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