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 import java.util.function.Predicate;
36 import java.util.function.UnaryOperator;
37 import java.util.stream.IntStream;
38 import java.util.stream.Stream;
39 import java.util.stream.StreamSupport;
40
41 /**
42 * This class consists exclusively of static methods that operate on or return
43 * collections. It contains polymorphic algorithms that operate on
44 * collections, "wrappers", which return a new collection backed by a
45 * specified collection, and a few other odds and ends.
46 *
47 * <p>The methods of this class all throw a <tt>NullPointerException</tt>
48 * if the collections or class objects provided to them are null.
49 *
50 * <p>The documentation for the polymorphic algorithms contained in this class
51 * generally includes a brief description of the <i>implementation</i>. Such
52 * descriptions should be regarded as <i>implementation notes</i>, rather than
53 * parts of the <i>specification</i>. Implementors should feel free to
54 * substitute other algorithms, so long as the specification itself is adhered
55 * to. (For example, the algorithm used by <tt>sort</tt> does not have to be
56 * a mergesort, but it does have to be <i>stable</i>.)
57 *
58 * <p>The "destructive" algorithms contained in this class, that is, the
59 * algorithms that modify the collection on which they operate, are specified
60 * to throw <tt>UnsupportedOperationException</tt> if the collection does not
61 * support the appropriate mutation primitive(s), such as the <tt>set</tt>
62 * method. These algorithms may, but are not required to, throw this
63 * exception if an invocation would have no effect on the collection. For
64 * example, invoking the <tt>sort</tt> method on an unmodifiable list that is
65 * already sorted may or may not throw <tt>UnsupportedOperationException</tt>.
66 *
67 * <p>This class is a member of the
68 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
69 * Java Collections Framework</a>.
70 *
71 * @author Josh Bloch
72 * @author Neal Gafter
73 * @see Collection
74 * @see Set
75 * @see List
76 * @see Map
77 * @since 1.2
78 */
79
80 public class Collections {
81 // Suppresses default constructor, ensuring non-instantiability.
82 private Collections() {
83 }
84
85 // Algorithms
86
87 /*
88 * Tuning parameters for algorithms - Many of the List algorithms have
89 * two implementations, one of which is appropriate for RandomAccess
90 * lists, the other for "sequential." Often, the random access variant
91 * yields better performance on small sequential access lists. The
92 * tuning parameters below determine the cutoff point for what constitutes
93 * a "small" sequential access list for each algorithm. The values below
94 * were empirically determined to work well for LinkedList. Hopefully
95 * they should be reasonable for other sequential access List
96 * implementations. Those doing performance work on this code would
97 * do well to validate the values of these parameters from time to time.
98 * (The first word of each tuning parameter name is the algorithm to which
99 * it applies.)
100 */
101 private static final int BINARYSEARCH_THRESHOLD = 5000;
102 private static final int REVERSE_THRESHOLD = 18;
103 private static final int SHUFFLE_THRESHOLD = 5;
104 private static final int FILL_THRESHOLD = 25;
105 private static final int ROTATE_THRESHOLD = 100;
106 private static final int COPY_THRESHOLD = 10;
107 private static final int REPLACEALL_THRESHOLD = 11;
108 private static final int INDEXOFSUBLIST_THRESHOLD = 35;
109
110 /**
111 * Sorts the specified list into ascending order, according to the
112 * {@linkplain Comparable natural ordering} of its elements.
113 * All elements in the list must implement the {@link Comparable}
114 * interface. Furthermore, all elements in the list must be
115 * <i>mutually comparable</i> (that is, {@code e1.compareTo(e2)}
116 * must not throw a {@code ClassCastException} for any elements
117 * {@code e1} and {@code e2} in the list).
118 *
119 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will
120 * not be reordered as a result of the sort.
121 *
122 * <p>The specified list must be modifiable, but need not be resizable.
123 *
124 * <p>Implementation note: This implementation is a stable, adaptive,
125 * iterative mergesort that requires far fewer than n lg(n) comparisons
126 * when the input array is partially sorted, while offering the
127 * performance of a traditional mergesort when the input array is
128 * randomly ordered. If the input array is nearly sorted, the
129 * implementation requires approximately n comparisons. Temporary
130 * storage requirements vary from a small constant for nearly sorted
131 * input arrays to n/2 object references for randomly ordered input
132 * arrays.
133 *
134 * <p>The implementation takes equal advantage of ascending and
135 * descending order in its input array, and can take advantage of
136 * ascending and descending order in different parts of the same
137 * input array. It is well-suited to merging two or more sorted arrays:
138 * simply concatenate the arrays and sort the resulting array.
139 *
140 * <p>The implementation was adapted from Tim Peters's list sort for Python
141 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt">
142 * TimSort</a>). It uses techniques from Peter McIlroy's "Optimistic
143 * Sorting and Information Theoretic Complexity", in Proceedings of the
144 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474,
145 * January 1993.
146 *
147 * <p>This implementation dumps the specified list into an array, sorts
148 * the array, and iterates over the list resetting each element
149 * from the corresponding position in the array. This avoids the
150 * n<sup>2</sup> log(n) performance that would result from attempting
151 * to sort a linked list in place.
152 *
153 * @param <T> the class of the objects in the list
154 * @param list the list to be sorted.
155 * @throws ClassCastException if the list contains elements that are not
156 * <i>mutually comparable</i> (for example, strings and integers).
157 * @throws UnsupportedOperationException if the specified list's
158 * list-iterator does not support the {@code set} operation.
159 * @throws IllegalArgumentException (optional) if the implementation
160 * detects that the natural ordering of the list elements is
161 * found to violate the {@link Comparable} contract
162 */
163 @SuppressWarnings("unchecked")
164 public static <T extends Comparable<? super T>> void sort(List<T> list) {
165 Object[] a = list.toArray();
166 Arrays.sort(a);
167 ListIterator<T> i = list.listIterator();
168 for (int j=0; j<a.length; j++) {
169 i.next();
170 i.set((T)a[j]);
171 }
172 }
173
174 /**
175 * Sorts the specified list according to the order induced by the
176 * specified comparator. All elements in the list must be <i>mutually
177 * comparable</i> using the specified comparator (that is,
178 * {@code c.compare(e1, e2)} must not throw a {@code ClassCastException}
179 * for any elements {@code e1} and {@code e2} in the list).
180 *
181 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will
182 * not be reordered as a result of the sort.
183 *
184 * <p>The specified list must be modifiable, but need not be resizable.
185 *
186 * <p>Implementation note: This implementation is a stable, adaptive,
187 * iterative mergesort that requires far fewer than n lg(n) comparisons
188 * when the input array is partially sorted, while offering the
189 * performance of a traditional mergesort when the input array is
190 * randomly ordered. If the input array is nearly sorted, the
191 * implementation requires approximately n comparisons. Temporary
192 * storage requirements vary from a small constant for nearly sorted
193 * input arrays to n/2 object references for randomly ordered input
194 * arrays.
195 *
196 * <p>The implementation takes equal advantage of ascending and
197 * descending order in its input array, and can take advantage of
198 * ascending and descending order in different parts of the same
199 * input array. It is well-suited to merging two or more sorted arrays:
200 * simply concatenate the arrays and sort the resulting array.
201 *
202 * <p>The implementation was adapted from Tim Peters's list sort for Python
203 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt">
204 * TimSort</a>). It uses techniques from Peter McIlroy's "Optimistic
205 * Sorting and Information Theoretic Complexity", in Proceedings of the
206 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474,
207 * January 1993.
208 *
209 * <p>This implementation dumps the specified list into an array, sorts
210 * the array, and iterates over the list resetting each element
211 * from the corresponding position in the array. This avoids the
212 * n<sup>2</sup> log(n) performance that would result from attempting
213 * to sort a linked list in place.
214 *
215 * @param <T> the class of the objects in the list
216 * @param list the list to be sorted.
217 * @param c the comparator to determine the order of the list. A
218 * {@code null} value indicates that the elements' <i>natural
219 * ordering</i> should be used.
220 * @throws ClassCastException if the list contains elements that are not
221 * <i>mutually comparable</i> using the specified comparator.
222 * @throws UnsupportedOperationException if the specified list's
223 * list-iterator does not support the {@code set} operation.
224 * @throws IllegalArgumentException (optional) if the comparator is
225 * found to violate the {@link Comparator} contract
226 */
227 @SuppressWarnings({"unchecked", "rawtypes"})
228 public static <T> void sort(List<T> list, Comparator<? super T> c) {
229 Object[] a = list.toArray();
230 Arrays.sort(a, (Comparator)c);
231 ListIterator<T> i = list.listIterator();
232 for (int j=0; j<a.length; j++) {
233 i.next();
234 i.set((T)a[j]);
235 }
236 }
237
238
239 /**
240 * Searches the specified list for the specified object using the binary
241 * search algorithm. The list must be sorted into ascending order
242 * according to the {@linkplain Comparable natural ordering} of its
243 * elements (as by the {@link #sort(List)} method) prior to making this
244 * call. If it is not sorted, the results are undefined. If the list
245 * contains multiple elements equal to the specified object, there is no
246 * guarantee which one will be found.
247 *
248 * <p>This method runs in log(n) time for a "random access" list (which
249 * provides near-constant-time positional access). If the specified list
250 * does not implement the {@link RandomAccess} interface and is large,
251 * this method will do an iterator-based binary search that performs
252 * O(n) link traversals and O(log n) element comparisons.
253 *
254 * @param <T> the class of the objects in the list
255 * @param list the list to be searched.
256 * @param key the key to be searched for.
257 * @return the index of the search key, if it is contained in the list;
258 * otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The
259 * <i>insertion point</i> is defined as the point at which the
260 * key would be inserted into the list: the index of the first
261 * element greater than the key, or <tt>list.size()</tt> if all
262 * elements in the list are less than the specified key. Note
263 * that this guarantees that the return value will be >= 0 if
264 * and only if the key is found.
265 * @throws ClassCastException if the list contains elements that are not
266 * <i>mutually comparable</i> (for example, strings and
267 * integers), or the search key is not mutually comparable
268 * with the elements of the list.
269 */
270 public static <T>
271 int binarySearch(List<? extends Comparable<? super T>> list, T key) {
272 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
273 return Collections.indexedBinarySearch(list, key);
274 else
275 return Collections.iteratorBinarySearch(list, key);
276 }
277
278 private static <T>
279 int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key) {
280 int low = 0;
281 int high = list.size()-1;
282
283 while (low <= high) {
284 int mid = (low + high) >>> 1;
285 Comparable<? super T> midVal = list.get(mid);
286 int cmp = midVal.compareTo(key);
287
288 if (cmp < 0)
289 low = mid + 1;
290 else if (cmp > 0)
291 high = mid - 1;
292 else
293 return mid; // key found
294 }
295 return -(low + 1); // key not found
296 }
297
298 private static <T>
299 int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key)
300 {
301 int low = 0;
302 int high = list.size()-1;
303 ListIterator<? extends Comparable<? super T>> i = list.listIterator();
304
305 while (low <= high) {
306 int mid = (low + high) >>> 1;
307 Comparable<? super T> midVal = get(i, mid);
308 int cmp = midVal.compareTo(key);
309
310 if (cmp < 0)
311 low = mid + 1;
312 else if (cmp > 0)
313 high = mid - 1;
314 else
315 return mid; // key found
316 }
317 return -(low + 1); // key not found
318 }
319
320 /**
321 * Gets the ith element from the given list by repositioning the specified
322 * list listIterator.
323 */
324 private static <T> T get(ListIterator<? extends T> i, int index) {
325 T obj = null;
326 int pos = i.nextIndex();
327 if (pos <= index) {
328 do {
329 obj = i.next();
330 } while (pos++ < index);
331 } else {
332 do {
333 obj = i.previous();
334 } while (--pos > index);
335 }
336 return obj;
337 }
338
339 /**
340 * Searches the specified list for the specified object using the binary
341 * search algorithm. The list must be sorted into ascending order
342 * according to the specified comparator (as by the
343 * {@link #sort(List, Comparator) sort(List, Comparator)}
344 * method), prior to making this call. If it is
345 * not sorted, the results are undefined. If the list contains multiple
346 * elements equal to the specified object, there is no guarantee which one
347 * will be found.
348 *
349 * <p>This method runs in log(n) time for a "random access" list (which
350 * provides near-constant-time positional access). If the specified list
351 * does not implement the {@link RandomAccess} interface and is large,
352 * this method will do an iterator-based binary search that performs
353 * O(n) link traversals and O(log n) element comparisons.
354 *
355 * @param <T> the class of the objects in the list
356 * @param list the list to be searched.
357 * @param key the key to be searched for.
358 * @param c the comparator by which the list is ordered.
359 * A <tt>null</tt> value indicates that the elements'
360 * {@linkplain Comparable natural ordering} should be used.
361 * @return the index of the search key, if it is contained in the list;
362 * otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The
363 * <i>insertion point</i> is defined as the point at which the
364 * key would be inserted into the list: the index of the first
365 * element greater than the key, or <tt>list.size()</tt> if all
366 * elements in the list are less than the specified key. Note
367 * that this guarantees that the return value will be >= 0 if
368 * and only if the key is found.
369 * @throws ClassCastException if the list contains elements that are not
370 * <i>mutually comparable</i> using the specified comparator,
371 * or the search key is not mutually comparable with the
372 * elements of the list using this comparator.
373 */
374 @SuppressWarnings("unchecked")
375 public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) {
376 if (c==null)
377 return binarySearch((List<? extends Comparable<? super T>>) list, key);
378
379 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
380 return Collections.indexedBinarySearch(list, key, c);
381 else
382 return Collections.iteratorBinarySearch(list, key, c);
383 }
384
385 private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
386 int low = 0;
387 int high = l.size()-1;
388
389 while (low <= high) {
390 int mid = (low + high) >>> 1;
391 T midVal = l.get(mid);
392 int cmp = c.compare(midVal, key);
393
394 if (cmp < 0)
395 low = mid + 1;
396 else if (cmp > 0)
397 high = mid - 1;
398 else
399 return mid; // key found
400 }
401 return -(low + 1); // key not found
402 }
403
404 private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
405 int low = 0;
406 int high = l.size()-1;
407 ListIterator<? extends T> i = l.listIterator();
408
409 while (low <= high) {
410 int mid = (low + high) >>> 1;
411 T midVal = get(i, mid);
412 int cmp = c.compare(midVal, key);
413
414 if (cmp < 0)
415 low = mid + 1;
416 else if (cmp > 0)
417 high = mid - 1;
418 else
419 return mid; // key found
420 }
421 return -(low + 1); // key not found
422 }
423
424 /**
425 * Reverses the order of the elements in the specified list.<p>
426 *
427 * This method runs in linear time.
428 *
429 * @param list the list whose elements are to be reversed.
430 * @throws UnsupportedOperationException if the specified list or
431 * its list-iterator does not support the <tt>set</tt> operation.
432 */
433 @SuppressWarnings({"rawtypes", "unchecked"})
434 public static void reverse(List<?> list) {
435 int size = list.size();
436 if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) {
437 for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--)
438 swap(list, i, j);
439 } else {
440 // instead of using a raw type here, it's possible to capture
441 // the wildcard but it will require a call to a supplementary
442 // private method
443 ListIterator fwd = list.listIterator();
444 ListIterator rev = list.listIterator(size);
445 for (int i=0, mid=list.size()>>1; i<mid; i++) {
446 Object tmp = fwd.next();
447 fwd.set(rev.previous());
448 rev.set(tmp);
449 }
450 }
451 }
452
453 /**
454 * Randomly permutes the specified list using a default source of
455 * randomness. All permutations occur with approximately equal
456 * likelihood.
457 *
458 * <p>The hedge "approximately" is used in the foregoing description because
459 * default source of randomness is only approximately an unbiased source
460 * of independently chosen bits. If it were a perfect source of randomly
461 * chosen bits, then the algorithm would choose permutations with perfect
462 * uniformity.
463 *
464 * <p>This implementation traverses the list backwards, from the last
465 * element up to the second, repeatedly swapping a randomly selected element
466 * into the "current position". Elements are randomly selected from the
467 * portion of the list that runs from the first element to the current
468 * position, inclusive.
469 *
470 * <p>This method runs in linear time. If the specified list does not
471 * implement the {@link RandomAccess} interface and is large, this
472 * implementation dumps the specified list into an array before shuffling
473 * it, and dumps the shuffled array back into the list. This avoids the
474 * quadratic behavior that would result from shuffling a "sequential
475 * access" list in place.
476 *
477 * @param list the list to be shuffled.
478 * @throws UnsupportedOperationException if the specified list or
479 * its list-iterator does not support the <tt>set</tt> operation.
480 */
481 public static void shuffle(List<?> list) {
482 Random rnd = r;
483 if (rnd == null)
484 r = rnd = new Random(); // harmless race.
485 shuffle(list, rnd);
486 }
487
488 private static Random r;
489
490 /**
491 * Randomly permute the specified list using the specified source of
492 * randomness. All permutations occur with equal likelihood
493 * assuming that the source of randomness is fair.<p>
494 *
495 * This implementation traverses the list backwards, from the last element
496 * up to the second, repeatedly swapping a randomly selected element into
497 * the "current position". Elements are randomly selected from the
498 * portion of the list that runs from the first element to the current
499 * position, inclusive.<p>
500 *
501 * This method runs in linear time. If the specified list does not
502 * implement the {@link RandomAccess} interface and is large, this
503 * implementation dumps the specified list into an array before shuffling
504 * it, and dumps the shuffled array back into the list. This avoids the
505 * quadratic behavior that would result from shuffling a "sequential
506 * access" list in place.
507 *
508 * @param list the list to be shuffled.
509 * @param rnd the source of randomness to use to shuffle the list.
510 * @throws UnsupportedOperationException if the specified list or its
511 * list-iterator does not support the <tt>set</tt> operation.
512 */
513 @SuppressWarnings({"rawtypes", "unchecked"})
514 public static void shuffle(List<?> list, Random rnd) {
515 int size = list.size();
516 if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) {
517 for (int i=size; i>1; i--)
518 swap(list, i-1, rnd.nextInt(i));
519 } else {
520 Object arr[] = list.toArray();
521
522 // Shuffle array
523 for (int i=size; i>1; i--)
524 swap(arr, i-1, rnd.nextInt(i));
525
526 // Dump array back into list
527 // instead of using a raw type here, it's possible to capture
528 // the wildcard but it will require a call to a supplementary
529 // private method
530 ListIterator it = list.listIterator();
531 for (int i=0; i<arr.length; i++) {
532 it.next();
533 it.set(arr[i]);
534 }
535 }
536 }
537
538 /**
539 * Swaps the elements at the specified positions in the specified list.
540 * (If the specified positions are equal, invoking this method leaves
541 * the list unchanged.)
542 *
543 * @param list The list in which to swap elements.
544 * @param i the index of one element to be swapped.
545 * @param j the index of the other element to be swapped.
546 * @throws IndexOutOfBoundsException if either <tt>i</tt> or <tt>j</tt>
547 * is out of range (i < 0 || i >= list.size()
548 * || j < 0 || j >= list.size()).
549 * @since 1.4
550 */
551 @SuppressWarnings({"rawtypes", "unchecked"})
552 public static void swap(List<?> list, int i, int j) {
553 // instead of using a raw type here, it's possible to capture
554 // the wildcard but it will require a call to a supplementary
555 // private method
556 final List l = list;
557 l.set(i, l.set(j, l.get(i)));
558 }
559
560 /**
561 * Swaps the two specified elements in the specified array.
562 */
563 private static void swap(Object[] arr, int i, int j) {
564 Object tmp = arr[i];
565 arr[i] = arr[j];
566 arr[j] = tmp;
567 }
568
569 /**
570 * Replaces all of the elements of the specified list with the specified
571 * element. <p>
572 *
573 * This method runs in linear time.
574 *
575 * @param <T> the class of the objects in the list
576 * @param list the list to be filled with the specified element.
577 * @param obj The element with which to fill the specified list.
578 * @throws UnsupportedOperationException if the specified list or its
579 * list-iterator does not support the <tt>set</tt> operation.
580 */
581 public static <T> void fill(List<? super T> list, T obj) {
582 int size = list.size();
583
584 if (size < FILL_THRESHOLD || list instanceof RandomAccess) {
585 for (int i=0; i<size; i++)
586 list.set(i, obj);
587 } else {
588 ListIterator<? super T> itr = list.listIterator();
589 for (int i=0; i<size; i++) {
590 itr.next();
591 itr.set(obj);
592 }
593 }
594 }
595
596 /**
597 * Copies all of the elements from one list into another. After the
598 * operation, the index of each copied element in the destination list
599 * will be identical to its index in the source list. The destination
600 * list must be at least as long as the source list. If it is longer, the
601 * remaining elements in the destination list are unaffected. <p>
602 *
603 * This method runs in linear time.
604 *
605 * @param <T> the class of the objects in the lists
606 * @param dest The destination list.
607 * @param src The source list.
608 * @throws IndexOutOfBoundsException if the destination list is too small
609 * to contain the entire source List.
610 * @throws UnsupportedOperationException if the destination list's
611 * list-iterator does not support the <tt>set</tt> operation.
612 */
613 public static <T> void copy(List<? super T> dest, List<? extends T> src) {
614 int srcSize = src.size();
615 if (srcSize > dest.size())
616 throw new IndexOutOfBoundsException("Source does not fit in dest");
617
618 if (srcSize < COPY_THRESHOLD ||
619 (src instanceof RandomAccess && dest instanceof RandomAccess)) {
620 for (int i=0; i<srcSize; i++)
621 dest.set(i, src.get(i));
622 } else {
623 ListIterator<? super T> di=dest.listIterator();
624 ListIterator<? extends T> si=src.listIterator();
625 for (int i=0; i<srcSize; i++) {
626 di.next();
627 di.set(si.next());
628 }
629 }
630 }
631
632 /**
633 * Returns the minimum element of the given collection, according to the
634 * <i>natural ordering</i> of its elements. All elements in the
635 * collection must implement the <tt>Comparable</tt> interface.
636 * Furthermore, all elements in the collection must be <i>mutually
637 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
638 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
639 * <tt>e2</tt> in the collection).<p>
640 *
641 * This method iterates over the entire collection, hence it requires
642 * time proportional to the size of the collection.
643 *
644 * @param <T> the class of the objects in the collection
645 * @param coll the collection whose minimum element is to be determined.
646 * @return the minimum element of the given collection, according
647 * to the <i>natural ordering</i> of its elements.
648 * @throws ClassCastException if the collection contains elements that are
649 * not <i>mutually comparable</i> (for example, strings and
650 * integers).
651 * @throws NoSuchElementException if the collection is empty.
652 * @see Comparable
653 */
654 public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) {
655 Iterator<? extends T> i = coll.iterator();
656 T candidate = i.next();
657
658 while (i.hasNext()) {
659 T next = i.next();
660 if (next.compareTo(candidate) < 0)
661 candidate = next;
662 }
663 return candidate;
664 }
665
666 /**
667 * Returns the minimum element of the given collection, according to the
668 * order induced by the specified comparator. All elements in the
669 * collection must be <i>mutually comparable</i> by the specified
670 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
671 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
672 * <tt>e2</tt> in the collection).<p>
673 *
674 * This method iterates over the entire collection, hence it requires
675 * time proportional to the size of the collection.
676 *
677 * @param <T> the class of the objects in the collection
678 * @param coll the collection whose minimum element is to be determined.
679 * @param comp the comparator with which to determine the minimum element.
680 * A <tt>null</tt> value indicates that the elements' <i>natural
681 * ordering</i> should be used.
682 * @return the minimum element of the given collection, according
683 * to the specified comparator.
684 * @throws ClassCastException if the collection contains elements that are
685 * not <i>mutually comparable</i> using the specified comparator.
686 * @throws NoSuchElementException if the collection is empty.
687 * @see Comparable
688 */
689 @SuppressWarnings({"unchecked", "rawtypes"})
690 public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) {
691 if (comp==null)
692 return (T)min((Collection) coll);
693
694 Iterator<? extends T> i = coll.iterator();
695 T candidate = i.next();
696
697 while (i.hasNext()) {
698 T next = i.next();
699 if (comp.compare(next, candidate) < 0)
700 candidate = next;
701 }
702 return candidate;
703 }
704
705 /**
706 * Returns the maximum element of the given collection, according to the
707 * <i>natural ordering</i> of its elements. All elements in the
708 * collection must implement the <tt>Comparable</tt> interface.
709 * Furthermore, all elements in the collection must be <i>mutually
710 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
711 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
712 * <tt>e2</tt> in the collection).<p>
713 *
714 * This method iterates over the entire collection, hence it requires
715 * time proportional to the size of the collection.
716 *
717 * @param <T> the class of the objects in the collection
718 * @param coll the collection whose maximum element is to be determined.
