1 /*
2 * Copyright (c) 1997, 2011, 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 (!(o instanceof Map.Entry))
1493 return false;
1494 Map.Entry t = (Map.Entry)o;
1495 return eq(e.getKey(), t.getKey()) &&
1496 eq(e.getValue(), t.getValue());
1497 }
1498 public String toString() {return e.toString();}
1499 }
1500 }
1501 }
1502
1503 /**
1504 * Returns an unmodifiable view of the specified sorted map. This method
1505 * allows modules to provide users with "read-only" access to internal
1506 * sorted maps. Query operations on the returned sorted map "read through"
1507 * to the specified sorted map. Attempts to modify the returned
1508 * sorted map, whether direct, via its collection views, or via its
1509 * <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in
1510 * an <tt>UnsupportedOperationException</tt>.<p>
1511 *
1512 * The returned sorted map will be serializable if the specified sorted map
1513 * is serializable.
1514 *
1515 * @param m the sorted map for which an unmodifiable view is to be
1516 * returned.
1517 * @return an unmodifiable view of the specified sorted map.
1518 */
1519 public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) {
1520 return new UnmodifiableSortedMap<>(m);
1521 }
1522
1523 /**
1524 * @serial include
1525 */
1526 static class UnmodifiableSortedMap<K,V>
1527 extends UnmodifiableMap<K,V>
1528 implements SortedMap<K,V>, Serializable {
1529 private static final long serialVersionUID = -8806743815996713206L;
1530
1531 private final SortedMap<K, ? extends V> sm;
1532
1533 UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m;}
1534
1535 public Comparator<? super K> comparator() {return sm.comparator();}
1536
1537 public SortedMap<K,V> subMap(K fromKey, K toKey) {
1538 return new UnmodifiableSortedMap<>(sm.subMap(fromKey, toKey));
1539 }
1540 public SortedMap<K,V> headMap(K toKey) {
1541 return new UnmodifiableSortedMap<>(sm.headMap(toKey));
1542 }
1543 public SortedMap<K,V> tailMap(K fromKey) {
1544 return new UnmodifiableSortedMap<>(sm.tailMap(fromKey));
1545 }
1546
1547 public K firstKey() {return sm.firstKey();}
1548 public K lastKey() {return sm.lastKey();}
1549 }
1550
1551
1552 // Synch Wrappers
1553
1554 /**
1555 * Returns a synchronized (thread-safe) collection backed by the specified
1556 * collection. In order to guarantee serial access, it is critical that
1557 * <strong>all</strong> access to the backing collection is accomplished
1558 * through the returned collection.<p>
1559 *
1560 * It is imperative that the user manually synchronize on the returned
1561 * collection when iterating over it:
1562 * <pre>
1563 * Collection c = Collections.synchronizedCollection(myCollection);
1564 * ...
1565 * synchronized (c) {
1566 * Iterator i = c.iterator(); // Must be in the synchronized block
1567 * while (i.hasNext())
1568 * foo(i.next());
1569 * }
1570 * </pre>
1571 * Failure to follow this advice may result in non-deterministic behavior.
1572 *
1573 * <p>The returned collection does <i>not</i> pass the <tt>hashCode</tt>
1574 * and <tt>equals</tt> operations through to the backing collection, but
1575 * relies on <tt>Object</tt>'s equals and hashCode methods. This is
1576 * necessary to preserve the contracts of these operations in the case
1577 * that the backing collection is a set or a list.<p>
1578 *
1579 * The returned collection will be serializable if the specified collection
1580 * is serializable.
1581 *
1582 * @param c the collection to be "wrapped" in a synchronized collection.
1583 * @return a synchronized view of the specified collection.
1584 */
1585 public static <T> Collection<T> synchronizedCollection(Collection<T> c) {
1586 return new SynchronizedCollection<>(c);
1587 }
1588
1589 static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) {
1590 return new SynchronizedCollection<>(c, mutex);
1591 }
1592
1593 /**
1594 * @serial include
1595 */
1596 static class SynchronizedCollection<E> implements Collection<E>, Serializable {
1597 private static final long serialVersionUID = 3053995032091335093L;
1598
1599 final Collection<E> c; // Backing Collection
1600 final Object mutex; // Object on which to synchronize
1601
1602 SynchronizedCollection(Collection<E> c) {
1603 if (c==null)
1604 throw new NullPointerException();
1605 this.c = c;
1606 mutex = this;
1607 }
1608 SynchronizedCollection(Collection<E> c, Object mutex) {
1609 this.c = c;
1610 this.mutex = mutex;
1611 }
1612
1613 public int size() {
1614 synchronized (mutex) {return c.size();}
1615 }
1616 public boolean isEmpty() {
1617 synchronized (mutex) {return c.isEmpty();}
1618 }
1619 public boolean contains(Object o) {
1620 synchronized (mutex) {return c.contains(o);}
1621 }
1622 public Object[] toArray() {
1623 synchronized (mutex) {return c.toArray();}
1624 }
1625 public <T> T[] toArray(T[] a) {
1626 synchronized (mutex) {return c.toArray(a);}
1627 }
1628
1629 public Iterator<E> iterator() {
1630 return c.iterator(); // Must be manually synched by user!
1631 }
1632
1633 public boolean add(E e) {
1634 synchronized (mutex) {return c.add(e);}
1635 }
1636 public boolean remove(Object o) {
1637 synchronized (mutex) {return c.remove(o);}
1638 }
1639
1640 public boolean containsAll(Collection<?> coll) {
1641 synchronized (mutex) {return c.containsAll(coll);}
1642 }
1643 public boolean addAll(Collection<? extends E> coll) {
1644 synchronized (mutex) {return c.addAll(coll);}
1645 }
1646 public boolean removeAll(Collection<?> coll) {
1647 synchronized (mutex) {return c.removeAll(coll);}
1648 }
1649 public boolean retainAll(Collection<?> coll) {
1650 synchronized (mutex) {return c.retainAll(coll);}
1651 }
1652 public void clear() {
1653 synchronized (mutex) {c.clear();}
1654 }
1655 public String toString() {
1656 synchronized (mutex) {return c.toString();}
1657 }
1658 private void writeObject(ObjectOutputStream s) throws IOException {
1659 synchronized (mutex) {s.defaultWriteObject();}
1660 }
1661 }
1662
1663 /**
1664 * Returns a synchronized (thread-safe) set backed by the specified
1665 * set. In order to guarantee serial access, it is critical that
1666 * <strong>all</strong> access to the backing set is accomplished
1667 * through the returned set.<p>
1668 *
1669 * It is imperative that the user manually synchronize on the returned
1670 * set when iterating over it:
1671 * <pre>
1672 * Set s = Collections.synchronizedSet(new HashSet());
1673 * ...
1674 * synchronized (s) {
1675 * Iterator i = s.iterator(); // Must be in the synchronized block
1676 * while (i.hasNext())
1677 * foo(i.next());
1678 * }
1679 * </pre>
1680 * Failure to follow this advice may result in non-deterministic behavior.
1681 *
1682 * <p>The returned set will be serializable if the specified set is
1683 * serializable.
1684 *
1685 * @param s the set to be "wrapped" in a synchronized set.
1686 * @return a synchronized view of the specified set.
1687 */
1688 public static <T> Set<T> synchronizedSet(Set<T> s) {
1689 return new SynchronizedSet<>(s);
1690 }
1691
1692 static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) {
1693 return new SynchronizedSet<>(s, mutex);
1694 }
1695
1696 /**
1697 * @serial include
1698 */
1699 static class SynchronizedSet<E>
1700 extends SynchronizedCollection<E>
1701 implements Set<E> {
1702 private static final long serialVersionUID = 487447009682186044L;
1703
1704 SynchronizedSet(Set<E> s) {
1705 super(s);
1706 }
1707 SynchronizedSet(Set<E> s, Object mutex) {
1708 super(s, mutex);
1709 }
1710
1711 public boolean equals(Object o) {
1712 synchronized (mutex) {return c.equals(o);}
1713 }
1714 public int hashCode() {
1715 synchronized (mutex) {return c.hashCode();}
1716 }
1717 }
1718
1719 /**
1720 * Returns a synchronized (thread-safe) sorted set backed by the specified
1721 * sorted set. In order to guarantee serial access, it is critical that
1722 * <strong>all</strong> access to the backing sorted set is accomplished
1723 * through the returned sorted set (or its views).<p>
1724 *
1725 * It is imperative that the user manually synchronize on the returned
1726 * sorted set when iterating over it or any of its <tt>subSet</tt>,
1727 * <tt>headSet</tt>, or <tt>tailSet</tt> views.
1728 * <pre>
1729 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
1730 * ...
1731 * synchronized (s) {
1732 * Iterator i = s.iterator(); // Must be in the synchronized block
1733 * while (i.hasNext())
1734 * foo(i.next());
1735 * }
1736 * </pre>
1737 * or:
1738 * <pre>
1739 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
1740 * SortedSet s2 = s.headSet(foo);
1741 * ...
1742 * synchronized (s) { // Note: s, not s2!!!
1743 * Iterator i = s2.iterator(); // Must be in the synchronized block
1744 * while (i.hasNext())
1745 * foo(i.next());
1746 * }
1747 * </pre>
1748 * Failure to follow this advice may result in non-deterministic behavior.
1749 *
1750 * <p>The returned sorted set will be serializable if the specified
1751 * sorted set is serializable.
1752 *
1753 * @param s the sorted set to be "wrapped" in a synchronized sorted set.
1754 * @return a synchronized view of the specified sorted set.
1755 */
1756 public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) {
1757 return new SynchronizedSortedSet<>(s);
1758 }
1759
1760 /**
1761 * @serial include
1762 */
1763 static class SynchronizedSortedSet<E>
1764 extends SynchronizedSet<E>
1765 implements SortedSet<E>
1766 {
1767 private static final long serialVersionUID = 8695801310862127406L;
1768
1769 private final SortedSet<E> ss;
1770
1771 SynchronizedSortedSet(SortedSet<E> s) {
1772 super(s);
1773 ss = s;
1774 }
1775 SynchronizedSortedSet(SortedSet<E> s, Object mutex) {
1776 super(s, mutex);
1777 ss = s;
1778 }
1779
1780 public Comparator<? super E> comparator() {
1781 synchronized (mutex) {return ss.comparator();}
1782 }
1783
1784 public SortedSet<E> subSet(E fromElement, E toElement) {
1785 synchronized (mutex) {
1786 return new SynchronizedSortedSet<>(
1787 ss.subSet(fromElement, toElement), mutex);
1788 }
1789 }
1790 public SortedSet<E> headSet(E toElement) {
1791 synchronized (mutex) {
1792 return new SynchronizedSortedSet<>(ss.headSet(toElement), mutex);
1793 }
1794 }
1795 public SortedSet<E> tailSet(E fromElement) {
1796 synchronized (mutex) {
1797 return new SynchronizedSortedSet<>(ss.tailSet(fromElement),mutex);
1798 }
1799 }
1800
1801 public E first() {
1802 synchronized (mutex) {return ss.first();}
1803 }
1804 public E last() {
1805 synchronized (mutex) {return ss.last();}
1806 }
1807 }
1808
1809 /**
1810 * Returns a synchronized (thread-safe) list backed by the specified
1811 * list. In order to guarantee serial access, it is critical that
1812 * <strong>all</strong> access to the backing list is accomplished
1813 * through the returned list.<p>
1814 *
1815 * It is imperative that the user manually synchronize on the returned
1816 * list when iterating over it:
1817 * <pre>
1818 * List list = Collections.synchronizedList(new ArrayList());
1819 * ...
