iterates over the entire collection, hence it requires 615 * time proportional to the size of the collection. 616 * 617 * @param coll the collection whose minimum element is to be determined. 618 * @return the minimum element of the given collection, according 619 * to the <i>natural ordering</i> of its elements. 620 * @throws ClassCastException if the collection contains elements that are 621 * not <i>mutually comparable</i> (for example, strings and 622 * integers). 623 * @throws NoSuchElementException if the collection is empty. 624 * @see Comparable 625 */ 626 public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) { 627 Iterator<? extends T> i = coll.iterator(); 628 T candidate = i.next(); 629 630 while (i.hasNext()) { 631 T next = i.next(); 632 if (next.compareTo(candidate) < 0) 633 candidate = next; 634 } 635 return candidate; 636 } 637 638 /** 639 * Returns the minimum element of the given collection, according to the 640 * order induced by the specified comparator. All elements in the 641 * collection must be <i>mutually comparable</i> by the specified 642 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a 643 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 644 * <tt>e2</tt> in the collection).<p> 645 * 646 * This method iterates over the entire collection, hence it requires 647 * time proportional to the size of the collection. 648 * 649 * @param coll the collection whose minimum element is to be determined. 650 * @param comp the comparator with which to determine the minimum element. 651 * A <tt>null</tt> value indicates that the elements' <i>natural 652 * ordering</i> should be used. 653 * @return the minimum element of the given collection, according 654 * to the specified comparator. 655 * @throws ClassCastException if the collection contains elements that are 656 * not <i>mutually comparable</i> using the specified comparator. 657 * @throws NoSuchElementException if the collection is empty. 658 * @see Comparable 659 */ 660 public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) { 661 if (comp==null) 662 return (T)min((Collection<SelfComparable>) (Collection) coll); 663 664 Iterator<? extends T> i = coll.iterator(); 665 T candidate = i.next(); 666 667 while (i.hasNext()) { 668 T next = i.next(); 669 if (comp.compare(next, candidate) < 0) 670 candidate = next; 671 } 672 return candidate; 673 } 674 675 /** 676 * Returns the maximum element of the given collection, according to the 677 * <i>natural ordering</i> of its elements. All elements in the 678 * collection must implement the <tt>Comparable</tt> interface. 679 * Furthermore, all elements in the collection must be <i>mutually 680 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a 681 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 682 * <tt>e2</tt> in the collection).<p> 683 * 684 * This method iterates over the entire collection, hence it requires 685 * time proportional to the size of the collection. 686 * 687 * @param coll the collection whose maximum element is to be determined. 688 * @return the maximum element of the given collection, according 689 * to the <i>natural ordering</i> of its elements. 690 * @throws ClassCastException if the collection contains elements that are 691 * not <i>mutually comparable</i> (for example, strings and 692 * integers). 693 * @throws NoSuchElementException if the collection is empty. 694 * @see Comparable 695 */ 696 public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) { 697 Iterator<? extends T> i = coll.iterator(); 698 T candidate = i.next(); 699 700 while (i.hasNext()) { 701 T next = i.next(); 702 if (next.compareTo(candidate) > 0) 703 candidate = next; 704 } 705 return candidate; 706 } 707 708 /** 709 * Returns the maximum element of the given collection, according to the 710 * order induced by the specified comparator. All elements in the 711 * collection must be <i>mutually comparable</i> by the specified 712 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a 713 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and 714 * <tt>e2</tt> in the collection).<p> 715 * 716 * This method iterates over the entire collection, hence it requires 717 * time proportional to the size of the collection. 718 * 719 * @param coll the collection whose maximum element is to be determined. 720 * @param comp the comparator with which to determine the maximum element. 721 * A <tt>null</tt> value indicates that the elements' <i>natural 722 * ordering</i> should be used. 723 * @return the maximum element of the given collection, according 724 * to the specified comparator. 725 * @throws ClassCastException if the collection contains elements that are 726 * not <i>mutually comparable</i> using the specified comparator. 727 * @throws NoSuchElementException if the collection is empty. 728 * @see Comparable 729 */ 730 public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) { 731 if (comp==null) 732 return (T)max((Collection<SelfComparable>) (Collection) coll); 733 734 Iterator<? extends T> i = coll.iterator(); 735 T candidate = i.next(); 736 737 while (i.hasNext()) { 738 T next = i.next(); 739 if (comp.compare(next, candidate) > 0) 740 candidate = next; 741 } 742 return candidate; 743 } 744 745 /** 746 * Rotates the elements in the specified list by the specified distance. 747 * After calling this method, the element at index <tt>i</tt> will be 748 * the element previously at index <tt>(i - distance)</tt> mod 749 * <tt>list.size()</tt>, for all values of <tt>i</tt> between <tt>0</tt> 750 * and <tt>list.size()-1</tt>, inclusive. (This method has no effect on 751 * the size of the list.) 752 * 753 * <p>For example, suppose <tt>list</tt> comprises<tt> [t, a, n, k, s]</tt>. 754 * After invoking <tt>Collections.rotate(list, 1)</tt> (or 755 * <tt>Collections.rotate(list, -4)</tt>), <tt>list</tt> will comprise 756 * <tt>[s, t, a, n, k]</tt>. 757 * 758 * <p>Note that this method can usefully be applied to sublists to 759 * move one or more elements within a list while preserving the 760 * order of the remaining elements. For example, the following idiom 761 * moves the element at index <tt>j</tt> forward to position 762 * <tt>k</tt> (which must be greater than or equal to <tt>j</tt>): 763 * <pre> 764 * Collections.rotate(list.subList(j, k+1), -1); 765 * </pre> 766 * To make this concrete, suppose <tt>list</tt> comprises 767 * <tt>[a, b, c, d, e]</tt>. To move the element at index <tt>1</tt> 768 * (<tt>b</tt>) forward two positions, perform the following invocation: 769 * <pre> 770 * Collections.rotate(l.subList(1, 4), -1); 771 * </pre> 772 * The resulting list is <tt>[a, c, d, b, e]</tt>. 773 * 774 * <p>To move more than one element forward, increase the absolute value 775 * of the rotation distance. To move elements backward, use a positive 776 * shift distance. 777 * 778 * <p>If the specified list is small or implements the {@link 779 * RandomAccess} interface, this implementation exchanges the first 780 * element into the location it should go, and then repeatedly exchanges 781 * the displaced element into the location it should go until a displaced 782 * element is swapped into the first element. If necessary, the process 783 * is repeated on the second and successive elements, until the rotation 784 * is complete. If the specified list is large and doesn't implement the 785 * <tt>RandomAccess</tt> interface, this implementation breaks the 786 * list into two sublist views around index <tt>-distance mod size</tt>. 787 * Then the {@link #reverse(List)} method is invoked on each sublist view, 788 * and finally it is invoked on the entire list. For a more complete 789 * description of both algorithms, see Section 2.3 of Jon Bentley's 790 * <i>Programming Pearls</i> (Addison-Wesley, 1986). 791 * 792 * @param list the list to be rotated. 793 * @param distance the distance to rotate the list. There are no 794 * constraints on this value; it may be zero, negative, or 795 * greater than <tt>list.size()</tt>. 796 * @throws UnsupportedOperationException if the specified list or 797 * its list-iterator does not support the <tt>set</tt> operation. 798 * @since 1.4 799 */ 800 public static void rotate(List<?> list, int distance) { 801 if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD) 802 rotate1(list, distance); 803 else 804 rotate2(list, distance); 805 } 806 807 private static <T> void rotate1(List<T> list, int distance) { 808 int size = list.size(); 809 if (size == 0) 810 return; 811 distance = distance % size; 812 if (distance < 0) 813 distance += size; 814 if (distance == 0) 815 return; 816 817 for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) { 818 T displaced = list.get(cycleStart); 819 int i = cycleStart; 820 do { 821 i += distance; 822 if (i >= size) 823 i -= size; 824 displaced = list.set(i, displaced); 825 nMoved ++; 826 } while (i != cycleStart); 827 } 828 } 829 830 private static void rotate2(List<?> list, int distance) { 831 int size = list.size(); 832 if (size == 0) 833 return; 834 int mid = -distance % size; 835 if (mid < 0) 836 mid += size; 837 if (mid == 0) 838 return; 839 840 reverse(list.subList(0, mid)); 841 reverse(list.subList(mid, size)); 842 reverse(list); 843 } 844 845 /** 846 * Replaces all occurrences of one specified value in a list with another. 847 * More formally, replaces with <tt>newVal</tt> each element <tt>e</tt> 848 * in <tt>list</tt> such that 849 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>. 850 * (This method has no effect on the size of the list.) 851 * 852 * @param list the list in which replacement is to occur. 853 * @param oldVal the old value to be replaced. 854 * @param newVal the new value with which <tt>oldVal</tt> is to be 855 * replaced. 856 * @return <tt>true</tt> if <tt>list</tt> contained one or more elements 857 * <tt>e</tt> such that 858 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>. 859 * @throws UnsupportedOperationException if the specified list or 860 * its list-iterator does not support the <tt>set</tt> operation. 861 * @since 1.4 862 */ 863 public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) { 864 boolean result = false; 865 int size = list.size(); 866 if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) { 867 if (oldVal==null) { 868 for (int i=0; i<size; i++) { 869 if (list.get(i)==null) { 870 list.set(i, newVal); 871 result = true; 872 } 873 } 874 } else { 875 for (int i=0; i<size; i++) { 876 if (oldVal.equals(list.get(i))) { 877 list.set(i, newVal); 878 result = true; 879 } 880 } 881 } 882 } else { 883 ListIterator<T> itr=list.listIterator(); 884 if (oldVal==null) { 885 for (int i=0; i<size; i++) { 886 if (itr.next()==null) { 887 itr.set(newVal); 888 result = true; 889 } 890 } 891 } else { 892 for (int i=0; i<size; i++) { 893 if (oldVal.equals(itr.next())) { 894 itr.set(newVal); 895 result = true; 896 } 897 } 898 } 899 } 900 return result; 901 } 902 903 /** 904 * Returns the starting position of the first occurrence of the specified 905 * target list within the specified source list, or -1 if there is no 906 * such occurrence. More formally, returns the lowest index <tt>i</tt> 907 * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>, 908 * or -1 if there is no such index. (Returns -1 if 909 * <tt>target.size() > source.size()</tt>.) 910 * 911 * <p>This implementation uses the "brute force" technique of scanning 912 * over the source list, looking for a match with the target at each 913 * location in turn. 914 * 915 * @param source the list in which to search for the first occurrence 916 * of <tt>target</tt>. 917 * @param target the list to search for as a subList of <tt>source</tt>. 918 * @return the starting position of the first occurrence of the specified 919 * target list within the specified source list, or -1 if there 920 * is no such occurrence. 921 * @since 1.4 922 */ 923 public static int indexOfSubList(List<?> source, List<?> target) { 924 int sourceSize = source.size(); 925 int targetSize = target.size(); 926 int maxCandidate = sourceSize - targetSize; 927 928 if (sourceSize < INDEXOFSUBLIST_THRESHOLD || 929 (source instanceof RandomAccess&&target instanceof RandomAccess)) { 930 nextCand: 931 for (int candidate = 0; candidate <= maxCandidate; candidate++) { 932 for (int i=0, j=candidate; i<targetSize; i++, j++) 933 if (!eq(target.get(i), source.get(j))) 934 continue nextCand; // Element mismatch, try next cand 935 return candidate; // All elements of candidate matched target 936 } 937 } else { // Iterator version of above algorithm 938 ListIterator<?> si = source.listIterator(); 939 nextCand: 940 for (int candidate = 0; candidate <= maxCandidate; candidate++) { 941 ListIterator<?> ti = target.listIterator(); 942 for (int i=0; i<targetSize; i++) { 943 if (!eq(ti.next(), si.next())) { 944 // Back up source iterator to next candidate 945 for (int j=0; j<i; j++) 946 si.previous(); 947 continue nextCand; 948 } 949 } 950 return candidate; 951 } 952 } 953 return -1; // No candidate matched the target 954 } 955 956 /** 957 * Returns the starting position of the last occurrence of the specified 958 * target list within the specified source list, or -1 if there is no such 959 * occurrence. More formally, returns the highest index <tt>i</tt> 960 * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>, 961 * or -1 if there is no such index. (Returns -1 if 962 * <tt>target.size() > source.size()</tt>.) 963 * 964 * <p>This implementation uses the "brute force" technique of iterating 965 * over the source list, looking for a match with the target at each 966 * location in turn. 967 * 968 * @param source the list in which to search for the last occurrence 969 * of <tt>target</tt>. 970 * @param target the list to search for as a subList of <tt>source</tt>. 971 * @return the starting position of the last occurrence of the specified 972 * target list within the specified source list, or -1 if there 973 * is no such occurrence. 974 * @since 1.4 975 */ 976 public static int lastIndexOfSubList(List<?> source, List<?> target) { 977 int sourceSize = source.size(); 978 int targetSize = target.size(); 979 int maxCandidate = sourceSize - targetSize; 980 981 if (sourceSize < INDEXOFSUBLIST_THRESHOLD || 982 source instanceof RandomAccess) { // Index access version 983 nextCand: 984 for (int candidate = maxCandidate; candidate >= 0; candidate--) { 985 for (int i=0, j=candidate; i<targetSize; i++, j++) 986 if (!eq(target.get(i), source.get(j))) 987 continue nextCand; // Element mismatch, try next cand 988 return candidate; // All elements of candidate matched target 989 } 990 } else { // Iterator version of above algorithm 991 if (maxCandidate < 0) 992 return -1; 993 ListIterator<?