1 /*
2 * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.util;
27 import java.io.Serializable;
28 import java.io.ObjectOutputStream;
29 import java.io.IOException;
30 import java.lang.reflect.Array;
31 import java.util.function.BiConsumer;
32 import java.util.function.BiFunction;
33 import java.util.function.Consumer;
34 import java.util.function.Function;
35
36 /**
37 * This class consists exclusively of static methods that operate on or return
38 * collections. It contains polymorphic algorithms that operate on
39 * collections, "wrappers", which return a new collection backed by a
40 * specified collection, and a few other odds and ends.
41 *
42 * <p>The methods of this class all throw a <tt>NullPointerException</tt>
43 * if the collections or class objects provided to them are null.
44 *
45 * <p>The documentation for the polymorphic algorithms contained in this class
46 * generally includes a brief description of the <i>implementation</i>. Such
47 * descriptions should be regarded as <i>implementation notes</i>, rather than
48 * parts of the <i>specification</i>. Implementors should feel free to
49 * substitute other algorithms, so long as the specification itself is adhered
50 * to. (For example, the algorithm used by <tt>sort</tt> does not have to be
51 * a mergesort, but it does have to be <i>stable</i>.)
52 *
53 * <p>The "destructive" algorithms contained in this class, that is, the
54 * algorithms that modify the collection on which they operate, are specified
55 * to throw <tt>UnsupportedOperationException</tt> if the collection does not
56 * support the appropriate mutation primitive(s), such as the <tt>set</tt>
57 * method. These algorithms may, but are not required to, throw this
58 * exception if an invocation would have no effect on the collection. For
59 * example, invoking the <tt>sort</tt> method on an unmodifiable list that is
60 * already sorted may or may not throw <tt>UnsupportedOperationException</tt>.
61 *
62 * <p>This class is a member of the
63 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
64 * Java Collections Framework</a>.
65 *
66 * @author Josh Bloch
67 * @author Neal Gafter
68 * @see Collection
69 * @see Set
70 * @see List
71 * @see Map
72 * @since 1.2
73 */
74
75 public class Collections {
76 // Suppresses default constructor, ensuring non-instantiability.
77 private Collections() {
78 }
79
80 // Algorithms
81
82 /*
83 * Tuning parameters for algorithms - Many of the List algorithms have
84 * two implementations, one of which is appropriate for RandomAccess
85 * lists, the other for "sequential." Often, the random access variant
86 * yields better performance on small sequential access lists. The
87 * tuning parameters below determine the cutoff point for what constitutes
88 * a "small" sequential access list for each algorithm. The values below
89 * were empirically determined to work well for LinkedList. Hopefully
90 * they should be reasonable for other sequential access List
91 * implementations. Those doing performance work on this code would
92 * do well to validate the values of these parameters from time to time.
93 * (The first word of each tuning parameter name is the algorithm to which
94 * it applies.)
95 */
96 private static final int BINARYSEARCH_THRESHOLD = 5000;
97 private static final int REVERSE_THRESHOLD = 18;
98 private static final int SHUFFLE_THRESHOLD = 5;
99 private static final int FILL_THRESHOLD = 25;
100 private static final int ROTATE_THRESHOLD = 100;
101 private static final int COPY_THRESHOLD = 10;
102 private static final int REPLACEALL_THRESHOLD = 11;
103 private static final int INDEXOFSUBLIST_THRESHOLD = 35;
104
105 /**
106 * Sorts the specified list into ascending order, according to the
107 * {@linkplain Comparable natural ordering} of its elements.
108 * All elements in the list must implement the {@link Comparable}
109 * interface. Furthermore, all elements in the list must be
110 * <i>mutually comparable</i> (that is, {@code e1.compareTo(e2)}
111 * must not throw a {@code ClassCastException} for any elements
112 * {@code e1} and {@code e2} in the list).
113 *
114 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will
115 * not be reordered as a result of the sort.
116 *
117 * <p>The specified list must be modifiable, but need not be resizable.
118 *
119 * <p>Implementation note: This implementation is a stable, adaptive,
120 * iterative mergesort that requires far fewer than n lg(n) comparisons
121 * when the input array is partially sorted, while offering the
122 * performance of a traditional mergesort when the input array is
123 * randomly ordered. If the input array is nearly sorted, the
124 * implementation requires approximately n comparisons. Temporary
125 * storage requirements vary from a small constant for nearly sorted
126 * input arrays to n/2 object references for randomly ordered input
127 * arrays.
128 *
129 * <p>The implementation takes equal advantage of ascending and
130 * descending order in its input array, and can take advantage of
131 * ascending and descending order in different parts of the same
132 * input array. It is well-suited to merging two or more sorted arrays:
133 * simply concatenate the arrays and sort the resulting array.
134 *
135 * <p>The implementation was adapted from Tim Peters's list sort for Python
136 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt">
137 * TimSort</a>). It uses techiques from Peter McIlroy's "Optimistic
138 * Sorting and Information Theoretic Complexity", in Proceedings of the
139 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474,
140 * January 1993.
141 *
142 * <p>This implementation dumps the specified list into an array, sorts
143 * the array, and iterates over the list resetting each element
144 * from the corresponding position in the array. This avoids the
145 * n<sup>2</sup> log(n) performance that would result from attempting
146 * to sort a linked list in place.
147 *
148 * @param list the list to be sorted.
149 * @throws ClassCastException if the list contains elements that are not
150 * <i>mutually comparable</i> (for example, strings and integers).
151 * @throws UnsupportedOperationException if the specified list's
152 * list-iterator does not support the {@code set} operation.
153 * @throws IllegalArgumentException (optional) if the implementation
154 * detects that the natural ordering of the list elements is
155 * found to violate the {@link Comparable} contract
156 */
157 @SuppressWarnings("unchecked")
158 public static <T extends Comparable<? super T>> void sort(List<T> list) {
159 Object[] a = list.toArray();
160 Arrays.sort(a);
161 ListIterator<T> i = list.listIterator();
162 for (int j=0; j<a.length; j++) {
163 i.next();
164 i.set((T)a[j]);
165 }
166 }
167
168 /**
169 * Sorts the specified list according to the order induced by the
170 * specified comparator. All elements in the list must be <i>mutually
171 * comparable</i> using the specified comparator (that is,
172 * {@code c.compare(e1, e2)} must not throw a {@code ClassCastException}
173 * for any elements {@code e1} and {@code e2} in the list).
174 *
175 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will
176 * not be reordered as a result of the sort.
177 *
178 * <p>The specified list must be modifiable, but need not be resizable.
179 *
180 * <p>Implementation note: This implementation is a stable, adaptive,
181 * iterative mergesort that requires far fewer than n lg(n) comparisons
182 * when the input array is partially sorted, while offering the
183 * performance of a traditional mergesort when the input array is
184 * randomly ordered. If the input array is nearly sorted, the
185 * implementation requires approximately n comparisons. Temporary
186 * storage requirements vary from a small constant for nearly sorted
187 * input arrays to n/2 object references for randomly ordered input
188 * arrays.
189 *
190 * <p>The implementation takes equal advantage of ascending and
191 * descending order in its input array, and can take advantage of
192 * ascending and descending order in different parts of the same
193 * input array. It is well-suited to merging two or more sorted arrays:
194 * simply concatenate the arrays and sort the resulting array.
195 *
196 * <p>The implementation was adapted from Tim Peters's list sort for Python
197 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt">
198 * TimSort</a>). It uses techiques from Peter McIlroy's "Optimistic
199 * Sorting and Information Theoretic Complexity", in Proceedings of the
200 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474,
201 * January 1993.
202 *
203 * <p>This implementation dumps the specified list into an array, sorts
204 * the array, and iterates over the list resetting each element
205 * from the corresponding position in the array. This avoids the
206 * n<sup>2</sup> log(n) performance that would result from attempting
207 * to sort a linked list in place.
208 *
209 * @param list the list to be sorted.
210 * @param c the comparator to determine the order of the list. A
211 * {@code null} value indicates that the elements' <i>natural
212 * ordering</i> should be used.
213 * @throws ClassCastException if the list contains elements that are not
214 * <i>mutually comparable</i> using the specified comparator.
215 * @throws UnsupportedOperationException if the specified list's
216 * list-iterator does not support the {@code set} operation.
217 * @throws IllegalArgumentException (optional) if the comparator is
218 * found to violate the {@link Comparator} contract
219 */
220 @SuppressWarnings({"unchecked", "rawtypes"})
221 public static <T> void sort(List<T> list, Comparator<? super T> c) {
222 Object[] a = list.toArray();
223 Arrays.sort(a, (Comparator)c);
224 ListIterator<T> i = list.listIterator();
225 for (int j=0; j<a.length; j++) {
226 i.next();
227 i.set((T)a[j]);
228 }
229 }
230
231
232 /**
233 * Searches the specified list for the specified object using the binary
234 * search algorithm. The list must be sorted into ascending order
235 * according to the {@linkplain Comparable natural ordering} of its
236 * elements (as by the {@link #sort(List)} method) prior to making this
237 * call. If it is not sorted, the results are undefined. If the list
238 * contains multiple elements equal to the specified object, there is no
239 * guarantee which one will be found.
240 *
241 * <p>This method runs in log(n) time for a "random access" list (which
242 * provides near-constant-time positional access). If the specified list
243 * does not implement the {@link RandomAccess} interface and is large,
244 * this method will do an iterator-based binary search that performs
245 * O(n) link traversals and O(log n) element comparisons.
246 *
247 * @param list the list to be searched.
248 * @param key the key to be searched for.
249 * @return the index of the search key, if it is contained in the list;
250 * otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The
251 * <i>insertion point</i> is defined as the point at which the
252 * key would be inserted into the list: the index of the first
253 * element greater than the key, or <tt>list.size()</tt> if all
254 * elements in the list are less than the specified key. Note
255 * that this guarantees that the return value will be >= 0 if
256 * and only if the key is found.
257 * @throws ClassCastException if the list contains elements that are not
258 * <i>mutually comparable</i> (for example, strings and
259 * integers), or the search key is not mutually comparable
260 * with the elements of the list.
261 */
262 public static <T>
263 int binarySearch(List<? extends Comparable<? super T>> list, T key) {
264 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
265 return Collections.indexedBinarySearch(list, key);
266 else
267 return Collections.iteratorBinarySearch(list, key);
268 }
269
270 private static <T>
271 int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key) {
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.
448 *
449 * <p>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.
454 *
455 * <p>This implementation traverses the list backwards, from the last
456 * element up to the second, repeatedly swapping a randomly selected element
457 * into 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.
460 *
461 * <p>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(); // harmless race.
476 shuffle(list, rnd);
477 }
478
479 private static Random r;
480
481 /**
482 * Randomly permute the specified list using the specified source of
483 * randomness. All permutations occur with equal likelihood
484 * assuming that the source of randomness is fair.<p>
485 *
486 * This implementation traverses the list backwards, from the last element
487 * up to the second, repeatedly swapping a randomly selected element into
488 * the "current position". Elements are randomly selected from the
489 * portion of the list that runs from the first element to the current
490 * position, inclusive.<p>
491 *
492 * This method runs in linear time. If the specified list does not
493 * implement the {@link RandomAccess} interface and is large, this
494 * implementation dumps the specified list into an array before shuffling
495 * it, and dumps the shuffled array back into the list. This avoids the
496 * quadratic behavior that would result from shuffling a "sequential
497 * access" list in place.
498 *
499 * @param list the list to be shuffled.
500 * @param rnd the source of randomness to use to shuffle the list.
501 * @throws UnsupportedOperationException if the specified list or its
502 * list-iterator does not support the <tt>set</tt> operation.
503 */
504 @SuppressWarnings({"rawtypes", "unchecked"})
505 public static void shuffle(List<?> list, Random rnd) {
506 int size = list.size();
507 if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) {
508 for (int i=size; i>1; i--)
509 swap(list, i-1, rnd.nextInt(i));
510 } else {
511 Object arr[] = list.toArray();
512
513 // Shuffle array
514 for (int i=size; i>1; i--)
515 swap(arr, i-1, rnd.nextInt(i));
516
517 // Dump array back into list
518 // instead of using a raw type here, it's possible to capture
519 // the wildcard but it will require a call to a supplementary
520 // private method
521 ListIterator it = list.listIterator();
522 for (int i=0; i<arr.length; i++) {
523 it.next();
524 it.set(arr[i]);
525 }
526 }
527 }
528
529 /**
530 * Swaps the elements at the specified positions in the specified list.
531 * (If the specified positions are equal, invoking this method leaves
532 * the list unchanged.)
533 *
534 * @param list The list in which to swap elements.
535 * @param i the index of one element to be swapped.
536 * @param j the index of the other element to be swapped.
537 * @throws IndexOutOfBoundsException if either <tt>i</tt> or <tt>j</tt>
538 * is out of range (i < 0 || i >= list.size()
539 * || j < 0 || j >= list.size()).
540 * @since 1.4
541 */
542 @SuppressWarnings({"rawtypes", "unchecked"})
543 public static void swap(List<?> list, int i, int j) {
544 // instead of using a raw type here, it's possible to capture
545 // the wildcard but it will require a call to a supplementary
546 // private method
547 final List l = list;
548 l.set(i, l.set(j, l.get(i)));
549 }
550
551 /**
552 * Swaps the two specified elements in the specified array.
553 */
554 private static void swap(Object[] arr, int i, int j) {
555 Object tmp = arr[i];
556 arr[i] = arr[j];
557 arr[j] = tmp;
558 }
559
560 /**
561 * Replaces all of the elements of the specified list with the specified
562 * element. <p>
563 *
564 * This method runs in linear time.
565 *
566 * @param list the list to be filled with the specified element.
567 * @param obj The element with which to fill the specified list.
568 * @throws UnsupportedOperationException if the specified list or its
569 * list-iterator does not support the <tt>set</tt> operation.
570 */
571 public static <T> void fill(List<? super T> list, T obj) {
572 int size = list.size();
573
574 if (size < FILL_THRESHOLD || list instanceof RandomAccess) {
575 for (int i=0; i<size; i++)
576 list.set(i, obj);
577 } else {
578 ListIterator<? super T> itr = list.listIterator();
579 for (int i=0; i<size; i++) {
580 itr.next();
581 itr.set(obj);
582 }
583 }
584 }
585
586 /**
587 * Copies all of the elements from one list into another. After the
588 * operation, the index of each copied element in the destination list
589 * will be identical to its index in the source list. The destination
590 * list must be at least as long as the source list. If it is longer, the
591 * remaining elements in the destination list are unaffected. <p>
592 *
593 * This method runs in linear time.
594 *
595 * @param dest The destination list.
596 * @param src The source list.
597 * @throws IndexOutOfBoundsException if the destination list is too small
598 * to contain the entire source List.
599 * @throws UnsupportedOperationException if the destination list's
600 * list-iterator does not support the <tt>set</tt> operation.
601 */
602 public static <T> void copy(List<? super T> dest, List<? extends T> src) {
603 int srcSize = src.size();
604 if (srcSize > dest.size())
605 throw new IndexOutOfBoundsException("Source does not fit in dest");
606
607 if (srcSize < COPY_THRESHOLD ||
608 (src instanceof RandomAccess && dest instanceof RandomAccess)) {
609 for (int i=0; i<srcSize; i++)
610 dest.set(i, src.get(i));
611 } else {
612 ListIterator<? super T> di=dest.listIterator();
613 ListIterator<? extends T> si=src.listIterator();
614 for (int i=0; i<srcSize; i++) {
615 di.next();
616 di.set(si.next());
617 }
618 }
619 }
620
621 /**
622 * Returns the minimum element of the given collection, according to the
623 * <i>natural ordering</i> of its elements. All elements in the
624 * collection must implement the <tt>Comparable</tt> interface.
625 * Furthermore, all elements in the collection must be <i>mutually
626 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
627 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
628 * <tt>e2</tt> in the collection).<p>
629 *
630 * This method iterates over the entire collection, hence it requires
631 * time proportional to the size of the collection.
632 *
633 * @param coll the collection whose minimum element is to be determined.
634 * @return the minimum element of the given collection, according
635 * to the <i>natural ordering</i> of its elements.
636 * @throws ClassCastException if the collection contains elements that are
637 * not <i>mutually comparable</i> (for example, strings and
638 * integers).
639 * @throws NoSuchElementException if the collection is empty.
640 * @see Comparable
641 */
642 public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) {
643 Iterator<? extends T> i = coll.iterator();
644 T candidate = i.next();
645
646 while (i.hasNext()) {
647 T next = i.next();
648 if (next.compareTo(candidate) < 0)
649 candidate = next;
650 }
651 return candidate;
652 }
653
654 /**
655 * Returns the minimum element of the given collection, according to the
656 * order induced by the specified comparator. All elements in the
657 * collection must be <i>mutually comparable</i> by the specified
658 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
659 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
660 * <tt>e2</tt> in the collection).<p>
661 *
662 * This method iterates over the entire collection, hence it requires
663 * time proportional to the size of the collection.
664 *
665 * @param coll the collection whose minimum element is to be determined.
666 * @param comp the comparator with which to determine the minimum element.
667 * A <tt>null</tt> value indicates that the elements' <i>natural
668 * ordering</i> should be used.
669 * @return the minimum element of the given collection, according
670 * to the specified comparator.
671 * @throws ClassCastException if the collection contains elements that are
672 * not <i>mutually comparable</i> using the specified comparator.
673 * @throws NoSuchElementException if the collection is empty.
674 * @see Comparable
675 */
676 @SuppressWarnings({"unchecked", "rawtypes"})
677 public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) {
678 if (comp==null)
679 return (T)min((Collection) coll);
680
681 Iterator<? extends T> i = coll.iterator();
682 T candidate = i.next();
683
684 while (i.hasNext()) {
685 T next = i.next();
686 if (comp.compare(next, candidate) < 0)
687 candidate = next;
688 }
689 return candidate;
690 }
691
692 /**
693 * Returns the maximum element of the given collection, according to the
694 * <i>natural ordering</i> of its elements. All elements in the
695 * collection must implement the <tt>Comparable</tt> interface.
696 * Furthermore, all elements in the collection must be <i>mutually
697 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
698 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
699 * <tt>e2</tt> in the collection).<p>
700 *
701 * This method iterates over the entire collection, hence it requires
702 * time proportional to the size of the collection.
703 *
704 * @param coll the collection whose maximum element is to be determined.
705 * @return the maximum element of the given collection, according
706 * to the <i>natural ordering</i> of its elements.
707 * @throws ClassCastException if the collection contains elements that are
708 * not <i>mutually comparable</i> (for example, strings and
709 * integers).