1820 * synchronized (list) {
1821 * Iterator i = list.iterator(); // Must be in synchronized block
1822 * while (i.hasNext())
1823 * foo(i.next());
1824 * }
1825 * </pre>
1826 * Failure to follow this advice may result in non-deterministic behavior.
1827 *
1828 * <p>The returned list will be serializable if the specified list is
1829 * serializable.
1830 *
1831 * @param list the list to be "wrapped" in a synchronized list.
1832 * @return a synchronized view of the specified list.
1833 */
1834 public static <T> List<T> synchronizedList(List<T> list) {
1835 return (list instanceof RandomAccess ?
1836 new SynchronizedRandomAccessList<>(list) :
1837 new SynchronizedList<>(list));
1838 }
1839
1840 static <T> List<T> synchronizedList(List<T> list, Object mutex) {
1841 return (list instanceof RandomAccess ?
1842 new SynchronizedRandomAccessList<>(list, mutex) :
1843 new SynchronizedList<>(list, mutex));
1844 }
1845
1846 /**
1847 * @serial include
1848 */
1849 static class SynchronizedList<E>
1850 extends SynchronizedCollection<E>
1851 implements List<E> {
1852 private static final long serialVersionUID = -7754090372962971524L;
1853
1854 final List<E> list;
1855
1856 SynchronizedList(List<E> list) {
1857 super(list);
1858 this.list = list;
1859 }
1860 SynchronizedList(List<E> list, Object mutex) {
1861 super(list, mutex);
1862 this.list = list;
1863 }
1864
1865 public boolean equals(Object o) {
1866 synchronized (mutex) {return list.equals(o);}
1867 }
1868 public int hashCode() {
1869 synchronized (mutex) {return list.hashCode();}
1870 }
1871
1872 public E get(int index) {
1873 synchronized (mutex) {return list.get(index);}
1874 }
1875 public E set(int index, E element) {
1876 synchronized (mutex) {return list.set(index, element);}
1877 }
1878 public void add(int index, E element) {
1879 synchronized (mutex) {list.add(index, element);}
1880 }
1881 public E remove(int index) {
1882 synchronized (mutex) {return list.remove(index);}
1883 }
1884
1885 public int indexOf(Object o) {
1886 synchronized (mutex) {return list.indexOf(o);}
1887 }
1888 public int lastIndexOf(Object o) {
1889 synchronized (mutex) {return list.lastIndexOf(o);}
1890 }
1891
1892 public boolean addAll(int index, Collection<? extends E> c) {
1893 synchronized (mutex) {return list.addAll(index, c);}
1894 }
1895
1896 public ListIterator<E> listIterator() {
1897 return list.listIterator(); // Must be manually synched by user
1898 }
1899
1900 public ListIterator<E> listIterator(int index) {
1901 return list.listIterator(index); // Must be manually synched by user
1902 }
1903
1904 public List<E> subList(int fromIndex, int toIndex) {
1905 synchronized (mutex) {
1906 return new SynchronizedList<>(list.subList(fromIndex, toIndex),
1907 mutex);
1908 }
1909 }
1910
1911 /**
1912 * SynchronizedRandomAccessList instances are serialized as
1913 * SynchronizedList instances to allow them to be deserialized
1914 * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList).
1915 * This method inverts the transformation. As a beneficial
1916 * side-effect, it also grafts the RandomAccess marker onto
1917 * SynchronizedList instances that were serialized in pre-1.4 JREs.
1918 *
1919 * Note: Unfortunately, SynchronizedRandomAccessList instances
1920 * serialized in 1.4.1 and deserialized in 1.4 will become
1921 * SynchronizedList instances, as this method was missing in 1.4.
1922 */
1923 private Object readResolve() {
1924 return (list instanceof RandomAccess
1925 ? new SynchronizedRandomAccessList<>(list)
1926 : this);
1927 }
1928 }
1929
1930 /**
1931 * @serial include
1932 */
1933 static class SynchronizedRandomAccessList<E>
1934 extends SynchronizedList<E>
1935 implements RandomAccess {
1936
1937 SynchronizedRandomAccessList(List<E> list) {
1938 super(list);
1939 }
1940
1941 SynchronizedRandomAccessList(List<E> list, Object mutex) {
1942 super(list, mutex);
1943 }
1944
1945 public List<E> subList(int fromIndex, int toIndex) {
1946 synchronized (mutex) {
1947 return new SynchronizedRandomAccessList<>(
1948 list.subList(fromIndex, toIndex), mutex);
1949 }
1950 }
1951
1952 private static final long serialVersionUID = 1530674583602358482L;
1953
1954 /**
1955 * Allows instances to be deserialized in pre-1.4 JREs (which do
1956 * not have SynchronizedRandomAccessList). SynchronizedList has
1957 * a readResolve method that inverts this transformation upon
1958 * deserialization.
1959 */
1960 private Object writeReplace() {
1961 return new SynchronizedList<>(list);
1962 }
1963 }
1964
1965 /**
1966 * Returns a synchronized (thread-safe) map backed by the specified
1967 * map. In order to guarantee serial access, it is critical that
1968 * <strong>all</strong> access to the backing map is accomplished
1969 * through the returned map.<p>
1970 *
1971 * It is imperative that the user manually synchronize on the returned
1972 * map when iterating over any of its collection views:
1973 * <pre>
1974 * Map m = Collections.synchronizedMap(new HashMap());
1975 * ...
1976 * Set s = m.keySet(); // Needn't be in synchronized block
1977 * ...
1978 * synchronized (m) { // Synchronizing on m, not s!
1979 * Iterator i = s.iterator(); // Must be in synchronized block
1980 * while (i.hasNext())
1981 * foo(i.next());
1982 * }
1983 * </pre>
1984 * Failure to follow this advice may result in non-deterministic behavior.
1985 *
1986 * <p>The returned map will be serializable if the specified map is
1987 * serializable.
1988 *
1989 * @param m the map to be "wrapped" in a synchronized map.
1990 * @return a synchronized view of the specified map.
1991 */
1992 public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) {
1993 return new SynchronizedMap<>(m);
1994 }
1995
1996 /**
1997 * @serial include
1998 */
1999 private static class SynchronizedMap<K,V>
2000 implements Map<K,V>, Serializable {
2001 private static final long serialVersionUID = 1978198479659022715L;
2002
2003 private final Map<K,V> m; // Backing Map
2004 final Object mutex; // Object on which to synchronize
2005
2006 SynchronizedMap(Map<K,V> m) {
2007 if (m==null)
2008 throw new NullPointerException();
2009 this.m = m;
2010 mutex = this;
2011 }
2012
2013 SynchronizedMap(Map<K,V> m, Object mutex) {
2014 this.m = m;
2015 this.mutex = mutex;
2016 }
2017
2018 public int size() {
2019 synchronized (mutex) {return m.size();}
2020 }
2021 public boolean isEmpty() {
2022 synchronized (mutex) {return m.isEmpty();}
2023 }
2024 public boolean containsKey(Object key) {
2025 synchronized (mutex) {return m.containsKey(key);}
2026 }
2027 public boolean containsValue(Object value) {
2028 synchronized (mutex) {return m.containsValue(value);}
2029 }
2030 public V get(Object key) {
2031 synchronized (mutex) {return m.get(key);}
2032 }
2033
2034 public V put(K key, V value) {
2035 synchronized (mutex) {return m.put(key, value);}
2036 }
2037 public V remove(Object key) {
2038 synchronized (mutex) {return m.remove(key);}
2039 }
2040 public void putAll(Map<? extends K, ? extends V> map) {
2041 synchronized (mutex) {m.putAll(map);}
2042 }
2043 public void clear() {
2044 synchronized (mutex) {m.clear();}
2045 }
2046
2047 private transient Set<K> keySet = null;
2048 private transient Set<Map.Entry<K,V>> entrySet = null;
2049 private transient Collection<V> values = null;
2050
2051 public Set<K> keySet() {
2052 synchronized (mutex) {
2053 if (keySet==null)
2054 keySet = new SynchronizedSet<>(m.keySet(), mutex);
2055 return keySet;
2056 }
2057 }
2058
2059 public Set<Map.Entry<K,V>> entrySet() {
2060 synchronized (mutex) {
2061 if (entrySet==null)
2062 entrySet = new SynchronizedSet<>(m.entrySet(), mutex);
2063 return entrySet;
2064 }
2065 }
2066
2067 public Collection<V> values() {
2068 synchronized (mutex) {
2069 if (values==null)
2070 values = new SynchronizedCollection<>(m.values(), mutex);
2071 return values;
2072 }
2073 }
2074
2075 public boolean equals(Object o) {
2076 synchronized (mutex) {return m.equals(o);}
2077 }
2078 public int hashCode() {
2079 synchronized (mutex) {return m.hashCode();}
2080 }
2081 public String toString() {
2082 synchronized (mutex) {return m.toString();}
2083 }
2084 private void writeObject(ObjectOutputStream s) throws IOException {
2085 synchronized (mutex) {s.defaultWriteObject();}
2086 }
2087 }
2088
2089 /**
2090 * Returns a synchronized (thread-safe) sorted map backed by the specified
2091 * sorted map. In order to guarantee serial access, it is critical that
2092 * <strong>all</strong> access to the backing sorted map is accomplished
2093 * through the returned sorted map (or its views).<p>
2094 *
2095 * It is imperative that the user manually synchronize on the returned
2096 * sorted map when iterating over any of its collection views, or the
2097 * collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or
2098 * <tt>tailMap</tt> views.
2099 * <pre>
2100 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
2101 * ...
2102 * Set s = m.keySet(); // Needn't be in synchronized block
2103 * ...
2104 * synchronized (m) { // Synchronizing on m, not s!
2105 * Iterator i = s.iterator(); // Must be in synchronized block
2106 * while (i.hasNext())
2107 * foo(i.next());
2108 * }
2109 * </pre>
2110 * or:
2111 * <pre>
2112 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
2113 * SortedMap m2 = m.subMap(foo, bar);
2114 * ...
2115 * Set s2 = m2.keySet(); // Needn't be in synchronized block
2116 * ...
2117 * synchronized (m) { // Synchronizing on m, not m2 or s2!
2118 * Iterator i = s.iterator(); // Must be in synchronized block
2119 * while (i.hasNext())
2120 * foo(i.next());
2121 * }
2122 * </pre>
2123 * Failure to follow this advice may result in non-deterministic behavior.
2124 *
2125 * <p>The returned sorted map will be serializable if the specified
2126 * sorted map is serializable.
2127 *
2128 * @param m the sorted map to be "wrapped" in a synchronized sorted map.
2129 * @return a synchronized view of the specified sorted map.
2130 */
2131 public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) {
2132 return new SynchronizedSortedMap<>(m);
2133 }
2134
2135
2136 /**
2137 * @serial include
2138 */
2139 static class SynchronizedSortedMap<K,V>
2140 extends SynchronizedMap<K,V>
2141 implements SortedMap<K,V>
2142 {
2143 private static final long serialVersionUID = -8798146769416483793L;
2144
2145 private final SortedMap<K,V> sm;
2146
2147 SynchronizedSortedMap(SortedMap<K,V> m) {
2148 super(m);
2149 sm = m;
2150 }
2151 SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) {
2152 super(m, mutex);
2153 sm = m;
2154 }
2155
2156 public Comparator<? super K> comparator() {
2157 synchronized (mutex) {return sm.comparator();}
2158 }
2159
2160 public SortedMap<K,V> subMap(K fromKey, K toKey) {
2161 synchronized (mutex) {
2162 return new SynchronizedSortedMap<>(
2163 sm.subMap(fromKey, toKey), mutex);
2164 }
2165 }
2166 public SortedMap<K,V> headMap(K toKey) {
2167 synchronized (mutex) {
2168 return new SynchronizedSortedMap<>(sm.headMap(toKey), mutex);
2169 }
2170 }
2171 public SortedMap<K,V> tailMap(K fromKey) {
2172 synchronized (mutex) {
2173 return new SynchronizedSortedMap<>(sm.tailMap(fromKey),mutex);
2174 }
2175 }
2176
2177 public K firstKey() {
2178 synchronized (mutex) {return sm.firstKey();}
2179 }
2180 public K lastKey() {
2181 synchronized (mutex) {return sm.lastKey();}
2182 }
2183 }
2184
2185 // Dynamically typesafe collection wrappers
2186
2187 /**
2188 * Returns a dynamically typesafe view of the specified collection.