> si = source.listIterator(maxCandidate); 994 nextCand: 995 for (int candidate = maxCandidate; candidate >= 0; candidate--) { 996 ListIterator<?> ti = target.listIterator(); 997 for (int i=0; i<targetSize; i++) { 998 if (!eq(ti.next(), si.next())) { 999 if (candidate != 0) { 1000 // Back up source iterator to next candidate 1001 for (int j=0; j<=i+1; j++) 1002 si.previous(); 1003 } 1004 continue nextCand; 1005 } 1006 } 1007 return candidate; 1008 } 1009 } 1010 return -1; // No candidate matched the target 1011 } 1012 1013 1014 // Unmodifiable Wrappers 1015 1016 /** 1017 * Returns an unmodifiable view of the specified collection. This method 1018 * allows modules to provide users with "read-only" access to internal 1019 * collections. Query operations on the returned collection "read through" 1020 * to the specified collection, and attempts to modify the returned 1021 * collection, whether direct or via its iterator, result in an 1022 * <tt>UnsupportedOperationException</tt>.<p> 1023 * 1024 * The returned collection does <i>not</i> pass the hashCode and equals 1025 * operations through to the backing collection, but relies on 1026 * <tt>Object</tt>'s <tt>equals</tt> and <tt>hashCode</tt> methods. This 1027 * is necessary to preserve the contracts of these operations in the case 1028 * that the backing collection is a set or a list.<p> 1029 * 1030 * The returned collection will be serializable if the specified collection 1031 * is serializable. 1032 * 1033 * @param c the collection for which an unmodifiable view is to be 1034 * returned. 1035 * @return an unmodifiable view of the specified collection. 1036 */ 1037 public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) { 1038 return new UnmodifiableCollection<>(c); 1039 } 1040 1041 /** 1042 * @serial include 1043 */ 1044 static class UnmodifiableCollection<E> implements Collection<E>, Serializable { 1045 private static final long serialVersionUID = 1820017752578914078L; 1046 1047 final Collection<? extends E> c; 1048 1049 UnmodifiableCollection(Collection<? extends E> c) { 1050 if (c==null) 1051 throw new NullPointerException(); 1052 this.c = c; 1053 } 1054 1055 public int size() {return c.size();} 1056 public boolean isEmpty() {return c.isEmpty();} 1057 public boolean contains(Object o) {return c.contains(o);} 1058 public Object[] toArray() {return c.toArray();} 1059 public <T> T[] toArray(T[] a) {return c.toArray(a);} 1060 public String toString() {return c.toString();} 1061 1062 public Iterator<E> iterator() { 1063 return new Iterator<E>() { 1064 private final Iterator<? extends E> i = c.iterator(); 1065 1066 public boolean hasNext() {return i.hasNext();} 1067 public E next() {return i.next();} 1068 public void remove() { 1069 throw new UnsupportedOperationException(); 1070 } 1071 }; 1072 } 1073 1074 public boolean add(E e) { 1075 throw new UnsupportedOperationException(); 1076 } 1077 public boolean remove(Object o) { 1078 throw new UnsupportedOperationException(); 1079 } 1080 1081 public boolean containsAll(Collection<?> coll) { 1082 return c.containsAll(coll); 1083 } 1084 public boolean addAll(Collection<? extends E> coll) { 1085 throw new UnsupportedOperationException(); 1086 } 1087 public boolean removeAll(Collection<?> coll) { 1088 throw new UnsupportedOperationException(); 1089 } 1090 public boolean retainAll(Collection<?> coll) { 1091 throw new UnsupportedOperationException(); 1092 } 1093 public void clear() { 1094 throw new UnsupportedOperationException(); 1095 } 1096 } 1097 1098 /** 1099 * Returns an unmodifiable view of the specified set. This method allows 1100 * modules to provide users with "read-only" access to internal sets. 1101 * Query operations on the returned set "read through" to the specified 1102 * set, and attempts to modify the returned set, whether direct or via its 1103 * iterator, result in an <tt>UnsupportedOperationException</tt>.<p> 1104 * 1105 * The returned set will be serializable if the specified set 1106 * is serializable. 1107 * 1108 * @param s the set for which an unmodifiable view is to be returned. 1109 * @return an unmodifiable view of the specified set. 1110 */ 1111 public static <T> Set<T> unmodifiableSet(Set<? extends T> s) { 1112 return new UnmodifiableSet<>(s); 1113 } 1114 1115 /** 1116 * @serial include 1117 */ 1118 static class UnmodifiableSet<E> extends UnmodifiableCollection<E> 1119 implements Set<E>, Serializable { 1120 private static final long serialVersionUID = -9215047833775013803L; 1121 1122 UnmodifiableSet(Set<? extends E> s) {super(s);} 1123 public boolean equals(Object o) {return o == this || c.equals(o);} 1124 public int hashCode() {return c.hashCode();} 1125 } 1126 1127 /** 1128 * Returns an unmodifiable view of the specified sorted set. This method 1129 * allows modules to provide users with "read-only" access to internal 1130 * sorted sets. Query operations on the returned sorted set "read 1131 * through" to the specified sorted set. Attempts to modify the returned 1132 * sorted set, whether direct, via its iterator, or via its 1133 * <tt>subSet</tt>, <tt>headSet</tt>, or <tt>tailSet</tt> views, result in 1134 * an <tt>UnsupportedOperationException</tt>.<p> 1135 * 1136 * The returned sorted set will be serializable if the specified sorted set 1137 * is serializable. 1138 * 1139 * @param s the sorted set for which an unmodifiable view is to be 1140 * returned. 1141 * @return an unmodifiable view of the specified sorted set. 1142 */ 1143 public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) { 1144 return new UnmodifiableSortedSet<>(s); 1145 } 1146 1147 /** 1148 * @serial include 1149 */ 1150 static class UnmodifiableSortedSet<E> 1151 extends UnmodifiableSet<E> 1152 implements SortedSet<E>, Serializable { 1153 private static final long serialVersionUID = -4929149591599911165L; 1154 private final SortedSet<E> ss; 1155 1156 UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;} 1157 1158 public Comparator<? super E> comparator() {return ss.comparator();} 1159 1160 public SortedSet<E> subSet(E fromElement, E toElement) { 1161 return new UnmodifiableSortedSet<>(ss.subSet(fromElement,toElement)); 1162 } 1163 public SortedSet<E> headSet(E toElement) { 1164 return new UnmodifiableSortedSet<>(ss.headSet(toElement)); 1165 } 1166 public SortedSet<E> tailSet(E fromElement) { 1167 return new UnmodifiableSortedSet<>(ss.tailSet(fromElement)); 1168 } 1169 1170 public E first() {return ss.first();} 1171 public E last() {return ss.last();} 1172 } 1173 1174 /** 1175 * Returns an unmodifiable view of the specified list. This method allows 1176 * modules to provide users with "read-only" access to internal 1177 * lists. Query operations on the returned list "read through" to the 1178 * specified list, and attempts to modify the returned list, whether 1179 * direct or via its iterator, result in an 1180 * <tt>UnsupportedOperationException</tt>.<p> 1181 * 1182 * The returned list will be serializable if the specified list 1183 * is serializable. Similarly, the returned list will implement 1184 * {@link RandomAccess} if the specified list does. 1185 * 1186 * @param list the list for which an unmodifiable view is to be returned. 1187 * @return an unmodifiable view of the specified list. 1188 */ 1189 public static <T> List<T> unmodifiableList(List<? extends T> list) { 1190 return (list instanceof RandomAccess ? 1191 new UnmodifiableRandomAccessList<>(list) : 1192 new UnmodifiableList<>(list)); 1193 } 1194 1195 /** 1196 * @serial include 1197 */ 1198 static class UnmodifiableList<E> extends UnmodifiableCollection<E> 1199 implements List<E> { 1200 private static final long serialVersionUID = -283967356065247728L; 1201 final List<? extends E> list; 1202 1203 UnmodifiableList(List<? extends E> list) { 1204 super(list); 1205 this.list = list; 1206 } 1207 1208 public boolean equals(Object o) {return o == this || list.equals(o);} 1209 public int hashCode() {return list.hashCode();} 1210 1211 public E get(int index) {return list.get(index);} 1212 public E set(int index, E element) { 1213 throw new UnsupportedOperationException(); 1214 } 1215 public void add(int index, E element) { 1216 throw new UnsupportedOperationException(); 1217 } 1218 public E remove(int index) { 1219 throw new UnsupportedOperationException(); 1220 } 1221 public int indexOf(Object o) {return list.indexOf(o);} 1222 public int lastIndexOf(Object o) {return list.lastIndexOf(o);} 1223 public boolean addAll(int index, Collection<? extends E> c) { 1224 throw new UnsupportedOperationException(); 1225 } 1226 public ListIterator<E> listIterator() {return listIterator(0);} 1227 1228 public ListIterator<E> listIterator(final int index) { 1229 return new ListIterator<E>() { 1230 private final ListIterator<? extends E> i 1231 = list.listIterator(index); 1232 1233 public boolean hasNext() {return i.hasNext();} 1234 public E next() {return i.next();} 1235 public boolean hasPrevious() {return i.hasPrevious();} 1236 public E previous() {return i.previous();} 1237 public int nextIndex() {return i.nextIndex();} 1238 public int previousIndex() {return i.previousIndex();} 1239 1240 public void remove() { 1241 throw new UnsupportedOperationException(); 1242 } 1243 public void set(E e) { 1244 throw new UnsupportedOperationException(); 1245 } 1246 public void add(E e) { 1247 throw new UnsupportedOperationException(); 1248 } 1249 }; 1250 } 1251 1252 public List<E> subList(int fromIndex, int toIndex) { 1253 return new UnmodifiableList<>(list.subList(fromIndex, toIndex)); 1254 } 1255 1256 /** 1257 * UnmodifiableRandomAccessList instances are serialized as 1258 * UnmodifiableList instances to allow them to be deserialized 1259 * in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList). 1260 * This method inverts the transformation. As a beneficial 1261 * side-effect, it also grafts the RandomAccess marker onto 1262 * UnmodifiableList instances that were serialized in pre-1.4 JREs. 1263 * 1264 * Note: Unfortunately, UnmodifiableRandomAccessList instances 1265 * serialized in 1.4.1 and deserialized in 1.4 will become 1266 * UnmodifiableList instances, as this method was missing in 1.4. 1267 */ 1268 private Object readResolve() { 1269 return (list instanceof RandomAccess 1270 ? new UnmodifiableRandomAccessList<>(list) 1271 : this); 1272 } 1273 } 1274 1275 /** 1276 * @serial include 1277 */ 1278 static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E> 1279 implements RandomAccess 1280 { 1281 UnmodifiableRandomAccessList(List<? extends E> list) { 1282 super(list); 1283 } 1284 1285 public List<E> subList(int fromIndex, int toIndex) { 1286 return new UnmodifiableRandomAccessList<>( 1287 list.subList(fromIndex, toIndex)); 1288 } 1289 1290 private static final long serialVersionUID = -2542308836966382001L; 1291 1292 /** 1293 * Allows instances to be deserialized in pre-1.4 JREs (which do 1294 * not have UnmodifiableRandomAccessList). UnmodifiableList has 1295 * a readResolve method that inverts this transformation upon 1296 * deserialization. 1297 */ 1298 private Object writeReplace() { 1299 return new UnmodifiableList<>(list); 1300 } 1301 } 1302 1303 /** 1304 * Returns an unmodifiable view of the specified map. This method 1305 * allows modules to provide users with "read-only" access to internal 1306 * maps. Query operations on the returned map "read through" 1307 * to the specified map, and attempts to modify the returned 1308 * map, whether direct or via its collection views, result in an 1309 * <tt>UnsupportedOperationException</tt>.<p> 1310 * 1311 * The returned map will be serializable if the specified map 1312 * is serializable. 1313 * 1314 * @param m the map for which an unmodifiable view is to be returned. 1315 * @return an unmodifiable view of the specified map. 1316 */ 1317 public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) { 1318 return new UnmodifiableMap<>(m); 1319 } 1320 1321 /** 1322 * @serial include 1323 */ 1324 private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable { 1325 private static final long serialVersionUID = -1034234728574286014L; 1326 1327 private final Map<? extends K, ? extends V> m; 1328 1329 UnmodifiableMap(Map<? extends K, ? extends V> m) { 1330 if (m==null) 1331 throw new NullPointerException(); 1332 this.m = m; 1333 } 1334 1335 public int size() {return m.size();} 1336 public boolean isEmpty() {return m.isEmpty();} 1337 public boolean containsKey(Object key) {return m.containsKey(key);} 1338 public boolean containsValue(Object val) {return m.containsValue(val);} 1339 public V get(Object key) {return m.get(key);} 1340 1341 public V put(K key, V value) { 1342 throw new UnsupportedOperationException(); 1343 } 1344 public V remove(Object key) { 1345 throw new UnsupportedOperationException(); 1346 } 1347 public void putAll(Map<? extends K, ? extends V> m) { 1348 throw new UnsupportedOperationException(); 1349 } 1350 public void clear() { 1351 throw new UnsupportedOperationException(); 1352 } 1353 1354 private transient Set<K> keySet = null; 1355 private transient Set<Map.Entry<K,V>> entrySet = null; 1356 private transient Collection<V> values = null; 1357 1358 public Set<K> keySet() { 1359 if (keySet==null) 1360 keySet = unmodifiableSet(m.keySet()); 1361 return keySet; 1362 } 1363 1364 public Set<Map.Entry<K,V>> entrySet() { 1365 if (entrySet==null) 1366 entrySet = new UnmodifiableEntrySet<>(m.entrySet()); 1367 return entrySet; 1368 } 1369 1370 public Collection<V> values() { 1371 if (values==null) 1372 values = unmodifiableCollection(m.values()); 1373 return values; 1374 } 1375 1376 public boolean equals(Object o) {return o == this || m.equals(o);} 1377 public int hashCode() {return m.hashCode();} 1378 public String toString() {return m.toString();} 1379 1380 /** 1381 * We need this class in addition to UnmodifiableSet as 1382 * Map.Entries themselves permit modification of the backing Map 1383 * via their setValue operation. This class is subtle: there are 1384 * many possible attacks that must be thwarted. 