710 * @throws NoSuchElementException if the collection is empty.
711 * @see Comparable
712 */
713 public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) {
714 Iterator<? extends T> i = coll.iterator();
715 T candidate = i.next();
716
717 while (i.hasNext()) {
718 T next = i.next();
719 if (next.compareTo(candidate) > 0)
720 candidate = next;
721 }
722 return candidate;
723 }
724
725 /**
726 * Returns the maximum element of the given collection, according to the
727 * order induced by the specified comparator. All elements in the
728 * collection must be <i>mutually comparable</i> by the specified
729 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
730 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
731 * <tt>e2</tt> in the collection).<p>
732 *
733 * This method iterates over the entire collection, hence it requires
734 * time proportional to the size of the collection.
735 *
736 * @param coll the collection whose maximum element is to be determined.
737 * @param comp the comparator with which to determine the maximum element.
738 * A <tt>null</tt> value indicates that the elements' <i>natural
739 * ordering</i> should be used.
740 * @return the maximum element of the given collection, according
741 * to the specified comparator.
742 * @throws ClassCastException if the collection contains elements that are
743 * not <i>mutually comparable</i> using the specified comparator.
744 * @throws NoSuchElementException if the collection is empty.
745 * @see Comparable
746 */
747 @SuppressWarnings({"unchecked", "rawtypes"})
748 public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) {
749 if (comp==null)
750 return (T)max((Collection) coll);
751
752 Iterator<? extends T> i = coll.iterator();
753 T candidate = i.next();
754
755 while (i.hasNext()) {
756 T next = i.next();
757 if (comp.compare(next, candidate) > 0)
758 candidate = next;
759 }
760 return candidate;
761 }
762
763 /**
764 * Rotates the elements in the specified list by the specified distance.
765 * After calling this method, the element at index <tt>i</tt> will be
766 * the element previously at index <tt>(i - distance)</tt> mod
767 * <tt>list.size()</tt>, for all values of <tt>i</tt> between <tt>0</tt>
768 * and <tt>list.size()-1</tt>, inclusive. (This method has no effect on
769 * the size of the list.)
770 *
771 * <p>For example, suppose <tt>list</tt> comprises<tt> [t, a, n, k, s]</tt>.
772 * After invoking <tt>Collections.rotate(list, 1)</tt> (or
773 * <tt>Collections.rotate(list, -4)</tt>), <tt>list</tt> will comprise
774 * <tt>[s, t, a, n, k]</tt>.
775 *
776 * <p>Note that this method can usefully be applied to sublists to
777 * move one or more elements within a list while preserving the
778 * order of the remaining elements. For example, the following idiom
779 * moves the element at index <tt>j</tt> forward to position
780 * <tt>k</tt> (which must be greater than or equal to <tt>j</tt>):
781 * <pre>
782 * Collections.rotate(list.subList(j, k+1), -1);
783 * </pre>
784 * To make this concrete, suppose <tt>list</tt> comprises
785 * <tt>[a, b, c, d, e]</tt>. To move the element at index <tt>1</tt>
786 * (<tt>b</tt>) forward two positions, perform the following invocation:
787 * <pre>
788 * Collections.rotate(l.subList(1, 4), -1);
789 * </pre>
790 * The resulting list is <tt>[a, c, d, b, e]</tt>.
791 *
792 * <p>To move more than one element forward, increase the absolute value
793 * of the rotation distance. To move elements backward, use a positive
794 * shift distance.
795 *
796 * <p>If the specified list is small or implements the {@link
797 * RandomAccess} interface, this implementation exchanges the first
798 * element into the location it should go, and then repeatedly exchanges
799 * the displaced element into the location it should go until a displaced
800 * element is swapped into the first element. If necessary, the process
801 * is repeated on the second and successive elements, until the rotation
802 * is complete. If the specified list is large and doesn't implement the
803 * <tt>RandomAccess</tt> interface, this implementation breaks the
804 * list into two sublist views around index <tt>-distance mod size</tt>.
805 * Then the {@link #reverse(List)} method is invoked on each sublist view,
806 * and finally it is invoked on the entire list. For a more complete
807 * description of both algorithms, see Section 2.3 of Jon Bentley's
808 * <i>Programming Pearls</i> (Addison-Wesley, 1986).
809 *
810 * @param list the list to be rotated.
811 * @param distance the distance to rotate the list. There are no
812 * constraints on this value; it may be zero, negative, or
813 * greater than <tt>list.size()</tt>.
814 * @throws UnsupportedOperationException if the specified list or
815 * its list-iterator does not support the <tt>set</tt> operation.
816 * @since 1.4
817 */
818 public static void rotate(List<?> list, int distance) {
819 if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD)
820 rotate1(list, distance);
821 else
822 rotate2(list, distance);
823 }
824
825 private static <T> void rotate1(List<T> list, int distance) {
826 int size = list.size();
827 if (size == 0)
828 return;
829 distance = distance % size;
830 if (distance < 0)
831 distance += size;
832 if (distance == 0)
833 return;
834
835 for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) {
836 T displaced = list.get(cycleStart);
837 int i = cycleStart;
838 do {
839 i += distance;
840 if (i >= size)
841 i -= size;
842 displaced = list.set(i, displaced);
843 nMoved ++;
844 } while (i != cycleStart);
845 }
846 }
847
848 private static void rotate2(List<?> list, int distance) {
849 int size = list.size();
850 if (size == 0)
851 return;
852 int mid = -distance % size;
853 if (mid < 0)
854 mid += size;
855 if (mid == 0)
856 return;
857
858 reverse(list.subList(0, mid));
859 reverse(list.subList(mid, size));
860 reverse(list);
861 }
862
863 /**
864 * Replaces all occurrences of one specified value in a list with another.
865 * More formally, replaces with <tt>newVal</tt> each element <tt>e</tt>
866 * in <tt>list</tt> such that
867 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
868 * (This method has no effect on the size of the list.)
869 *
870 * @param list the list in which replacement is to occur.
871 * @param oldVal the old value to be replaced.
872 * @param newVal the new value with which <tt>oldVal</tt> is to be
873 * replaced.
874 * @return <tt>true</tt> if <tt>list</tt> contained one or more elements
875 * <tt>e</tt> such that
876 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
877 * @throws UnsupportedOperationException if the specified list or
878 * its list-iterator does not support the <tt>set</tt> operation.
879 * @since 1.4
880 */
881 public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) {
882 boolean result = false;
883 int size = list.size();
884 if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) {
885 if (oldVal==null) {
886 for (int i=0; i<size; i++) {
887 if (list.get(i)==null) {
888 list.set(i, newVal);
889 result = true;
890 }
891 }
892 } else {
893 for (int i=0; i<size; i++) {
894 if (oldVal.equals(list.get(i))) {
895 list.set(i, newVal);
896 result = true;
897 }
898 }
899 }
900 } else {
901 ListIterator<T> itr=list.listIterator();
902 if (oldVal==null) {
903 for (int i=0; i<size; i++) {
904 if (itr.next()==null) {
905 itr.set(newVal);
906 result = true;
907 }
908 }
909 } else {
910 for (int i=0; i<size; i++) {
911 if (oldVal.equals(itr.next())) {
912 itr.set(newVal);
913 result = true;
914 }
915 }
916 }
917 }
918 return result;
919 }
920
921 /**
922 * Returns the starting position of the first occurrence of the specified
923 * target list within the specified source list, or -1 if there is no
924 * such occurrence. More formally, returns the lowest index <tt>i</tt>
925 * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
926 * or -1 if there is no such index. (Returns -1 if
927 * <tt>target.size() > source.size()</tt>.)
928 *
929 * <p>This implementation uses the "brute force" technique of scanning
930 * over the source list, looking for a match with the target at each
931 * location in turn.
932 *
933 * @param source the list in which to search for the first occurrence
934 * of <tt>target</tt>.
935 * @param target the list to search for as a subList of <tt>source</tt>.
936 * @return the starting position of the first occurrence of the specified
937 * target list within the specified source list, or -1 if there
938 * is no such occurrence.
939 * @since 1.4
940 */
941 public static int indexOfSubList(List<?> source, List<?> target) {
942 int sourceSize = source.size();
943 int targetSize = target.size();
944 int maxCandidate = sourceSize - targetSize;
945
946 if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
947 (source instanceof RandomAccess&&target instanceof RandomAccess)) {
948 nextCand:
949 for (int candidate = 0; candidate <= maxCandidate; candidate++) {
950 for (int i=0, j=candidate; i<targetSize; i++, j++)
951 if (!eq(target.get(i), source.get(j)))
952 continue nextCand; // Element mismatch, try next cand
953 return candidate; // All elements of candidate matched target
954 }
955 } else { // Iterator version of above algorithm
956 ListIterator<?> si = source.listIterator();
957 nextCand:
958 for (int candidate = 0; candidate <= maxCandidate; candidate++) {
959 ListIterator<?> ti = target.listIterator();
960 for (int i=0; i<targetSize; i++) {
961 if (!eq(ti.next(), si.next())) {
962 // Back up source iterator to next candidate
963 for (int j=0; j<i; j++)
964 si.previous();
965 continue nextCand;
966 }
967 }
968 return candidate;
969 }
970 }
971 return -1; // No candidate matched the target
972 }
973
974 /**
975 * Returns the starting position of the last occurrence of the specified
976 * target list within the specified source list, or -1 if there is no such
977 * occurrence. More formally, returns the highest index <tt>i</tt>
978 * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
979 * or -1 if there is no such index. (Returns -1 if
980 * <tt>target.size() > source.size()</tt>.)
981 *
982 * <p>This implementation uses the "brute force" technique of iterating
983 * over the source list, looking for a match with the target at each
984 * location in turn.
985 *
986 * @param source the list in which to search for the last occurrence
987 * of <tt>target</tt>.
988 * @param target the list to search for as a subList of <tt>source</tt>.
989 * @return the starting position of the last occurrence of the specified
990 * target list within the specified source list, or -1 if there
991 * is no such occurrence.
992 * @since 1.4
993 */
994 public static int lastIndexOfSubList(List<?> source, List<?> target) {
995 int sourceSize = source.size();
996 int targetSize = target.size();
997 int maxCandidate = sourceSize - targetSize;
998
999 if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
1000 source instanceof RandomAccess) { // Index access version
1001 nextCand:
1002 for (int candidate = maxCandidate; candidate >= 0; candidate--) {
1003 for (int i=0, j=candidate; i<targetSize; i++, j++)
1004 if (!eq(target.get(i), source.get(j)))
1005 continue nextCand; // Element mismatch, try next cand
1006 return candidate; // All elements of candidate matched target
1007 }
1008 } else { // Iterator version of above algorithm
1009 if (maxCandidate < 0)
1010 return -1;
1011 ListIterator<?> si = source.listIterator(maxCandidate);
1012 nextCand:
1013 for (int candidate = maxCandidate; candidate >= 0; candidate--) {
1014 ListIterator<?> ti = target.listIterator();
1015 for (int i=0; i<targetSize; i++) {
1016 if (!eq(ti.next(), si.next())) {
1017 if (candidate != 0) {
1018 // Back up source iterator to next candidate
1019 for (int j=0; j<=i+1; j++)
1020 si.previous();
1021 }
1022 continue nextCand;
1023 }
1024 }
1025 return candidate;
1026 }
1027 }
1028 return -1; // No candidate matched the target
1029 }
1030
1031
1032 // Unmodifiable Wrappers
1033
1034 /**
1035 * Returns an unmodifiable view of the specified collection. This method
1036 * allows modules to provide users with "read-only" access to internal
1037 * collections. Query operations on the returned collection "read through"
1038 * to the specified collection, and attempts to modify the returned
1039 * collection, whether direct or via its iterator, result in an
1040 * <tt>UnsupportedOperationException</tt>.<p>
1041 *
1042 * The returned collection does <i>not</i> pass the hashCode and equals
1043 * operations through to the backing collection, but relies on
1044 * <tt>Object</tt>'s <tt>equals</tt> and <tt>hashCode</tt> methods. This
1045 * is necessary to preserve the contracts of these operations in the case
1046 * that the backing collection is a set or a list.<p>
1047 *
1048 * The returned collection will be serializable if the specified collection
1049 * is serializable.
1050 *
1051 * @param c the collection for which an unmodifiable view is to be
1052 * returned.
1053 * @return an unmodifiable view of the specified collection.
1054 */
1055 public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) {
1056 return new UnmodifiableCollection<>(c);
1057 }
1058
1059 /**
1060 * @serial include
1061 */
1062 static class UnmodifiableCollection<E> implements Collection<E>, Serializable {
1063 private static final long serialVersionUID = 1820017752578914078L;
1064
1065 final Collection<? extends E> c;
1066
1067 UnmodifiableCollection(Collection<? extends E> c) {
1068 if (c==null)
1069 throw new NullPointerException();
1070 this.c = c;
1071 }
1072
1073 public int size() {return c.size();}
1074 public boolean isEmpty() {return c.isEmpty();}
1075 public boolean contains(Object o) {return c.contains(o);}
1076 public Object[] toArray() {return c.toArray();}
1077 public <T> T[] toArray(T[] a) {return c.toArray(a);}
1078 public String toString() {return c.toString();}
1079
1080 public Iterator<E> iterator() {
1081 return new Iterator<E>() {
1082 private final Iterator<? extends E> i = c.iterator();
1083
1084 public boolean hasNext() {return i.hasNext();}
1085 public E next() {return i.next();}
1086 public void remove() {
1087 throw new UnsupportedOperationException();
1088 }
1089 @Override
1090 public void forEachRemaining(Consumer<? super E> action) {
1091 i.forEachRemaining(action);
1092 }
1093 };
1094 }
1095
1096 public boolean add(E e) {
1097 throw new UnsupportedOperationException();
1098 }
1099 public boolean remove(Object o) {
1100 throw new UnsupportedOperationException();
1101 }
1102
1103 public boolean containsAll(Collection<?> coll) {
1104 return c.containsAll(coll);
1105 }
1106 public boolean addAll(Collection<? extends E> coll) {
1107 throw new UnsupportedOperationException();
1108 }
1109 public boolean removeAll(Collection<?> coll) {
1110 throw new UnsupportedOperationException();
1111 }
1112 public boolean retainAll(Collection<?> coll) {
1113 throw new UnsupportedOperationException();
1114 }
1115 public void clear() {
1116 throw new UnsupportedOperationException();
1117 }
1118 }
1119
1120 /**
1121 * Returns an unmodifiable view of the specified set. This method allows
1122 * modules to provide users with "read-only" access to internal sets.
1123 * Query operations on the returned set "read through" to the specified
1124 * set, and attempts to modify the returned set, whether direct or via its
1125 * iterator, result in an <tt>UnsupportedOperationException</tt>.<p>
1126 *
1127 * The returned set will be serializable if the specified set
1128 * is serializable.
1129 *
1130 * @param s the set for which an unmodifiable view is to be returned.
1131 * @return an unmodifiable view of the specified set.
1132 */
1133 public static <T> Set<T> unmodifiableSet(Set<? extends T> s) {
1134 return new UnmodifiableSet<>(s);
1135 }
1136
1137 /**
1138 * @serial include
1139 */
1140 static class UnmodifiableSet<E> extends UnmodifiableCollection<E>
1141 implements Set<E>, Serializable {
1142 private static final long serialVersionUID = -9215047833775013803L;
1143
1144 UnmodifiableSet(Set<? extends E> s) {super(s);}
1145 public boolean equals(Object o) {return o == this || c.equals(o);}
1146 public int hashCode() {return c.hashCode();}
1147 }
1148
1149 /**
1150 * Returns an unmodifiable view of the specified sorted set. This method
1151 * allows modules to provide users with "read-only" access to internal
1152 * sorted sets. Query operations on the returned sorted set "read
1153 * through" to the specified sorted set. Attempts to modify the returned
1154 * sorted set, whether direct, via its iterator, or via its
1155 * <tt>subSet</tt>, <tt>headSet</tt>, or <tt>tailSet</tt> views, result in
1156 * an <tt>UnsupportedOperationException</tt>.<p>
1157 *
1158 * The returned sorted set will be serializable if the specified sorted set
1159 * is serializable.
1160 *
1161 * @param s the sorted set for which an unmodifiable view is to be
1162 * returned.
1163 * @return an unmodifiable view of the specified sorted set.
1164 */
1165 public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) {
1166 return new UnmodifiableSortedSet<>(s);
1167 }
1168
1169 /**
1170 * @serial include
1171 */
1172 static class UnmodifiableSortedSet<E>
1173 extends UnmodifiableSet<E>
1174 implements SortedSet<E>, Serializable {
1175 private static final long serialVersionUID = -4929149591599911165L;
1176 private final SortedSet<E> ss;
1177
1178 UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;}
1179
1180 public Comparator<? super E> comparator() {return ss.comparator();}
1181
1182 public SortedSet<E> subSet(E fromElement, E toElement) {
1183 return new UnmodifiableSortedSet<>(ss.subSet(fromElement,toElement));
1184 }
1185 public SortedSet<E> headSet(E toElement) {
1186 return new UnmodifiableSortedSet<>(ss.headSet(toElement));
1187 }
1188 public SortedSet<E> tailSet(E fromElement) {
1189 return new UnmodifiableSortedSet<>(ss.tailSet(fromElement));
1190 }
1191
1192 public E first() {return ss.first();}
1193 public E last() {return ss.last();}
1194 }
1195
1196 /**
1197 * Returns an unmodifiable view of the specified list. This method allows
1198 * modules to provide users with "read-only" access to internal
1199 * lists. Query operations on the returned list "read through" to the
1200 * specified list, and attempts to modify the returned list, whether
1201 * direct or via its iterator, result in an
1202 * <tt>UnsupportedOperationException</tt>.<p>
1203 *
1204 * The returned list will be serializable if the specified list
1205 * is serializable. Similarly, the returned list will implement
1206 * {@link RandomAccess} if the specified list does.
1207 *
1208 * @param list the list for which an unmodifiable view is to be returned.
1209 * @return an unmodifiable view of the specified list.
1210 */
1211 public static <T> List<T> unmodifiableList(List<? extends T> list) {
1212 return (list instanceof RandomAccess ?