2189 * Any attempt to insert an element of the wrong type will result in an
2190 * immediate {@link ClassCastException}. Assuming a collection
2191 * contains no incorrectly typed elements prior to the time a
2192 * dynamically typesafe view is generated, and that all subsequent
2193 * access to the collection takes place through the view, it is
2194 * <i>guaranteed</i> that the collection cannot contain an incorrectly
2195 * typed element.
2196 *
2197 * <p>The generics mechanism in the language provides compile-time
2198 * (static) type checking, but it is possible to defeat this mechanism
2199 * with unchecked casts. Usually this is not a problem, as the compiler
2200 * issues warnings on all such unchecked operations. There are, however,
2201 * times when static type checking alone is not sufficient. For example,
2202 * suppose a collection is passed to a third-party library and it is
2203 * imperative that the library code not corrupt the collection by
2204 * inserting an element of the wrong type.
2205 *
2206 * <p>Another use of dynamically typesafe views is debugging. Suppose a
2207 * program fails with a {@code ClassCastException}, indicating that an
2208 * incorrectly typed element was put into a parameterized collection.
2209 * Unfortunately, the exception can occur at any time after the erroneous
2210 * element is inserted, so it typically provides little or no information
2211 * as to the real source of the problem. If the problem is reproducible,
2212 * one can quickly determine its source by temporarily modifying the
2213 * program to wrap the collection with a dynamically typesafe view.
2214 * For example, this declaration:
2215 * <pre> {@code
2216 * Collection<String> c = new HashSet<String>();
2217 * }</pre>
2218 * may be replaced temporarily by this one:
2219 * <pre> {@code
2220 * Collection<String> c = Collections.checkedCollection(
2221 * new HashSet<String>(), String.class);
2222 * }</pre>
2223 * Running the program again will cause it to fail at the point where
2224 * an incorrectly typed element is inserted into the collection, clearly
2225 * identifying the source of the problem. Once the problem is fixed, the
2226 * modified declaration may be reverted back to the original.
2227 *
2228 * <p>The returned collection does <i>not</i> pass the hashCode and equals
2229 * operations through to the backing collection, but relies on
2230 * {@code Object}'s {@code equals} and {@code hashCode} methods. This
2231 * is necessary to preserve the contracts of these operations in the case
2232 * that the backing collection is a set or a list.
2233 *
2234 * <p>The returned collection will be serializable if the specified
2235 * collection is serializable.
2236 *
2237 * <p>Since {@code null} is considered to be a value of any reference
2238 * type, the returned collection permits insertion of null elements
2239 * whenever the backing collection does.
2240 *
2241 * @param c the collection for which a dynamically typesafe view is to be
2242 * returned
2243 * @param type the type of element that {@code c} is permitted to hold
2244 * @return a dynamically typesafe view of the specified collection
2245 * @since 1.5
2246 */
2247 public static <E> Collection<E> checkedCollection(Collection<E> c,
2248 Class<E> type) {
2249 return new CheckedCollection<>(c, type);
2250 }
2251
2252 @SuppressWarnings("unchecked")
2253 static <T> T[] zeroLengthArray(Class<T> type) {
2254 return (T[]) Array.newInstance(type, 0);
2255 }
2256
2257 /**
2258 * @serial include
2259 */
2260 static class CheckedCollection<E> implements Collection<E>, Serializable {
2261 private static final long serialVersionUID = 1578914078182001775L;
2262
2263 final Collection<E> c;
2264 final Class<E> type;
2265
2266 void typeCheck(Object o) {
2267 if (o != null && !type.isInstance(o))
2268 throw new ClassCastException(badElementMsg(o));
2269 }
2270
2271 private String badElementMsg(Object o) {
2272 return "Attempt to insert " + o.getClass() +
2273 " element into collection with element type " + type;
2274 }
2275
2276 CheckedCollection(Collection<E> c, Class<E> type) {
2277 if (c==null || type == null)
2278 throw new NullPointerException();
2279 this.c = c;
2280 this.type = type;
2281 }
2282
2283 public int size() { return c.size(); }
2284 public boolean isEmpty() { return c.isEmpty(); }
2285 public boolean contains(Object o) { return c.contains(o); }
2286 public Object[] toArray() { return c.toArray(); }
2287 public <T> T[] toArray(T[] a) { return c.toArray(a); }
2288 public String toString() { return c.toString(); }
2289 public boolean remove(Object o) { return c.remove(o); }
2290 public void clear() { c.clear(); }
2291
2292 public boolean containsAll(Collection<?> coll) {
2293 return c.containsAll(coll);
2294 }
2295 public boolean removeAll(Collection<?> coll) {
2296 return c.removeAll(coll);
2297 }
2298 public boolean retainAll(Collection<?> coll) {
2299 return c.retainAll(coll);
2300 }
2301
2302 public Iterator<E> iterator() {
2303 final Iterator<E> it = c.iterator();
2304 return new Iterator<E>() {
2305 public boolean hasNext() { return it.hasNext(); }
2306 public E next() { return it.next(); }
2307 public void remove() { it.remove(); }};
2308 }
2309
2310 public boolean add(E e) {
2311 typeCheck(e);
2312 return c.add(e);
2313 }
2314
2315 private E[] zeroLengthElementArray = null; // Lazily initialized
2316
2317 private E[] zeroLengthElementArray() {
2318 return zeroLengthElementArray != null ? zeroLengthElementArray :
2319 (zeroLengthElementArray = zeroLengthArray(type));
2320 }
2321
2322 @SuppressWarnings("unchecked")
2323 Collection<E> checkedCopyOf(Collection<? extends E> coll) {
2324 Object[] a = null;
2325 try {
2326 E[] z = zeroLengthElementArray();
2327 a = coll.toArray(z);
2328 // Defend against coll violating the toArray contract
2329 if (a.getClass() != z.getClass())
2330 a = Arrays.copyOf(a, a.length, z.getClass());
2331 } catch (ArrayStoreException ignore) {
2332 // To get better and consistent diagnostics,
2333 // we call typeCheck explicitly on each element.
2334 // We call clone() to defend against coll retaining a
2335 // reference to the returned array and storing a bad
2336 // element into it after it has been type checked.
2337 a = coll.toArray().clone();
2338 for (Object o : a)
2339 typeCheck(o);
2340 }
2341 // A slight abuse of the type system, but safe here.
2342 return (Collection<E>) Arrays.asList(a);
2343 }
2344
2345 public boolean addAll(Collection<? extends E> coll) {
2346 // Doing things this way insulates us from concurrent changes
2347 // in the contents of coll and provides all-or-nothing
2348 // semantics (which we wouldn't get if we type-checked each
2349 // element as we added it)
2350 return c.addAll(checkedCopyOf(coll));
2351 }
2352 }
2353
2354 /**
2355 * Returns a dynamically typesafe view of the specified queue.
2356 * Any attempt to insert an element of the wrong type will result in
2357 * an immediate {@link ClassCastException}. Assuming a queue contains
2358 * no incorrectly typed elements prior to the time a dynamically typesafe
2359 * view is generated, and that all subsequent access to the queue
2360 * takes place through the view, it is <i>guaranteed</i> that the
2361 * queue cannot contain an incorrectly typed element.
2362 *
2363 * <p>A discussion of the use of dynamically typesafe views may be
2364 * found in the documentation for the {@link #checkedCollection
2365 * checkedCollection} method.
2366 *
2367 * <p>The returned queue will be serializable if the specified queue
2368 * is serializable.
2369 *
2370 * <p>Since {@code null} is considered to be a value of any reference
2371 * type, the returned queue permits insertion of {@code null} elements
2372 * whenever the backing queue does.
2373 *
2374 * @param queue the queue for which a dynamically typesafe view is to be
2375 * returned
2376 * @param type the type of element that {@code queue} is permitted to hold
2377 * @return a dynamically typesafe view of the specified queue
2378 * @since 1.8
2379 */
2380 public static <E> Queue<E> checkedQueue(Queue<E> queue, Class<E> type) {
2381 return new CheckedQueue<>(queue, type);
2382 }
2383
2384 /**
2385 * @serial include
2386 */
2387 static class CheckedQueue<E>
2388 extends CheckedCollection<E>
2389 implements Queue<E>, Serializable
2390 {
2391 private static final long serialVersionUID = 1433151992604707767L;
2392 final Queue<E> queue;
2393
2394 CheckedQueue(Queue<E> queue, Class<E> elementType) {
2395 super(queue, elementType);
2396 this.queue = queue;
2397 }
2398
2399 public E element() {return queue.element();}
2400 public boolean equals(Object o) {return o == this || c.equals(o);}
2401 public int hashCode() {return c.hashCode();}
2402 public E peek() {return queue.peek();}
2403 public E poll() {return queue.poll();}
2404 public E remove() {return queue.remove();}
2405
2406 public boolean offer(E e) {
2407 typeCheck(e);
2408 return add(e);
2409 }
2410 }
2411
2412 /**
2413 * Returns a dynamically typesafe view of the specified set.
2414 * Any attempt to insert an element of the wrong type will result in
2415 * an immediate {@link ClassCastException}. Assuming a set contains
2416 * no incorrectly typed elements prior to the time a dynamically typesafe
2417 * view is generated, and that all subsequent access to the set
2418 * takes place through the view, it is <i>guaranteed</i> that the
2419 * set cannot contain an incorrectly typed element.
2420 *
2421 * <p>A discussion of the use of dynamically typesafe views may be
2422 * found in the documentation for the {@link #checkedCollection
2423 * checkedCollection} method.
2424 *
2425 * <p>The returned set will be serializable if the specified set is
2426 * serializable.
2427 *
2428 * <p>Since {@code null} is considered to be a value of any reference
2429 * type, the returned set permits insertion of null elements whenever
2430 * the backing set does.
2431 *
2432 * @param s the set for which a dynamically typesafe view is to be
2433 * returned
2434 * @param type the type of element that {@code s} is permitted to hold
2435 * @return a dynamically typesafe view of the specified set
2436 * @since 1.5
2437 */
2438 public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) {
2439 return new CheckedSet<>(s, type);
2440 }
2441
2442 /**
2443 * @serial include
2444 */
2445 static class CheckedSet<E> extends CheckedCollection<E>
2446 implements Set<E>, Serializable
2447 {
2448 private static final long serialVersionUID = 4694047833775013803L;
2449
2450 CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); }
2451
2452 public boolean equals(Object o) { return o == this || c.equals(o); }
2453 public int hashCode() { return c.hashCode(); }
2454 }
2455
2456 /**
2457 * Returns a dynamically typesafe view of the specified sorted set.
2458 * Any attempt to insert an element of the wrong type will result in an
2459 * immediate {@link ClassCastException}. Assuming a sorted set
2460 * contains no incorrectly typed elements prior to the time a
2461 * dynamically typesafe view is generated, and that all subsequent
2462 * access to the sorted set takes place through the view, it is
2463 * <i>guaranteed</i> that the sorted set cannot contain an incorrectly
2464 * typed element.