1385 * 1386 * @serial include 1387 */ 1388 static class UnmodifiableEntrySet<K,V> 1389 extends UnmodifiableSet<Map.Entry<K,V>> { 1390 private static final long serialVersionUID = 7854390611657943733L; 1391 1392 UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) { 1393 super((Set)s); 1394 } 1395 public Iterator<Map.Entry<K,V>> iterator() { 1396 return new Iterator<Map.Entry<K,V>>() { 1397 private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator(); 1398 1399 public boolean hasNext() { 1400 return i.hasNext(); 1401 } 1402 public Map.Entry<K,V> next() { 1403 return new UnmodifiableEntry<>(i.next()); 1404 } 1405 public void remove() { 1406 throw new UnsupportedOperationException(); 1407 } 1408 }; 1409 } 1410 1411 public Object[] toArray() { 1412 Object[] a = c.toArray(); 1413 for (int i=0; i<a.length; i++) 1414 a[i] = new UnmodifiableEntry<>((Map.Entry<K,V>)a[i]); 1415 return a; 1416 } 1417 1418 public <T> T[] toArray(T[] a) { 1419 // We don't pass a to c.toArray, to avoid window of 1420 // vulnerability wherein an unscrupulous multithreaded client 1421 // could get his hands on raw (unwrapped) Entries from c. 1422 Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0)); 1423 1424 for (int i=0; i<arr.length; i++) 1425 arr[i] = new UnmodifiableEntry<>((Map.Entry<K,V>)arr[i]); 1426 1427 if (arr.length > a.length) 1428 return (T[])arr; 1429 1430 System.arraycopy(arr, 0, a, 0, arr.length); 1431 if (a.length > arr.length) 1432 a[arr.length] = null; 1433 return a; 1434 } 1435 1436 /** 1437 * This method is overridden to protect the backing set against 1438 * an object with a nefarious equals function that senses 1439 * that the equality-candidate is Map.Entry and calls its 1440 * setValue method. 1441 */ 1442 public boolean contains(Object o) { 1443 if (!(o instanceof Map.Entry)) 1444 return false; 1445 return c.contains( 1446 new UnmodifiableEntry<>((Map.Entry<?,?>) o)); 1447 } 1448 1449 /** 1450 * The next two methods are overridden to protect against 1451 * an unscrupulous List whose contains(Object o) method senses 1452 * when o is a Map.Entry, and calls o.setValue. 1453 */ 1454 public boolean containsAll(Collection<?> coll) { 1455 for (Object e : coll) { 1456 if (!contains(e)) // Invokes safe contains() above 1457 return false; 1458 } 1459 return true; 1460 } 1461 public boolean equals(Object o) { 1462 if (o == this) 1463 return true; 1464 1465 if (!(o instanceof Set)) 1466 return false; 1467 Set s = (Set) o; 1468 if (s.size() != c.size()) 1469 return false; 1470 return containsAll(s); // Invokes safe containsAll() above 1471 } 1472 1473 /** 1474 * This "wrapper class" serves two purposes: it prevents 1475 * the client from modifying the backing Map, by short-circuiting 1476 * the setValue method, and it protects the backing Map against 1477 * an ill-behaved Map.Entry that attempts to modify another 1478 * Map Entry when asked to perform an equality check. 1479 */ 1480 private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> { 1481 private Map.Entry<? extends K, ? extends V> e; 1482 1483 UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) {this.e = e;} 1484 1485 public K getKey() {return e.getKey();} 1486 public V getValue() {return e.getValue();} 1487 public V setValue(V value) { 1488 throw new UnsupportedOperationException(); 1489 } 1490 public int hashCode() {return e.hashCode();} 1491 public boolean equals(Object o) { 1492 if (this == o) 1493 return true; 1494 if (!(o instanceof Map.Entry)) 1495 return false; 1496 Map.Entry t = (Map.Entry)o; 1497 return eq(e.getKey(), t.getKey()) && 1498 eq(e.getValue(), t.getValue()); 1499 } 1500 public String toString() {return e.toString();} 1501 } 1502 } 1503 } 1504 1505 /** 1506 * Returns an unmodifiable view of the specified sorted map. This method 1507 * allows modules to provide users with "read-only" access to internal 1508 * sorted maps. Query operations on the returned sorted map "read through" 1509 * to the specified sorted map. Attempts to modify the returned 1510 * sorted map, whether direct, via its collection views, or via its 1511 * <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in 1512 * an <tt>UnsupportedOperationException</tt>.<p> 1513 * 1514 * The returned sorted map will be serializable if the specified sorted map 1515 * is serializable. 1516 * 1517 * @param m the sorted map for which an unmodifiable view is to be 1518 * returned. 1519 * @return an unmodifiable view of the specified sorted map. 1520 */ 1521 public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) { 1522 return new UnmodifiableSortedMap<>(m); 1523 } 1524 1525 /** 1526 * @serial include 1527 */ 1528 static class UnmodifiableSortedMap<K,V> 1529 extends UnmodifiableMap<K,V> 1530 implements SortedMap<K,V>, Serializable { 1531 private static final long serialVersionUID = -8806743815996713206L; 1532 1533 private final SortedMap<K, ? extends V> sm; 1534 1535 UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m;} 1536 1537 public Comparator<? super K> comparator() {return sm.comparator();} 1538 1539 public SortedMap<K,V> subMap(K fromKey, K toKey) { 1540 return new UnmodifiableSortedMap<>(sm.subMap(fromKey, toKey)); 1541 } 1542 public SortedMap<K,V> headMap(K toKey) { 1543 return new UnmodifiableSortedMap<>(sm.headMap(toKey)); 1544 } 1545 public SortedMap<K,V> tailMap(K fromKey) { 1546 return new UnmodifiableSortedMap<>(sm.tailMap(fromKey)); 1547 } 1548 1549 public K firstKey() {return sm.firstKey();} 1550 public K lastKey() {return sm.lastKey();} 1551 } 1552 1553 1554 // Synch Wrappers 1555 1556 /** 1557 * Returns a synchronized (thread-safe) collection backed by the specified 1558 * collection. In order to guarantee serial access, it is critical that 1559 * <strong>all</strong> access to the backing collection is accomplished 1560 * through the returned collection.<p> 1561 * 1562 * It is imperative that the user manually synchronize on the returned 1563 * collection when iterating over it: 1564 * <pre> 1565 * Collection c = Collections.synchronizedCollection(myCollection); 1566 * ... 1567 * synchronized (c) { 1568 * Iterator i = c.iterator(); // Must be in the synchronized block 1569 * while (i.hasNext()) 1570 * foo(i.next()); 1571 * } 1572 * </pre> 1573 * Failure to follow this advice may result in non-deterministic behavior. 1574 * 1575 * <p>The returned collection does <i>not</i> pass the <tt>hashCode</tt> 1576 * and <tt>equals</tt> operations through to the backing collection, but 1577 * relies on <tt>Object</tt>'s equals and hashCode methods. This is 1578 * necessary to preserve the contracts of these operations in the case 1579 * that the backing collection is a set or a list.<p> 1580 * 1581 * The returned collection will be serializable if the specified collection 1582 * is serializable. 1583 * 1584 * @param c the collection to be "wrapped" in a synchronized collection. 1585 * @return a synchronized view of the specified collection. 1586 */ 1587 public static <T> Collection<T> synchronizedCollection(Collection<T> c) { 1588 return new SynchronizedCollection<>(c); 1589 } 1590 1591 static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) { 1592 return new SynchronizedCollection<>(c, mutex); 1593 } 1594 1595 /** 1596 * @serial include 1597 */ 1598 static class SynchronizedCollection<E> implements Collection<E>, Serializable { 1599 private static final long serialVersionUID = 3053995032091335093L; 1600 1601 final Collection<E> c; // Backing Collection 1602 final Object mutex; // Object on which to synchronize 1603 1604 SynchronizedCollection(Collection<E> c) { 1605 if (c==null) 1606 throw new NullPointerException(); 1607 this.c = c; 1608 mutex = this; 1609 } 1610 SynchronizedCollection(Collection<E> c, Object mutex) { 1611 this.c = c; 1612 this.mutex = mutex; 1613 } 1614 1615 public int size() { 1616 synchronized (mutex) {return c.size();} 1617 } 1618 public boolean isEmpty() { 1619 synchronized (mutex) {return c.isEmpty();} 1620 } 1621 public boolean contains(Object o) { 1622 synchronized (mutex) {return c.contains(o);} 1623 } 1624 public Object[] toArray() { 1625 synchronized (mutex) {return c.toArray();} 1626 } 1627 public <T> T[] toArray(T[] a) { 1628 synchronized (mutex) {return c.toArray(a);} 1629 } 1630 1631 public Iterator<E> iterator() { 1632 return c.iterator(); // Must be manually synched by user! 1633 } 1634 1635 public boolean add(E e) { 1636 synchronized (mutex) {return c.add(e);} 1637 } 1638 public boolean remove(Object o) { 1639 synchronized (mutex) {return c.remove(o);} 1640 } 1641 1642 public boolean containsAll(Collection<?> coll) { 1643 synchronized (mutex) {return c.containsAll(coll);} 1644 } 1645 public boolean addAll(Collection<? extends E> coll) { 1646 synchronized (mutex) {return c.addAll(coll);} 1647 } 1648 public boolean removeAll(Collection<?> coll) { 1649 synchronized (mutex) {return c.removeAll(coll);} 1650 } 1651 public boolean retainAll(Collection<?> coll) { 1652 synchronized (mutex) {return c.retainAll(coll);} 1653 } 1654 public void clear() { 1655 synchronized (mutex) {c.clear();} 1656 } 1657 public String toString() { 1658 synchronized (mutex) {return c.toString();} 1659 } 1660 private void writeObject(ObjectOutputStream s) throws IOException { 1661 synchronized (mutex) {s.defaultWriteObject();} 1662 } 1663 } 1664 1665 /** 1666 * Returns a synchronized (thread-safe) set backed by the specified 1667 * set. In order to guarantee serial access, it is critical that 1668 * <strong>all</strong> access to the backing set is accomplished 1669 * through the returned set.<p> 1670 * 1671 * It is imperative that the user manually synchronize on the returned 1672 * set when iterating over it: 1673 * <pre> 1674 * Set s = Collections.synchronizedSet(new HashSet()); 1675 * ... 1676 * synchronized (s) { 1677 * Iterator i = s.iterator(); // Must be in the synchronized block 1678 * while (i.hasNext()) 1679 * foo(i.next()); 1680 * } 1681 * </pre> 1682 * Failure to follow this advice may result in non-deterministic behavior. 1683 * 1684 * <p>The returned set will be serializable if the specified set is 1685 * serializable. 1686 * 1687 * @param s the set to be "wrapped" in a synchronized set. 1688 * @return a synchronized view of the specified set. 1689 */ 1690 public static <T> Set<T> synchronizedSet(Set<T> s) { 1691 return new SynchronizedSet<>(s); 1692 } 1693 1694 static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) { 1695 return new SynchronizedSet<>(s, mutex); 1696 } 1697 1698 /** 1699 * @serial include 1700 */ 1701 static class SynchronizedSet<E> 1702 extends SynchronizedCollection<E> 1703 implements Set<E> { 1704 private static final long serialVersionUID = 487447009682186044L; 1705 1706 SynchronizedSet(Set<E> s) { 1707 super(s); 1708 } 1709 SynchronizedSet(Set<E> s, Object mutex) { 1710 super(s, mutex); 1711 } 1712 1713 public boolean equals(Object o) { 1714 if (this == o) 1715 return true; 1716 synchronized (mutex) {return c.equals(o);} 1717 } 1718 public int hashCode() { 1719 synchronized (mutex) {return c.hashCode();} 1720 } 1721 } 1722 1723 /** 1724 * Returns a synchronized (thread-safe) sorted set backed by the specified 1725 * sorted set. In order to guarantee serial access, it is critical that 1726 * <strong>all</strong> access to the backing sorted set is accomplished 1727 * through the returned sorted set (or its views).<p> 1728 * 1729 * It is imperative that the user manually synchronize on the returned 1730 * sorted set when iterating over it or any of its <tt>subSet</tt>, 1731 * <tt>headSet</tt>, or <tt>tailSet</tt> views. 1732 * <pre> 1733 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet()); 1734 * ... 1735 * synchronized (s) { 1736 * Iterator i = s.iterator(); // Must be in the synchronized block 1737 * while (i.hasNext()) 1738 * foo(i.next()); 1739 * } 1740 * </pre> 1741 * or: 1742 * <pre> 1743 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet()); 1744 * SortedSet s2 = s.headSet(foo); 1745 * ... 1746 * synchronized (s) { // Note: s, not s2!!! 1747 * Iterator i = s2.iterator(); // Must be in the synchronized block 1748 * while (i.hasNext()) 1749 * foo(i.next()); 1750 * } 1751 * </pre> 1752 * Failure to follow this advice may result in non-deterministic behavior. 1753 * 1754 * <p>The returned sorted set will be serializable if the specified 1755 * sorted set is serializable. 1756 * 1757 * @param s the sorted set to be "wrapped" in a synchronized sorted set. 1758 * @return a synchronized view of the specified sorted set. 1759 */ 1760 public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) { 1761 return new SynchronizedSortedSet<>(s); 1762 } 1763 1764 /** 1765 * @serial include 1766 */ 1767 static class SynchronizedSortedSet<E> 1768 extends SynchronizedSet<E> 1769 implements SortedSet<E> 1770 { 1771 private static final long serialVersionUID = 8695801310862127406L; 1772 1773 private final SortedSet<E> ss; 1774 1775 SynchronizedSortedSet(SortedSet<E> s) { 1776 super(s); 1777 ss = s; 1778 } 1779 SynchronizedSortedSet(SortedSet<E> s, Object mutex) { 1780 super(s, mutex); 1781 ss = s; 1782 } 1783 1784 public Comparator<? super E> comparator() { 1785 synchronized (mutex) {return ss.comparator();} 1786 } 1787 1788 public SortedSet<E> subSet(E fromElement, E toElement) { 1789 synchronized (mutex) { 1790 return new SynchronizedSortedSet<>( 1791 ss.subSet(fromElement, toElement), mutex); 1792 } 1793 } 1794 public SortedSet<E> headSet(E toElement) { 1795 synchronized (mutex) { 1796 return new SynchronizedSortedSet<>(ss.headSet(toElement), mutex); 1797 } 1798 } 1799 public SortedSet<E> tailSet(E fromElement) { 1800 synchronized (mutex) { 1801 return new SynchronizedSortedSet<>(ss.tailSet(fromElement),mutex); 1802 } 1803 } 1804 1805 public E first() { 1806 synchronized (mutex) {return ss.first();} 1807 } 1808 public E last() { 1809 synchronized (mutex) {return ss.last();} 1810 } 1811 } 1812 1813 /** 1814 * Returns a synchronized (thread-safe) list backed by the specified 1815 * list. In order to guarantee serial access, it is critical that 1816 * <strong>all</strong> access to the backing list is accomplished 1817 * through the returned list.<p> 1818 * 1819 * It is imperative that the user manually synchronize on the returned 1820 * list when iterating over it: 1821 * <pre> 1822 * List list = Collections.synchronizedList(new ArrayList()); 1823 * ... 1824 * synchronized (list) { 1825 * Iterator i = list.iterator(); // Must be in synchronized block 1826 * while (i.hasNext()) 1827 * foo(i.next()); 1828 * } 1829 * </pre> 1830 * Failure to follow this advice may result in non-deterministic behavior. 1831 * 1832 * <p>The returned list will be serializable if the specified list is 1833 * serializable. 1834 * 1835 * @param list the list to be "wrapped" in a synchronized list. 1836 * @return a synchronized view of the specified list. 1837 */ 1838 public static <T> List<T> synchronizedList(List<T> list) { 1839 return (list instanceof RandomAccess ? 1840 new SynchronizedRandomAccessList<>(list) : 1841 new SynchronizedList<>(list)); 1842 } 1843 1844 static <T> List<T> synchronizedList(List<T> list, Object mutex) { 1845 return (list instanceof RandomAccess ? 