1 /*
2 * Copyright 1997-2007 Sun Microsystems, Inc. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any questions.
24 */
25
26 package java.util;
27 import java.io.Serializable;
28 import java.io.ObjectOutputStream;
29 import java.io.IOException;
30 import java.lang.reflect.Array;
31
32 /**
33 * This class consists exclusively of static methods that operate on or return
34 * collections. It contains polymorphic algorithms that operate on
35 * collections, "wrappers", which return a new collection backed by a
36 * specified collection, and a few other odds and ends.
37 *
38 * <p>The methods of this class all throw a <tt>NullPointerException</tt>
39 * if the collections or class objects provided to them are null.
40 *
41 * <p>The documentation for the polymorphic algorithms contained in this class
42 * generally includes a brief description of the <i>implementation</i>. Such
43 * descriptions should be regarded as <i>implementation notes</i>, rather than
44 * parts of the <i>specification</i>. Implementors should feel free to
45 * substitute other algorithms, so long as the specification itself is adhered
46 * to. (For example, the algorithm used by <tt>sort</tt> does not have to be
47 * a mergesort, but it does have to be <i>stable</i>.)
48 *
49 * <p>The "destructive" algorithms contained in this class, that is, the
50 * algorithms that modify the collection on which they operate, are specified
51 * to throw <tt>UnsupportedOperationException</tt> if the collection does not
52 * support the appropriate mutation primitive(s), such as the <tt>set</tt>
53 * method. These algorithms may, but are not required to, throw this
54 * exception if an invocation would have no effect on the collection. For
55 * example, invoking the <tt>sort</tt> method on an unmodifiable list that is
56 * already sorted may or may not throw <tt>UnsupportedOperationException</tt>.
57 *
58 * <p>This class is a member of the
59 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
60 * Java Collections Framework</a>.
61 *
62 * @author Josh Bloch
63 * @author Neal Gafter
64 * @see Collection
65 * @see Set
66 * @see List
67 * @see Map
68 * @since 1.2
69 */
70
71 public class Collections {
72 // Suppresses default constructor, ensuring non-instantiability.
73 private Collections() {
74 }
75
76 // Algorithms
77
78 /*
79 * Tuning parameters for algorithms - Many of the List algorithms have
80 * two implementations, one of which is appropriate for RandomAccess
81 * lists, the other for "sequential." Often, the random access variant
82 * yields better performance on small sequential access lists. The
83 * tuning parameters below determine the cutoff point for what constitutes
84 * a "small" sequential access list for each algorithm. The values below
85 * were empirically determined to work well for LinkedList. Hopefully
86 * they should be reasonable for other sequential access List
87 * implementations. Those doing performance work on this code would
88 * do well to validate the values of these parameters from time to time.
89 * (The first word of each tuning parameter name is the algorithm to which
90 * it applies.)
91 */
92 private static final int BINARYSEARCH_THRESHOLD = 5000;
93 private static final int REVERSE_THRESHOLD = 18;
94 private static final int SHUFFLE_THRESHOLD = 5;
95 private static final int FILL_THRESHOLD = 25;
96 private static final int ROTATE_THRESHOLD = 100;
97 private static final int COPY_THRESHOLD = 10;
98 private static final int REPLACEALL_THRESHOLD = 11;
99 private static final int INDEXOFSUBLIST_THRESHOLD = 35;
100
101 /**
102 * Sorts the specified list into ascending order, according to the
103 * <i>natural ordering</i> of its elements. All elements in the list must
104 * implement the <tt>Comparable</tt> interface. Furthermore, all elements
105 * in the list must be <i>mutually comparable</i> (that is,
106 * <tt>e1.compareTo(e2)</tt> must not throw a <tt>ClassCastException</tt>
107 * for any elements <tt>e1</tt> and <tt>e2</tt> in the list).<p>
108 *
109 * This sort is guaranteed to be <i>stable</i>: equal elements will
110 * not be reordered as a result of the sort.<p>
111 *
112 * The specified list must be modifiable, but need not be resizable.<p>
113 *
114 * The sorting algorithm is a modified mergesort (in which the merge is
115 * omitted if the highest element in the low sublist is less than the
116 * lowest element in the high sublist). This algorithm offers guaranteed
117 * n log(n) performance.
118 *
119 * This implementation dumps the specified list into an array, sorts
120 * the array, and iterates over the list resetting each element
121 * from the corresponding position in the array. This avoids the
122 * n<sup>2</sup> log(n) performance that would result from attempting
123 * to sort a linked list in place.
124 *
125 * @param list the list to be sorted.
