Don't obfuscate names of fields in objects - otherwise fields provided by two modules may clash
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27 import java.io.Serializable;
28 import java.io.IOException;
29 import java.lang.reflect.Array;
32 * This class consists exclusively of static methods that operate on or return
33 * collections. It contains polymorphic algorithms that operate on
34 * collections, "wrappers", which return a new collection backed by a
35 * specified collection, and a few other odds and ends.
37 * <p>The methods of this class all throw a <tt>NullPointerException</tt>
38 * if the collections or class objects provided to them are null.
40 * <p>The documentation for the polymorphic algorithms contained in this class
41 * generally includes a brief description of the <i>implementation</i>. Such
42 * descriptions should be regarded as <i>implementation notes</i>, rather than
43 * parts of the <i>specification</i>. Implementors should feel free to
44 * substitute other algorithms, so long as the specification itself is adhered
45 * to. (For example, the algorithm used by <tt>sort</tt> does not have to be
46 * a mergesort, but it does have to be <i>stable</i>.)
48 * <p>The "destructive" algorithms contained in this class, that is, the
49 * algorithms that modify the collection on which they operate, are specified
50 * to throw <tt>UnsupportedOperationException</tt> if the collection does not
51 * support the appropriate mutation primitive(s), such as the <tt>set</tt>
52 * method. These algorithms may, but are not required to, throw this
53 * exception if an invocation would have no effect on the collection. For
54 * example, invoking the <tt>sort</tt> method on an unmodifiable list that is
55 * already sorted may or may not throw <tt>UnsupportedOperationException</tt>.
57 * <p>This class is a member of the
58 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
59 * Java Collections Framework</a>.
70 public class Collections {
71 // Suppresses default constructor, ensuring non-instantiability.
72 private Collections() {
78 * Tuning parameters for algorithms - Many of the List algorithms have
79 * two implementations, one of which is appropriate for RandomAccess
80 * lists, the other for "sequential." Often, the random access variant
81 * yields better performance on small sequential access lists. The
82 * tuning parameters below determine the cutoff point for what constitutes
83 * a "small" sequential access list for each algorithm. The values below
84 * were empirically determined to work well for LinkedList. Hopefully
85 * they should be reasonable for other sequential access List
86 * implementations. Those doing performance work on this code would
87 * do well to validate the values of these parameters from time to time.
88 * (The first word of each tuning parameter name is the algorithm to which
91 private static final int BINARYSEARCH_THRESHOLD = 5000;
92 private static final int REVERSE_THRESHOLD = 18;
93 private static final int SHUFFLE_THRESHOLD = 5;
94 private static final int FILL_THRESHOLD = 25;
95 private static final int ROTATE_THRESHOLD = 100;
96 private static final int COPY_THRESHOLD = 10;
97 private static final int REPLACEALL_THRESHOLD = 11;
98 private static final int INDEXOFSUBLIST_THRESHOLD = 35;
101 * Sorts the specified list into ascending order, according to the
102 * {@linkplain Comparable natural ordering} of its elements.
103 * All elements in the list must implement the {@link Comparable}
104 * interface. Furthermore, all elements in the list must be
105 * <i>mutually comparable</i> (that is, {@code e1.compareTo(e2)}
106 * must not throw a {@code ClassCastException} for any elements
107 * {@code e1} and {@code e2} in the list).
109 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will
110 * not be reordered as a result of the sort.
112 * <p>The specified list must be modifiable, but need not be resizable.
114 * <p>Implementation note: This implementation is a stable, adaptive,
115 * iterative mergesort that requires far fewer than n lg(n) comparisons
116 * when the input array is partially sorted, while offering the
117 * performance of a traditional mergesort when the input array is
118 * randomly ordered. If the input array is nearly sorted, the
119 * implementation requires approximately n comparisons. Temporary
120 * storage requirements vary from a small constant for nearly sorted
121 * input arrays to n/2 object references for randomly ordered input
124 * <p>The implementation takes equal advantage of ascending and
125 * descending order in its input array, and can take advantage of
126 * ascending and descending order in different parts of the same
127 * input array. It is well-suited to merging two or more sorted arrays:
128 * simply concatenate the arrays and sort the resulting array.
130 * <p>The implementation was adapted from Tim Peters's list sort for Python
131 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt">
132 * TimSort</a>). It uses techiques from Peter McIlroy's "Optimistic
133 * Sorting and Information Theoretic Complexity", in Proceedings of the
134 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474,
137 * <p>This implementation dumps the specified list into an array, sorts
138 * the array, and iterates over the list resetting each element
139 * from the corresponding position in the array. This avoids the
140 * n<sup>2</sup> log(n) performance that would result from attempting
141 * to sort a linked list in place.
143 * @param list the list to be sorted.
144 * @throws ClassCastException if the list contains elements that are not
145 * <i>mutually comparable</i> (for example, strings and integers).
146 * @throws UnsupportedOperationException if the specified list's
147 * list-iterator does not support the {@code set} operation.
148 * @throws IllegalArgumentException (optional) if the implementation
149 * detects that the natural ordering of the list elements is
150 * found to violate the {@link Comparable} contract
152 public static <T extends Comparable<? super T>> void sort(List<T> list) {
153 Object[] a = list.toArray();
155 ListIterator<T> i = list.listIterator();
156 for (int j=0; j<a.length; j++) {
163 * Sorts the specified list according to the order induced by the
164 * specified comparator. All elements in the list must be <i>mutually
165 * comparable</i> using the specified comparator (that is,
166 * {@code c.compare(e1, e2)} must not throw a {@code ClassCastException}
167 * for any elements {@code e1} and {@code e2} in the list).
169 * <p>This sort is guaranteed to be <i>stable</i>: equal elements will
170 * not be reordered as a result of the sort.
172 * <p>The specified list must be modifiable, but need not be resizable.
174 * <p>Implementation note: This implementation is a stable, adaptive,
175 * iterative mergesort that requires far fewer than n lg(n) comparisons
176 * when the input array is partially sorted, while offering the
177 * performance of a traditional mergesort when the input array is
178 * randomly ordered. If the input array is nearly sorted, the
179 * implementation requires approximately n comparisons. Temporary
180 * storage requirements vary from a small constant for nearly sorted
181 * input arrays to n/2 object references for randomly ordered input
184 * <p>The implementation takes equal advantage of ascending and
185 * descending order in its input array, and can take advantage of
186 * ascending and descending order in different parts of the same
187 * input array. It is well-suited to merging two or more sorted arrays:
188 * simply concatenate the arrays and sort the resulting array.
190 * <p>The implementation was adapted from Tim Peters's list sort for Python
191 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt">
192 * TimSort</a>). It uses techiques from Peter McIlroy's "Optimistic
193 * Sorting and Information Theoretic Complexity", in Proceedings of the
194 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474,
197 * <p>This implementation dumps the specified list into an array, sorts
198 * the array, and iterates over the list resetting each element
199 * from the corresponding position in the array. This avoids the
200 * n<sup>2</sup> log(n) performance that would result from attempting
201 * to sort a linked list in place.
203 * @param list the list to be sorted.
204 * @param c the comparator to determine the order of the list. A
205 * {@code null} value indicates that the elements' <i>natural
206 * ordering</i> should be used.
207 * @throws ClassCastException if the list contains elements that are not
208 * <i>mutually comparable</i> using the specified comparator.
209 * @throws UnsupportedOperationException if the specified list's
210 * list-iterator does not support the {@code set} operation.
211 * @throws IllegalArgumentException (optional) if the comparator is
212 * found to violate the {@link Comparator} contract
214 public static <T> void sort(List<T> list, Comparator<? super T> c) {
215 Object[] a = list.toArray();
216 Arrays.sort(a, (Comparator)c);
217 ListIterator i = list.listIterator();
218 for (int j=0; j<a.length; j++) {
226 * Searches the specified list for the specified object using the binary
227 * search algorithm. The list must be sorted into ascending order
228 * according to the {@linkplain Comparable natural ordering} of its
229 * elements (as by the {@link #sort(List)} method) prior to making this
230 * call. If it is not sorted, the results are undefined. If the list
231 * contains multiple elements equal to the specified object, there is no
232 * guarantee which one will be found.
234 * <p>This method runs in log(n) time for a "random access" list (which
235 * provides near-constant-time positional access). If the specified list
236 * does not implement the {@link RandomAccess} interface and is large,
237 * this method will do an iterator-based binary search that performs
238 * O(n) link traversals and O(log n) element comparisons.
240 * @param list the list to be searched.
241 * @param key the key to be searched for.
242 * @return the index of the search key, if it is contained in the list;
243 * otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The
244 * <i>insertion point</i> is defined as the point at which the
245 * key would be inserted into the list: the index of the first
246 * element greater than the key, or <tt>list.size()</tt> if all
247 * elements in the list are less than the specified key. Note
248 * that this guarantees that the return value will be >= 0 if
249 * and only if the key is found.
250 * @throws ClassCastException if the list contains elements that are not
251 * <i>mutually comparable</i> (for example, strings and
252 * integers), or the search key is not mutually comparable
253 * with the elements of the list.
256 int binarySearch(List<? extends Comparable<? super T>> list, T key) {
257 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
258 return Collections.indexedBinarySearch(list, key);
260 return Collections.iteratorBinarySearch(list, key);
264 int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key)
267 int high = list.size()-1;
269 while (low <= high) {
270 int mid = (low + high) >>> 1;
271 Comparable<? super T> midVal = list.get(mid);
272 int cmp = midVal.compareTo(key);
279 return mid; // key found
281 return -(low + 1); // key not found
285 int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key)
288 int high = list.size()-1;
289 ListIterator<? extends Comparable<? super T>> i = list.listIterator();
291 while (low <= high) {
292 int mid = (low + high) >>> 1;
293 Comparable<? super T> midVal = get(i, mid);
294 int cmp = midVal.compareTo(key);
301 return mid; // key found
303 return -(low + 1); // key not found
307 * Gets the ith element from the given list by repositioning the specified
310 private static <T> T get(ListIterator<? extends T> i, int index) {
312 int pos = i.nextIndex();
316 } while (pos++ < index);
320 } while (--pos > index);
326 * Searches the specified list for the specified object using the binary
327 * search algorithm. The list must be sorted into ascending order
328 * according to the specified comparator (as by the
329 * {@link #sort(List, Comparator) sort(List, Comparator)}
330 * method), prior to making this call. If it is
331 * not sorted, the results are undefined. If the list contains multiple
332 * elements equal to the specified object, there is no guarantee which one
335 * <p>This method runs in log(n) time for a "random access" list (which
336 * provides near-constant-time positional access). If the specified list
337 * does not implement the {@link RandomAccess} interface and is large,
338 * this method will do an iterator-based binary search that performs
339 * O(n) link traversals and O(log n) element comparisons.
341 * @param list the list to be searched.
342 * @param key the key to be searched for.
343 * @param c the comparator by which the list is ordered.
344 * A <tt>null</tt> value indicates that the elements'
345 * {@linkplain Comparable natural ordering} should be used.
346 * @return the index of the search key, if it is contained in the list;
347 * otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The
348 * <i>insertion point</i> is defined as the point at which the
349 * key would be inserted into the list: the index of the first
350 * element greater than the key, or <tt>list.size()</tt> if all
351 * elements in the list are less than the specified key. Note
352 * that this guarantees that the return value will be >= 0 if
353 * and only if the key is found.
354 * @throws ClassCastException if the list contains elements that are not
355 * <i>mutually comparable</i> using the specified comparator,
356 * or the search key is not mutually comparable with the
357 * elements of the list using this comparator.
359 public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) {
361 return binarySearch((List) list, key);
363 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
364 return Collections.indexedBinarySearch(list, key, c);
366 return Collections.iteratorBinarySearch(list, key, c);
369 private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
371 int high = l.size()-1;
373 while (low <= high) {
374 int mid = (low + high) >>> 1;
375 T midVal = l.get(mid);
376 int cmp = c.compare(midVal, key);
383 return mid; // key found
385 return -(low + 1); // key not found
388 private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
390 int high = l.size()-1;
391 ListIterator<? extends T> i = l.listIterator();
393 while (low <= high) {
394 int mid = (low + high) >>> 1;
395 T midVal = get(i, mid);
396 int cmp = c.compare(midVal, key);
403 return mid; // key found
405 return -(low + 1); // key not found
408 private interface SelfComparable extends Comparable<SelfComparable> {}
412 * Reverses the order of the elements in the specified list.<p>
414 * This method runs in linear time.
416 * @param list the list whose elements are to be reversed.
417 * @throws UnsupportedOperationException if the specified list or
418 * its list-iterator does not support the <tt>set</tt> operation.
420 public static void reverse(List<?> list) {
421 int size = list.size();
422 if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) {
423 for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--)
426 ListIterator fwd = list.listIterator();
427 ListIterator rev = list.listIterator(size);
428 for (int i=0, mid=list.size()>>1; i<mid; i++) {
429 Object tmp = fwd.next();
430 fwd.set(rev.previous());
437 * Randomly permutes the specified list using a default source of
438 * randomness. All permutations occur with approximately equal
441 * The hedge "approximately" is used in the foregoing description because
442 * default source of randomness is only approximately an unbiased source
443 * of independently chosen bits. If it were a perfect source of randomly
444 * chosen bits, then the algorithm would choose permutations with perfect
447 * This implementation traverses the list backwards, from the last element
448 * up to the second, repeatedly swapping a randomly selected element into
449 * the "current position". Elements are randomly selected from the
450 * portion of the list that runs from the first element to the current
451 * position, inclusive.<p>
453 * This method runs in linear time. If the specified list does not
454 * implement the {@link RandomAccess} interface and is large, this
455 * implementation dumps the specified list into an array before shuffling
456 * it, and dumps the shuffled array back into the list. This avoids the
457 * quadratic behavior that would result from shuffling a "sequential
458 * access" list in place.
460 * @param list the list to be shuffled.
461 * @throws UnsupportedOperationException if the specified list or
462 * its list-iterator does not support the <tt>set</tt> operation.