719 * @return the maximum element of the given collection, according
720 * to the <i>natural ordering</i> of its elements.
721 * @throws ClassCastException if the collection contains elements that are
722 * not <i>mutually comparable</i> (for example, strings and
723 * integers).
724 * @throws NoSuchElementException if the collection is empty.
725 * @see Comparable
726 */
727 public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) {
728 Iterator<? extends T> i = coll.iterator();
729 T candidate = i.next();
730
731 while (i.hasNext()) {
732 T next = i.next();
733 if (next.compareTo(candidate) > 0)
734 candidate = next;
735 }
736 return candidate;
737 }
738
739 /**
740 * Returns the maximum element of the given collection, according to the
741 * order induced by the specified comparator. All elements in the
742 * collection must be <i>mutually comparable</i> by the specified
743 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
744 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
745 * <tt>e2</tt> in the collection).<p>
746 *
747 * This method iterates over the entire collection, hence it requires
748 * time proportional to the size of the collection.
749 *
750 * @param <T> the class of the objects in the collection
751 * @param coll the collection whose maximum element is to be determined.
752 * @param comp the comparator with which to determine the maximum element.
753 * A <tt>null</tt> value indicates that the elements' <i>natural
754 * ordering</i> should be used.
755 * @return the maximum element of the given collection, according
756 * to the specified comparator.
757 * @throws ClassCastException if the collection contains elements that are
758 * not <i>mutually comparable</i> using the specified comparator.
759 * @throws NoSuchElementException if the collection is empty.
760 * @see Comparable
761 */
762 @SuppressWarnings({"unchecked", "rawtypes"})
763 public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) {
764 if (comp==null)
765 return (T)max((Collection) coll);
766
767 Iterator<? extends T> i = coll.iterator();
768 T candidate = i.next();
769
770 while (i.hasNext()) {
771 T next = i.next();
772 if (comp.compare(next, candidate) > 0)
773 candidate = next;
774 }
775 return candidate;
776 }
777
778 /**
779 * Rotates the elements in the specified list by the specified distance.
780 * After calling this method, the element at index <tt>i</tt> will be
781 * the element previously at index <tt>(i - distance)</tt> mod
782 * <tt>list.size()</tt>, for all values of <tt>i</tt> between <tt>0</tt>
783 * and <tt>list.size()-1</tt>, inclusive. (This method has no effect on
784 * the size of the list.)
785 *
786 * <p>For example, suppose <tt>list</tt> comprises<tt> [t, a, n, k, s]</tt>.
787 * After invoking <tt>Collections.rotate(list, 1)</tt> (or
788 * <tt>Collections.rotate(list, -4)</tt>), <tt>list</tt> will comprise
789 * <tt>[s, t, a, n, k]</tt>.
790 *
791 * <p>Note that this method can usefully be applied to sublists to
792 * move one or more elements within a list while preserving the
793 * order of the remaining elements. For example, the following idiom
794 * moves the element at index <tt>j</tt> forward to position
795 * <tt>k</tt> (which must be greater than or equal to <tt>j</tt>):
796 * <pre>
797 * Collections.rotate(list.subList(j, k+1), -1);
798 * </pre>
799 * To make this concrete, suppose <tt>list</tt> comprises
800 * <tt>[a, b, c, d, e]</tt>. To move the element at index <tt>1</tt>
801 * (<tt>b</tt>) forward two positions, perform the following invocation:
802 * <pre>
803 * Collections.rotate(l.subList(1, 4), -1);
804 * </pre>
805 * The resulting list is <tt>[a, c, d, b, e]</tt>.
806 *
807 * <p>To move more than one element forward, increase the absolute value
808 * of the rotation distance. To move elements backward, use a positive
809 * shift distance.
810 *
811 * <p>If the specified list is small or implements the {@link
812 * RandomAccess} interface, this implementation exchanges the first
813 * element into the location it should go, and then repeatedly exchanges
814 * the displaced element into the location it should go until a displaced
815 * element is swapped into the first element. If necessary, the process
816 * is repeated on the second and successive elements, until the rotation
817 * is complete. If the specified list is large and doesn't implement the
818 * <tt>RandomAccess</tt> interface, this implementation breaks the
819 * list into two sublist views around index <tt>-distance mod size</tt>.
820 * Then the {@link #reverse(List)} method is invoked on each sublist view,
821 * and finally it is invoked on the entire list. For a more complete
822 * description of both algorithms, see Section 2.3 of Jon Bentley's
823 * <i>Programming Pearls</i> (Addison-Wesley, 1986).
824 *
825 * @param list the list to be rotated.
826 * @param distance the distance to rotate the list. There are no
827 * constraints on this value; it may be zero, negative, or
828 * greater than <tt>list.size()</tt>.
829 * @throws UnsupportedOperationException if the specified list or
830 * its list-iterator does not support the <tt>set</tt> operation.
831 * @since 1.4
832 */
833 public static void rotate(List<?> list, int distance) {
834 if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD)
835 rotate1(list, distance);
836 else
837 rotate2(list, distance);
838 }
839
840 private static <T> void rotate1(List<T> list, int distance) {
841 int size = list.size();
842 if (size == 0)
843 return;
844 distance = distance % size;
845 if (distance < 0)
846 distance += size;
847 if (distance == 0)
848 return;
849
850 for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) {
851 T displaced = list.get(cycleStart);
852 int i = cycleStart;
853 do {
854 i += distance;
855 if (i >= size)
856 i -= size;
857 displaced = list.set(i, displaced);
858 nMoved ++;
859 } while (i != cycleStart);
860 }
861 }
862
863 private static void rotate2(List<?> list, int distance) {
864 int size = list.size();
865 if (size == 0)
866 return;
867 int mid = -distance % size;
868 if (mid < 0)
869 mid += size;
870 if (mid == 0)
871 return;
872
873 reverse(list.subList(0, mid));
874 reverse(list.subList(mid, size));
875 reverse(list);
876 }
877
878 /**
879 * Replaces all occurrences of one specified value in a list with another.
880 * More formally, replaces with <tt>newVal</tt> each element <tt>e</tt>
881 * in <tt>list</tt> such that
882 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
883 * (This method has no effect on the size of the list.)
884 *
885 * @param <T> the class of the objects in the list
886 * @param list the list in which replacement is to occur.
887 * @param oldVal the old value to be replaced.
888 * @param newVal the new value with which <tt>oldVal</tt> is to be
889 * replaced.
890 * @return <tt>true</tt> if <tt>list</tt> contained one or more elements
891 * <tt>e</tt> such that
892 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
893 * @throws UnsupportedOperationException if the specified list or
894 * its list-iterator does not support the <tt>set</tt> operation.
895 * @since 1.4
896 */
897 public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) {
898 boolean result = false;
899 int size = list.size();
900 if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) {
901 if (oldVal==null) {
902 for (int i=0; i<size; i++) {
903 if (list.get(i)==null) {
904 list.set(i, newVal);
905 result = true;
906 }
907 }
908 } else {
909 for (int i=0; i<size; i++) {
910 if (oldVal.equals(list.get(i))) {
911 list.set(i, newVal);
912 result = true;
913 }
914 }
915 }
916 } else {
917 ListIterator<T> itr=list.listIterator();
918 if (oldVal==null) {
919 for (int i=0; i<size; i++) {
920 if (itr.next()==null) {
921 itr.set(newVal);
922 result = true;
923 }
924 }
925 } else {
926 for (int i=0; i<size; i++) {
927 if (oldVal.equals(itr.next())) {
928 itr.set(newVal);
929 result = true;
930 }
931 }
932 }
933 }
934 return result;
935 }
936
937 /**
938 * Returns the starting position of the first occurrence of the specified
939 * target list within the specified source list, or -1 if there is no
940 * such occurrence. More formally, returns the lowest index <tt>i</tt>
941 * such that {@code source.subList(i, i+target.size()).equals(target)},
942 * or -1 if there is no such index. (Returns -1 if
943 * {@code target.size() > source.size()})
944 *
945 * <p>This implementation uses the "brute force" technique of scanning
946 * over the source list, looking for a match with the target at each
947 * location in turn.
948 *
949 * @param source the list in which to search for the first occurrence
950 * of <tt>target</tt>.
951 * @param target the list to search for as a subList of <tt>source</tt>.
952 * @return the starting position of the first occurrence of the specified
953 * target list within the specified source list, or -1 if there
954 * is no such occurrence.
955 * @since 1.4
956 */
957 public static int indexOfSubList(List<?> source, List<?> target) {
958 int sourceSize = source.size();
959 int targetSize = target.size();
960 int maxCandidate = sourceSize - targetSize;
961
962 if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
963 (source instanceof RandomAccess&&target instanceof RandomAccess)) {
964 nextCand:
965 for (int candidate = 0; candidate <= maxCandidate; candidate++) {
966 for (int i=0, j=candidate; i<targetSize; i++, j++)
967 if (!eq(target.get(i), source.get(j)))
968 continue nextCand; // Element mismatch, try next cand
969 return candidate; // All elements of candidate matched target
970 }
971 } else { // Iterator version of above algorithm
972 ListIterator<?> si = source.listIterator();
973 nextCand:
974 for (int candidate = 0; candidate <= maxCandidate; candidate++) {
975 ListIterator<?> ti = target.listIterator();
976 for (int i=0; i<targetSize; i++) {
977 if (!eq(ti.next(), si.next())) {
978 // Back up source iterator to next candidate
979 for (int j=0; j<i; j++)
980 si.previous();
981 continue nextCand;
982 }
983 }
984 return candidate;
985 }
986 }
987 return -1; // No candidate matched the target
988 }
989
990 /**
991 * Returns the starting position of the last occurrence of the specified
992 * target list within the specified source list, or -1 if there is no such
993 * occurrence. More formally, returns the highest index <tt>i</tt>
994 * such that {@code source.subList(i, i+target.size()).equals(target)},
995 * or -1 if there is no such index. (Returns -1 if
996 * {@code target.size() > source.size()})
997 *
998 * <p>This implementation uses the "brute force" technique of iterating
999 * over the source list, looking for a match with the target at each
1000 * location in turn.
1001 *
1002 * @param source the list in which to search for the last occurrence
1003 * of <tt>target</tt>.
1004 * @param target the list to search for as a subList of <tt>source</tt>.
1005 * @return the starting position of the last occurrence of the specified
1006 * target list within the specified source list, or -1 if there
1007 * is no such occurrence.
1008 * @since 1.4
1009 */
1010 public static int lastIndexOfSubList(List<?> source, List<?> target) {
1011 int sourceSize = source.size();
1012 int targetSize = target.size();
1013 int maxCandidate = sourceSize - targetSize;
1014
1015 if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
1016 source instanceof RandomAccess) { // Index access version
1017 nextCand:
1018 for (int candidate = maxCandidate; candidate >= 0; candidate--) {
1019 for (int i=0, j=candidate; i<targetSize; i++, j++)
1020 if (!eq(target.get(i), source.get(j)))
1021 continue nextCand; // Element mismatch, try next cand
1022 return candidate; // All elements of candidate matched target
1023 }
1024 } else { // Iterator version of above algorithm
1025 if (maxCandidate < 0)
1026 return -1;
1027 ListIterator<?> si = source.listIterator(maxCandidate);
1028 nextCand:
1029 for (int candidate = maxCandidate; candidate >= 0; candidate--) {
1030 ListIterator<?> ti = target.listIterator();
1031 for (int i=0; i<targetSize; i++) {
1032 if (!eq(ti.next(), si.next())) {
1033 if (candidate != 0) {
1034 // Back up source iterator to next candidate
1035 for (int j=0; j<=i+1; j++)
1036 si.previous();
1037 }
1038 continue nextCand;
1039 }
1040 }
1041 return candidate;
1042 }
1043 }
1044 return -1; // No candidate matched the target
1045 }
1046
1047
1048 // Unmodifiable Wrappers
1049
1050 /**
1051 * Returns an unmodifiable view of the specified collection. This method
1052 * allows modules to provide users with "read-only" access to internal
1053 * collections. Query operations on the returned collection "read through"
1054 * to the specified collection, and attempts to modify the returned
1055 * collection, whether direct or via its iterator, result in an
1056 * <tt>UnsupportedOperationException</tt>.<p>
1057 *
1058 * The returned collection does <i>not</i> pass the hashCode and equals
1059 * operations through to the backing collection, but relies on
1060 * <tt>Object</tt>'s <tt>equals</tt> and <tt>hashCode</tt> methods. This
1061 * is necessary to preserve the contracts of these operations in the case
1062 * that the backing collection is a set or a list.<p>
1063 *
1064 * The returned collection will be serializable if the specified collection
1065 * is serializable.
1066 *
1067 * @param <T> the class of the objects in the collection
1068 * @param c the collection for which an unmodifiable view is to be
1069 * returned.
1070 * @return an unmodifiable view of the specified collection.
1071 */
1072 public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) {
1073 return new UnmodifiableCollection<>(c);
1074 }
1075
1076 /**
1077 * @serial include
1078 */
1079 static class UnmodifiableCollection<E> implements Collection<E>, Serializable {
1080 private static final long serialVersionUID = 1820017752578914078L;
1081
1082 final Collection<? extends E> c;
1083
1084 UnmodifiableCollection(Collection<? extends E> c) {
1085 if (c==null)
1086 throw new NullPointerException();
1087 this.c = c;
1088 }
1089
1090 public int size() {return c.size();}
1091 public boolean isEmpty() {return c.isEmpty();}
1092 public boolean contains(Object o) {return c.contains(o);}
1093 public Object[] toArray() {return c.toArray();}
1094 public <T> T[] toArray(T[] a) {return c.toArray(a);}
1095 public String toString() {return c.toString();}
1096
1097 public Iterator<E> iterator() {
1098 return new Iterator<E>() {
1099 private final Iterator<? extends E> i = c.iterator();
1100
1101 public boolean hasNext() {return i.hasNext();}
1102 public E next() {return i.next();}
1103 public void remove() {
1104 throw new UnsupportedOperationException();
1105 }
1106 @Override
1107 public void forEachRemaining(Consumer<? super E> action) {
1108 // Use backing collection version
1109 i.forEachRemaining(action);
1110 }
1111 };
1112 }
1113
1114 public boolean add(E e) {
1115 throw new UnsupportedOperationException();
1116 }
1117 public boolean remove(Object o) {
1118 throw new UnsupportedOperationException();
1119 }
1120
1121 public boolean containsAll(Collection<?> coll) {
1122 return c.containsAll(coll);
1123 }
1124 public boolean addAll(Collection<? extends E> coll) {
1125 throw new UnsupportedOperationException();
1126 }
1127 public boolean removeAll(Collection<?> coll) {
1128 throw new UnsupportedOperationException();
1129 }
1130 public boolean retainAll(Collection<?> coll) {
1131 throw new UnsupportedOperationException();
1132 }
1133 public void clear() {
1134 throw new UnsupportedOperationException();
1135 }
1136
1137 // Override default methods in Collection
1138 @Override
1139 public void forEach(Consumer<? super E> action) {
1140 c.forEach(action);
1141 }
1142 @Override
1143 public boolean removeAll(Predicate<? super E> filter) {
1144 throw new UnsupportedOperationException();
1145 }
1146 @SuppressWarnings("unchecked")
1147 @Override
1148 public Spliterator<E> spliterator() {
1149 return (Spliterator<E>)c.spliterator();
1150 }
1151 @SuppressWarnings("unchecked")
1152 @Override
1153 public Stream<E> stream() {
1154 return (Stream<E>)c.stream();
1155 }
1156 @SuppressWarnings("unchecked")
1157 @Override
1158 public Stream<E> parallelStream() {
1159 return (Stream<E>)c.parallelStream();
1160 }
1161 }
1162
1163 /**
1164 * Returns an unmodifiable view of the specified set. This method allows
1165 * modules to provide users with "read-only" access to internal sets.
1166 * Query operations on the returned set "read through" to the specified
1167 * set, and attempts to modify the returned set, whether direct or via its
1168 * iterator, result in an <tt>UnsupportedOperationException</tt>.<p>
1169 *
1170 * The returned set will be serializable if the specified set
1171 * is serializable.
1172 *
1173 * @param <T> the class of the objects in the set
1174 * @param s the set for which an unmodifiable view is to be returned.
1175 * @return an unmodifiable view of the specified set.
1176 */
1177 public static <T> Set<T> unmodifiableSet(Set<? extends T> s) {
1178 return new UnmodifiableSet<>(s);
1179 }
1180
1181 /**
1182 * @serial include
1183 */
1184 static class UnmodifiableSet<E> extends UnmodifiableCollection<E>
1185 implements Set<E>, Serializable {
1186 private static final long serialVersionUID = -9215047833775013803L;
1187
1188 UnmodifiableSet(Set<? extends E> s) {super(s);}
1189 public boolean equals(Object o) {return o == this || c.equals(o);}
1190 public int hashCode() {return c.hashCode();}
1191 }
1192
1193 /**
1194 * Returns an unmodifiable view of the specified sorted set. This method
1195 * allows modules to provide users with "read-only" access to internal
1196 * sorted sets. Query operations on the returned sorted set "read
1197 * through" to the specified sorted set. Attempts to modify the returned
1198 * sorted set, whether direct, via its iterator, or via its
1199 * <tt>subSet</tt>, <tt>headSet</tt>, or <tt>tailSet</tt> views, result in
1200 * an <tt>UnsupportedOperationException</tt>.<p>
1201 *
1202 * The returned sorted set will be serializable if the specified sorted set
1203 * is serializable.
1204 *
1205 * @param <T> the class of the objects in the set
1206 * @param s the sorted set for which an unmodifiable view is to be
1207 * returned.
1208 * @return an unmodifiable view of the specified sorted set.
1209 */
1210 public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) {
1211 return new UnmodifiableSortedSet<>(s);
1212 }
1213
1214 /**
1215 * @serial include
1216 */
1217 static class UnmodifiableSortedSet<E>
1218 extends UnmodifiableSet<E>
1219 implements SortedSet<E>, Serializable {
1220 private static final long serialVersionUID = -4929149591599911165L;
1221 private final SortedSet<E> ss;
1222
1223 UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;}
1224
1225 public Comparator<? super E> comparator() {return ss.comparator();}
1226
1227 public SortedSet<E> subSet(E fromElement, E toElement) {
1228 return new UnmodifiableSortedSet<>(ss.subSet(fromElement,toElement));
1229 }
1230 public SortedSet<E> headSet(E toElement) {
1231 return new UnmodifiableSortedSet<>(ss.headSet(toElement));
1232 }
1233 public SortedSet<E> tailSet(E fromElement) {
1234 return new UnmodifiableSortedSet<>(ss.tailSet(fromElement));
1235 }
1236
1237 public E first() {return ss.first();}
1238 public E last() {return ss.last();}
1239 }
1240
1241 /**
1242 * Returns an unmodifiable view of the specified navigable set. This method
1243 * allows modules to provide users with "read-only" access to internal
1244 * navigable sets. Query operations on the returned navigable set "read
1245 * through" to the specified navigable set. Attempts to modify the returned
1246 * navigable set, whether direct, via its iterator, or via its
1247 * {@code subSet}, {@code headSet}, or {@code tailSet} views, result in
1248 * an {@code UnsupportedOperationException}.<p>
1249 *
1250 * The returned navigable set will be serializable if the specified
1251 * navigable set is serializable.
1252 *
1253 * @param <T> the class of the objects in the set
1254 * @param s the navigable set for which an unmodifiable view is to be
1255 * returned
1256 * @return an unmodifiable view of the specified navigable set
1257 * @since 1.8
1258 */
1259 public static <T> NavigableSet<T> unmodifiableNavigableSet(NavigableSet<T> s) {
1260 return new UnmodifiableNavigableSet<>(s);
1261 }
1262
1263 /**
1264 * Wraps a navigable set and disables all of the mutative operations.
1265 *
1266 * @param <E> type of elements
1267 * @serial include
1268 */
1269 static class UnmodifiableNavigableSet<E>
1270 extends UnmodifiableSortedSet<E>
1271 implements NavigableSet<E>, Serializable {
1272
1273 private static final long serialVersionUID = -6027448201786391929L;
1274
1275 /**
1276 * A singleton empty unmodifiable navigable set used for
1277 * {@link #emptyNavigableSet()}.
1278 *
1279 * @param <E> type of elements, if there were any, and bounds
1280 */
1281 private static class EmptyNavigableSet<E> extends UnmodifiableNavigableSet<E>
1282 implements Serializable {
1283 private static final long serialVersionUID = -6291252904449939134L;
1284
1285 public EmptyNavigableSet() {
1286 super(new TreeSet<E>());
1287 }
1288
1289 private Object readResolve() { return EMPTY_NAVIGABLE_SET; }
1290 }
1291
1292 @SuppressWarnings("rawtypes")
1293 private static final NavigableSet<?> EMPTY_NAVIGABLE_SET =
1294 new EmptyNavigableSet<>();
1295
1296 /**
1297 * The instance we are protecting.
1298 */
1299 private final NavigableSet<E> ns;
1300
1301 UnmodifiableNavigableSet(NavigableSet<E> s) {super(s); ns = s;}
1302
1303 public E lower(E e) { return ns.lower(e); }
1304 public E floor(E e) { return ns.floor(e); }
1305 public E ceiling(E e) { return ns.ceiling(e); }
1306 public E higher(E e) { return ns.higher(e); }
1307 public E pollFirst() { throw new UnsupportedOperationException(); }
1308 public E pollLast() { throw new UnsupportedOperationException(); }
1309 public NavigableSet<E> descendingSet()
1310 { return new UnmodifiableNavigableSet<>(ns.descendingSet()); }
1311 public Iterator<E> descendingIterator()
1312 { return descendingSet().iterator(); }
1313
1314 public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
1315 return new UnmodifiableNavigableSet<>(
1316 ns.subSet(fromElement, fromInclusive, toElement, toInclusive));
1317 }
1318
1319 public NavigableSet<E> headSet(E toElement, boolean inclusive) {
1320 return new UnmodifiableNavigableSet<>(
1321 ns.headSet(toElement, inclusive));
1322 }
1323
1324 public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
1325 return new UnmodifiableNavigableSet<>(
1326 ns.tailSet(fromElement, inclusive));
1327 }
1328 }
1329
1330 /**
1331 * Returns an unmodifiable view of the specified list. This method allows
1332 * modules to provide users with "read-only" access to internal
1333 * lists. Query operations on the returned list "read through" to the
1334 * specified list, and attempts to modify the returned list, whether
1335 * direct or via its iterator, result in an
1336 * <tt>UnsupportedOperationException</tt>.<p>
1337 *
1338 * The returned list will be serializable if the specified list
1339 * is serializable. Similarly, the returned list will implement
1340 * {@link RandomAccess} if the specified list does.
1341 *
1342 * @param <T> the class of the objects in the list
1343 * @param list the list for which an unmodifiable view is to be returned.
1344 * @return an unmodifiable view of the specified list.
1345 */
1346 public static <T> List<T> unmodifiableList(List<? extends T> list) {
1347 return (list instanceof RandomAccess ?
1348 new UnmodifiableRandomAccessList<>(list) :
1349 new UnmodifiableList<>(list));
1350 }
1351
1352 /**
1353 * @serial include
1354 */
1355 static class UnmodifiableList<E> extends UnmodifiableCollection<E>
1356 implements List<E> {
1357 private static final long serialVersionUID = -283967356065247728L;
1358
1359 final List<? extends E> list;
1360
1361 UnmodifiableList(List<? extends E> list) {
1362 super(list);
1363 this.list = list;
1364 }
1365
1366 public boolean equals(Object o) {return o == this || list.equals(o);}
1367 public int hashCode() {return list.hashCode();}
1368
1369 public E get(int index) {return list.get(index);}
1370 public E set(int index, E element) {
1371 throw new UnsupportedOperationException();
1372 }
1373 public void add(int index, E element) {
1374 throw new UnsupportedOperationException();
1375 }
1376 public E remove(int index) {
1377 throw new UnsupportedOperationException();
1378 }
1379 public int indexOf(Object o) {return list.indexOf(o);}
1380 public int lastIndexOf(Object o) {return list.lastIndexOf(o);}
1381 public boolean addAll(int index, Collection<? extends E> c) {
1382 throw new UnsupportedOperationException();
1383 }
1384
1385 @Override
1386 public void replaceAll(UnaryOperator<E> operator) {
1387 throw new UnsupportedOperationException();
1388 }
1389 @Override
1390 public void sort(Comparator<? super E> c) {
1391 throw new UnsupportedOperationException();
1392 }
1393
1394 public ListIterator<E> listIterator() {return listIterator(0);}
1395
1396 public ListIterator<E> listIterator(final int index) {
1397 return new ListIterator<E>() {
1398 private final ListIterator<? extends E> i
1399 = list.listIterator(index);
1400
1401 public boolean hasNext() {return i.hasNext();}
1402 public E next() {return i.next();}
1403 public boolean hasPrevious() {return i.hasPrevious();}
1404 public E previous() {return i.previous();}
1405 public int nextIndex() {return i.nextIndex();}
1406 public int previousIndex() {return i.previousIndex();}
1407
1408 public void remove() {
1409 throw new UnsupportedOperationException();
1410 }
1411 public void set(E e) {
1412 throw new UnsupportedOperationException();
1413 }
1414 public void add(E e) {
1415 throw new UnsupportedOperationException();
1416 }
1417
1418 @Override
1419 public void forEachRemaining(Consumer<? super E> action) {
1420 i.forEachRemaining(action);
1421 }
1422 };
1423 }
1424
1425 public List<E> subList(int fromIndex, int toIndex) {
1426 return new UnmodifiableList<>(list.subList(fromIndex, toIndex));
1427 }
1428
1429 /**
1430 * UnmodifiableRandomAccessList instances are serialized as
1431 * UnmodifiableList instances to allow them to be deserialized
1432 * in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList).