1213 new UnmodifiableRandomAccessList<>(list) :
1214 new UnmodifiableList<>(list));
1215 }
1216
1217 /**
1218 * @serial include
1219 */
1220 static class UnmodifiableList<E> extends UnmodifiableCollection<E>
1221 implements List<E> {
1222 private static final long serialVersionUID = -283967356065247728L;
1223 final List<? extends E> list;
1224
1225 UnmodifiableList(List<? extends E> list) {
1226 super(list);
1227 this.list = list;
1228 }
1229
1230 public boolean equals(Object o) {return o == this || list.equals(o);}
1231 public int hashCode() {return list.hashCode();}
1232
1233 public E get(int index) {return list.get(index);}
1234 public E set(int index, E element) {
1235 throw new UnsupportedOperationException();
1236 }
1237 public void add(int index, E element) {
1238 throw new UnsupportedOperationException();
1239 }
1240 public E remove(int index) {
1241 throw new UnsupportedOperationException();
1242 }
1243 public int indexOf(Object o) {return list.indexOf(o);}
1244 public int lastIndexOf(Object o) {return list.lastIndexOf(o);}
1245 public boolean addAll(int index, Collection<? extends E> c) {
1246 throw new UnsupportedOperationException();
1247 }
1248 public ListIterator<E> listIterator() {return listIterator(0);}
1249
1250 public ListIterator<E> listIterator(final int index) {
1251 return new ListIterator<E>() {
1252 private final ListIterator<? extends E> i
1253 = list.listIterator(index);
1254
1255 public boolean hasNext() {return i.hasNext();}
1256 public E next() {return i.next();}
1257 public boolean hasPrevious() {return i.hasPrevious();}
1258 public E previous() {return i.previous();}
1259 public int nextIndex() {return i.nextIndex();}
1260 public int previousIndex() {return i.previousIndex();}
1261
1262 public void remove() {
1263 throw new UnsupportedOperationException();
1264 }
1265 public void set(E e) {
1266 throw new UnsupportedOperationException();
1267 }
1268 public void add(E e) {
1269 throw new UnsupportedOperationException();
1270 }
1271
1272 @Override
1273 public void forEachRemaining(Consumer<? super E> action) {
1274 i.forEachRemaining(action);
1275 }
1276 };
1277 }
1278
1279 public List<E> subList(int fromIndex, int toIndex) {
1280 return new UnmodifiableList<>(list.subList(fromIndex, toIndex));
1281 }
1282
1283 /**
1284 * UnmodifiableRandomAccessList instances are serialized as
1285 * UnmodifiableList instances to allow them to be deserialized
1286 * in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList).
1287 * This method inverts the transformation. As a beneficial
1288 * side-effect, it also grafts the RandomAccess marker onto
1289 * UnmodifiableList instances that were serialized in pre-1.4 JREs.
1290 *
1291 * Note: Unfortunately, UnmodifiableRandomAccessList instances
1292 * serialized in 1.4.1 and deserialized in 1.4 will become
1293 * UnmodifiableList instances, as this method was missing in 1.4.
1294 */
1295 private Object readResolve() {
1296 return (list instanceof RandomAccess
1297 ? new UnmodifiableRandomAccessList<>(list)
1298 : this);
1299 }
1300 }
1301
1302 /**
1303 * @serial include
1304 */
1305 static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E>
1306 implements RandomAccess
1307 {
1308 UnmodifiableRandomAccessList(List<? extends E> list) {
1309 super(list);
1310 }
1311
1312 public List<E> subList(int fromIndex, int toIndex) {
1313 return new UnmodifiableRandomAccessList<>(
1314 list.subList(fromIndex, toIndex));
1315 }
1316
1317 private static final long serialVersionUID = -2542308836966382001L;
1318
1319 /**
1320 * Allows instances to be deserialized in pre-1.4 JREs (which do
1321 * not have UnmodifiableRandomAccessList). UnmodifiableList has
1322 * a readResolve method that inverts this transformation upon
1323 * deserialization.
1324 */
1325 private Object writeReplace() {
1326 return new UnmodifiableList<>(list);
1327 }
1328 }
1329
1330 /**
1331 * Returns an unmodifiable view of the specified map. This method
1332 * allows modules to provide users with "read-only" access to internal
1333 * maps. Query operations on the returned map "read through"
1334 * to the specified map, and attempts to modify the returned
1335 * map, whether direct or via its collection views, result in an
1336 * <tt>UnsupportedOperationException</tt>.<p>
1337 *
1338 * The returned map will be serializable if the specified map
1339 * is serializable.
1340 *
1341 * @param m the map for which an unmodifiable view is to be returned.
1342 * @return an unmodifiable view of the specified map.
1343 */
1344 public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) {
1345 return new UnmodifiableMap<>(m);
1346 }
1347
1348 /**
1349 * @serial include
1350 */
1351 private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable {
1352 private static final long serialVersionUID = -1034234728574286014L;
1353
1354 private final Map<? extends K, ? extends V> m;
1355
1356 UnmodifiableMap(Map<? extends K, ? extends V> m) {
1357 if (m==null)
1358 throw new NullPointerException();
1359 this.m = m;
1360 }
1361
1362 public int size() {return m.size();}
1363 public boolean isEmpty() {return m.isEmpty();}
1364 public boolean containsKey(Object key) {return m.containsKey(key);}
1365 public boolean containsValue(Object val) {return m.containsValue(val);}
1366 public V get(Object key) {return m.get(key);}
1367
1368 public V put(K key, V value) {
1369 throw new UnsupportedOperationException();
1370 }
1371 public V remove(Object key) {
1372 throw new UnsupportedOperationException();
1373 }
1374 public void putAll(Map<? extends K, ? extends V> m) {
1375 throw new UnsupportedOperationException();
1376 }
1377 public void clear() {
1378 throw new UnsupportedOperationException();
1379 }
1380
1381 private transient Set<K> keySet = null;
1382 private transient Set<Map.Entry<K,V>> entrySet = null;
1383 private transient Collection<V> values = null;
1384
1385 public Set<K> keySet() {
1386 if (keySet==null)
1387 keySet = unmodifiableSet(m.keySet());
1388 return keySet;
1389 }
1390
1391 public Set<Map.Entry<K,V>> entrySet() {
1392 if (entrySet==null)
1393 entrySet = new UnmodifiableEntrySet<>(m.entrySet());
1394 return entrySet;
1395 }
1396
1397 public Collection<V> values() {
1398 if (values==null)
1399 values = unmodifiableCollection(m.values());
1400 return values;
1401 }
1402
1403 public boolean equals(Object o) {return o == this || m.equals(o);}
1404 public int hashCode() {return m.hashCode();}
1405 public String toString() {return m.toString();}
1406
1407 // Override default methods in Map
1408 @Override
1409 @SuppressWarnings("unchecked")
1410 public V getOrDefault(Object k, V defaultValue) {
1411 // Safe cast as we don't change the value
1412 return ((Map<K, V>)m).getOrDefault(k, defaultValue);
1413 }
1414
1415 @Override
1416 public void forEach(BiConsumer<? super K, ? super V> action) {
1417 m.forEach(action);
1418 }
1419
1420 @Override
1421 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
1422 throw new UnsupportedOperationException();
1423 }
1424
1425 @Override
1426 public V putIfAbsent(K key, V value) {
1427 throw new UnsupportedOperationException();
1428 }
1429
1430 @Override
1431 public boolean remove(Object key, Object value) {
1432 throw new UnsupportedOperationException();
1433 }
1434
1435 @Override
1436 public boolean replace(K key, V oldValue, V newValue) {
1437 throw new UnsupportedOperationException();
1438 }
1439
1440 @Override
1441 public V replace(K key, V value) {
1442 throw new UnsupportedOperationException();
1443 }
1444
1445 @Override
1446 public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
1447 throw new UnsupportedOperationException();
1448 }
1449
1450 @Override
1451 public V computeIfPresent(K key,
1452 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1453 throw new UnsupportedOperationException();
1454 }
1455
1456 @Override
1457 public V compute(K key,
1458 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1459 throw new UnsupportedOperationException();
1460 }
1461
1462 @Override
1463 public V merge(K key, V value,
1464 BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
1465 throw new UnsupportedOperationException();
1466 }
1467
1468 /**
1469 * We need this class in addition to UnmodifiableSet as
1470 * Map.Entries themselves permit modification of the backing Map
1471 * via their setValue operation. This class is subtle: there are
1472 * many possible attacks that must be thwarted.
1473 *
1474 * @serial include
1475 */
1476 static class UnmodifiableEntrySet<K,V>
1477 extends UnmodifiableSet<Map.Entry<K,V>> {
1478 private static final long serialVersionUID = 7854390611657943733L;
1479
1480 @SuppressWarnings({"unchecked", "rawtypes"})
1481 UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) {
1482 // Need to cast to raw in order to work around a limitation in the type system
1483 super((Set)s);
1484 }
1485 public Iterator<Map.Entry<K,V>> iterator() {
1486 return new Iterator<Map.Entry<K,V>>() {
1487 private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator();
1488
1489 public boolean hasNext() {
1490 return i.hasNext();
1491 }
1492 public Map.Entry<K,V> next() {
1493 return new UnmodifiableEntry<>(i.next());
1494 }
1495 public void remove() {
1496 throw new UnsupportedOperationException();
1497 }
1498 };
1499 }
1500
1501 @SuppressWarnings("unchecked")
1502 public Object[] toArray() {
1503 Object[] a = c.toArray();
1504 for (int i=0; i<a.length; i++)
1505 a[i] = new UnmodifiableEntry<>((Map.Entry<? extends K, ? extends V>)a[i]);
1506 return a;
1507 }
1508
1509 @SuppressWarnings("unchecked")
1510 public <T> T[] toArray(T[] a) {
1511 // We don't pass a to c.toArray, to avoid window of
1512 // vulnerability wherein an unscrupulous multithreaded client
1513 // could get his hands on raw (unwrapped) Entries from c.
1514 Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
1515
1516 for (int i=0; i<arr.length; i++)
1517 arr[i] = new UnmodifiableEntry<>((Map.Entry<? extends K, ? extends V>)arr[i]);
1518
1519 if (arr.length > a.length)
1520 return (T[])arr;
1521
1522 System.arraycopy(arr, 0, a, 0, arr.length);
1523 if (a.length > arr.length)
1524 a[arr.length] = null;
1525 return a;
1526 }
1527
1528 /**
1529 * This method is overridden to protect the backing set against
1530 * an object with a nefarious equals function that senses
1531 * that the equality-candidate is Map.Entry and calls its
1532 * setValue method.
1533 */
1534 public boolean contains(Object o) {
1535 if (!(o instanceof Map.Entry))
1536 return false;
1537 return c.contains(
1538 new UnmodifiableEntry<>((Map.Entry<?,?>) o));
1539 }
1540
1541 /**
1542 * The next two methods are overridden to protect against
1543 * an unscrupulous List whose contains(Object o) method senses
1544 * when o is a Map.Entry, and calls o.setValue.
1545 */
1546 public boolean containsAll(Collection<?> coll) {
1547 for (Object e : coll) {
1548 if (!contains(e)) // Invokes safe contains() above
1549 return false;
1550 }
1551 return true;
1552 }
1553 public boolean equals(Object o) {
1554 if (o == this)
1555 return true;
1556
1557 if (!(o instanceof Set))
1558 return false;
1559 Set<?> s = (Set<?>) o;
1560 if (s.size() != c.size())
1561 return false;
1562 return containsAll(s); // Invokes safe containsAll() above
1563 }
1564
1565 /**
1566 * This "wrapper class" serves two purposes: it prevents
1567 * the client from modifying the backing Map, by short-circuiting
1568 * the setValue method, and it protects the backing Map against
1569 * an ill-behaved Map.Entry that attempts to modify another
1570 * Map Entry when asked to perform an equality check.
1571 */
1572 private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> {
1573 private Map.Entry<? extends K, ? extends V> e;
1574
1575 UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) {this.e = e;}
1576
1577 public K getKey() {return e.getKey();}
1578 public V getValue() {return e.getValue();}
1579 public V setValue(V value) {
1580 throw new UnsupportedOperationException();
1581 }
1582 public int hashCode() {return e.hashCode();}
1583 public boolean equals(Object o) {
1584 if (this == o)
1585 return true;
1586 if (!(o instanceof Map.Entry))
1587 return false;
1588 Map.Entry<?,?> t = (Map.Entry<?,?>)o;
1589 return eq(e.getKey(), t.getKey()) &&
1590 eq(e.getValue(), t.getValue());
1591 }
1592 public String toString() {return e.toString();}
1593 }
1594 }
1595 }
1596
1597 /**
1598 * Returns an unmodifiable view of the specified sorted map. This method
1599 * allows modules to provide users with "read-only" access to internal
1600 * sorted maps. Query operations on the returned sorted map "read through"
1601 * to the specified sorted map. Attempts to modify the returned
1602 * sorted map, whether direct, via its collection views, or via its
1603 * <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in
1604 * an <tt>UnsupportedOperationException</tt>.<p>
1605 *
1606 * The returned sorted map will be serializable if the specified sorted map
1607 * is serializable.
1608 *
1609 * @param m the sorted map for which an unmodifiable view is to be
1610 * returned.
1611 * @return an unmodifiable view of the specified sorted map.
1612 */
1613 public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) {
1614 return new UnmodifiableSortedMap<>(m);
1615 }
1616
1617 /**
1618 * @serial include
1619 */
1620 static class UnmodifiableSortedMap<K,V>
1621 extends UnmodifiableMap<K,V>
1622 implements SortedMap<K,V>, Serializable {
1623 private static final long serialVersionUID = -8806743815996713206L;
1624
1625 private final SortedMap<K, ? extends V> sm;
1626
1627 UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m;}
1628
1629 public Comparator<? super K> comparator() {return sm.comparator();}
1630
1631 public SortedMap<K,V> subMap(K fromKey, K toKey) {
1632 return new UnmodifiableSortedMap<>(sm.subMap(fromKey, toKey));
1633 }
1634 public SortedMap<K,V> headMap(K toKey) {
1635 return new UnmodifiableSortedMap<>(sm.headMap(toKey));
1636 }
1637 public SortedMap<K,V> tailMap(K fromKey) {
1638 return new UnmodifiableSortedMap<>(sm.tailMap(fromKey));
1639 }
1640
1641 public K firstKey() {return sm.firstKey();}
1642 public K lastKey() {return sm.lastKey();}
1643 }
1644
1645
1646 // Synch Wrappers
1647
1648 /**
1649 * Returns a synchronized (thread-safe) collection backed by the specified
1650 * collection. In order to guarantee serial access, it is critical that
1651 * <strong>all</strong> access to the backing collection is accomplished
1652 * through the returned collection.<p>
1653 *
1654 * It is imperative that the user manually synchronize on the returned
1655 * collection when iterating over it:
1656 * <pre>
1657 * Collection c = Collections.synchronizedCollection(myCollection);
1658 * ...
1659 * synchronized (c) {
1660 * Iterator i = c.iterator(); // Must be in the synchronized block
1661 * while (i.hasNext())
1662 * foo(i.next());
1663 * }
1664 * </pre>
1665 * Failure to follow this advice may result in non-deterministic behavior.
1666 *
1667 * <p>The returned collection does <i>not</i> pass the {@code hashCode}
1668 * and {@code equals} operations through to the backing collection, but
1669 * relies on {@code Object}'s equals and hashCode methods. This is
1670 * necessary to preserve the contracts of these operations in the case
1671 * that the backing collection is a set or a list.<p>
1672 *
1673 * The returned collection will be serializable if the specified collection
1674 * is serializable.
1675 *
1676 * @param c the collection to be "wrapped" in a synchronized collection.
1677 * @return a synchronized view of the specified collection.
1678 */
1679 public static <T> Collection<T> synchronizedCollection(Collection<T> c) {
1680 return new SynchronizedCollection<>(c);
1681 }
1682
1683 static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) {
1684 return new SynchronizedCollection<>(c, mutex);
1685 }
1686
1687 /**
1688 * @serial include
1689 */
1690 static class SynchronizedCollection<E> implements Collection<E>, Serializable {
1691 private static final long serialVersionUID = 3053995032091335093L;
1692
1693 final Collection<E> c; // Backing Collection
1694 final Object mutex; // Object on which to synchronize
1695
1696 SynchronizedCollection(Collection<E> c) {
1697 if (c==null)
1698 throw new NullPointerException();
1699 this.c = c;
1700 mutex = this;
1701 }
1702 SynchronizedCollection(Collection<E> c, Object mutex) {
1703 this.c = c;
1704 this.mutex = mutex;
1705 }
1706
1707 public int size() {
1708 synchronized (mutex) {return c.size();}
1709 }
1710 public boolean isEmpty() {
1711 synchronized (mutex) {return c.isEmpty();}
1712 }
1713 public boolean contains(Object o) {
1714 synchronized (mutex) {return c.contains(o);}
1715 }
1716 public Object[] toArray() {
1717 synchronized (mutex) {return c.toArray();}
1718 }
1719 public <T> T[] toArray(T[] a) {
1720 synchronized (mutex) {return c.toArray(a);}
1721 }
1722
1723 public Iterator<E> iterator() {
1724 return c.iterator(); // Must be manually synched by user!
1725 }
1726
1727 public boolean add(E e) {
1728 synchronized (mutex) {return c.add(e);}
1729 }
1730 public boolean remove(Object o) {
1731 synchronized (mutex) {return c.remove(o);}
1732 }
1733
1734 public boolean containsAll(Collection<?> coll) {
1735 synchronized (mutex) {return c.containsAll(coll);}
1736 }
1737 public boolean addAll(Collection<? extends E> coll) {
1738 synchronized (mutex) {return c.addAll(coll);}
1739 }
1740 public boolean removeAll(Collection<?> coll) {
1741 synchronized (mutex) {return c.removeAll(coll);}
1742 }
1743 public boolean retainAll(Collection<?> coll) {
1744 synchronized (mutex) {return c.retainAll(coll);}
1745 }
1746 public void clear() {
1747 synchronized (mutex) {c.clear();}
1748 }
1749 public String toString() {
1750 synchronized (mutex) {return c.toString();}
1751 }
1752 private void writeObject(ObjectOutputStream s) throws IOException {
1753 synchronized (mutex) {s.defaultWriteObject();}
1754 }
1755 }
1756
1757 /**
1758 * Returns a synchronized (thread-safe) set backed by the specified
1759 * set. In order to guarantee serial access, it is critical that
1760 * <strong>all</strong> access to the backing set is accomplished
1761 * through the returned set.<p>
1762 *
1763 * It is imperative that the user manually synchronize on the returned
1764 * set when iterating over it:
1765 * <pre>
1766 * Set s = Collections.synchronizedSet(new HashSet());
1767 * ...
1768 * synchronized (s) {
1769 * Iterator i = s.iterator(); // Must be in the synchronized block
1770 * while (i.hasNext())
1771 * foo(i.next());
1772 * }
1773 * </pre>
1774 * Failure to follow this advice may result in non-deterministic behavior.
1775 *
1776 * <p>The returned set will be serializable if the specified set is
1777 * serializable.