464 public static void shuffle(List<?> list) {
467 r = rnd = new Random();
470 private static Random r;
473 * Randomly permute the specified list using the specified source of
474 * randomness. All permutations occur with equal likelihood
475 * assuming that the source of randomness is fair.<p>
477 * This implementation traverses the list backwards, from the last element
478 * up to the second, repeatedly swapping a randomly selected element into
479 * the "current position". Elements are randomly selected from the
480 * portion of the list that runs from the first element to the current
481 * position, inclusive.<p>
483 * This method runs in linear time. If the specified list does not
484 * implement the {@link RandomAccess} interface and is large, this
485 * implementation dumps the specified list into an array before shuffling
486 * it, and dumps the shuffled array back into the list. This avoids the
487 * quadratic behavior that would result from shuffling a "sequential
488 * access" list in place.
490 * @param list the list to be shuffled.
491 * @param rnd the source of randomness to use to shuffle the list.
492 * @throws UnsupportedOperationException if the specified list or its
493 * list-iterator does not support the <tt>set</tt> operation.
495 public static void shuffle(List<?> list, Random rnd) {
496 int size = list.size();
497 if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) {
498 for (int i=size; i>1; i--)
499 swap(list, i-1, rnd.nextInt(i));
501 Object arr[] = list.toArray();
504 for (int i=size; i>1; i--)
505 swap(arr, i-1, rnd.nextInt(i));
507 // Dump array back into list
508 ListIterator it = list.listIterator();
509 for (int i=0; i<arr.length; i++) {
517 * Swaps the elements at the specified positions in the specified list.
518 * (If the specified positions are equal, invoking this method leaves
519 * the list unchanged.)
521 * @param list The list in which to swap elements.
522 * @param i the index of one element to be swapped.
523 * @param j the index of the other element to be swapped.
524 * @throws IndexOutOfBoundsException if either <tt>i</tt> or <tt>j</tt>
525 * is out of range (i < 0 || i >= list.size()
526 * || j < 0 || j >= list.size()).
529 public static void swap(List<?> list, int i, int j) {
531 l.set(i, l.set(j, l.get(i)));
535 * Swaps the two specified elements in the specified array.
537 private static void swap(Object[] arr, int i, int j) {
544 * Replaces all of the elements of the specified list with the specified
547 * This method runs in linear time.
549 * @param list the list to be filled with the specified element.
550 * @param obj The element with which to fill the specified list.
551 * @throws UnsupportedOperationException if the specified list or its
552 * list-iterator does not support the <tt>set</tt> operation.
554 public static <T> void fill(List<? super T> list, T obj) {
555 int size = list.size();
557 if (size < FILL_THRESHOLD || list instanceof RandomAccess) {
558 for (int i=0; i<size; i++)
561 ListIterator<? super T> itr = list.listIterator();
562 for (int i=0; i<size; i++) {
570 * Copies all of the elements from one list into another. After the
571 * operation, the index of each copied element in the destination list
572 * will be identical to its index in the source list. The destination
573 * list must be at least as long as the source list. If it is longer, the
574 * remaining elements in the destination list are unaffected. <p>
576 * This method runs in linear time.
578 * @param dest The destination list.
579 * @param src The source list.
580 * @throws IndexOutOfBoundsException if the destination list is too small
581 * to contain the entire source List.
582 * @throws UnsupportedOperationException if the destination list's
583 * list-iterator does not support the <tt>set</tt> operation.
585 public static <T> void copy(List<? super T> dest, List<? extends T> src) {
586 int srcSize = src.size();
587 if (srcSize > dest.size())
588 throw new IndexOutOfBoundsException("Source does not fit in dest");
590 if (srcSize < COPY_THRESHOLD ||
591 (src instanceof RandomAccess && dest instanceof RandomAccess)) {
592 for (int i=0; i<srcSize; i++)
593 dest.set(i, src.get(i));
595 ListIterator<? super T> di=dest.listIterator();
596 ListIterator<? extends T> si=src.listIterator();
597 for (int i=0; i<srcSize; i++) {
605 * Returns the minimum element of the given collection, according to the
606 * <i>natural ordering</i> of its elements. All elements in the
607 * collection must implement the <tt>Comparable</tt> interface.
608 * Furthermore, all elements in the collection must be <i>mutually
609 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
610 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
611 * <tt>e2</tt> in the collection).<p>
613 * This method iterates over the entire collection, hence it requires
614 * time proportional to the size of the collection.
616 * @param coll the collection whose minimum element is to be determined.
617 * @return the minimum element of the given collection, according
618 * to the <i>natural ordering</i> of its elements.
619 * @throws ClassCastException if the collection contains elements that are
620 * not <i>mutually comparable</i> (for example, strings and
622 * @throws NoSuchElementException if the collection is empty.
625 public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) {
626 Iterator<? extends T> i = coll.iterator();
627 T candidate = i.next();
629 while (i.hasNext()) {
631 if (next.compareTo(candidate) < 0)
638 * Returns the minimum element of the given collection, according to the
639 * order induced by the specified comparator. All elements in the
640 * collection must be <i>mutually comparable</i> by the specified
641 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
642 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
643 * <tt>e2</tt> in the collection).<p>
645 * This method iterates over the entire collection, hence it requires
646 * time proportional to the size of the collection.
648 * @param coll the collection whose minimum element is to be determined.
649 * @param comp the comparator with which to determine the minimum element.
650 * A <tt>null</tt> value indicates that the elements' <i>natural
651 * ordering</i> should be used.
652 * @return the minimum element of the given collection, according
653 * to the specified comparator.
654 * @throws ClassCastException if the collection contains elements that are
655 * not <i>mutually comparable</i> using the specified comparator.
656 * @throws NoSuchElementException if the collection is empty.
659 public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) {
661 return (T)min((Collection<SelfComparable>) (Collection) coll);
663 Iterator<? extends T> i = coll.iterator();
664 T candidate = i.next();
666 while (i.hasNext()) {
668 if (comp.compare(next, candidate) < 0)
675 * Returns the maximum element of the given collection, according to the
676 * <i>natural ordering</i> of its elements. All elements in the
677 * collection must implement the <tt>Comparable</tt> interface.
678 * Furthermore, all elements in the collection must be <i>mutually
679 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
680 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
681 * <tt>e2</tt> in the collection).<p>
683 * This method iterates over the entire collection, hence it requires
684 * time proportional to the size of the collection.
686 * @param coll the collection whose maximum element is to be determined.
687 * @return the maximum element of the given collection, according
688 * to the <i>natural ordering</i> of its elements.
689 * @throws ClassCastException if the collection contains elements that are
690 * not <i>mutually comparable</i> (for example, strings and
692 * @throws NoSuchElementException if the collection is empty.
695 public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) {
696 Iterator<? extends T> i = coll.iterator();
697 T candidate = i.next();
699 while (i.hasNext()) {
701 if (next.compareTo(candidate) > 0)
708 * Returns the maximum element of the given collection, according to the
709 * order induced by the specified comparator. All elements in the
710 * collection must be <i>mutually comparable</i> by the specified
711 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
712 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
713 * <tt>e2</tt> in the collection).<p>
715 * This method iterates over the entire collection, hence it requires
716 * time proportional to the size of the collection.
718 * @param coll the collection whose maximum element is to be determined.
719 * @param comp the comparator with which to determine the maximum element.
720 * A <tt>null</tt> value indicates that the elements' <i>natural
721 * ordering</i> should be used.
722 * @return the maximum element of the given collection, according
723 * to the specified comparator.
724 * @throws ClassCastException if the collection contains elements that are
725 * not <i>mutually comparable</i> using the specified comparator.
726 * @throws NoSuchElementException if the collection is empty.
729 public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) {
731 return (T)max((Collection<SelfComparable>) (Collection) coll);
733 Iterator<? extends T> i = coll.iterator();
734 T candidate = i.next();
736 while (i.hasNext()) {
738 if (comp.compare(next, candidate) > 0)
745 * Rotates the elements in the specified list by the specified distance.
746 * After calling this method, the element at index <tt>i</tt> will be
747 * the element previously at index <tt>(i - distance)</tt> mod
748 * <tt>list.size()</tt>, for all values of <tt>i</tt> between <tt>0</tt>
749 * and <tt>list.size()-1</tt>, inclusive. (This method has no effect on
750 * the size of the list.)
752 * <p>For example, suppose <tt>list</tt> comprises<tt> [t, a, n, k, s]</tt>.
753 * After invoking <tt>Collections.rotate(list, 1)</tt> (or
754 * <tt>Collections.rotate(list, -4)</tt>), <tt>list</tt> will comprise
755 * <tt>[s, t, a, n, k]</tt>.
757 * <p>Note that this method can usefully be applied to sublists to
758 * move one or more elements within a list while preserving the
759 * order of the remaining elements. For example, the following idiom
760 * moves the element at index <tt>j</tt> forward to position
761 * <tt>k</tt> (which must be greater than or equal to <tt>j</tt>):
763 * Collections.rotate(list.subList(j, k+1), -1);
765 * To make this concrete, suppose <tt>list</tt> comprises
766 * <tt>[a, b, c, d, e]</tt>. To move the element at index <tt>1</tt>
767 * (<tt>b</tt>) forward two positions, perform the following invocation:
769 * Collections.rotate(l.subList(1, 4), -1);
771 * The resulting list is <tt>[a, c, d, b, e]</tt>.
773 * <p>To move more than one element forward, increase the absolute value
774 * of the rotation distance. To move elements backward, use a positive
777 * <p>If the specified list is small or implements the {@link
778 * RandomAccess} interface, this implementation exchanges the first
779 * element into the location it should go, and then repeatedly exchanges
780 * the displaced element into the location it should go until a displaced
781 * element is swapped into the first element. If necessary, the process
782 * is repeated on the second and successive elements, until the rotation
783 * is complete. If the specified list is large and doesn't implement the
784 * <tt>RandomAccess</tt> interface, this implementation breaks the
785 * list into two sublist views around index <tt>-distance mod size</tt>.
786 * Then the {@link #reverse(List)} method is invoked on each sublist view,
787 * and finally it is invoked on the entire list. For a more complete
788 * description of both algorithms, see Section 2.3 of Jon Bentley's
789 * <i>Programming Pearls</i> (Addison-Wesley, 1986).
791 * @param list the list to be rotated.
792 * @param distance the distance to rotate the list. There are no
793 * constraints on this value; it may be zero, negative, or
794 * greater than <tt>list.size()</tt>.
795 * @throws UnsupportedOperationException if the specified list or
796 * its list-iterator does not support the <tt>set</tt> operation.
799 public static void rotate(List<?> list, int distance) {
800 if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD)
801 rotate1(list, distance);
803 rotate2(list, distance);
806 private static <T> void rotate1(List<T> list, int distance) {
807 int size = list.size();
810 distance = distance % size;
816 for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) {
817 T displaced = list.get(cycleStart);
823 displaced = list.set(i, displaced);
825 } while (i != cycleStart);
829 private static void rotate2(List<?> list, int distance) {
830 int size = list.size();
833 int mid = -distance % size;
839 reverse(list.subList(0, mid));
840 reverse(list.subList(mid, size));
845 * Replaces all occurrences of one specified value in a list with another.
846 * More formally, replaces with <tt>newVal</tt> each element <tt>e</tt>
847 * in <tt>list</tt> such that
848 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
849 * (This method has no effect on the size of the list.)
851 * @param list the list in which replacement is to occur.
852 * @param oldVal the old value to be replaced.
853 * @param newVal the new value with which <tt>oldVal</tt> is to be
855 * @return <tt>true</tt> if <tt>list</tt> contained one or more elements
856 * <tt>e</tt> such that
857 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
858 * @throws UnsupportedOperationException if the specified list or
859 * its list-iterator does not support the <tt>set</tt> operation.
862 public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) {
863 boolean result = false;
864 int size = list.size();
865 if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) {
867 for (int i=0; i<size; i++) {
868 if (list.get(i)==null) {
874 for (int i=0; i<size; i++) {
875 if (oldVal.equals(list.get(i))) {
882 ListIterator<T> itr=list.listIterator();
884 for (int i=0; i<size; i++) {
885 if (itr.next()==null) {
891 for (int i=0; i<size; i++) {
892 if (oldVal.equals(itr.next())) {
903 * Returns the starting position of the first occurrence of the specified
904 * target list within the specified source list, or -1 if there is no
905 * such occurrence. More formally, returns the lowest index <tt>i</tt>
906 * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
907 * or -1 if there is no such index. (Returns -1 if
908 * <tt>target.size() > source.size()</tt>.)
910 * <p>This implementation uses the "brute force" technique of scanning
911 * over the source list, looking for a match with the target at each
914 * @param source the list in which to search for the first occurrence
915 * of <tt>target</tt>.
916 * @param target the list to search for as a subList of <tt>source</tt>.
917 * @return the starting position of the first occurrence of the specified
918 * target list within the specified source list, or -1 if there
919 * is no such occurrence.
922 public static int indexOfSubList(List<?> source, List<?> target) {
923 int sourceSize = source.size();
924 int targetSize = target.size();
925 int maxCandidate = sourceSize - targetSize;
927 if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
928 (source instanceof RandomAccess&&target instanceof RandomAccess)) {
930 for (int candidate = 0; candidate <= maxCandidate; candidate++) {
931 for (int i=0, j=candidate; i<targetSize; i++, j++)
932 if (!eq(target.get(i), source.get(j)))
933 continue nextCand; // Element mismatch, try next cand
934 return candidate; // All elements of candidate matched target
936 } else { // Iterator version of above algorithm
937 ListIterator<?> si = source.listIterator();
939 for (int candidate = 0; candidate <= maxCandidate; candidate++) {
940 ListIterator<?> ti = target.listIterator();
941 for (int i=0; i<targetSize; i++) {
942 if (!eq(ti.next(), si.next())) {
943 // Back up source iterator to next candidate
944 for (int j=0; j<i; j++)
952 return -1; // No candidate matched the target
956 * Returns the starting position of the last occurrence of the specified
957 * target list within the specified source list, or -1 if there is no such
958 * occurrence. More formally, returns the highest index <tt>i</tt>
959 * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
960 * or -1 if there is no such index. (Returns -1 if
961 * <tt>target.size() > source.size()</tt>.)
963 * <p>This implementation uses the "brute force" technique of iterating
964 * over the source list, looking for a match with the target at each
967 * @param source the list in which to search for the last occurrence
968 * of <tt>target</tt>.
969 * @param target the list to search for as a subList of <tt>source</tt>.
970 * @return the starting position of the last occurrence of the specified
971 * target list within the specified source list, or -1 if there
972 * is no such occurrence.