1433 * This method inverts the transformation. As a beneficial
1434 * side-effect, it also grafts the RandomAccess marker onto
1435 * UnmodifiableList instances that were serialized in pre-1.4 JREs.
1436 *
1437 * Note: Unfortunately, UnmodifiableRandomAccessList instances
1438 * serialized in 1.4.1 and deserialized in 1.4 will become
1439 * UnmodifiableList instances, as this method was missing in 1.4.
1440 */
1441 private Object readResolve() {
1442 return (list instanceof RandomAccess
1443 ? new UnmodifiableRandomAccessList<>(list)
1444 : this);
1445 }
1446 }
1447
1448 /**
1449 * @serial include
1450 */
1451 static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E>
1452 implements RandomAccess
1453 {
1454 UnmodifiableRandomAccessList(List<? extends E> list) {
1455 super(list);
1456 }
1457
1458 public List<E> subList(int fromIndex, int toIndex) {
1459 return new UnmodifiableRandomAccessList<>(
1460 list.subList(fromIndex, toIndex));
1461 }
1462
1463 private static final long serialVersionUID = -2542308836966382001L;
1464
1465 /**
1466 * Allows instances to be deserialized in pre-1.4 JREs (which do
1467 * not have UnmodifiableRandomAccessList). UnmodifiableList has
1468 * a readResolve method that inverts this transformation upon
1469 * deserialization.
1470 */
1471 private Object writeReplace() {
1472 return new UnmodifiableList<>(list);
1473 }
1474 }
1475
1476 /**
1477 * Returns an unmodifiable view of the specified map. This method
1478 * allows modules to provide users with "read-only" access to internal
1479 * maps. Query operations on the returned map "read through"
1480 * to the specified map, and attempts to modify the returned
1481 * map, whether direct or via its collection views, result in an
1482 * <tt>UnsupportedOperationException</tt>.<p>
1483 *
1484 * The returned map will be serializable if the specified map
1485 * is serializable.
1486 *
1487 * @param <K> the class of the map keys
1488 * @param <V> the class of the map values
1489 * @param m the map for which an unmodifiable view is to be returned.
1490 * @return an unmodifiable view of the specified map.
1491 */
1492 public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) {
1493 return new UnmodifiableMap<>(m);
1494 }
1495
1496 /**
1497 * @serial include
1498 */
1499 private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable {
1500 private static final long serialVersionUID = -1034234728574286014L;
1501
1502 private final Map<? extends K, ? extends V> m;
1503
1504 UnmodifiableMap(Map<? extends K, ? extends V> m) {
1505 if (m==null)
1506 throw new NullPointerException();
1507 this.m = m;
1508 }
1509
1510 public int size() {return m.size();}
1511 public boolean isEmpty() {return m.isEmpty();}
1512 public boolean containsKey(Object key) {return m.containsKey(key);}
1513 public boolean containsValue(Object val) {return m.containsValue(val);}
1514 public V get(Object key) {return m.get(key);}
1515
1516 public V put(K key, V value) {
1517 throw new UnsupportedOperationException();
1518 }
1519 public V remove(Object key) {
1520 throw new UnsupportedOperationException();
1521 }
1522 public void putAll(Map<? extends K, ? extends V> m) {
1523 throw new UnsupportedOperationException();
1524 }
1525 public void clear() {
1526 throw new UnsupportedOperationException();
1527 }
1528
1529 private transient Set<K> keySet = null;
1530 private transient Set<Map.Entry<K,V>> entrySet = null;
1531 private transient Collection<V> values = null;
1532
1533 public Set<K> keySet() {
1534 if (keySet==null)
1535 keySet = unmodifiableSet(m.keySet());
1536 return keySet;
1537 }
1538
1539 public Set<Map.Entry<K,V>> entrySet() {
1540 if (entrySet==null)
1541 entrySet = new UnmodifiableEntrySet<>(m.entrySet());
1542 return entrySet;
1543 }
1544
1545 public Collection<V> values() {
1546 if (values==null)
1547 values = unmodifiableCollection(m.values());
1548 return values;
1549 }
1550
1551 public boolean equals(Object o) {return o == this || m.equals(o);}
1552 public int hashCode() {return m.hashCode();}
1553 public String toString() {return m.toString();}
1554
1555 // Override default methods in Map
1556 @Override
1557 @SuppressWarnings("unchecked")
1558 public V getOrDefault(Object k, V defaultValue) {
1559 // Safe cast as we don't change the value
1560 return ((Map<K, V>)m).getOrDefault(k, defaultValue);
1561 }
1562
1563 @Override
1564 public void forEach(BiConsumer<? super K, ? super V> action) {
1565 m.forEach(action);
1566 }
1567
1568 @Override
1569 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
1570 throw new UnsupportedOperationException();
1571 }
1572
1573 @Override
1574 public V putIfAbsent(K key, V value) {
1575 throw new UnsupportedOperationException();
1576 }
1577
1578 @Override
1579 public boolean remove(Object key, Object value) {
1580 throw new UnsupportedOperationException();
1581 }
1582
1583 @Override
1584 public boolean replace(K key, V oldValue, V newValue) {
1585 throw new UnsupportedOperationException();
1586 }
1587
1588 @Override
1589 public V replace(K key, V value) {
1590 throw new UnsupportedOperationException();
1591 }
1592
1593 @Override
1594 public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
1595 throw new UnsupportedOperationException();
1596 }
1597
1598 @Override
1599 public V computeIfPresent(K key,
1600 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1601 throw new UnsupportedOperationException();
1602 }
1603
1604 @Override
1605 public V compute(K key,
1606 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1607 throw new UnsupportedOperationException();
1608 }
1609
1610 @Override
1611 public V merge(K key, V value,
1612 BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
1613 throw new UnsupportedOperationException();
1614 }
1615
1616 /**
1617 * We need this class in addition to UnmodifiableSet as
1618 * Map.Entries themselves permit modification of the backing Map
1619 * via their setValue operation. This class is subtle: there are
1620 * many possible attacks that must be thwarted.
1621 *
1622 * @serial include
1623 */
1624 static class UnmodifiableEntrySet<K,V>
1625 extends UnmodifiableSet<Map.Entry<K,V>> {
1626 private static final long serialVersionUID = 7854390611657943733L;
1627
1628 @SuppressWarnings({"unchecked", "rawtypes"})
1629 UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) {
1630 // Need to cast to raw in order to work around a limitation in the type system
1631 super((Set)s);
1632 }
1633
1634 static <K, V> Consumer<Map.Entry<K, V>> entryConsumer(Consumer<? super Entry<K, V>> action) {
1635 return e -> action.accept(new UnmodifiableEntry<>(e));
1636 }
1637
1638 public void forEach(Consumer<? super Entry<K, V>> action) {
1639 Objects.requireNonNull(action);
1640 c.forEach(entryConsumer(action));
1641 }
1642
1643 static final class UnmodifiableEntrySetSpliterator<K, V>
1644 implements Spliterator<Entry<K,V>> {
1645 final Spliterator<Map.Entry<K, V>> s;
1646
1647 UnmodifiableEntrySetSpliterator(Spliterator<Entry<K, V>> s) {
1648 this.s = s;
1649 }
1650
1651 @Override
1652 public boolean tryAdvance(Consumer<? super Entry<K, V>> action) {
1653 Objects.requireNonNull(action);
1654 return s.tryAdvance(entryConsumer(action));
1655 }
1656
1657 @Override
1658 public void forEachRemaining(Consumer<? super Entry<K, V>> action) {
1659 Objects.requireNonNull(action);
1660 s.forEachRemaining(entryConsumer(action));
1661 }
1662
1663 @Override
1664 public Spliterator<Entry<K, V>> trySplit() {
1665 Spliterator<Entry<K, V>> split = s.trySplit();
1666 return split == null
1667 ? null
1668 : new UnmodifiableEntrySetSpliterator<>(split);
1669 }
1670
1671 @Override
1672 public long estimateSize() {
1673 return s.estimateSize();
1674 }
1675
1676 @Override
1677 public long getExactSizeIfKnown() {
1678 return s.getExactSizeIfKnown();
1679 }
1680
1681 @Override
1682 public int characteristics() {
1683 return s.characteristics();
1684 }
1685
1686 @Override
1687 public boolean hasCharacteristics(int characteristics) {
1688 return s.hasCharacteristics(characteristics);
1689 }
1690
1691 @Override
1692 public Comparator<? super Entry<K, V>> getComparator() {
1693 return s.getComparator();
1694 }
1695 }
1696
1697 @SuppressWarnings("unchecked")
1698 public Spliterator<Entry<K,V>> spliterator() {
1699 return new UnmodifiableEntrySetSpliterator<>(
1700 (Spliterator<Map.Entry<K, V>>) c.spliterator());
1701 }
1702
1703 @Override
1704 public Stream<Entry<K,V>> stream() {
1705 return StreamSupport.stream(spliterator(), false);
1706 }
1707
1708 @Override
1709 public Stream<Entry<K,V>> parallelStream() {
1710 return StreamSupport.stream(spliterator(), true);
1711 }
1712
1713 public Iterator<Map.Entry<K,V>> iterator() {
1714 return new Iterator<Map.Entry<K,V>>() {
1715 private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator();
1716
1717 public boolean hasNext() {
1718 return i.hasNext();
1719 }
1720 public Map.Entry<K,V> next() {
1721 return new UnmodifiableEntry<>(i.next());
1722 }
1723 public void remove() {
1724 throw new UnsupportedOperationException();
1725 }
1726 };
1727 }
1728
1729 @SuppressWarnings("unchecked")
1730 public Object[] toArray() {
1731 Object[] a = c.toArray();
1732 for (int i=0; i<a.length; i++)
1733 a[i] = new UnmodifiableEntry<>((Map.Entry<? extends K, ? extends V>)a[i]);
1734 return a;
1735 }
1736
1737 @SuppressWarnings("unchecked")
1738 public <T> T[] toArray(T[] a) {
1739 // We don't pass a to c.toArray, to avoid window of
1740 // vulnerability wherein an unscrupulous multithreaded client
1741 // could get his hands on raw (unwrapped) Entries from c.
1742 Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
1743
1744 for (int i=0; i<arr.length; i++)
1745 arr[i] = new UnmodifiableEntry<>((Map.Entry<? extends K, ? extends V>)arr[i]);
1746
1747 if (arr.length > a.length)
1748 return (T[])arr;
1749
1750 System.arraycopy(arr, 0, a, 0, arr.length);
1751 if (a.length > arr.length)
1752 a[arr.length] = null;
1753 return a;
1754 }
1755
1756 /**
1757 * This method is overridden to protect the backing set against
1758 * an object with a nefarious equals function that senses
1759 * that the equality-candidate is Map.Entry and calls its
1760 * setValue method.
1761 */
1762 public boolean contains(Object o) {
1763 if (!(o instanceof Map.Entry))
1764 return false;
1765 return c.contains(
1766 new UnmodifiableEntry<>((Map.Entry<?,?>) o));
1767 }
1768
1769 /**
1770 * The next two methods are overridden to protect against
1771 * an unscrupulous List whose contains(Object o) method senses
1772 * when o is a Map.Entry, and calls o.setValue.
1773 */
1774 public boolean containsAll(Collection<?> coll) {
1775 for (Object e : coll) {
1776 if (!contains(e)) // Invokes safe contains() above
1777 return false;
1778 }
1779 return true;
1780 }
1781 public boolean equals(Object o) {
1782 if (o == this)
1783 return true;
1784
1785 if (!(o instanceof Set))
1786 return false;
1787 Set<?> s = (Set<?>) o;
1788 if (s.size() != c.size())
1789 return false;
1790 return containsAll(s); // Invokes safe containsAll() above
1791 }
1792
1793 /**
1794 * This "wrapper class" serves two purposes: it prevents
1795 * the client from modifying the backing Map, by short-circuiting
1796 * the setValue method, and it protects the backing Map against
1797 * an ill-behaved Map.Entry that attempts to modify another
1798 * Map Entry when asked to perform an equality check.
1799 */
1800 private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> {
1801 private Map.Entry<? extends K, ? extends V> e;
1802
1803 UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e)
1804 {this.e = Objects.requireNonNull(e);}
1805
1806 public K getKey() {return e.getKey();}
1807 public V getValue() {return e.getValue();}
1808 public V setValue(V value) {
1809 throw new UnsupportedOperationException();
1810 }
1811 public int hashCode() {return e.hashCode();}
1812 public boolean equals(Object o) {
1813 if (this == o)
1814 return true;
1815 if (!(o instanceof Map.Entry))
1816 return false;
1817 Map.Entry<?,?> t = (Map.Entry<?,?>)o;
1818 return eq(e.getKey(), t.getKey()) &&
1819 eq(e.getValue(), t.getValue());
1820 }
1821 public String toString() {return e.toString();}
1822 }
1823 }
1824 }
1825
1826 /**
1827 * Returns an unmodifiable view of the specified sorted map. This method
1828 * allows modules to provide users with "read-only" access to internal
1829 * sorted maps. Query operations on the returned sorted map "read through"
1830 * to the specified sorted map. Attempts to modify the returned
1831 * sorted map, whether direct, via its collection views, or via its
1832 * <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in
1833 * an <tt>UnsupportedOperationException</tt>.<p>
1834 *
1835 * The returned sorted map will be serializable if the specified sorted map
1836 * is serializable.
1837 *
1838 * @param <K> the class of the map keys
1839 * @param <V> the class of the map values
1840 * @param m the sorted map for which an unmodifiable view is to be
1841 * returned.
1842 * @return an unmodifiable view of the specified sorted map.
1843 */
1844 public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) {
1845 return new UnmodifiableSortedMap<>(m);
1846 }
1847
1848 /**
1849 * @serial include
1850 */
1851 static class UnmodifiableSortedMap<K,V>
1852 extends UnmodifiableMap<K,V>
1853 implements SortedMap<K,V>, Serializable {
1854 private static final long serialVersionUID = -8806743815996713206L;
1855
1856 private final SortedMap<K, ? extends V> sm;
1857
1858 UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m; }
1859 public Comparator<? super K> comparator() { return sm.comparator(); }
1860 public SortedMap<K,V> subMap(K fromKey, K toKey)
1861 { return new UnmodifiableSortedMap<>(sm.subMap(fromKey, toKey)); }
1862 public SortedMap<K,V> headMap(K toKey)
1863 { return new UnmodifiableSortedMap<>(sm.headMap(toKey)); }
1864 public SortedMap<K,V> tailMap(K fromKey)
1865 { return new UnmodifiableSortedMap<>(sm.tailMap(fromKey)); }
1866 public K firstKey() { return sm.firstKey(); }
1867 public K lastKey() { return sm.lastKey(); }
1868 }
1869
1870 /**
1871 * Returns an unmodifiable view of the specified navigable map. This method
1872 * allows modules to provide users with "read-only" access to internal
1873 * navigable maps. Query operations on the returned navigable map "read
1874 * through" to the specified navigable map. Attempts to modify the returned
1875 * navigable map, whether direct, via its collection views, or via its
1876 * {@code subMap}, {@code headMap}, or {@code tailMap} views, result in
1877 * an {@code UnsupportedOperationException}.<p>
1878 *
1879 * The returned navigable map will be serializable if the specified
1880 * navigable map is serializable.
1881 *
1882 * @param <K> the class of the map keys
1883 * @param <V> the class of the map values
1884 * @param m the navigable map for which an unmodifiable view is to be
1885 * returned
1886 * @return an unmodifiable view of the specified navigable map
1887 * @since 1.8
1888 */
1889 public static <K,V> NavigableMap<K,V> unmodifiableNavigableMap(NavigableMap<K, ? extends V> m) {
1890 return new UnmodifiableNavigableMap<>(m);
1891 }
1892
1893 /**
1894 * @serial include
1895 */
1896 static class UnmodifiableNavigableMap<K,V>
1897 extends UnmodifiableSortedMap<K,V>
1898 implements NavigableMap<K,V>, Serializable {
1899 private static final long serialVersionUID = -4858195264774772197L;
1900
1901 /**
1902 * A class for the {@link EMPTY_NAVIGABLE_MAP} which needs readResolve
1903 * to preserve singleton property.
1904 *
1905 * @param <K> type of keys, if there were any, and of bounds
1906 * @param <V> type of values, if there were any
1907 */
1908 private static class EmptyNavigableMap<K,V> extends UnmodifiableNavigableMap<K,V>
1909 implements Serializable {
1910
1911 private static final long serialVersionUID = -2239321462712562324L;
1912
1913 EmptyNavigableMap() { super(new TreeMap<K,V>()); }
1914
1915 @Override
1916 public NavigableSet<K> navigableKeySet()
1917 { return emptyNavigableSet(); }
1918
1919 private Object readResolve() { return EMPTY_NAVIGABLE_MAP; }
1920 }
1921
1922 /**
1923 * Singleton for {@link emptyNavigableMap()} which is also immutable.
1924 */
1925 private static final EmptyNavigableMap<?,?> EMPTY_NAVIGABLE_MAP =
1926 new EmptyNavigableMap<>();
1927
1928 /**
1929 * The instance we wrap and protect.
1930 */
1931 private final NavigableMap<K, ? extends V> nm;
1932
1933 UnmodifiableNavigableMap(NavigableMap<K, ? extends V> m)
1934 {super(m); nm = m;}
1935
1936 public K lowerKey(K key) { return nm.lowerKey(key); }
1937 public K floorKey(K key) { return nm.floorKey(key); }
1938 public K ceilingKey(K key) { return nm.ceilingKey(key); }
1939 public K higherKey(K key) { return nm.higherKey(key); }
1940
1941 @SuppressWarnings("unchecked")
1942 public Entry<K, V> lowerEntry(K key) {
1943 Entry<K,V> lower = (Entry<K, V>) nm.lowerEntry(key);
1944 return (null != lower)
1945 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(lower)
1946 : null;
1947 }
1948
1949 @SuppressWarnings("unchecked")
1950 public Entry<K, V> floorEntry(K key) {
1951 Entry<K,V> floor = (Entry<K, V>) nm.floorEntry(key);
1952 return (null != floor)
1953 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(floor)
1954 : null;
1955 }
1956
1957 @SuppressWarnings("unchecked")
1958 public Entry<K, V> ceilingEntry(K key) {
1959 Entry<K,V> ceiling = (Entry<K, V>) nm.ceilingEntry(key);
1960 return (null != ceiling)
1961 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(ceiling)
1962 : null;
1963 }
1964
1965
1966 @SuppressWarnings("unchecked")
1967 public Entry<K, V> higherEntry(K key) {
1968 Entry<K,V> higher = (Entry<K, V>) nm.higherEntry(key);
1969 return (null != higher)
1970 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(higher)
1971 : null;
1972 }
1973
1974 @SuppressWarnings("unchecked")
1975 public Entry<K, V> firstEntry() {
1976 Entry<K,V> first = (Entry<K, V>) nm.firstEntry();
1977 return (null != first)
1978 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(first)
1979 : null;
1980 }
1981
1982 @SuppressWarnings("unchecked")
1983 public Entry<K, V> lastEntry() {
1984 Entry<K,V> last = (Entry<K, V>) nm.lastEntry();
1985 return (null != last)
1986 ? new UnmodifiableEntrySet.UnmodifiableEntry<>(last)
1987 : null;
1988 }
1989
1990 public Entry<K, V> pollFirstEntry()
1991 { throw new UnsupportedOperationException(); }
1992 public Entry<K, V> pollLastEntry()
1993 { throw new UnsupportedOperationException(); }
1994 public NavigableMap<K, V> descendingMap()
1995 { return unmodifiableNavigableMap(nm.descendingMap()); }
1996 public NavigableSet<K> navigableKeySet()
1997 { return unmodifiableNavigableSet(nm.navigableKeySet()); }
1998 public NavigableSet<K> descendingKeySet()
1999 { return unmodifiableNavigableSet(nm.descendingKeySet()); }
2000
2001 public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
2002 return unmodifiableNavigableMap(
2003 nm.subMap(fromKey, fromInclusive, toKey, toInclusive));
2004 }
2005
2006 public NavigableMap<K, V> headMap(K toKey, boolean inclusive)
2007 { return unmodifiableNavigableMap(nm.headMap(toKey, inclusive)); }
2008 public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive)
2009 { return unmodifiableNavigableMap(nm.tailMap(fromKey, inclusive)); }
2010 }
2011
2012 // Synch Wrappers
2013
2014 /**
2015 * Returns a synchronized (thread-safe) collection backed by the specified
2016 * collection. In order to guarantee serial access, it is critical that
2017 * <strong>all</strong> access to the backing collection is accomplished
2018 * through the returned collection.<p>
2019 *
2020 * It is imperative that the user manually synchronize on the returned
2021 * collection when traversing it via {@link Iterator}, {@link Spliterator}
2022 * or {@link Stream}:
2023 * <pre>
2024 * Collection c = Collections.synchronizedCollection(myCollection);
2025 * ...
2026 * synchronized (c) {
2027 * Iterator i = c.iterator(); // Must be in the synchronized block
2028 * while (i.hasNext())
2029 * foo(i.next());
2030 * }
2031 * </pre>
2032 * Failure to follow this advice may result in non-deterministic behavior.
2033 *
2034 * <p>The returned collection does <i>not</i> pass the {@code hashCode}
2035 * and {@code equals} operations through to the backing collection, but
2036 * relies on {@code Object}'s equals and hashCode methods. This is
2037 * necessary to preserve the contracts of these operations in the case
2038 * that the backing collection is a set or a list.<p>
2039 *
2040 * The returned collection will be serializable if the specified collection
2041 * is serializable.
2042 *
2043 * @param <T> the class of the objects in the collection
2044 * @param c the collection to be "wrapped" in a synchronized collection.
2045 * @return a synchronized view of the specified collection.
2046 */
2047 public static <T> Collection<T> synchronizedCollection(Collection<T> c) {
2048 return new SynchronizedCollection<>(c);
2049 }
2050
2051 static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) {
2052 return new SynchronizedCollection<>(c, mutex);
2053 }
2054
2055 /**
2056 * @serial include
2057 */
2058 static class SynchronizedCollection<E> implements Collection<E>, Serializable {
2059 private static final long serialVersionUID = 3053995032091335093L;
2060
2061 final Collection<E> c; // Backing Collection
2062 final Object mutex; // Object on which to synchronize
2063
2064 SynchronizedCollection(Collection<E> c) {
2065 this.c = Objects.requireNonNull(c);
2066 mutex = this;
2067 }
2068
2069 SynchronizedCollection(Collection<E> c, Object mutex) {
2070 this.c = Objects.requireNonNull(c);
2071 this.mutex = Objects.requireNonNull(mutex);
2072 }
2073
2074 public int size() {
2075 synchronized (mutex) {return c.size();}
2076 }
2077 public boolean isEmpty() {
2078 synchronized (mutex) {return c.isEmpty();}
2079 }
2080 public boolean contains(Object o) {
2081 synchronized (mutex) {return c.contains(o);}
2082 }
2083 public Object[] toArray() {
2084 synchronized (mutex) {return c.toArray();}
2085 }
2086 public <T> T[] toArray(T[] a) {
2087 synchronized (mutex) {return c.toArray(a);}
2088 }
2089
2090 public Iterator<E> iterator() {
2091 return c.iterator(); // Must be manually synched by user!