2465 *
2466 * <p>A discussion of the use of dynamically typesafe views may be
2467 * found in the documentation for the {@link #checkedCollection
2468 * checkedCollection} method.
2469 *
2470 * <p>The returned sorted set will be serializable if the specified sorted
2471 * set is serializable.
2472 *
2473 * <p>Since {@code null} is considered to be a value of any reference
2474 * type, the returned sorted set permits insertion of null elements
2475 * whenever the backing sorted set does.
2476 *
2477 * @param s the sorted set for which a dynamically typesafe view is to be
2478 * returned
2479 * @param type the type of element that {@code s} is permitted to hold
2480 * @return a dynamically typesafe view of the specified sorted set
2481 * @since 1.5
2482 */
2483 public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s,
2484 Class<E> type) {
2485 return new CheckedSortedSet<>(s, type);
2486 }
2487
2488 /**
2489 * @serial include
2490 */
2491 static class CheckedSortedSet<E> extends CheckedSet<E>
2492 implements SortedSet<E>, Serializable
2493 {
2494 private static final long serialVersionUID = 1599911165492914959L;
2495 private final SortedSet<E> ss;
2496
2497 CheckedSortedSet(SortedSet<E> s, Class<E> type) {
2498 super(s, type);
2499 ss = s;
2500 }
2501
2502 public Comparator<? super E> comparator() { return ss.comparator(); }
2503 public E first() { return ss.first(); }
2504 public E last() { return ss.last(); }
2505
2506 public SortedSet<E> subSet(E fromElement, E toElement) {
2507 return checkedSortedSet(ss.subSet(fromElement,toElement), type);
2508 }
2509 public SortedSet<E> headSet(E toElement) {
2510 return checkedSortedSet(ss.headSet(toElement), type);
2511 }
2512 public SortedSet<E> tailSet(E fromElement) {
2513 return checkedSortedSet(ss.tailSet(fromElement), type);
2514 }
2515 }
2516
2517 /**
2518 * Returns a dynamically typesafe view of the specified list.
2519 * Any attempt to insert an element of the wrong type will result in
2520 * an immediate {@link ClassCastException}. Assuming a list contains
2521 * no incorrectly typed elements prior to the time a dynamically typesafe
2522 * view is generated, and that all subsequent access to the list
2523 * takes place through the view, it is <i>guaranteed</i> that the
2524 * list cannot contain an incorrectly typed element.
2525 *
2526 * <p>A discussion of the use of dynamically typesafe views may be
2527 * found in the documentation for the {@link #checkedCollection
2528 * checkedCollection} method.
2529 *
2530 * <p>The returned list will be serializable if the specified list
2531 * is serializable.
2532 *
2533 * <p>Since {@code null} is considered to be a value of any reference
2534 * type, the returned list permits insertion of null elements whenever
2535 * the backing list does.
2536 *
2537 * @param list the list for which a dynamically typesafe view is to be
2538 * returned
2539 * @param type the type of element that {@code list} is permitted to hold
2540 * @return a dynamically typesafe view of the specified list
2541 * @since 1.5
2542 */
2543 public static <E> List<E> checkedList(List<E> list, Class<E> type) {
2544 return (list instanceof RandomAccess ?
2545 new CheckedRandomAccessList<>(list, type) :
2546 new CheckedList<>(list, type));
2547 }
2548
2549 /**
2550 * @serial include
2551 */
2552 static class CheckedList<E>
2553 extends CheckedCollection<E>
2554 implements List<E>
2555 {
2556 private static final long serialVersionUID = 65247728283967356L;
2557 final List<E> list;
2558
2559 CheckedList(List<E> list, Class<E> type) {
2560 super(list, type);
2561 this.list = list;
2562 }
2563
2564 public boolean equals(Object o) { return o == this || list.equals(o); }
2565 public int hashCode() { return list.hashCode(); }
2566 public E get(int index) { return list.get(index); }
2567 public E remove(int index) { return list.remove(index); }
2568 public int indexOf(Object o) { return list.indexOf(o); }
2569 public int lastIndexOf(Object o) { return list.lastIndexOf(o); }
2570
2571 public E set(int index, E element) {
2572 typeCheck(element);
2573 return list.set(index, element);
2574 }
2575
2576 public void add(int index, E element) {
2577 typeCheck(element);
2578 list.add(index, element);
2579 }
2580
2581 public boolean addAll(int index, Collection<? extends E> c) {
2582 return list.addAll(index, checkedCopyOf(c));
2583 }
2584 public ListIterator<E> listIterator() { return listIterator(0); }
2585
2586 public ListIterator<E> listIterator(final int index) {
2587 final ListIterator<E> i = list.listIterator(index);
2588
2589 return new ListIterator<E>() {
2590 public boolean hasNext() { return i.hasNext(); }
2591 public E next() { return i.next(); }
2592 public boolean hasPrevious() { return i.hasPrevious(); }
2593 public E previous() { return i.previous(); }
2594 public int nextIndex() { return i.nextIndex(); }
2595 public int previousIndex() { return i.previousIndex(); }
2596 public void remove() { i.remove(); }
2597
2598 public void set(E e) {
2599 typeCheck(e);
2600 i.set(e);
2601 }
2602
2603 public void add(E e) {
2604 typeCheck(e);
2605 i.add(e);
2606 }
2607 };
2608 }
2609
2610 public List<E> subList(int fromIndex, int toIndex) {
2611 return new CheckedList<>(list.subList(fromIndex, toIndex), type);
2612 }
2613 }
2614
2615 /**
2616 * @serial include
2617 */
2618 static class CheckedRandomAccessList<E> extends CheckedList<E>
2619 implements RandomAccess
2620 {
2621 private static final long serialVersionUID = 1638200125423088369L;
2622
2623 CheckedRandomAccessList(List<E> list, Class<E> type) {
2624 super(list, type);
2625 }
2626
2627 public List<E> subList(int fromIndex, int toIndex) {
2628 return new CheckedRandomAccessList<>(
2629 list.subList(fromIndex, toIndex), type);
2630 }
2631 }
2632
2633 /**
2634 * Returns a dynamically typesafe view of the specified map.
2635 * Any attempt to insert a mapping whose key or value have the wrong
2636 * type will result in an immediate {@link ClassCastException}.
2637 * Similarly, any attempt to modify the value currently associated with
2638 * a key will result in an immediate {@link ClassCastException},
2639 * whether the modification is attempted directly through the map
2640 * itself, or through a {@link Map.Entry} instance obtained from the
2641 * map's {@link Map#entrySet() entry set} view.
2642 *
2643 * <p>Assuming a map contains no incorrectly typed keys or values
2644 * prior to the time a dynamically typesafe view is generated, and
2645 * that all subsequent access to the map takes place through the view
2646 * (or one of its collection views), it is <i>guaranteed</i> that the
2647 * map cannot contain an incorrectly typed key or value.
2648 *
2649 * <p>A discussion of the use of dynamically typesafe views may be
2650 * found in the documentation for the {@link #checkedCollection
2651 * checkedCollection} method.
2652 *
2653 * <p>The returned map will be serializable if the specified map is
2654 * serializable.
2655 *
2656 * <p>Since {@code null} is considered to be a value of any reference
2657 * type, the returned map permits insertion of null keys or values
2658 * whenever the backing map does.
2659 *
2660 * @param m the map for which a dynamically typesafe view is to be
2661 * returned
2662 * @param keyType the type of key that {@code m} is permitted to hold
2663 * @param valueType the type of value that {@code m} is permitted to hold
2664 * @return a dynamically typesafe view of the specified map
2665 * @since 1.5
2666 */
2667 public static <K, V> Map<K, V> checkedMap(Map<K, V> m,
2668 Class<K> keyType,
2669 Class<V> valueType) {
2670 return new CheckedMap<>(m, keyType, valueType);
2671 }
2672
2673
2674 /**
2675 * @serial include
2676 */
2677 private static class CheckedMap<K,V>
2678 implements Map<K,V>, Serializable
2679 {
2680 private static final long serialVersionUID = 5742860141034234728L;
2681
2682 private final Map<K, V> m;
2683 final Class<K> keyType;
2684 final Class<V> valueType;
2685
2686 private void typeCheck(Object key, Object value) {
2687 if (key != null && !keyType.isInstance(key))
2688 throw new ClassCastException(badKeyMsg(key));
2689
2690 if (value != null && !valueType.isInstance(value))
2691 throw new ClassCastException(badValueMsg(value));
2692 }
2693
2694 private String badKeyMsg(Object key) {
2695 return "Attempt to insert " + key.getClass() +
2696 " key into map with key type " + keyType;
2697 }
2698
2699 private String badValueMsg(Object value) {
2700 return "Attempt to insert " + value.getClass() +
2701 " value into map with value type " + valueType;
2702 }
2703
2704 CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) {
2705 if (m == null || keyType == null || valueType == null)
2706 throw new NullPointerException();
2707 this.m = m;
2708 this.keyType = keyType;
2709 this.valueType = valueType;
2710 }
2711
2712 public int size() { return m.size(); }
2713 public boolean isEmpty() { return m.isEmpty(); }
2714 public boolean containsKey(Object key) { return m.containsKey(key); }
2715 public boolean containsValue(Object v) { return m.containsValue(v); }
2716 public V get(Object key) { return m.get(key); }
2717 public V remove(Object key) { return m.remove(key); }
2718 public void clear() { m.clear(); }
2719 public Set<K> keySet() { return m.keySet(); }
2720 public Collection<V> values() { return m.values(); }
2721 public boolean equals(Object o) { return o == this || m.equals(o); }
2722 public int hashCode() { return m.hashCode(); }
2723 public String toString() { return m.toString(); }
2724
2725 public V put(K key, V value) {
2726 typeCheck(key, value);
2727 return m.put(key, value);
2728 }
2729
2730 @SuppressWarnings("unchecked")
2731 public void putAll(Map<? extends K, ? extends V> t) {
2732 // Satisfy the following goals:
2733 // - good diagnostics in case of type mismatch
2734 // - all-or-nothing semantics
2735 // - protection from malicious t
2736 // - correct behavior if t is a concurrent map
2737 Object[] entries = t.entrySet().toArray();
2738 List<Map.Entry<K,V>> checked = new ArrayList<>(entries.length);
2739 for (Object o : entries) {
2740 Map.Entry<?,?> e = (Map.Entry<?,?>) o;
2741 Object k = e.getKey();
2742 Object v = e.getValue();
2743 typeCheck(k, v);
2744 checked.add(
2745 new AbstractMap.SimpleImmutableEntry<>((K) k, (V) v));
2746 }
2747 for (Map.Entry<K,V> e : checked)
2748 m.put(e.getKey(), e.getValue());
2749 }
2750
2751 private transient Set<Map.Entry<K,V>> entrySet = null;
2752
2753 public Set<Map.Entry<K,V>> entrySet() {
2754 if (entrySet==null)
2755 entrySet = new CheckedEntrySet<>(m.entrySet(), valueType);
2756 return entrySet;
2757 }
2758
2759 /**
2760 * We need this class in addition to CheckedSet as Map.Entry permits
2761 * modification of the backing Map via the setValue operation. This
2762 * class is subtle: there are many possible attacks that must be
2763 * thwarted.