975 public static int lastIndexOfSubList(List<?> source, List<?> target) {
976 int sourceSize = source.size();
977 int targetSize = target.size();
978 int maxCandidate = sourceSize - targetSize;
980 if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
981 source instanceof RandomAccess) { // Index access version
983 for (int candidate = maxCandidate; candidate >= 0; candidate--) {
984 for (int i=0, j=candidate; i<targetSize; i++, j++)
985 if (!eq(target.get(i), source.get(j)))
986 continue nextCand; // Element mismatch, try next cand
987 return candidate; // All elements of candidate matched target
989 } else { // Iterator version of above algorithm
990 if (maxCandidate < 0)
992 ListIterator<?> si = source.listIterator(maxCandidate);
994 for (int candidate = maxCandidate; candidate >= 0; candidate--) {
995 ListIterator<?> ti = target.listIterator();
996 for (int i=0; i<targetSize; i++) {
997 if (!eq(ti.next(), si.next())) {
998 if (candidate != 0) {
999 // Back up source iterator to next candidate
1000 for (int j=0; j<=i+1; j++)
1009 return -1; // No candidate matched the target
1013 // Unmodifiable Wrappers
1016 * Returns an unmodifiable view of the specified collection. This method
1017 * allows modules to provide users with "read-only" access to internal
1018 * collections. Query operations on the returned collection "read through"
1019 * to the specified collection, and attempts to modify the returned
1020 * collection, whether direct or via its iterator, result in an
1021 * <tt>UnsupportedOperationException</tt>.<p>
1023 * The returned collection does <i>not</i> pass the hashCode and equals
1024 * operations through to the backing collection, but relies on
1025 * <tt>Object</tt>'s <tt>equals</tt> and <tt>hashCode</tt> methods. This
1026 * is necessary to preserve the contracts of these operations in the case
1027 * that the backing collection is a set or a list.<p>
1029 * The returned collection will be serializable if the specified collection
1032 * @param c the collection for which an unmodifiable view is to be
1034 * @return an unmodifiable view of the specified collection.
1036 public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) {
1037 return new UnmodifiableCollection<>(c);
1043 static class UnmodifiableCollection<E> implements Collection<E>, Serializable {
1044 private static final long serialVersionUID = 1820017752578914078L;
1046 final Collection<? extends E> c;
1048 UnmodifiableCollection(Collection<? extends E> c) {
1050 throw new NullPointerException();
1054 public int size() {return c.size();}
1055 public boolean isEmpty() {return c.isEmpty();}
1056 public boolean contains(Object o) {return c.contains(o);}
1057 public Object[] toArray() {return c.toArray();}
1058 public <T> T[] toArray(T[] a) {return c.toArray(a);}
1059 public String toString() {return c.toString();}
1061 public Iterator<E> iterator() {
1062 return new Iterator<E>() {
1063 private final Iterator<? extends E> i = c.iterator();
1065 public boolean hasNext() {return i.hasNext();}
1066 public E next() {return i.next();}
1067 public void remove() {
1068 throw new UnsupportedOperationException();
1073 public boolean add(E e) {
1074 throw new UnsupportedOperationException();
1076 public boolean remove(Object o) {
1077 throw new UnsupportedOperationException();
1080 public boolean containsAll(Collection<?> coll) {
1081 return c.containsAll(coll);
1083 public boolean addAll(Collection<? extends E> coll) {
1084 throw new UnsupportedOperationException();
1086 public boolean removeAll(Collection<?> coll) {
1087 throw new UnsupportedOperationException();
1089 public boolean retainAll(Collection<?> coll) {
1090 throw new UnsupportedOperationException();
1092 public void clear() {
1093 throw new UnsupportedOperationException();
1098 * Returns an unmodifiable view of the specified set. This method allows
1099 * modules to provide users with "read-only" access to internal sets.
1100 * Query operations on the returned set "read through" to the specified
1101 * set, and attempts to modify the returned set, whether direct or via its
1102 * iterator, result in an <tt>UnsupportedOperationException</tt>.<p>
1104 * The returned set will be serializable if the specified set
1107 * @param s the set for which an unmodifiable view is to be returned.
1108 * @return an unmodifiable view of the specified set.
1110 public static <T> Set<T> unmodifiableSet(Set<? extends T> s) {
1111 return new UnmodifiableSet<>(s);
1117 static class UnmodifiableSet<E> extends UnmodifiableCollection<E>
1118 implements Set<E>, Serializable {
1119 private static final long serialVersionUID = -9215047833775013803L;
1121 UnmodifiableSet(Set<? extends E> s) {super(s);}
1122 public boolean equals(Object o) {return o == this || c.equals(o);}
1123 public int hashCode() {return c.hashCode();}
1127 * Returns an unmodifiable view of the specified sorted set. This method
1128 * allows modules to provide users with "read-only" access to internal
1129 * sorted sets. Query operations on the returned sorted set "read
1130 * through" to the specified sorted set. Attempts to modify the returned
1131 * sorted set, whether direct, via its iterator, or via its
1132 * <tt>subSet</tt>, <tt>headSet</tt>, or <tt>tailSet</tt> views, result in
1133 * an <tt>UnsupportedOperationException</tt>.<p>
1135 * The returned sorted set will be serializable if the specified sorted set
1138 * @param s the sorted set for which an unmodifiable view is to be
1140 * @return an unmodifiable view of the specified sorted set.
1142 public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) {
1143 return new UnmodifiableSortedSet<>(s);
1149 static class UnmodifiableSortedSet<E>
1150 extends UnmodifiableSet<E>
1151 implements SortedSet<E>, Serializable {
1152 private static final long serialVersionUID = -4929149591599911165L;
1153 private final SortedSet<E> ss;
1155 UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;}
1157 public Comparator<? super E> comparator() {return ss.comparator();}
1159 public SortedSet<E> subSet(E fromElement, E toElement) {
1160 return new UnmodifiableSortedSet<>(ss.subSet(fromElement,toElement));
1162 public SortedSet<E> headSet(E toElement) {
1163 return new UnmodifiableSortedSet<>(ss.headSet(toElement));
1165 public SortedSet<E> tailSet(E fromElement) {
1166 return new UnmodifiableSortedSet<>(ss.tailSet(fromElement));
1169 public E first() {return ss.first();}
1170 public E last() {return ss.last();}
1174 * Returns an unmodifiable view of the specified list. This method allows
1175 * modules to provide users with "read-only" access to internal
1176 * lists. Query operations on the returned list "read through" to the
1177 * specified list, and attempts to modify the returned list, whether
1178 * direct or via its iterator, result in an
1179 * <tt>UnsupportedOperationException</tt>.<p>
1181 * The returned list will be serializable if the specified list
1182 * is serializable. Similarly, the returned list will implement
1183 * {@link RandomAccess} if the specified list does.
1185 * @param list the list for which an unmodifiable view is to be returned.
1186 * @return an unmodifiable view of the specified list.
1188 public static <T> List<T> unmodifiableList(List<? extends T> list) {
1189 return (list instanceof RandomAccess ?
1190 new UnmodifiableRandomAccessList<>(list) :
1191 new UnmodifiableList<>(list));
1197 static class UnmodifiableList<E> extends UnmodifiableCollection<E>
1198 implements List<E> {
1199 private static final long serialVersionUID = -283967356065247728L;
1200 final List<? extends E> list;
1202 UnmodifiableList(List<? extends E> list) {
1207 public boolean equals(Object o) {return o == this || list.equals(o);}
1208 public int hashCode() {return list.hashCode();}
1210 public E get(int index) {return list.get(index);}
1211 public E set(int index, E element) {
1212 throw new UnsupportedOperationException();
1214 public void add(int index, E element) {
1215 throw new UnsupportedOperationException();
1217 public E remove(int index) {
1218 throw new UnsupportedOperationException();
1220 public int indexOf(Object o) {return list.indexOf(o);}
1221 public int lastIndexOf(Object o) {return list.lastIndexOf(o);}
1222 public boolean addAll(int index, Collection<? extends E> c) {
1223 throw new UnsupportedOperationException();
1225 public ListIterator<E> listIterator() {return listIterator(0);}
1227 public ListIterator<E> listIterator(final int index) {
1228 return new ListIterator<E>() {
1229 private final ListIterator<? extends E> i
1230 = list.listIterator(index);
1232 public boolean hasNext() {return i.hasNext();}
1233 public E next() {return i.next();}
1234 public boolean hasPrevious() {return i.hasPrevious();}
1235 public E previous() {return i.previous();}
1236 public int nextIndex() {return i.nextIndex();}
1237 public int previousIndex() {return i.previousIndex();}
1239 public void remove() {
1240 throw new UnsupportedOperationException();
1242 public void set(E e) {
1243 throw new UnsupportedOperationException();
1245 public void add(E e) {
1246 throw new UnsupportedOperationException();
1251 public List<E> subList(int fromIndex, int toIndex) {
1252 return new UnmodifiableList<>(list.subList(fromIndex, toIndex));
1256 * UnmodifiableRandomAccessList instances are serialized as
1257 * UnmodifiableList instances to allow them to be deserialized
1258 * in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList).
1259 * This method inverts the transformation. As a beneficial
1260 * side-effect, it also grafts the RandomAccess marker onto
1261 * UnmodifiableList instances that were serialized in pre-1.4 JREs.
1263 * Note: Unfortunately, UnmodifiableRandomAccessList instances
1264 * serialized in 1.4.1 and deserialized in 1.4 will become
1265 * UnmodifiableList instances, as this method was missing in 1.4.
1267 private Object readResolve() {
1268 return (list instanceof RandomAccess
1269 ? new UnmodifiableRandomAccessList<>(list)
1277 static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E>
1278 implements RandomAccess
1280 UnmodifiableRandomAccessList(List<? extends E> list) {
1284 public List<E> subList(int fromIndex, int toIndex) {
1285 return new UnmodifiableRandomAccessList<>(
1286 list.subList(fromIndex, toIndex));
1289 private static final long serialVersionUID = -2542308836966382001L;
1292 * Allows instances to be deserialized in pre-1.4 JREs (which do
1293 * not have UnmodifiableRandomAccessList). UnmodifiableList has
1294 * a readResolve method that inverts this transformation upon
1297 private Object writeReplace() {
1298 return new UnmodifiableList<>(list);
1303 * Returns an unmodifiable view of the specified map. This method
1304 * allows modules to provide users with "read-only" access to internal
1305 * maps. Query operations on the returned map "read through"
1306 * to the specified map, and attempts to modify the returned
1307 * map, whether direct or via its collection views, result in an
1308 * <tt>UnsupportedOperationException</tt>.<p>
1310 * The returned map will be serializable if the specified map
1313 * @param m the map for which an unmodifiable view is to be returned.
1314 * @return an unmodifiable view of the specified map.
1316 public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) {
1317 return new UnmodifiableMap<>(m);
1323 private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable {
1324 private static final long serialVersionUID = -1034234728574286014L;
1326 private final Map<? extends K, ? extends V> m;
1328 UnmodifiableMap(Map<? extends K, ? extends V> m) {
1330 throw new NullPointerException();
1334 public int size() {return m.size();}
1335 public boolean isEmpty() {return m.isEmpty();}
1336 public boolean containsKey(Object key) {return m.containsKey(key);}
1337 public boolean containsValue(Object val) {return m.containsValue(val);}
1338 public V get(Object key) {return m.get(key);}
1340 public V put(K key, V value) {
1341 throw new UnsupportedOperationException();
1343 public V remove(Object key) {
1344 throw new UnsupportedOperationException();
1346 public void putAll(Map<? extends K, ? extends V> m) {
1347 throw new UnsupportedOperationException();
1349 public void clear() {
1350 throw new UnsupportedOperationException();
1353 private transient Set<K> keySet = null;
1354 private transient Set<Map.Entry<K,V>> entrySet = null;
1355 private transient Collection<V> values = null;
1357 public Set<K> keySet() {
1359 keySet = unmodifiableSet(m.keySet());
1363 public Set<Map.Entry<K,V>> entrySet() {
1365 entrySet = new UnmodifiableEntrySet<>(m.entrySet());
1369 public Collection<V> values() {
1371 values = unmodifiableCollection(m.values());
1375 public boolean equals(Object o) {return o == this || m.equals(o);}
1376 public int hashCode() {return m.hashCode();}
1377 public String toString() {return m.toString();}
1380 * We need this class in addition to UnmodifiableSet as
1381 * Map.Entries themselves permit modification of the backing Map
1382 * via their setValue operation. This class is subtle: there are
1383 * many possible attacks that must be thwarted.
1387 static class UnmodifiableEntrySet<K,V>
1388 extends UnmodifiableSet<Map.Entry<K,V>> {
1389 private static final long serialVersionUID = 7854390611657943733L;
1391 UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) {
1394 public Iterator<Map.Entry<K,V>> iterator() {
1395 return new Iterator<Map.Entry<K,V>>() {
1396 private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator();
1398 public boolean hasNext() {
1401 public Map.Entry<K,V> next() {
1402 return new UnmodifiableEntry<>(i.next());
1404 public void remove() {
1405 throw new UnsupportedOperationException();
1410 public Object[] toArray() {
1411 Object[] a = c.toArray();
1412 for (int i=0; i<a.length; i++)
1413 a[i] = new UnmodifiableEntry<>((Map.Entry<K,V>)a[i]);
1417 public <T> T[] toArray(T[] a) {
1418 // We don't pass a to c.toArray, to avoid window of
1419 // vulnerability wherein an unscrupulous multithreaded client
1420 // could get his hands on raw (unwrapped) Entries from c.
1421 Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
1423 for (int i=0; i<arr.length; i++)
1424 arr[i] = new UnmodifiableEntry<>((Map.Entry<K,V>)arr[i]);
1426 if (arr.length > a.length)
1429 System.arraycopy(arr, 0, a, 0, arr.length);
1430 if (a.length > arr.length)
1431 a[arr.length] = null;
1436 * This method is overridden to protect the backing set against
1437 * an object with a nefarious equals function that senses
1438 * that the equality-candidate is Map.Entry and calls its
1441 public boolean contains(Object o) {
1442 if (!(o instanceof Map.Entry))
1445 new UnmodifiableEntry<>((Map.Entry<?,?>) o));
1449 * The next two methods are overridden to protect against
1450 * an unscrupulous List whose contains(Object o) method senses
1451 * when o is a Map.Entry, and calls o.setValue.