2092 }
2093
2094 public boolean add(E e) {
2095 synchronized (mutex) {return c.add(e);}
2096 }
2097 public boolean remove(Object o) {
2098 synchronized (mutex) {return c.remove(o);}
2099 }
2100
2101 public boolean containsAll(Collection<?> coll) {
2102 synchronized (mutex) {return c.containsAll(coll);}
2103 }
2104 public boolean addAll(Collection<? extends E> coll) {
2105 synchronized (mutex) {return c.addAll(coll);}
2106 }
2107 public boolean removeAll(Collection<?> coll) {
2108 synchronized (mutex) {return c.removeAll(coll);}
2109 }
2110 public boolean retainAll(Collection<?> coll) {
2111 synchronized (mutex) {return c.retainAll(coll);}
2112 }
2113 public void clear() {
2114 synchronized (mutex) {c.clear();}
2115 }
2116 public String toString() {
2117 synchronized (mutex) {return c.toString();}
2118 }
2119 // Override default methods in Collection
2120 @Override
2121 public void forEach(Consumer<? super E> consumer) {
2122 synchronized (mutex) {c.forEach(consumer);}
2123 }
2124 @Override
2125 public boolean removeAll(Predicate<? super E> filter) {
2126 synchronized (mutex) {return c.removeAll(filter);}
2127 }
2128 @Override
2129 public Spliterator<E> spliterator() {
2130 return c.spliterator(); // Must be manually synched by user!
2131 }
2132 @Override
2133 public Stream<E> stream() {
2134 return c.stream(); // Must be manually synched by user!
2135 }
2136 @Override
2137 public Stream<E> parallelStream() {
2138 return c.parallelStream(); // Must be manually synched by user!
2139 }
2140 private void writeObject(ObjectOutputStream s) throws IOException {
2141 synchronized (mutex) {s.defaultWriteObject();}
2142 }
2143 }
2144
2145 /**
2146 * Returns a synchronized (thread-safe) set backed by the specified
2147 * set. In order to guarantee serial access, it is critical that
2148 * <strong>all</strong> access to the backing set is accomplished
2149 * through the returned set.<p>
2150 *
2151 * It is imperative that the user manually synchronize on the returned
2152 * set when iterating over it:
2153 * <pre>
2154 * Set s = Collections.synchronizedSet(new HashSet());
2155 * ...
2156 * synchronized (s) {
2157 * Iterator i = s.iterator(); // Must be in the synchronized block
2158 * while (i.hasNext())
2159 * foo(i.next());
2160 * }
2161 * </pre>
2162 * Failure to follow this advice may result in non-deterministic behavior.
2163 *
2164 * <p>The returned set will be serializable if the specified set is
2165 * serializable.
2166 *
2167 * @param <T> the class of the objects in the set
2168 * @param s the set to be "wrapped" in a synchronized set.
2169 * @return a synchronized view of the specified set.
2170 */
2171 public static <T> Set<T> synchronizedSet(Set<T> s) {
2172 return new SynchronizedSet<>(s);
2173 }
2174
2175 static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) {
2176 return new SynchronizedSet<>(s, mutex);
2177 }
2178
2179 /**
2180 * @serial include
2181 */
2182 static class SynchronizedSet<E>
2183 extends SynchronizedCollection<E>
2184 implements Set<E> {
2185 private static final long serialVersionUID = 487447009682186044L;
2186
2187 SynchronizedSet(Set<E> s) {
2188 super(s);
2189 }
2190 SynchronizedSet(Set<E> s, Object mutex) {
2191 super(s, mutex);
2192 }
2193
2194 public boolean equals(Object o) {
2195 if (this == o)
2196 return true;
2197 synchronized (mutex) {return c.equals(o);}
2198 }
2199 public int hashCode() {
2200 synchronized (mutex) {return c.hashCode();}
2201 }
2202 }
2203
2204 /**
2205 * Returns a synchronized (thread-safe) sorted set backed by the specified
2206 * sorted set. In order to guarantee serial access, it is critical that
2207 * <strong>all</strong> access to the backing sorted set is accomplished
2208 * through the returned sorted set (or its views).<p>
2209 *
2210 * It is imperative that the user manually synchronize on the returned
2211 * sorted set when iterating over it or any of its <tt>subSet</tt>,
2212 * <tt>headSet</tt>, or <tt>tailSet</tt> views.
2213 * <pre>
2214 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
2215 * ...
2216 * synchronized (s) {
2217 * Iterator i = s.iterator(); // Must be in the synchronized block
2218 * while (i.hasNext())
2219 * foo(i.next());
2220 * }
2221 * </pre>
2222 * or:
2223 * <pre>
2224 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
2225 * SortedSet s2 = s.headSet(foo);
2226 * ...
2227 * synchronized (s) { // Note: s, not s2!!!
2228 * Iterator i = s2.iterator(); // Must be in the synchronized block
2229 * while (i.hasNext())
2230 * foo(i.next());
2231 * }
2232 * </pre>
2233 * Failure to follow this advice may result in non-deterministic behavior.
2234 *
2235 * <p>The returned sorted set will be serializable if the specified
2236 * sorted set is serializable.
2237 *
2238 * @param <T> the class of the objects in the set
2239 * @param s the sorted set to be "wrapped" in a synchronized sorted set.
2240 * @return a synchronized view of the specified sorted set.
2241 */
2242 public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) {
2243 return new SynchronizedSortedSet<>(s);
2244 }
2245
2246 /**
2247 * @serial include
2248 */
2249 static class SynchronizedSortedSet<E>
2250 extends SynchronizedSet<E>
2251 implements SortedSet<E>
2252 {
2253 private static final long serialVersionUID = 8695801310862127406L;
2254
2255 private final SortedSet<E> ss;
2256
2257 SynchronizedSortedSet(SortedSet<E> s) {
2258 super(s);
2259 ss = s;
2260 }
2261 SynchronizedSortedSet(SortedSet<E> s, Object mutex) {
2262 super(s, mutex);
2263 ss = s;
2264 }
2265
2266 public Comparator<? super E> comparator() {
2267 synchronized (mutex) {return ss.comparator();}
2268 }
2269
2270 public SortedSet<E> subSet(E fromElement, E toElement) {
2271 synchronized (mutex) {
2272 return new SynchronizedSortedSet<>(
2273 ss.subSet(fromElement, toElement), mutex);
2274 }
2275 }
2276 public SortedSet<E> headSet(E toElement) {
2277 synchronized (mutex) {
2278 return new SynchronizedSortedSet<>(ss.headSet(toElement), mutex);
2279 }
2280 }
2281 public SortedSet<E> tailSet(E fromElement) {
2282 synchronized (mutex) {
2283 return new SynchronizedSortedSet<>(ss.tailSet(fromElement),mutex);
2284 }
2285 }
2286
2287 public E first() {
2288 synchronized (mutex) {return ss.first();}
2289 }
2290 public E last() {
2291 synchronized (mutex) {return ss.last();}
2292 }
2293 }
2294
2295 /**
2296 * Returns a synchronized (thread-safe) navigable set backed by the
2297 * specified navigable set. In order to guarantee serial access, it is
2298 * critical that <strong>all</strong> access to the backing navigable set is
2299 * accomplished through the returned navigable set (or its views).<p>
2300 *
2301 * It is imperative that the user manually synchronize on the returned
2302 * navigable set when iterating over it or any of its {@code subSet},
2303 * {@code headSet}, or {@code tailSet} views.
2304 * <pre>
2305 * NavigableSet s = Collections.synchronizedNavigableSet(new TreeSet());
2306 * ...
2307 * synchronized (s) {
2308 * Iterator i = s.iterator(); // Must be in the synchronized block
2309 * while (i.hasNext())
2310 * foo(i.next());
2311 * }
2312 * </pre>
2313 * or:
2314 * <pre>
2315 * NavigableSet s = Collections.synchronizedNavigableSet(new TreeSet());
2316 * NavigableSet s2 = s.headSet(foo, true);
2317 * ...
2318 * synchronized (s) { // Note: s, not s2!!!
2319 * Iterator i = s2.iterator(); // Must be in the synchronized block
2320 * while (i.hasNext())
2321 * foo(i.next());
2322 * }
2323 * </pre>
2324 * Failure to follow this advice may result in non-deterministic behavior.
2325 *
2326 * <p>The returned navigable set will be serializable if the specified
2327 * navigable set is serializable.
2328 *
2329 * @param <T> the class of the objects in the set
2330 * @param s the navigable set to be "wrapped" in a synchronized navigable
2331 * set
2332 * @return a synchronized view of the specified navigable set
2333 * @since 1.8
2334 */
2335 public static <T> NavigableSet<T> synchronizedNavigableSet(NavigableSet<T> s) {
2336 return new SynchronizedNavigableSet<>(s);
2337 }
2338
2339 /**
2340 * @serial include
2341 */
2342 static class SynchronizedNavigableSet<E>
2343 extends SynchronizedSortedSet<E>
2344 implements NavigableSet<E>
2345 {
2346 private static final long serialVersionUID = -5505529816273629798L;
2347
2348 private final NavigableSet<E> ns;
2349
2350 SynchronizedNavigableSet(NavigableSet<E> s) {
2351 super(s);
2352 ns = s;
2353 }
2354
2355 SynchronizedNavigableSet(NavigableSet<E> s, Object mutex) {
2356 super(s, mutex);
2357 ns = s;
2358 }
2359 public E lower(E e) { synchronized (mutex) {return ns.lower(e);} }
2360 public E floor(E e) { synchronized (mutex) {return ns.floor(e);} }
2361 public E ceiling(E e) { synchronized (mutex) {return ns.ceiling(e);} }
2362 public E higher(E e) { synchronized (mutex) {return ns.higher(e);} }
2363 public E pollFirst() { synchronized (mutex) {return ns.pollFirst();} }
2364 public E pollLast() { synchronized (mutex) {return ns.pollLast();} }
2365
2366 public NavigableSet<E> descendingSet() {
2367 synchronized (mutex) {
2368 return new SynchronizedNavigableSet<>(ns.descendingSet(), mutex);
2369 }
2370 }
2371
2372 public Iterator<E> descendingIterator()
2373 { synchronized (mutex) { return descendingSet().iterator(); } }
2374
2375 public NavigableSet<E> subSet(E fromElement, E toElement) {
2376 synchronized (mutex) {
2377 return new SynchronizedNavigableSet<>(ns.subSet(fromElement, true, toElement, false), mutex);
2378 }
2379 }
2380 public NavigableSet<E> headSet(E toElement) {
2381 synchronized (mutex) {
2382 return new SynchronizedNavigableSet<>(ns.headSet(toElement, false), mutex);
2383 }
2384 }
2385 public NavigableSet<E> tailSet(E fromElement) {
2386 synchronized (mutex) {
2387 return new SynchronizedNavigableSet<>(ns.tailSet(fromElement, true), mutex);
2388 }
2389 }
2390
2391 public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
2392 synchronized (mutex) {
2393 return new SynchronizedNavigableSet<>(ns.subSet(fromElement, fromInclusive, toElement, toInclusive), mutex);
2394 }
2395 }
2396
2397 public NavigableSet<E> headSet(E toElement, boolean inclusive) {
2398 synchronized (mutex) {
2399 return new SynchronizedNavigableSet<>(ns.headSet(toElement, inclusive), mutex);
2400 }
2401 }
2402
2403 public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
2404 synchronized (mutex) {
2405 return new SynchronizedNavigableSet<>(ns.tailSet(fromElement, inclusive));
2406 }
2407 }
2408 }
2409
2410 /**
2411 * Returns a synchronized (thread-safe) list backed by the specified
2412 * list. In order to guarantee serial access, it is critical that
2413 * <strong>all</strong> access to the backing list is accomplished
2414 * through the returned list.<p>
2415 *
2416 * It is imperative that the user manually synchronize on the returned
2417 * list when iterating over it:
2418 * <pre>
2419 * List list = Collections.synchronizedList(new ArrayList());
2420 * ...
2421 * synchronized (list) {
2422 * Iterator i = list.iterator(); // Must be in synchronized block
2423 * while (i.hasNext())
2424 * foo(i.next());
2425 * }
2426 * </pre>
2427 * Failure to follow this advice may result in non-deterministic behavior.
2428 *
2429 * <p>The returned list will be serializable if the specified list is
2430 * serializable.
2431 *
2432 * @param <T> the class of the objects in the list
2433 * @param list the list to be "wrapped" in a synchronized list.
2434 * @return a synchronized view of the specified list.
2435 */
2436 public static <T> List<T> synchronizedList(List<T> list) {
2437 return (list instanceof RandomAccess ?
2438 new SynchronizedRandomAccessList<>(list) :
2439 new SynchronizedList<>(list));
2440 }
2441
2442 static <T> List<T> synchronizedList(List<T> list, Object mutex) {
2443 return (list instanceof RandomAccess ?
2444 new SynchronizedRandomAccessList<>(list, mutex) :
2445 new SynchronizedList<>(list, mutex));
2446 }
2447
2448 /**
2449 * @serial include
2450 */
2451 static class SynchronizedList<E>
2452 extends SynchronizedCollection<E>
2453 implements List<E> {
2454 private static final long serialVersionUID = -7754090372962971524L;
2455
2456 final List<E> list;
2457
2458 SynchronizedList(List<E> list) {
2459 super(list);
2460 this.list = list;
2461 }
2462 SynchronizedList(List<E> list, Object mutex) {
2463 super(list, mutex);
2464 this.list = list;
2465 }
2466
2467 public boolean equals(Object o) {
2468 if (this == o)
2469 return true;
2470 synchronized (mutex) {return list.equals(o);}
2471 }
2472 public int hashCode() {
2473 synchronized (mutex) {return list.hashCode();}
2474 }
2475
2476 public E get(int index) {
2477 synchronized (mutex) {return list.get(index);}
2478 }
2479 public E set(int index, E element) {
2480 synchronized (mutex) {return list.set(index, element);}
2481 }
2482 public void add(int index, E element) {
2483 synchronized (mutex) {list.add(index, element);}
2484 }
2485 public E remove(int index) {
2486 synchronized (mutex) {return list.remove(index);}
2487 }
2488
2489 public int indexOf(Object o) {
2490 synchronized (mutex) {return list.indexOf(o);}
2491 }
2492 public int lastIndexOf(Object o) {
2493 synchronized (mutex) {return list.lastIndexOf(o);}
2494 }
2495
2496 public boolean addAll(int index, Collection<? extends E> c) {
2497 synchronized (mutex) {return list.addAll(index, c);}
2498 }
2499
2500 public ListIterator<E> listIterator() {
2501 return list.listIterator(); // Must be manually synched by user
2502 }
2503
2504 public ListIterator<E> listIterator(int index) {
2505 return list.listIterator(index); // Must be manually synched by user
2506 }
2507
2508 public List<E> subList(int fromIndex, int toIndex) {
2509 synchronized (mutex) {
2510 return new SynchronizedList<>(list.subList(fromIndex, toIndex),
2511 mutex);
2512 }
2513 }
2514
2515 @Override
2516 public void replaceAll(UnaryOperator<E> operator) {
2517 synchronized (mutex) {list.replaceAll(operator);}
2518 }
2519 @Override
2520 public void sort(Comparator<? super E> c) {
2521 synchronized (mutex) {list.sort(c);}
2522 }
2523
2524 /**
2525 * SynchronizedRandomAccessList instances are serialized as
2526 * SynchronizedList instances to allow them to be deserialized
2527 * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList).
2528 * This method inverts the transformation. As a beneficial
2529 * side-effect, it also grafts the RandomAccess marker onto
2530 * SynchronizedList instances that were serialized in pre-1.4 JREs.
2531 *
2532 * Note: Unfortunately, SynchronizedRandomAccessList instances
2533 * serialized in 1.4.1 and deserialized in 1.4 will become
2534 * SynchronizedList instances, as this method was missing in 1.4.
2535 */
2536 private Object readResolve() {
2537 return (list instanceof RandomAccess
2538 ? new SynchronizedRandomAccessList<>(list)
2539 : this);
2540 }
2541 }
2542
2543 /**
2544 * @serial include
2545 */
2546 static class SynchronizedRandomAccessList<E>
2547 extends SynchronizedList<E>
2548 implements RandomAccess {
2549
2550 SynchronizedRandomAccessList(List<E> list) {
2551 super(list);
2552 }
2553
2554 SynchronizedRandomAccessList(List<E> list, Object mutex) {
2555 super(list, mutex);
2556 }
2557
2558 public List<E> subList(int fromIndex, int toIndex) {
2559 synchronized (mutex) {
2560 return new SynchronizedRandomAccessList<>(
2561 list.subList(fromIndex, toIndex), mutex);
2562 }
2563 }
2564
2565 private static final long serialVersionUID = 1530674583602358482L;
2566
2567 /**
2568 * Allows instances to be deserialized in pre-1.4 JREs (which do
2569 * not have SynchronizedRandomAccessList). SynchronizedList has
2570 * a readResolve method that inverts this transformation upon
2571 * deserialization.
2572 */
2573 private Object writeReplace() {
2574 return new SynchronizedList<>(list);
2575 }
2576 }
2577
2578 /**
2579 * Returns a synchronized (thread-safe) map backed by the specified
2580 * map. In order to guarantee serial access, it is critical that
2581 * <strong>all</strong> access to the backing map is accomplished
2582 * through the returned map.<p>
2583 *
2584 * It is imperative that the user manually synchronize on the returned
2585 * map when iterating over any of its collection views:
2586 * <pre>
2587 * Map m = Collections.synchronizedMap(new HashMap());
2588 * ...
2589 * Set s = m.keySet(); // Needn't be in synchronized block
2590 * ...
2591 * synchronized (m) { // Synchronizing on m, not s!
2592 * Iterator i = s.iterator(); // Must be in synchronized block
2593 * while (i.hasNext())
2594 * foo(i.next());
2595 * }
2596 * </pre>
2597 * Failure to follow this advice may result in non-deterministic behavior.
2598 *
2599 * <p>The returned map will be serializable if the specified map is
2600 * serializable.
2601 *
2602 * @param <K> the class of the map keys
2603 * @param <V> the class of the map values
2604 * @param m the map to be "wrapped" in a synchronized map.
2605 * @return a synchronized view of the specified map.
2606 */
2607 public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) {
2608 return new SynchronizedMap<>(m);
2609 }
2610
2611 /**
2612 * @serial include
2613 */
2614 private static class SynchronizedMap<K,V>
2615 implements Map<K,V>, Serializable {
2616 private static final long serialVersionUID = 1978198479659022715L;
2617
2618 private final Map<K,V> m; // Backing Map
2619 final Object mutex; // Object on which to synchronize
2620
2621 SynchronizedMap(Map<K,V> m) {
2622 this.m = Objects.requireNonNull(m);
2623 mutex = this;
2624 }
2625
2626 SynchronizedMap(Map<K,V> m, Object mutex) {
2627 this.m = m;
2628 this.mutex = mutex;
2629 }
2630
2631 public int size() {
2632 synchronized (mutex) {return m.size();}
2633 }
2634 public boolean isEmpty() {
2635 synchronized (mutex) {return m.isEmpty();}
2636 }
2637 public boolean containsKey(Object key) {
2638 synchronized (mutex) {return m.containsKey(key);}
2639 }
2640 public boolean containsValue(Object value) {
2641 synchronized (mutex) {return m.containsValue(value);}
2642 }
2643 public V get(Object key) {
2644 synchronized (mutex) {return m.get(key);}
2645 }
2646
2647 public V put(K key, V value) {
2648 synchronized (mutex) {return m.put(key, value);}
2649 }
2650 public V remove(Object key) {
2651 synchronized (mutex) {return m.remove(key);}
2652 }
2653 public void putAll(Map<? extends K, ? extends V> map) {
2654 synchronized (mutex) {m.putAll(map);}
2655 }
2656 public void clear() {
2657 synchronized (mutex) {m.clear();}
2658 }
2659
2660 private transient Set<K> keySet = null;
2661 private transient Set<Map.Entry<K,V>> entrySet = null;
2662 private transient Collection<V> values = null;
2663
2664 public Set<K> keySet() {
2665 synchronized (mutex) {
2666 if (keySet==null)
2667 keySet = new SynchronizedSet<>(m.keySet(), mutex);
2668 return keySet;
2669 }
2670 }
2671
2672 public Set<Map.Entry<K,V>> entrySet() {
2673 synchronized (mutex) {
2674 if (entrySet==null)
2675 entrySet = new SynchronizedSet<>(m.entrySet(), mutex);
2676 return entrySet;
2677 }
2678 }
2679
2680 public Collection<V> values() {
2681 synchronized (mutex) {
2682 if (values==null)
2683 values = new SynchronizedCollection<>(m.values(), mutex);
2684 return values;
2685 }
2686 }
2687
2688 public boolean equals(Object o) {
2689 if (this == o)
2690 return true;
2691 synchronized (mutex) {return m.equals(o);}
2692 }
2693 public int hashCode() {
2694 synchronized (mutex) {return m.hashCode();}
2695 }
2696 public String toString() {
2697 synchronized (mutex) {return m.toString();}
2698 }
2699
2700 // Override default methods in Map
2701 @Override
2702 public V getOrDefault(Object k, V defaultValue) {
2703 synchronized (mutex) {return m.getOrDefault(k, defaultValue);}
2704 }
2705 @Override
2706 public void forEach(BiConsumer<? super K, ? super V> action) {
2707 synchronized (mutex) {m.forEach(action);}
2708 }
2709 @Override
2710 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
2711 synchronized (mutex) {m.replaceAll(function);}
2712 }
2713 @Override
2714 public V putIfAbsent(K key, V value) {
2715 synchronized (mutex) {return m.putIfAbsent(key, value);}
2716 }
2717 @Override
2718 public boolean remove(Object key, Object value) {
2719 synchronized (mutex) {return m.remove(key, value);}
2720 }
2721 @Override
2722 public boolean replace(K key, V oldValue, V newValue) {
2723 synchronized (mutex) {return m.replace(key, oldValue, newValue);}
2724 }
2725 @Override
2726 public V replace(K key, V value) {
2727 synchronized (mutex) {return m.replace(key, value);}
2728 }
2729 @Override
2730 public V computeIfAbsent(K key,
2731 Function<? super K, ? extends V> mappingFunction) {
2732 synchronized (mutex) {return m.computeIfAbsent(key, mappingFunction);}
2733 }
2734 @Override
2735 public V computeIfPresent(K key,
2736 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
2737 synchronized (mutex) {return m.computeIfPresent(key, remappingFunction);}
2738 }
2739 @Override
2740 public V compute(K key,
2741 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
2742 synchronized (mutex) {return m.compute(key, remappingFunction);}
2743 }
2744 @Override
2745 public V merge(K key, V value,
2746 BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
2747 synchronized (mutex) {return m.merge(key, value, remappingFunction);}
2748 }
2749
2750 private void writeObject(ObjectOutputStream s) throws IOException {
2751 synchronized (mutex) {s.defaultWriteObject();}
2752 }
2753 }
2754
2755 /**
2756 * Returns a synchronized (thread-safe) sorted map backed by the specified
2757 * sorted map. In order to guarantee serial access, it is critical that
2758 * <strong>all</strong> access to the backing sorted map is accomplished
2759 * through the returned sorted map (or its views).<p>
2760 *
2761 * It is imperative that the user manually synchronize on the returned
2762 * sorted map when iterating over any of its collection views, or the
2763 * collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or
2764 * <tt>tailMap</tt> views.
2765 * <pre>
2766 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
2767 * ...
2768 * Set s = m.keySet(); // Needn't be in synchronized block
2769 * ...
2770 * synchronized (m) { // Synchronizing on m, not s!
2771 * Iterator i = s.iterator(); // Must be in synchronized block
2772 * while (i.hasNext())
2773 * foo(i.next());
2774 * }
2775 * </pre>
2776 * or:
2777 * <pre>
2778 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
2779 * SortedMap m2 = m.subMap(foo, bar);
2780 * ...
2781 * Set s2 = m2.keySet(); // Needn't be in synchronized block
2782 * ...
2783 * synchronized (m) { // Synchronizing on m, not m2 or s2!
2784 * Iterator i = s.iterator(); // Must be in synchronized block
2785 * while (i.hasNext())
2786 * foo(i.next());
2787 * }
2788 * </pre>
2789 * Failure to follow this advice may result in non-deterministic behavior.
2790 *
2791 * <p>The returned sorted map will be serializable if the specified
2792 * sorted map is serializable.
2793 *
2794 * @param <K> the class of the map keys
2795 * @param <V> the class of the map values
2796 * @param m the sorted map to be "wrapped" in a synchronized sorted map.
2797 * @return a synchronized view of the specified sorted map.