1846 new SynchronizedRandomAccessList<>(list, mutex) : 1847 new SynchronizedList<>(list, mutex)); 1848 } 1849 1850 /** 1851 * @serial include 1852 */ 1853 static class SynchronizedList<E> 1854 extends SynchronizedCollection<E> 1855 implements List<E> { 1856 private static final long serialVersionUID = -7754090372962971524L; 1857 1858 final List<E> list; 1859 1860 SynchronizedList(List<E> list) { 1861 super(list); 1862 this.list = list; 1863 } 1864 SynchronizedList(List<E> list, Object mutex) { 1865 super(list, mutex); 1866 this.list = list; 1867 } 1868 1869 public boolean equals(Object o) { 1870 if (this == o) 1871 return true; 1872 synchronized (mutex) {return list.equals(o);} 1873 } 1874 public int hashCode() { 1875 synchronized (mutex) {return list.hashCode();} 1876 } 1877 1878 public E get(int index) { 1879 synchronized (mutex) {return list.get(index);} 1880 } 1881 public E set(int index, E element) { 1882 synchronized (mutex) {return list.set(index, element);} 1883 } 1884 public void add(int index, E element) { 1885 synchronized (mutex) {list.add(index, element);} 1886 } 1887 public E remove(int index) { 1888 synchronized (mutex) {return list.remove(index);} 1889 } 1890 1891 public int indexOf(Object o) { 1892 synchronized (mutex) {return list.indexOf(o);} 1893 } 1894 public int lastIndexOf(Object o) { 1895 synchronized (mutex) {return list.lastIndexOf(o);} 1896 } 1897 1898 public boolean addAll(int index, Collection<? extends E> c) { 1899 synchronized (mutex) {return list.addAll(index, c);} 1900 } 1901 1902 public ListIterator<E> listIterator() { 1903 return list.listIterator(); // Must be manually synched by user 1904 } 1905 1906 public ListIterator<E> listIterator(int index) { 1907 return list.listIterator(index); // Must be manually synched by user 1908 } 1909 1910 public List<E> subList(int fromIndex, int toIndex) { 1911 synchronized (mutex) { 1912 return new SynchronizedList<>(list.subList(fromIndex, toIndex), 1913 mutex); 1914 } 1915 } 1916 1917 /** 1918 * SynchronizedRandomAccessList instances are serialized as 1919 * SynchronizedList instances to allow them to be deserialized 1920 * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList). 1921 * This method inverts the transformation. As a beneficial 1922 * side-effect, it also grafts the RandomAccess marker onto 1923 * SynchronizedList instances that were serialized in pre-1.4 JREs. 1924 * 1925 * Note: Unfortunately, SynchronizedRandomAccessList instances 1926 * serialized in 1.4.1 and deserialized in 1.4 will become 1927 * SynchronizedList instances, as this method was missing in 1.4. 1928 */ 1929 private Object readResolve() { 1930 return (list instanceof RandomAccess 1931 ? new SynchronizedRandomAccessList<>(list) 1932 : this); 1933 } 1934 } 1935 1936 /** 1937 * @serial include 1938 */ 1939 static class SynchronizedRandomAccessList<E> 1940 extends SynchronizedList<E> 1941 implements RandomAccess { 1942 1943 SynchronizedRandomAccessList(List<E> list) { 1944 super(list); 1945 } 1946 1947 SynchronizedRandomAccessList(List<E> list, Object mutex) { 1948 super(list, mutex); 1949 } 1950 1951 public List<E> subList(int fromIndex, int toIndex) { 1952 synchronized (mutex) { 1953 return new SynchronizedRandomAccessList<>( 1954 list.subList(fromIndex, toIndex), mutex); 1955 } 1956 } 1957 1958 private static final long serialVersionUID = 1530674583602358482L; 1959 1960 /** 1961 * Allows instances to be deserialized in pre-1.4 JREs (which do 1962 * not have SynchronizedRandomAccessList). SynchronizedList has 1963 * a readResolve method that inverts this transformation upon 1964 * deserialization. 1965 */ 1966 private Object writeReplace() { 1967 return new SynchronizedList<>(list); 1968 } 1969 } 1970 1971 /** 1972 * Returns a synchronized (thread-safe) map backed by the specified 1973 * map. In order to guarantee serial access, it is critical that 1974 * <strong>all</strong> access to the backing map is accomplished 1975 * through the returned map.<p> 1976 * 1977 * It is imperative that the user manually synchronize on the returned 1978 * map when iterating over any of its collection views: 1979 * <pre> 1980 * Map m = Collections.synchronizedMap(new HashMap()); 1981 * ... 1982 * Set s = m.keySet(); // Needn't be in synchronized block 1983 * ... 1984 * synchronized (m) { // Synchronizing on m, not s! 1985 * Iterator i = s.iterator(); // Must be in synchronized block 1986 * while (i.hasNext()) 1987 * foo(i.next()); 1988 * } 1989 * </pre> 1990 * Failure to follow this advice may result in non-deterministic behavior. 1991 * 1992 * <p>The returned map will be serializable if the specified map is 1993 * serializable. 1994 * 1995 * @param m the map to be "wrapped" in a synchronized map. 1996 * @return a synchronized view of the specified map. 1997 */ 1998 public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) { 1999 return new SynchronizedMap<>(m); 2000 } 2001 2002 /** 2003 * @serial include 2004 */ 2005 private static class SynchronizedMap<K,V> 2006 implements Map<K,V>, Serializable { 2007 private static final long serialVersionUID = 1978198479659022715L; 2008 2009 private final Map<K,V> m; // Backing Map 2010 final Object mutex; // Object on which to synchronize 2011 2012 SynchronizedMap(Map<K,V> m) { 2013 if (m==null) 2014 throw new NullPointerException(); 2015 this.m = m; 2016 mutex = this; 2017 } 2018 2019 SynchronizedMap(Map<K,V> m, Object mutex) { 2020 this.m = m; 2021 this.mutex = mutex; 2022 } 2023 2024 public int size() { 2025 synchronized (mutex) {return m.size();} 2026 } 2027 public boolean isEmpty() { 2028 synchronized (mutex) {return m.isEmpty();} 2029 } 2030 public boolean containsKey(Object key) { 2031 synchronized (mutex) {return m.containsKey(key);} 2032 } 2033 public boolean containsValue(Object value) { 2034 synchronized (mutex) {return m.containsValue(value);} 2035 } 2036 public V get(Object key) { 2037 synchronized (mutex) {return m.get(key);} 2038 } 2039 2040 public V put(K key, V value) { 2041 synchronized (mutex) {return m.put(key, value);} 2042 } 2043 public V remove(Object key) { 2044 synchronized (mutex) {return m.remove(key);} 2045 } 2046 public void putAll(Map<? extends K, ? extends V> map) { 2047 synchronized (mutex) {m.putAll(map);} 2048 } 2049 public void clear() { 2050 synchronized (mutex) {m.clear();} 2051 } 2052 2053 private transient Set<K> keySet = null; 2054 private transient Set<Map.Entry<K,V>> entrySet = null; 2055 private transient Collection<V> values = null; 2056 2057 public Set<K> keySet() { 2058 synchronized (mutex) { 2059 if (keySet==null) 2060 keySet = new SynchronizedSet<>(m.keySet(), mutex); 2061 return keySet; 2062 } 2063 } 2064 2065 public Set<Map.Entry<K,V>> entrySet() { 2066 synchronized (mutex) { 2067 if (entrySet==null) 2068 entrySet = new SynchronizedSet<>(m.entrySet(), mutex); 2069 return entrySet; 2070 } 2071 } 2072 2073 public Collection<V> values() { 2074 synchronized (mutex) { 2075 if (values==null) 2076 values = new SynchronizedCollection<>(m.values(), mutex); 2077 return values; 2078 } 2079 } 2080 2081 public boolean equals(Object o) { 2082 if (this == o) 2083 return true; 2084 synchronized (mutex) {return m.equals(o);} 2085 } 2086 public int hashCode() { 2087 synchronized (mutex) {return m.hashCode();} 2088 } 2089 public String toString() { 2090 synchronized (mutex) {return m.toString();} 2091 } 2092 private void writeObject(ObjectOutputStream s) throws IOException { 2093 synchronized (mutex) {s.defaultWriteObject();} 2094 } 2095 } 2096 2097 /** 2098 * Returns a synchronized (thread-safe) sorted map backed by the specified 2099 * sorted map. In order to guarantee serial access, it is critical that 2100 * <strong>all</strong> access to the backing sorted map is accomplished 2101 * through the returned sorted map (or its views).<p> 2102 * 2103 * It is imperative that the user manually synchronize on the returned 2104 * sorted map when iterating over any of its collection views, or the 2105 * collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or 2106 * <tt>tailMap</tt> views. 2107 * <pre> 2108 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap()); 2109 * ... 2110 * Set s = m.keySet(); // Needn't be in synchronized block 2111 * ... 2112 * synchronized (m) { // Synchronizing on m, not s! 2113 * Iterator i = s.iterator(); // Must be in synchronized block 2114 * while (i.hasNext()) 2115 * foo(i.next()); 2116 * } 2117 * </pre> 2118 * or: 2119 * <pre> 2120 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap()); 2121 * SortedMap m2 = m.subMap(foo, bar); 2122 * ... 2123 * Set s2 = m2.keySet(); // Needn't be in synchronized block 2124 * ... 2125 * synchronized (m) { // Synchronizing on m, not m2 or s2! 2126 * Iterator i = s.iterator(); // Must be in synchronized block 2127 * while (i.hasNext()) 2128 * foo(i.next()); 2129 * } 2130 * </pre> 2131 * Failure to follow this advice may result in non-deterministic behavior. 2132 * 2133 * <p>The returned sorted map will be serializable if the specified 2134 * sorted map is serializable. 2135 * 2136 * @param m the sorted map to be "wrapped" in a synchronized sorted map. 2137 * @return a synchronized view of the specified sorted map. 2138 */ 2139 public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) { 2140 return new SynchronizedSortedMap<>(m); 2141 } 2142 2143 2144 /** 2145 * @serial include 2146 */ 2147 static class SynchronizedSortedMap<K,V> 2148 extends SynchronizedMap<K,V> 2149 implements SortedMap<K,V> 2150 { 2151 private static final long serialVersionUID = -8798146769416483793L; 2152 2153 private final SortedMap<K,V> sm; 2154 2155 SynchronizedSortedMap(SortedMap<K,V> m) { 2156 super(m); 2157 sm = m; 2158 } 2159 SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) { 2160 super(m, mutex); 2161 sm = m; 2162 } 2163 2164 public Comparator<? super K> comparator() { 2165 synchronized (mutex) {return sm.comparator();} 2166 } 2167 2168 public SortedMap<K,V> subMap(K fromKey, K toKey) { 2169 synchronized (mutex) { 2170 return new SynchronizedSortedMap<>( 2171 sm.subMap(fromKey, toKey), mutex); 2172 } 2173 } 2174 public SortedMap<K,V> headMap(K toKey) { 2175 synchronized (mutex) { 2176 return new SynchronizedSortedMap<>(sm.headMap(toKey), mutex); 2177 } 2178 } 2179 public SortedMap<K,V> tailMap(K fromKey) { 2180 synchronized (mutex) { 2181 return new SynchronizedSortedMap<>(sm.tailMap(fromKey),mutex); 2182 } 2183 } 2184 2185 public K firstKey() { 2186 synchronized (mutex) {return sm.firstKey();} 2187 } 2188 public K lastKey() { 2189 synchronized (mutex) {return sm.lastKey();} 2190 } 2191 } 2192 2193 // Dynamically typesafe collection wrappers 2194 2195 /** 2196 * Returns a dynamically typesafe view of the specified collection. 2197 * Any attempt to insert an element of the wrong type will result in an 2198 * immediate {@link ClassCastException}. Assuming a collection 2199 * contains no incorrectly typed elements prior to the time a 2200 * dynamically typesafe view is generated, and that all subsequent 2201 * access to the collection takes place through the view, it is 2202 * <i>guaranteed</i> that the collection cannot contain an incorrectly 2203 * typed element. 2204 * 2205 * <p>The generics mechanism in the language provides compile-time 2206 * (static) type checking, but it is possible to defeat this mechanism 2207 * with unchecked casts. Usually this is not a problem, as the compiler 2208 * issues warnings on all such unchecked operations. There are, however, 2209 * times when static type checking alone is not sufficient. For example, 2210 * suppose a collection is passed to a third-party library and it is 2211 * imperative that the library code not corrupt the collection by 2212 * inserting an element of the wrong type. 2213 * 2214 * <p>Another use of dynamically typesafe views is debugging. Suppose a 2215 * program fails with a {@code ClassCastException}, indicating that an 2216 * incorrectly typed element was put into a parameterized collection. 2217 * Unfortunately, the exception can occur at any time after the erroneous 2218 * element is inserted, so it typically provides little or no information 2219 * as to the real source of the problem. If the problem is reproducible, 2220 * one can quickly determine its source by temporarily modifying the 2221 * program to wrap the collection with a dynamically typesafe view. 2222 * For example, this declaration: 2223 * <pre> {@code 2224 * Collection<String> c = new HashSet<String>(); 2225 * }</pre> 2226 * may be replaced temporarily by this one: 2227 * <pre> {@code 2228 * Collection<String> c = Collections.checkedCollection( 2229 * new HashSet<String>(), String.class); 2230 * }</pre> 2231 * Running the program again will cause it to fail at the point where 2232 * an incorrectly typed element is inserted into the collection, clearly 2233 * identifying the source of the problem. Once the problem is fixed, the 2234 * modified declaration may be reverted back to the original. 2235 * 2236 * <p>The returned collection does <i>not</i> pass the hashCode and equals 2237 * operations through to the backing collection, but relies on 2238 * {@code Object}'s {@code equals} and {@code hashCode} methods. This 2239 * is necessary to preserve the contracts of these operations in the case 2240 * that the backing collection is a set or a list. 2241 * 2242 * <p>The returned collection will be serializable if the specified 2243 * collection is serializable. 2244 * 2245 * <p>Since {@code null} is considered to be a value of any reference 2246 * type, the returned collection permits insertion of null elements 2247 * whenever the backing collection does. 2248 * 2249 * @param c the collection for which a dynamically typesafe view is to be 2250 * returned 2251 * @param type the type of element that {@code c} is permitted to hold 2252 * @return a dynamically typesafe view of the specified collection 2253 * @since 1.5 2254 */ 2255 public static <E> Collection<E> checkedCollection(Collection<E> c, 2256 Class<E> type) { 2257 return new CheckedCollection<>(c, type); 2258 } 2259 2260 @SuppressWarnings("unchecked") 2261 static <T> T[] zeroLengthArray(Class<T> type) { 2262 return (T[]) Array.newInstance(type, 0); 2263 } 2264 2265 /** 2266 * @serial include 2267 */ 2268 static class CheckedCollection<E> implements Collection<E>, Serializable { 2269 private static final long serialVersionUID = 1578914078182001775L; 2270 2271 final Collection<E> c; 2272 final Class<E> type; 2273 2274 void typeCheck(Object o) { 2275 if (o != null && !type.isInstance(o)) 2276 throw new ClassCastException(badElementMsg(o)); 2277 } 2278 2279 private String badElementMsg(Object o) { 2280 return "Attempt to insert " + o.getClass() + 2281 " element into collection with element type " + type; 2282 } 2283 2284 CheckedCollection(Collection<E> c, Class<E> type) { 2285 if (c==null || type == null) 2286 throw new NullPointerException(); 2287 this.c = c; 2288 this.type = type; 2289 } 2290 2291 public int size() { return c.size(); } 2292 public boolean isEmpty() { return c.isEmpty(); } 2293 public boolean contains(Object o) { return c.contains(o); } 2294 public Object[] toArray() { return c.toArray(); } 2295 public <T> T[] toArray(T[] a) { return c.toArray(a); } 2296 public String toString() { return c.toString(); } 2297 public boolean remove(Object o) { return c.remove(o); } 2298 public void clear() { c.clear(); } 2299 2300 public boolean containsAll(Collection<?