1778 *
1779 * @param s the set to be "wrapped" in a synchronized set.
1780 * @return a synchronized view of the specified set.
1781 */
1782 public static <T> Set<T> synchronizedSet(Set<T> s) {
1783 return new SynchronizedSet<>(s);
1784 }
1785
1786 static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) {
1787 return new SynchronizedSet<>(s, mutex);
1788 }
1789
1790 /**
1791 * @serial include
1792 */
1793 static class SynchronizedSet<E>
1794 extends SynchronizedCollection<E>
1795 implements Set<E> {
1796 private static final long serialVersionUID = 487447009682186044L;
1797
1798 SynchronizedSet(Set<E> s) {
1799 super(s);
1800 }
1801 SynchronizedSet(Set<E> s, Object mutex) {
1802 super(s, mutex);
1803 }
1804
1805 public boolean equals(Object o) {
1806 if (this == o)
1807 return true;
1808 synchronized (mutex) {return c.equals(o);}
1809 }
1810 public int hashCode() {
1811 synchronized (mutex) {return c.hashCode();}
1812 }
1813 }
1814
1815 /**
1816 * Returns a synchronized (thread-safe) sorted set backed by the specified
1817 * sorted set. In order to guarantee serial access, it is critical that
1818 * <strong>all</strong> access to the backing sorted set is accomplished
1819 * through the returned sorted set (or its views).<p>
1820 *
1821 * It is imperative that the user manually synchronize on the returned
1822 * sorted set when iterating over it or any of its <tt>subSet</tt>,
1823 * <tt>headSet</tt>, or <tt>tailSet</tt> views.
1824 * <pre>
1825 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
1826 * ...
1827 * synchronized (s) {
1828 * Iterator i = s.iterator(); // Must be in the synchronized block
1829 * while (i.hasNext())
1830 * foo(i.next());
1831 * }
1832 * </pre>
1833 * or:
1834 * <pre>
1835 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
1836 * SortedSet s2 = s.headSet(foo);
1837 * ...
1838 * synchronized (s) { // Note: s, not s2!!!
1839 * Iterator i = s2.iterator(); // Must be in the synchronized block
1840 * while (i.hasNext())
1841 * foo(i.next());
1842 * }
1843 * </pre>
1844 * Failure to follow this advice may result in non-deterministic behavior.
1845 *
1846 * <p>The returned sorted set will be serializable if the specified
1847 * sorted set is serializable.
1848 *
1849 * @param s the sorted set to be "wrapped" in a synchronized sorted set.
1850 * @return a synchronized view of the specified sorted set.
1851 */
1852 public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) {
1853 return new SynchronizedSortedSet<>(s);
1854 }
1855
1856 /**
1857 * @serial include
1858 */
1859 static class SynchronizedSortedSet<E>
1860 extends SynchronizedSet<E>
1861 implements SortedSet<E>
1862 {
1863 private static final long serialVersionUID = 8695801310862127406L;
1864
1865 private final SortedSet<E> ss;
1866
1867 SynchronizedSortedSet(SortedSet<E> s) {
1868 super(s);
1869 ss = s;
1870 }
1871 SynchronizedSortedSet(SortedSet<E> s, Object mutex) {
1872 super(s, mutex);
1873 ss = s;
1874 }
1875
1876 public Comparator<? super E> comparator() {
1877 synchronized (mutex) {return ss.comparator();}
1878 }
1879
1880 public SortedSet<E> subSet(E fromElement, E toElement) {
1881 synchronized (mutex) {
1882 return new SynchronizedSortedSet<>(
1883 ss.subSet(fromElement, toElement), mutex);
1884 }
1885 }
1886 public SortedSet<E> headSet(E toElement) {
1887 synchronized (mutex) {
1888 return new SynchronizedSortedSet<>(ss.headSet(toElement), mutex);
1889 }
1890 }
1891 public SortedSet<E> tailSet(E fromElement) {
1892 synchronized (mutex) {
1893 return new SynchronizedSortedSet<>(ss.tailSet(fromElement),mutex);
1894 }
1895 }
1896
1897 public E first() {
1898 synchronized (mutex) {return ss.first();}
1899 }
1900 public E last() {
1901 synchronized (mutex) {return ss.last();}
1902 }
1903 }
1904
1905 /**
1906 * Returns a synchronized (thread-safe) list backed by the specified
1907 * list. In order to guarantee serial access, it is critical that
1908 * <strong>all</strong> access to the backing list is accomplished
1909 * through the returned list.<p>
1910 *
1911 * It is imperative that the user manually synchronize on the returned
1912 * list when iterating over it:
1913 * <pre>
1914 * List list = Collections.synchronizedList(new ArrayList());
1915 * ...
1916 * synchronized (list) {
1917 * Iterator i = list.iterator(); // Must be in synchronized block
1918 * while (i.hasNext())
1919 * foo(i.next());
1920 * }
1921 * </pre>
1922 * Failure to follow this advice may result in non-deterministic behavior.
1923 *
1924 * <p>The returned list will be serializable if the specified list is
1925 * serializable.
1926 *
1927 * @param list the list to be "wrapped" in a synchronized list.
1928 * @return a synchronized view of the specified list.
1929 */
1930 public static <T> List<T> synchronizedList(List<T> list) {
1931 return (list instanceof RandomAccess ?
1932 new SynchronizedRandomAccessList<>(list) :
1933 new SynchronizedList<>(list));
1934 }
1935
1936 static <T> List<T> synchronizedList(List<T> list, Object mutex) {
1937 return (list instanceof RandomAccess ?
1938 new SynchronizedRandomAccessList<>(list, mutex) :
1939 new SynchronizedList<>(list, mutex));
1940 }
1941
1942 /**
1943 * @serial include
1944 */
1945 static class SynchronizedList<E>
1946 extends SynchronizedCollection<E>
1947 implements List<E> {
1948 private static final long serialVersionUID = -7754090372962971524L;
1949
1950 final List<E> list;
1951
1952 SynchronizedList(List<E> list) {
1953 super(list);
1954 this.list = list;
1955 }
1956 SynchronizedList(List<E> list, Object mutex) {
1957 super(list, mutex);
1958 this.list = list;
1959 }
1960
1961 public boolean equals(Object o) {
1962 if (this == o)
1963 return true;
1964 synchronized (mutex) {return list.equals(o);}
1965 }
1966 public int hashCode() {
1967 synchronized (mutex) {return list.hashCode();}
1968 }
1969
1970 public E get(int index) {
1971 synchronized (mutex) {return list.get(index);}
1972 }
1973 public E set(int index, E element) {
1974 synchronized (mutex) {return list.set(index, element);}
1975 }
1976 public void add(int index, E element) {
1977 synchronized (mutex) {list.add(index, element);}
1978 }
1979 public E remove(int index) {
1980 synchronized (mutex) {return list.remove(index);}
1981 }
1982
1983 public int indexOf(Object o) {
1984 synchronized (mutex) {return list.indexOf(o);}
1985 }
1986 public int lastIndexOf(Object o) {
1987 synchronized (mutex) {return list.lastIndexOf(o);}
1988 }
1989
1990 public boolean addAll(int index, Collection<? extends E> c) {
1991 synchronized (mutex) {return list.addAll(index, c);}
1992 }
1993
1994 public ListIterator<E> listIterator() {
1995 return list.listIterator(); // Must be manually synched by user
1996 }
1997
1998 public ListIterator<E> listIterator(int index) {
1999 return list.listIterator(index); // Must be manually synched by user
2000 }
2001
2002 public List<E> subList(int fromIndex, int toIndex) {
2003 synchronized (mutex) {
2004 return new SynchronizedList<>(list.subList(fromIndex, toIndex),
2005 mutex);
2006 }
2007 }
2008
2009 /**
2010 * SynchronizedRandomAccessList instances are serialized as
2011 * SynchronizedList instances to allow them to be deserialized
2012 * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList).
2013 * This method inverts the transformation. As a beneficial
2014 * side-effect, it also grafts the RandomAccess marker onto
2015 * SynchronizedList instances that were serialized in pre-1.4 JREs.
2016 *
2017 * Note: Unfortunately, SynchronizedRandomAccessList instances
2018 * serialized in 1.4.1 and deserialized in 1.4 will become
2019 * SynchronizedList instances, as this method was missing in 1.4.
2020 */
2021 private Object readResolve() {
2022 return (list instanceof RandomAccess
2023 ? new SynchronizedRandomAccessList<>(list)
2024 : this);
2025 }
2026 }
2027
2028 /**
2029 * @serial include
2030 */
2031 static class SynchronizedRandomAccessList<E>
2032 extends SynchronizedList<E>
2033 implements RandomAccess {
2034
2035 SynchronizedRandomAccessList(List<E> list) {
2036 super(list);
2037 }
2038
2039 SynchronizedRandomAccessList(List<E> list, Object mutex) {
2040 super(list, mutex);
2041 }
2042
2043 public List<E> subList(int fromIndex, int toIndex) {
2044 synchronized (mutex) {
2045 return new SynchronizedRandomAccessList<>(
2046 list.subList(fromIndex, toIndex), mutex);
2047 }
2048 }
2049
2050 private static final long serialVersionUID = 1530674583602358482L;
2051
2052 /**
2053 * Allows instances to be deserialized in pre-1.4 JREs (which do
2054 * not have SynchronizedRandomAccessList). SynchronizedList has
2055 * a readResolve method that inverts this transformation upon
2056 * deserialization.
2057 */
2058 private Object writeReplace() {
2059 return new SynchronizedList<>(list);
2060 }
2061 }
2062
2063 /**
2064 * Returns a synchronized (thread-safe) map backed by the specified
2065 * map. In order to guarantee serial access, it is critical that
2066 * <strong>all</strong> access to the backing map is accomplished
2067 * through the returned map.<p>
2068 *
2069 * It is imperative that the user manually synchronize on the returned
2070 * map when iterating over any of its collection views:
2071 * <pre>
2072 * Map m = Collections.synchronizedMap(new HashMap());
2073 * ...
2074 * Set s = m.keySet(); // Needn't be in synchronized block
2075 * ...
2076 * synchronized (m) { // Synchronizing on m, not s!
2077 * Iterator i = s.iterator(); // Must be in synchronized block
2078 * while (i.hasNext())
2079 * foo(i.next());
2080 * }
2081 * </pre>
2082 * Failure to follow this advice may result in non-deterministic behavior.
2083 *
2084 * <p>The returned map will be serializable if the specified map is
2085 * serializable.
2086 *
2087 * @param m the map to be "wrapped" in a synchronized map.
2088 * @return a synchronized view of the specified map.
2089 */
2090 public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) {
2091 return new SynchronizedMap<>(m);
2092 }
2093
2094 /**
2095 * @serial include
2096 */
2097 private static class SynchronizedMap<K,V>
2098 implements Map<K,V>, Serializable {
2099 private static final long serialVersionUID = 1978198479659022715L;
2100
2101 private final Map<K,V> m; // Backing Map
2102 final Object mutex; // Object on which to synchronize
2103
2104 SynchronizedMap(Map<K,V> m) {
2105 if (m==null)
2106 throw new NullPointerException();
2107 this.m = m;
2108 mutex = this;
2109 }
2110
2111 SynchronizedMap(Map<K,V> m, Object mutex) {
2112 this.m = m;
2113 this.mutex = mutex;
2114 }
2115
2116 public int size() {
2117 synchronized (mutex) {return m.size();}
2118 }
2119 public boolean isEmpty() {
2120 synchronized (mutex) {return m.isEmpty();}
2121 }
2122 public boolean containsKey(Object key) {
2123 synchronized (mutex) {return m.containsKey(key);}
2124 }
2125 public boolean containsValue(Object value) {
2126 synchronized (mutex) {return m.containsValue(value);}
2127 }
2128 public V get(Object key) {
2129 synchronized (mutex) {return m.get(key);}
2130 }
2131
2132 public V put(K key, V value) {
2133 synchronized (mutex) {return m.put(key, value);}
2134 }
2135 public V remove(Object key) {
2136 synchronized (mutex) {return m.remove(key);}
2137 }
2138 public void putAll(Map<? extends K, ? extends V> map) {
2139 synchronized (mutex) {m.putAll(map);}
2140 }
2141 public void clear() {
2142 synchronized (mutex) {m.clear();}
2143 }
2144
2145 private transient Set<K> keySet = null;
2146 private transient Set<Map.Entry<K,V>> entrySet = null;
2147 private transient Collection<V> values = null;
2148
2149 public Set<K> keySet() {
2150 synchronized (mutex) {
2151 if (keySet==null)
2152 keySet = new SynchronizedSet<>(m.keySet(), mutex);
2153 return keySet;
2154 }
2155 }
2156
2157 public Set<Map.Entry<K,V>> entrySet() {
2158 synchronized (mutex) {
2159 if (entrySet==null)
2160 entrySet = new SynchronizedSet<>(m.entrySet(), mutex);
2161 return entrySet;
2162 }
2163 }
2164
2165 public Collection<V> values() {
2166 synchronized (mutex) {
2167 if (values==null)
2168 values = new SynchronizedCollection<>(m.values(), mutex);
2169 return values;
2170 }
2171 }
2172
2173 public boolean equals(Object o) {
2174 if (this == o)
2175 return true;
2176 synchronized (mutex) {return m.equals(o);}
2177 }
2178 public int hashCode() {
2179 synchronized (mutex) {return m.hashCode();}
2180 }
2181 public String toString() {
2182 synchronized (mutex) {return m.toString();}
2183 }
2184
2185 // Override default methods in Map
2186 @Override
2187 public V getOrDefault(Object k, V defaultValue) {
2188 synchronized (mutex) {return m.getOrDefault(k, defaultValue);}
2189 }
2190 @Override
2191 public void forEach(BiConsumer<? super K, ? super V> action) {
2192 synchronized (mutex) {m.forEach(action);}
2193 }
2194 @Override
2195 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
2196 synchronized (mutex) {m.replaceAll(function);}
2197 }
2198 @Override
2199 public V putIfAbsent(K key, V value) {
2200 synchronized (mutex) {return m.putIfAbsent(key, value);}
2201 }
2202 @Override
2203 public boolean remove(Object key, Object value) {
2204 synchronized (mutex) {return m.remove(key, value);}
2205 }
2206 @Override
2207 public boolean replace(K key, V oldValue, V newValue) {
2208 synchronized (mutex) {return m.replace(key, oldValue, newValue);}
2209 }
2210 @Override
2211 public V replace(K key, V value) {
2212 synchronized (mutex) {return m.replace(key, value);}
2213 }
2214 @Override
2215 public V computeIfAbsent(K key,
2216 Function<? super K, ? extends V> mappingFunction) {
2217 synchronized (mutex) {return m.computeIfAbsent(key, mappingFunction);}
2218 }
2219 @Override
2220 public V computeIfPresent(K key,
2221 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
2222 synchronized (mutex) {return m.computeIfPresent(key, remappingFunction);}
2223 }
2224 @Override
2225 public V compute(K key,
2226 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
2227 synchronized (mutex) {return m.compute(key, remappingFunction);}
2228 }
2229 @Override
2230 public V merge(K key, V value,
2231 BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
2232 synchronized (mutex) {return m.merge(key, value, remappingFunction);}
2233 }
2234
2235 private void writeObject(ObjectOutputStream s) throws IOException {
2236 synchronized (mutex) {s.defaultWriteObject();}
2237 }
2238 }
2239
2240 /**
2241 * Returns a synchronized (thread-safe) sorted map backed by the specified
2242 * sorted map. In order to guarantee serial access, it is critical that
2243 * <strong>all</strong> access to the backing sorted map is accomplished
2244 * through the returned sorted map (or its views).<p>
2245 *
2246 * It is imperative that the user manually synchronize on the returned
2247 * sorted map when iterating over any of its collection views, or the
2248 * collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or
2249 * <tt>tailMap</tt> views.
2250 * <pre>
2251 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
2252 * ...
2253 * Set s = m.keySet(); // Needn't be in synchronized block
2254 * ...
2255 * synchronized (m) { // Synchronizing on m, not s!
2256 * Iterator i = s.iterator(); // Must be in synchronized block
2257 * while (i.hasNext())
2258 * foo(i.next());
2259 * }
2260 * </pre>
2261 * or:
2262 * <pre>
2263 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
2264 * SortedMap m2 = m.subMap(foo, bar);
2265 * ...
2266 * Set s2 = m2.keySet(); // Needn't be in synchronized block
2267 * ...
2268 * synchronized (m) { // Synchronizing on m, not m2 or s2!
2269 * Iterator i = s.iterator(); // Must be in synchronized block
2270 * while (i.hasNext())
2271 * foo(i.next());
2272 * }
2273 * </pre>
2274 * Failure to follow this advice may result in non-deterministic behavior.
2275 *
2276 * <p>The returned sorted map will be serializable if the specified
2277 * sorted map is serializable.
2278 *
2279 * @param m the sorted map to be "wrapped" in a synchronized sorted map.
2280 * @return a synchronized view of the specified sorted map.
2281 */
2282 public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) {
2283 return new SynchronizedSortedMap<>(m);
2284 }
2285
2286
2287 /**
2288 * @serial include
2289 */
2290 static class SynchronizedSortedMap<K,V>
2291 extends SynchronizedMap<K,V>
2292 implements SortedMap<K,V>
2293 {
2294 private static final long serialVersionUID = -8798146769416483793L;
2295
2296 private final SortedMap<K,V> sm;
2297
2298 SynchronizedSortedMap(SortedMap<K,V> m) {
2299 super(m);
2300 sm = m;
2301 }
2302 SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) {
2303 super(m, mutex);
2304 sm = m;
2305 }
2306
2307 public Comparator<? super K> comparator() {
2308 synchronized (mutex) {return sm.comparator();}
2309 }
2310
2311 public SortedMap<K,V> subMap(K fromKey, K toKey) {
2312 synchronized (mutex) {
2313 return new SynchronizedSortedMap<>(
2314 sm.subMap(fromKey, toKey), mutex);
2315 }
2316 }
2317 public SortedMap<K,V> headMap(K toKey) {
2318 synchronized (mutex) {
2319 return new SynchronizedSortedMap<>(sm.headMap(toKey), mutex);
2320 }
2321 }
2322 public SortedMap<K,V> tailMap(K fromKey) {
2323 synchronized (mutex) {
2324 return new SynchronizedSortedMap<>(sm.tailMap(fromKey),mutex);
2325 }
2326 }
2327
2328 public K firstKey() {
2329 synchronized (mutex) {return sm.firstKey();}
2330 }
2331 public K lastKey() {
2332 synchronized (mutex) {return sm.lastKey();}
2333 }
2334 }
2335
2336 // Dynamically typesafe collection wrappers
2337
2338 /**
2339 * Returns a dynamically typesafe view of the specified collection.