1453 public boolean containsAll(Collection<?> coll) {
1454 for (Object e : coll) {
1455 if (!contains(e)) // Invokes safe contains() above
1460 public boolean equals(Object o) {
1464 if (!(o instanceof Set))
1467 if (s.size() != c.size())
1469 return containsAll(s); // Invokes safe containsAll() above
1473 * This "wrapper class" serves two purposes: it prevents
1474 * the client from modifying the backing Map, by short-circuiting
1475 * the setValue method, and it protects the backing Map against
1476 * an ill-behaved Map.Entry that attempts to modify another
1477 * Map Entry when asked to perform an equality check.
1479 private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> {
1480 private Map.Entry<? extends K, ? extends V> e;
1482 UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) {this.e = e;}
1484 public K getKey() {return e.getKey();}
1485 public V getValue() {return e.getValue();}
1486 public V setValue(V value) {
1487 throw new UnsupportedOperationException();
1489 public int hashCode() {return e.hashCode();}
1490 public boolean equals(Object o) {
1491 if (!(o instanceof Map.Entry))
1493 Map.Entry t = (Map.Entry)o;
1494 return eq(e.getKey(), t.getKey()) &&
1495 eq(e.getValue(), t.getValue());
1497 public String toString() {return e.toString();}
1503 * Returns an unmodifiable view of the specified sorted map. This method
1504 * allows modules to provide users with "read-only" access to internal
1505 * sorted maps. Query operations on the returned sorted map "read through"
1506 * to the specified sorted map. Attempts to modify the returned
1507 * sorted map, whether direct, via its collection views, or via its
1508 * <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in
1509 * an <tt>UnsupportedOperationException</tt>.<p>
1511 * The returned sorted map will be serializable if the specified sorted map
1514 * @param m the sorted map for which an unmodifiable view is to be
1516 * @return an unmodifiable view of the specified sorted map.
1518 public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) {
1519 return new UnmodifiableSortedMap<>(m);
1525 static class UnmodifiableSortedMap<K,V>
1526 extends UnmodifiableMap<K,V>
1527 implements SortedMap<K,V>, Serializable {
1528 private static final long serialVersionUID = -8806743815996713206L;
1530 private final SortedMap<K, ? extends V> sm;
1532 UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m;}
1534 public Comparator<? super K> comparator() {return sm.comparator();}
1536 public SortedMap<K,V> subMap(K fromKey, K toKey) {
1537 return new UnmodifiableSortedMap<>(sm.subMap(fromKey, toKey));
1539 public SortedMap<K,V> headMap(K toKey) {
1540 return new UnmodifiableSortedMap<>(sm.headMap(toKey));
1542 public SortedMap<K,V> tailMap(K fromKey) {
1543 return new UnmodifiableSortedMap<>(sm.tailMap(fromKey));
1546 public K firstKey() {return sm.firstKey();}
1547 public K lastKey() {return sm.lastKey();}
1554 * Returns a synchronized (thread-safe) collection backed by the specified
1555 * collection. In order to guarantee serial access, it is critical that
1556 * <strong>all</strong> access to the backing collection is accomplished
1557 * through the returned collection.<p>
1559 * It is imperative that the user manually synchronize on the returned
1560 * collection when iterating over it:
1562 * Collection c = Collections.synchronizedCollection(myCollection);
1564 * synchronized (c) {
1565 * Iterator i = c.iterator(); // Must be in the synchronized block
1566 * while (i.hasNext())
1570 * Failure to follow this advice may result in non-deterministic behavior.
1572 * <p>The returned collection does <i>not</i> pass the <tt>hashCode</tt>
1573 * and <tt>equals</tt> operations through to the backing collection, but
1574 * relies on <tt>Object</tt>'s equals and hashCode methods. This is
1575 * necessary to preserve the contracts of these operations in the case
1576 * that the backing collection is a set or a list.<p>
1578 * The returned collection will be serializable if the specified collection
1581 * @param c the collection to be "wrapped" in a synchronized collection.
1582 * @return a synchronized view of the specified collection.
1584 public static <T> Collection<T> synchronizedCollection(Collection<T> c) {
1585 return new SynchronizedCollection<>(c);
1588 static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) {
1589 return new SynchronizedCollection<>(c, mutex);
1595 static class SynchronizedCollection<E> implements Collection<E>, Serializable {
1596 private static final long serialVersionUID = 3053995032091335093L;
1598 final Collection<E> c; // Backing Collection
1599 final Object mutex; // Object on which to synchronize
1601 SynchronizedCollection(Collection<E> c) {
1603 throw new NullPointerException();
1607 SynchronizedCollection(Collection<E> c, Object mutex) {
1613 synchronized (mutex) {return c.size();}
1615 public boolean isEmpty() {
1616 synchronized (mutex) {return c.isEmpty();}
1618 public boolean contains(Object o) {
1619 synchronized (mutex) {return c.contains(o);}
1621 public Object[] toArray() {
1622 synchronized (mutex) {return c.toArray();}
1624 public <T> T[] toArray(T[] a) {
1625 synchronized (mutex) {return c.toArray(a);}
1628 public Iterator<E> iterator() {
1629 return c.iterator(); // Must be manually synched by user!
1632 public boolean add(E e) {
1633 synchronized (mutex) {return c.add(e);}
1635 public boolean remove(Object o) {
1636 synchronized (mutex) {return c.remove(o);}
1639 public boolean containsAll(Collection<?> coll) {
1640 synchronized (mutex) {return c.containsAll(coll);}
1642 public boolean addAll(Collection<? extends E> coll) {
1643 synchronized (mutex) {return c.addAll(coll);}
1645 public boolean removeAll(Collection<?> coll) {
1646 synchronized (mutex) {return c.removeAll(coll);}
1648 public boolean retainAll(Collection<?> coll) {
1649 synchronized (mutex) {return c.retainAll(coll);}
1651 public void clear() {
1652 synchronized (mutex) {c.clear();}
1654 public String toString() {
1655 synchronized (mutex) {return c.toString();}
1660 * Returns a synchronized (thread-safe) set backed by the specified
1661 * set. In order to guarantee serial access, it is critical that
1662 * <strong>all</strong> access to the backing set is accomplished
1663 * through the returned set.<p>
1665 * It is imperative that the user manually synchronize on the returned
1666 * set when iterating over it:
1668 * Set s = Collections.synchronizedSet(new HashSet());
1670 * synchronized (s) {
1671 * Iterator i = s.iterator(); // Must be in the synchronized block
1672 * while (i.hasNext())
1676 * Failure to follow this advice may result in non-deterministic behavior.
1678 * <p>The returned set will be serializable if the specified set is
1681 * @param s the set to be "wrapped" in a synchronized set.
1682 * @return a synchronized view of the specified set.
1684 public static <T> Set<T> synchronizedSet(Set<T> s) {
1685 return new SynchronizedSet<>(s);
1688 static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) {
1689 return new SynchronizedSet<>(s, mutex);
1695 static class SynchronizedSet<E>
1696 extends SynchronizedCollection<E>
1698 private static final long serialVersionUID = 487447009682186044L;
1700 SynchronizedSet(Set<E> s) {
1703 SynchronizedSet(Set<E> s, Object mutex) {
1707 public boolean equals(Object o) {
1708 synchronized (mutex) {return c.equals(o);}
1710 public int hashCode() {
1711 synchronized (mutex) {return c.hashCode();}
1716 * Returns a synchronized (thread-safe) sorted set backed by the specified
1717 * sorted set. In order to guarantee serial access, it is critical that
1718 * <strong>all</strong> access to the backing sorted set is accomplished
1719 * through the returned sorted set (or its views).<p>
1721 * It is imperative that the user manually synchronize on the returned
1722 * sorted set when iterating over it or any of its <tt>subSet</tt>,
1723 * <tt>headSet</tt>, or <tt>tailSet</tt> views.
1725 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
1727 * synchronized (s) {
1728 * Iterator i = s.iterator(); // Must be in the synchronized block
1729 * while (i.hasNext())
1735 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
1736 * SortedSet s2 = s.headSet(foo);
1738 * synchronized (s) { // Note: s, not s2!!!
1739 * Iterator i = s2.iterator(); // Must be in the synchronized block
1740 * while (i.hasNext())
1744 * Failure to follow this advice may result in non-deterministic behavior.
1746 * <p>The returned sorted set will be serializable if the specified
1747 * sorted set is serializable.
1749 * @param s the sorted set to be "wrapped" in a synchronized sorted set.
1750 * @return a synchronized view of the specified sorted set.
1752 public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) {
1753 return new SynchronizedSortedSet<>(s);
1759 static class SynchronizedSortedSet<E>
1760 extends SynchronizedSet<E>
1761 implements SortedSet<E>
1763 private static final long serialVersionUID = 8695801310862127406L;
1765 private final SortedSet<E> ss;
1767 SynchronizedSortedSet(SortedSet<E> s) {
1771 SynchronizedSortedSet(SortedSet<E> s, Object mutex) {
1776 public Comparator<? super E> comparator() {
1777 synchronized (mutex) {return ss.comparator();}
1780 public SortedSet<E> subSet(E fromElement, E toElement) {
1781 synchronized (mutex) {
1782 return new SynchronizedSortedSet<>(
1783 ss.subSet(fromElement, toElement), mutex);
1786 public SortedSet<E> headSet(E toElement) {
1787 synchronized (mutex) {
1788 return new SynchronizedSortedSet<>(ss.headSet(toElement), mutex);
1791 public SortedSet<E> tailSet(E fromElement) {
1792 synchronized (mutex) {
1793 return new SynchronizedSortedSet<>(ss.tailSet(fromElement),mutex);
1798 synchronized (mutex) {return ss.first();}
1801 synchronized (mutex) {return ss.last();}
1806 * Returns a synchronized (thread-safe) list backed by the specified
1807 * list. In order to guarantee serial access, it is critical that
1808 * <strong>all</strong> access to the backing list is accomplished
1809 * through the returned list.<p>
1811 * It is imperative that the user manually synchronize on the returned
1812 * list when iterating over it:
1814 * List list = Collections.synchronizedList(new ArrayList());
1816 * synchronized (list) {
1817 * Iterator i = list.iterator(); // Must be in synchronized block
1818 * while (i.hasNext())
1822 * Failure to follow this advice may result in non-deterministic behavior.
1824 * <p>The returned list will be serializable if the specified list is
1827 * @param list the list to be "wrapped" in a synchronized list.
1828 * @return a synchronized view of the specified list.
1830 public static <T> List<T> synchronizedList(List<T> list) {
1831 return (list instanceof RandomAccess ?
1832 new SynchronizedRandomAccessList<>(list) :
1833 new SynchronizedList<>(list));
1836 static <T> List<T> synchronizedList(List<T> list, Object mutex) {
1837 return (list instanceof RandomAccess ?
1838 new SynchronizedRandomAccessList<>(list, mutex) :
1839 new SynchronizedList<>(list, mutex));
1845 static class SynchronizedList<E>
1846 extends SynchronizedCollection<E>
1847 implements List<E> {
1848 private static final long serialVersionUID = -7754090372962971524L;
1852 SynchronizedList(List<E> list) {
1856 SynchronizedList(List<E> list, Object mutex) {
1861 public boolean equals(Object o) {
1862 synchronized (mutex) {return list.equals(o);}
1864 public int hashCode() {
1865 synchronized (mutex) {return list.hashCode();}
1868 public E get(int index) {
1869 synchronized (mutex) {return list.get(index);}
1871 public E set(int index, E element) {
1872 synchronized (mutex) {return list.set(index, element);}
1874 public void add(int index, E element) {
1875 synchronized (mutex) {list.add(index, element);}
1877 public E remove(int index) {
1878 synchronized (mutex) {return list.remove(index);}
1881 public int indexOf(Object o) {
1882 synchronized (mutex) {return list.indexOf(o);}
1884 public int lastIndexOf(Object o) {
1885 synchronized (mutex) {return list.lastIndexOf(o);}
1888 public boolean addAll(int index, Collection<? extends E> c) {
1889 synchronized (mutex) {return list.addAll(index, c);}
1892 public ListIterator<E> listIterator() {
1893 return list.listIterator(); // Must be manually synched by user
1896 public ListIterator<E> listIterator(int index) {
1897 return list.listIterator(index); // Must be manually synched by user
1900 public List<E> subList(int fromIndex, int toIndex) {
1901 synchronized (mutex) {
1902 return new SynchronizedList<>(list.subList(fromIndex, toIndex),
1908 * SynchronizedRandomAccessList instances are serialized as
1909 * SynchronizedList instances to allow them to be deserialized
1910 * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList).
1911 * This method inverts the transformation. As a beneficial
1912 * side-effect, it also grafts the RandomAccess marker onto
1913 * SynchronizedList instances that were serialized in pre-1.4 JREs.
1915 * Note: Unfortunately, SynchronizedRandomAccessList instances
1916 * serialized in 1.4.1 and deserialized in 1.4 will become
1917 * SynchronizedList instances, as this method was missing in 1.4.
1919 private Object readResolve() {
1920 return (list instanceof RandomAccess
1921 ? new SynchronizedRandomAccessList<>(list)
1929 static class SynchronizedRandomAccessList<E>
1930 extends SynchronizedList<E>
1931 implements RandomAccess {
1933 SynchronizedRandomAccessList(List<E> list) {
1937 SynchronizedRandomAccessList(List<E> list, Object mutex) {
1941 public List<E> subList(int fromIndex, int toIndex) {
1942 synchronized (mutex) {
1943 return new SynchronizedRandomAccessList<>(
1944 list.subList(fromIndex, toIndex), mutex);
1948 private static final long serialVersionUID = 1530674583602358482L;
1951 * Allows instances to be deserialized in pre-1.4 JREs (which do
1952 * not have SynchronizedRandomAccessList). SynchronizedList has
1953 * a readResolve method that inverts this transformation upon
1956 private Object writeReplace() {
1957 return new SynchronizedList<>(list);
1962 * Returns a synchronized (thread-safe) map backed by the specified
1963 * map. In order to guarantee serial access, it is critical that
1964 * <strong>all</strong> access to the backing map is accomplished
1965 * through the returned map.<p>
1967 * It is imperative that the user manually synchronize on the returned
1968 * map when iterating over any of its collection views:
1970 * Map m = Collections.synchronizedMap(new HashMap());
1972 * Set s = m.keySet(); // Needn't be in synchronized block
1974 * synchronized (m) { // Synchronizing on m, not s!