2798 */
2799 public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) {
2800 return new SynchronizedSortedMap<>(m);
2801 }
2802
2803 /**
2804 * @serial include
2805 */
2806 static class SynchronizedSortedMap<K,V>
2807 extends SynchronizedMap<K,V>
2808 implements SortedMap<K,V>
2809 {
2810 private static final long serialVersionUID = -8798146769416483793L;
2811
2812 private final SortedMap<K,V> sm;
2813
2814 SynchronizedSortedMap(SortedMap<K,V> m) {
2815 super(m);
2816 sm = m;
2817 }
2818 SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) {
2819 super(m, mutex);
2820 sm = m;
2821 }
2822
2823 public Comparator<? super K> comparator() {
2824 synchronized (mutex) {return sm.comparator();}
2825 }
2826
2827 public SortedMap<K,V> subMap(K fromKey, K toKey) {
2828 synchronized (mutex) {
2829 return new SynchronizedSortedMap<>(
2830 sm.subMap(fromKey, toKey), mutex);
2831 }
2832 }
2833 public SortedMap<K,V> headMap(K toKey) {
2834 synchronized (mutex) {
2835 return new SynchronizedSortedMap<>(sm.headMap(toKey), mutex);
2836 }
2837 }
2838 public SortedMap<K,V> tailMap(K fromKey) {
2839 synchronized (mutex) {
2840 return new SynchronizedSortedMap<>(sm.tailMap(fromKey),mutex);
2841 }
2842 }
2843
2844 public K firstKey() {
2845 synchronized (mutex) {return sm.firstKey();}
2846 }
2847 public K lastKey() {
2848 synchronized (mutex) {return sm.lastKey();}
2849 }
2850 }
2851
2852 /**
2853 * Returns a synchronized (thread-safe) navigable map backed by the
2854 * specified navigable map. In order to guarantee serial access, it is
2855 * critical that <strong>all</strong> access to the backing navigable map is
2856 * accomplished through the returned navigable map (or its views).<p>
2857 *
2858 * It is imperative that the user manually synchronize on the returned
2859 * navigable map when iterating over any of its collection views, or the
2860 * collections views of any of its {@code subMap}, {@code headMap} or
2861 * {@code tailMap} views.
2862 * <pre>
2863 * NavigableMap m = Collections.synchronizedNavigableMap(new TreeMap());
2864 * ...
2865 * Set s = m.keySet(); // Needn't be in synchronized block
2866 * ...
2867 * synchronized (m) { // Synchronizing on m, not s!
2868 * Iterator i = s.iterator(); // Must be in synchronized block
2869 * while (i.hasNext())
2870 * foo(i.next());
2871 * }
2872 * </pre>
2873 * or:
2874 * <pre>
2875 * NavigableMap m = Collections.synchronizedNavigableMap(new TreeMap());
2876 * NavigableMap m2 = m.subMap(foo, true, bar, false);
2877 * ...
2878 * Set s2 = m2.keySet(); // Needn't be in synchronized block
2879 * ...
2880 * synchronized (m) { // Synchronizing on m, not m2 or s2!
2881 * Iterator i = s.iterator(); // Must be in synchronized block
2882 * while (i.hasNext())
2883 * foo(i.next());
2884 * }
2885 * </pre>
2886 * Failure to follow this advice may result in non-deterministic behavior.
2887 *
2888 * <p>The returned navigable map will be serializable if the specified
2889 * navigable map is serializable.
2890 *
2891 * @param <K> the class of the map keys
2892 * @param <V> the class of the map values
2893 * @param m the navigable map to be "wrapped" in a synchronized navigable
2894 * map
2895 * @return a synchronized view of the specified navigable map.
2896 * @since 1.8
2897 */
2898 public static <K,V> NavigableMap<K,V> synchronizedNavigableMap(NavigableMap<K,V> m) {
2899 return new SynchronizedNavigableMap<>(m);
2900 }
2901
2902 /**
2903 * A synchronized NavigableMap.
2904 *
2905 * @serial include
2906 */
2907 static class SynchronizedNavigableMap<K,V>
2908 extends SynchronizedSortedMap<K,V>
2909 implements NavigableMap<K,V>
2910 {
2911 private static final long serialVersionUID = 699392247599746807L;
2912
2913 private final NavigableMap<K,V> nm;
2914
2915 SynchronizedNavigableMap(NavigableMap<K,V> m) {
2916 super(m);
2917 nm = m;
2918 }
2919 SynchronizedNavigableMap(NavigableMap<K,V> m, Object mutex) {
2920 super(m, mutex);
2921 nm = m;
2922 }
2923
2924 public Entry<K, V> lowerEntry(K key)
2925 { synchronized (mutex) { return nm.lowerEntry(key); } }
2926 public K lowerKey(K key)
2927 { synchronized (mutex) { return nm.lowerKey(key); } }
2928 public Entry<K, V> floorEntry(K key)
2929 { synchronized (mutex) { return nm.floorEntry(key); } }
2930 public K floorKey(K key)
2931 { synchronized (mutex) { return nm.floorKey(key); } }
2932 public Entry<K, V> ceilingEntry(K key)
2933 { synchronized (mutex) { return nm.ceilingEntry(key); } }
2934 public K ceilingKey(K key)
2935 { synchronized (mutex) { return nm.ceilingKey(key); } }
2936 public Entry<K, V> higherEntry(K key)
2937 { synchronized (mutex) { return nm.higherEntry(key); } }
2938 public K higherKey(K key)
2939 { synchronized (mutex) { return nm.higherKey(key); } }
2940 public Entry<K, V> firstEntry()
2941 { synchronized (mutex) { return nm.firstEntry(); } }
2942 public Entry<K, V> lastEntry()
2943 { synchronized (mutex) { return nm.lastEntry(); } }
2944 public Entry<K, V> pollFirstEntry()
2945 { synchronized (mutex) { return nm.pollFirstEntry(); } }
2946 public Entry<K, V> pollLastEntry()
2947 { synchronized (mutex) { return nm.pollLastEntry(); } }
2948
2949 public NavigableMap<K, V> descendingMap() {
2950 synchronized (mutex) {
2951 return
2952 new SynchronizedNavigableMap<>(nm.descendingMap(), mutex);
2953 }
2954 }
2955
2956 public NavigableSet<K> keySet() {
2957 return navigableKeySet();
2958 }
2959
2960 public NavigableSet<K> navigableKeySet() {
2961 synchronized (mutex) {
2962 return new SynchronizedNavigableSet<>(nm.navigableKeySet(), mutex);
2963 }
2964 }
2965
2966 public NavigableSet<K> descendingKeySet() {
2967 synchronized (mutex) {
2968 return new SynchronizedNavigableSet<>(nm.descendingKeySet(), mutex);
2969 }
2970 }
2971
2972
2973 public SortedMap<K,V> subMap(K fromKey, K toKey) {
2974 synchronized (mutex) {
2975 return new SynchronizedNavigableMap<>(
2976 nm.subMap(fromKey, true, toKey, false), mutex);
2977 }
2978 }
2979 public SortedMap<K,V> headMap(K toKey) {
2980 synchronized (mutex) {
2981 return new SynchronizedNavigableMap<>(nm.headMap(toKey, false), mutex);
2982 }
2983 }
2984 public SortedMap<K,V> tailMap(K fromKey) {
2985 synchronized (mutex) {
2986 return new SynchronizedNavigableMap<>(nm.tailMap(fromKey, true),mutex);
2987 }
2988 }
2989
2990 public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
2991 synchronized (mutex) {
2992 return new SynchronizedNavigableMap<>(
2993 nm.subMap(fromKey, fromInclusive, toKey, toInclusive), mutex);
2994 }
2995 }
2996
2997 public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
2998 synchronized (mutex) {
2999 return new SynchronizedNavigableMap<>(
3000 nm.headMap(toKey, inclusive), mutex);
3001 }
3002 }
3003
3004 public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) {
3005 synchronized (mutex) {
3006 return new SynchronizedNavigableMap<>(
3007 nm.tailMap(fromKey, inclusive), mutex);
3008 }
3009 }
3010 }
3011
3012 // Dynamically typesafe collection wrappers
3013
3014 /**
3015 * Returns a dynamically typesafe view of the specified collection.
3016 * Any attempt to insert an element of the wrong type will result in an
3017 * immediate {@link ClassCastException}. Assuming a collection
3018 * contains no incorrectly typed elements prior to the time a
3019 * dynamically typesafe view is generated, and that all subsequent
3020 * access to the collection takes place through the view, it is
3021 * <i>guaranteed</i> that the collection cannot contain an incorrectly
3022 * typed element.
3023 *
3024 * <p>The generics mechanism in the language provides compile-time
3025 * (static) type checking, but it is possible to defeat this mechanism
3026 * with unchecked casts. Usually this is not a problem, as the compiler
3027 * issues warnings on all such unchecked operations. There are, however,
3028 * times when static type checking alone is not sufficient. For example,
3029 * suppose a collection is passed to a third-party library and it is
3030 * imperative that the library code not corrupt the collection by
3031 * inserting an element of the wrong type.
3032 *
3033 * <p>Another use of dynamically typesafe views is debugging. Suppose a
3034 * program fails with a {@code ClassCastException}, indicating that an
3035 * incorrectly typed element was put into a parameterized collection.
3036 * Unfortunately, the exception can occur at any time after the erroneous
3037 * element is inserted, so it typically provides little or no information
3038 * as to the real source of the problem. If the problem is reproducible,
3039 * one can quickly determine its source by temporarily modifying the
3040 * program to wrap the collection with a dynamically typesafe view.
3041 * For example, this declaration:
3042 * <pre> {@code
3043 * Collection<String> c = new HashSet<>();
3044 * }</pre>
3045 * may be replaced temporarily by this one:
3046 * <pre> {@code
3047 * Collection<String> c = Collections.checkedCollection(
3048 * new HashSet<>(), String.class);
3049 * }</pre>
3050 * Running the program again will cause it to fail at the point where
3051 * an incorrectly typed element is inserted into the collection, clearly
3052 * identifying the source of the problem. Once the problem is fixed, the
3053 * modified declaration may be reverted back to the original.
3054 *
3055 * <p>The returned collection does <i>not</i> pass the hashCode and equals
3056 * operations through to the backing collection, but relies on
3057 * {@code Object}'s {@code equals} and {@code hashCode} methods. This
3058 * is necessary to preserve the contracts of these operations in the case
3059 * that the backing collection is a set or a list.
3060 *
3061 * <p>The returned collection will be serializable if the specified
3062 * collection is serializable.
3063 *
3064 * <p>Since {@code null} is considered to be a value of any reference
3065 * type, the returned collection permits insertion of null elements
3066 * whenever the backing collection does.
3067 *
3068 * @param <E> the class of the objects in the collection
3069 * @param c the collection for which a dynamically typesafe view is to be
3070 * returned
3071 * @param type the type of element that {@code c} is permitted to hold
3072 * @return a dynamically typesafe view of the specified collection
3073 * @since 1.5
3074 */
3075 public static <E> Collection<E> checkedCollection(Collection<E> c,
3076 Class<E> type) {
3077 return new CheckedCollection<>(c, type);
3078 }
3079
3080 @SuppressWarnings("unchecked")
3081 static <T> T[] zeroLengthArray(Class<T> type) {
3082 return (T[]) Array.newInstance(type, 0);
3083 }
3084
3085 /**
3086 * @serial include
3087 */
3088 static class CheckedCollection<E> implements Collection<E>, Serializable {
3089 private static final long serialVersionUID = 1578914078182001775L;
3090
3091 final Collection<E> c;
3092 final Class<E> type;
3093
3094 void typeCheck(Object o) {
3095 if (o != null && !type.isInstance(o))
3096 throw new ClassCastException(badElementMsg(o));
3097 }
3098
3099 private String badElementMsg(Object o) {
3100 return "Attempt to insert " + o.getClass() +
3101 " element into collection with element type " + type;
3102 }
3103
3104 CheckedCollection(Collection<E> c, Class<E> type) {
3105 if (c==null || type == null)
3106 throw new NullPointerException();
3107 this.c = c;
3108 this.type = type;
3109 }
3110
3111 public int size() { return c.size(); }
3112 public boolean isEmpty() { return c.isEmpty(); }
3113 public boolean contains(Object o) { return c.contains(o); }
3114 public Object[] toArray() { return c.toArray(); }
3115 public <T> T[] toArray(T[] a) { return c.toArray(a); }
3116 public String toString() { return c.toString(); }
3117 public boolean remove(Object o) { return c.remove(o); }
3118 public void clear() { c.clear(); }
3119
3120 public boolean containsAll(Collection<?> coll) {
3121 return c.containsAll(coll);
3122 }
3123 public boolean removeAll(Collection<?> coll) {
3124 return c.removeAll(coll);
3125 }
3126 public boolean retainAll(Collection<?> coll) {
3127 return c.retainAll(coll);
3128 }
3129
3130 public Iterator<E> iterator() {
3131 // JDK-6363904 - unwrapped iterator could be typecast to
3132 // ListIterator with unsafe set()
3133 final Iterator<E> it = c.iterator();
3134 return new Iterator<E>() {
3135 public boolean hasNext() { return it.hasNext(); }
3136 public E next() { return it.next(); }
3137 public void remove() { it.remove(); }};
3138 }
3139
3140 public boolean add(E e) {
3141 typeCheck(e);
3142 return c.add(e);
3143 }
3144
3145 private E[] zeroLengthElementArray = null; // Lazily initialized
3146
3147 private E[] zeroLengthElementArray() {
3148 return zeroLengthElementArray != null ? zeroLengthElementArray :
3149 (zeroLengthElementArray = zeroLengthArray(type));
3150 }
3151
3152 @SuppressWarnings("unchecked")
3153 Collection<E> checkedCopyOf(Collection<? extends E> coll) {
3154 Object[] a = null;
3155 try {
3156 E[] z = zeroLengthElementArray();
3157 a = coll.toArray(z);
3158 // Defend against coll violating the toArray contract
3159 if (a.getClass() != z.getClass())
3160 a = Arrays.copyOf(a, a.length, z.getClass());
3161 } catch (ArrayStoreException ignore) {
3162 // To get better and consistent diagnostics,
3163 // we call typeCheck explicitly on each element.
3164 // We call clone() to defend against coll retaining a
3165 // reference to the returned array and storing a bad
3166 // element into it after it has been type checked.
3167 a = coll.toArray().clone();
3168 for (Object o : a)
3169 typeCheck(o);
3170 }
3171 // A slight abuse of the type system, but safe here.
3172 return (Collection<E>) Arrays.asList(a);
3173 }
3174
3175 public boolean addAll(Collection<? extends E> coll) {
3176 // Doing things this way insulates us from concurrent changes
3177 // in the contents of coll and provides all-or-nothing
3178 // semantics (which we wouldn't get if we type-checked each
3179 // element as we added it)
3180 return c.addAll(checkedCopyOf(coll));
3181 }
3182
3183 // Override default methods in Collection
3184 @Override
3185 public void forEach(Consumer<? super E> action) {c.forEach(action);}
3186 @Override
3187 public boolean removeAll(Predicate<? super E> filter) {
3188 return c.removeAll(filter);
3189 }
3190 @Override
3191 public Spliterator<E> spliterator() {return c.spliterator();}
3192 @Override
3193 public Stream<E> stream() {return c.stream();}
3194 @Override
3195 public Stream<E> parallelStream() {return c.parallelStream();}
3196 }
3197
3198 /**
3199 * Returns a dynamically typesafe view of the specified queue.
3200 * Any attempt to insert an element of the wrong type will result in
3201 * an immediate {@link ClassCastException}. Assuming a queue contains
3202 * no incorrectly typed elements prior to the time a dynamically typesafe
3203 * view is generated, and that all subsequent access to the queue
3204 * takes place through the view, it is <i>guaranteed</i> that the
3205 * queue cannot contain an incorrectly typed element.
3206 *
3207 * <p>A discussion of the use of dynamically typesafe views may be
3208 * found in the documentation for the {@link #checkedCollection
3209 * checkedCollection} method.
3210 *
3211 * <p>The returned queue will be serializable if the specified queue
3212 * is serializable.
3213 *
3214 * <p>Since {@code null} is considered to be a value of any reference
3215 * type, the returned queue permits insertion of {@code null} elements
3216 * whenever the backing queue does.
3217 *
3218 * @param <E> the class of the objects in the queue
3219 * @param queue the queue for which a dynamically typesafe view is to be
3220 * returned
3221 * @param type the type of element that {@code queue} is permitted to hold
3222 * @return a dynamically typesafe view of the specified queue
3223 * @since 1.8
3224 */
3225 public static <E> Queue<E> checkedQueue(Queue<E> queue, Class<E> type) {
3226 return new CheckedQueue<>(queue, type);
3227 }
3228
3229 /**
3230 * @serial include
3231 */
3232 static class CheckedQueue<E>
3233 extends CheckedCollection<E>
3234 implements Queue<E>, Serializable
3235 {
3236 private static final long serialVersionUID = 1433151992604707767L;
3237 final Queue<E> queue;
3238
3239 CheckedQueue(Queue<E> queue, Class<E> elementType) {
3240 super(queue, elementType);
3241 this.queue = queue;
3242 }
3243
3244 public E element() {return queue.element();}
3245 public boolean equals(Object o) {return o == this || c.equals(o);}
3246 public int hashCode() {return c.hashCode();}
3247 public E peek() {return queue.peek();}
3248 public E poll() {return queue.poll();}
3249 public E remove() {return queue.remove();}
3250
3251 public boolean offer(E e) {
3252 typeCheck(e);
3253 return add(e);
3254 }
3255 }
3256
3257 /**
3258 * Returns a dynamically typesafe view of the specified set.
3259 * Any attempt to insert an element of the wrong type will result in
3260 * an immediate {@link ClassCastException}. Assuming a set contains
3261 * no incorrectly typed elements prior to the time a dynamically typesafe
3262 * view is generated, and that all subsequent access to the set
3263 * takes place through the view, it is <i>guaranteed</i> that the
3264 * set cannot contain an incorrectly typed element.
3265 *
3266 * <p>A discussion of the use of dynamically typesafe views may be
3267 * found in the documentation for the {@link #checkedCollection
3268 * checkedCollection} method.
3269 *
3270 * <p>The returned set will be serializable if the specified set is
3271 * serializable.
3272 *
3273 * <p>Since {@code null} is considered to be a value of any reference
3274 * type, the returned set permits insertion of null elements whenever
3275 * the backing set does.
3276 *
3277 * @param <E> the class of the objects in the set
3278 * @param s the set for which a dynamically typesafe view is to be
3279 * returned
3280 * @param type the type of element that {@code s} is permitted to hold
3281 * @return a dynamically typesafe view of the specified set
3282 * @since 1.5
3283 */
3284 public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) {
3285 return new CheckedSet<>(s, type);
3286 }
3287
3288 /**
3289 * @serial include
3290 */
3291 static class CheckedSet<E> extends CheckedCollection<E>
3292 implements Set<E>, Serializable
3293 {
3294 private static final long serialVersionUID = 4694047833775013803L;
3295
3296 CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); }
3297
3298 public boolean equals(Object o) { return o == this || c.equals(o); }
3299 public int hashCode() { return c.hashCode(); }
3300 }
3301
3302 /**
3303 * Returns a dynamically typesafe view of the specified sorted set.
3304 * Any attempt to insert an element of the wrong type will result in an
3305 * immediate {@link ClassCastException}. Assuming a sorted set
3306 * contains no incorrectly typed elements prior to the time a
3307 * dynamically typesafe view is generated, and that all subsequent
3308 * access to the sorted set takes place through the view, it is
3309 * <i>guaranteed</i> that the sorted set cannot contain an incorrectly
3310 * typed element.
3311 *
3312 * <p>A discussion of the use of dynamically typesafe views may be
3313 * found in the documentation for the {@link #checkedCollection
3314 * checkedCollection} method.
3315 *
3316 * <p>The returned sorted set will be serializable if the specified sorted
3317 * set is serializable.
3318 *
3319 * <p>Since {@code null} is considered to be a value of any reference
3320 * type, the returned sorted set permits insertion of null elements
3321 * whenever the backing sorted set does.
3322 *
3323 * @param <E> the class of the objects in the set
3324 * @param s the sorted set for which a dynamically typesafe view is to be
3325 * returned
3326 * @param type the type of element that {@code s} is permitted to hold
3327 * @return a dynamically typesafe view of the specified sorted set
3328 * @since 1.5
3329 */
3330 public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s,
3331 Class<E> type) {
3332 return new CheckedSortedSet<>(s, type);
3333 }
3334
3335 /**
3336 * @serial include
3337 */
3338 static class CheckedSortedSet<E> extends CheckedSet<E>
3339 implements SortedSet<E>, Serializable
3340 {
3341 private static final long serialVersionUID = 1599911165492914959L;
3342
3343 private final SortedSet<E> ss;
3344
3345 CheckedSortedSet(SortedSet<E> s, Class<E> type) {
3346 super(s, type);
3347 ss = s;
3348 }
3349
3350 public Comparator<? super E> comparator() { return ss.comparator(); }
3351 public E first() { return ss.first(); }
3352 public E last() { return ss.last(); }
3353
3354 public SortedSet<E> subSet(E fromElement, E toElement) {
3355 return checkedSortedSet(ss.subSet(fromElement,toElement), type);
3356 }
3357 public SortedSet<E> headSet(E toElement) {
3358 return checkedSortedSet(ss.headSet(toElement), type);
3359 }
3360 public SortedSet<E> tailSet(E fromElement) {
3361 return checkedSortedSet(ss.tailSet(fromElement), type);
3362 }
3363 }
3364
3365 /**
3366 * Returns a dynamically typesafe view of the specified navigable set.
3367 * Any attempt to insert an element of the wrong type will result in an
3368 * immediate {@link ClassCastException}. Assuming a navigable set
3369 * contains no incorrectly typed elements prior to the time a
3370 * dynamically typesafe view is generated, and that all subsequent
3371 * access to the navigable set takes place through the view, it is
3372 * <em>guaranteed</em> that the navigable set cannot contain an incorrectly
3373 * typed element.
3374 *
3375 * <p>A discussion of the use of dynamically typesafe views may be
3376 * found in the documentation for the {@link #checkedCollection
3377 * checkedCollection} method.
3378 *
3379 * <p>The returned navigable set will be serializable if the specified
3380 * navigable set is serializable.
3381 *
3382 * <p>Since {@code null} is considered to be a value of any reference
3383 * type, the returned navigable set permits insertion of null elements
3384 * whenever the backing sorted set does.
3385 *
3386 * @param <E> the class of the objects in the set
3387 * @param s the navigable set for which a dynamically typesafe view is to be
3388 * returned
3389 * @param type the type of element that {@code s} is permitted to hold
3390 * @return a dynamically typesafe view of the specified navigable set
3391 * @since 1.8
3392 */
3393 public static <E> NavigableSet<E> checkedNavigableSet(NavigableSet<E> s,
3394 Class<E> type) {
3395 return new CheckedNavigableSet<>(s, type);
3396 }
3397
3398 /**
3399 * @serial include
3400 */
3401 static class CheckedNavigableSet<E> extends CheckedSortedSet<E>
3402 implements NavigableSet<E>, Serializable
3403 {
3404 private static final long serialVersionUID = -5429120189805438922L;
3405
3406 private final NavigableSet<E> ns;
3407
3408 CheckedNavigableSet(NavigableSet<E> s, Class<E> type) {
3409 super(s, type);
3410 ns = s;
3411 }
3412
3413 public E lower(E e) { return ns.lower(e); }
3414 public E floor(E e) { return ns.floor(e); }
3415 public E ceiling(E e) { return ns.ceiling(e); }
3416 public E higher(E e) { return ns.higher(e); }
3417 public E pollFirst() { return ns.pollFirst(); }
3418 public E pollLast() {return ns.pollLast(); }
3419 public NavigableSet<E> descendingSet()
3420 { return checkedNavigableSet(ns.descendingSet(), type); }
3421 public Iterator<E> descendingIterator()
3422 {return checkedNavigableSet(ns.descendingSet(), type).iterator(); }
3423
3424 public NavigableSet<E> subSet(E fromElement, E toElement) {
3425 return checkedNavigableSet(ns.subSet(fromElement, true, toElement, false), type);
3426 }
3427 public NavigableSet<E> headSet(E toElement) {
3428 return checkedNavigableSet(ns.headSet(toElement, false), type);
3429 }
3430 public NavigableSet<E> tailSet(E fromElement) {
3431 return checkedNavigableSet(ns.tailSet(fromElement, true), type);
3432 }
3433
3434 public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
3435 return checkedNavigableSet(ns.subSet(fromElement, fromInclusive, toElement, toInclusive), type);
3436 }
3437
3438 public NavigableSet<E> headSet(E toElement, boolean inclusive) {
3439 return checkedNavigableSet(ns.headSet(toElement, inclusive), type);
3440 }
3441
3442 public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
3443 return checkedNavigableSet(ns.tailSet(fromElement, inclusive), type);
3444 }
3445 }
3446
3447 /**
3448 * Returns a dynamically typesafe view of the specified list.
3449 * Any attempt to insert an element of the wrong type will result in
3450 * an immediate {@link ClassCastException}. Assuming a list contains
3451 * no incorrectly typed elements prior to the time a dynamically typesafe
3452 * view is generated, and that all subsequent access to the list
3453 * takes place through the view, it is <i>guaranteed</i> that the
3454 * list cannot contain an incorrectly typed element.
