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