2764 *
2765 * @serial exclude
2766 */
2767 static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> {
2768 private final Set<Map.Entry<K,V>> s;
2769 private final Class<V> valueType;
2770
2771 CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) {
2772 this.s = s;
2773 this.valueType = valueType;
2774 }
2775
2776 public int size() { return s.size(); }
2777 public boolean isEmpty() { return s.isEmpty(); }
2778 public String toString() { return s.toString(); }
2779 public int hashCode() { return s.hashCode(); }
2780 public void clear() { s.clear(); }
2781
2782 public boolean add(Map.Entry<K, V> e) {
2783 throw new UnsupportedOperationException();
2784 }
2785 public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) {
2786 throw new UnsupportedOperationException();
2787 }
2788
2789 public Iterator<Map.Entry<K,V>> iterator() {
2790 final Iterator<Map.Entry<K, V>> i = s.iterator();
2791 final Class<V> valueType = this.valueType;
2792
2793 return new Iterator<Map.Entry<K,V>>() {
2794 public boolean hasNext() { return i.hasNext(); }
2795 public void remove() { i.remove(); }
2796
2797 public Map.Entry<K,V> next() {
2798 return checkedEntry(i.next(), valueType);
2799 }
2800 };
2801 }
2802
2803 @SuppressWarnings("unchecked")
2804 public Object[] toArray() {
2805 Object[] source = s.toArray();
2806
2807 /*
2808 * Ensure that we don't get an ArrayStoreException even if
2809 * s.toArray returns an array of something other than Object
2810 */
2811 Object[] dest = (CheckedEntry.class.isInstance(
2812 source.getClass().getComponentType()) ? source :
2813 new Object[source.length]);
2814
2815 for (int i = 0; i < source.length; i++)
2816 dest[i] = checkedEntry((Map.Entry<K,V>)source[i],
2817 valueType);
2818 return dest;
2819 }
2820
2821 @SuppressWarnings("unchecked")
2822 public <T> T[] toArray(T[] a) {
2823 // We don't pass a to s.toArray, to avoid window of
2824 // vulnerability wherein an unscrupulous multithreaded client
2825 // could get his hands on raw (unwrapped) Entries from s.
2826 T[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
2827
2828 for (int i=0; i<arr.length; i++)
2829 arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i],
2830 valueType);
2831 if (arr.length > a.length)
2832 return arr;
2833
2834 System.arraycopy(arr, 0, a, 0, arr.length);
2835 if (a.length > arr.length)
2836 a[arr.length] = null;
2837 return a;
2838 }
2839
2840 /**
2841 * This method is overridden to protect the backing set against
2842 * an object with a nefarious equals function that senses
2843 * that the equality-candidate is Map.Entry and calls its
2844 * setValue method.
2845 */
2846 public boolean contains(Object o) {
2847 if (!(o instanceof Map.Entry))
2848 return false;
2849 Map.Entry<?,?> e = (Map.Entry<?,?>) o;
2850 return s.contains(
2851 (e instanceof CheckedEntry) ? e : checkedEntry(e, valueType));
2852 }
2853
2854 /**
2855 * The bulk collection methods are overridden to protect
2856 * against an unscrupulous collection whose contains(Object o)
2857 * method senses when o is a Map.Entry, and calls o.setValue.
2858 */
2859 public boolean containsAll(Collection<?> c) {
2860 for (Object o : c)
2861 if (!contains(o)) // Invokes safe contains() above
2862 return false;
2863 return true;
2864 }
2865
2866 public boolean remove(Object o) {
2867 if (!(o instanceof Map.Entry))
2868 return false;
2869 return s.remove(new AbstractMap.SimpleImmutableEntry
2870 <>((Map.Entry<?,?>)o));
2871 }
2872
2873 public boolean removeAll(Collection<?> c) {
2874 return batchRemove(c, false);
2875 }
2876 public boolean retainAll(Collection<?> c) {
2877 return batchRemove(c, true);
2878 }
2879 private boolean batchRemove(Collection<?> c, boolean complement) {
2880 boolean modified = false;
2881 Iterator<Map.Entry<K,V>> it = iterator();
2882 while (it.hasNext()) {
2883 if (c.contains(it.next()) != complement) {
2884 it.remove();
2885 modified = true;
2886 }
2887 }
2888 return modified;
2889 }
2890
2891 public boolean equals(Object o) {
2892 if (o == this)
2893 return true;
2894 if (!(o instanceof Set))
2895 return false;
2896 Set<?> that = (Set<?>) o;
2897 return that.size() == s.size()
2898 && containsAll(that); // Invokes safe containsAll() above
2899 }
2900
2901 static <K,V,T> CheckedEntry<K,V,T> checkedEntry(Map.Entry<K,V> e,
2902 Class<T> valueType) {
2903 return new CheckedEntry<>(e, valueType);
2904 }
2905
2906 /**
2907 * This "wrapper class" serves two purposes: it prevents
2908 * the client from modifying the backing Map, by short-circuiting
2909 * the setValue method, and it protects the backing Map against
2910 * an ill-behaved Map.Entry that attempts to modify another
2911 * Map.Entry when asked to perform an equality check.
2912 */
2913 private static class CheckedEntry<K,V,T> implements Map.Entry<K,V> {
2914 private final Map.Entry<K, V> e;
2915 private final Class<T> valueType;
2916
2917 CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) {
2918 this.e = e;
2919 this.valueType = valueType;
2920 }
2921
2922 public K getKey() { return e.getKey(); }
2923 public V getValue() { return e.getValue(); }
2924 public int hashCode() { return e.hashCode(); }
2925 public String toString() { return e.toString(); }
2926
2927 public V setValue(V value) {
2928 if (value != null && !valueType.isInstance(value))
2929 throw new ClassCastException(badValueMsg(value));
2930 return e.setValue(value);
2931 }
2932
2933 private String badValueMsg(Object value) {
2934 return "Attempt to insert " + value.getClass() +
2935 " value into map with value type " + valueType;
2936 }
2937
2938 public boolean equals(Object o) {
2939 if (o == this)
2940 return true;
2941 if (!(o instanceof Map.Entry))
2942 return false;
2943 return e.equals(new AbstractMap.SimpleImmutableEntry
2944 <>((Map.Entry<?,?>)o));
2945 }
2946 }
2947 }
2948 }
2949
2950 /**
2951 * Returns a dynamically typesafe view of the specified sorted map.
2952 * Any attempt to insert a mapping whose key or value have the wrong
2953 * type will result in an immediate {@link ClassCastException}.
2954 * Similarly, any attempt to modify the value currently associated with
2955 * a key will result in an immediate {@link ClassCastException},
2956 * whether the modification is attempted directly through the map
2957 * itself, or through a {@link Map.Entry} instance obtained from the
2958 * map's {@link Map#entrySet() entry set} view.
2959 *
2960 * <p>Assuming a map contains no incorrectly typed keys or values
2961 * prior to the time a dynamically typesafe view is generated, and
2962 * that all subsequent access to the map takes place through the view
2963 * (or one of its collection views), it is <i>guaranteed</i> that the
2964 * map cannot contain an incorrectly typed key or value.
2965 *
2966 * <p>A discussion of the use of dynamically typesafe views may be
2967 * found in the documentation for the {@link #checkedCollection
2968 * checkedCollection} method.
2969 *
2970 * <p>The returned map will be serializable if the specified map is
2971 * serializable.
2972 *
2973 * <p>Since {@code null} is considered to be a value of any reference
2974 * type, the returned map permits insertion of null keys or values
2975 * whenever the backing map does.
2976 *
2977 * @param m the map for which a dynamically typesafe view is to be
2978 * returned
2979 * @param keyType the type of key that {@code m} is permitted to hold
2980 * @param valueType the type of value that {@code m} is permitted to hold
2981 * @return a dynamically typesafe view of the specified map
2982 * @since 1.5
2983 */
2984 public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m,
2985 Class<K> keyType,
2986 Class<V> valueType) {
2987 return new CheckedSortedMap<>(m, keyType, valueType);
2988 }
2989
2990 /**
2991 * @serial include
2992 */
2993 static class CheckedSortedMap<K,V> extends CheckedMap<K,V>
2994 implements SortedMap<K,V>, Serializable
2995 {
2996 private static final long serialVersionUID = 1599671320688067438L;
2997
2998 private final SortedMap<K, V> sm;
2999
3000 CheckedSortedMap(SortedMap<K, V> m,
3001 Class<K> keyType, Class<V> valueType) {
3002 super(m, keyType, valueType);
3003 sm = m;
3004 }
3005
3006 public Comparator<? super K> comparator() { return sm.comparator(); }
3007 public K firstKey() { return sm.firstKey(); }
3008 public K lastKey() { return sm.lastKey(); }
3009
3010 public SortedMap<K,V> subMap(K fromKey, K toKey) {
3011 return checkedSortedMap(sm.subMap(fromKey, toKey),
3012 keyType, valueType);
3013 }
3014 public SortedMap<K,V> headMap(K toKey) {
3015 return checkedSortedMap(sm.headMap(toKey), keyType, valueType);
3016 }
3017 public SortedMap<K,V> tailMap(K fromKey) {
3018 return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType);
3019 }
3020 }
3021
3022 // Empty collections
3023
3024 /**
3025 * Returns an iterator that has no elements. More precisely,
3026 *
3027 * <ul compact>
3028 *
3029 * <li>{@link Iterator#hasNext hasNext} always returns {@code
3030 * false}.
3031 *
3032 * <li>{@link Iterator#next next} always throws {@link
3033 * NoSuchElementException}.
3034 *
3035 * <li>{@link Iterator#remove remove} always throws {@link
3036 * IllegalStateException}.
3037 *
3038 * </ul>
3039 *
3040 * <p>Implementations of this method are permitted, but not
3041 * required, to return the same object from multiple invocations.
3042 *
3043 * @return an empty iterator
3044 * @since 1.7
3045 */
3046 @SuppressWarnings("unchecked")
3047 public static <T> Iterator<T> emptyIterator() {
3048 return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR;
3049 }
3050
3051 private static class EmptyIterator<E> implements Iterator<E> {
3052 static final EmptyIterator<Object> EMPTY_ITERATOR
3053 = new EmptyIterator<>();
3054
3055 public boolean hasNext() { return false; }
3056 public E next() { throw new NoSuchElementException(); }
3057 public void remove() { throw new IllegalStateException(); }
3058 }
3059
3060 /**
3061 * Returns a list iterator that has no elements. More precisely,
3062 *
3063 * <ul compact>
3064 *
3065 * <li>{@link Iterator#hasNext hasNext} and {@link
3066 * ListIterator#hasPrevious hasPrevious} always return {@code
3067 * false}.
3068 *
3069 * <li>{@link Iterator#next next} and {@link ListIterator#previous
3070 * previous} always throw {@link NoSuchElementException}.
3071 *
3072 * <li>{@link Iterator#remove remove} and {@link ListIterator#set
3073 * set} always throw {@link IllegalStateException}.
3074 *
3075 * <li>{@link ListIterator#add add} always throws {@link
3076 * UnsupportedOperationException}.
3077 *
3078 * <li>{@link ListIterator#nextIndex nextIndex} always returns
3079 * {@code 0} .
3080 *
3081 * <li>{@link ListIterator#previousIndex previousIndex} always
3082 * returns {@code -1}.
3083 *
3084 * </ul>
3085 *
3086 * <p>Implementations of this method are permitted, but not
3087 * required, to return the same object from multiple invocations.