3455 *
3456 * <p>A discussion of the use of dynamically typesafe views may be
3457 * found in the documentation for the {@link #checkedCollection
3458 * checkedCollection} method.
3459 *
3460 * <p>The returned list will be serializable if the specified list
3461 * is serializable.
3462 *
3463 * <p>Since {@code null} is considered to be a value of any reference
3464 * type, the returned list permits insertion of null elements whenever
3465 * the backing list does.
3466 *
3467 * @param <E> the class of the objects in the list
3468 * @param list the list for which a dynamically typesafe view is to be
3469 * returned
3470 * @param type the type of element that {@code list} is permitted to hold
3471 * @return a dynamically typesafe view of the specified list
3472 * @since 1.5
3473 */
3474 public static <E> List<E> checkedList(List<E> list, Class<E> type) {
3475 return (list instanceof RandomAccess ?
3476 new CheckedRandomAccessList<>(list, type) :
3477 new CheckedList<>(list, type));
3478 }
3479
3480 /**
3481 * @serial include
3482 */
3483 static class CheckedList<E>
3484 extends CheckedCollection<E>
3485 implements List<E>
3486 {
3487 private static final long serialVersionUID = 65247728283967356L;
3488 final List<E> list;
3489
3490 CheckedList(List<E> list, Class<E> type) {
3491 super(list, type);
3492 this.list = list;
3493 }
3494
3495 public boolean equals(Object o) { return o == this || list.equals(o); }
3496 public int hashCode() { return list.hashCode(); }
3497 public E get(int index) { return list.get(index); }
3498 public E remove(int index) { return list.remove(index); }
3499 public int indexOf(Object o) { return list.indexOf(o); }
3500 public int lastIndexOf(Object o) { return list.lastIndexOf(o); }
3501
3502 public E set(int index, E element) {
3503 typeCheck(element);
3504 return list.set(index, element);
3505 }
3506
3507 public void add(int index, E element) {
3508 typeCheck(element);
3509 list.add(index, element);
3510 }
3511
3512 public boolean addAll(int index, Collection<? extends E> c) {
3513 return list.addAll(index, checkedCopyOf(c));
3514 }
3515 public ListIterator<E> listIterator() { return listIterator(0); }
3516
3517 public ListIterator<E> listIterator(final int index) {
3518 final ListIterator<E> i = list.listIterator(index);
3519
3520 return new ListIterator<E>() {
3521 public boolean hasNext() { return i.hasNext(); }
3522 public E next() { return i.next(); }
3523 public boolean hasPrevious() { return i.hasPrevious(); }
3524 public E previous() { return i.previous(); }
3525 public int nextIndex() { return i.nextIndex(); }
3526 public int previousIndex() { return i.previousIndex(); }
3527 public void remove() { i.remove(); }
3528
3529 public void set(E e) {
3530 typeCheck(e);
3531 i.set(e);
3532 }
3533
3534 public void add(E e) {
3535 typeCheck(e);
3536 i.add(e);
3537 }
3538
3539 @Override
3540 public void forEachRemaining(Consumer<? super E> action) {
3541 i.forEachRemaining(action);
3542 }
3543 };
3544 }
3545
3546 public List<E> subList(int fromIndex, int toIndex) {
3547 return new CheckedList<>(list.subList(fromIndex, toIndex), type);
3548 }
3549
3550 @Override
3551 public void replaceAll(UnaryOperator<E> operator) {
3552 list.replaceAll(operator);
3553 }
3554 @Override
3555 public void sort(Comparator<? super E> c) {
3556 list.sort(c);
3557 }
3558 }
3559
3560 /**
3561 * @serial include
3562 */
3563 static class CheckedRandomAccessList<E> extends CheckedList<E>
3564 implements RandomAccess
3565 {
3566 private static final long serialVersionUID = 1638200125423088369L;
3567
3568 CheckedRandomAccessList(List<E> list, Class<E> type) {
3569 super(list, type);
3570 }
3571
3572 public List<E> subList(int fromIndex, int toIndex) {
3573 return new CheckedRandomAccessList<>(
3574 list.subList(fromIndex, toIndex), type);
3575 }
3576 }
3577
3578 /**
3579 * Returns a dynamically typesafe view of the specified map.
3580 * Any attempt to insert a mapping whose key or value have the wrong
3581 * type will result in an immediate {@link ClassCastException}.
3582 * Similarly, any attempt to modify the value currently associated with
3583 * a key will result in an immediate {@link ClassCastException},
3584 * whether the modification is attempted directly through the map
3585 * itself, or through a {@link Map.Entry} instance obtained from the
3586 * map's {@link Map#entrySet() entry set} view.
3587 *
3588 * <p>Assuming a map contains no incorrectly typed keys or values
3589 * prior to the time a dynamically typesafe view is generated, and
3590 * that all subsequent access to the map takes place through the view
3591 * (or one of its collection views), it is <i>guaranteed</i> that the
3592 * map cannot contain an incorrectly typed key or value.
3593 *
3594 * <p>A discussion of the use of dynamically typesafe views may be
3595 * found in the documentation for the {@link #checkedCollection
3596 * checkedCollection} method.
3597 *
3598 * <p>The returned map will be serializable if the specified map is
3599 * serializable.
3600 *
3601 * <p>Since {@code null} is considered to be a value of any reference
3602 * type, the returned map permits insertion of null keys or values
3603 * whenever the backing map does.
3604 *
3605 * @param <K> the class of the map keys
3606 * @param <V> the class of the map values
3607 * @param m the map for which a dynamically typesafe view is to be
3608 * returned
3609 * @param keyType the type of key that {@code m} is permitted to hold
3610 * @param valueType the type of value that {@code m} is permitted to hold
3611 * @return a dynamically typesafe view of the specified map
3612 * @since 1.5
3613 */
3614 public static <K, V> Map<K, V> checkedMap(Map<K, V> m,
3615 Class<K> keyType,
3616 Class<V> valueType) {
3617 return new CheckedMap<>(m, keyType, valueType);
3618 }
3619
3620
3621 /**
3622 * @serial include
3623 */
3624 private static class CheckedMap<K,V>
3625 implements Map<K,V>, Serializable
3626 {
3627 private static final long serialVersionUID = 5742860141034234728L;
3628
3629 private final Map<K, V> m;
3630 final Class<K> keyType;
3631 final Class<V> valueType;
3632
3633 private void typeCheck(Object key, Object value) {
3634 if (key != null && !keyType.isInstance(key))
3635 throw new ClassCastException(badKeyMsg(key));
3636
3637 if (value != null && !valueType.isInstance(value))
3638 throw new ClassCastException(badValueMsg(value));
3639 }
3640
3641 private BiFunction<? super K, ? super V, ? extends V> typeCheck(
3642 BiFunction<? super K, ? super V, ? extends V> func) {
3643 Objects.requireNonNull(func);
3644 return (k, v) -> {
3645 V newValue = func.apply(k, v);
3646 typeCheck(k, newValue);
3647 return newValue;
3648 };
3649 }
3650
3651 private String badKeyMsg(Object key) {
3652 return "Attempt to insert " + key.getClass() +
3653 " key into map with key type " + keyType;
3654 }
3655
3656 private String badValueMsg(Object value) {
3657 return "Attempt to insert " + value.getClass() +
3658 " value into map with value type " + valueType;
3659 }
3660
3661 CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) {
3662 this.m = Objects.requireNonNull(m);
3663 this.keyType = Objects.requireNonNull(keyType);
3664 this.valueType = Objects.requireNonNull(valueType);
3665 }
3666
3667 public int size() { return m.size(); }
3668 public boolean isEmpty() { return m.isEmpty(); }
3669 public boolean containsKey(Object key) { return m.containsKey(key); }
3670 public boolean containsValue(Object v) { return m.containsValue(v); }
3671 public V get(Object key) { return m.get(key); }
3672 public V remove(Object key) { return m.remove(key); }
3673 public void clear() { m.clear(); }
3674 public Set<K> keySet() { return m.keySet(); }
3675 public Collection<V> values() { return m.values(); }
3676 public boolean equals(Object o) { return o == this || m.equals(o); }
3677 public int hashCode() { return m.hashCode(); }
3678 public String toString() { return m.toString(); }
3679
3680 public V put(K key, V value) {
3681 typeCheck(key, value);
3682 return m.put(key, value);
3683 }
3684
3685 @SuppressWarnings("unchecked")
3686 public void putAll(Map<? extends K, ? extends V> t) {
3687 // Satisfy the following goals:
3688 // - good diagnostics in case of type mismatch
3689 // - all-or-nothing semantics
3690 // - protection from malicious t
3691 // - correct behavior if t is a concurrent map
3692 Object[] entries = t.entrySet().toArray();
3693 List<Map.Entry<K,V>> checked = new ArrayList<>(entries.length);
3694 for (Object o : entries) {
3695 Map.Entry<?,?> e = (Map.Entry<?,?>) o;
3696 Object k = e.getKey();
3697 Object v = e.getValue();
3698 typeCheck(k, v);
3699 checked.add(
3700 new AbstractMap.SimpleImmutableEntry<>((K)k, (V)v));
3701 }
3702 for (Map.Entry<K,V> e : checked)
3703 m.put(e.getKey(), e.getValue());
3704 }
3705
3706 private transient Set<Map.Entry<K,V>> entrySet = null;
3707
3708 public Set<Map.Entry<K,V>> entrySet() {
3709 if (entrySet==null)
3710 entrySet = new CheckedEntrySet<>(m.entrySet(), valueType);
3711 return entrySet;
3712 }
3713
3714 // Override default methods in Map
3715 @Override
3716 public void forEach(BiConsumer<? super K, ? super V> action) {
3717 m.forEach(action);
3718 }
3719
3720 @Override
3721 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
3722 m.replaceAll(typeCheck(function));
3723 }
3724
3725 @Override
3726 public V putIfAbsent(K key, V value) {
3727 typeCheck(key, value);
3728 return m.putIfAbsent(key, value);
3729 }
3730
3731 @Override
3732 public boolean remove(Object key, Object value) {
3733 return m.remove(key, value);
3734 }
3735
3736 @Override
3737 public boolean replace(K key, V oldValue, V newValue) {
3738 typeCheck(key, newValue);
3739 return m.replace(key, oldValue, newValue);
3740 }
3741
3742 @Override
3743 public V replace(K key, V value) {
3744 typeCheck(key, value);
3745 return m.replace(key, value);
3746 }
3747
3748 @Override
3749 public V computeIfAbsent(K key,
3750 Function<? super K, ? extends V> mappingFunction) {
3751 Objects.requireNonNull(mappingFunction);
3752 return m.computeIfAbsent(key, k -> {
3753 V value = mappingFunction.apply(k);
3754 typeCheck(k, value);
3755 return value;
3756 });
3757 }
3758
3759 @Override
3760 public V computeIfPresent(K key,
3761 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
3762 return m.computeIfPresent(key, typeCheck(remappingFunction));
3763 }
3764
3765 @Override
3766 public V compute(K key,
3767 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
3768 return m.compute(key, typeCheck(remappingFunction));
3769 }
3770
3771 @Override
3772 public V merge(K key, V value,
3773 BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
3774 Objects.requireNonNull(remappingFunction);
3775 return m.merge(key, value, (v1, v2) -> {
3776 V newValue = remappingFunction.apply(v1, v2);
3777 typeCheck(null, newValue);
3778 return newValue;
3779 });
3780 }
3781
3782 /**
3783 * We need this class in addition to CheckedSet as Map.Entry permits
3784 * modification of the backing Map via the setValue operation. This
3785 * class is subtle: there are many possible attacks that must be
3786 * thwarted.
3787 *
3788 * @serial exclude
3789 */
3790 static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> {
3791 private final Set<Map.Entry<K,V>> s;
3792 private final Class<V> valueType;
3793
3794 CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) {
3795 this.s = s;
3796 this.valueType = valueType;
3797 }
3798
3799 public int size() { return s.size(); }
3800 public boolean isEmpty() { return s.isEmpty(); }
3801 public String toString() { return s.toString(); }
3802 public int hashCode() { return s.hashCode(); }
3803 public void clear() { s.clear(); }
3804
3805 public boolean add(Map.Entry<K, V> e) {
3806 throw new UnsupportedOperationException();
3807 }
3808 public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) {
3809 throw new UnsupportedOperationException();
3810 }
3811
3812 public Iterator<Map.Entry<K,V>> iterator() {
3813 final Iterator<Map.Entry<K, V>> i = s.iterator();
3814 final Class<V> valueType = this.valueType;
3815
3816 return new Iterator<Map.Entry<K,V>>() {
3817 public boolean hasNext() { return i.hasNext(); }
3818 public void remove() { i.remove(); }
3819
3820 public Map.Entry<K,V> next() {
3821 return checkedEntry(i.next(), valueType);
3822 }
3823 };
3824 }
3825
3826 @SuppressWarnings("unchecked")
3827 public Object[] toArray() {
3828 Object[] source = s.toArray();
3829
3830 /*
3831 * Ensure that we don't get an ArrayStoreException even if
3832 * s.toArray returns an array of something other than Object
3833 */
3834 Object[] dest = (CheckedEntry.class.isInstance(
3835 source.getClass().getComponentType()) ? source :
3836 new Object[source.length]);
3837
3838 for (int i = 0; i < source.length; i++)
3839 dest[i] = checkedEntry((Map.Entry<K,V>)source[i],
3840 valueType);
3841 return dest;
3842 }
3843
3844 @SuppressWarnings("unchecked")
3845 public <T> T[] toArray(T[] a) {
3846 // We don't pass a to s.toArray, to avoid window of
3847 // vulnerability wherein an unscrupulous multithreaded client
3848 // could get his hands on raw (unwrapped) Entries from s.
3849 T[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
3850
3851 for (int i=0; i<arr.length; i++)
3852 arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i],
3853 valueType);
3854 if (arr.length > a.length)
3855 return arr;
3856
3857 System.arraycopy(arr, 0, a, 0, arr.length);
3858 if (a.length > arr.length)
3859 a[arr.length] = null;
3860 return a;
3861 }
3862
3863 /**
3864 * This method is overridden to protect the backing set against
3865 * an object with a nefarious equals function that senses
3866 * that the equality-candidate is Map.Entry and calls its
3867 * setValue method.
3868 */
3869 public boolean contains(Object o) {
3870 if (!(o instanceof Map.Entry))
3871 return false;
3872 Map.Entry<?,?> e = (Map.Entry<?,?>) o;
3873 return s.contains(
3874 (e instanceof CheckedEntry) ? e : checkedEntry(e, valueType));
3875 }
3876
3877 /**
3878 * The bulk collection methods are overridden to protect
3879 * against an unscrupulous collection whose contains(Object o)
3880 * method senses when o is a Map.Entry, and calls o.setValue.
3881 */
3882 public boolean containsAll(Collection<?> c) {
3883 for (Object o : c)
3884 if (!contains(o)) // Invokes safe contains() above
3885 return false;
3886 return true;
3887 }
3888
3889 public boolean remove(Object o) {
3890 if (!(o instanceof Map.Entry))
3891 return false;
3892 return s.remove(new AbstractMap.SimpleImmutableEntry
3893 <>((Map.Entry<?,?>)o));
3894 }
3895
3896 public boolean removeAll(Collection<?> c) {
3897 return batchRemove(c, false);
3898 }
3899 public boolean retainAll(Collection<?> c) {
3900 return batchRemove(c, true);
3901 }
3902 private boolean batchRemove(Collection<?> c, boolean complement) {
3903 boolean modified = false;
3904 Iterator<Map.Entry<K,V>> it = iterator();
3905 while (it.hasNext()) {
3906 if (c.contains(it.next()) != complement) {
3907 it.remove();
3908 modified = true;
3909 }
3910 }
3911 return modified;
3912 }
3913
3914 public boolean equals(Object o) {
3915 if (o == this)
3916 return true;
3917 if (!(o instanceof Set))
3918 return false;
3919 Set<?> that = (Set<?>) o;
3920 return that.size() == s.size()
3921 && containsAll(that); // Invokes safe containsAll() above
3922 }
3923
3924 static <K,V,T> CheckedEntry<K,V,T> checkedEntry(Map.Entry<K,V> e,
3925 Class<T> valueType) {
3926 return new CheckedEntry<>(e, valueType);
3927 }
3928
3929 /**
3930 * This "wrapper class" serves two purposes: it prevents
3931 * the client from modifying the backing Map, by short-circuiting
3932 * the setValue method, and it protects the backing Map against
3933 * an ill-behaved Map.Entry that attempts to modify another
3934 * Map.Entry when asked to perform an equality check.
3935 */
3936 private static class CheckedEntry<K,V,T> implements Map.Entry<K,V> {
3937 private final Map.Entry<K, V> e;
3938 private final Class<T> valueType;
3939
3940 CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) {
3941 this.e = Objects.requireNonNull(e);
3942 this.valueType = Objects.requireNonNull(valueType);
3943 }
3944
3945 public K getKey() { return e.getKey(); }
3946 public V getValue() { return e.getValue(); }
3947 public int hashCode() { return e.hashCode(); }
3948 public String toString() { return e.toString(); }
3949
3950 public V setValue(V value) {
3951 if (value != null && !valueType.isInstance(value))
3952 throw new ClassCastException(badValueMsg(value));
3953 return e.setValue(value);
3954 }
3955
3956 private String badValueMsg(Object value) {
3957 return "Attempt to insert " + value.getClass() +
3958 " value into map with value type " + valueType;
3959 }
3960
3961 public boolean equals(Object o) {
3962 if (o == this)
3963 return true;
3964 if (!(o instanceof Map.Entry))
3965 return false;
3966 return e.equals(new AbstractMap.SimpleImmutableEntry
3967 <>((Map.Entry<?,?>)o));
3968 }
3969 }
3970 }
3971 }
3972
3973 /**
3974 * Returns a dynamically typesafe view of the specified sorted map.
3975 * Any attempt to insert a mapping whose key or value have the wrong
3976 * type will result in an immediate {@link ClassCastException}.
3977 * Similarly, any attempt to modify the value currently associated with
3978 * a key will result in an immediate {@link ClassCastException},
3979 * whether the modification is attempted directly through the map
3980 * itself, or through a {@link Map.Entry} instance obtained from the
3981 * map's {@link Map#entrySet() entry set} view.
3982 *
3983 * <p>Assuming a map contains no incorrectly typed keys or values
3984 * prior to the time a dynamically typesafe view is generated, and
3985 * that all subsequent access to the map takes place through the view
3986 * (or one of its collection views), it is <i>guaranteed</i> that the
3987 * map cannot contain an incorrectly typed key or value.
3988 *
3989 * <p>A discussion of the use of dynamically typesafe views may be
3990 * found in the documentation for the {@link #checkedCollection
3991 * checkedCollection} method.
3992 *
3993 * <p>The returned map will be serializable if the specified map is
3994 * serializable.
3995 *
3996 * <p>Since {@code null} is considered to be a value of any reference
3997 * type, the returned map permits insertion of null keys or values
3998 * whenever the backing map does.
3999 *
4000 * @param <K> the class of the map keys
4001 * @param <V> the class of the map values
4002 * @param m the map for which a dynamically typesafe view is to be
4003 * returned
4004 * @param keyType the type of key that {@code m} is permitted to hold
4005 * @param valueType the type of value that {@code m} is permitted to hold
4006 * @return a dynamically typesafe view of the specified map
4007 * @since 1.5
4008 */
4009 public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m,
4010 Class<K> keyType,
4011 Class<V> valueType) {
4012 return new CheckedSortedMap<>(m, keyType, valueType);
4013 }
4014
4015 /**
4016 * @serial include
4017 */
4018 static class CheckedSortedMap<K,V> extends CheckedMap<K,V>
4019 implements SortedMap<K,V>, Serializable
4020 {
4021 private static final long serialVersionUID = 1599671320688067438L;
4022
4023 private final SortedMap<K, V> sm;
4024
4025 CheckedSortedMap(SortedMap<K, V> m,
4026 Class<K> keyType, Class<V> valueType) {
4027 super(m, keyType, valueType);
4028 sm = m;
4029 }
4030
4031 public Comparator<? super K> comparator() { return sm.comparator(); }
4032 public K firstKey() { return sm.firstKey(); }
4033 public K lastKey() { return sm.lastKey(); }
4034
4035 public SortedMap<K,V> subMap(K fromKey, K toKey) {
4036 return checkedSortedMap(sm.subMap(fromKey, toKey),
4037 keyType, valueType);
4038 }
4039 public SortedMap<K,V> headMap(K toKey) {
4040 return checkedSortedMap(sm.headMap(toKey), keyType, valueType);
4041 }
4042 public SortedMap<K,V> tailMap(K fromKey) {
4043 return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType);
4044 }
4045 }
4046
4047 /**
4048 * Returns a dynamically typesafe view of the specified navigable map.
4049 * Any attempt to insert a mapping whose key or value have the wrong
4050 * type will result in an immediate {@link ClassCastException}.
4051 * Similarly, any attempt to modify the value currently associated with
4052 * a key will result in an immediate {@link ClassCastException},
4053 * whether the modification is attempted directly through the map
4054 * itself, or through a {@link Map.Entry} instance obtained from the
4055 * map's {@link Map#entrySet() entry set} view.
4056 *
4057 * <p>Assuming a map contains no incorrectly typed keys or values
4058 * prior to the time a dynamically typesafe view is generated, and
4059 * that all subsequent access to the map takes place through the view
4060 * (or one of its collection views), it is <em>guaranteed</em> that the
4061 * map cannot contain an incorrectly typed key or value.
4062 *
4063 * <p>A discussion of the use of dynamically typesafe views may be
4064 * found in the documentation for the {@link #checkedCollection
4065 * checkedCollection} method.
4066 *
4067 * <p>The returned map will be serializable if the specified map is
4068 * serializable.
4069 *
4070 * <p>Since {@code null} is considered to be a value of any reference
4071 * type, the returned map permits insertion of null keys or values
4072 * whenever the backing map does.