> coll) { 2301 return c.containsAll(coll); 2302 } 2303 public boolean removeAll(Collection<?> coll) { 2304 return c.removeAll(coll); 2305 } 2306 public boolean retainAll(Collection<?> coll) { 2307 return c.retainAll(coll); 2308 } 2309 2310 public Iterator<E> iterator() { 2311 final Iterator<E> it = c.iterator(); 2312 return new Iterator<E>() { 2313 public boolean hasNext() { return it.hasNext(); } 2314 public E next() { return it.next(); } 2315 public void remove() { it.remove(); }}; 2316 } 2317 2318 public boolean add(E e) { 2319 typeCheck(e); 2320 return c.add(e); 2321 } 2322 2323 private E[] zeroLengthElementArray = null; // Lazily initialized 2324 2325 private E[] zeroLengthElementArray() { 2326 return zeroLengthElementArray != null ? zeroLengthElementArray : 2327 (zeroLengthElementArray = zeroLengthArray(type)); 2328 } 2329 2330 @SuppressWarnings("unchecked") 2331 Collection<E> checkedCopyOf(Collection<? extends E> coll) { 2332 Object[] a = null; 2333 try { 2334 E[] z = zeroLengthElementArray(); 2335 a = coll.toArray(z); 2336 // Defend against coll violating the toArray contract 2337 if (a.getClass() != z.getClass()) 2338 a = Arrays.copyOf(a, a.length, z.getClass()); 2339 } catch (ArrayStoreException ignore) { 2340 // To get better and consistent diagnostics, 2341 // we call typeCheck explicitly on each element. 2342 // We call clone() to defend against coll retaining a 2343 // reference to the returned array and storing a bad 2344 // element into it after it has been type checked. 2345 a = coll.toArray().clone(); 2346 for (Object o : a) 2347 typeCheck(o); 2348 } 2349 // A slight abuse of the type system, but safe here. 2350 return (Collection<E>) Arrays.asList(a); 2351 } 2352 2353 public boolean addAll(Collection<? extends E> coll) { 2354 // Doing things this way insulates us from concurrent changes 2355 // in the contents of coll and provides all-or-nothing 2356 // semantics (which we wouldn't get if we type-checked each 2357 // element as we added it) 2358 return c.addAll(checkedCopyOf(coll)); 2359 } 2360 } 2361 2362 /** 2363 * Returns a dynamically typesafe view of the specified set. 2364 * Any attempt to insert an element of the wrong type will result in 2365 * an immediate {@link ClassCastException}. Assuming a set contains 2366 * no incorrectly typed elements prior to the time a dynamically typesafe 2367 * view is generated, and that all subsequent access to the set 2368 * takes place through the view, it is <i>guaranteed</i> that the 2369 * set cannot contain an incorrectly typed element. 2370 * 2371 * <p>A discussion of the use of dynamically typesafe views may be 2372 * found in the documentation for the {@link #checkedCollection 2373 * checkedCollection} method. 2374 * 2375 * <p>The returned set will be serializable if the specified set is 2376 * serializable. 2377 * 2378 * <p>Since {@code null} is considered to be a value of any reference 2379 * type, the returned set permits insertion of null elements whenever 2380 * the backing set does. 2381 * 2382 * @param s the set for which a dynamically typesafe view is to be 2383 * returned 2384 * @param type the type of element that {@code s} is permitted to hold 2385 * @return a dynamically typesafe view of the specified set 2386 * @since 1.5 2387 */ 2388 public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) { 2389 return new CheckedSet<>(s, type); 2390 } 2391 2392 /** 2393 * @serial include 2394 */ 2395 static class CheckedSet<E> extends CheckedCollection<E> 2396 implements Set<E>, Serializable 2397 { 2398 private static final long serialVersionUID = 4694047833775013803L; 2399 2400 CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); } 2401 2402 public boolean equals(Object o) { return o == this || c.equals(o); } 2403 public int hashCode() { return c.hashCode(); } 2404 } 2405 2406 /** 2407 * Returns a dynamically typesafe view of the specified sorted set. 2408 * Any attempt to insert an element of the wrong type will result in an 2409 * immediate {@link ClassCastException}. Assuming a sorted set 2410 * contains no incorrectly typed elements prior to the time a 2411 * dynamically typesafe view is generated, and that all subsequent 2412 * access to the sorted set takes place through the view, it is 2413 * <i>guaranteed</i> that the sorted set cannot contain an incorrectly 2414 * typed element. 2415 * 2416 * <p>A discussion of the use of dynamically typesafe views may be 2417 * found in the documentation for the {@link #checkedCollection 2418 * checkedCollection} method. 2419 * 2420 * <p>The returned sorted set will be serializable if the specified sorted 2421 * set is serializable. 2422 * 2423 * <p>Since {@code null} is considered to be a value of any reference 2424 * type, the returned sorted set permits insertion of null elements 2425 * whenever the backing sorted set does. 2426 * 2427 * @param s the sorted set for which a dynamically typesafe view is to be 2428 * returned 2429 * @param type the type of element that {@code s} is permitted to hold 2430 * @return a dynamically typesafe view of the specified sorted set 2431 * @since 1.5 2432 */ 2433 public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s, 2434 Class<E> type) { 2435 return new CheckedSortedSet<>(s, type); 2436 } 2437 2438 /** 2439 * @serial include 2440 */ 2441 static class CheckedSortedSet<E> extends CheckedSet<E> 2442 implements SortedSet<E>, Serializable 2443 { 2444 private static final long serialVersionUID = 1599911165492914959L; 2445 private final SortedSet<E> ss; 2446 2447 CheckedSortedSet(SortedSet<E> s, Class<E> type) { 2448 super(s, type); 2449 ss = s; 2450 } 2451 2452 public Comparator<? super E> comparator() { return ss.comparator(); } 2453 public E first() { return ss.first(); } 2454 public E last() { return ss.last(); } 2455 2456 public SortedSet<E> subSet(E fromElement, E toElement) { 2457 return checkedSortedSet(ss.subSet(fromElement,toElement), type); 2458 } 2459 public SortedSet<E> headSet(E toElement) { 2460 return checkedSortedSet(ss.headSet(toElement), type); 2461 } 2462 public SortedSet<E> tailSet(E fromElement) { 2463 return checkedSortedSet(ss.tailSet(fromElement), type); 2464 } 2465 } 2466 2467 /** 2468 * Returns a dynamically typesafe view of the specified list. 2469 * Any attempt to insert an element of the wrong type will result in 2470 * an immediate {@link ClassCastException}. Assuming a list contains 2471 * no incorrectly typed elements prior to the time a dynamically typesafe 2472 * view is generated, and that all subsequent access to the list 2473 * takes place through the view, it is <i>guaranteed</i> that the 2474 * list cannot contain an incorrectly typed element. 2475 * 2476 * <p>A discussion of the use of dynamically typesafe views may be 2477 * found in the documentation for the {@link #checkedCollection 2478 * checkedCollection} method. 2479 * 2480 * <p>The returned list will be serializable if the specified list 2481 * is serializable. 2482 * 2483 * <p>Since {@code null} is considered to be a value of any reference 2484 * type, the returned list permits insertion of null elements whenever 2485 * the backing list does. 2486 * 2487 * @param list the list for which a dynamically typesafe view is to be 2488 * returned 2489 * @param type the type of element that {@code list} is permitted to hold 2490 * @return a dynamically typesafe view of the specified list 2491 * @since 1.5 2492 */ 2493 public static <E> List<E> checkedList(List<E> list, Class<E> type) { 2494 return (list instanceof RandomAccess ? 2495 new CheckedRandomAccessList<>(list, type) : 2496 new CheckedList<>(list, type)); 2497 } 2498 2499 /** 2500 * @serial include 2501 */ 2502 static class CheckedList<E> 2503 extends CheckedCollection<E> 2504 implements List<E> 2505 { 2506 private static final long serialVersionUID = 65247728283967356L; 2507 final List<E> list; 2508 2509 CheckedList(List<E> list, Class<E> type) { 2510 super(list, type); 2511 this.list = list; 2512 } 2513 2514 public boolean equals(Object o) { return o == this || list.equals(o); } 2515 public int hashCode() { return list.hashCode(); } 2516 public E get(int index) { return list.get(index); } 2517 public E remove(int index) { return list.remove(index); } 2518 public int indexOf(Object o) { return list.indexOf(o); } 2519 public int lastIndexOf(Object o) { return list.lastIndexOf(o); } 2520 2521 public E set(int index, E element) { 2522 typeCheck(element); 2523 return list.set(index, element); 2524 } 2525 2526 public void add(int index, E element) { 2527 typeCheck(element); 2528 list.add(index, element); 2529 } 2530 2531 public boolean addAll(int index, Collection<? extends E> c) { 2532 return list.addAll(index, checkedCopyOf(c)); 2533 } 2534 public ListIterator<E> listIterator() { return listIterator(0); } 2535 2536 public ListIterator<E> listIterator(final int index) { 2537 final ListIterator<E> i = list.listIterator(index); 2538 2539 return new ListIterator<E>() { 2540 public boolean hasNext() { return i.hasNext(); } 2541 public E next() { return i.next(); } 2542 public boolean hasPrevious() { return i.hasPrevious(); } 2543 public E previous() { return i.previous(); } 2544 public int nextIndex() { return i.nextIndex(); } 2545 public int previousIndex() { return i.previousIndex(); } 2546 public void remove() { i.remove(); } 2547 2548 public void set(E e) { 2549 typeCheck(e); 2550 i.set(e); 2551 } 2552 2553 public void add(E e) { 2554 typeCheck(e); 2555 i.add(e); 2556 } 2557 }; 2558 } 2559 2560 public List<E> subList(int fromIndex, int toIndex) { 2561 return new CheckedList<>(list.subList(fromIndex, toIndex), type); 2562 } 2563 } 2564 2565 /** 2566 * @serial include 2567 */ 2568 static class CheckedRandomAccessList<E> extends CheckedList<E> 2569 implements RandomAccess 2570 { 2571 private static final long serialVersionUID = 1638200125423088369L; 2572 2573 CheckedRandomAccessList(List<E> list, Class<E> type) { 2574 super(list, type); 2575 } 2576 2577 public List<E> subList(int fromIndex, int toIndex) { 2578 return new CheckedRandomAccessList<>( 2579 list.subList(fromIndex, toIndex), type); 2580 } 2581 } 2582 2583 /** 2584 * Returns a dynamically typesafe view of the specified map. 2585 * Any attempt to insert a mapping whose key or value have the wrong 2586 * type will result in an immediate {@link ClassCastException}. 2587 * Similarly, any attempt to modify the value currently associated with 2588 * a key will result in an immediate {@link ClassCastException}, 2589 * whether the modification is attempted directly through the map 2590 * itself, or through a {@link Map.Entry} instance obtained from the 2591 * map's {@link Map#entrySet() entry set} view. 2592 * 2593 * <p>Assuming a map contains no incorrectly typed keys or values 2594 * prior to the time a dynamically typesafe view is generated, and 2595 * that all subsequent access to the map takes place through the view 2596 * (or one of its collection views), it is <i>guaranteed</i> that the 2597 * map cannot contain an incorrectly typed key or value. 2598 * 2599 * <p>A discussion of the use of dynamically typesafe views may be 2600 * found in the documentation for the {@link #checkedCollection 2601 * checkedCollection} method. 2602 * 2603 * <p>The returned map will be serializable if the specified map is 2604 * serializable. 2605 * 2606 * <p>Since {@code null} is considered to be a value of any reference 2607 * type, the returned map permits insertion of null keys or values 2608 * whenever the backing map does. 2609 * 2610 * @param m the map for which a dynamically typesafe view is to be 2611 * returned 2612 * @param keyType the type of key that {@code m} is permitted to hold 2613 * @param valueType the type of value that {@code m} is permitted to hold 2614 * @return a dynamically typesafe view of the specified map 2615 * @since 1.5 2616 */ 2617 public static <K, V> Map<K, V> checkedMap(Map<K, V> m, 2618 Class<K> keyType, 2619 Class<V> valueType) { 2620 return new CheckedMap<>(m, keyType, valueType); 2621 } 2622 2623 2624 /** 2625 * @serial include 2626 */ 2627 private static class CheckedMap<K,V> 2628 implements Map<K,V>, Serializable 2629 { 2630 private static final long serialVersionUID = 5742860141034234728L; 2631 2632 private final Map<K, V> m; 2633 final Class<K> keyType; 2634 final Class<V> valueType; 2635 2636 private void typeCheck(Object key, Object value) { 2637 if (key != null && !keyType.isInstance(key)) 2638 throw new ClassCastException(badKeyMsg(key)); 2639 2640 if (value != null && !valueType.isInstance(value)) 2641 throw new ClassCastException(badValueMsg(value)); 2642 } 2643 2644 private String badKeyMsg(Object key) { 2645 return "Attempt to insert " + key.getClass() + 2646 " key into map with key type " + keyType; 2647 } 2648 2649 private String badValueMsg(Object value) { 2650 return "Attempt to insert " + value.getClass() + 2651 " value into map with value type " + valueType; 2652 } 2653 2654 CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) { 2655 if (m == null || keyType == null || valueType == null) 2656 throw new NullPointerException(); 2657 this.m = m; 2658 this.keyType = keyType; 2659 this.valueType = valueType; 2660 } 2661 2662 public int size() { return m.size(); } 2663 public boolean isEmpty() { return m.isEmpty(); } 2664 public boolean containsKey(Object key) { return m.containsKey(key); } 2665 public boolean containsValue(Object v) { return m.containsValue(v); } 2666 public V get(Object key) { return m.get(key); } 2667 public V remove(Object key) { return m.remove(key); } 2668 public void clear() { m.clear(); } 2669 public Set<K> keySet() { return m.keySet(); } 2670 public Collection<V> values() { return m.values(); } 2671 public boolean equals(Object o) { return o == this || m.equals(o); } 2672 public int hashCode() { return m.hashCode(); } 2673 public String toString() { return m.toString(); } 2674 2675 public V put(K key, V value) { 2676 typeCheck(key, value); 2677 return m.put(key, value); 2678 } 2679 2680 @SuppressWarnings("unchecked") 2681 public void putAll(Map<? extends K, ? extends V> t) { 2682 // Satisfy the following goals: 2683 // - good diagnostics in case of type mismatch 2684 // - all-or-nothing semantics 2685 // - protection from malicious t 2686 // - correct behavior if t is a concurrent map 2687 Object[] entries = t.entrySet().toArray(); 2688 List<Map.Entry<K,V>> checked = new ArrayList<>(entries.length); 2689 for (Object o : entries) { 2690 Map.Entry<?,?