2340 * Any attempt to insert an element of the wrong type will result in an
2341 * immediate {@link ClassCastException}. Assuming a collection
2342 * contains no incorrectly typed elements prior to the time a
2343 * dynamically typesafe view is generated, and that all subsequent
2344 * access to the collection takes place through the view, it is
2345 * <i>guaranteed</i> that the collection cannot contain an incorrectly
2346 * typed element.
2347 *
2348 * <p>The generics mechanism in the language provides compile-time
2349 * (static) type checking, but it is possible to defeat this mechanism
2350 * with unchecked casts. Usually this is not a problem, as the compiler
2351 * issues warnings on all such unchecked operations. There are, however,
2352 * times when static type checking alone is not sufficient. For example,
2353 * suppose a collection is passed to a third-party library and it is
2354 * imperative that the library code not corrupt the collection by
2355 * inserting an element of the wrong type.
2356 *
2357 * <p>Another use of dynamically typesafe views is debugging. Suppose a
2358 * program fails with a {@code ClassCastException}, indicating that an
2359 * incorrectly typed element was put into a parameterized collection.
2360 * Unfortunately, the exception can occur at any time after the erroneous
2361 * element is inserted, so it typically provides little or no information
2362 * as to the real source of the problem. If the problem is reproducible,
2363 * one can quickly determine its source by temporarily modifying the
2364 * program to wrap the collection with a dynamically typesafe view.
2365 * For example, this declaration:
2366 * <pre> {@code
2367 * Collection<String> c = new HashSet<String>();
2368 * }</pre>
2369 * may be replaced temporarily by this one:
2370 * <pre> {@code
2371 * Collection<String> c = Collections.checkedCollection(
2372 * new HashSet<String>(), String.class);
2373 * }</pre>
2374 * Running the program again will cause it to fail at the point where
2375 * an incorrectly typed element is inserted into the collection, clearly
2376 * identifying the source of the problem. Once the problem is fixed, the
2377 * modified declaration may be reverted back to the original.
2378 *
2379 * <p>The returned collection does <i>not</i> pass the hashCode and equals
2380 * operations through to the backing collection, but relies on
2381 * {@code Object}'s {@code equals} and {@code hashCode} methods. This
2382 * is necessary to preserve the contracts of these operations in the case
2383 * that the backing collection is a set or a list.
2384 *
2385 * <p>The returned collection will be serializable if the specified
2386 * collection is serializable.
2387 *
2388 * <p>Since {@code null} is considered to be a value of any reference
2389 * type, the returned collection permits insertion of null elements
2390 * whenever the backing collection does.
2391 *
2392 * @param c the collection for which a dynamically typesafe view is to be
2393 * returned
2394 * @param type the type of element that {@code c} is permitted to hold
2395 * @return a dynamically typesafe view of the specified collection
2396 * @since 1.5
2397 */
2398 public static <E> Collection<E> checkedCollection(Collection<E> c,
2399 Class<E> type) {
2400 return new CheckedCollection<>(c, type);
2401 }
2402
2403 @SuppressWarnings("unchecked")
2404 static <T> T[] zeroLengthArray(Class<T> type) {
2405 return (T[]) Array.newInstance(type, 0);
2406 }
2407
2408 /**
2409 * @serial include
2410 */
2411 static class CheckedCollection<E> implements Collection<E>, Serializable {
2412 private static final long serialVersionUID = 1578914078182001775L;
2413
2414 final Collection<E> c;
2415 final Class<E> type;
2416
2417 void typeCheck(Object o) {
2418 if (o != null && !type.isInstance(o))
2419 throw new ClassCastException(badElementMsg(o));
2420 }
2421
2422 private String badElementMsg(Object o) {
2423 return "Attempt to insert " + o.getClass() +
2424 " element into collection with element type " + type;
2425 }
2426
2427 CheckedCollection(Collection<E> c, Class<E> type) {
2428 if (c==null || type == null)
2429 throw new NullPointerException();
2430 this.c = c;
2431 this.type = type;
2432 }
2433
2434 public int size() { return c.size(); }
2435 public boolean isEmpty() { return c.isEmpty(); }
2436 public boolean contains(Object o) { return c.contains(o); }
2437 public Object[] toArray() { return c.toArray(); }
2438 public <T> T[] toArray(T[] a) { return c.toArray(a); }
2439 public String toString() { return c.toString(); }
2440 public boolean remove(Object o) { return c.remove(o); }
2441 public void clear() { c.clear(); }
2442
2443 public boolean containsAll(Collection<?> coll) {
2444 return c.containsAll(coll);
2445 }
2446 public boolean removeAll(Collection<?> coll) {
2447 return c.removeAll(coll);
2448 }
2449 public boolean retainAll(Collection<?> coll) {
2450 return c.retainAll(coll);
2451 }
2452
2453 public Iterator<E> iterator() {
2454 // JDK-6363904 - unwrapped iterator could be typecast to
2455 // ListIterator with unsafe set()
2456 final Iterator<E> it = c.iterator();
2457 return new Iterator<E>() {
2458 public boolean hasNext() { return it.hasNext(); }
2459 public E next() { return it.next(); }
2460 public void remove() { it.remove(); }};
2461 }
2462
2463 public boolean add(E e) {
2464 typeCheck(e);
2465 return c.add(e);
2466 }
2467
2468 private E[] zeroLengthElementArray = null; // Lazily initialized
2469
2470 private E[] zeroLengthElementArray() {
2471 return zeroLengthElementArray != null ? zeroLengthElementArray :
2472 (zeroLengthElementArray = zeroLengthArray(type));
2473 }
2474
2475 @SuppressWarnings("unchecked")
2476 Collection<E> checkedCopyOf(Collection<? extends E> coll) {
2477 Object[] a = null;
2478 try {
2479 E[] z = zeroLengthElementArray();
2480 a = coll.toArray(z);
2481 // Defend against coll violating the toArray contract
2482 if (a.getClass() != z.getClass())
2483 a = Arrays.copyOf(a, a.length, z.getClass());
2484 } catch (ArrayStoreException ignore) {
2485 // To get better and consistent diagnostics,
2486 // we call typeCheck explicitly on each element.
2487 // We call clone() to defend against coll retaining a
2488 // reference to the returned array and storing a bad
2489 // element into it after it has been type checked.
2490 a = coll.toArray().clone();
2491 for (Object o : a)
2492 typeCheck(o);
2493 }
2494 // A slight abuse of the type system, but safe here.
2495 return (Collection<E>) Arrays.asList(a);
2496 }
2497
2498 public boolean addAll(Collection<? extends E> coll) {
2499 // Doing things this way insulates us from concurrent changes
2500 // in the contents of coll and provides all-or-nothing
2501 // semantics (which we wouldn't get if we type-checked each
2502 // element as we added it)
2503 return c.addAll(checkedCopyOf(coll));
2504 }
2505 }
2506
2507 /**
2508 * Returns a dynamically typesafe view of the specified queue.
2509 * Any attempt to insert an element of the wrong type will result in
2510 * an immediate {@link ClassCastException}. Assuming a queue contains
2511 * no incorrectly typed elements prior to the time a dynamically typesafe
2512 * view is generated, and that all subsequent access to the queue
2513 * takes place through the view, it is <i>guaranteed</i> that the
2514 * queue cannot contain an incorrectly 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 queue will be serializable if the specified queue
2521 * is serializable.
2522 *
2523 * <p>Since {@code null} is considered to be a value of any reference
2524 * type, the returned queue permits insertion of {@code null} elements
2525 * whenever the backing queue does.
2526 *
2527 * @param queue the queue for which a dynamically typesafe view is to be
2528 * returned
2529 * @param type the type of element that {@code queue} is permitted to hold
2530 * @return a dynamically typesafe view of the specified queue
2531 * @since 1.8
2532 */
2533 public static <E> Queue<E> checkedQueue(Queue<E> queue, Class<E> type) {
2534 return new CheckedQueue<>(queue, type);
2535 }
2536
2537 /**
2538 * @serial include
2539 */
2540 static class CheckedQueue<E>
2541 extends CheckedCollection<E>
2542 implements Queue<E>, Serializable
2543 {
2544 private static final long serialVersionUID = 1433151992604707767L;
2545 final Queue<E> queue;
2546
2547 CheckedQueue(Queue<E> queue, Class<E> elementType) {
2548 super(queue, elementType);
2549 this.queue = queue;
2550 }
2551
2552 public E element() {return queue.element();}
2553 public boolean equals(Object o) {return o == this || c.equals(o);}
2554 public int hashCode() {return c.hashCode();}
2555 public E peek() {return queue.peek();}
2556 public E poll() {return queue.poll();}
2557 public E remove() {return queue.remove();}
2558
2559 public boolean offer(E e) {
2560 typeCheck(e);
2561 return add(e);
2562 }
2563 }
2564
2565 /**
2566 * Returns a dynamically typesafe view of the specified set.
2567 * Any attempt to insert an element of the wrong type will result in
2568 * an immediate {@link ClassCastException}. Assuming a set contains
2569 * no incorrectly typed elements prior to the time a dynamically typesafe
2570 * view is generated, and that all subsequent access to the set
2571 * takes place through the view, it is <i>guaranteed</i> that the
2572 * set cannot contain an incorrectly typed element.
2573 *
2574 * <p>A discussion of the use of dynamically typesafe views may be
2575 * found in the documentation for the {@link #checkedCollection
2576 * checkedCollection} method.
2577 *
2578 * <p>The returned set will be serializable if the specified set is
2579 * serializable.
2580 *
2581 * <p>Since {@code null} is considered to be a value of any reference
2582 * type, the returned set permits insertion of null elements whenever
2583 * the backing set does.
2584 *
2585 * @param s the set for which a dynamically typesafe view is to be
2586 * returned
2587 * @param type the type of element that {@code s} is permitted to hold
2588 * @return a dynamically typesafe view of the specified set
2589 * @since 1.5
2590 */
2591 public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) {
2592 return new CheckedSet<>(s, type);
2593 }
2594
2595 /**
2596 * @serial include
2597 */
2598 static class CheckedSet<E> extends CheckedCollection<E>
2599 implements Set<E>, Serializable
2600 {
2601 private static final long serialVersionUID = 4694047833775013803L;
2602
2603 CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); }
2604
2605 public boolean equals(Object o) { return o == this || c.equals(o); }
2606 public int hashCode() { return c.hashCode(); }
2607 }
2608
2609 /**
2610 * Returns a dynamically typesafe view of the specified sorted set.
2611 * Any attempt to insert an element of the wrong type will result in an
2612 * immediate {@link ClassCastException}. Assuming a sorted set
2613 * contains no incorrectly typed elements prior to the time a
2614 * dynamically typesafe view is generated, and that all subsequent
2615 * access to the sorted set takes place through the view, it is
2616 * <i>guaranteed</i> that the sorted set cannot contain an incorrectly
2617 * typed element.
2618 *
2619 * <p>A discussion of the use of dynamically typesafe views may be
2620 * found in the documentation for the {@link #checkedCollection
2621 * checkedCollection} method.
2622 *
2623 * <p>The returned sorted set will be serializable if the specified sorted
2624 * set is serializable.
2625 *
2626 * <p>Since {@code null} is considered to be a value of any reference
2627 * type, the returned sorted set permits insertion of null elements
2628 * whenever the backing sorted set does.
2629 *
2630 * @param s the sorted set for which a dynamically typesafe view is to be
2631 * returned
2632 * @param type the type of element that {@code s} is permitted to hold
2633 * @return a dynamically typesafe view of the specified sorted set
2634 * @since 1.5
2635 */
2636 public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s,
2637 Class<E> type) {
2638 return new CheckedSortedSet<>(s, type);
2639 }
2640
2641 /**
2642 * @serial include
2643 */
2644 static class CheckedSortedSet<E> extends CheckedSet<E>
2645 implements SortedSet<E>, Serializable
2646 {
2647 private static final long serialVersionUID = 1599911165492914959L;
2648 private final SortedSet<E> ss;
2649
2650 CheckedSortedSet(SortedSet<E> s, Class<E> type) {
2651 super(s, type);
2652 ss = s;
2653 }
2654
2655 public Comparator<? super E> comparator() { return ss.comparator(); }
2656 public E first() { return ss.first(); }
2657 public E last() { return ss.last(); }
2658
2659 public SortedSet<E> subSet(E fromElement, E toElement) {
2660 return checkedSortedSet(ss.subSet(fromElement,toElement), type);
2661 }
2662 public SortedSet<E> headSet(E toElement) {
2663 return checkedSortedSet(ss.headSet(toElement), type);
2664 }
2665 public SortedSet<E> tailSet(E fromElement) {
2666 return checkedSortedSet(ss.tailSet(fromElement), type);
2667 }
2668 }
2669
2670 /**
2671 * Returns a dynamically typesafe view of the specified list.
2672 * Any attempt to insert an element of the wrong type will result in
2673 * an immediate {@link ClassCastException}. Assuming a list contains
2674 * no incorrectly typed elements prior to the time a dynamically typesafe
2675 * view is generated, and that all subsequent access to the list
2676 * takes place through the view, it is <i>guaranteed</i> that the
2677 * list cannot contain an incorrectly typed element.
2678 *
2679 * <p>A discussion of the use of dynamically typesafe views may be
2680 * found in the documentation for the {@link #checkedCollection
2681 * checkedCollection} method.
2682 *
2683 * <p>The returned list will be serializable if the specified list
2684 * is serializable.
2685 *
2686 * <p>Since {@code null} is considered to be a value of any reference
2687 * type, the returned list permits insertion of null elements whenever
2688 * the backing list does.
2689 *
2690 * @param list the list for which a dynamically typesafe view is to be
2691 * returned
2692 * @param type the type of element that {@code list} is permitted to hold
2693 * @return a dynamically typesafe view of the specified list
2694 * @since 1.5
2695 */
2696 public static <E> List<E> checkedList(List<E> list, Class<E> type) {
2697 return (list instanceof RandomAccess ?
2698 new CheckedRandomAccessList<>(list, type) :
2699 new CheckedList<>(list, type));
2700 }
2701
2702 /**
2703 * @serial include
2704 */
2705 static class CheckedList<E>
2706 extends CheckedCollection<E>
2707 implements List<E>
2708 {
2709 private static final long serialVersionUID = 65247728283967356L;
2710 final List<E> list;
2711
2712 CheckedList(List<E> list, Class<E> type) {
2713 super(list, type);
2714 this.list = list;
2715 }
2716
2717 public boolean equals(Object o) { return o == this || list.equals(o); }
2718 public int hashCode() { return list.hashCode(); }
2719 public E get(int index) { return list.get(index); }
2720 public E remove(int index) { return list.remove(index); }
2721 public int indexOf(Object o) { return list.indexOf(o); }
2722 public int lastIndexOf(Object o) { return list.lastIndexOf(o); }
2723
2724 public E set(int index, E element) {
2725 typeCheck(element);
2726 return list.set(index, element);
2727 }
2728
2729 public void add(int index, E element) {
2730 typeCheck(element);
2731 list.add(index, element);
2732 }
2733
2734 public boolean addAll(int index, Collection<? extends E> c) {
2735 return list.addAll(index, checkedCopyOf(c));
2736 }
2737 public ListIterator<E> listIterator() { return listIterator(0); }
2738
2739 public ListIterator<E> listIterator(final int index) {
2740 final ListIterator<E> i = list.listIterator(index);
2741
2742 return new ListIterator<E>() {
2743 public boolean hasNext() { return i.hasNext(); }
2744 public E next() { return i.next(); }
2745 public boolean hasPrevious() { return i.hasPrevious(); }
2746 public E previous() { return i.previous(); }
2747 public int nextIndex() { return i.nextIndex(); }
2748 public int previousIndex() { return i.previousIndex(); }
2749 public void remove() { i.remove(); }
2750
2751 public void set(E e) {
2752 typeCheck(e);
2753 i.set(e);
2754 }
2755
2756 public void add(E e) {
2757 typeCheck(e);
2758 i.add(e);
2759 }
2760
2761 @Override
2762 public void forEachRemaining(Consumer<? super E> action) {
2763 i.forEachRemaining(action);
2764 }
2765 };
2766 }
2767
2768 public List<E> subList(int fromIndex, int toIndex) {
2769 return new CheckedList<>(list.subList(fromIndex, toIndex), type);
2770 }
2771 }
2772
2773 /**
2774 * @serial include
2775 */
2776 static class CheckedRandomAccessList<E> extends CheckedList<E>
2777 implements RandomAccess
2778 {
2779 private static final long serialVersionUID = 1638200125423088369L;
2780
2781 CheckedRandomAccessList(List<E> list, Class<E> type) {
2782 super(list, type);
2783 }
2784
2785 public List<E> subList(int fromIndex, int toIndex) {
2786 return new CheckedRandomAccessList<>(
2787 list.subList(fromIndex, toIndex), type);
2788 }
2789 }
2790
2791 /**
2792 * Returns a dynamically typesafe view of the specified map.
2793 * Any attempt to insert a mapping whose key or value have the wrong
2794 * type will result in an immediate {@link ClassCastException}.
2795 * Similarly, any attempt to modify the value currently associated with
2796 * a key will result in an immediate {@link ClassCastException},
2797 * whether the modification is attempted directly through the map
2798 * itself, or through a {@link Map.Entry} instance obtained from the
2799 * map's {@link Map#entrySet() entry set} view.
2800 *
2801 * <p>Assuming a map contains no incorrectly typed keys or values
2802 * prior to the time a dynamically typesafe view is generated, and
2803 * that all subsequent access to the map takes place through the view
2804 * (or one of its collection views), it is <i>guaranteed</i> that the
2805 * map cannot contain an incorrectly typed key or value.
2806 *
2807 * <p>A discussion of the use of dynamically typesafe views may be
2808 * found in the documentation for the {@link #checkedCollection
2809 * checkedCollection} method.
2810 *
2811 * <p>The returned map will be serializable if the specified map is
2812 * serializable.
2813 *
2814 * <p>Since {@code null} is considered to be a value of any reference
2815 * type, the returned map permits insertion of null keys or values
2816 * whenever the backing map does.