4073 *
4074 * @param <K> type of map keys
4075 * @param <V> type of map values
4076 * @param m the map for which a dynamically typesafe view is to be
4077 * returned
4078 * @param keyType the type of key that {@code m} is permitted to hold
4079 * @param valueType the type of value that {@code m} is permitted to hold
4080 * @return a dynamically typesafe view of the specified map
4081 * @since 1.8
4082 */
4083 public static <K,V> NavigableMap<K,V> checkedNavigableMap(NavigableMap<K, V> m,
4084 Class<K> keyType,
4085 Class<V> valueType) {
4086 return new CheckedNavigableMap<>(m, keyType, valueType);
4087 }
4088
4089 /**
4090 * @serial include
4091 */
4092 static class CheckedNavigableMap<K,V> extends CheckedSortedMap<K,V>
4093 implements NavigableMap<K,V>, Serializable
4094 {
4095 private static final long serialVersionUID = -4852462692372534096L;
4096
4097 private final NavigableMap<K, V> nm;
4098
4099 CheckedNavigableMap(NavigableMap<K, V> m,
4100 Class<K> keyType, Class<V> valueType) {
4101 super(m, keyType, valueType);
4102 nm = m;
4103 }
4104
4105 public Comparator<? super K> comparator() { return nm.comparator(); }
4106 public K firstKey() { return nm.firstKey(); }
4107 public K lastKey() { return nm.lastKey(); }
4108
4109 public Entry<K, V> lowerEntry(K key) {
4110 Entry<K,V> lower = nm.lowerEntry(key);
4111 return (null != lower)
4112 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(lower, valueType)
4113 : null;
4114 }
4115
4116 public K lowerKey(K key) { return nm.lowerKey(key); }
4117
4118 public Entry<K, V> floorEntry(K key) {
4119 Entry<K,V> floor = nm.floorEntry(key);
4120 return (null != floor)
4121 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(floor, valueType)
4122 : null;
4123 }
4124
4125 public K floorKey(K key) { return nm.floorKey(key); }
4126
4127 public Entry<K, V> ceilingEntry(K key) {
4128 Entry<K,V> ceiling = nm.ceilingEntry(key);
4129 return (null != ceiling)
4130 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(ceiling, valueType)
4131 : null;
4132 }
4133
4134 public K ceilingKey(K key) { return nm.ceilingKey(key); }
4135
4136 public Entry<K, V> higherEntry(K key) {
4137 Entry<K,V> higher = nm.higherEntry(key);
4138 return (null != higher)
4139 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(higher, valueType)
4140 : null;
4141 }
4142
4143 public K higherKey(K key) { return nm.higherKey(key); }
4144
4145 public Entry<K, V> firstEntry() {
4146 Entry<K,V> first = nm.firstEntry();
4147 return (null != first)
4148 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(first, valueType)
4149 : null;
4150 }
4151
4152 public Entry<K, V> lastEntry() {
4153 Entry<K,V> last = nm.lastEntry();
4154 return (null != last)
4155 ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(last, valueType)
4156 : null;
4157 }
4158
4159 public Entry<K, V> pollFirstEntry() {
4160 Entry<K,V> entry = nm.pollFirstEntry();
4161 return (null == entry)
4162 ? null
4163 : new CheckedMap.CheckedEntrySet.CheckedEntry<>(entry, valueType);
4164 }
4165
4166 public Entry<K, V> pollLastEntry() {
4167 Entry<K,V> entry = nm.pollLastEntry();
4168 return (null == entry)
4169 ? null
4170 : new CheckedMap.CheckedEntrySet.CheckedEntry<>(entry, valueType);
4171 }
4172
4173 public NavigableMap<K, V> descendingMap() {
4174 return checkedNavigableMap(nm.descendingMap(), keyType, valueType);
4175 }
4176
4177 public NavigableSet<K> keySet() {
4178 return navigableKeySet();
4179 }
4180
4181 public NavigableSet<K> navigableKeySet() {
4182 return checkedNavigableSet(nm.navigableKeySet(), keyType);
4183 }
4184
4185 public NavigableSet<K> descendingKeySet() {
4186 return checkedNavigableSet(nm.descendingKeySet(), keyType);
4187 }
4188
4189 @Override
4190 public NavigableMap<K,V> subMap(K fromKey, K toKey) {
4191 return checkedNavigableMap(nm.subMap(fromKey, true, toKey, false),
4192 keyType, valueType);
4193 }
4194
4195 @Override
4196 public NavigableMap<K,V> headMap(K toKey) {
4197 return checkedNavigableMap(nm.headMap(toKey, false), keyType, valueType);
4198 }
4199
4200 @Override
4201 public NavigableMap<K,V> tailMap(K fromKey) {
4202 return checkedNavigableMap(nm.tailMap(fromKey, true), keyType, valueType);
4203 }
4204
4205 public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
4206 return checkedNavigableMap(nm.subMap(fromKey, fromInclusive, toKey, toInclusive), keyType, valueType);
4207 }
4208
4209 public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
4210 return checkedNavigableMap(nm.headMap(toKey, inclusive), keyType, valueType);
4211 }
4212
4213 public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) {
4214 return checkedNavigableMap(nm.tailMap(fromKey, inclusive), keyType, valueType);
4215 }
4216 }
4217
4218 // Empty collections
4219
4220 /**
4221 * Returns an iterator that has no elements. More precisely,
4222 *
4223 * <ul>
4224 * <li>{@link Iterator#hasNext hasNext} always returns {@code
4225 * false}.</li>
4226 * <li>{@link Iterator#next next} always throws {@link
4227 * NoSuchElementException}.</li>
4228 * <li>{@link Iterator#remove remove} always throws {@link
4229 * IllegalStateException}.</li>
4230 * </ul>
4231 *
4232 * <p>Implementations of this method are permitted, but not
4233 * required, to return the same object from multiple invocations.
4234 *
4235 * @param <T> type of elements, if there were any, in the iterator
4236 * @return an empty iterator
4237 * @since 1.7
4238 */
4239 @SuppressWarnings("unchecked")
4240 public static <T> Iterator<T> emptyIterator() {
4241 return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR;
4242 }
4243
4244 private static class EmptyIterator<E> implements Iterator<E> {
4245 static final EmptyIterator<Object> EMPTY_ITERATOR
4246 = new EmptyIterator<>();
4247
4248 public boolean hasNext() { return false; }
4249 public E next() { throw new NoSuchElementException(); }
4250 public void remove() { throw new IllegalStateException(); }
4251 @Override
4252 public void forEachRemaining(Consumer<? super E> action) {
4253 Objects.requireNonNull(action);
4254 }
4255 }
4256
4257 /**
4258 * Returns a list iterator that has no elements. More precisely,
4259 *
4260 * <ul>
4261 * <li>{@link Iterator#hasNext hasNext} and {@link
4262 * ListIterator#hasPrevious hasPrevious} always return {@code
4263 * false}.</li>
4264 * <li>{@link Iterator#next next} and {@link ListIterator#previous
4265 * previous} always throw {@link NoSuchElementException}.</li>
4266 * <li>{@link Iterator#remove remove} and {@link ListIterator#set
4267 * set} always throw {@link IllegalStateException}.</li>
4268 * <li>{@link ListIterator#add add} always throws {@link
4269 * UnsupportedOperationException}.</li>
4270 * <li>{@link ListIterator#nextIndex nextIndex} always returns
4271 * {@code 0}.</li>
4272 * <li>{@link ListIterator#previousIndex previousIndex} always
4273 * returns {@code -1}.</li>
4274 * </ul>
4275 *
4276 * <p>Implementations of this method are permitted, but not
4277 * required, to return the same object from multiple invocations.
4278 *
4279 * @param <T> type of elements, if there were any, in the iterator
4280 * @return an empty list iterator
4281 * @since 1.7
4282 */
4283 @SuppressWarnings("unchecked")
4284 public static <T> ListIterator<T> emptyListIterator() {
4285 return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR;
4286 }
4287
4288 private static class EmptyListIterator<E>
4289 extends EmptyIterator<E>
4290 implements ListIterator<E>
4291 {
4292 static final EmptyListIterator<Object> EMPTY_ITERATOR
4293 = new EmptyListIterator<>();
4294
4295 public boolean hasPrevious() { return false; }
4296 public E previous() { throw new NoSuchElementException(); }
4297 public int nextIndex() { return 0; }
4298 public int previousIndex() { return -1; }
4299 public void set(E e) { throw new IllegalStateException(); }
4300 public void add(E e) { throw new UnsupportedOperationException(); }
4301 }
4302
4303 /**
4304 * Returns an enumeration that has no elements. More precisely,
4305 *
4306 * <ul>
4307 * <li>{@link Enumeration#hasMoreElements hasMoreElements} always
4308 * returns {@code false}.</li>
4309 * <li> {@link Enumeration#nextElement nextElement} always throws
4310 * {@link NoSuchElementException}.</li>
4311 * </ul>
4312 *
4313 * <p>Implementations of this method are permitted, but not
4314 * required, to return the same object from multiple invocations.
4315 *
4316 * @param <T> the class of the objects in the enumeration
4317 * @return an empty enumeration
4318 * @since 1.7
4319 */
4320 @SuppressWarnings("unchecked")
4321 public static <T> Enumeration<T> emptyEnumeration() {
4322 return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION;
4323 }
4324
4325 private static class EmptyEnumeration<E> implements Enumeration<E> {
4326 static final EmptyEnumeration<Object> EMPTY_ENUMERATION
4327 = new EmptyEnumeration<>();
4328
4329 public boolean hasMoreElements() { return false; }
4330 public E nextElement() { throw new NoSuchElementException(); }
4331 }
4332
4333 /**
4334 * The empty set (immutable). This set is serializable.
4335 *
4336 * @see #emptySet()
4337 */
4338 @SuppressWarnings("rawtypes")
4339 public static final Set EMPTY_SET = new EmptySet<>();
4340
4341 /**
4342 * Returns an empty set (immutable). This set is serializable.
4343 * Unlike the like-named field, this method is parameterized.
4344 *
4345 * <p>This example illustrates the type-safe way to obtain an empty set:
4346 * <pre>
4347 * Set<String> s = Collections.emptySet();
4348 * </pre>
4349 * @implNote Implementations of this method need not create a separate
4350 * {@code Set} object for each call. Using this method is likely to have
4351 * comparable cost to using the like-named field. (Unlike this method, the
4352 * field does not provide type safety.)
4353 *
4354 * @param <T> the class of the objects in the set
4355 * @return the empty set
4356 *
4357 * @see #EMPTY_SET
4358 * @since 1.5
4359 */
4360 @SuppressWarnings("unchecked")
4361 public static final <T> Set<T> emptySet() {
4362 return (Set<T>) EMPTY_SET;
4363 }
4364
4365 /**
4366 * @serial include
4367 */
4368 private static class EmptySet<E>
4369 extends AbstractSet<E>
4370 implements Serializable
4371 {
4372 private static final long serialVersionUID = 1582296315990362920L;
4373
4374 public Iterator<E> iterator() { return emptyIterator(); }
4375
4376 public int size() {return 0;}
4377 public boolean isEmpty() {return true;}
4378
4379 public boolean contains(Object obj) {return false;}
4380 public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
4381
4382 public Object[] toArray() { return new Object[0]; }
4383
4384 public <T> T[] toArray(T[] a) {
4385 if (a.length > 0)
4386 a[0] = null;
4387 return a;
4388 }
4389
4390 // Override default methods in Collection
4391 @Override
4392 public void forEach(Consumer<? super E> action) {
4393 Objects.requireNonNull(action);
4394 }
4395 @Override
4396 public boolean removeAll(Predicate<? super E> filter) {
4397 Objects.requireNonNull(filter);
4398 return false;
4399 }
4400 @Override
4401 public Spliterator<E> spliterator() { return Spliterators.emptySpliterator(); }
4402
4403 // Preserves singleton property
4404 private Object readResolve() {
4405 return EMPTY_SET;
4406 }
4407 }
4408
4409 /**
4410 * Returns an empty sorted set (immutable). This set is serializable.
4411 *
4412 * <p>This example illustrates the type-safe way to obtain an empty
4413 * sorted set:
4414 * <pre> {@code
4415 * SortedSet<String> s = Collections.emptySortedSet();
4416 * }</pre>
4417 *
4418 * @implNote Implementations of this method need not create a separate
4419 * {@code SortedSet} object for each call.
4420 *
4421 * @param <E> type of elements, if there were any, in the set
4422 * @return the empty sorted set
4423 * @since 1.8
4424 */
4425 @SuppressWarnings("unchecked")
4426 public static <E> SortedSet<E> emptySortedSet() {
4427 return (SortedSet<E>) UnmodifiableNavigableSet.EMPTY_NAVIGABLE_SET;
4428 }
4429
4430 /**
4431 * Returns an empty navigable set (immutable). This set is serializable.
4432 *
4433 * <p>This example illustrates the type-safe way to obtain an empty
4434 * navigable set:
4435 * <pre> {@code
4436 * NavigableSet<String> s = Collections.emptyNavigableSet();
4437 * }</pre>
4438 *
4439 * @implNote Implementations of this method need not
4440 * create a separate {@code NavigableSet} object for each call.
4441 *
4442 * @param <E> type of elements, if there were any, in the set
4443 * @return the empty navigable set
4444 * @since 1.8
4445 */
4446 @SuppressWarnings("unchecked")
4447 public static <E> NavigableSet<E> emptyNavigableSet() {
4448 return (NavigableSet<E>) UnmodifiableNavigableSet.EMPTY_NAVIGABLE_SET;
4449 }
4450
4451 /**
4452 * The empty list (immutable). This list is serializable.
4453 *
4454 * @see #emptyList()
4455 */
4456 @SuppressWarnings("rawtypes")
4457 public static final List EMPTY_LIST = new EmptyList<>();
4458
4459 /**
4460 * Returns an empty list (immutable). This list is serializable.
4461 *
4462 * <p>This example illustrates the type-safe way to obtain an empty list:
4463 * <pre>
4464 * List<String> s = Collections.emptyList();
4465 * </pre>
4466 * Implementation note: Implementations of this method need not
4467 * create a separate <tt>List</tt> object for each call. Using this
4468 * method is likely to have comparable cost to using the like-named
4469 * field. (Unlike this method, the field does not provide type safety.)
4470 *
4471 * @param <T> type of elements, if there were any, in the list
4472 * @return an empty immutable list
4473 *
4474 * @see #EMPTY_LIST
4475 * @since 1.5
4476 */
4477 @SuppressWarnings("unchecked")
4478 public static final <T> List<T> emptyList() {
4479 return (List<T>) EMPTY_LIST;
4480 }
4481
4482 /**
4483 * @serial include
4484 */
4485 private static class EmptyList<E>
4486 extends AbstractList<E>
4487 implements RandomAccess, Serializable {
4488 private static final long serialVersionUID = 8842843931221139166L;
4489
4490 public Iterator<E> iterator() {
4491 return emptyIterator();
4492 }
4493 public ListIterator<E> listIterator() {
4494 return emptyListIterator();
4495 }
4496
4497 public int size() {return 0;}
4498 public boolean isEmpty() {return true;}
4499
4500 public boolean contains(Object obj) {return false;}
4501 public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
4502
4503 public Object[] toArray() { return new Object[0]; }
4504
4505 public <T> T[] toArray(T[] a) {
4506 if (a.length > 0)
4507 a[0] = null;
4508 return a;
4509 }
4510
4511 public E get(int index) {
4512 throw new IndexOutOfBoundsException("Index: "+index);
4513 }
4514
4515 public boolean equals(Object o) {
4516 return (o instanceof List) && ((List<?>)o).isEmpty();
4517 }
4518
4519 public int hashCode() { return 1; }
4520
4521 @Override
4522 public boolean removeAll(Predicate<? super E> filter) {
4523 Objects.requireNonNull(filter);
4524 return false;
4525 }
4526 @Override
4527 public void replaceAll(UnaryOperator<E> operator) {
4528 Objects.requireNonNull(operator);
4529 }
4530 @Override
4531 public void sort(Comparator<? super E> c) {
4532 }
4533
4534 // Override default methods in Collection
4535 @Override
4536 public void forEach(Consumer<? super E> action) {
4537 Objects.requireNonNull(action);
4538 }
4539
4540 @Override
4541 public Spliterator<E> spliterator() { return Spliterators.emptySpliterator(); }
4542
4543 // Preserves singleton property
4544 private Object readResolve() {
4545 return EMPTY_LIST;
4546 }
4547 }
4548
4549 /**
4550 * The empty map (immutable). This map is serializable.
4551 *
4552 * @see #emptyMap()
4553 * @since 1.3
4554 */
4555 @SuppressWarnings("rawtypes")
4556 public static final Map EMPTY_MAP = new EmptyMap<>();
4557
4558 /**
4559 * Returns an empty map (immutable). This map is serializable.
4560 *
4561 * <p>This example illustrates the type-safe way to obtain an empty map:
4562 * <pre>
4563 * Map<String, Date> s = Collections.emptyMap();
4564 * </pre>
4565 * @implNote Implementations of this method need not create a separate
4566 * {@code Map} object for each call. Using this method is likely to have
4567 * comparable cost to using the like-named field. (Unlike this method, the
4568 * field does not provide type safety.)
4569 *
4570 * @param <K> the class of the map keys
4571 * @param <V> the class of the map values
4572 * @return an empty map
4573 * @see #EMPTY_MAP
4574 * @since 1.5
4575 */
4576 @SuppressWarnings("unchecked")
4577 public static final <K,V> Map<K,V> emptyMap() {
4578 return (Map<K,V>) EMPTY_MAP;
4579 }
4580
4581 /**
4582 * Returns an empty sorted map (immutable). This map is serializable.
4583 *
4584 * <p>This example illustrates the type-safe way to obtain an empty map:
4585 * <pre> {@code
4586 * SortedMap<String, Date> s = Collections.emptySortedMap();
4587 * }</pre>
4588 *
4589 * @implNote Implementations of this method need not create a separate
4590 * {@code SortedMap} object for each call.
4591 *
4592 * @param <K> the class of the map keys
4593 * @param <V> the class of the map values
4594 * @return an empty sorted map
4595 * @since 1.8
4596 */
4597 @SuppressWarnings("unchecked")
4598 public static final <K,V> SortedMap<K,V> emptySortedMap() {
4599 return (SortedMap<K,V>) UnmodifiableNavigableMap.EMPTY_NAVIGABLE_MAP;
4600 }
4601
4602 /**
4603 * Returns an empty navigable map (immutable). This map is serializable.
4604 *
4605 * <p>This example illustrates the type-safe way to obtain an empty map:
4606 * <pre> {@code
4607 * NavigableMap<String, Date> s = Collections.emptyNavigableMap();
4608 * }</pre>
4609 *
4610 * @implNote Implementations of this method need not create a separate
4611 * {@code NavigableMap} object for each call.
4612 *
4613 * @param <K> the class of the map keys
4614 * @param <V> the class of the map values
4615 * @return an empty navigable map
4616 * @since 1.8
4617 */
4618 @SuppressWarnings("unchecked")
4619 public static final <K,V> NavigableMap<K,V> emptyNavigableMap() {
4620 return (NavigableMap<K,V>) UnmodifiableNavigableMap.EMPTY_NAVIGABLE_MAP;
4621 }
4622
4623 /**
4624 * @serial include
4625 */
4626 private static class EmptyMap<K,V>
4627 extends AbstractMap<K,V>
4628 implements Serializable
4629 {
4630 private static final long serialVersionUID = 6428348081105594320L;
4631
4632 public int size() {return 0;}
4633 public boolean isEmpty() {return true;}
4634 public boolean containsKey(Object key) {return false;}
4635 public boolean containsValue(Object value) {return false;}
4636 public V get(Object key) {return null;}
4637 public Set<K> keySet() {return emptySet();}
4638 public Collection<V> values() {return emptySet();}
4639 public Set<Map.Entry<K,V>> entrySet() {return emptySet();}
4640
4641 public boolean equals(Object o) {
4642 return (o instanceof Map) && ((Map<?,?>)o).isEmpty();
4643 }
4644
4645 public int hashCode() {return 0;}
4646
4647 // Override default methods in Map
4648 @Override
4649 @SuppressWarnings("unchecked")
4650 public V getOrDefault(Object k, V defaultValue) {
4651 return defaultValue;
4652 }
4653
4654 @Override
4655 public void forEach(BiConsumer<? super K, ? super V> action) {
4656 Objects.requireNonNull(action);
4657 }
4658
4659 @Override
4660 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
4661 Objects.requireNonNull(function);
4662 }
4663
4664 @Override
4665 public V putIfAbsent(K key, V value) {
4666 throw new UnsupportedOperationException();
4667 }
4668
4669 @Override
4670 public boolean remove(Object key, Object value) {
4671 throw new UnsupportedOperationException();
4672 }
4673
4674 @Override
4675 public boolean replace(K key, V oldValue, V newValue) {
4676 throw new UnsupportedOperationException();
4677 }
4678
4679 @Override
4680 public V replace(K key, V value) {
4681 throw new UnsupportedOperationException();
4682 }
4683
4684 @Override
4685 public V computeIfAbsent(K key,
4686 Function<? super K, ? extends V> mappingFunction) {
4687 throw new UnsupportedOperationException();
4688 }
4689
4690 @Override
4691 public V computeIfPresent(K key,
4692 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
4693 throw new UnsupportedOperationException();
4694 }
4695
4696 @Override
4697 public V compute(K key,
4698 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
4699 throw new UnsupportedOperationException();
4700 }
4701
4702 @Override
4703 public V merge(K key, V value,
4704 BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
4705 throw new UnsupportedOperationException();
4706 }
4707
4708 // Preserves singleton property
4709 private Object readResolve() {
4710 return EMPTY_MAP;
4711 }
4712 }
4713
4714 // Singleton collections
4715
4716 /**
4717 * Returns an immutable set containing only the specified object.
4718 * The returned set is serializable.
4719 *
4720 * @param <T> the class of the objects in the set
4721 * @param o the sole object to be stored in the returned set.
4722 * @return an immutable set containing only the specified object.
4723 */
4724 public static <T> Set<T> singleton(T o) {
4725 return new SingletonSet<>(o);
4726 }
4727
4728 static <E> Iterator<E> singletonIterator(final E e) {
4729 return new Iterator<E>() {
4730 private boolean hasNext = true;
4731 public boolean hasNext() {
4732 return hasNext;
4733 }
4734 public E next() {
4735 if (hasNext) {
4736 hasNext = false;
4737 return e;
4738 }
4739 throw new NoSuchElementException();
4740 }
4741 public void remove() {
4742 throw new UnsupportedOperationException();
4743 }
4744 @Override
4745 public void forEachRemaining(Consumer<? super E> action) {
4746 Objects.requireNonNull(action);
4747 if (hasNext) {
4748 action.accept(e);
4749 hasNext = false;
4750 }
4751 }
4752 };
4753 }
4754
4755 /**
4756 * Creates a {@code Spliterator} with only the specified element
4757 *
4758 * @param <T> Type of elements
4759 * @return A singleton {@code Spliterator}
4760 */
4761 static <T> Spliterator<T> singletonSpliterator(final T element) {
4762 return new Spliterator<T>() {
4763 long est = 1;
4764
4765 @Override
4766 public Spliterator<T> trySplit() {
4767 return null;
4768 }
4769
4770 @Override
4771 public boolean tryAdvance(Consumer<? super T> consumer) {
4772 Objects.requireNonNull(consumer);
4773 if (est > 0) {
4774 est--;
4775 consumer.accept(element);
4776 return true;
4777 }
4778 return false;
4779 }
4780
4781 @Override
4782 public void forEachRemaining(Consumer<? super T> consumer) {
4783 tryAdvance(consumer);
4784 }
4785
4786 @Override
4787 public long estimateSize() {
4788 return est;
4789 }
4790
4791 @Override
4792 public int characteristics() {
4793 int value = (element != null) ? Spliterator.NONNULL : 0;
4794
4795 return value | Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.IMMUTABLE |
4796 Spliterator.DISTINCT | Spliterator.ORDERED;
4797 }
4798 };
4799 }
4800
4801 /**
4802 * @serial include
4803 */
4804 private static class SingletonSet<E>
4805 extends AbstractSet<E>
4806 implements Serializable
4807 {
4808 private static final long serialVersionUID = 3193687207550431679L;
4809
4810 private final E element;
4811
4812 SingletonSet(E e) {element = e;}
4813
4814 public Iterator<E> iterator() {
4815 return singletonIterator(element);
4816 }
4817
4818 public int size() {return 1;}
4819
4820 public boolean contains(Object o) {return eq(o, element);}
4821
4822 // Override default methods for Collection
4823 @Override
4824 public void forEach(Consumer<? super E> action) {
4825 action.accept(element);
4826 }
4827 @Override
4828 public Spliterator<E> spliterator() {
4829 return singletonSpliterator(element);
4830 }
4831 @Override
4832 public boolean removeAll(Predicate<? super E> filter) {
4833 throw new UnsupportedOperationException();
4834 }
4835 }
4836
4837 /**
4838 * Returns an immutable list containing only the specified object.
4839 * The returned list is serializable.
4840 *
4841 * @param <T> the class of the objects in the list
4842 * @param o the sole object to be stored in the returned list.
4843 * @return an immutable list containing only the specified object.
4844 * @since 1.3
4845 */
4846 public static <T> List<T> singletonList(T o) {
4847 return new SingletonList<>(o);
4848 }
4849
4850 /**
4851 * @serial include
4852 */
4853 private static class SingletonList<E>
4854 extends AbstractList<E>
4855 implements RandomAccess, Serializable {
4856
4857 private static final long serialVersionUID = 3093736618740652951L;
4858
4859 private final E element;
4860
4861 SingletonList(E obj) {element = obj;}
4862
4863 public Iterator<E> iterator() {
4864 return singletonIterator(element);
4865 }
4866
4867 public int size() {return 1;}
4868
4869 public boolean contains(Object obj) {return eq(obj, element);}
4870
4871 public E get(int index) {
4872 if (index != 0)
4873 throw new IndexOutOfBoundsException("Index: "+index+", Size: 1");
4874 return element;
4875 }
4876
4877 // Override default methods for Collection
4878 @Override
4879 public void forEach(Consumer<? super E> action) {
4880 action.accept(element);
4881 }
4882 @Override
4883 public boolean removeAll(Predicate<? super E> filter) {
4884 throw new UnsupportedOperationException();
4885 }
4886 @Override
4887 public void replaceAll(UnaryOperator<E> operator) {
4888 throw new UnsupportedOperationException();
4889 }
4890 @Override
4891 public void sort(Comparator<? super E> c) {
4892 }
4893 @Override
4894 public Spliterator<E> spliterator() {
4895 return singletonSpliterator(element);
4896 }
4897 }
4898
4899 /**
4900 * Returns an immutable map, mapping only the specified key to the
4901 * specified value. The returned map is serializable.
4902 *
4903 * @param <K> the class of the map keys
4904 * @param <V> the class of the map values
4905 * @param key the sole key to be stored in the returned map.
4906 * @param value the value to which the returned map maps <tt>key</tt>.
4907 * @return an immutable map containing only the specified key-value
4908 * mapping.