1975 * Iterator i = s.iterator(); // Must be in synchronized block
1976 * while (i.hasNext())
1980 * Failure to follow this advice may result in non-deterministic behavior.
1982 * <p>The returned map will be serializable if the specified map is
1985 * @param m the map to be "wrapped" in a synchronized map.
1986 * @return a synchronized view of the specified map.
1988 public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) {
1989 return new SynchronizedMap<>(m);
1995 private static class SynchronizedMap<K,V>
1996 implements Map<K,V>, Serializable {
1997 private static final long serialVersionUID = 1978198479659022715L;
1999 private final Map<K,V> m; // Backing Map
2000 final Object mutex; // Object on which to synchronize
2002 SynchronizedMap(Map<K,V> m) {
2004 throw new NullPointerException();
2009 SynchronizedMap(Map<K,V> m, Object mutex) {
2015 synchronized (mutex) {return m.size();}
2017 public boolean isEmpty() {
2018 synchronized (mutex) {return m.isEmpty();}
2020 public boolean containsKey(Object key) {
2021 synchronized (mutex) {return m.containsKey(key);}
2023 public boolean containsValue(Object value) {
2024 synchronized (mutex) {return m.containsValue(value);}
2026 public V get(Object key) {
2027 synchronized (mutex) {return m.get(key);}
2030 public V put(K key, V value) {
2031 synchronized (mutex) {return m.put(key, value);}
2033 public V remove(Object key) {
2034 synchronized (mutex) {return m.remove(key);}
2036 public void putAll(Map<? extends K, ? extends V> map) {
2037 synchronized (mutex) {m.putAll(map);}
2039 public void clear() {
2040 synchronized (mutex) {m.clear();}
2043 private transient Set<K> keySet = null;
2044 private transient Set<Map.Entry<K,V>> entrySet = null;
2045 private transient Collection<V> values = null;
2047 public Set<K> keySet() {
2048 synchronized (mutex) {
2050 keySet = new SynchronizedSet<>(m.keySet(), mutex);
2055 public Set<Map.Entry<K,V>> entrySet() {
2056 synchronized (mutex) {
2058 entrySet = new SynchronizedSet<>(m.entrySet(), mutex);
2063 public Collection<V> values() {
2064 synchronized (mutex) {
2066 values = new SynchronizedCollection<>(m.values(), mutex);
2071 public boolean equals(Object o) {
2072 synchronized (mutex) {return m.equals(o);}
2074 public int hashCode() {
2075 synchronized (mutex) {return m.hashCode();}
2077 public String toString() {
2078 synchronized (mutex) {return m.toString();}
2083 * Returns a synchronized (thread-safe) sorted map backed by the specified
2084 * sorted map. In order to guarantee serial access, it is critical that
2085 * <strong>all</strong> access to the backing sorted map is accomplished
2086 * through the returned sorted map (or its views).<p>
2088 * It is imperative that the user manually synchronize on the returned
2089 * sorted map when iterating over any of its collection views, or the
2090 * collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or
2091 * <tt>tailMap</tt> views.
2093 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
2095 * Set s = m.keySet(); // Needn't be in synchronized block
2097 * synchronized (m) { // Synchronizing on m, not s!
2098 * Iterator i = s.iterator(); // Must be in synchronized block
2099 * while (i.hasNext())
2105 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
2106 * SortedMap m2 = m.subMap(foo, bar);
2108 * Set s2 = m2.keySet(); // Needn't be in synchronized block
2110 * synchronized (m) { // Synchronizing on m, not m2 or s2!
2111 * Iterator i = s.iterator(); // Must be in synchronized block
2112 * while (i.hasNext())
2116 * Failure to follow this advice may result in non-deterministic behavior.
2118 * <p>The returned sorted map will be serializable if the specified
2119 * sorted map is serializable.
2121 * @param m the sorted map to be "wrapped" in a synchronized sorted map.
2122 * @return a synchronized view of the specified sorted map.
2124 public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) {
2125 return new SynchronizedSortedMap<>(m);
2132 static class SynchronizedSortedMap<K,V>
2133 extends SynchronizedMap<K,V>
2134 implements SortedMap<K,V>
2136 private static final long serialVersionUID = -8798146769416483793L;
2138 private final SortedMap<K,V> sm;
2140 SynchronizedSortedMap(SortedMap<K,V> m) {
2144 SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) {
2149 public Comparator<? super K> comparator() {
2150 synchronized (mutex) {return sm.comparator();}
2153 public SortedMap<K,V> subMap(K fromKey, K toKey) {
2154 synchronized (mutex) {
2155 return new SynchronizedSortedMap<>(
2156 sm.subMap(fromKey, toKey), mutex);
2159 public SortedMap<K,V> headMap(K toKey) {
2160 synchronized (mutex) {
2161 return new SynchronizedSortedMap<>(sm.headMap(toKey), mutex);
2164 public SortedMap<K,V> tailMap(K fromKey) {
2165 synchronized (mutex) {
2166 return new SynchronizedSortedMap<>(sm.tailMap(fromKey),mutex);
2170 public K firstKey() {
2171 synchronized (mutex) {return sm.firstKey();}
2173 public K lastKey() {
2174 synchronized (mutex) {return sm.lastKey();}
2178 // Dynamically typesafe collection wrappers
2181 * Returns a dynamically typesafe view of the specified collection.
2182 * Any attempt to insert an element of the wrong type will result in an
2183 * immediate {@link ClassCastException}. Assuming a collection
2184 * contains no incorrectly typed elements prior to the time a
2185 * dynamically typesafe view is generated, and that all subsequent
2186 * access to the collection takes place through the view, it is
2187 * <i>guaranteed</i> that the collection cannot contain an incorrectly
2190 * <p>The generics mechanism in the language provides compile-time
2191 * (static) type checking, but it is possible to defeat this mechanism
2192 * with unchecked casts. Usually this is not a problem, as the compiler
2193 * issues warnings on all such unchecked operations. There are, however,
2194 * times when static type checking alone is not sufficient. For example,
2195 * suppose a collection is passed to a third-party library and it is
2196 * imperative that the library code not corrupt the collection by
2197 * inserting an element of the wrong type.
2199 * <p>Another use of dynamically typesafe views is debugging. Suppose a
2200 * program fails with a {@code ClassCastException}, indicating that an
2201 * incorrectly typed element was put into a parameterized collection.
2202 * Unfortunately, the exception can occur at any time after the erroneous
2203 * element is inserted, so it typically provides little or no information
2204 * as to the real source of the problem. If the problem is reproducible,
2205 * one can quickly determine its source by temporarily modifying the
2206 * program to wrap the collection with a dynamically typesafe view.
2207 * For example, this declaration:
2209 * Collection<String> c = new HashSet<String>();
2211 * may be replaced temporarily by this one:
2213 * Collection<String> c = Collections.checkedCollection(
2214 * new HashSet<String>(), String.class);
2216 * Running the program again will cause it to fail at the point where
2217 * an incorrectly typed element is inserted into the collection, clearly
2218 * identifying the source of the problem. Once the problem is fixed, the
2219 * modified declaration may be reverted back to the original.
2221 * <p>The returned collection does <i>not</i> pass the hashCode and equals
2222 * operations through to the backing collection, but relies on
2223 * {@code Object}'s {@code equals} and {@code hashCode} methods. This
2224 * is necessary to preserve the contracts of these operations in the case
2225 * that the backing collection is a set or a list.
2227 * <p>The returned collection will be serializable if the specified
2228 * collection is serializable.
2230 * <p>Since {@code null} is considered to be a value of any reference
2231 * type, the returned collection permits insertion of null elements
2232 * whenever the backing collection does.
2234 * @param c the collection for which a dynamically typesafe view is to be
2236 * @param type the type of element that {@code c} is permitted to hold
2237 * @return a dynamically typesafe view of the specified collection
2240 public static <E> Collection<E> checkedCollection(Collection<E> c,
2242 return new CheckedCollection<>(c, type);
2245 @SuppressWarnings("unchecked")
2246 static <T> T[] zeroLengthArray(Class<T> type) {
2247 return (T[]) Array.newInstance(type, 0);
2253 static class CheckedCollection<E> implements Collection<E>, Serializable {
2254 private static final long serialVersionUID = 1578914078182001775L;
2256 final Collection<E> c;
2257 final Class<E> type;
2259 void typeCheck(Object o) {
2260 if (o != null && !type.isInstance(o))
2261 throw new ClassCastException(badElementMsg(o));
2264 private String badElementMsg(Object o) {
2265 return "Attempt to insert " + o.getClass() +
2266 " element into collection with element type " + type;
2269 CheckedCollection(Collection<E> c, Class<E> type) {
2270 if (c==null || type == null)
2271 throw new NullPointerException();
2276 public int size() { return c.size(); }
2277 public boolean isEmpty() { return c.isEmpty(); }
2278 public boolean contains(Object o) { return c.contains(o); }
2279 public Object[] toArray() { return c.toArray(); }
2280 public <T> T[] toArray(T[] a) { return c.toArray(a); }
2281 public String toString() { return c.toString(); }
2282 public boolean remove(Object o) { return c.remove(o); }
2283 public void clear() { c.clear(); }
2285 public boolean containsAll(Collection<?> coll) {
2286 return c.containsAll(coll);
2288 public boolean removeAll(Collection<?> coll) {
2289 return c.removeAll(coll);
2291 public boolean retainAll(Collection<?> coll) {
2292 return c.retainAll(coll);
2295 public Iterator<E> iterator() {
2296 final Iterator<E> it = c.iterator();
2297 return new Iterator<E>() {
2298 public boolean hasNext() { return it.hasNext(); }
2299 public E next() { return it.next(); }
2300 public void remove() { it.remove(); }};
2303 public boolean add(E e) {
2308 private E[] zeroLengthElementArray = null; // Lazily initialized
2310 private E[] zeroLengthElementArray() {
2311 return zeroLengthElementArray != null ? zeroLengthElementArray :
2312 (zeroLengthElementArray = zeroLengthArray(type));
2315 @SuppressWarnings("unchecked")
2316 Collection<E> checkedCopyOf(Collection<? extends E> coll) {
2319 E[] z = zeroLengthElementArray();
2320 a = coll.toArray(z);
2321 // Defend against coll violating the toArray contract
2322 if (a.getClass() != z.getClass())
2323 a = Arrays.copyOf(a, a.length, z.getClass());
2324 } catch (ArrayStoreException ignore) {
2325 // To get better and consistent diagnostics,
2326 // we call typeCheck explicitly on each element.
2327 // We call clone() to defend against coll retaining a
2328 // reference to the returned array and storing a bad
2329 // element into it after it has been type checked.
2330 a = coll.toArray().clone();
2334 // A slight abuse of the type system, but safe here.
2335 return (Collection<E>) Arrays.asList(a);
2338 public boolean addAll(Collection<? extends E> coll) {
2339 // Doing things this way insulates us from concurrent changes
2340 // in the contents of coll and provides all-or-nothing
2341 // semantics (which we wouldn't get if we type-checked each
2342 // element as we added it)
2343 return c.addAll(checkedCopyOf(coll));
2348 * Returns a dynamically typesafe view of the specified set.
2349 * Any attempt to insert an element of the wrong type will result in
2350 * an immediate {@link ClassCastException}. Assuming a set contains
2351 * no incorrectly typed elements prior to the time a dynamically typesafe
2352 * view is generated, and that all subsequent access to the set
2353 * takes place through the view, it is <i>guaranteed</i> that the
2354 * set cannot contain an incorrectly typed element.
2356 * <p>A discussion of the use of dynamically typesafe views may be
2357 * found in the documentation for the {@link #checkedCollection
2358 * checkedCollection} method.
2360 * <p>The returned set will be serializable if the specified set is
2363 * <p>Since {@code null} is considered to be a value of any reference
2364 * type, the returned set permits insertion of null elements whenever
2365 * the backing set does.
2367 * @param s the set for which a dynamically typesafe view is to be
2369 * @param type the type of element that {@code s} is permitted to hold
2370 * @return a dynamically typesafe view of the specified set
2373 public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) {
2374 return new CheckedSet<>(s, type);
2380 static class CheckedSet<E> extends CheckedCollection<E>
2381 implements Set<E>, Serializable
2383 private static final long serialVersionUID = 4694047833775013803L;
2385 CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); }
2387 public boolean equals(Object o) { return o == this || c.equals(o); }
2388 public int hashCode() { return c.hashCode(); }
2392 * Returns a dynamically typesafe view of the specified sorted set.
2393 * Any attempt to insert an element of the wrong type will result in an
2394 * immediate {@link ClassCastException}. Assuming a sorted set
2395 * contains no incorrectly typed elements prior to the time a
2396 * dynamically typesafe view is generated, and that all subsequent
2397 * access to the sorted set takes place through the view, it is
2398 * <i>guaranteed</i> that the sorted set cannot contain an incorrectly
2401 * <p>A discussion of the use of dynamically typesafe views may be
2402 * found in the documentation for the {@link #checkedCollection
2403 * checkedCollection} method.
2405 * <p>The returned sorted set will be serializable if the specified sorted
2406 * set is serializable.
2408 * <p>Since {@code null} is considered to be a value of any reference
2409 * type, the returned sorted set permits insertion of null elements
2410 * whenever the backing sorted set does.
2412 * @param s the sorted set for which a dynamically typesafe view is to be
2414 * @param type the type of element that {@code s} is permitted to hold
2415 * @return a dynamically typesafe view of the specified sorted set
2418 public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s,
2420 return new CheckedSortedSet<>(s, type);
2426 static class CheckedSortedSet<E> extends CheckedSet<E>
2427 implements SortedSet<E>, Serializable
2429 private static final long serialVersionUID = 1599911165492914959L;
2430 private final SortedSet<E> ss;
2432 CheckedSortedSet(SortedSet<E> s, Class<E> type) {
2437 public Comparator<? super E> comparator() { return ss.comparator(); }
2438 public E first() { return ss.first(); }
2439 public E last() { return ss.last(); }
2441 public SortedSet<E> subSet(E fromElement, E toElement) {
2442 return checkedSortedSet(ss.subSet(fromElement,toElement), type);
2444 public SortedSet<E> headSet(E toElement) {
2445 return checkedSortedSet(ss.headSet(toElement), type);
2447 public SortedSet<E> tailSet(E fromElement) {
2448 return checkedSortedSet(ss.tailSet(fromElement), type);
2453 * Returns a dynamically typesafe view of the specified list.