> e = (Map.Entry<?,?>) o; 2691 Object k = e.getKey(); 2692 Object v = e.getValue(); 2693 typeCheck(k, v); 2694 checked.add( 2695 new AbstractMap.SimpleImmutableEntry<>((K) k, (V) v)); 2696 } 2697 for (Map.Entry<K,V> e : checked) 2698 m.put(e.getKey(), e.getValue()); 2699 } 2700 2701 private transient Set<Map.Entry<K,V>> entrySet = null; 2702 2703 public Set<Map.Entry<K,V>> entrySet() { 2704 if (entrySet==null) 2705 entrySet = new CheckedEntrySet<>(m.entrySet(), valueType); 2706 return entrySet; 2707 } 2708 2709 /** 2710 * We need this class in addition to CheckedSet as Map.Entry permits 2711 * modification of the backing Map via the setValue operation. This 2712 * class is subtle: there are many possible attacks that must be 2713 * thwarted. 2714 * 2715 * @serial exclude 2716 */ 2717 static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> { 2718 private final Set<Map.Entry<K,V>> s; 2719 private final Class<V> valueType; 2720 2721 CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) { 2722 this.s = s; 2723 this.valueType = valueType; 2724 } 2725 2726 public int size() { return s.size(); } 2727 public boolean isEmpty() { return s.isEmpty(); } 2728 public String toString() { return s.toString(); } 2729 public int hashCode() { return s.hashCode(); } 2730 public void clear() { s.clear(); } 2731 2732 public boolean add(Map.Entry<K, V> e) { 2733 throw new UnsupportedOperationException(); 2734 } 2735 public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) { 2736 throw new UnsupportedOperationException(); 2737 } 2738 2739 public Iterator<Map.Entry<K,V>> iterator() { 2740 final Iterator<Map.Entry<K, V>> i = s.iterator(); 2741 final Class<V> valueType = this.valueType; 2742 2743 return new Iterator<Map.Entry<K,V>>() { 2744 public boolean hasNext() { return i.hasNext(); } 2745 public void remove() { i.remove(); } 2746 2747 public Map.Entry<K,V> next() { 2748 return checkedEntry(i.next(), valueType); 2749 } 2750 }; 2751 } 2752 2753 @SuppressWarnings("unchecked") 2754 public Object[] toArray() { 2755 Object[] source = s.toArray(); 2756 2757 /* 2758 * Ensure that we don't get an ArrayStoreException even if 2759 * s.toArray returns an array of something other than Object 2760 */ 2761 Object[] dest = (CheckedEntry.class.isInstance( 2762 source.getClass().getComponentType()) ? source : 2763 new Object[source.length]); 2764 2765 for (int i = 0; i < source.length; i++) 2766 dest[i] = checkedEntry((Map.Entry<K,V>)source[i], 2767 valueType); 2768 return dest; 2769 } 2770 2771 @SuppressWarnings("unchecked") 2772 public <T> T[] toArray(T[] a) { 2773 // We don't pass a to s.toArray, to avoid window of 2774 // vulnerability wherein an unscrupulous multithreaded client 2775 // could get his hands on raw (unwrapped) Entries from s. 2776 T[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0)); 2777 2778 for (int i=0; i<arr.length; i++) 2779 arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i], 2780 valueType); 2781 if (arr.length > a.length) 2782 return arr; 2783 2784 System.arraycopy(arr, 0, a, 0, arr.length); 2785 if (a.length > arr.length) 2786 a[arr.length] = null; 2787 return a; 2788 } 2789 2790 /** 2791 * This method is overridden to protect the backing set against 2792 * an object with a nefarious equals function that senses 2793 * that the equality-candidate is Map.Entry and calls its 2794 * setValue method. 2795 */ 2796 public boolean contains(Object o) { 2797 if (!(o instanceof Map.Entry)) 2798 return false; 2799 Map.Entry<?,?> e = (Map.Entry<?,?>) o; 2800 return s.contains( 2801 (e instanceof CheckedEntry) ? e : checkedEntry(e, valueType)); 2802 } 2803 2804 /** 2805 * The bulk collection methods are overridden to protect 2806 * against an unscrupulous collection whose contains(Object o) 2807 * method senses when o is a Map.Entry, and calls o.setValue. 2808 */ 2809 public boolean containsAll(Collection<?> c) { 2810 for (Object o : c) 2811 if (!contains(o)) // Invokes safe contains() above 2812 return false; 2813 return true; 2814 } 2815 2816 public boolean remove(Object o) { 2817 if (!(o instanceof Map.Entry)) 2818 return false; 2819 return s.remove(new AbstractMap.SimpleImmutableEntry 2820 <>((Map.Entry<?,?>)o)); 2821 } 2822 2823 public boolean removeAll(Collection<?> c) { 2824 return batchRemove(c, false); 2825 } 2826 public boolean retainAll(Collection<?> c) { 2827 return batchRemove(c, true); 2828 } 2829 private boolean batchRemove(Collection<?> c, boolean complement) { 2830 boolean modified = false; 2831 Iterator<Map.Entry<K,V>> it = iterator(); 2832 while (it.hasNext()) { 2833 if (c.contains(it.next()) != complement) { 2834 it.remove(); 2835 modified = true; 2836 } 2837 } 2838 return modified; 2839 } 2840 2841 public boolean equals(Object o) { 2842 if (o == this) 2843 return true; 2844 if (!(o instanceof Set)) 2845 return false; 2846 Set<?> that = (Set<?>) o; 2847 return that.size() == s.size() 2848 && containsAll(that); // Invokes safe containsAll() above 2849 } 2850 2851 static <K,V,T> CheckedEntry<K,V,T> checkedEntry(Map.Entry<K,V> e, 2852 Class<T> valueType) { 2853 return new CheckedEntry<>(e, valueType); 2854 } 2855 2856 /** 2857 * This "wrapper class" serves two purposes: it prevents 2858 * the client from modifying the backing Map, by short-circuiting 2859 * the setValue method, and it protects the backing Map against 2860 * an ill-behaved Map.Entry that attempts to modify another 2861 * Map.Entry when asked to perform an equality check. 2862 */ 2863 private static class CheckedEntry<K,V,T> implements Map.Entry<K,V> { 2864 private final Map.Entry<K, V> e; 2865 private final Class<T> valueType; 2866 2867 CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) { 2868 this.e = e; 2869 this.valueType = valueType; 2870 } 2871 2872 public K getKey() { return e.getKey(); } 2873 public V getValue() { return e.getValue(); } 2874 public int hashCode() { return e.hashCode(); } 2875 public String toString() { return e.toString(); } 2876 2877 public V setValue(V value) { 2878 if (value != null && !valueType.isInstance(value)) 2879 throw new ClassCastException(badValueMsg(value)); 2880 return e.setValue(value); 2881 } 2882 2883 private String badValueMsg(Object value) { 2884 return "Attempt to insert " + value.getClass() + 2885 " value into map with value type " + valueType; 2886 } 2887 2888 public boolean equals(Object o) { 2889 if (o == this) 2890 return true; 2891 if (!(o instanceof Map.Entry)) 2892 return false; 2893 return e.equals(new AbstractMap.SimpleImmutableEntry 2894 <>((Map.Entry<?,?>)o)); 2895 } 2896 } 2897 } 2898 } 2899 2900 /** 2901 * Returns a dynamically typesafe view of the specified sorted map. 2902 * Any attempt to insert a mapping whose key or value have the wrong 2903 * type will result in an immediate {@link ClassCastException}. 2904 * Similarly, any attempt to modify the value currently associated with 2905 * a key will result in an immediate {@link ClassCastException}, 2906 * whether the modification is attempted directly through the map 2907 * itself, or through a {@link Map.Entry} instance obtained from the 2908 * map's {@link Map#entrySet() entry set} view. 2909 * 2910 * <p>Assuming a map contains no incorrectly typed keys or values 2911 * prior to the time a dynamically typesafe view is generated, and 2912 * that all subsequent access to the map takes place through the view 2913 * (or one of its collection views), it is <i>guaranteed</i> that the 2914 * map cannot contain an incorrectly typed key or value. 2915 * 2916 * <p>A discussion of the use of dynamically typesafe views may be 2917 * found in the documentation for the {@link #checkedCollection 2918 * checkedCollection} method. 2919 * 2920 * <p>The returned map will be serializable if the specified map is 2921 * serializable. 2922 * 2923 * <p>Since {@code null} is considered to be a value of any reference 2924 * type, the returned map permits insertion of null keys or values 2925 * whenever the backing map does. 2926 * 2927 * @param m the map for which a dynamically typesafe view is to be 2928 * returned 2929 * @param keyType the type of key that {@code m} is permitted to hold 2930 * @param valueType the type of value that {@code m} is permitted to hold 2931 * @return a dynamically typesafe view of the specified map 2932 * @since 1.5 2933 */ 2934 public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m, 2935 Class<K> keyType, 2936 Class<V> valueType) { 2937 return new CheckedSortedMap<>(m, keyType, valueType); 2938 } 2939 2940 /** 2941 * @serial include 2942 */ 2943 static class CheckedSortedMap<K,V> extends CheckedMap<K,V> 2944 implements SortedMap<K,V>, Serializable 2945 { 2946 private static final long serialVersionUID = 1599671320688067438L; 2947 2948 private final SortedMap<K, V> sm; 2949 2950 CheckedSortedMap(SortedMap<K, V> m, 2951 Class<K> keyType, Class<V> valueType) { 2952 super(m, keyType, valueType); 2953 sm = m; 2954 } 2955 2956 public Comparator<? super K> comparator() { return sm.comparator(); } 2957 public K firstKey() { return sm.firstKey(); } 2958 public K lastKey() { return sm.lastKey(); } 2959 2960 public SortedMap<K,V> subMap(K fromKey, K toKey) { 2961 return checkedSortedMap(sm.subMap(fromKey, toKey), 2962 keyType, valueType); 2963 } 2964 public SortedMap<K,V> headMap(K toKey) { 2965 return checkedSortedMap(sm.headMap(toKey), keyType, valueType); 2966 } 2967 public SortedMap<K,V> tailMap(K fromKey) { 2968 return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType); 2969 } 2970 } 2971 2972 // Empty collections 2973 2974 /** 2975 * Returns an iterator that has no elements. More precisely, 2976 * 2977 * <ul compact> 2978 * 2979 * <li>{@link Iterator#hasNext hasNext} always returns {@code 2980 * false}. 2981 * 2982 * <li>{@link Iterator#next next} always throws {@link 2983 * NoSuchElementException}. 2984 * 2985 * <li>{@link Iterator#remove remove} always throws {@link 2986 * IllegalStateException}. 2987 * 2988 * </ul> 2989 * 2990 * <p>Implementations of this method are permitted, but not 2991 * required, to return the same object from multiple invocations. 2992 * 2993 * @return an empty iterator 2994 * @since 1.7 2995 */ 2996 @SuppressWarnings("unchecked") 2997 public static <T> Iterator<T> emptyIterator() { 2998 return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR; 2999 } 3000 3001 private static class EmptyIterator<E> implements Iterator<E> { 3002 static final EmptyIterator<Object> EMPTY_ITERATOR 3003 = new EmptyIterator<>(); 3004 3005 public boolean hasNext() { return false; } 3006 public E next() { throw new NoSuchElementException(); } 3007 public void remove() { throw new IllegalStateException(); } 3008 } 3009 3010 /** 3011 * Returns a list iterator that has no elements. More precisely, 3012 * 3013 * <ul compact> 3014 * 3015 * <li>{@link Iterator#hasNext hasNext} and {@link 3016 * ListIterator#hasPrevious hasPrevious} always return {@code 3017 * false}. 3018 * 3019 * <li>{@link Iterator#next next} and {@link ListIterator#previous 3020 * previous} always throw {@link NoSuchElementException}. 3021 * 3022 * <li>{@link Iterator#remove remove} and {@link ListIterator#set 3023 * set} always throw {@link IllegalStateException}. 3024 * 3025 * <li>{@link ListIterator#add add} always throws {@link 3026 * UnsupportedOperationException}. 3027 * 3028 * <li>{@link ListIterator#nextIndex nextIndex} always returns 3029 * {@code 0} . 3030 * 3031 * <li>{@link ListIterator#previousIndex previousIndex} always 3032 * returns {@code -1}. 3033 * 3034 * </ul> 3035 * 3036 * <p>Implementations of this method are permitted, but not 3037 * required, to return the same object from multiple invocations. 3038 * 3039 * @return an empty list iterator 3040 * @since 1.7 3041 */ 3042 @SuppressWarnings("unchecked") 3043 public static <T> ListIterator<T> emptyListIterator() { 3044 return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR; 3045 } 3046 3047 private static class EmptyListIterator<E> 3048 extends EmptyIterator<E> 3049 implements ListIterator<E> 3050 { 3051 static final EmptyListIterator<Object> EMPTY_ITERATOR 3052 = new EmptyListIterator<>(); 3053 3054 public boolean hasPrevious() { return false; } 3055 public E previous() { throw new NoSuchElementException(); } 3056 public int nextIndex() { return 0; } 3057 public int previousIndex() { return -1; } 3058 public void set(E e) { throw new IllegalStateException(); } 3059 public void add(E e) { throw new UnsupportedOperationException(); } 3060 } 3061 3062 /** 3063 * Returns an enumeration that has no elements. More precisely, 3064 * 3065 * <ul compact> 3066 * 3067 * <li>{@link Enumeration#hasMoreElements hasMoreElements} always 3068 * returns {@code false}. 3069 * 3070 * <li> {@link Enumeration#nextElement nextElement} always throws 3071 * {@link NoSuchElementException}. 3072 * 3073 * </ul> 3074 * 3075 * <p>Implementations of this method are permitted, but not 3076 * required, to return the same object from multiple invocations. 3077 * 3078 * @return an empty enumeration 3079 * @since 1.7 3080 */ 3081 @SuppressWarnings("unchecked") 3082 public static <T> Enumeration<T> emptyEnumeration() { 3083 return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION; 3084 } 3085 3086 private static class EmptyEnumeration<E> implements Enumeration<E> { 3087 static final EmptyEnumeration<Object> EMPTY_ENUMERATION 3088 = new EmptyEnumeration<>(); 3089 3090 public boolean hasMoreElements() { return false; } 3091 public E nextElement() { throw new NoSuchElementException(); } 3092 } 3093 3094 /** 3095 * The empty set (immutable). This set is serializable. 3096 * 3097 * @see #emptySet() 3098 */ 3099 @SuppressWarnings("unchecked") 3100 public static final Set EMPTY_SET = new EmptySet<>(); 3101 3102 /** 3103 * Returns the empty set (immutable). This set is serializable. 3104 * Unlike the like-named field, this method is parameterized. 