126 * @throws ClassCastException if the list contains elements that are not
127 * <i>mutually comparable</i> (for example, strings and integers).
128 * @throws UnsupportedOperationException if the specified list's
129 * list-iterator does not support the <tt>set</tt> operation.
130 * @see Comparable
131 */
132 public static <T extends Comparable<? super T>> void sort(List<T> list) {
133 Object[] a = list.toArray();
134 Arrays.sort(a);
135 ListIterator<T> i = list.listIterator();
136 for (int j=0; j<a.length; j++) {
137 i.next();
138 i.set((T)a[j]);
139 }
140 }
141
142 /**
143 * Sorts the specified list according to the order induced by the
144 * specified comparator. All elements in the list must be <i>mutually
145 * comparable</i> using the specified comparator (that is,
146 * <tt>c.compare(e1, e2)</tt> must not throw a <tt>ClassCastException</tt>
147 * for any elements <tt>e1</tt> and <tt>e2</tt> in the list).<p>
148 *
149 * This sort is guaranteed to be <i>stable</i>: equal elements will
150 * not be reordered as a result of the sort.<p>
151 *
152 * The sorting algorithm is a modified mergesort (in which the merge is
153 * omitted if the highest element in the low sublist is less than the
154 * lowest element in the high sublist). This algorithm offers guaranteed
155 * n log(n) performance.
156 *
157 * The specified list must be modifiable, but need not be resizable.
158 * This implementation dumps the specified list into an array, sorts
159 * the array, and iterates over the list resetting each element
160 * from the corresponding position in the array. This avoids the
161 * n<sup>2</sup> log(n) performance that would result from attempting
162 * to sort a linked list in place.
163 *
164 * @param list the list to be sorted.
165 * @param c the comparator to determine the order of the list. A
166 * <tt>null</tt> value indicates that the elements' <i>natural
167 * ordering</i> should be used.
168 * @throws ClassCastException if the list contains elements that are not
169 * <i>mutually comparable</i> using the specified comparator.
170 * @throws UnsupportedOperationException if the specified list's
171 * list-iterator does not support the <tt>set</tt> operation.
172 * @see Comparator
173 */
174 public static <T> void sort(List<T> list, Comparator<? super T> c) {
175 Object[] a = list.toArray();
176 Arrays.sort(a, (Comparator)c);
177 ListIterator i = list.listIterator();
178 for (int j=0; j<a.length; j++) {
179 i.next();
180 i.set(a[j]);
181 }
182 }
183
184
185 /**
186 * Searches the specified list for the specified object using the binary
187 * search algorithm. The list must be sorted into ascending order
188 * according to the {@linkplain Comparable natural ordering} of its
189 * elements (as by the {@link #sort(List)} method) prior to making this
190 * call. If it is not sorted, the results are undefined. If the list
191 * contains multiple elements equal to the specified object, there is no
192 * guarantee which one will be found.
193 *
194 * <p>This method runs in log(n) time for a "random access" list (which
195 * provides near-constant-time positional access). If the specified list
196 * does not implement the {@link RandomAccess} interface and is large,
197 * this method will do an iterator-based binary search that performs
198 * O(n) link traversals and O(log n) element comparisons.
199 *
200 * @param list the list to be searched.
201 * @param key the key to be searched for.
202 * @return the index of the search key, if it is contained in the list;
203 * otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The
204 * <i>insertion point</i> is defined as the point at which the
205 * key would be inserted into the list: the index of the first
206 * element greater than the key, or <tt>list.size()</tt> if all
207 * elements in the list are less than the specified key. Note
208 * that this guarantees that the return value will be >= 0 if
209 * and only if the key is found.
210 * @throws ClassCastException if the list contains elements that are not
211 * <i>mutually comparable</i> (for example, strings and
212 * integers), or the search key is not mutually comparable
213 * with the elements of the list.
214 */
215 public static <T>
216 int binarySearch(List<? extends Comparable<? super T>> list, T key) {
217 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
218 return Collections.indexedBinarySearch(list, key);
219 else
220 return Collections.iteratorBinarySearch(list, key);
221 }
222
223 private static <T>
224 int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key)
225 {
226 int low = 0;
227 int high = list.size()-1;
228
229 while (low <= high) {
230 int mid = (low + high) >>> 1;
231 Comparable<? super T> midVal = list.get(mid);
232 int cmp = midVal.compareTo(key);
233
234 if (cmp < 0)
235 low = mid + 1;
236 else if (cmp > 0)
237 high = mid - 1;
238 else
239 return mid; // key found
240 }
241 return -(low + 1); // key not found
242 }
243
244 private static <T>
245 int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key)
246 {
247 int low = 0;
248 int high = list.size()-1;
249 ListIterator<? extends Comparable<? super T>> i = list.listIterator();
250
251 while (low <= high) {
252 int mid = (low + high) >>> 1;
253 Comparable<? super T> midVal = get(i, mid);
254 int cmp = midVal.compareTo(key);
255
256 if (cmp < 0)
257 low = mid + 1;
258 else if (cmp > 0)
259 high = mid - 1;
260 else
261 return mid; // key found
262 }
263 return -(low + 1); // key not found
264 }
265
266 /**
267 * Gets the ith element from the given list by repositioning the specified
268 * list listIterator.