2454 * Any attempt to insert an element of the wrong type will result in
2455 * an immediate {@link ClassCastException}. Assuming a list contains
2456 * no incorrectly typed elements prior to the time a dynamically typesafe
2457 * view is generated, and that all subsequent access to the list
2458 * takes place through the view, it is <i>guaranteed</i> that the
2459 * list cannot contain an incorrectly typed element.
2461 * <p>A discussion of the use of dynamically typesafe views may be
2462 * found in the documentation for the {@link #checkedCollection
2463 * checkedCollection} method.
2465 * <p>The returned list will be serializable if the specified list
2468 * <p>Since {@code null} is considered to be a value of any reference
2469 * type, the returned list permits insertion of null elements whenever
2470 * the backing list does.
2472 * @param list the list for which a dynamically typesafe view is to be
2474 * @param type the type of element that {@code list} is permitted to hold
2475 * @return a dynamically typesafe view of the specified list
2478 public static <E> List<E> checkedList(List<E> list, Class<E> type) {
2479 return (list instanceof RandomAccess ?
2480 new CheckedRandomAccessList<>(list, type) :
2481 new CheckedList<>(list, type));
2487 static class CheckedList<E>
2488 extends CheckedCollection<E>
2491 private static final long serialVersionUID = 65247728283967356L;
2494 CheckedList(List<E> list, Class<E> type) {
2499 public boolean equals(Object o) { return o == this || list.equals(o); }
2500 public int hashCode() { return list.hashCode(); }
2501 public E get(int index) { return list.get(index); }
2502 public E remove(int index) { return list.remove(index); }
2503 public int indexOf(Object o) { return list.indexOf(o); }
2504 public int lastIndexOf(Object o) { return list.lastIndexOf(o); }
2506 public E set(int index, E element) {
2508 return list.set(index, element);
2511 public void add(int index, E element) {
2513 list.add(index, element);
2516 public boolean addAll(int index, Collection<? extends E> c) {
2517 return list.addAll(index, checkedCopyOf(c));
2519 public ListIterator<E> listIterator() { return listIterator(0); }
2521 public ListIterator<E> listIterator(final int index) {
2522 final ListIterator<E> i = list.listIterator(index);
2524 return new ListIterator<E>() {
2525 public boolean hasNext() { return i.hasNext(); }
2526 public E next() { return i.next(); }
2527 public boolean hasPrevious() { return i.hasPrevious(); }
2528 public E previous() { return i.previous(); }
2529 public int nextIndex() { return i.nextIndex(); }
2530 public int previousIndex() { return i.previousIndex(); }
2531 public void remove() { i.remove(); }
2533 public void set(E e) {
2538 public void add(E e) {
2545 public List<E> subList(int fromIndex, int toIndex) {
2546 return new CheckedList<>(list.subList(fromIndex, toIndex), type);
2553 static class CheckedRandomAccessList<E> extends CheckedList<E>
2554 implements RandomAccess
2556 private static final long serialVersionUID = 1638200125423088369L;
2558 CheckedRandomAccessList(List<E> list, Class<E> type) {
2562 public List<E> subList(int fromIndex, int toIndex) {
2563 return new CheckedRandomAccessList<>(
2564 list.subList(fromIndex, toIndex), type);
2569 * Returns a dynamically typesafe view of the specified map.
2570 * Any attempt to insert a mapping whose key or value have the wrong
2571 * type will result in an immediate {@link ClassCastException}.
2572 * Similarly, any attempt to modify the value currently associated with
2573 * a key will result in an immediate {@link ClassCastException},
2574 * whether the modification is attempted directly through the map
2575 * itself, or through a {@link Map.Entry} instance obtained from the
2576 * map's {@link Map#entrySet() entry set} view.
2578 * <p>Assuming a map contains no incorrectly typed keys or values
2579 * prior to the time a dynamically typesafe view is generated, and
2580 * that all subsequent access to the map takes place through the view
2581 * (or one of its collection views), it is <i>guaranteed</i> that the
2582 * map cannot contain an incorrectly typed key or value.
2584 * <p>A discussion of the use of dynamically typesafe views may be
2585 * found in the documentation for the {@link #checkedCollection
2586 * checkedCollection} method.
2588 * <p>The returned map will be serializable if the specified map is
2591 * <p>Since {@code null} is considered to be a value of any reference
2592 * type, the returned map permits insertion of null keys or values
2593 * whenever the backing map does.
2595 * @param m the map for which a dynamically typesafe view is to be
2597 * @param keyType the type of key that {@code m} is permitted to hold
2598 * @param valueType the type of value that {@code m} is permitted to hold
2599 * @return a dynamically typesafe view of the specified map
2602 public static <K, V> Map<K, V> checkedMap(Map<K, V> m,
2604 Class<V> valueType) {
2605 return new CheckedMap<>(m, keyType, valueType);
2612 private static class CheckedMap<K,V>
2613 implements Map<K,V>, Serializable
2615 private static final long serialVersionUID = 5742860141034234728L;
2617 private final Map<K, V> m;
2618 final Class<K> keyType;
2619 final Class<V> valueType;
2621 private void typeCheck(Object key, Object value) {
2622 if (key != null && !keyType.isInstance(key))
2623 throw new ClassCastException(badKeyMsg(key));
2625 if (value != null && !valueType.isInstance(value))
2626 throw new ClassCastException(badValueMsg(value));
2629 private String badKeyMsg(Object key) {
2630 return "Attempt to insert " + key.getClass() +
2631 " key into map with key type " + keyType;
2634 private String badValueMsg(Object value) {
2635 return "Attempt to insert " + value.getClass() +
2636 " value into map with value type " + valueType;
2639 CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) {
2640 if (m == null || keyType == null || valueType == null)
2641 throw new NullPointerException();
2643 this.keyType = keyType;
2644 this.valueType = valueType;
2647 public int size() { return m.size(); }
2648 public boolean isEmpty() { return m.isEmpty(); }
2649 public boolean containsKey(Object key) { return m.containsKey(key); }
2650 public boolean containsValue(Object v) { return m.containsValue(v); }
2651 public V get(Object key) { return m.get(key); }
2652 public V remove(Object key) { return m.remove(key); }
2653 public void clear() { m.clear(); }
2654 public Set<K> keySet() { return m.keySet(); }
2655 public Collection<V> values() { return m.values(); }
2656 public boolean equals(Object o) { return o == this || m.equals(o); }
2657 public int hashCode() { return m.hashCode(); }
2658 public String toString() { return m.toString(); }
2660 public V put(K key, V value) {
2661 typeCheck(key, value);
2662 return m.put(key, value);
2665 @SuppressWarnings("unchecked")
2666 public void putAll(Map<? extends K, ? extends V> t) {
2667 // Satisfy the following goals:
2668 // - good diagnostics in case of type mismatch
2669 // - all-or-nothing semantics
2670 // - protection from malicious t
2671 // - correct behavior if t is a concurrent map
2672 Object[] entries = t.entrySet().toArray();
2673 List<Map.Entry<K,V>> checked = new ArrayList<>(entries.length);
2674 for (Object o : entries) {
2675 Map.Entry<?,?> e = (Map.Entry<?,?>) o;
2676 Object k = e.getKey();
2677 Object v = e.getValue();
2680 new AbstractMap.SimpleImmutableEntry<>((K) k, (V) v));
2682 for (Map.Entry<K,V> e : checked)
2683 m.put(e.getKey(), e.getValue());
2686 private transient Set<Map.Entry<K,V>> entrySet = null;
2688 public Set<Map.Entry<K,V>> entrySet() {
2690 entrySet = new CheckedEntrySet<>(m.entrySet(), valueType);
2695 * We need this class in addition to CheckedSet as Map.Entry permits
2696 * modification of the backing Map via the setValue operation. This
2697 * class is subtle: there are many possible attacks that must be
2702 static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> {
2703 private final Set<Map.Entry<K,V>> s;
2704 private final Class<V> valueType;
2706 CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) {
2708 this.valueType = valueType;
2711 public int size() { return s.size(); }
2712 public boolean isEmpty() { return s.isEmpty(); }
2713 public String toString() { return s.toString(); }
2714 public int hashCode() { return s.hashCode(); }
2715 public void clear() { s.clear(); }
2717 public boolean add(Map.Entry<K, V> e) {
2718 throw new UnsupportedOperationException();
2720 public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) {
2721 throw new UnsupportedOperationException();
2724 public Iterator<Map.Entry<K,V>> iterator() {
2725 final Iterator<Map.Entry<K, V>> i = s.iterator();
2726 final Class<V> valueType = this.valueType;
2728 return new Iterator<Map.Entry<K,V>>() {
2729 public boolean hasNext() { return i.hasNext(); }
2730 public void remove() { i.remove(); }
2732 public Map.Entry<K,V> next() {
2733 return checkedEntry(i.next(), valueType);
2738 @SuppressWarnings("unchecked")
2739 public Object[] toArray() {
2740 Object[] source = s.toArray();
2743 * Ensure that we don't get an ArrayStoreException even if
2744 * s.toArray returns an array of something other than Object
2746 Object[] dest = (CheckedEntry.class.isInstance(
2747 source.getClass().getComponentType()) ? source :
2748 new Object[source.length]);
2750 for (int i = 0; i < source.length; i++)
2751 dest[i] = checkedEntry((Map.Entry<K,V>)source[i],
2756 @SuppressWarnings("unchecked")
2757 public <T> T[] toArray(T[] a) {
2758 // We don't pass a to s.toArray, to avoid window of
2759 // vulnerability wherein an unscrupulous multithreaded client
2760 // could get his hands on raw (unwrapped) Entries from s.
2761 T[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
2763 for (int i=0; i<arr.length; i++)
2764 arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i],
2766 if (arr.length > a.length)
2769 System.arraycopy(arr, 0, a, 0, arr.length);
2770 if (a.length > arr.length)
2771 a[arr.length] = null;
2776 * This method is overridden to protect the backing set against
2777 * an object with a nefarious equals function that senses
2778 * that the equality-candidate is Map.Entry and calls its
2781 public boolean contains(Object o) {
2782 if (!(o instanceof Map.Entry))
2784 Map.Entry<?,?> e = (Map.Entry<?,?>) o;
2786 (e instanceof CheckedEntry) ? e : checkedEntry(e, valueType));
2790 * The bulk collection methods are overridden to protect
2791 * against an unscrupulous collection whose contains(Object o)
2792 * method senses when o is a Map.Entry, and calls o.setValue.
2794 public boolean containsAll(Collection<?> c) {
2796 if (!contains(o)) // Invokes safe contains() above
2801 public boolean remove(Object o) {
2802 if (!(o instanceof Map.Entry))
2804 return s.remove(new AbstractMap.SimpleImmutableEntry
2805 <>((Map.Entry<?,?>)o));
2808 public boolean removeAll(Collection<?> c) {
2809 return batchRemove(c, false);
2811 public boolean retainAll(Collection<?> c) {
2812 return batchRemove(c, true);
2814 private boolean batchRemove(Collection<?> c, boolean complement) {
2815 boolean modified = false;
2816 Iterator<Map.Entry<K,V>> it = iterator();
2817 while (it.hasNext()) {
2818 if (c.contains(it.next()) != complement) {
2826 public boolean equals(Object o) {
2829 if (!(o instanceof Set))
2831 Set<?> that = (Set<?>) o;
2832 return that.size() == s.size()
2833 && containsAll(that); // Invokes safe containsAll() above
2836 static <K,V,T> CheckedEntry<K,V,T> checkedEntry(Map.Entry<K,V> e,
2837 Class<T> valueType) {
2838 return new CheckedEntry<>(e, valueType);
2842 * This "wrapper class" serves two purposes: it prevents
2843 * the client from modifying the backing Map, by short-circuiting
2844 * the setValue method, and it protects the backing Map against
2845 * an ill-behaved Map.Entry that attempts to modify another
2846 * Map.Entry when asked to perform an equality check.
2848 private static class CheckedEntry<K,V,T> implements Map.Entry<K,V> {
2849 private final Map.Entry<K, V> e;
2850 private final Class<T> valueType;
2852 CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) {
2854 this.valueType = valueType;
2857 public K getKey() { return e.getKey(); }
2858 public V getValue() { return e.getValue(); }
2859 public int hashCode() { return e.hashCode(); }
2860 public String toString() { return e.toString(); }
2862 public V setValue(V value) {
2863 if (value != null && !valueType.isInstance(value))
2864 throw new ClassCastException(badValueMsg(value));
2865 return e.setValue(value);
2868 private String badValueMsg(Object value) {
2869 return "Attempt to insert " + value.getClass() +
2870 " value into map with value type " + valueType;
2873 public boolean equals(Object o) {
2876 if (!(o instanceof Map.Entry))
2878 return e.equals(new AbstractMap.SimpleImmutableEntry
2879 <>((Map.Entry<?,?>)o));
2886 * Returns a dynamically typesafe view of the specified sorted map.
2887 * Any attempt to insert a mapping whose key or value have the wrong
2888 * type will result in an immediate {@link ClassCastException}.
2889 * Similarly, any attempt to modify the value currently associated with
2890 * a key will result in an immediate {@link ClassCastException},
2891 * whether the modification is attempted directly through the map
2892 * itself, or through a {@link Map.Entry} instance obtained from the
2893 * map's {@link Map#entrySet() entry set} view.
2895 * <p>Assuming a map contains no incorrectly typed keys or values
2896 * prior to the time a dynamically typesafe view is generated, and
2897 * that all subsequent access to the map takes place through the view
2898 * (or one of its collection views), it is <i>guaranteed</i> that the
2899 * map cannot contain an incorrectly typed key or value.
2901 * <p>A discussion of the use of dynamically typesafe views may be
2902 * found in the documentation for the {@link #checkedCollection
2903 * checkedCollection} method.
2905 * <p>The returned map will be serializable if the specified map is
2908 * <p>Since {@code null} is considered to be a value of any reference
2909 * type, the returned map permits insertion of null keys or values
2910 * whenever the backing map does.
