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