3088 *
3089 * @return an empty list iterator
3090 * @since 1.7
3091 */
3092 @SuppressWarnings("unchecked")
3093 public static <T> ListIterator<T> emptyListIterator() {
3094 return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR;
3095 }
3096
3097 private static class EmptyListIterator<E>
3098 extends EmptyIterator<E>
3099 implements ListIterator<E>
3100 {
3101 static final EmptyListIterator<Object> EMPTY_ITERATOR
3102 = new EmptyListIterator<>();
3103
3104 public boolean hasPrevious() { return false; }
3105 public E previous() { throw new NoSuchElementException(); }
3106 public int nextIndex() { return 0; }
3107 public int previousIndex() { return -1; }
3108 public void set(E e) { throw new IllegalStateException(); }
3109 public void add(E e) { throw new UnsupportedOperationException(); }
3110 }
3111
3112 /**
3113 * Returns an enumeration that has no elements. More precisely,
3114 *
3115 * <ul compact>
3116 *
3117 * <li>{@link Enumeration#hasMoreElements hasMoreElements} always
3118 * returns {@code false}.
3119 *
3120 * <li> {@link Enumeration#nextElement nextElement} always throws
3121 * {@link NoSuchElementException}.
3122 *
3123 * </ul>
3124 *
3125 * <p>Implementations of this method are permitted, but not
3126 * required, to return the same object from multiple invocations.
3127 *
3128 * @return an empty enumeration
3129 * @since 1.7
3130 */
3131 @SuppressWarnings("unchecked")
3132 public static <T> Enumeration<T> emptyEnumeration() {
3133 return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION;
3134 }
3135
3136 private static class EmptyEnumeration<E> implements Enumeration<E> {
3137 static final EmptyEnumeration<Object> EMPTY_ENUMERATION
3138 = new EmptyEnumeration<>();
3139
3140 public boolean hasMoreElements() { return false; }
3141 public E nextElement() { throw new NoSuchElementException(); }
3142 }
3143
3144 /**
3145 * The empty set (immutable). This set is serializable.
3146 *
3147 * @see #emptySet()
3148 */
3149 @SuppressWarnings("unchecked")
3150 public static final Set EMPTY_SET = new EmptySet<>();
3151
3152 /**
3153 * Returns the empty set (immutable). This set is serializable.
3154 * Unlike the like-named field, this method is parameterized.
3155 *
3156 * <p>This example illustrates the type-safe way to obtain an empty set:
3157 * <pre>
3158 * Set<String> s = Collections.emptySet();
3159 * </pre>
3160 * Implementation note: Implementations of this method need not
3161 * create a separate <tt>Set</tt> object for each call. Using this
3162 * method is likely to have comparable cost to using the like-named
3163 * field. (Unlike this method, the field does not provide type safety.)
3164 *
3165 * @see #EMPTY_SET
3166 * @since 1.5
3167 */
3168 @SuppressWarnings("unchecked")
3169 public static final <T> Set<T> emptySet() {
3170 return (Set<T>) EMPTY_SET;
3171 }
3172
3173 /**
3174 * @serial include
3175 */
3176 private static class EmptySet<E>
3177 extends AbstractSet<E>
3178 implements Serializable
3179 {
3180 private static final long serialVersionUID = 1582296315990362920L;
3181
3182 public Iterator<E> iterator() { return emptyIterator(); }
3183
3184 public int size() {return 0;}
3185 public boolean isEmpty() {return true;}
3186
3187 public boolean contains(Object obj) {return false;}
3188 public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
3189
3190 public Object[] toArray() { return new Object[0]; }
3191
3192 public <T> T[] toArray(T[] a) {
3193 if (a.length > 0)
3194 a[0] = null;
3195 return a;
3196 }
3197
3198 // Preserves singleton property
3199 private Object readResolve() {
3200 return EMPTY_SET;
3201 }
3202 }
3203
3204 /**
3205 * Returns the empty sorted set (immutable). This set is serializable.
3206 *
3207 * <p>This example illustrates the type-safe way to obtain an empty sorted
3208 * set:
3209 * <pre>
3210 * SortedSet<String> s = Collections.emptySortedSet();
3211 * </pre>
3212 * Implementation note: Implementations of this method need not
3213 * create a separate <tt>SortedSet</tt> object for each call.
3214 *
3215 * @since 1.8
3216 */
3217 @SuppressWarnings("unchecked")
3218 public static final <E> SortedSet<E> emptySortedSet() {
3219 return (SortedSet<E>) new EmptySortedSet<>();
3220 }
3221
3222 /**
3223 * @serial include
3224 */
3225 private static class EmptySortedSet<E>
3226 extends AbstractSet<E>
3227 implements SortedSet<E>, Serializable
3228 {
3229 private static final long serialVersionUID = 6316515401502265487L;
3230 public Iterator<E> iterator() { return emptyIterator(); }
3231 public int size() {return 0;}
3232 public boolean isEmpty() {return true;}
3233 public boolean contains(Object obj) {return false;}
3234 public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
3235 public Object[] toArray() { return new Object[0]; }
3236
3237 public <E> E[] toArray(E[] a) {
3238 if (a.length > 0)
3239 a[0] = null;
3240 return a;
3241 }
3242
3243 // Preserves singleton property
3244 private Object readResolve() {
3245 return new EmptySortedSet<>();
3246 }
3247
3248 public Comparator comparator() {
3249 return null;
3250 }
3251
3252 public SortedSet<E> subSet(Object fromElement, Object toElement) {
3253 Objects.requireNonNull(fromElement);
3254 Objects.requireNonNull(toElement);
3255
3256 if (!(fromElement instanceof Comparable) ||
3257 !(toElement instanceof Comparable))
3258 {
3259 throw new ClassCastException();
3260 }
3261
3262 if ((((Comparable)fromElement).compareTo(toElement) >= 0) ||
3263 (((Comparable)toElement).compareTo(fromElement) < 0))
3264 {
3265 throw new IllegalArgumentException();
3266 }
3267
3268 return emptySortedSet();
3269 }
3270
3271 public SortedSet<E> headSet(Object toElement) {
3272 Objects.requireNonNull(toElement);
3273
3274 if (!(toElement instanceof Comparable)) {
3275 throw new ClassCastException();
3276 }
3277
3278 return emptySortedSet();
3279 }
3280
3281 public SortedSet<E> tailSet(Object fromElement) {
3282 Objects.requireNonNull(fromElement);
3283
3284 if (!(fromElement instanceof Comparable)) {
3285 throw new ClassCastException();
3286 }
3287
3288 return emptySortedSet();
3289 }
3290
3291 public E first() {
3292 throw new NoSuchElementException();
3293 }
3294
3295 public E last() {
3296 throw new NoSuchElementException();
3297 }
3298 }
3299
3300 /**
3301 * The empty list (immutable). This list is serializable.
3302 *
3303 * @see #emptyList()
3304 */
3305 @SuppressWarnings("unchecked")
3306 public static final List EMPTY_LIST = new EmptyList<>();
3307
3308 /**
3309 * Returns the empty list (immutable). This list is serializable.
3310 *
3311 * <p>This example illustrates the type-safe way to obtain an empty list:
3312 * <pre>
3313 * List<String> s = Collections.emptyList();
3314 * </pre>
3315 * Implementation note: Implementations of this method need not
3316 * create a separate <tt>List</tt> object for each call. Using this
3317 * method is likely to have comparable cost to using the like-named
3318 * field. (Unlike this method, the field does not provide type safety.)
3319 *
3320 * @see #EMPTY_LIST
3321 * @since 1.5
3322 */
3323 @SuppressWarnings("unchecked")
3324 public static final <T> List<T> emptyList() {
3325 return (List<T>) EMPTY_LIST;
3326 }
3327
3328 /**
3329 * @serial include
3330 */
3331 private static class EmptyList<E>
3332 extends AbstractList<E>
3333 implements RandomAccess, Serializable {
3334 private static final long serialVersionUID = 8842843931221139166L;
3335
3336 public Iterator<E> iterator() {
3337 return emptyIterator();
3338 }
3339 public ListIterator<E> listIterator() {
3340 return emptyListIterator();
3341 }
3342
3343 public int size() {return 0;}
3344 public boolean isEmpty() {return true;}
3345
3346 public boolean contains(Object obj) {return false;}
3347 public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
3348
3349 public Object[] toArray() { return new Object[0]; }
3350
3351 public <T> T[] toArray(T[] a) {
3352 if (a.length > 0)
3353 a[0] = null;
3354 return a;
3355 }
3356
3357 public E get(int index) {
3358 throw new IndexOutOfBoundsException("Index: "+index);
3359 }
3360
3361 public boolean equals(Object o) {
3362 return (o instanceof List) && ((List<?>)o).isEmpty();
3363 }
3364
3365 public int hashCode() { return 1; }
3366
3367 // Preserves singleton property
3368 private Object readResolve() {
3369 return EMPTY_LIST;
3370 }
3371 }
3372
3373 /**
3374 * The empty map (immutable). This map is serializable.
3375 *
3376 * @see #emptyMap()
3377 * @since 1.3
3378 */
3379 @SuppressWarnings("unchecked")
3380 public static final Map EMPTY_MAP = new EmptyMap<>();
3381
3382 /**
3383 * Returns the empty map (immutable). This map is serializable.
3384 *
3385 * <p>This example illustrates the type-safe way to obtain an empty set:
3386 * <pre>
3387 * Map<String, Date> s = Collections.emptyMap();
3388 * </pre>
3389 * Implementation note: Implementations of this method need not
3390 * create a separate <tt>Map</tt> object for each call. Using this
3391 * method is likely to have comparable cost to using the like-named
3392 * field. (Unlike this method, the field does not provide type safety.)
3393 *
3394 * @see #EMPTY_MAP
3395 * @since 1.5
3396 */
3397 @SuppressWarnings("unchecked")
3398 public static final <K,V> Map<K,V> emptyMap() {
3399 return (Map<K,V>) EMPTY_MAP;
3400 }
3401
3402 /**
3403 * @serial include
3404 */
3405 private static class EmptyMap<K,V>
3406 extends AbstractMap<K,V>
3407 implements Serializable
3408 {
3409 private static final long serialVersionUID = 6428348081105594320L;
3410
3411 public int size() {return 0;}
3412 public boolean isEmpty() {return true;}
3413 public boolean containsKey(Object key) {return false;}
3414 public boolean containsValue(Object value) {return false;}
3415 public V get(Object key) {return null;}
3416 public Set<K> keySet() {return emptySet();}
3417 public Collection<V> values() {return emptySet();}
3418 public Set<Map.Entry<K,V>> entrySet() {return emptySet();}
3419
3420 public boolean equals(Object o) {
3421 return (o instanceof Map) && ((Map<?,?>)o).isEmpty();
3422 }
3423
3424 public int hashCode() {return 0;}
3425
3426 // Preserves singleton property
3427 private Object readResolve() {
3428 return EMPTY_MAP;
3429 }
3430 }
3431
3432 // Singleton collections
3433
3434 /**
3435 * Returns an immutable set containing only the specified object.
3436 * The returned set is serializable.
3437 *
3438 * @param o the sole object to be stored in the returned set.
3439 * @return an immutable set containing only the specified object.
3440 */
3441 public static <T> Set<T> singleton(T o) {
3442 return new SingletonSet<>(o);
3443 }
3444
3445 static <E> Iterator<E> singletonIterator(final E e) {
3446 return new Iterator<E>() {
3447 private boolean hasNext = true;
3448 public boolean hasNext() {
3449 return hasNext;
3450 }
3451 public E next() {
3452 if (hasNext) {
3453 hasNext = false;
3454 return e;
3455 }
3456 throw new NoSuchElementException();
3457 }
3458 public void remove() {
3459 throw new UnsupportedOperationException();
3460 }
3461 };
3462 }
3463
3464 /**
3465 * @serial include
3466 */
3467 private static class SingletonSet<E>
3468 extends AbstractSet<E>
3469 implements Serializable
3470 {
3471 private static final long serialVersionUID = 3193687207550431679L;
3472
3473 private final E element;
3474
3475 SingletonSet(E e) {element = e;}
3476
3477 public Iterator<E> iterator() {
3478 return singletonIterator(element);
3479 }
3480
3481 public int size() {return 1;}
3482
3483 public boolean contains(Object o) {return eq(o, element);}
3484 }
3485
3486 /**
3487 * Returns an immutable list containing only the specified object.