2912 * @param m the map for which a dynamically typesafe view is to be
2914 * @param keyType the type of key that {@code m} is permitted to hold
2915 * @param valueType the type of value that {@code m} is permitted to hold
2916 * @return a dynamically typesafe view of the specified map
2919 public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m,
2921 Class<V> valueType) {
2922 return new CheckedSortedMap<>(m, keyType, valueType);
2928 static class CheckedSortedMap<K,V> extends CheckedMap<K,V>
2929 implements SortedMap<K,V>, Serializable
2931 private static final long serialVersionUID = 1599671320688067438L;
2933 private final SortedMap<K, V> sm;
2935 CheckedSortedMap(SortedMap<K, V> m,
2936 Class<K> keyType, Class<V> valueType) {
2937 super(m, keyType, valueType);
2941 public Comparator<? super K> comparator() { return sm.comparator(); }
2942 public K firstKey() { return sm.firstKey(); }
2943 public K lastKey() { return sm.lastKey(); }
2945 public SortedMap<K,V> subMap(K fromKey, K toKey) {
2946 return checkedSortedMap(sm.subMap(fromKey, toKey),
2947 keyType, valueType);
2949 public SortedMap<K,V> headMap(K toKey) {
2950 return checkedSortedMap(sm.headMap(toKey), keyType, valueType);
2952 public SortedMap<K,V> tailMap(K fromKey) {
2953 return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType);
2957 // Empty collections
2960 * Returns an iterator that has no elements. More precisely,
2964 * <li>{@link Iterator#hasNext hasNext} always returns {@code
2967 * <li>{@link Iterator#next next} always throws {@link
2968 * NoSuchElementException}.
2970 * <li>{@link Iterator#remove remove} always throws {@link
2971 * IllegalStateException}.
2975 * <p>Implementations of this method are permitted, but not
2976 * required, to return the same object from multiple invocations.
2978 * @return an empty iterator
2981 @SuppressWarnings("unchecked")
2982 public static <T> Iterator<T> emptyIterator() {
2983 return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR;
2986 private static class EmptyIterator<E> implements Iterator<E> {
2987 static final EmptyIterator<Object> EMPTY_ITERATOR
2988 = new EmptyIterator<>();
2990 public boolean hasNext() { return false; }
2991 public E next() { throw new NoSuchElementException(); }
2992 public void remove() { throw new IllegalStateException(); }
2996 * Returns a list iterator that has no elements. More precisely,
3000 * <li>{@link Iterator#hasNext hasNext} and {@link
3001 * ListIterator#hasPrevious hasPrevious} always return {@code
3004 * <li>{@link Iterator#next next} and {@link ListIterator#previous
3005 * previous} always throw {@link NoSuchElementException}.
3007 * <li>{@link Iterator#remove remove} and {@link ListIterator#set
3008 * set} always throw {@link IllegalStateException}.
3010 * <li>{@link ListIterator#add add} always throws {@link
3011 * UnsupportedOperationException}.
3013 * <li>{@link ListIterator#nextIndex nextIndex} always returns
3016 * <li>{@link ListIterator#previousIndex previousIndex} always
3017 * returns {@code -1}.
3021 * <p>Implementations of this method are permitted, but not
3022 * required, to return the same object from multiple invocations.
3024 * @return an empty list iterator
3027 @SuppressWarnings("unchecked")
3028 public static <T> ListIterator<T> emptyListIterator() {
3029 return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR;
3032 private static class EmptyListIterator<E>
3033 extends EmptyIterator<E>
3034 implements ListIterator<E>
3036 static final EmptyListIterator<Object> EMPTY_ITERATOR
3037 = new EmptyListIterator<>();
3039 public boolean hasPrevious() { return false; }
3040 public E previous() { throw new NoSuchElementException(); }
3041 public int nextIndex() { return 0; }
3042 public int previousIndex() { return -1; }
3043 public void set(E e) { throw new IllegalStateException(); }
3044 public void add(E e) { throw new UnsupportedOperationException(); }
3048 * Returns an enumeration that has no elements. More precisely,
3052 * <li>{@link Enumeration#hasMoreElements hasMoreElements} always
3053 * returns {@code false}.
3055 * <li> {@link Enumeration#nextElement nextElement} always throws
3056 * {@link NoSuchElementException}.
3060 * <p>Implementations of this method are permitted, but not
3061 * required, to return the same object from multiple invocations.
3063 * @return an empty enumeration
3066 @SuppressWarnings("unchecked")
3067 public static <T> Enumeration<T> emptyEnumeration() {
3068 return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION;
3071 private static class EmptyEnumeration<E> implements Enumeration<E> {
3072 static final EmptyEnumeration<Object> EMPTY_ENUMERATION
3073 = new EmptyEnumeration<>();
3075 public boolean hasMoreElements() { return false; }
3076 public E nextElement() { throw new NoSuchElementException(); }
3080 * The empty set (immutable). This set is serializable.
3084 @SuppressWarnings("unchecked")
3085 public static final Set EMPTY_SET = new EmptySet<>();
3088 * Returns the empty set (immutable). This set is serializable.
3089 * Unlike the like-named field, this method is parameterized.
3091 * <p>This example illustrates the type-safe way to obtain an empty set:
3093 * Set<String> s = Collections.emptySet();
3095 * Implementation note: Implementations of this method need not
3096 * create a separate <tt>Set</tt> object for each call. Using this
3097 * method is likely to have comparable cost to using the like-named
3098 * field. (Unlike this method, the field does not provide type safety.)
3103 @SuppressWarnings("unchecked")
3104 public static final <T> Set<T> emptySet() {
3105 return (Set<T>) EMPTY_SET;
3111 private static class EmptySet<E>
3112 extends AbstractSet<E>
3113 implements Serializable
3115 private static final long serialVersionUID = 1582296315990362920L;
3117 public Iterator<E> iterator() { return emptyIterator(); }
3119 public int size() {return 0;}
3120 public boolean isEmpty() {return true;}
3122 public boolean contains(Object obj) {return false;}
3123 public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
3125 public Object[] toArray() { return new Object[0]; }
3127 public <T> T[] toArray(T[] a) {
3133 // Preserves singleton property
3134 private Object readResolve() {
3140 * The empty list (immutable). This list is serializable.
3144 @SuppressWarnings("unchecked")
3145 public static final List EMPTY_LIST = new EmptyList<>();
3148 * Returns the empty list (immutable). This list is serializable.
3150 * <p>This example illustrates the type-safe way to obtain an empty list:
3152 * List<String> s = Collections.emptyList();
3154 * Implementation note: Implementations of this method need not
3155 * create a separate <tt>List</tt> object for each call. Using this
3156 * method is likely to have comparable cost to using the like-named
3157 * field. (Unlike this method, the field does not provide type safety.)
3162 @SuppressWarnings("unchecked")
3163 public static final <T> List<T> emptyList() {
3164 return (List<T>) EMPTY_LIST;
3170 private static class EmptyList<E>
3171 extends AbstractList<E>
3172 implements RandomAccess, Serializable {
3173 private static final long serialVersionUID = 8842843931221139166L;
3175 public Iterator<E> iterator() {
3176 return emptyIterator();
3178 public ListIterator<E> listIterator() {
3179 return emptyListIterator();
3182 public int size() {return 0;}
3183 public boolean isEmpty() {return true;}
3185 public boolean contains(Object obj) {return false;}
3186 public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
3188 public Object[] toArray() { return new Object[0]; }
3190 public <T> T[] toArray(T[] a) {
3196 public E get(int index) {
3197 throw new IndexOutOfBoundsException("Index: "+index);
3200 public boolean equals(Object o) {
3201 return (o instanceof List) && ((List<?>)o).isEmpty();
3204 public int hashCode() { return 1; }
3206 // Preserves singleton property
3207 private Object readResolve() {
3213 * The empty map (immutable). This map is serializable.
3218 @SuppressWarnings("unchecked")
3219 public static final Map EMPTY_MAP = new EmptyMap<>();
3222 * Returns the empty map (immutable). This map is serializable.
3224 * <p>This example illustrates the type-safe way to obtain an empty set:
3226 * Map<String, Date> s = Collections.emptyMap();
3228 * Implementation note: Implementations of this method need not
3229 * create a separate <tt>Map</tt> object for each call. Using this
3230 * method is likely to have comparable cost to using the like-named
3231 * field. (Unlike this method, the field does not provide type safety.)
3236 @SuppressWarnings("unchecked")
3237 public static final <K,V> Map<K,V> emptyMap() {
3238 return (Map<K,V>) EMPTY_MAP;
3244 private static class EmptyMap<K,V>
3245 extends AbstractMap<K,V>
3246 implements Serializable
3248 private static final long serialVersionUID = 6428348081105594320L;
3250 public int size() {return 0;}
3251 public boolean isEmpty() {return true;}
3252 public boolean containsKey(Object key) {return false;}
3253 public boolean containsValue(Object value) {return false;}
3254 public V get(Object key) {return null;}
3255 public Set<K> keySet() {return emptySet();}
3256 public Collection<V> values() {return emptySet();}
3257 public Set<Map.Entry<K,V>> entrySet() {return emptySet();}
3259 public boolean equals(Object o) {
3260 return (o instanceof Map) && ((Map<?,?>)o).isEmpty();
3263 public int hashCode() {return 0;}
3265 // Preserves singleton property
3266 private Object readResolve() {
3271 // Singleton collections
3274 * Returns an immutable set containing only the specified object.
3275 * The returned set is serializable.
3277 * @param o the sole object to be stored in the returned set.
3278 * @return an immutable set containing only the specified object.
3280 public static <T> Set<T> singleton(T o) {
3281 return new SingletonSet<>(o);
3284 static <E> Iterator<E> singletonIterator(final E e) {
3285 return new Iterator<E>() {
3286 private boolean hasNext = true;
3287 public boolean hasNext() {
3295 throw new NoSuchElementException();
3297 public void remove() {
3298 throw new UnsupportedOperationException();
3306 private static class SingletonSet<E>
3307 extends AbstractSet<E>
3308 implements Serializable
3310 private static final long serialVersionUID = 3193687207550431679L;
3312 private final E element;
3314 SingletonSet(E e) {element = e;}
3316 public Iterator<E> iterator() {
3317 return singletonIterator(element);
3320 public int size() {return 1;}
3322 public boolean contains(Object o) {return eq(o, element);}
3326 * Returns an immutable list containing only the specified object.
3327 * The returned list is serializable.
3329 * @param o the sole object to be stored in the returned list.
3330 * @return an immutable list containing only the specified object.
3333 public static <T> List<T> singletonList(T o) {
3334 return new SingletonList<>(o);
3340 private static class SingletonList<E>
3341 extends AbstractList<E>
3342 implements RandomAccess, Serializable {
3344 private static final long serialVersionUID = 3093736618740652951L;
3346 private final E element;
3348 SingletonList(E obj) {element = obj;}
3350 public Iterator<E> iterator() {
3351 return singletonIterator(element);
3354 public int size() {return 1;}
3356 public boolean contains(Object obj) {return eq(obj, element);}
3358 public E get(int index) {
3360 throw new IndexOutOfBoundsException("Index: "+index+", Size: 1");
3366 * Returns an immutable map, mapping only the specified key to the
3367 * specified value. The returned map is serializable.
3369 * @param key the sole key to be stored in the returned map.
3370 * @param value the value to which the returned map maps <tt>key</tt>.
3371 * @return an immutable map containing only the specified key-value
3375 public static <K,V> Map<K,V> singletonMap(K key, V value) {
3376 return new SingletonMap<>(key, value);
3382 private static class SingletonMap<K,V>
3383 extends AbstractMap<K,V>
3384 implements Serializable {
3385 private static final long serialVersionUID = -6979724477215052911L;
3390 SingletonMap(K key, V value) {
3395 public int size() {return 1;}
3397 public boolean isEmpty() {return false;}
3399 public boolean containsKey(Object key) {return eq(key, k);}
3401 public boolean containsValue(Object value) {return eq(value, v);}
3403 public V get(Object key) {return (eq(key, k) ? v : null);}
3405 private transient Set<K> keySet = null;
3406 private transient Set<Map.Entry<K,V>> entrySet = null;
3407 private transient Collection<V> values = null;
3409 public Set<K> keySet() {
3411 keySet = singleton(k);
3415 public Set<Map.Entry<K,V>> entrySet() {
3417 entrySet = Collections.<Map.Entry<K,V>>singleton(
3418 new SimpleImmutableEntry<>(k, v));
3422 public Collection<V> values() {
3424 values = singleton(v);
3433 * Returns an immutable list consisting of <tt>n</tt> copies of the
3434 * specified object. The newly allocated data object is tiny (it contains
3435 * a single reference to the data object). This method is useful in
3436 * combination with the <tt>List.addAll</tt> method to grow lists.
3437 * The returned list is serializable.
3439 * @param n the number of elements in the returned list.
3440 * @param o the element to appear repeatedly in the returned list.
3441 * @return an immutable list consisting of <tt>n</tt> copies of the
3443 * @throws IllegalArgumentException if {@code n < 0}
3444 * @see List#addAll(Collection)
3445 * @see List#addAll(int, Collection)
3447 public static <T> List<T> nCopies(int n, T o) {
3449 throw new IllegalArgumentException("List length = " + n);
3450 return new CopiesList<>(n, o);
3456 private static class CopiesList<E>
3457 extends AbstractList<E>
3458 implements RandomAccess, Serializable
3460 private static final long serialVersionUID = 2739099268398711800L;
3465 CopiesList(int n, E e) {
3475 public boolean contains(Object obj) {
3476 return n != 0 && eq(obj, element);
3479 public int indexOf(Object o) {
3480 return contains(o) ? 0 : -1;
3483 public int lastIndexOf(Object o) {
3484 return contains(o) ? n - 1 : -1;
3487 public E get(int index) {
3488 if (index < 0 || index >= n)
3489 throw new IndexOutOfBoundsException("Index: "+index+
3494 public Object[] toArray() {
3495 final Object[] a = new Object[n];
3496 if (element != null)
3497 Arrays.fill(a, 0, n, element);
3501 public <T> T[] toArray(T[] a) {
3502 final int n = this.n;
3504 a = (T[])java.lang.reflect.Array
3505 .newInstance(a.getClass().getComponentType(), n);
3506 if (element != null)
3507 Arrays.fill(a, 0, n, element);
3509 Arrays.fill(a, 0, n, element);
3516 public List<E> subList(int fromIndex, int toIndex) {
3518 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
3520 throw new IndexOutOfBoundsException("toIndex = " + toIndex);
3521 if (fromIndex > toIndex)
3522 throw new IllegalArgumentException("fromIndex(" + fromIndex +
3523 ") > toIndex(" + toIndex + ")");
3524 return new CopiesList<>(toIndex - fromIndex, element);
3529 * Returns a comparator that imposes the reverse of the <em>natural
3530 * ordering</em> on a collection of objects that implement the
3531 * {@code Comparable} interface. (The natural ordering is the ordering
3532 * imposed by the objects' own {@code compareTo} method.) This enables a
3533 * simple idiom for sorting (or maintaining) collections (or arrays) of
3534 * objects that implement the {@code Comparable} interface in
3535 * reverse-natural-order. For example, suppose {@code a} is an array of
3536 * strings. Then: <pre>
3537 * Arrays.sort(a, Collections.reverseOrder());
3538 * </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p>
3540 * The returned comparator is serializable.