2817 *
2818 * @param m the map for which a dynamically typesafe view is to be
2819 * returned
2820 * @param keyType the type of key that {@code m} is permitted to hold
2821 * @param valueType the type of value that {@code m} is permitted to hold
2822 * @return a dynamically typesafe view of the specified map
2823 * @since 1.5
2824 */
2825 public static <K, V> Map<K, V> checkedMap(Map<K, V> m,
2826 Class<K> keyType,
2827 Class<V> valueType) {
2828 return new CheckedMap<>(m, keyType, valueType);
2829 }
2830
2831
2832 /**
2833 * @serial include
2834 */
2835 private static class CheckedMap<K,V>
2836 implements Map<K,V>, Serializable
2837 {
2838 private static final long serialVersionUID = 5742860141034234728L;
2839
2840 private final Map<K, V> m;
2841 final Class<K> keyType;
2842 final Class<V> valueType;
2843
2844 private void typeCheck(Object key, Object value) {
2845 if (key != null && !keyType.isInstance(key))
2846 throw new ClassCastException(badKeyMsg(key));
2847
2848 if (value != null && !valueType.isInstance(value))
2849 throw new ClassCastException(badValueMsg(value));
2850 }
2851
2852 private BiFunction<? super K, ? super V, ? extends V> typeCheck(
2853 BiFunction<? super K, ? super V, ? extends V> func) {
2854 Objects.requireNonNull(func);
2855 return (k, v) -> {
2856 V newValue = func.apply(k, v);
2857 typeCheck(k, newValue);
2858 return newValue;
2859 };
2860 }
2861
2862 private String badKeyMsg(Object key) {
2863 return "Attempt to insert " + key.getClass() +
2864 " key into map with key type " + keyType;
2865 }
2866
2867 private String badValueMsg(Object value) {
2868 return "Attempt to insert " + value.getClass() +
2869 " value into map with value type " + valueType;
2870 }
2871
2872 CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) {
2873 if (m == null || keyType == null || valueType == null)
2874 throw new NullPointerException();
2875 this.m = m;
2876 this.keyType = keyType;
2877 this.valueType = valueType;
2878 }
2879
2880 public int size() { return m.size(); }
2881 public boolean isEmpty() { return m.isEmpty(); }
2882 public boolean containsKey(Object key) { return m.containsKey(key); }
2883 public boolean containsValue(Object v) { return m.containsValue(v); }
2884 public V get(Object key) { return m.get(key); }
2885 public V remove(Object key) { return m.remove(key); }
2886 public void clear() { m.clear(); }
2887 public Set<K> keySet() { return m.keySet(); }
2888 public Collection<V> values() { return m.values(); }
2889 public boolean equals(Object o) { return o == this || m.equals(o); }
2890 public int hashCode() { return m.hashCode(); }
2891 public String toString() { return m.toString(); }
2892
2893 public V put(K key, V value) {
2894 typeCheck(key, value);
2895 return m.put(key, value);
2896 }
2897
2898 @SuppressWarnings("unchecked")
2899 public void putAll(Map<? extends K, ? extends V> t) {
2900 // Satisfy the following goals:
2901 // - good diagnostics in case of type mismatch
2902 // - all-or-nothing semantics
2903 // - protection from malicious t
2904 // - correct behavior if t is a concurrent map
2905 Object[] entries = t.entrySet().toArray();
2906 List<Map.Entry<K,V>> checked = new ArrayList<>(entries.length);
2907 for (Object o : entries) {
2908 Map.Entry<?,?> e = (Map.Entry<?,?>) o;
2909 Object k = e.getKey();
2910 Object v = e.getValue();
2911 typeCheck(k, v);
2912 checked.add(
2913 new AbstractMap.SimpleImmutableEntry<>((K)k, (V)v));
2914 }
2915 for (Map.Entry<K,V> e : checked)
2916 m.put(e.getKey(), e.getValue());
2917 }
2918
2919 private transient Set<Map.Entry<K,V>> entrySet = null;
2920
2921 public Set<Map.Entry<K,V>> entrySet() {
2922 if (entrySet==null)
2923 entrySet = new CheckedEntrySet<>(m.entrySet(), valueType);
2924 return entrySet;
2925 }
2926
2927 // Override default methods in Map
2928 @Override
2929 public void forEach(BiConsumer<? super K, ? super V> action) {
2930 m.forEach(action);
2931 }
2932
2933 @Override
2934 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
2935 m.replaceAll(typeCheck(function));
2936 }
2937
2938 @Override
2939 public V putIfAbsent(K key, V value) {
2940 typeCheck(key, value);
2941 return m.putIfAbsent(key, value);
2942 }
2943
2944 @Override
2945 public boolean remove(Object key, Object value) {
2946 return m.remove(key, value);
2947 }
2948
2949 @Override
2950 public boolean replace(K key, V oldValue, V newValue) {
2951 typeCheck(key, newValue);
2952 return m.replace(key, oldValue, newValue);
2953 }
2954
2955 @Override
2956 public V replace(K key, V value) {
2957 typeCheck(key, value);
2958 return m.replace(key, value);
2959 }
2960
2961 @Override
2962 public V computeIfAbsent(K key,
2963 Function<? super K, ? extends V> mappingFunction) {
2964 Objects.requireNonNull(mappingFunction);
2965 return m.computeIfAbsent(key, k -> {
2966 V value = mappingFunction.apply(k);
2967 typeCheck(k, value);
2968 return value;
2969 });
2970 }
2971
2972 @Override
2973 public V computeIfPresent(K key,
2974 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
2975 return m.computeIfPresent(key, typeCheck(remappingFunction));
2976 }
2977
2978 @Override
2979 public V compute(K key,
2980 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
2981 return m.compute(key, typeCheck(remappingFunction));
2982 }
2983
2984 @Override
2985 public V merge(K key, V value,
2986 BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
2987 Objects.requireNonNull(remappingFunction);
2988 return m.merge(key, value, (v1, v2) -> {
2989 V newValue = remappingFunction.apply(v1, v2);
2990 typeCheck(null, newValue);
2991 return newValue;
2992 });
2993 }
2994
2995 /**
2996 * We need this class in addition to CheckedSet as Map.Entry permits
2997 * modification of the backing Map via the setValue operation. This
2998 * class is subtle: there are many possible attacks that must be
2999 * thwarted.
3000 *
3001 * @serial exclude
3002 */
3003 static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> {
3004 private final Set<Map.Entry<K,V>> s;
3005 private final Class<V> valueType;
3006
3007 CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) {
3008 this.s = s;
3009 this.valueType = valueType;
3010 }
3011
3012 public int size() { return s.size(); }
3013 public boolean isEmpty() { return s.isEmpty(); }
3014 public String toString() { return s.toString(); }
3015 public int hashCode() { return s.hashCode(); }
3016 public void clear() { s.clear(); }
3017
3018 public boolean add(Map.Entry<K, V> e) {
3019 throw new UnsupportedOperationException();
3020 }
3021 public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) {
3022 throw new UnsupportedOperationException();
3023 }
3024
3025 public Iterator<Map.Entry<K,V>> iterator() {
3026 final Iterator<Map.Entry<K, V>> i = s.iterator();
3027 final Class<V> valueType = this.valueType;
3028
3029 return new Iterator<Map.Entry<K,V>>() {
3030 public boolean hasNext() { return i.hasNext(); }
3031 public void remove() { i.remove(); }
3032
3033 public Map.Entry<K,V> next() {
3034 return checkedEntry(i.next(), valueType);
3035 }
3036 };
3037 }
3038
3039 @SuppressWarnings("unchecked")
3040 public Object[] toArray() {
3041 Object[] source = s.toArray();
3042
3043 /*
3044 * Ensure that we don't get an ArrayStoreException even if
3045 * s.toArray returns an array of something other than Object
3046 */
3047 Object[] dest = (CheckedEntry.class.isInstance(
3048 source.getClass().getComponentType()) ? source :
3049 new Object[source.length]);
3050
3051 for (int i = 0; i < source.length; i++)
3052 dest[i] = checkedEntry((Map.Entry<K,V>)source[i],
3053 valueType);
3054 return dest;
3055 }
3056
3057 @SuppressWarnings("unchecked")
3058 public <T> T[] toArray(T[] a) {
3059 // We don't pass a to s.toArray, to avoid window of
3060 // vulnerability wherein an unscrupulous multithreaded client
3061 // could get his hands on raw (unwrapped) Entries from s.
3062 T[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
3063
3064 for (int i=0; i<arr.length; i++)
3065 arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i],
3066 valueType);
3067 if (arr.length > a.length)
3068 return arr;
3069
3070 System.arraycopy(arr, 0, a, 0, arr.length);
3071 if (a.length > arr.length)
3072 a[arr.length] = null;
3073 return a;
3074 }
3075
3076 /**
3077 * This method is overridden to protect the backing set against
3078 * an object with a nefarious equals function that senses
3079 * that the equality-candidate is Map.Entry and calls its
3080 * setValue method.
3081 */
3082 public boolean contains(Object o) {
3083 if (!(o instanceof Map.Entry))
3084 return false;
3085 Map.Entry<?,?> e = (Map.Entry<?,?>) o;
3086 return s.contains(
3087 (e instanceof CheckedEntry) ? e : checkedEntry(e, valueType));
3088 }
3089
3090 /**
3091 * The bulk collection methods are overridden to protect
3092 * against an unscrupulous collection whose contains(Object o)
3093 * method senses when o is a Map.Entry, and calls o.setValue.
3094 */
3095 public boolean containsAll(Collection<?> c) {
3096 for (Object o : c)
3097 if (!contains(o)) // Invokes safe contains() above
3098 return false;
3099 return true;
3100 }
3101
3102 public boolean remove(Object o) {
3103 if (!(o instanceof Map.Entry))
3104 return false;
3105 return s.remove(new AbstractMap.SimpleImmutableEntry
3106 <>((Map.Entry<?,?>)o));
3107 }
3108
3109 public boolean removeAll(Collection<?> c) {
3110 return batchRemove(c, false);
3111 }
3112 public boolean retainAll(Collection<?> c) {
3113 return batchRemove(c, true);
3114 }
3115 private boolean batchRemove(Collection<?> c, boolean complement) {
3116 boolean modified = false;
3117 Iterator<Map.Entry<K,V>> it = iterator();
3118 while (it.hasNext()) {
3119 if (c.contains(it.next()) != complement) {
3120 it.remove();
3121 modified = true;
3122 }
3123 }
3124 return modified;
3125 }
3126
3127 public boolean equals(Object o) {
3128 if (o == this)
3129 return true;
3130 if (!(o instanceof Set))
3131 return false;
3132 Set<?> that = (Set<?>) o;
3133 return that.size() == s.size()
3134 && containsAll(that); // Invokes safe containsAll() above
3135 }
3136
3137 static <K,V,T> CheckedEntry<K,V,T> checkedEntry(Map.Entry<K,V> e,
3138 Class<T> valueType) {
3139 return new CheckedEntry<>(e, valueType);
3140 }
3141
3142 /**
3143 * This "wrapper class" serves two purposes: it prevents
3144 * the client from modifying the backing Map, by short-circuiting
3145 * the setValue method, and it protects the backing Map against
3146 * an ill-behaved Map.Entry that attempts to modify another
3147 * Map.Entry when asked to perform an equality check.
3148 */
3149 private static class CheckedEntry<K,V,T> implements Map.Entry<K,V> {
3150 private final Map.Entry<K, V> e;
3151 private final Class<T> valueType;
3152
3153 CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) {
3154 this.e = e;
3155 this.valueType = valueType;
3156 }
3157
3158 public K getKey() { return e.getKey(); }
3159 public V getValue() { return e.getValue(); }
3160 public int hashCode() { return e.hashCode(); }
3161 public String toString() { return e.toString(); }
3162
3163 public V setValue(V value) {
3164 if (value != null && !valueType.isInstance(value))
3165 throw new ClassCastException(badValueMsg(value));
3166 return e.setValue(value);
3167 }
3168
3169 private String badValueMsg(Object value) {
3170 return "Attempt to insert " + value.getClass() +
3171 " value into map with value type " + valueType;
3172 }
3173
3174 public boolean equals(Object o) {
3175 if (o == this)
3176 return true;
3177 if (!(o instanceof Map.Entry))
3178 return false;
3179 return e.equals(new AbstractMap.SimpleImmutableEntry
3180 <>((Map.Entry<?,?>)o));
3181 }
3182 }
3183 }
3184 }
3185
3186 /**
3187 * Returns a dynamically typesafe view of the specified sorted map.
3188 * Any attempt to insert a mapping whose key or value have the wrong
3189 * type will result in an immediate {@link ClassCastException}.
3190 * Similarly, any attempt to modify the value currently associated with
3191 * a key will result in an immediate {@link ClassCastException},
3192 * whether the modification is attempted directly through the map
3193 * itself, or through a {@link Map.Entry} instance obtained from the
3194 * map's {@link Map#entrySet() entry set} view.
3195 *
3196 * <p>Assuming a map contains no incorrectly typed keys or values
3197 * prior to the time a dynamically typesafe view is generated, and
3198 * that all subsequent access to the map takes place through the view
3199 * (or one of its collection views), it is <i>guaranteed</i> that the
3200 * map cannot contain an incorrectly typed key or value.
3201 *
3202 * <p>A discussion of the use of dynamically typesafe views may be
3203 * found in the documentation for the {@link #checkedCollection
3204 * checkedCollection} method.
3205 *
3206 * <p>The returned map will be serializable if the specified map is
3207 * serializable.
3208 *
3209 * <p>Since {@code null} is considered to be a value of any reference
3210 * type, the returned map permits insertion of null keys or values
3211 * whenever the backing map does.
3212 *
3213 * @param m the map for which a dynamically typesafe view is to be
3214 * returned
3215 * @param keyType the type of key that {@code m} is permitted to hold
3216 * @param valueType the type of value that {@code m} is permitted to hold
3217 * @return a dynamically typesafe view of the specified map
3218 * @since 1.5
3219 */
3220 public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m,
3221 Class<K> keyType,
3222 Class<V> valueType) {
3223 return new CheckedSortedMap<>(m, keyType, valueType);
3224 }
3225
3226 /**
3227 * @serial include
3228 */
3229 static class CheckedSortedMap<K,V> extends CheckedMap<K,V>
3230 implements SortedMap<K,V>, Serializable
3231 {
3232 private static final long serialVersionUID = 1599671320688067438L;
3233
3234 private final SortedMap<K, V> sm;
3235
3236 CheckedSortedMap(SortedMap<K, V> m,
3237 Class<K> keyType, Class<V> valueType) {
3238 super(m, keyType, valueType);
3239 sm = m;
3240 }
3241
3242 public Comparator<? super K> comparator() { return sm.comparator(); }
3243 public K firstKey() { return sm.firstKey(); }
3244 public K lastKey() { return sm.lastKey(); }
3245
3246 public SortedMap<K,V> subMap(K fromKey, K toKey) {
3247 return checkedSortedMap(sm.subMap(fromKey, toKey),
3248 keyType, valueType);
3249 }
3250 public SortedMap<K,V> headMap(K toKey) {
3251 return checkedSortedMap(sm.headMap(toKey), keyType, valueType);
3252 }
3253 public SortedMap<K,V> tailMap(K fromKey) {
3254 return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType);
3255 }
3256 }
3257
3258 // Empty collections
3259
3260 /**
3261 * Returns an iterator that has no elements. More precisely,
3262 *
3263 * <ul compact>
3264 *
3265 * <li>{@link Iterator#hasNext hasNext} always returns {@code
3266 * false}.
3267 *
3268 * <li>{@link Iterator#next next} always throws {@link
3269 * NoSuchElementException}.
3270 *
3271 * <li>{@link Iterator#remove remove} always throws {@link
3272 * IllegalStateException}.
3273 *
3274 * </ul>
3275 *
3276 * <p>Implementations of this method are permitted, but not
3277 * required, to return the same object from multiple invocations.
3278 *
3279 * @return an empty iterator
3280 * @since 1.7
3281 */
3282 @SuppressWarnings("unchecked")
3283 public static <T> Iterator<T> emptyIterator() {
3284 return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR;
3285 }
3286
3287 private static class EmptyIterator<E> implements Iterator<E> {
3288 static final EmptyIterator<Object> EMPTY_ITERATOR
3289 = new EmptyIterator<>();
3290
3291 public boolean hasNext() { return false; }
3292 public E next() { throw new NoSuchElementException(); }
3293 public void remove() { throw new IllegalStateException(); }
3294 @Override
3295 public void forEachRemaining(Consumer<? super E> action) {
3296 Objects.requireNonNull(action);
3297 }
3298 }
3299
3300 /**
3301 * Returns a list iterator that has no elements. More precisely,
3302 *
3303 * <ul compact>
3304 *
3305 * <li>{@link Iterator#hasNext hasNext} and {@link
3306 * ListIterator#hasPrevious hasPrevious} always return {@code
3307 * false}.
3308 *
3309 * <li>{@link Iterator#next next} and {@link ListIterator#previous
3310 * previous} always throw {@link NoSuchElementException}.
3311 *
3312 * <li>{@link Iterator#remove remove} and {@link ListIterator#set
3313 * set} always throw {@link IllegalStateException}.
3314 *
3315 * <li>{@link ListIterator#add add} always throws {@link
3316 * UnsupportedOperationException}.
3317 *
3318 * <li>{@link ListIterator#nextIndex nextIndex} always returns
3319 * {@code 0} .
3320 *
3321 * <li>{@link ListIterator#previousIndex previousIndex} always
3322 * returns {@code -1}.
3323 *
3324 * </ul>
3325 *
3326 * <p>Implementations of this method are permitted, but not
3327 * required, to return the same object from multiple invocations.
3328 *
3329 * @return an empty list iterator
3330 * @since 1.7
3331 */
3332 @SuppressWarnings("unchecked")
3333 public static <T> ListIterator<T> emptyListIterator() {
3334 return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR;
3335 }
3336
3337 private static class EmptyListIterator<E>
3338 extends EmptyIterator<E>
3339 implements ListIterator<E>
3340 {
3341 static final EmptyListIterator<Object> EMPTY_ITERATOR
3342 = new EmptyListIterator<>();
3343
3344 public boolean hasPrevious() { return false; }
3345 public E previous() { throw new NoSuchElementException(); }
3346 public int nextIndex() { return 0; }
3347 public int previousIndex() { return -1; }
3348 public void set(E e) { throw new IllegalStateException(); }
3349 public void add(E e) { throw new UnsupportedOperationException(); }
3350 }
3351
3352 /**
3353 * Returns an enumeration that has no elements. More precisely,
3354 *
3355 * <ul compact>
3356 *
3357 * <li>{@link Enumeration#hasMoreElements hasMoreElements} always
3358 * returns {@code false}.
3359 *
3360 * <li> {@link Enumeration#nextElement nextElement} always throws
3361 * {@link NoSuchElementException}.