269 */
270 private static <T> T get(ListIterator<? extends T> i, int index) {
271 T obj = null;
272 int pos = i.nextIndex();
273 if (pos <= index) {
274 do {
275 obj = i.next();
276 } while (pos++ < index);
277 } else {
278 do {
279 obj = i.previous();
280 } while (--pos > index);
281 }
282 return obj;
283 }
284
285 /**
286 * Searches the specified list for the specified object using the binary
287 * search algorithm. The list must be sorted into ascending order
288 * according to the specified comparator (as by the
289 * {@link #sort(List, Comparator) sort(List, Comparator)}
290 * method), prior to making this call. If it is
291 * not sorted, the results are undefined. If the list contains multiple
292 * elements equal to the specified object, there is no guarantee which one
293 * will be found.
294 *
295 * <p>This method runs in log(n) time for a "random access" list (which
296 * provides near-constant-time positional access). If the specified list
297 * does not implement the {@link RandomAccess} interface and is large,
298 * this method will do an iterator-based binary search that performs
299 * O(n) link traversals and O(log n) element comparisons.
300 *
301 * @param list the list to be searched.
302 * @param key the key to be searched for.
303 * @param c the comparator by which the list is ordered.
304 * A <tt>null</tt> value indicates that the elements'
305 * {@linkplain Comparable natural ordering} should be used.
306 * @return the index of the search key, if it is contained in the list;
307 * otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. The
308 * <i>insertion point</i> is defined as the point at which the
309 * key would be inserted into the list: the index of the first
310 * element greater than the key, or <tt>list.size()</tt> if all
311 * elements in the list are less than the specified key. Note
312 * that this guarantees that the return value will be >= 0 if
313 * and only if the key is found.
314 * @throws ClassCastException if the list contains elements that are not
315 * <i>mutually comparable</i> using the specified comparator,
316 * or the search key is not mutually comparable with the
317 * elements of the list using this comparator.
318 */
319 public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) {
320 if (c==null)
321 return binarySearch((List) list, key);
322
323 if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
324 return Collections.indexedBinarySearch(list, key, c);
325 else
326 return Collections.iteratorBinarySearch(list, key, c);
327 }
328
329 private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
330 int low = 0;
331 int high = l.size()-1;
332
333 while (low <= high) {
334 int mid = (low + high) >>> 1;
335 T midVal = l.get(mid);
336 int cmp = c.compare(midVal, key);
337
338 if (cmp < 0)
339 low = mid + 1;
340 else if (cmp > 0)
341 high = mid - 1;
342 else
343 return mid; // key found
344 }
345 return -(low + 1); // key not found
346 }
347
348 private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
349 int low = 0;
350 int high = l.size()-1;
351 ListIterator<? extends T> i = l.listIterator();
352
353 while (low <= high) {
354 int mid = (low + high) >>> 1;
355 T midVal = get(i, mid);
356 int cmp = c.compare(midVal, key);
357
358 if (cmp < 0)
359 low = mid + 1;
360 else if (cmp > 0)
361 high = mid - 1;
362 else
363 return mid; // key found
364 }
365 return -(low + 1); // key not found
366 }
367
368 private interface SelfComparable extends Comparable<SelfComparable> {}
369
370
371 /**
372 * Reverses the order of the elements in the specified list.<p>
373 *
374 * This method runs in linear time.
375 *
376 * @param list the list whose elements are to be reversed.
377 * @throws UnsupportedOperationException if the specified list or
378 * its list-iterator does not support the <tt>set</tt> operation.