3542 * @return A comparator that imposes the reverse of the <i>natural
3543 * ordering</i> on a collection of objects that implement
3544 * the <tt>Comparable</tt> interface.
3547 public static <T> Comparator<T> reverseOrder() {
3548 return (Comparator<T>) ReverseComparator.REVERSE_ORDER;
3554 private static class ReverseComparator
3555 implements Comparator<Comparable<Object>>, Serializable {
3557 private static final long serialVersionUID = 7207038068494060240L;
3559 static final ReverseComparator REVERSE_ORDER
3560 = new ReverseComparator();
3562 public int compare(Comparable<Object> c1, Comparable<Object> c2) {
3563 return c2.compareTo(c1);
3566 private Object readResolve() { return reverseOrder(); }
3570 * Returns a comparator that imposes the reverse ordering of the specified
3571 * comparator. If the specified comparator is {@code null}, this method is
3572 * equivalent to {@link #reverseOrder()} (in other words, it returns a
3573 * comparator that imposes the reverse of the <em>natural ordering</em> on
3574 * a collection of objects that implement the Comparable interface).
3576 * <p>The returned comparator is serializable (assuming the specified
3577 * comparator is also serializable or {@code null}).
3579 * @param cmp a comparator who's ordering is to be reversed by the returned
3580 * comparator or {@code null}
3581 * @return A comparator that imposes the reverse ordering of the
3582 * specified comparator.
3585 public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) {
3587 return reverseOrder();
3589 if (cmp instanceof ReverseComparator2)
3590 return ((ReverseComparator2<T>)cmp).cmp;
3592 return new ReverseComparator2<>(cmp);
3598 private static class ReverseComparator2<T> implements Comparator<T>,
3601 private static final long serialVersionUID = 4374092139857L;
3604 * The comparator specified in the static factory. This will never
3605 * be null, as the static factory returns a ReverseComparator
3606 * instance if its argument is null.
3610 final Comparator<T> cmp;
3612 ReverseComparator2(Comparator<T> cmp) {
3617 public int compare(T t1, T t2) {
3618 return cmp.compare(t2, t1);
3621 public boolean equals(Object o) {
3622 return (o == this) ||
3623 (o instanceof ReverseComparator2 &&
3624 cmp.equals(((ReverseComparator2)o).cmp));
3627 public int hashCode() {
3628 return cmp.hashCode() ^ Integer.MIN_VALUE;
3633 * Returns an enumeration over the specified collection. This provides
3634 * interoperability with legacy APIs that require an enumeration
3637 * @param c the collection for which an enumeration is to be returned.
3638 * @return an enumeration over the specified collection.
3641 public static <T> Enumeration<T> enumeration(final Collection<T> c) {
3642 return new Enumeration<T>() {
3643 private final Iterator<T> i = c.iterator();
3645 public boolean hasMoreElements() {
3649 public T nextElement() {
3656 * Returns an array list containing the elements returned by the
3657 * specified enumeration in the order they are returned by the
3658 * enumeration. This method provides interoperability between
3659 * legacy APIs that return enumerations and new APIs that require
3662 * @param e enumeration providing elements for the returned
3664 * @return an array list containing the elements returned
3665 * by the specified enumeration.
3670 public static <T> ArrayList<T> list(Enumeration<T> e) {
3671 ArrayList<T> l = new ArrayList<>();
3672 while (e.hasMoreElements())
3673 l.add(e.nextElement());
3678 * Returns true if the specified arguments are equal, or both null.
3680 static boolean eq(Object o1, Object o2) {
3681 return o1==null ? o2==null : o1.equals(o2);
3685 * Returns the number of elements in the specified collection equal to the
3686 * specified object. More formally, returns the number of elements
3687 * <tt>e</tt> in the collection such that
3688 * <tt>(o == null ? e == null : o.equals(e))</tt>.
3690 * @param c the collection in which to determine the frequency
3692 * @param o the object whose frequency is to be determined
3693 * @throws NullPointerException if <tt>c</tt> is null
3696 public static int frequency(Collection<?> c, Object o) {
3711 * Returns {@code true} if the two specified collections have no
3712 * elements in common.
3714 * <p>Care must be exercised if this method is used on collections that
3715 * do not comply with the general contract for {@code Collection}.
3716 * Implementations may elect to iterate over either collection and test
3717 * for containment in the other collection (or to perform any equivalent
3718 * computation). If either collection uses a nonstandard equality test
3719 * (as does a {@link SortedSet} whose ordering is not <em>compatible with
3720 * equals</em>, or the key set of an {@link IdentityHashMap}), both
3721 * collections must use the same nonstandard equality test, or the
3722 * result of this method is undefined.
3724 * <p>Care must also be exercised when using collections that have
3725 * restrictions on the elements that they may contain. Collection
3726 * implementations are allowed to throw exceptions for any operation
3727 * involving elements they deem ineligible. For absolute safety the
3728 * specified collections should contain only elements which are
3729 * eligible elements for both collections.
3731 * <p>Note that it is permissible to pass the same collection in both
3732 * parameters, in which case the method will return {@code true} if and
3733 * only if the collection is empty.
3735 * @param c1 a collection
3736 * @param c2 a collection
3737 * @return {@code true} if the two specified collections have no
3738 * elements in common.
3739 * @throws NullPointerException if either collection is {@code null}.
3740 * @throws NullPointerException if one collection contains a {@code null}
3741 * element and {@code null} is not an eligible element for the other collection.
3742 * (<a href="Collection.html#optional-restrictions">optional</a>)
3743 * @throws ClassCastException if one collection contains an element that is
3744 * of a type which is ineligible for the other collection.
3745 * (<a href="Collection.html#optional-restrictions">optional</a>)
3748 public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
3749 // The collection to be used for contains(). Preference is given to
3750 // the collection who's contains() has lower O() complexity.
3751 Collection<?> contains = c2;
3752 // The collection to be iterated. If the collections' contains() impl
3753 // are of different O() complexity, the collection with slower
3754 // contains() will be used for iteration. For collections who's
3755 // contains() are of the same complexity then best performance is
3756 // achieved by iterating the smaller collection.
3757 Collection<?> iterate = c1;
3759 // Performance optimization cases. The heuristics:
3760 // 1. Generally iterate over c1.
3761 // 2. If c1 is a Set then iterate over c2.
3762 // 3. If either collection is empty then result is always true.
3763 // 4. Iterate over the smaller Collection.
3764 if (c1 instanceof Set) {
3765 // Use c1 for contains as a Set's contains() is expected to perform
3766 // better than O(N/2)
3769 } else if (!(c2 instanceof Set)) {
3770 // Both are mere Collections. Iterate over smaller collection.
3771 // Example: If c1 contains 3 elements and c2 contains 50 elements and
3772 // assuming contains() requires ceiling(N/2) comparisons then
3773 // checking for all c1 elements in c2 would require 75 comparisons
3774 // (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring
3775 // 100 comparisons (50 * ceiling(3/2)).
3776 int c1size = c1.size();
3777 int c2size = c2.size();
3778 if (c1size == 0 || c2size == 0) {
3779 // At least one collection is empty. Nothing will match.
3783 if (c1size > c2size) {
3789 for (Object e : iterate) {
3790 if (contains.contains(e)) {
3791 // Found a common element. Collections are not disjoint.
3796 // No common elements were found.
3801 * Adds all of the specified elements to the specified collection.
3802 * Elements to be added may be specified individually or as an array.
3803 * The behavior of this convenience method is identical to that of
3804 * <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely
3805 * to run significantly faster under most implementations.
3807 * <p>When elements are specified individually, this method provides a
3808 * convenient way to add a few elements to an existing collection:
3810 * Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon");
3813 * @param c the collection into which <tt>elements</tt> are to be inserted
3814 * @param elements the elements to insert into <tt>c</tt>
3815 * @return <tt>true</tt> if the collection changed as a result of the call
3816 * @throws UnsupportedOperationException if <tt>c</tt> does not support
3817 * the <tt>add</tt> operation
3818 * @throws NullPointerException if <tt>elements</tt> contains one or more
3819 * null values and <tt>c</tt> does not permit null elements, or
3820 * if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt>
3821 * @throws IllegalArgumentException if some property of a value in
3822 * <tt>elements</tt> prevents it from being added to <tt>c</tt>
3823 * @see Collection#addAll(Collection)
3827 public static <T> boolean addAll(Collection<? super T> c, T... elements) {
3828 boolean result = false;
3829 for (T element : elements)
3830 result |= c.add(element);
3835 * Returns a set backed by the specified map. The resulting set displays
3836 * the same ordering, concurrency, and performance characteristics as the
3837 * backing map. In essence, this factory method provides a {@link Set}
3838 * implementation corresponding to any {@link Map} implementation. There
3839 * is no need to use this method on a {@link Map} implementation that
3840 * already has a corresponding {@link Set} implementation (such as {@link
3841 * HashMap} or {@link TreeMap}).
3843 * <p>Each method invocation on the set returned by this method results in
3844 * exactly one method invocation on the backing map or its <tt>keySet</tt>
3845 * view, with one exception. The <tt>addAll</tt> method is implemented
3846 * as a sequence of <tt>put</tt> invocations on the backing map.
3848 * <p>The specified map must be empty at the time this method is invoked,
3849 * and should not be accessed directly after this method returns. These
3850 * conditions are ensured if the map is created empty, passed directly
3851 * to this method, and no reference to the map is retained, as illustrated
3852 * in the following code fragment:
3854 * Set<Object> weakHashSet = Collections.newSetFromMap(
3855 * new WeakHashMap<Object, Boolean>());
3858 * @param map the backing map
3859 * @return the set backed by the map
3860 * @throws IllegalArgumentException if <tt>map</tt> is not empty
3863 public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
3864 return new SetFromMap<>(map);
3870 private static class SetFromMap<E> extends AbstractSet<E>
3871 implements Set<E>, Serializable
3873 private final Map<E, Boolean> m; // The backing map
3874 private transient Set<E> s; // Its keySet
3876 SetFromMap(Map<E, Boolean> map) {
3878 throw new IllegalArgumentException("Map is non-empty");
3883 public void clear() { m.clear(); }
3884 public int size() { return m.size(); }
3885 public boolean isEmpty() { return m.isEmpty(); }
3886 public boolean contains(Object o) { return m.containsKey(o); }
3887 public boolean remove(Object o) { return m.remove(o) != null; }
3888 public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; }
3889 public Iterator<E> iterator() { return s.iterator(); }
3890 public Object[] toArray() { return s.toArray(); }
3891 public <T> T[] toArray(T[] a) { return s.toArray(a); }
3892 public String toString() { return s.toString(); }
3893 public int hashCode() { return s.hashCode(); }
3894 public boolean equals(Object o) { return o == this || s.equals(o); }
3895 public boolean containsAll(Collection<?> c) {return s.containsAll(c);}
3896 public boolean removeAll(Collection<?> c) {return s.removeAll(c);}
3897 public boolean retainAll(Collection<?> c) {return s.retainAll(c);}
3898 // addAll is the only inherited implementation
3900 private static final long serialVersionUID = 2454657854757543876L;
3905 * Returns a view of a {@link Deque} as a Last-in-first-out (Lifo)
3906 * {@link Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>,
3907 * <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This
3908 * view can be useful when you would like to use a method
3909 * requiring a <tt>Queue</tt> but you need Lifo ordering.
3911 * <p>Each method invocation on the queue returned by this method
3912 * results in exactly one method invocation on the backing deque, with
3913 * one exception. The {@link Queue#addAll addAll} method is
3914 * implemented as a sequence of {@link Deque#addFirst addFirst}
3915 * invocations on the backing deque.
3917 * @param deque the deque
3921 public static <T> Queue<T> asLifoQueue(Deque<T> deque) {
3922 return new AsLIFOQueue<>(deque);
3928 static class AsLIFOQueue<E> extends AbstractQueue<E>
3929 implements Queue<E>, Serializable {
3930 private static final long serialVersionUID = 1802017725587941708L;
3931 private final Deque<E> q;
3932 AsLIFOQueue(Deque<E> q) { this.q = q; }
3933 public boolean add(E e) { q.addFirst(e); return true; }
3934 public boolean offer(E e) { return q.offerFirst(e); }
3935 public E poll() { return q.pollFirst(); }
3936 public E remove() { return q.removeFirst(); }
3937 public E peek() { return q.peekFirst(); }
3938 public E element() { return q.getFirst(); }
3939 public void clear() { q.clear(); }
3940 public int size() { return q.size(); }
3941 public boolean isEmpty() { return q.isEmpty(); }
3942 public boolean contains(Object o) { return q.contains(o); }
3943 public boolean remove(Object o) { return q.remove(o); }
3944 public Iterator<E> iterator() { return q.iterator(); }
3945 public Object[] toArray() { return q.toArray(); }
3946 public <T> T[] toArray(T[] a) { return q.toArray(a); }
3947 public String toString() { return q.toString(); }
3948 public boolean containsAll(Collection<?> c) {return q.containsAll(c);}
3949 public boolean removeAll(Collection<?> c) {return q.removeAll(c);}
3950 public boolean retainAll(Collection<?> c) {return q.retainAll(c);}
3951 // We use inherited addAll; forwarding addAll would be wrong