3362 *
3363 * </ul>
3364 *
3365 * <p>Implementations of this method are permitted, but not
3366 * required, to return the same object from multiple invocations.
3367 *
3368 * @return an empty enumeration
3369 * @since 1.7
3370 */
3371 @SuppressWarnings("unchecked")
3372 public static <T> Enumeration<T> emptyEnumeration() {
3373 return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION;
3374 }
3375
3376 private static class EmptyEnumeration<E> implements Enumeration<E> {
3377 static final EmptyEnumeration<Object> EMPTY_ENUMERATION
3378 = new EmptyEnumeration<>();
3379
3380 public boolean hasMoreElements() { return false; }
3381 public E nextElement() { throw new NoSuchElementException(); }
3382 }
3383
3384 /**
3385 * The empty set (immutable). This set is serializable.
3386 *
3387 * @see #emptySet()
3388 */
3389 @SuppressWarnings("rawtypes")
3390 public static final Set EMPTY_SET = new EmptySet<>();
3391
3392 /**
3393 * Returns the empty set (immutable). This set is serializable.
3394 * Unlike the like-named field, this method is parameterized.
3395 *
3396 * <p>This example illustrates the type-safe way to obtain an empty set:
3397 * <pre>
3398 * Set<String> s = Collections.emptySet();
3399 * </pre>
3400 * Implementation note: Implementations of this method need not
3401 * create a separate <tt>Set</tt> object for each call. Using this
3402 * method is likely to have comparable cost to using the like-named
3403 * field. (Unlike this method, the field does not provide type safety.)
3404 *
3405 * @see #EMPTY_SET
3406 * @since 1.5
3407 */
3408 @SuppressWarnings("unchecked")
3409 public static final <T> Set<T> emptySet() {
3410 return (Set<T>) EMPTY_SET;
3411 }
3412
3413 /**
3414 * @serial include
3415 */
3416 private static class EmptySet<E>
3417 extends AbstractSet<E>
3418 implements Serializable
3419 {
3420 private static final long serialVersionUID = 1582296315990362920L;
3421
3422 public Iterator<E> iterator() { return emptyIterator(); }
3423
3424 public int size() {return 0;}
3425 public boolean isEmpty() {return true;}
3426
3427 public boolean contains(Object obj) {return false;}
3428 public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
3429
3430 public Object[] toArray() { return new Object[0]; }
3431
3432 public <T> T[] toArray(T[] a) {
3433 if (a.length > 0)
3434 a[0] = null;
3435 return a;
3436 }
3437
3438 // Preserves singleton property
3439 private Object readResolve() {
3440 return EMPTY_SET;
3441 }
3442 }
3443
3444 /**
3445 * Returns the empty sorted set (immutable). This set is serializable.
3446 *
3447 * <p>This example illustrates the type-safe way to obtain an empty sorted
3448 * set:
3449 * <pre>
3450 * SortedSet<String> s = Collections.emptySortedSet();
3451 * </pre>
3452 * Implementation note: Implementations of this method need not
3453 * create a separate <tt>SortedSet</tt> object for each call.
3454 *
3455 * @since 1.8
3456 */
3457 @SuppressWarnings("unchecked")
3458 public static final <E> SortedSet<E> emptySortedSet() {
3459 return (SortedSet<E>) new EmptySortedSet<>();
3460 }
3461
3462 /**
3463 * @serial include
3464 */
3465 private static class EmptySortedSet<E>
3466 extends AbstractSet<E>
3467 implements SortedSet<E>, Serializable
3468 {
3469 private static final long serialVersionUID = 6316515401502265487L;
3470 public Iterator<E> iterator() { return emptyIterator(); }
3471 public int size() {return 0;}
3472 public boolean isEmpty() {return true;}
3473 public boolean contains(Object obj) {return false;}
3474 public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
3475 public Object[] toArray() { return new Object[0]; }
3476
3477 public <E> E[] toArray(E[] a) {
3478 if (a.length > 0)
3479 a[0] = null;
3480 return a;
3481 }
3482
3483 // Preserves singleton property
3484 private Object readResolve() {
3485 return new EmptySortedSet<>();
3486 }
3487
3488 @Override
3489 public Comparator<? super E> comparator() {
3490 return null;
3491 }
3492
3493 @Override
3494 @SuppressWarnings("unchecked")
3495 public SortedSet<E> subSet(Object fromElement, Object toElement) {
3496 Objects.requireNonNull(fromElement);
3497 Objects.requireNonNull(toElement);
3498
3499 if (!(fromElement instanceof Comparable) ||
3500 !(toElement instanceof Comparable))
3501 {
3502 throw new ClassCastException();
3503 }
3504
3505 if ((((Comparable)fromElement).compareTo(toElement) >= 0) ||
3506 (((Comparable)toElement).compareTo(fromElement) < 0))
3507 {
3508 throw new IllegalArgumentException();
3509 }
3510
3511 return emptySortedSet();
3512 }
3513
3514 @Override
3515 public SortedSet<E> headSet(Object toElement) {
3516 Objects.requireNonNull(toElement);
3517
3518 if (!(toElement instanceof Comparable)) {
3519 throw new ClassCastException();
3520 }
3521
3522 return emptySortedSet();
3523 }
3524
3525 @Override
3526 public SortedSet<E> tailSet(Object fromElement) {
3527 Objects.requireNonNull(fromElement);
3528
3529 if (!(fromElement instanceof Comparable)) {
3530 throw new ClassCastException();
3531 }
3532
3533 return emptySortedSet();
3534 }
3535
3536 @Override
3537 public E first() {
3538 throw new NoSuchElementException();
3539 }
3540
3541 @Override
3542 public E last() {
3543 throw new NoSuchElementException();
3544 }
3545 }
3546
3547 /**
3548 * The empty list (immutable). This list is serializable.
3549 *
3550 * @see #emptyList()
3551 */
3552 @SuppressWarnings("rawtypes")
3553 public static final List EMPTY_LIST = new EmptyList<>();
3554
3555 /**
3556 * Returns the empty list (immutable). This list is serializable.
3557 *
3558 * <p>This example illustrates the type-safe way to obtain an empty list:
3559 * <pre>
3560 * List<String> s = Collections.emptyList();
3561 * </pre>
3562 * Implementation note: Implementations of this method need not
3563 * create a separate <tt>List</tt> object for each call. Using this
3564 * method is likely to have comparable cost to using the like-named
3565 * field. (Unlike this method, the field does not provide type safety.)
3566 *
3567 * @see #EMPTY_LIST
3568 * @since 1.5
3569 */
3570 @SuppressWarnings("unchecked")
3571 public static final <T> List<T> emptyList() {
3572 return (List<T>) EMPTY_LIST;
3573 }
3574
3575 /**
3576 * @serial include
3577 */
3578 private static class EmptyList<E>
3579 extends AbstractList<E>
3580 implements RandomAccess, Serializable {
3581 private static final long serialVersionUID = 8842843931221139166L;
3582
3583 public Iterator<E> iterator() {
3584 return emptyIterator();
3585 }
3586 public ListIterator<E> listIterator() {
3587 return emptyListIterator();
3588 }
3589
3590 public int size() {return 0;}
3591 public boolean isEmpty() {return true;}
3592
3593 public boolean contains(Object obj) {return false;}
3594 public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
3595
3596 public Object[] toArray() { return new Object[0]; }
3597
3598 public <T> T[] toArray(T[] a) {
3599 if (a.length > 0)
3600 a[0] = null;
3601 return a;
3602 }
3603
3604 public E get(int index) {
3605 throw new IndexOutOfBoundsException("Index: "+index);
3606 }
3607
3608 public boolean equals(Object o) {
3609 return (o instanceof List) && ((List<?>)o).isEmpty();
3610 }
3611
3612 public int hashCode() { return 1; }
3613
3614 // Preserves singleton property
3615 private Object readResolve() {
3616 return EMPTY_LIST;
3617 }
3618 }
3619
3620 /**
3621 * The empty map (immutable). This map is serializable.
3622 *
3623 * @see #emptyMap()
3624 * @since 1.3
3625 */
3626 @SuppressWarnings("rawtypes")
3627 public static final Map EMPTY_MAP = new EmptyMap<>();
3628
3629 /**
3630 * Returns the empty map (immutable). This map is serializable.
3631 *
3632 * <p>This example illustrates the type-safe way to obtain an empty set:
3633 * <pre>
3634 * Map<String, Date> s = Collections.emptyMap();
3635 * </pre>
3636 * Implementation note: Implementations of this method need not
3637 * create a separate <tt>Map</tt> object for each call. Using this
3638 * method is likely to have comparable cost to using the like-named
3639 * field. (Unlike this method, the field does not provide type safety.)
3640 *
3641 * @see #EMPTY_MAP
3642 * @since 1.5
3643 */
3644 @SuppressWarnings("unchecked")
3645 public static final <K,V> Map<K,V> emptyMap() {
3646 return (Map<K,V>) EMPTY_MAP;
3647 }
3648
3649 /**
3650 * @serial include
3651 */
3652 private static class EmptyMap<K,V>
3653 extends AbstractMap<K,V>
3654 implements Serializable
3655 {
3656 private static final long serialVersionUID = 6428348081105594320L;
3657
3658 public int size() {return 0;}
3659 public boolean isEmpty() {return true;}
3660 public boolean containsKey(Object key) {return false;}
3661 public boolean containsValue(Object value) {return false;}
3662 public V get(Object key) {return null;}
3663 public Set<K> keySet() {return emptySet();}
3664 public Collection<V> values() {return emptySet();}
3665 public Set<Map.Entry<K,V>> entrySet() {return emptySet();}
3666
3667 public boolean equals(Object o) {
3668 return (o instanceof Map) && ((Map<?,?>)o).isEmpty();
3669 }
3670
3671 public int hashCode() {return 0;}
3672
3673 // Override default methods in Map
3674 @Override
3675 @SuppressWarnings("unchecked")
3676 public V getOrDefault(Object k, V defaultValue) {
3677 return defaultValue;
3678 }
3679
3680 @Override
3681 public void forEach(BiConsumer<? super K, ? super V> action) {
3682 Objects.requireNonNull(action);
3683 }
3684
3685 @Override
3686 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
3687 Objects.requireNonNull(function);
3688 }
3689
3690 @Override
3691 public V putIfAbsent(K key, V value) {
3692 throw new UnsupportedOperationException();
3693 }
3694
3695 @Override
3696 public boolean remove(Object key, Object value) {
3697 throw new UnsupportedOperationException();
3698 }
3699
3700 @Override
3701 public boolean replace(K key, V oldValue, V newValue) {
3702 throw new UnsupportedOperationException();
3703 }
3704
3705 @Override
3706 public V replace(K key, V value) {
3707 throw new UnsupportedOperationException();
3708 }
3709
3710 @Override
3711 public V computeIfAbsent(K key,
3712 Function<? super K, ? extends V> mappingFunction) {
3713 throw new UnsupportedOperationException();
3714 }
3715
3716 @Override
3717 public V computeIfPresent(K key,
3718 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
3719 throw new UnsupportedOperationException();
3720 }
3721
3722 @Override
3723 public V compute(K key,
3724 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
3725 throw new UnsupportedOperationException();
3726 }
3727
3728 @Override
3729 public V merge(K key, V value,
3730 BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
3731 throw new UnsupportedOperationException();
3732 }
3733
3734 // Preserves singleton property
3735 private Object readResolve() {
3736 return EMPTY_MAP;
3737 }
3738 }
3739
3740 // Singleton collections
3741
3742 /**
3743 * Returns an immutable set containing only the specified object.
3744 * The returned set is serializable.
3745 *
3746 * @param o the sole object to be stored in the returned set.
3747 * @return an immutable set containing only the specified object.
3748 */
3749 public static <T> Set<T> singleton(T o) {
3750 return new SingletonSet<>(o);
3751 }
3752
3753 static <E> Iterator<E> singletonIterator(final E e) {
3754 return new Iterator<E>() {
3755 private boolean hasNext = true;
3756 public boolean hasNext() {
3757 return hasNext;
3758 }
3759 public E next() {
3760 if (hasNext) {
3761 hasNext = false;
3762 return e;
3763 }
3764 throw new NoSuchElementException();
3765 }
3766 public void remove() {
3767 throw new UnsupportedOperationException();
3768 }
3769 @Override
3770 public void forEachRemaining(Consumer<? super E> action) {
3771 Objects.requireNonNull(action);
3772 if (hasNext) {
3773 action.accept(e);
3774 hasNext = false;
3775 }
3776 }
3777 };
3778 }
3779
3780 /**
3781 * @serial include
3782 */
3783 private static class SingletonSet<E>
3784 extends AbstractSet<E>
3785 implements Serializable
3786 {
3787 private static final long serialVersionUID = 3193687207550431679L;
3788
3789 private final E element;
3790
3791 SingletonSet(E e) {element = e;}
3792
3793 public Iterator<E> iterator() {
3794 return singletonIterator(element);
3795 }
3796
3797 public int size() {return 1;}
3798
3799 public boolean contains(Object o) {return eq(o, element);}
3800 }
3801
3802 /**
3803 * Returns an immutable list containing only the specified object.
3804 * The returned list is serializable.
3805 *
3806 * @param o the sole object to be stored in the returned list.
3807 * @return an immutable list containing only the specified object.
3808 * @since 1.3
3809 */
3810 public static <T> List<T> singletonList(T o) {
3811 return new SingletonList<>(o);
3812 }
3813
3814 /**
3815 * @serial include
3816 */
3817 private static class SingletonList<E>
3818 extends AbstractList<E>
3819 implements RandomAccess, Serializable {
3820
3821 private static final long serialVersionUID = 3093736618740652951L;
3822
3823 private final E element;
3824
3825 SingletonList(E obj) {element = obj;}
3826
3827 public Iterator<E> iterator() {
3828 return singletonIterator(element);
3829 }
3830
3831 public int size() {return 1;}
3832
3833 public boolean contains(Object obj) {return eq(obj, element);}
3834
3835 public E get(int index) {
3836 if (index != 0)
3837 throw new IndexOutOfBoundsException("Index: "+index+", Size: 1");
3838 return element;
3839 }
3840 }
3841
3842 /**
3843 * Returns an immutable map, mapping only the specified key to the
3844 * specified value. The returned map is serializable.
3845 *
3846 * @param key the sole key to be stored in the returned map.
3847 * @param value the value to which the returned map maps <tt>key</tt>.
3848 * @return an immutable map containing only the specified key-value
3849 * mapping.
3850 * @since 1.3
3851 */
3852 public static <K,V> Map<K,V> singletonMap(K key, V value) {
3853 return new SingletonMap<>(key, value);
3854 }
3855
3856 /**
3857 * @serial include
3858 */
3859 private static class SingletonMap<K,V>
3860 extends AbstractMap<K,V>
3861 implements Serializable {
3862 private static final long serialVersionUID = -6979724477215052911L;
3863
3864 private final K k;
3865 private final V v;
3866
3867 SingletonMap(K key, V value) {
3868 k = key;
3869 v = value;
3870 }
3871
3872 public int size() {return 1;}
3873
3874 public boolean isEmpty() {return false;}
3875
3876 public boolean containsKey(Object key) {return eq(key, k);}
3877
3878 public boolean containsValue(Object value) {return eq(value, v);}
3879
3880 public V get(Object key) {return (eq(key, k) ? v : null);}
3881
3882 private transient Set<K> keySet = null;
3883 private transient Set<Map.Entry<K,V>> entrySet = null;
3884 private transient Collection<V> values = null;
3885
3886 public Set<K> keySet() {
3887 if (keySet==null)
3888 keySet = singleton(k);
3889 return keySet;
3890 }
3891
3892 public Set<Map.Entry<K,V>> entrySet() {
3893 if (entrySet==null)
3894 entrySet = Collections.<Map.Entry<K,V>>singleton(
3895 new SimpleImmutableEntry<>(k, v));
3896 return entrySet;
3897 }
3898
3899 public Collection<V> values() {
3900 if (values==null)
3901 values = singleton(v);
3902 return values;
3903 }
3904
3905 // Override default methods in Map
3906 @Override
3907 public V getOrDefault(Object key, V defaultValue) {
3908 return eq(key, k) ? v : defaultValue;
3909 }
3910
3911 @Override
3912 public void forEach(BiConsumer<? super K, ? super V> action) {
3913 action.accept(k, v);
3914 }
3915
3916 @Override
3917 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
3918 throw new UnsupportedOperationException();
3919 }
3920
3921 @Override
3922 public V putIfAbsent(K key, V value) {
3923 throw new UnsupportedOperationException();
3924 }
3925
3926 @Override
3927 public boolean remove(Object key, Object value) {
3928 throw new UnsupportedOperationException();
3929 }
3930
3931 @Override
3932 public boolean replace(K key, V oldValue, V newValue) {
3933 throw new UnsupportedOperationException();
3934 }
3935
3936 @Override
3937 public V replace(K key, V value) {
3938 throw new UnsupportedOperationException();
3939 }
3940
3941 @Override
3942 public V computeIfAbsent(K key,
3943 Function<? super K, ? extends V> mappingFunction) {
3944 throw new UnsupportedOperationException();
3945 }
3946
3947 @Override
3948 public V computeIfPresent(K key,
3949 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
3950 throw new UnsupportedOperationException();
3951 }
3952
3953 @Override
3954 public V compute(K key,
3955 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
3956 throw new UnsupportedOperationException();
3957 }
3958
3959 @Override
3960 public V merge(K key, V value,
3961 BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
3962 throw new UnsupportedOperationException();
3963 }
3964 }
3965
3966 // Miscellaneous
3967
3968 /**
3969 * Returns an immutable list consisting of <tt>n</tt> copies of the
3970 * specified object. The newly allocated data object is tiny (it contains
3971 * a single reference to the data object). This method is useful in
3972 * combination with the <tt>List.addAll</tt> method to grow lists.
3973 * The returned list is serializable.
3974 *
3975 * @param n the number of elements in the returned list.
3976 * @param o the element to appear repeatedly in the returned list.
3977 * @return an immutable list consisting of <tt>n</tt> copies of the
3978 * specified object.