3488 * The returned list is serializable.
3489 *
3490 * @param o the sole object to be stored in the returned list.
3491 * @return an immutable list containing only the specified object.
3492 * @since 1.3
3493 */
3494 public static <T> List<T> singletonList(T o) {
3495 return new SingletonList<>(o);
3496 }
3497
3498 /**
3499 * @serial include
3500 */
3501 private static class SingletonList<E>
3502 extends AbstractList<E>
3503 implements RandomAccess, Serializable {
3504
3505 private static final long serialVersionUID = 3093736618740652951L;
3506
3507 private final E element;
3508
3509 SingletonList(E obj) {element = obj;}
3510
3511 public Iterator<E> iterator() {
3512 return singletonIterator(element);
3513 }
3514
3515 public int size() {return 1;}
3516
3517 public boolean contains(Object obj) {return eq(obj, element);}
3518
3519 public E get(int index) {
3520 if (index != 0)
3521 throw new IndexOutOfBoundsException("Index: "+index+", Size: 1");
3522 return element;
3523 }
3524 }
3525
3526 /**
3527 * Returns an immutable map, mapping only the specified key to the
3528 * specified value. The returned map is serializable.
3529 *
3530 * @param key the sole key to be stored in the returned map.
3531 * @param value the value to which the returned map maps <tt>key</tt>.
3532 * @return an immutable map containing only the specified key-value
3533 * mapping.
3534 * @since 1.3
3535 */
3536 public static <K,V> Map<K,V> singletonMap(K key, V value) {
3537 return new SingletonMap<>(key, value);
3538 }
3539
3540 /**
3541 * @serial include
3542 */
3543 private static class SingletonMap<K,V>
3544 extends AbstractMap<K,V>
3545 implements Serializable {
3546 private static final long serialVersionUID = -6979724477215052911L;
3547
3548 private final K k;
3549 private final V v;
3550
3551 SingletonMap(K key, V value) {
3552 k = key;
3553 v = value;
3554 }
3555
3556 public int size() {return 1;}
3557
3558 public boolean isEmpty() {return false;}
3559
3560 public boolean containsKey(Object key) {return eq(key, k);}
3561
3562 public boolean containsValue(Object value) {return eq(value, v);}
3563
3564 public V get(Object key) {return (eq(key, k) ? v : null);}
3565
3566 private transient Set<K> keySet = null;
3567 private transient Set<Map.Entry<K,V>> entrySet = null;
3568 private transient Collection<V> values = null;
3569
3570 public Set<K> keySet() {
3571 if (keySet==null)
3572 keySet = singleton(k);
3573 return keySet;
3574 }
3575
3576 public Set<Map.Entry<K,V>> entrySet() {
3577 if (entrySet==null)
3578 entrySet = Collections.<Map.Entry<K,V>>singleton(
3579 new SimpleImmutableEntry<>(k, v));
3580 return entrySet;
3581 }
3582
3583 public Collection<V> values() {
3584 if (values==null)
3585 values = singleton(v);
3586 return values;
3587 }
3588
3589 }
3590
3591 // Miscellaneous
3592
3593 /**
3594 * Returns an immutable list consisting of <tt>n</tt> copies of the
3595 * specified object. The newly allocated data object is tiny (it contains
3596 * a single reference to the data object). This method is useful in
3597 * combination with the <tt>List.addAll</tt> method to grow lists.
3598 * The returned list is serializable.
3599 *
3600 * @param n the number of elements in the returned list.
3601 * @param o the element to appear repeatedly in the returned list.
3602 * @return an immutable list consisting of <tt>n</tt> copies of the
3603 * specified object.
3604 * @throws IllegalArgumentException if {@code n < 0}
3605 * @see List#addAll(Collection)
3606 * @see List#addAll(int, Collection)
3607 */
3608 public static <T> List<T> nCopies(int n, T o) {
3609 if (n < 0)
3610 throw new IllegalArgumentException("List length = " + n);
3611 return new CopiesList<>(n, o);
3612 }
3613
3614 /**
3615 * @serial include
3616 */
3617 private static class CopiesList<E>
3618 extends AbstractList<E>
3619 implements RandomAccess, Serializable
3620 {
3621 private static final long serialVersionUID = 2739099268398711800L;
3622
3623 final int n;
3624 final E element;
3625
3626 CopiesList(int n, E e) {
3627 assert n >= 0;
3628 this.n = n;
3629 element = e;
3630 }
3631
3632 public int size() {
3633 return n;
3634 }
3635
3636 public boolean contains(Object obj) {
3637 return n != 0 && eq(obj, element);
3638 }
3639
3640 public int indexOf(Object o) {
3641 return contains(o) ? 0 : -1;
3642 }
3643
3644 public int lastIndexOf(Object o) {
3645 return contains(o) ? n - 1 : -1;
3646 }
3647
3648 public E get(int index) {
3649 if (index < 0 || index >= n)
3650 throw new IndexOutOfBoundsException("Index: "+index+
3651 ", Size: "+n);
3652 return element;
3653 }
3654
3655 public Object[] toArray() {
3656 final Object[] a = new Object[n];
3657 if (element != null)
3658 Arrays.fill(a, 0, n, element);
3659 return a;
3660 }
3661
3662 public <T> T[] toArray(T[] a) {
3663 final int n = this.n;
3664 if (a.length < n) {
3665 a = (T[])java.lang.reflect.Array
3666 .newInstance(a.getClass().getComponentType(), n);
3667 if (element != null)
3668 Arrays.fill(a, 0, n, element);
3669 } else {
3670 Arrays.fill(a, 0, n, element);
3671 if (a.length > n)
3672 a[n] = null;
3673 }
3674 return a;
3675 }
3676
3677 public List<E> subList(int fromIndex, int toIndex) {
3678 if (fromIndex < 0)
3679 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
3680 if (toIndex > n)
3681 throw new IndexOutOfBoundsException("toIndex = " + toIndex);
3682 if (fromIndex > toIndex)
3683 throw new IllegalArgumentException("fromIndex(" + fromIndex +
3684 ") > toIndex(" + toIndex + ")");
3685 return new CopiesList<>(toIndex - fromIndex, element);
3686 }
3687 }
3688
3689 /**
3690 * Returns a comparator that imposes the reverse of the <em>natural
3691 * ordering</em> on a collection of objects that implement the
3692 * {@code Comparable} interface. (The natural ordering is the ordering
3693 * imposed by the objects' own {@code compareTo} method.) This enables a
3694 * simple idiom for sorting (or maintaining) collections (or arrays) of
3695 * objects that implement the {@code Comparable} interface in
3696 * reverse-natural-order. For example, suppose {@code a} is an array of
3697 * strings. Then: <pre>
3698 * Arrays.sort(a, Collections.reverseOrder());
3699 * </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p>
3700 *
3701 * The returned comparator is serializable.
3702 *
3703 * @return A comparator that imposes the reverse of the <i>natural
3704 * ordering</i> on a collection of objects that implement
3705 * the <tt>Comparable</tt> interface.
3706 * @see Comparable
3707 */
3708 public static <T> Comparator<T> reverseOrder() {
3709 return (Comparator<T>) ReverseComparator.REVERSE_ORDER;
3710 }
3711
3712 /**
3713 * @serial include
3714 */
3715 private static class ReverseComparator
3716 implements Comparator<Comparable<Object>>, Serializable {
3717
3718 private static final long serialVersionUID = 7207038068494060240L;
3719
3720 static final ReverseComparator REVERSE_ORDER
3721 = new ReverseComparator();
3722
3723 public int compare(Comparable<Object> c1, Comparable<Object> c2) {
3724 return c2.compareTo(c1);
3725 }
3726
3727 private Object readResolve() { return reverseOrder(); }
3728 }
3729
3730 /**
3731 * Returns a comparator that imposes the reverse ordering of the specified
3732 * comparator. If the specified comparator is {@code null}, this method is
3733 * equivalent to {@link #reverseOrder()} (in other words, it returns a
3734 * comparator that imposes the reverse of the <em>natural ordering</em> on
3735 * a collection of objects that implement the Comparable interface).
3736 *
3737 * <p>The returned comparator is serializable (assuming the specified
3738 * comparator is also serializable or {@code null}).
3739 *
3740 * @param cmp a comparator who's ordering is to be reversed by the returned
3741 * comparator or {@code null}
3742 * @return A comparator that imposes the reverse ordering of the
3743 * specified comparator.
3744 * @since 1.5
3745 */
3746 public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) {
3747 if (cmp == null)
3748 return reverseOrder();
3749
3750 if (cmp instanceof ReverseComparator2)
3751 return ((ReverseComparator2<T>)cmp).cmp;
3752
3753 return new ReverseComparator2<>(cmp);
3754 }
3755
3756 /**
3757 * @serial include
3758 */
3759 private static class ReverseComparator2<T> implements Comparator<T>,
3760 Serializable
3761 {
3762 private static final long serialVersionUID = 4374092139857L;
3763
3764 /**
3765 * The comparator specified in the static factory. This will never
3766 * be null, as the static factory returns a ReverseComparator
3767 * instance if its argument is null.
3768 *
3769 * @serial
3770 */
3771 final Comparator<T> cmp;
3772
3773 ReverseComparator2(Comparator<T> cmp) {
3774 assert cmp != null;
3775 this.cmp = cmp;
3776 }
3777
3778 public int compare(T t1, T t2) {
3779 return cmp.compare(t2, t1);
3780 }
3781
3782 public boolean equals(Object o) {
3783 return (o == this) ||
3784 (o instanceof ReverseComparator2 &&
3785 cmp.equals(((ReverseComparator2)o).cmp));
3786 }
3787
3788 public int hashCode() {
3789 return cmp.hashCode() ^ Integer.MIN_VALUE;
3790 }
3791 }
3792
3793 /**
3794 * Returns an enumeration over the specified collection. This provides
3795 * interoperability with legacy APIs that require an enumeration
3796 * as input.
3797 *
3798 * @param c the collection for which an enumeration is to be returned.
3799 * @return an enumeration over the specified collection.
3800 * @see Enumeration
3801 */
3802 public static <T> Enumeration<T> enumeration(final Collection<T> c) {
3803 return new Enumeration<T>() {
3804 private final Iterator<T> i = c.iterator();
3805
3806 public boolean hasMoreElements() {
3807 return i.hasNext();
3808 }
3809
3810 public T nextElement() {
3811 return i.next();
3812 }
3813 };
3814 }
3815
3816 /**
3817 * Returns an array list containing the elements returned by the
3818 * specified enumeration in the order they are returned by the
3819 * enumeration. This method provides interoperability between
3820 * legacy APIs that return enumerations and new APIs that require
3821 * collections.
3822 *
3823 * @param e enumeration providing elements for the returned
3824 * array list
3825 * @return an array list containing the elements returned
3826 * by the specified enumeration.
3827 * @since 1.4
3828 * @see Enumeration
3829 * @see ArrayList
3830 */
3831 public static <T> ArrayList<T> list(Enumeration<T> e) {
3832 ArrayList<T> l = new ArrayList<>();
3833 while (e.hasMoreElements())
3834 l.add(e.nextElement());
3835 return l;
3836 }
3837
3838 /**
3839 * Returns true if the specified arguments are equal, or both null.