3105 * 3106 * <p>This example illustrates the type-safe way to obtain an empty set: 3107 * <pre> 3108 * Set<String> s = Collections.emptySet(); 3109 * </pre> 3110 * Implementation note: Implementations of this method need not 3111 * create a separate <tt>Set</tt> object for each call. Using this 3112 * method is likely to have comparable cost to using the like-named 3113 * field. (Unlike this method, the field does not provide type safety.) 3114 * 3115 * @see #EMPTY_SET 3116 * @since 1.5 3117 */ 3118 @SuppressWarnings("unchecked") 3119 public static final <T> Set<T> emptySet() { 3120 return (Set<T>) EMPTY_SET; 3121 } 3122 3123 /** 3124 * @serial include 3125 */ 3126 private static class EmptySet<E> 3127 extends AbstractSet<E> 3128 implements Serializable 3129 { 3130 private static final long serialVersionUID = 1582296315990362920L; 3131 3132 public Iterator<E> iterator() { return emptyIterator(); } 3133 3134 public int size() {return 0;} 3135 public boolean isEmpty() {return true;} 3136 3137 public boolean contains(Object obj) {return false;} 3138 public boolean containsAll(Collection<?> c) { return c.isEmpty(); } 3139 3140 public Object[] toArray() { return new Object[0]; } 3141 3142 public <T> T[] toArray(T[] a) { 3143 if (a.length > 0) 3144 a[0] = null; 3145 return a; 3146 } 3147 3148 // Preserves singleton property 3149 private Object readResolve() { 3150 return EMPTY_SET; 3151 } 3152 } 3153 3154 /** 3155 * The empty list (immutable). This list is serializable. 3156 * 3157 * @see #emptyList() 3158 */ 3159 @SuppressWarnings("unchecked") 3160 public static final List EMPTY_LIST = new EmptyList<>(); 3161 3162 /** 3163 * Returns the empty list (immutable). This list is serializable. 3164 * 3165 * <p>This example illustrates the type-safe way to obtain an empty list: 3166 * <pre> 3167 * List<String> s = Collections.emptyList(); 3168 * </pre> 3169 * Implementation note: Implementations of this method need not 3170 * create a separate <tt>List</tt> object for each call. Using this 3171 * method is likely to have comparable cost to using the like-named 3172 * field. (Unlike this method, the field does not provide type safety.) 3173 * 3174 * @see #EMPTY_LIST 3175 * @since 1.5 3176 */ 3177 @SuppressWarnings("unchecked") 3178 public static final <T> List<T> emptyList() { 3179 return (List<T>) EMPTY_LIST; 3180 } 3181 3182 /** 3183 * @serial include 3184 */ 3185 private static class EmptyList<E> 3186 extends AbstractList<E> 3187 implements RandomAccess, Serializable { 3188 private static final long serialVersionUID = 8842843931221139166L; 3189 3190 public Iterator<E> iterator() { 3191 return emptyIterator(); 3192 } 3193 public ListIterator<E> listIterator() { 3194 return emptyListIterator(); 3195 } 3196 3197 public int size() {return 0;} 3198 public boolean isEmpty() {return true;} 3199 3200 public boolean contains(Object obj) {return false;} 3201 public boolean containsAll(Collection<?> c) { return c.isEmpty(); } 3202 3203 public Object[] toArray() { return new Object[0]; } 3204 3205 public <T> T[] toArray(T[] a) { 3206 if (a.length > 0) 3207 a[0] = null; 3208 return a; 3209 } 3210 3211 public E get(int index) { 3212 throw new IndexOutOfBoundsException("Index: "+index); 3213 } 3214 3215 public boolean equals(Object o) { 3216 return (o instanceof List) && ((List<?>)o).isEmpty(); 3217 } 3218 3219 public int hashCode() { return 1; } 3220 3221 // Preserves singleton property 3222 private Object readResolve() { 3223 return EMPTY_LIST; 3224 } 3225 } 3226 3227 /** 3228 * The empty map (immutable). This map is serializable. 3229 * 3230 * @see #emptyMap() 3231 * @since 1.3 3232 */ 3233 @SuppressWarnings("unchecked") 3234 public static final Map EMPTY_MAP = new EmptyMap<>(); 3235 3236 /** 3237 * Returns the empty map (immutable). This map is serializable. 3238 * 3239 * <p>This example illustrates the type-safe way to obtain an empty set: 3240 * <pre> 3241 * Map<String, Date> s = Collections.emptyMap(); 3242 * </pre> 3243 * Implementation note: Implementations of this method need not 3244 * create a separate <tt>Map</tt> object for each call. Using this 3245 * method is likely to have comparable cost to using the like-named 3246 * field. (Unlike this method, the field does not provide type safety.) 3247 * 3248 * @see #EMPTY_MAP 3249 * @since 1.5 3250 */ 3251 @SuppressWarnings("unchecked") 3252 public static final <K,V> Map<K,V> emptyMap() { 3253 return (Map<K,V>) EMPTY_MAP; 3254 } 3255 3256 /** 3257 * @serial include 3258 */ 3259 private static class EmptyMap<K,V> 3260 extends AbstractMap<K,V> 3261 implements Serializable 3262 { 3263 private static final long serialVersionUID = 6428348081105594320L; 3264 3265 public int size() {return 0;} 3266 public boolean isEmpty() {return true;} 3267 public boolean containsKey(Object key) {return false;} 3268 public boolean containsValue(Object value) {return false;} 3269 public V get(Object key) {return null;} 3270 public Set<K> keySet() {return emptySet();} 3271 public Collection<V> values() {return emptySet();} 3272 public Set<Map.Entry<K,V>> entrySet() {return emptySet();} 3273 3274 public boolean equals(Object o) { 3275 return (o instanceof Map) && ((Map<?,?>)o).isEmpty(); 3276 } 3277 3278 public int hashCode() {return 0;} 3279 3280 // Preserves singleton property 3281 private Object readResolve() { 3282 return EMPTY_MAP; 3283 } 3284 } 3285 3286 // Singleton collections 3287 3288 /** 3289 * Returns an immutable set containing only the specified object. 3290 * The returned set is serializable. 3291 * 3292 * @param o the sole object to be stored in the returned set. 3293 * @return an immutable set containing only the specified object. 3294 */ 3295 public static <T> Set<T> singleton(T o) { 3296 return new SingletonSet<>(o); 3297 } 3298 3299 static <E> Iterator<E> singletonIterator(final E e) { 3300 return new Iterator<E>() { 3301 private boolean hasNext = true; 3302 public boolean hasNext() { 3303 return hasNext; 3304 } 3305 public E next() { 3306 if (hasNext) { 3307 hasNext = false; 3308 return e; 3309 } 3310 throw new NoSuchElementException(); 3311 } 3312 public void remove() { 3313 throw new UnsupportedOperationException(); 3314 } 3315 }; 3316 } 3317 3318 /** 3319 * @serial include 3320 */ 3321 private static class SingletonSet<E> 3322 extends AbstractSet<E> 3323 implements Serializable 3324 { 3325 private static final long serialVersionUID = 3193687207550431679L; 3326 3327 private final E element; 3328 3329 SingletonSet(E e) {element = e;} 3330 3331 public Iterator<E> iterator() { 3332 return singletonIterator(element); 3333 } 3334 3335 public int size() {return 1;} 3336 3337 public boolean contains(Object o) {return eq(o, element);} 3338 } 3339 3340 /** 3341 * Returns an immutable list containing only the specified object. 3342 * The returned list is serializable. 3343 * 3344 * @param o the sole object to be stored in the returned list. 3345 * @return an immutable list containing only the specified object. 3346 * @since 1.3 3347 */ 3348 public static <T> List<T> singletonList(T o) { 3349 return new SingletonList<>(o); 3350 } 3351 3352 /** 3353 * @serial include 3354 */ 3355 private static class SingletonList<E> 3356 extends AbstractList<E> 3357 implements RandomAccess, Serializable { 3358 3359 private static final long serialVersionUID = 3093736618740652951L; 3360 3361 private final E element; 3362 3363 SingletonList(E obj) {element = obj;} 3364 3365 public Iterator<E> iterator() { 3366 return singletonIterator(element); 3367 } 3368 3369 public int size() {return 1;} 3370 3371 public boolean contains(Object obj) {return eq(obj, element);} 3372 3373 public E get(int index) { 3374 if (index != 0) 3375 throw new IndexOutOfBoundsException("Index: "+index+", Size: 1"); 3376 return element; 3377 } 3378 } 3379 3380 /** 3381 * Returns an immutable map, mapping only the specified key to the 3382 * specified value. The returned map is serializable. 3383 * 3384 * @param key the sole key to be stored in the returned map. 3385 * @param value the value to which the returned map maps <tt>key</tt>. 3386 * @return an immutable map containing only the specified key-value 3387 * mapping. 3388 * @since 1.3 3389 */ 3390 public static <K,V> Map<K,V> singletonMap(K key, V value) { 3391 return new SingletonMap<>(key, value); 3392 } 3393 3394 /** 3395 * @serial include 3396 */ 3397 private static class SingletonMap<K,V> 3398 extends AbstractMap<K,V> 3399 implements Serializable { 3400 private static final long serialVersionUID = -6979724477215052911L; 3401 3402 private final K k; 3403 private final V v; 3404 3405 SingletonMap(K key, V value) { 3406 k = key; 3407 v = value; 3408 } 3409 3410 public int size() {return 1;} 3411 3412 public boolean isEmpty() {return false;} 3413 3414 public boolean containsKey(Object key) {return eq(key, k);} 3415 3416 public boolean containsValue(Object value) {return eq(value, v);} 3417 3418 public V get(Object key) {return (eq(key, k) ? v : null);} 3419 3420 private transient Set<K> keySet = null; 3421 private transient Set<Map.Entry<K,V>> entrySet = null; 3422 private transient Collection<V> values = null; 3423 3424 public Set<K> keySet() { 3425 if (keySet==null) 3426 keySet = singleton(k); 3427 return keySet; 3428 } 3429 3430 public Set<Map.Entry<K,V>> entrySet() { 3431 if (entrySet==null) 3432 entrySet = Collections.<Map.Entry<K,V>>singleton( 3433 new SimpleImmutableEntry<>(k, v)); 3434 return entrySet; 3435 } 3436 3437 public Collection<V> values() { 3438 if (values==null) 3439 values = singleton(v); 3440 return values; 3441 } 3442 3443 } 3444 3445 // Miscellaneous 3446 3447 /** 3448 * Returns an immutable list consisting of <tt>n</tt> copies of the 3449 * specified object. The newly allocated data object is tiny (it contains 3450 * a single reference to the data object). This method is useful in 3451 * combination with the <tt>List.addAll</tt> method to grow lists. 3452 * The returned list is serializable. 3453 * 3454 * @param n the number of elements in the returned list. 3455 * @param o the element to appear repeatedly in the returned list. 3456 * @return an immutable list consisting of <tt>n</tt> copies of the 3457 * specified object. 3458 * @throws IllegalArgumentException if {@code n < 0} 3459 * @see List#addAll(Collection) 3460 * @see List#addAll(int, Collection) 3461 */ 3462 public static <T> List<T> nCopies(int n, T o) { 3463 if (n < 0) 3464 throw new IllegalArgumentException("List length = " + n); 3465 return new CopiesList<>(n, o); 3466 } 3467 3468 /** 3469 * @serial include 3470 */ 3471 private static class CopiesList<E> 3472 extends AbstractList<E> 3473 implements RandomAccess, Serializable 3474 { 3475 private static final long serialVersionUID = 2739099268398711800L; 3476 3477 final int n; 3478 final E element; 3479 3480 CopiesList(int n, E e) { 3481 assert n >= 0; 3482 this.n = n; 3483 element = e; 3484 } 3485 3486 public int size() { 3487 return n; 3488 } 3489 3490 public boolean contains(Object obj) { 3491 return n != 0 && eq(obj, element); 3492 } 3493 3494 public int indexOf(Object o) { 3495 return contains(o) ? 0 : -1; 3496 } 3497 3498 public int lastIndexOf(Object o) { 3499 return contains(o) ? n - 1 : -1; 3500 } 3501 3502 public E get(int index) { 3503 if (index < 0 || index >= n) 3504 throw new IndexOutOfBoundsException("Index: "+index+ 3505 ", Size: "+n); 3506 return element; 3507 } 3508 3509 public Object[] toArray() { 3510 final Object[] a = new Object[n]; 3511 if (element != null) 3512 Arrays.fill(a, 0, n, element); 3513 return a; 3514 } 3515 3516 public <T> T[] toArray(T[] a) { 3517 final int n = this.n; 3518 if (a.length < n) { 3519 a = (T[])java.lang.reflect.Array 3520 .newInstance(a.getClass().getComponentType(), n); 3521 if (element != null) 3522 Arrays.fill(a, 0, n, element); 3523 } else { 3524 Arrays.fill(a, 0, n, element); 3525 if (a.length > n) 3526 a[n] = null; 3527 } 3528 return a; 3529 } 3530 3531 public List<E> subList(int fromIndex, int toIndex) { 3532 if (fromIndex < 0) 3533 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex); 3534 if (toIndex > n) 3535 throw new IndexOutOfBoundsException("toIndex = " + toIndex); 3536 if (fromIndex > toIndex) 3537 throw new IllegalArgumentException("fromIndex(" + fromIndex + 3538 ") > toIndex(" + toIndex + ")"); 3539 return new CopiesList<>(toIndex - fromIndex, element); 3540 } 3541 } 3542 3543 /** 3544 * Returns a comparator that imposes the reverse of the <em>natural 3545 * ordering</em> on a collection of objects that implement the 3546 * {@code Comparable} interface. (The natural ordering is the ordering 3547 * imposed by the objects' own {@code compareTo} method.) This enables a 3548 * simple idiom for sorting (or maintaining) collections (or arrays) of 3549 * objects that implement the {@code Comparable} interface in 3550 * reverse-natural-order. For example, suppose {@code a} is an array of 3551 * strings. Then: <pre> 3552 * Arrays.sort(a, Collections.reverseOrder()); 3553 * </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p> 3554 * 3555 * The returned comparator is serializable. 3556 * 3557 * @return A comparator that imposes the reverse of the <i>natural 3558 * ordering</i> on a collection of objects that implement 3559 * the <tt>Comparable</tt> interface. 3560 * @see Comparable 3561 */ 3562 public static <T> Comparator<T> reverseOrder() { 3563 return (Comparator<T>) ReverseComparator.REVERSE_ORDER; 3564 } 3565 3566 /** 3567 * @serial include 3568 */ 3569 private static class ReverseComparator 3570 implements Comparator<Comparable<Object>>, Serializable { 3571 3572 private static final long serialVersionUID = 7207038068494060240L; 3573 3574 static final ReverseComparator REVERSE_ORDER 3575 = new ReverseComparator(); 3576 3577 public int compare(Comparable<Object> c1, Comparable<Object> c2) { 3578 return c2.compareTo(c1); 3579 } 3580 3581 private Object readResolve() { return reverseOrder(); } 3582 } 3583 3584 /** 3585 * Returns a comparator that imposes the reverse ordering of the specified 3586 * comparator. If the specified comparator is {@code null}, this method is 3587 * equivalent to {@link #reverseOrder()} (in other words, it returns a 3588 * comparator that imposes the reverse of the <em>natural ordering</em> on 3589 * a collection of objects that implement the Comparable interface). 3590 * 3591 * <p>The returned comparator is serializable (assuming the specified 3592 * comparator is also serializable or {@code null}). 3593 * 3594 * @param cmp a comparator who's ordering is to be reversed by the returned 3595 * comparator or {@code null} 3596 * @return A comparator that imposes the reverse ordering of the 3597 * specified comparator. 