3979 * @throws IllegalArgumentException if {@code n < 0}
3980 * @see List#addAll(Collection)
3981 * @see List#addAll(int, Collection)
3982 */
3983 public static <T> List<T> nCopies(int n, T o) {
3984 if (n < 0)
3985 throw new IllegalArgumentException("List length = " + n);
3986 return new CopiesList<>(n, o);
3987 }
3988
3989 /**
3990 * @serial include
3991 */
3992 private static class CopiesList<E>
3993 extends AbstractList<E>
3994 implements RandomAccess, Serializable
3995 {
3996 private static final long serialVersionUID = 2739099268398711800L;
3997
3998 final int n;
3999 final E element;
4000
4001 CopiesList(int n, E e) {
4002 assert n >= 0;
4003 this.n = n;
4004 element = e;
4005 }
4006
4007 public int size() {
4008 return n;
4009 }
4010
4011 public boolean contains(Object obj) {
4012 return n != 0 && eq(obj, element);
4013 }
4014
4015 public int indexOf(Object o) {
4016 return contains(o) ? 0 : -1;
4017 }
4018
4019 public int lastIndexOf(Object o) {
4020 return contains(o) ? n - 1 : -1;
4021 }
4022
4023 public E get(int index) {
4024 if (index < 0 || index >= n)
4025 throw new IndexOutOfBoundsException("Index: "+index+
4026 ", Size: "+n);
4027 return element;
4028 }
4029
4030 public Object[] toArray() {
4031 final Object[] a = new Object[n];
4032 if (element != null)
4033 Arrays.fill(a, 0, n, element);
4034 return a;
4035 }
4036
4037 @SuppressWarnings("unchecked")
4038 public <T> T[] toArray(T[] a) {
4039 final int n = this.n;
4040 if (a.length < n) {
4041 a = (T[])java.lang.reflect.Array
4042 .newInstance(a.getClass().getComponentType(), n);
4043 if (element != null)
4044 Arrays.fill(a, 0, n, element);
4045 } else {
4046 Arrays.fill(a, 0, n, element);
4047 if (a.length > n)
4048 a[n] = null;
4049 }
4050 return a;
4051 }
4052
4053 public List<E> subList(int fromIndex, int toIndex) {
4054 if (fromIndex < 0)
4055 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
4056 if (toIndex > n)
4057 throw new IndexOutOfBoundsException("toIndex = " + toIndex);
4058 if (fromIndex > toIndex)
4059 throw new IllegalArgumentException("fromIndex(" + fromIndex +
4060 ") > toIndex(" + toIndex + ")");
4061 return new CopiesList<>(toIndex - fromIndex, element);
4062 }
4063 }
4064
4065 /**
4066 * Returns a comparator that imposes the reverse of the <em>natural
4067 * ordering</em> on a collection of objects that implement the
4068 * {@code Comparable} interface. (The natural ordering is the ordering
4069 * imposed by the objects' own {@code compareTo} method.) This enables a
4070 * simple idiom for sorting (or maintaining) collections (or arrays) of
4071 * objects that implement the {@code Comparable} interface in
4072 * reverse-natural-order. For example, suppose {@code a} is an array of
4073 * strings. Then: <pre>
4074 * Arrays.sort(a, Collections.reverseOrder());
4075 * </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p>
4076 *
4077 * The returned comparator is serializable.
4078 *
4079 * @return A comparator that imposes the reverse of the <i>natural
4080 * ordering</i> on a collection of objects that implement
4081 * the <tt>Comparable</tt> interface.
4082 * @see Comparable
4083 */
4084 @SuppressWarnings("unchecked")
4085 public static <T> Comparator<T> reverseOrder() {
4086 return (Comparator<T>) ReverseComparator.REVERSE_ORDER;
4087 }
4088
4089 /**
4090 * @serial include
4091 */
4092 private static class ReverseComparator
4093 implements Comparator<Comparable<Object>>, Serializable {
4094
4095 private static final long serialVersionUID = 7207038068494060240L;
4096
4097 static final ReverseComparator REVERSE_ORDER
4098 = new ReverseComparator();
4099
4100 public int compare(Comparable<Object> c1, Comparable<Object> c2) {
4101 return c2.compareTo(c1);
4102 }
4103
4104 private Object readResolve() { return Collections.reverseOrder(); }
4105 }
4106
4107 /**
4108 * Returns a comparator that imposes the reverse ordering of the specified
4109 * comparator. If the specified comparator is {@code null}, this method is
4110 * equivalent to {@link #reverseOrder()} (in other words, it returns a
4111 * comparator that imposes the reverse of the <em>natural ordering</em> on
4112 * a collection of objects that implement the Comparable interface).
4113 *
4114 * <p>The returned comparator is serializable (assuming the specified
4115 * comparator is also serializable or {@code null}).
4116 *
4117 * @param cmp a comparator who's ordering is to be reversed by the returned
4118 * comparator or {@code null}
4119 * @return A comparator that imposes the reverse ordering of the
4120 * specified comparator.
4121 * @since 1.5
4122 */
4123 public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) {
4124 if (cmp == null)
4125 return reverseOrder();
4126
4127 if (cmp instanceof ReverseComparator2)
4128 return ((ReverseComparator2<T>)cmp).cmp;
4129
4130 return new ReverseComparator2<>(cmp);
4131 }
4132
4133 /**
4134 * @serial include
4135 */
4136 private static class ReverseComparator2<T> implements Comparator<T>,
4137 Serializable
4138 {
4139 private static final long serialVersionUID = 4374092139857L;
4140
4141 /**
4142 * The comparator specified in the static factory. This will never
4143 * be null, as the static factory returns a ReverseComparator
4144 * instance if its argument is null.
4145 *
4146 * @serial
4147 */
4148 final Comparator<T> cmp;
4149
4150 ReverseComparator2(Comparator<T> cmp) {
4151 assert cmp != null;
4152 this.cmp = cmp;
4153 }
4154
4155 public int compare(T t1, T t2) {
4156 return cmp.compare(t2, t1);
4157 }
4158
4159 public boolean equals(Object o) {
4160 return (o == this) ||
4161 (o instanceof ReverseComparator2 &&
4162 cmp.equals(((ReverseComparator2)o).cmp));
4163 }
4164
4165 public int hashCode() {
4166 return cmp.hashCode() ^ Integer.MIN_VALUE;
4167 }
4168 }
4169
4170 /**
4171 * Returns an enumeration over the specified collection. This provides
4172 * interoperability with legacy APIs that require an enumeration
4173 * as input.
4174 *
4175 * @param c the collection for which an enumeration is to be returned.
4176 * @return an enumeration over the specified collection.
4177 * @see Enumeration
4178 */
4179 public static <T> Enumeration<T> enumeration(final Collection<T> c) {
4180 return new Enumeration<T>() {
4181 private final Iterator<T> i = c.iterator();
4182
4183 public boolean hasMoreElements() {
4184 return i.hasNext();
4185 }
4186
4187 public T nextElement() {
4188 return i.next();
4189 }
4190 };
4191 }
4192
4193 /**
4194 * Returns an array list containing the elements returned by the
4195 * specified enumeration in the order they are returned by the
4196 * enumeration. This method provides interoperability between
4197 * legacy APIs that return enumerations and new APIs that require
4198 * collections.
4199 *
4200 * @param e enumeration providing elements for the returned
4201 * array list
4202 * @return an array list containing the elements returned
4203 * by the specified enumeration.
4204 * @since 1.4
4205 * @see Enumeration
4206 * @see ArrayList
4207 */
4208 public static <T> ArrayList<T> list(Enumeration<T> e) {
4209 ArrayList<T> l = new ArrayList<>();
4210 while (e.hasMoreElements())
4211 l.add(e.nextElement());
4212 return l;
4213 }
4214
4215 /**
4216 * Returns true if the specified arguments are equal, or both null.
4217 */
4218 static boolean eq(Object o1, Object o2) {
4219 return o1==null ? o2==null : o1.equals(o2);
4220 }
4221
4222 /**
4223 * Returns the number of elements in the specified collection equal to the
4224 * specified object. More formally, returns the number of elements
4225 * <tt>e</tt> in the collection such that
4226 * <tt>(o == null ? e == null : o.equals(e))</tt>.
4227 *
4228 * @param c the collection in which to determine the frequency
4229 * of <tt>o</tt>
4230 * @param o the object whose frequency is to be determined
4231 * @throws NullPointerException if <tt>c</tt> is null
4232 * @since 1.5
4233 */
4234 public static int frequency(Collection<?> c, Object o) {
4235 int result = 0;
4236 if (o == null) {
4237 for (Object e : c)
4238 if (e == null)
4239 result++;
4240 } else {
4241 for (Object e : c)
4242 if (o.equals(e))
4243 result++;
4244 }
4245 return result;
4246 }
4247
4248 /**
4249 * Returns {@code true} if the two specified collections have no
4250 * elements in common.
4251 *
4252 * <p>Care must be exercised if this method is used on collections that
4253 * do not comply with the general contract for {@code Collection}.
4254 * Implementations may elect to iterate over either collection and test
4255 * for containment in the other collection (or to perform any equivalent
4256 * computation). If either collection uses a nonstandard equality test
4257 * (as does a {@link SortedSet} whose ordering is not <em>compatible with
4258 * equals</em>, or the key set of an {@link IdentityHashMap}), both
4259 * collections must use the same nonstandard equality test, or the
4260 * result of this method is undefined.
4261 *
4262 * <p>Care must also be exercised when using collections that have
4263 * restrictions on the elements that they may contain. Collection
4264 * implementations are allowed to throw exceptions for any operation
4265 * involving elements they deem ineligible. For absolute safety the
4266 * specified collections should contain only elements which are
4267 * eligible elements for both collections.
4268 *
4269 * <p>Note that it is permissible to pass the same collection in both
4270 * parameters, in which case the method will return {@code true} if and
4271 * only if the collection is empty.
4272 *
4273 * @param c1 a collection
4274 * @param c2 a collection
4275 * @return {@code true} if the two specified collections have no
4276 * elements in common.
4277 * @throws NullPointerException if either collection is {@code null}.
4278 * @throws NullPointerException if one collection contains a {@code null}
4279 * element and {@code null} is not an eligible element for the other collection.
4280 * (<a href="Collection.html#optional-restrictions">optional</a>)
4281 * @throws ClassCastException if one collection contains an element that is
4282 * of a type which is ineligible for the other collection.
4283 * (<a href="Collection.html#optional-restrictions">optional</a>)
4284 * @since 1.5
4285 */
4286 public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
4287 // The collection to be used for contains(). Preference is given to
4288 // the collection who's contains() has lower O() complexity.
4289 Collection<?> contains = c2;
4290 // The collection to be iterated. If the collections' contains() impl
4291 // are of different O() complexity, the collection with slower
4292 // contains() will be used for iteration. For collections who's
4293 // contains() are of the same complexity then best performance is
4294 // achieved by iterating the smaller collection.
4295 Collection<?> iterate = c1;
4296
4297 // Performance optimization cases. The heuristics:
4298 // 1. Generally iterate over c1.
4299 // 2. If c1 is a Set then iterate over c2.
4300 // 3. If either collection is empty then result is always true.
4301 // 4. Iterate over the smaller Collection.
4302 if (c1 instanceof Set) {
4303 // Use c1 for contains as a Set's contains() is expected to perform
4304 // better than O(N/2)
4305 iterate = c2;
4306 contains = c1;
4307 } else if (!(c2 instanceof Set)) {
4308 // Both are mere Collections. Iterate over smaller collection.
4309 // Example: If c1 contains 3 elements and c2 contains 50 elements and
4310 // assuming contains() requires ceiling(N/2) comparisons then
4311 // checking for all c1 elements in c2 would require 75 comparisons
4312 // (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring
4313 // 100 comparisons (50 * ceiling(3/2)).
4314 int c1size = c1.size();
4315 int c2size = c2.size();
4316 if (c1size == 0 || c2size == 0) {
4317 // At least one collection is empty. Nothing will match.
4318 return true;
4319 }
4320
4321 if (c1size > c2size) {
4322 iterate = c2;
4323 contains = c1;
4324 }
4325 }
4326
4327 for (Object e : iterate) {
4328 if (contains.contains(e)) {
4329 // Found a common element. Collections are not disjoint.
4330 return false;
4331 }
4332 }
4333
4334 // No common elements were found.
4335 return true;
4336 }
4337
4338 /**
4339 * Adds all of the specified elements to the specified collection.
4340 * Elements to be added may be specified individually or as an array.
4341 * The behavior of this convenience method is identical to that of
4342 * <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely
4343 * to run significantly faster under most implementations.
4344 *
4345 * <p>When elements are specified individually, this method provides a
4346 * convenient way to add a few elements to an existing collection:
4347 * <pre>
4348 * Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon");
4349 * </pre>
4350 *
4351 * @param c the collection into which <tt>elements</tt> are to be inserted
4352 * @param elements the elements to insert into <tt>c</tt>
4353 * @return <tt>true</tt> if the collection changed as a result of the call
4354 * @throws UnsupportedOperationException if <tt>c</tt> does not support
4355 * the <tt>add</tt> operation
4356 * @throws NullPointerException if <tt>elements</tt> contains one or more
4357 * null values and <tt>c</tt> does not permit null elements, or
4358 * if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt>
4359 * @throws IllegalArgumentException if some property of a value in
4360 * <tt>elements</tt> prevents it from being added to <tt>c</tt>
4361 * @see Collection#addAll(Collection)
4362 * @since 1.5
4363 */
4364 @SafeVarargs
4365 public static <T> boolean addAll(Collection<? super T> c, T... elements) {
4366 boolean result = false;
4367 for (T element : elements)
4368 result |= c.add(element);
4369 return result;
4370 }
4371
4372 /**
4373 * Returns a set backed by the specified map. The resulting set displays
4374 * the same ordering, concurrency, and performance characteristics as the
4375 * backing map. In essence, this factory method provides a {@link Set}
4376 * implementation corresponding to any {@link Map} implementation. There
4377 * is no need to use this method on a {@link Map} implementation that
4378 * already has a corresponding {@link Set} implementation (such as {@link
4379 * HashMap} or {@link TreeMap}).
4380 *
4381 * <p>Each method invocation on the set returned by this method results in
4382 * exactly one method invocation on the backing map or its <tt>keySet</tt>
4383 * view, with one exception. The <tt>addAll</tt> method is implemented
4384 * as a sequence of <tt>put</tt> invocations on the backing map.
4385 *
4386 * <p>The specified map must be empty at the time this method is invoked,
4387 * and should not be accessed directly after this method returns. These
4388 * conditions are ensured if the map is created empty, passed directly
4389 * to this method, and no reference to the map is retained, as illustrated
4390 * in the following code fragment:
4391 * <pre>
4392 * Set<Object> weakHashSet = Collections.newSetFromMap(
4393 * new WeakHashMap<Object, Boolean>());
4394 * </pre>
4395 *
4396 * @param map the backing map
4397 * @return the set backed by the map
4398 * @throws IllegalArgumentException if <tt>map</tt> is not empty
4399 * @since 1.6
4400 */
4401 public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
4402 return new SetFromMap<>(map);
4403 }
4404
4405 /**
4406 * @serial include
4407 */
4408 private static class SetFromMap<E> extends AbstractSet<E>
4409 implements Set<E>, Serializable
4410 {
4411 private final Map<E, Boolean> m; // The backing map
4412 private transient Set<E> s; // Its keySet
4413
4414 SetFromMap(Map<E, Boolean> map) {
4415 if (!map.isEmpty())
4416 throw new IllegalArgumentException("Map is non-empty");
4417 m = map;
4418 s = map.keySet();
4419 }
4420
4421 public void clear() { m.clear(); }
4422 public int size() { return m.size(); }
4423 public boolean isEmpty() { return m.isEmpty(); }
4424 public boolean contains(Object o) { return m.containsKey(o); }
4425 public boolean remove(Object o) { return m.remove(o) != null; }
4426 public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; }
4427 public Iterator<E> iterator() { return s.iterator(); }
4428 public Object[] toArray() { return s.toArray(); }
4429 public <T> T[] toArray(T[] a) { return s.toArray(a); }
4430 public String toString() { return s.toString(); }
4431 public int hashCode() { return s.hashCode(); }
4432 public boolean equals(Object o) { return o == this || s.equals(o); }
4433 public boolean containsAll(Collection<?> c) {return s.containsAll(c);}
4434 public boolean removeAll(Collection<?> c) {return s.removeAll(c);}
4435 public boolean retainAll(Collection<?> c) {return s.retainAll(c);}
4436 // addAll is the only inherited implementation
4437
4438 private static final long serialVersionUID = 2454657854757543876L;
4439
4440 private void readObject(java.io.ObjectInputStream stream)
4441 throws IOException, ClassNotFoundException
4442 {
4443 stream.defaultReadObject();
4444 s = m.keySet();
4445 }
4446 }
4447
4448 /**
4449 * Returns a view of a {@link Deque} as a Last-in-first-out (Lifo)
4450 * {@link Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>,
4451 * <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This
4452 * view can be useful when you would like to use a method
4453 * requiring a <tt>Queue</tt> but you need Lifo ordering.
4454 *
4455 * <p>Each method invocation on the queue returned by this method
4456 * results in exactly one method invocation on the backing deque, with
4457 * one exception. The {@link Queue#addAll addAll} method is
4458 * implemented as a sequence of {@link Deque#addFirst addFirst}
4459 * invocations on the backing deque.
4460 *
4461 * @param deque the deque
4462 * @return the queue
4463 * @since 1.6
4464 */
4465 public static <T> Queue<T> asLifoQueue(Deque<T> deque) {
4466 return new AsLIFOQueue<>(deque);
4467 }
4468
4469 /**
4470 * @serial include
4471 */
4472 static class AsLIFOQueue<E> extends AbstractQueue<E>
4473 implements Queue<E>, Serializable {
4474 private static final long serialVersionUID = 1802017725587941708L;
4475 private final Deque<E> q;
4476 AsLIFOQueue(Deque<E> q) { this.q = q; }
4477 public boolean add(E e) { q.addFirst(e); return true; }
4478 public boolean offer(E e) { return q.offerFirst(e); }
4479 public E poll() { return q.pollFirst(); }
4480 public E remove() { return q.removeFirst(); }
4481 public E peek() { return q.peekFirst(); }
4482 public E element() { return q.getFirst(); }
4483 public void clear() { q.clear(); }
4484 public int size() { return q.size(); }
4485 public boolean isEmpty() { return q.isEmpty(); }
4486 public boolean contains(Object o) { return q.contains(o); }
4487 public boolean remove(Object o) { return q.remove(o); }
4488 public Iterator<E> iterator() { return q.iterator(); }
4489 public Object[] toArray() { return q.toArray(); }
4490 public <T> T[] toArray(T[] a) { return q.toArray(a); }
4491 public String toString() { return q.toString(); }
4492 public boolean containsAll(Collection<?> c) {return q.containsAll(c);}
4493 public boolean removeAll(Collection<?> c) {return q.removeAll(c);}
4494 public boolean retainAll(Collection<?> c) {return q.retainAll(c);}
4495 // We use inherited addAll; forwarding addAll would be wrong
4496 }
4497 }