3840 */
3841 static boolean eq(Object o1, Object o2) {
3842 return o1==null ? o2==null : o1.equals(o2);
3843 }
3844
3845 /**
3846 * Returns the number of elements in the specified collection equal to the
3847 * specified object. More formally, returns the number of elements
3848 * <tt>e</tt> in the collection such that
3849 * <tt>(o == null ? e == null : o.equals(e))</tt>.
3850 *
3851 * @param c the collection in which to determine the frequency
3852 * of <tt>o</tt>
3853 * @param o the object whose frequency is to be determined
3854 * @throws NullPointerException if <tt>c</tt> is null
3855 * @since 1.5
3856 */
3857 public static int frequency(Collection<?> c, Object o) {
3858 int result = 0;
3859 if (o == null) {
3860 for (Object e : c)
3861 if (e == null)
3862 result++;
3863 } else {
3864 for (Object e : c)
3865 if (o.equals(e))
3866 result++;
3867 }
3868 return result;
3869 }
3870
3871 /**
3872 * Returns {@code true} if the two specified collections have no
3873 * elements in common.
3874 *
3875 * <p>Care must be exercised if this method is used on collections that
3876 * do not comply with the general contract for {@code Collection}.
3877 * Implementations may elect to iterate over either collection and test
3878 * for containment in the other collection (or to perform any equivalent
3879 * computation). If either collection uses a nonstandard equality test
3880 * (as does a {@link SortedSet} whose ordering is not <em>compatible with
3881 * equals</em>, or the key set of an {@link IdentityHashMap}), both
3882 * collections must use the same nonstandard equality test, or the
3883 * result of this method is undefined.
3884 *
3885 * <p>Care must also be exercised when using collections that have
3886 * restrictions on the elements that they may contain. Collection
3887 * implementations are allowed to throw exceptions for any operation
3888 * involving elements they deem ineligible. For absolute safety the
3889 * specified collections should contain only elements which are
3890 * eligible elements for both collections.
3891 *
3892 * <p>Note that it is permissible to pass the same collection in both
3893 * parameters, in which case the method will return {@code true} if and
3894 * only if the collection is empty.
3895 *
3896 * @param c1 a collection
3897 * @param c2 a collection
3898 * @return {@code true} if the two specified collections have no
3899 * elements in common.
3900 * @throws NullPointerException if either collection is {@code null}.
3901 * @throws NullPointerException if one collection contains a {@code null}
3902 * element and {@code null} is not an eligible element for the other collection.
3903 * (<a href="Collection.html#optional-restrictions">optional</a>)
3904 * @throws ClassCastException if one collection contains an element that is
3905 * of a type which is ineligible for the other collection.
3906 * (<a href="Collection.html#optional-restrictions">optional</a>)
3907 * @since 1.5
3908 */
3909 public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
3910 // The collection to be used for contains(). Preference is given to
3911 // the collection who's contains() has lower O() complexity.
3912 Collection<?> contains = c2;
3913 // The collection to be iterated. If the collections' contains() impl
3914 // are of different O() complexity, the collection with slower
3915 // contains() will be used for iteration. For collections who's
3916 // contains() are of the same complexity then best performance is
3917 // achieved by iterating the smaller collection.
3918 Collection<?> iterate = c1;
3919
3920 // Performance optimization cases. The heuristics:
3921 // 1. Generally iterate over c1.
3922 // 2. If c1 is a Set then iterate over c2.
3923 // 3. If either collection is empty then result is always true.
3924 // 4. Iterate over the smaller Collection.
3925 if (c1 instanceof Set) {
3926 // Use c1 for contains as a Set's contains() is expected to perform
3927 // better than O(N/2)
3928 iterate = c2;
3929 contains = c1;
3930 } else if (!(c2 instanceof Set)) {
3931 // Both are mere Collections. Iterate over smaller collection.
3932 // Example: If c1 contains 3 elements and c2 contains 50 elements and
3933 // assuming contains() requires ceiling(N/2) comparisons then
3934 // checking for all c1 elements in c2 would require 75 comparisons
3935 // (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring
3936 // 100 comparisons (50 * ceiling(3/2)).
3937 int c1size = c1.size();
3938 int c2size = c2.size();
3939 if (c1size == 0 || c2size == 0) {
3940 // At least one collection is empty. Nothing will match.
3941 return true;
3942 }
3943
3944 if (c1size > c2size) {
3945 iterate = c2;
3946 contains = c1;
3947 }
3948 }
3949
3950 for (Object e : iterate) {
3951 if (contains.contains(e)) {
3952 // Found a common element. Collections are not disjoint.
3953 return false;
3954 }
3955 }
3956
3957 // No common elements were found.
3958 return true;
3959 }
3960
3961 /**
3962 * Adds all of the specified elements to the specified collection.
3963 * Elements to be added may be specified individually or as an array.
3964 * The behavior of this convenience method is identical to that of
3965 * <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely
3966 * to run significantly faster under most implementations.
3967 *
3968 * <p>When elements are specified individually, this method provides a
3969 * convenient way to add a few elements to an existing collection:
3970 * <pre>
3971 * Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon");
3972 * </pre>
3973 *
3974 * @param c the collection into which <tt>elements</tt> are to be inserted
3975 * @param elements the elements to insert into <tt>c</tt>
3976 * @return <tt>true</tt> if the collection changed as a result of the call
3977 * @throws UnsupportedOperationException if <tt>c</tt> does not support
3978 * the <tt>add</tt> operation
3979 * @throws NullPointerException if <tt>elements</tt> contains one or more
3980 * null values and <tt>c</tt> does not permit null elements, or
3981 * if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt>
3982 * @throws IllegalArgumentException if some property of a value in
3983 * <tt>elements</tt> prevents it from being added to <tt>c</tt>
3984 * @see Collection#addAll(Collection)
3985 * @since 1.5
3986 */
3987 @SafeVarargs
3988 public static <T> boolean addAll(Collection<? super T> c, T... elements) {
3989 boolean result = false;
3990 for (T element : elements)
3991 result |= c.add(element);
3992 return result;
3993 }
3994
3995 /**
3996 * Returns a set backed by the specified map. The resulting set displays
3997 * the same ordering, concurrency, and performance characteristics as the
3998 * backing map. In essence, this factory method provides a {@link Set}
3999 * implementation corresponding to any {@link Map} implementation. There
4000 * is no need to use this method on a {@link Map} implementation that
4001 * already has a corresponding {@link Set} implementation (such as {@link
4002 * HashMap} or {@link TreeMap}).
4003 *
4004 * <p>Each method invocation on the set returned by this method results in
4005 * exactly one method invocation on the backing map or its <tt>keySet</tt>
4006 * view, with one exception. The <tt>addAll</tt> method is implemented
4007 * as a sequence of <tt>put</tt> invocations on the backing map.
4008 *
4009 * <p>The specified map must be empty at the time this method is invoked,
4010 * and should not be accessed directly after this method returns. These
4011 * conditions are ensured if the map is created empty, passed directly
4012 * to this method, and no reference to the map is retained, as illustrated
4013 * in the following code fragment:
4014 * <pre>
4015 * Set<Object> weakHashSet = Collections.newSetFromMap(
4016 * new WeakHashMap<Object, Boolean>());
4017 * </pre>
4018 *
4019 * @param map the backing map
4020 * @return the set backed by the map
4021 * @throws IllegalArgumentException if <tt>map</tt> is not empty
4022 * @since 1.6
4023 */
4024 public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
4025 return new SetFromMap<>(map);
4026 }
4027
4028 /**
4029 * @serial include
4030 */
4031 private static class SetFromMap<E> extends AbstractSet<E>
4032 implements Set<E>, Serializable
4033 {
4034 private final Map<E, Boolean> m; // The backing map
4035 private transient Set<E> s; // Its keySet
4036
4037 SetFromMap(Map<E, Boolean> map) {
4038 if (!map.isEmpty())
4039 throw new IllegalArgumentException("Map is non-empty");
4040 m = map;
4041 s = map.keySet();
4042 }
4043
4044 public void clear() { m.clear(); }
4045 public int size() { return m.size(); }
4046 public boolean isEmpty() { return m.isEmpty(); }
4047 public boolean contains(Object o) { return m.containsKey(o); }
4048 public boolean remove(Object o) { return m.remove(o) != null; }
4049 public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; }
4050 public Iterator<E> iterator() { return s.iterator(); }
4051 public Object[] toArray() { return s.toArray(); }
4052 public <T> T[] toArray(T[] a) { return s.toArray(a); }
4053 public String toString() { return s.toString(); }
4054 public int hashCode() { return s.hashCode(); }
4055 public boolean equals(Object o) { return o == this || s.equals(o); }
4056 public boolean containsAll(Collection<?> c) {return s.containsAll(c);}
4057 public boolean removeAll(Collection<?> c) {return s.removeAll(c);}
4058 public boolean retainAll(Collection<?> c) {return s.retainAll(c);}
4059 // addAll is the only inherited implementation
4060
4061 private static final long serialVersionUID = 2454657854757543876L;
4062
4063 private void readObject(java.io.ObjectInputStream stream)
4064 throws IOException, ClassNotFoundException
4065 {
4066 stream.defaultReadObject();
4067 s = m.keySet();
4068 }
4069 }
4070
4071 /**
4072 * Returns a view of a {@link Deque} as a Last-in-first-out (Lifo)
4073 * {@link Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>,
4074 * <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This
4075 * view can be useful when you would like to use a method
4076 * requiring a <tt>Queue</tt> but you need Lifo ordering.
4077 *
4078 * <p>Each method invocation on the queue returned by this method
4079 * results in exactly one method invocation on the backing deque, with
4080 * one exception. The {@link Queue#addAll addAll} method is
4081 * implemented as a sequence of {@link Deque#addFirst addFirst}
4082 * invocations on the backing deque.
4083 *
4084 * @param deque the deque
4085 * @return the queue
4086 * @since 1.6
4087 */
4088 public static <T> Queue<T> asLifoQueue(Deque<T> deque) {
4089 return new AsLIFOQueue<>(deque);
4090 }
4091
4092 /**
4093 * @serial include
4094 */
4095 static class AsLIFOQueue<E> extends AbstractQueue<E>
4096 implements Queue<E>, Serializable {
4097 private static final long serialVersionUID = 1802017725587941708L;
4098 private final Deque<E> q;
4099 AsLIFOQueue(Deque<E> q) { this.q = q; }
4100 public boolean add(E e) { q.addFirst(e); return true; }
4101 public boolean offer(E e) { return q.offerFirst(e); }
4102 public E poll() { return q.pollFirst(); }
4103 public E remove() { return q.removeFirst(); }
4104 public E peek() { return q.peekFirst(); }
4105 public E element() { return q.getFirst(); }
4106 public void clear() { q.clear(); }
4107 public int size() { return q.size(); }
4108 public boolean isEmpty() { return q.isEmpty(); }
4109 public boolean contains(Object o) { return q.contains(o); }
4110 public boolean remove(Object o) { return q.remove(o); }
4111 public Iterator<E> iterator() { return q.iterator(); }
4112 public Object[] toArray() { return q.toArray(); }
4113 public <T> T[] toArray(T[] a) { return q.toArray(a); }
4114 public String toString() { return q.toString(); }
4115 public boolean containsAll(Collection<?> c) {return q.containsAll(c);}
4116 public boolean removeAll(Collection<?> c) {return q.removeAll(c);}
4117 public boolean retainAll(Collection<?> c) {return q.retainAll(c);}
4118 // We use inherited addAll; forwarding addAll would be wrong
4119 }
4120 }