3598 * @since 1.5 3599 */ 3600 public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) { 3601 if (cmp == null) 3602 return reverseOrder(); 3603 3604 if (cmp instanceof ReverseComparator2) 3605 return ((ReverseComparator2<T>)cmp).cmp; 3606 3607 return new ReverseComparator2<>(cmp); 3608 } 3609 3610 /** 3611 * @serial include 3612 */ 3613 private static class ReverseComparator2<T> implements Comparator<T>, 3614 Serializable 3615 { 3616 private static final long serialVersionUID = 4374092139857L; 3617 3618 /** 3619 * The comparator specified in the static factory. This will never 3620 * be null, as the static factory returns a ReverseComparator 3621 * instance if its argument is null. 3622 * 3623 * @serial 3624 */ 3625 final Comparator<T> cmp; 3626 3627 ReverseComparator2(Comparator<T> cmp) { 3628 assert cmp != null; 3629 this.cmp = cmp; 3630 } 3631 3632 public int compare(T t1, T t2) { 3633 return cmp.compare(t2, t1); 3634 } 3635 3636 public boolean equals(Object o) { 3637 return (o == this) || 3638 (o instanceof ReverseComparator2 && 3639 cmp.equals(((ReverseComparator2)o).cmp)); 3640 } 3641 3642 public int hashCode() { 3643 return cmp.hashCode() ^ Integer.MIN_VALUE; 3644 } 3645 } 3646 3647 /** 3648 * Returns an enumeration over the specified collection. This provides 3649 * interoperability with legacy APIs that require an enumeration 3650 * as input. 3651 * 3652 * @param c the collection for which an enumeration is to be returned. 3653 * @return an enumeration over the specified collection. 3654 * @see Enumeration 3655 */ 3656 public static <T> Enumeration<T> enumeration(final Collection<T> c) { 3657 return new Enumeration<T>() { 3658 private final Iterator<T> i = c.iterator(); 3659 3660 public boolean hasMoreElements() { 3661 return i.hasNext(); 3662 } 3663 3664 public T nextElement() { 3665 return i.next(); 3666 } 3667 }; 3668 } 3669 3670 /** 3671 * Returns an array list containing the elements returned by the 3672 * specified enumeration in the order they are returned by the 3673 * enumeration. This method provides interoperability between 3674 * legacy APIs that return enumerations and new APIs that require 3675 * collections. 3676 * 3677 * @param e enumeration providing elements for the returned 3678 * array list 3679 * @return an array list containing the elements returned 3680 * by the specified enumeration. 3681 * @since 1.4 3682 * @see Enumeration 3683 * @see ArrayList 3684 */ 3685 public static <T> ArrayList<T> list(Enumeration<T> e) { 3686 ArrayList<T> l = new ArrayList<>(); 3687 while (e.hasMoreElements()) 3688 l.add(e.nextElement()); 3689 return l; 3690 } 3691 3692 /** 3693 * Returns true if the specified arguments are equal, or both null. 3694 */ 3695 static boolean eq(Object o1, Object o2) { 3696 return o1==null ? o2==null : o1.equals(o2); 3697 } 3698 3699 /** 3700 * Returns the number of elements in the specified collection equal to the 3701 * specified object. More formally, returns the number of elements 3702 * <tt>e</tt> in the collection such that 3703 * <tt>(o == null ? e == null : o.equals(e))</tt>. 3704 * 3705 * @param c the collection in which to determine the frequency 3706 * of <tt>o</tt> 3707 * @param o the object whose frequency is to be determined 3708 * @throws NullPointerException if <tt>c</tt> is null 3709 * @since 1.5 3710 */ 3711 public static int frequency(Collection<?> c, Object o) { 3712 int result = 0; 3713 if (o == null) { 3714 for (Object e : c) 3715 if (e == null) 3716 result++; 3717 } else { 3718 for (Object e : c) 3719 if (o.equals(e)) 3720 result++; 3721 } 3722 return result; 3723 } 3724 3725 /** 3726 * Returns {@code true} if the two specified collections have no 3727 * elements in common. 3728 * 3729 * <p>Care must be exercised if this method is used on collections that 3730 * do not comply with the general contract for {@code Collection}. 3731 * Implementations may elect to iterate over either collection and test 3732 * for containment in the other collection (or to perform any equivalent 3733 * computation). If either collection uses a nonstandard equality test 3734 * (as does a {@link SortedSet} whose ordering is not <em>compatible with 3735 * equals</em>, or the key set of an {@link IdentityHashMap}), both 3736 * collections must use the same nonstandard equality test, or the 3737 * result of this method is undefined. 3738 * 3739 * <p>Care must also be exercised when using collections that have 3740 * restrictions on the elements that they may contain. Collection 3741 * implementations are allowed to throw exceptions for any operation 3742 * involving elements they deem ineligible. For absolute safety the 3743 * specified collections should contain only elements which are 3744 * eligible elements for both collections. 3745 * 3746 * <p>Note that it is permissible to pass the same collection in both 3747 * parameters, in which case the method will return {@code true} if and 3748 * only if the collection is empty. 3749 * 3750 * @param c1 a collection 3751 * @param c2 a collection 3752 * @return {@code true} if the two specified collections have no 3753 * elements in common. 3754 * @throws NullPointerException if either collection is {@code null}. 3755 * @throws NullPointerException if one collection contains a {@code null} 3756 * element and {@code null} is not an eligible element for the other collection. 3757 * (<a href="Collection.html#optional-restrictions">optional</a>) 3758 * @throws ClassCastException if one collection contains an element that is 3759 * of a type which is ineligible for the other collection. 3760 * (<a href="Collection.html#optional-restrictions">optional</a>) 3761 * @since 1.5 3762 */ 3763 public static boolean disjoint(Collection<?> c1, Collection<?> c2) { 3764 // The collection to be used for contains(). Preference is given to 3765 // the collection who's contains() has lower O() complexity. 3766 Collection<?> contains = c2; 3767 // The collection to be iterated. If the collections' contains() impl 3768 // are of different O() complexity, the collection with slower 3769 // contains() will be used for iteration. For collections who's 3770 // contains() are of the same complexity then best performance is 3771 // achieved by iterating the smaller collection. 3772 Collection<?> iterate = c1; 3773 3774 // Performance optimization cases. The heuristics: 3775 // 1. Generally iterate over c1. 3776 // 2. If c1 is a Set then iterate over c2. 3777 // 3. If either collection is empty then result is always true. 3778 // 4. Iterate over the smaller Collection. 3779 if (c1 instanceof Set) { 3780 // Use c1 for contains as a Set's contains() is expected to perform 3781 // better than O(N/2) 3782 iterate = c2; 3783 contains = c1; 3784 } else if (!(c2 instanceof Set)) { 3785 // Both are mere Collections. Iterate over smaller collection. 3786 // Example: If c1 contains 3 elements and c2 contains 50 elements and 3787 // assuming contains() requires ceiling(N/2) comparisons then 3788 // checking for all c1 elements in c2 would require 75 comparisons 3789 // (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring 3790 // 100 comparisons (50 * ceiling(3/2)). 3791 int c1size = c1.size(); 3792 int c2size = c2.size(); 3793 if (c1size == 0 || c2size == 0) { 3794 // At least one collection is empty. Nothing will match. 3795 return true; 3796 } 3797 3798 if (c1size > c2size) { 3799 iterate = c2; 3800 contains = c1; 3801 } 3802 } 3803 3804 for (Object e : iterate) { 3805 if (contains.contains(e)) { 3806 // Found a common element. Collections are not disjoint. 3807 return false; 3808 } 3809 } 3810 3811 // No common elements were found. 3812 return true; 3813 } 3814 3815 /** 3816 * Adds all of the specified elements to the specified collection. 3817 * Elements to be added may be specified individually or as an array. 3818 * The behavior of this convenience method is identical to that of 3819 * <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely 3820 * to run significantly faster under most implementations. 3821 * 3822 * <p>When elements are specified individually, this method provides a 3823 * convenient way to add a few elements to an existing collection: 3824 * <pre> 3825 * Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon"); 3826 * </pre> 3827 * 3828 * @param c the collection into which <tt>elements</tt> are to be inserted 3829 * @param elements the elements to insert into <tt>c</tt> 3830 * @return <tt>true</tt> if the collection changed as a result of the call 3831 * @throws UnsupportedOperationException if <tt>c</tt> does not support 3832 * the <tt>add</tt> operation 3833 * @throws NullPointerException if <tt>elements</tt> contains one or more 3834 * null values and <tt>c</tt> does not permit null elements, or 3835 * if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt> 3836 * @throws IllegalArgumentException if some property of a value in 3837 * <tt>elements</tt> prevents it from being added to <tt>c</tt> 3838 * @see Collection#addAll(Collection) 3839 * @since 1.5 3840 */ 3841 @SafeVarargs 3842 public static <T> boolean addAll(Collection<? super T> c, T... elements) { 3843 boolean result = false; 3844 for (T element : elements) 3845 result |= c.add(element); 3846 return result; 3847 } 3848 3849 /** 3850 * Returns a set backed by the specified map. The resulting set displays 3851 * the same ordering, concurrency, and performance characteristics as the 3852 * backing map. In essence, this factory method provides a {@link Set} 3853 * implementation corresponding to any {@link Map} implementation. There 3854 * is no need to use this method on a {@link Map} implementation that 3855 * already has a corresponding {@link Set} implementation (such as {@link 3856 * HashMap} or {@link TreeMap}). 3857 * 3858 * <p>Each method invocation on the set returned by this method results in 3859 * exactly one method invocation on the backing map or its <tt>keySet</tt> 3860 * view, with one exception. The <tt>addAll</tt> method is implemented 3861 * as a sequence of <tt>put</tt> invocations on the backing map. 3862 * 3863 * <p>The specified map must be empty at the time this method is invoked, 3864 * and should not be accessed directly after this method returns. These 3865 * conditions are ensured if the map is created empty, passed directly 3866 * to this method, and no reference to the map is retained, as illustrated 3867 * in the following code fragment: 3868 * <pre> 3869 * Set<Object> weakHashSet = Collections.newSetFromMap( 3870 * new WeakHashMap<Object, Boolean>()); 3871 * </pre> 3872 * 3873 * @param map the backing map 3874 * @return the set backed by the map 3875 * @throws IllegalArgumentException if <tt>map</tt> is not empty 3876 * @since 1.6 3877 */ 3878 public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) { 3879 return new SetFromMap<>(map); 3880 } 3881 3882 /** 3883 * @serial include 3884 */ 3885 private static class SetFromMap<E> extends AbstractSet<E> 3886 implements Set<E>, Serializable 3887 { 3888 private final Map<E, Boolean> m; // The backing map 3889 private transient Set<E> s; // Its keySet 3890 3891 SetFromMap(Map<E, Boolean> map) { 3892 if (!map.isEmpty()) 3893 throw new IllegalArgumentException("Map is non-empty"); 3894 m = map; 3895 s = map.keySet(); 3896 } 3897 3898 public void clear() { m.clear(); } 3899 public int size() { return m.size(); } 3900 public boolean isEmpty() { return m.isEmpty(); } 3901 public boolean contains(Object o) { return m.containsKey(o); } 3902 public boolean remove(Object o) { return m.remove(o) != null; } 3903 public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; } 3904 public Iterator<E> iterator() { return s.iterator(); } 3905 public Object[] toArray() { return s.toArray(); } 3906 public <T> T[] toArray(T[] a) { return s.toArray(a); } 3907 public String toString() { return s.toString(); } 3908 public int hashCode() { return s.hashCode(); } 3909 public boolean equals(Object o) { return o == this || s.equals(o); } 3910 public boolean containsAll(Collection<?> c) {return s.containsAll(c);} 3911 public boolean removeAll(Collection<?> c) {return s.removeAll(c);} 3912 public boolean retainAll(Collection<?> c) {return s.retainAll(c);} 3913 // addAll is the only inherited implementation 3914 3915 private static final long serialVersionUID = 2454657854757543876L; 3916 3917 private void readObject(java.io.ObjectInputStream stream) 3918 throws IOException, ClassNotFoundException 3919 { 3920 stream.defaultReadObject(); 3921 s = m.keySet(); 3922 } 3923 } 3924 3925 /** 3926 * Returns a view of a {@link Deque} as a Last-in-first-out (Lifo) 3927 * {@link Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>, 3928 * <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This 3929 * view can be useful when you would like to use a method 3930 * requiring a <tt>Queue</tt> but you need Lifo ordering. 3931 * 3932 * <p>Each method invocation on the queue returned by this method 3933 * results in exactly one method invocation on the backing deque, with 3934 * one exception. The {@link Queue#addAll addAll} method is 3935 * implemented as a sequence of {@link Deque#addFirst addFirst} 3936 * invocations on the backing deque. 3937 * 3938 * @param deque the deque 3939 * @return the queue 3940 * @since 1.6 3941 */ 3942 public static <T> Queue<T> asLifoQueue(Deque<T> deque) { 3943 return new AsLIFOQueue<>(deque); 3944 } 3945 3946 /** 3947 * @serial include 3948 */ 3949 static class AsLIFOQueue<E> extends AbstractQueue<E> 3950 implements Queue<E>, Serializable { 3951 private static final long serialVersionUID = 1802017725587941708L; 3952 private final Deque<E> q; 3953 AsLIFOQueue(Deque<E> q) { this.q = q; } 3954 public boolean add(E e) { q.addFirst(e); return true; } 3955 public boolean offer(E e) { return q.offerFirst(e); } 3956 public E poll() { return q.pollFirst(); } 3957 public E remove() { return q.removeFirst(); } 3958 public E peek() { return q.peekFirst(); } 3959 public E element() { return q.getFirst(); } 3960 public void clear() { q.clear(); } 3961 public int size() { return q.size(); } 3962 public boolean isEmpty() { return q.isEmpty(); } 3963 public boolean contains(Object o) { return q.contains(o); } 3964 public boolean remove(Object o) { return q.remove(o); } 3965 public Iterator<E> iterator() { return q.iterator(); } 3966 public Object[] toArray() { return q.toArray(); } 3967 public <T> T[] toArray(T[] a) { return q.toArray(a); } 3968 public String toString() { return q.toString(); } 3969 public boolean containsAll(Collection<?> c) {return q.containsAll(c);} 3970 public boolean removeAll(Collection<?> c) {return q.removeAll(c);} 3971 public boolean retainAll(Collection<?> c) {return q.retainAll(c);} 3972 // We use inherited addAll; forwarding addAll would be wrong 3973 } 3974} 3975