4909 * @since 1.3
4910 */
4911 public static <K,V> Map<K,V> singletonMap(K key, V value) {
4912 return new SingletonMap<>(key, value);
4913 }
4914
4915 /**
4916 * @serial include
4917 */
4918 private static class SingletonMap<K,V>
4919 extends AbstractMap<K,V>
4920 implements Serializable {
4921 private static final long serialVersionUID = -6979724477215052911L;
4922
4923 private final K k;
4924 private final V v;
4925
4926 SingletonMap(K key, V value) {
4927 k = key;
4928 v = value;
4929 }
4930
4931 public int size() {return 1;}
4932 public boolean isEmpty() {return false;}
4933 public boolean containsKey(Object key) {return eq(key, k);}
4934 public boolean containsValue(Object value) {return eq(value, v);}
4935 public V get(Object key) {return (eq(key, k) ? v : null);}
4936
4937 private transient Set<K> keySet = null;
4938 private transient Set<Map.Entry<K,V>> entrySet = null;
4939 private transient Collection<V> values = null;
4940
4941 public Set<K> keySet() {
4942 if (keySet==null)
4943 keySet = singleton(k);
4944 return keySet;
4945 }
4946
4947 public Set<Map.Entry<K,V>> entrySet() {
4948 if (entrySet==null)
4949 entrySet = Collections.<Map.Entry<K,V>>singleton(
4950 new SimpleImmutableEntry<>(k, v));
4951 return entrySet;
4952 }
4953
4954 public Collection<V> values() {
4955 if (values==null)
4956 values = singleton(v);
4957 return values;
4958 }
4959
4960 // Override default methods in Map
4961 @Override
4962 public V getOrDefault(Object key, V defaultValue) {
4963 return eq(key, k) ? v : defaultValue;
4964 }
4965
4966 @Override
4967 public void forEach(BiConsumer<? super K, ? super V> action) {
4968 action.accept(k, v);
4969 }
4970
4971 @Override
4972 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
4973 throw new UnsupportedOperationException();
4974 }
4975
4976 @Override
4977 public V putIfAbsent(K key, V value) {
4978 throw new UnsupportedOperationException();
4979 }
4980
4981 @Override
4982 public boolean remove(Object key, Object value) {
4983 throw new UnsupportedOperationException();
4984 }
4985
4986 @Override
4987 public boolean replace(K key, V oldValue, V newValue) {
4988 throw new UnsupportedOperationException();
4989 }
4990
4991 @Override
4992 public V replace(K key, V value) {
4993 throw new UnsupportedOperationException();
4994 }
4995
4996 @Override
4997 public V computeIfAbsent(K key,
4998 Function<? super K, ? extends V> mappingFunction) {
4999 throw new UnsupportedOperationException();
5000 }
5001
5002 @Override
5003 public V computeIfPresent(K key,
5004 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
5005 throw new UnsupportedOperationException();
5006 }
5007
5008 @Override
5009 public V compute(K key,
5010 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
5011 throw new UnsupportedOperationException();
5012 }
5013
5014 @Override
5015 public V merge(K key, V value,
5016 BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
5017 throw new UnsupportedOperationException();
5018 }
5019 }
5020
5021 // Miscellaneous
5022
5023 /**
5024 * Returns an immutable list consisting of <tt>n</tt> copies of the
5025 * specified object. The newly allocated data object is tiny (it contains
5026 * a single reference to the data object). This method is useful in
5027 * combination with the <tt>List.addAll</tt> method to grow lists.
5028 * The returned list is serializable.
5029 *
5030 * @param <T> the class of the object to copy and of the objects
5031 * in the returned list.
5032 * @param n the number of elements in the returned list.
5033 * @param o the element to appear repeatedly in the returned list.
5034 * @return an immutable list consisting of <tt>n</tt> copies of the
5035 * specified object.
5036 * @throws IllegalArgumentException if {@code n < 0}
5037 * @see List#addAll(Collection)
5038 * @see List#addAll(int, Collection)
5039 */
5040 public static <T> List<T> nCopies(int n, T o) {
5041 if (n < 0)
5042 throw new IllegalArgumentException("List length = " + n);
5043 return new CopiesList<>(n, o);
5044 }
5045
5046 /**
5047 * @serial include
5048 */
5049 private static class CopiesList<E>
5050 extends AbstractList<E>
5051 implements RandomAccess, Serializable
5052 {
5053 private static final long serialVersionUID = 2739099268398711800L;
5054
5055 final int n;
5056 final E element;
5057
5058 CopiesList(int n, E e) {
5059 assert n >= 0;
5060 this.n = n;
5061 element = e;
5062 }
5063
5064 public int size() {
5065 return n;
5066 }
5067
5068 public boolean contains(Object obj) {
5069 return n != 0 && eq(obj, element);
5070 }
5071
5072 public int indexOf(Object o) {
5073 return contains(o) ? 0 : -1;
5074 }
5075
5076 public int lastIndexOf(Object o) {
5077 return contains(o) ? n - 1 : -1;
5078 }
5079
5080 public E get(int index) {
5081 if (index < 0 || index >= n)
5082 throw new IndexOutOfBoundsException("Index: "+index+
5083 ", Size: "+n);
5084 return element;
5085 }
5086
5087 public Object[] toArray() {
5088 final Object[] a = new Object[n];
5089 if (element != null)
5090 Arrays.fill(a, 0, n, element);
5091 return a;
5092 }
5093
5094 @SuppressWarnings("unchecked")
5095 public <T> T[] toArray(T[] a) {
5096 final int n = this.n;
5097 if (a.length < n) {
5098 a = (T[])java.lang.reflect.Array
5099 .newInstance(a.getClass().getComponentType(), n);
5100 if (element != null)
5101 Arrays.fill(a, 0, n, element);
5102 } else {
5103 Arrays.fill(a, 0, n, element);
5104 if (a.length > n)
5105 a[n] = null;
5106 }
5107 return a;
5108 }
5109
5110 public List<E> subList(int fromIndex, int toIndex) {
5111 if (fromIndex < 0)
5112 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
5113 if (toIndex > n)
5114 throw new IndexOutOfBoundsException("toIndex = " + toIndex);
5115 if (fromIndex > toIndex)
5116 throw new IllegalArgumentException("fromIndex(" + fromIndex +
5117 ") > toIndex(" + toIndex + ")");
5118 return new CopiesList<>(toIndex - fromIndex, element);
5119 }
5120
5121 // Override default methods in Collection
5122 @Override
5123 public Stream<E> stream() {
5124 return IntStream.range(0, n).mapToObj(i -> element);
5125 }
5126
5127 @Override
5128 public Stream<E> parallelStream() {
5129 return IntStream.range(0, n).parallel().mapToObj(i -> element);
5130 }
5131
5132 @Override
5133 public Spliterator<E> spliterator() {
5134 return stream().spliterator();
5135 }
5136 }
5137
5138 /**
5139 * Returns a comparator that imposes the reverse of the <em>natural
5140 * ordering</em> on a collection of objects that implement the
5141 * {@code Comparable} interface. (The natural ordering is the ordering
5142 * imposed by the objects' own {@code compareTo} method.) This enables a
5143 * simple idiom for sorting (or maintaining) collections (or arrays) of
5144 * objects that implement the {@code Comparable} interface in
5145 * reverse-natural-order. For example, suppose {@code a} is an array of
5146 * strings. Then: <pre>
5147 * Arrays.sort(a, Collections.reverseOrder());
5148 * </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p>
5149 *
5150 * The returned comparator is serializable.
5151 *
5152 * @param <T> the class of the objects compared by the comparator
5153 * @return A comparator that imposes the reverse of the <i>natural
5154 * ordering</i> on a collection of objects that implement
5155 * the <tt>Comparable</tt> interface.
5156 * @see Comparable
5157 */
5158 @SuppressWarnings("unchecked")
5159 public static <T> Comparator<T> reverseOrder() {
5160 return (Comparator<T>) ReverseComparator.REVERSE_ORDER;
5161 }
5162
5163 /**
5164 * @serial include
5165 */
5166 private static class ReverseComparator
5167 implements Comparator<Comparable<Object>>, Serializable {
5168
5169 private static final long serialVersionUID = 7207038068494060240L;
5170
5171 static final ReverseComparator REVERSE_ORDER
5172 = new ReverseComparator();
5173
5174 public int compare(Comparable<Object> c1, Comparable<Object> c2) {
5175 return c2.compareTo(c1);
5176 }
5177
5178 private Object readResolve() { return Collections.reverseOrder(); }
5179
5180 @Override
5181 public Comparator<Comparable<Object>> reversed() {
5182 return Comparator.naturalOrder();
5183 }
5184 }
5185
5186 /**
5187 * Returns a comparator that imposes the reverse ordering of the specified
5188 * comparator. If the specified comparator is {@code null}, this method is
5189 * equivalent to {@link #reverseOrder()} (in other words, it returns a
5190 * comparator that imposes the reverse of the <em>natural ordering</em> on
5191 * a collection of objects that implement the Comparable interface).
5192 *
5193 * <p>The returned comparator is serializable (assuming the specified
5194 * comparator is also serializable or {@code null}).
5195 *
5196 * @param <T> the class of the objects compared by the comparator
5197 * @param cmp a comparator who's ordering is to be reversed by the returned
5198 * comparator or {@code null}
5199 * @return A comparator that imposes the reverse ordering of the
5200 * specified comparator.
5201 * @since 1.5
5202 */
5203 public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) {
5204 if (cmp == null)
5205 return reverseOrder();
5206
5207 if (cmp instanceof ReverseComparator2)
5208 return ((ReverseComparator2<T>)cmp).cmp;
5209
5210 return new ReverseComparator2<>(cmp);
5211 }
5212
5213 /**
5214 * @serial include
5215 */
5216 private static class ReverseComparator2<T> implements Comparator<T>,
5217 Serializable
5218 {
5219 private static final long serialVersionUID = 4374092139857L;
5220
5221 /**
5222 * The comparator specified in the static factory. This will never
5223 * be null, as the static factory returns a ReverseComparator
5224 * instance if its argument is null.
5225 *
5226 * @serial
5227 */
5228 final Comparator<T> cmp;
5229
5230 ReverseComparator2(Comparator<T> cmp) {
5231 assert cmp != null;
5232 this.cmp = cmp;
5233 }
5234
5235 public int compare(T t1, T t2) {
5236 return cmp.compare(t2, t1);
5237 }
5238
5239 public boolean equals(Object o) {
5240 return (o == this) ||
5241 (o instanceof ReverseComparator2 &&
5242 cmp.equals(((ReverseComparator2)o).cmp));
5243 }
5244
5245 public int hashCode() {
5246 return cmp.hashCode() ^ Integer.MIN_VALUE;
5247 }
5248
5249 @Override
5250 public Comparator<T> reversed() {
5251 return cmp;
5252 }
5253 }
5254
5255 /**
5256 * Returns an enumeration over the specified collection. This provides
5257 * interoperability with legacy APIs that require an enumeration
5258 * as input.
5259 *
5260 * @param <T> the class of the objects in the collection
5261 * @param c the collection for which an enumeration is to be returned.
5262 * @return an enumeration over the specified collection.
5263 * @see Enumeration
5264 */
5265 public static <T> Enumeration<T> enumeration(final Collection<T> c) {
5266 return new Enumeration<T>() {
5267 private final Iterator<T> i = c.iterator();
5268
5269 public boolean hasMoreElements() {
5270 return i.hasNext();
5271 }
5272
5273 public T nextElement() {
5274 return i.next();
5275 }
5276 };
5277 }
5278
5279 /**
5280 * Returns an array list containing the elements returned by the
5281 * specified enumeration in the order they are returned by the
5282 * enumeration. This method provides interoperability between
5283 * legacy APIs that return enumerations and new APIs that require
5284 * collections.
5285 *
5286 * @param <T> the class of the objects returned by the enumeration
5287 * @param e enumeration providing elements for the returned
5288 * array list
5289 * @return an array list containing the elements returned
5290 * by the specified enumeration.
5291 * @since 1.4
5292 * @see Enumeration
5293 * @see ArrayList
5294 */
5295 public static <T> ArrayList<T> list(Enumeration<T> e) {
5296 ArrayList<T> l = new ArrayList<>();
5297 while (e.hasMoreElements())
5298 l.add(e.nextElement());
5299 return l;
5300 }
5301
5302 /**
5303 * Returns true if the specified arguments are equal, or both null.
5304 *
5305 * NB: Do not replace with Object.equals until JDK-8015417 is resolved.
5306 */
5307 static boolean eq(Object o1, Object o2) {
5308 return o1==null ? o2==null : o1.equals(o2);
5309 }
5310
5311 /**
5312 * Returns the number of elements in the specified collection equal to the
5313 * specified object. More formally, returns the number of elements
5314 * <tt>e</tt> in the collection such that
5315 * <tt>(o == null ? e == null : o.equals(e))</tt>.
5316 *
5317 * @param c the collection in which to determine the frequency
5318 * of <tt>o</tt>
5319 * @param o the object whose frequency is to be determined
5320 * @return the number of elements in {@code c} equal to {@code o}
5321 * @throws NullPointerException if <tt>c</tt> is null
5322 * @since 1.5
5323 */
5324 public static int frequency(Collection<?> c, Object o) {
5325 int result = 0;
5326 if (o == null) {
5327 for (Object e : c)
5328 if (e == null)
5329 result++;
5330 } else {
5331 for (Object e : c)
5332 if (o.equals(e))
5333 result++;
5334 }
5335 return result;
5336 }
5337
5338 /**
5339 * Returns {@code true} if the two specified collections have no
5340 * elements in common.
5341 *
5342 * <p>Care must be exercised if this method is used on collections that
5343 * do not comply with the general contract for {@code Collection}.
5344 * Implementations may elect to iterate over either collection and test
5345 * for containment in the other collection (or to perform any equivalent
5346 * computation). If either collection uses a nonstandard equality test
5347 * (as does a {@link SortedSet} whose ordering is not <em>compatible with
5348 * equals</em>, or the key set of an {@link IdentityHashMap}), both
5349 * collections must use the same nonstandard equality test, or the
5350 * result of this method is undefined.
5351 *
5352 * <p>Care must also be exercised when using collections that have
5353 * restrictions on the elements that they may contain. Collection
5354 * implementations are allowed to throw exceptions for any operation
5355 * involving elements they deem ineligible. For absolute safety the
5356 * specified collections should contain only elements which are
5357 * eligible elements for both collections.
5358 *
5359 * <p>Note that it is permissible to pass the same collection in both
5360 * parameters, in which case the method will return {@code true} if and
5361 * only if the collection is empty.
5362 *
5363 * @param c1 a collection
5364 * @param c2 a collection
5365 * @return {@code true} if the two specified collections have no
5366 * elements in common.
5367 * @throws NullPointerException if either collection is {@code null}.
5368 * @throws NullPointerException if one collection contains a {@code null}
5369 * element and {@code null} is not an eligible element for the other collection.
5370 * (<a href="Collection.html#optional-restrictions">optional</a>)
5371 * @throws ClassCastException if one collection contains an element that is
5372 * of a type which is ineligible for the other collection.
5373 * (<a href="Collection.html#optional-restrictions">optional</a>)
5374 * @since 1.5
5375 */
5376 public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
5377 // The collection to be used for contains(). Preference is given to
5378 // the collection who's contains() has lower O() complexity.
5379 Collection<?> contains = c2;
5380 // The collection to be iterated. If the collections' contains() impl
5381 // are of different O() complexity, the collection with slower
5382 // contains() will be used for iteration. For collections who's
5383 // contains() are of the same complexity then best performance is
5384 // achieved by iterating the smaller collection.
5385 Collection<?> iterate = c1;
5386
5387 // Performance optimization cases. The heuristics:
5388 // 1. Generally iterate over c1.
5389 // 2. If c1 is a Set then iterate over c2.
5390 // 3. If either collection is empty then result is always true.
5391 // 4. Iterate over the smaller Collection.
5392 if (c1 instanceof Set) {
5393 // Use c1 for contains as a Set's contains() is expected to perform
5394 // better than O(N/2)
5395 iterate = c2;
5396 contains = c1;
5397 } else if (!(c2 instanceof Set)) {
5398 // Both are mere Collections. Iterate over smaller collection.
5399 // Example: If c1 contains 3 elements and c2 contains 50 elements and
5400 // assuming contains() requires ceiling(N/2) comparisons then
5401 // checking for all c1 elements in c2 would require 75 comparisons
5402 // (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring
5403 // 100 comparisons (50 * ceiling(3/2)).
5404 int c1size = c1.size();
5405 int c2size = c2.size();
5406 if (c1size == 0 || c2size == 0) {
5407 // At least one collection is empty. Nothing will match.
5408 return true;
5409 }
5410
5411 if (c1size > c2size) {
5412 iterate = c2;
5413 contains = c1;
5414 }
5415 }
5416
5417 for (Object e : iterate) {
5418 if (contains.contains(e)) {
5419 // Found a common element. Collections are not disjoint.
5420 return false;
5421 }
5422 }
5423
5424 // No common elements were found.
5425 return true;
5426 }
5427
5428 /**
5429 * Adds all of the specified elements to the specified collection.
5430 * Elements to be added may be specified individually or as an array.
5431 * The behavior of this convenience method is identical to that of
5432 * <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely
5433 * to run significantly faster under most implementations.
5434 *
5435 * <p>When elements are specified individually, this method provides a
5436 * convenient way to add a few elements to an existing collection:
5437 * <pre>
5438 * Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon");
5439 * </pre>
5440 *
5441 * @param <T> the class of the elements to add and of the collection
5442 * @param c the collection into which <tt>elements</tt> are to be inserted
5443 * @param elements the elements to insert into <tt>c</tt>
5444 * @return <tt>true</tt> if the collection changed as a result of the call
5445 * @throws UnsupportedOperationException if <tt>c</tt> does not support
5446 * the <tt>add</tt> operation
5447 * @throws NullPointerException if <tt>elements</tt> contains one or more
5448 * null values and <tt>c</tt> does not permit null elements, or
5449 * if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt>
5450 * @throws IllegalArgumentException if some property of a value in
5451 * <tt>elements</tt> prevents it from being added to <tt>c</tt>
5452 * @see Collection#addAll(Collection)
5453 * @since 1.5
5454 */
5455 @SafeVarargs
5456 public static <T> boolean addAll(Collection<? super T> c, T... elements) {
5457 boolean result = false;
5458 for (T element : elements)
5459 result |= c.add(element);
5460 return result;
5461 }
5462
5463 /**
5464 * Returns a set backed by the specified map. The resulting set displays
5465 * the same ordering, concurrency, and performance characteristics as the
5466 * backing map. In essence, this factory method provides a {@link Set}
5467 * implementation corresponding to any {@link Map} implementation. There
5468 * is no need to use this method on a {@link Map} implementation that
5469 * already has a corresponding {@link Set} implementation (such as {@link
5470 * HashMap} or {@link TreeMap}).
5471 *
5472 * <p>Each method invocation on the set returned by this method results in
5473 * exactly one method invocation on the backing map or its <tt>keySet</tt>
5474 * view, with one exception. The <tt>addAll</tt> method is implemented
5475 * as a sequence of <tt>put</tt> invocations on the backing map.
5476 *
5477 * <p>The specified map must be empty at the time this method is invoked,
5478 * and should not be accessed directly after this method returns. These
5479 * conditions are ensured if the map is created empty, passed directly
5480 * to this method, and no reference to the map is retained, as illustrated
5481 * in the following code fragment:
5482 * <pre>
5483 * Set<Object> weakHashSet = Collections.newSetFromMap(
5484 * new WeakHashMap<Object, Boolean>());
5485 * </pre>
5486 *
5487 * @param <E> the class of the map keys and of the objects in the
5488 * returned set
5489 * @param map the backing map
5490 * @return the set backed by the map
5491 * @throws IllegalArgumentException if <tt>map</tt> is not empty
5492 * @since 1.6
5493 */
5494 public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
5495 return new SetFromMap<>(map);
5496 }
5497
5498 /**
5499 * @serial include
5500 */
5501 private static class SetFromMap<E> extends AbstractSet<E>
5502 implements Set<E>, Serializable
5503 {
5504 private final Map<E, Boolean> m; // The backing map
5505 private transient Set<E> s; // Its keySet
5506
5507 SetFromMap(Map<E, Boolean> map) {
5508 if (!map.isEmpty())
5509 throw new IllegalArgumentException("Map is non-empty");
5510 m = map;
5511 s = map.keySet();
5512 }
5513
5514 public void clear() { m.clear(); }
5515 public int size() { return m.size(); }
5516 public boolean isEmpty() { return m.isEmpty(); }
5517 public boolean contains(Object o) { return m.containsKey(o); }
5518 public boolean remove(Object o) { return m.remove(o) != null; }
5519 public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; }
5520 public Iterator<E> iterator() { return s.iterator(); }
5521 public Object[] toArray() { return s.toArray(); }
5522 public <T> T[] toArray(T[] a) { return s.toArray(a); }
5523 public String toString() { return s.toString(); }
5524 public int hashCode() { return s.hashCode(); }
5525 public boolean equals(Object o) { return o == this || s.equals(o); }
5526 public boolean containsAll(Collection<?> c) {return s.containsAll(c);}
5527 public boolean removeAll(Collection<?> c) {return s.removeAll(c);}
5528 public boolean retainAll(Collection<?> c) {return s.retainAll(c);}
5529 // addAll is the only inherited implementation
5530
5531 // Override default methods in Collection
5532 @Override
5533 public void forEach(Consumer<? super E> action) {
5534 s.forEach(action);
5535 }
5536 @Override
5537 public boolean removeAll(Predicate<? super E> filter) {
5538 return s.removeAll(filter);
5539 }
5540
5541 @Override
5542 public Spliterator<E> spliterator() {return s.spliterator();}
5543 @Override
5544 public Stream<E> stream() {return s.stream();}
5545 @Override
5546 public Stream<E> parallelStream() {return s.parallelStream();}
5547
5548 private static final long serialVersionUID = 2454657854757543876L;
5549
5550 private void readObject(java.io.ObjectInputStream stream)
5551 throws IOException, ClassNotFoundException
5552 {
5553 stream.defaultReadObject();
5554 s = m.keySet();
5555 }
5556 }
5557
5558 /**
5559 * Returns a view of a {@link Deque} as a Last-in-first-out (Lifo)
5560 * {@link Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>,
5561 * <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This
5562 * view can be useful when you would like to use a method
5563 * requiring a <tt>Queue</tt> but you need Lifo ordering.
5564 *
5565 * <p>Each method invocation on the queue returned by this method
5566 * results in exactly one method invocation on the backing deque, with
5567 * one exception. The {@link Queue#addAll addAll} method is
5568 * implemented as a sequence of {@link Deque#addFirst addFirst}
5569 * invocations on the backing deque.
5570 *
5571 * @param <T> the class of the objects in the deque
5572 * @param deque the deque
5573 * @return the queue
5574 * @since 1.6
5575 */
5576 public static <T> Queue<T> asLifoQueue(Deque<T> deque) {
5577 return new AsLIFOQueue<>(deque);
5578 }
5579
5580 /**
5581 * @serial include
5582 */
5583 static class AsLIFOQueue<E> extends AbstractQueue<E>
5584 implements Queue<E>, Serializable {
5585 private static final long serialVersionUID = 1802017725587941708L;
5586 private final Deque<E> q;
5587 AsLIFOQueue(Deque<E> q) { this.q = q; }
5588 public boolean add(E e) { q.addFirst(e); return true; }
5589 public boolean offer(E e) { return q.offerFirst(e); }
5590 public E poll() { return q.pollFirst(); }
5591 public E remove() { return q.removeFirst(); }
5592 public E peek() { return q.peekFirst(); }
5593 public E element() { return q.getFirst(); }
5594 public void clear() { q.clear(); }
5595 public int size() { return q.size(); }
5596 public boolean isEmpty() { return q.isEmpty(); }
5597 public boolean contains(Object o) { return q.contains(o); }
5598 public boolean remove(Object o) { return q.remove(o); }
5599 public Iterator<E> iterator() { return q.iterator(); }
5600 public Object[] toArray() { return q.toArray(); }
5601 public <T> T[] toArray(T[] a) { return q.toArray(a); }
5602 public String toString() { return q.toString(); }
5603 public boolean containsAll(Collection<?> c) {return q.containsAll(c);}
5604 public boolean removeAll(Collection<?> c) {return q.removeAll(c);}
5605 public boolean retainAll(Collection<?> c) {return q.retainAll(c);}
5606 // We use inherited addAll; forwarding addAll would be wrong
5607
5608 // Override default methods in Collection
5609 @Override
5610 public void forEach(Consumer<? super E> action) {q.forEach(action);}
5611 @Override
5612 public boolean removeAll(Predicate<? super E> filter) {
5613 return q.removeAll(filter);
5614 }
5615 @Override
5616 public Spliterator<E> spliterator() {return q.spliterator();}
5617 @Override
5618 public Stream<E> stream() {return q.stream();}
5619 @Override
5620 public Stream<E> parallelStream() {return q.parallelStream();}
5621 }
5622 }