379 */
380 public static void reverse(List<?> list) {
381 int size = list.size();
382 if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) {
383 for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--)
384 swap(list, i, j);
385 } else {
386 ListIterator fwd = list.listIterator();
387 ListIterator rev = list.listIterator(size);
388 for (int i=0, mid=list.size()>>1; i<mid; i++) {
389 Object tmp = fwd.next();
390 fwd.set(rev.previous());
391 rev.set(tmp);
392 }
393 }
394 }
395
396 /**
397 * Randomly permutes the specified list using a default source of
398 * randomness. All permutations occur with approximately equal
399 * likelihood.<p>
400 *
401 * The hedge "approximately" is used in the foregoing description because
402 * default source of randomness is only approximately an unbiased source
403 * of independently chosen bits. If it were a perfect source of randomly
404 * chosen bits, then the algorithm would choose permutations with perfect
405 * uniformity.<p>
406 *
407 * This implementation traverses the list backwards, from the last element
408 * up to the second, repeatedly swapping a randomly selected element into
409 * the "current position". Elements are randomly selected from the
410 * portion of the list that runs from the first element to the current
411 * position, inclusive.<p>
412 *
413 * This method runs in linear time. If the specified list does not
414 * implement the {@link RandomAccess} interface and is large, this
415 * implementation dumps the specified list into an array before shuffling
416 * it, and dumps the shuffled array back into the list. This avoids the
417 * quadratic behavior that would result from shuffling a "sequential
418 * access" list in place.
419 *
420 * @param list the list to be shuffled.
421 * @throws UnsupportedOperationException if the specified list or
422 * its list-iterator does not support the <tt>set</tt> operation.
423 */
424 public static void shuffle(List<?> list) {
425 if (r == null) {
426 r = new Random();
427 }
428 shuffle(list, r);
429 }
430 private static Random r;
431
432 /**
433 * Randomly permute the specified list using the specified source of
434 * randomness. All permutations occur with equal likelihood
435 * assuming that the source of randomness is fair.<p>
436 *
437 * This implementation traverses the list backwards, from the last element
438 * up to the second, repeatedly swapping a randomly selected element into
439 * the "current position". Elements are randomly selected from the
440 * portion of the list that runs from the first element to the current
441 * position, inclusive.<p>
442 *
443 * This method runs in linear time. If the specified list does not
444 * implement the {@link RandomAccess} interface and is large, this
445 * implementation dumps the specified list into an array before shuffling
446 * it, and dumps the shuffled array back into the list. This avoids the
447 * quadratic behavior that would result from shuffling a "sequential
448 * access" list in place.
449 *
450 * @param list the list to be shuffled.
451 * @param rnd the source of randomness to use to shuffle the list.
452 * @throws UnsupportedOperationException if the specified list or its
453 * list-iterator does not support the <tt>set</tt> operation.
454 */
455 public static void shuffle(List<?> list, Random rnd) {
456 int size = list.size();
457 if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) {
458 for (int i=size; i>1; i--)
459 swap(list, i-1, rnd.nextInt(i));
460 } else {
461 Object arr[] = list.toArray();
462
463 // Shuffle array
464 for (int i=size; i>1; i--)
465 swap(arr, i-1, rnd.nextInt(i));
466
467 // Dump array back into list
468 ListIterator it = list.listIterator();
469 for (int i=0; i<arr.length; i++) {
470 it.next();
471 it.set(arr[i]);
472 }
473 }
474 }
475
476 /**
477 * Swaps the elements at the specified positions in the specified list.
478 * (If the specified positions are equal, invoking this method leaves
479 * the list unchanged.)
480 *
481 * @param list The list in which to swap elements.
482 * @param i the index of one element to be swapped.
483 * @param j the index of the other element to be swapped.
484 * @throws IndexOutOfBoundsException if either <tt>i</tt> or <tt>j</tt>
485 * is out of range (i < 0 || i >= list.size()
486 * || j < 0 || j >= list.size()).
487 * @since 1.4
488 */
489 public static void swap(List<?> list, int i, int j) {
490 final List l = list;
491 l.set(i, l.set(j, l.get(i)));
492 }
493
494 /**
495 * Swaps the two specified elements in the specified array.
496 */
497 private static void swap(Object[] arr, int i, int j) {
498 Object tmp = arr[i];
499 arr[i] = arr[j];
500 arr[j] = tmp;
501 }
502
503 /**
504 * Replaces all of the elements of the specified list with the specified
505 * element. <p>
506 *
507 * This method runs in linear time.
508 *
509 * @param list the list to be filled with the specified element.
510 * @param obj The element with which to fill the specified list.
511 * @throws UnsupportedOperationException if the specified list or its
512 * list-iterator does not support the <tt>set</tt> operation.
513 */
514 public static <T> void fill(List<? super T> list, T obj) {
515 int size = list.size();
516
517 if (size < FILL_THRESHOLD || list instanceof RandomAccess) {
518 for (int i=0; i<size; i++)
519 list.set(i, obj);
520 } else {
521 ListIterator<? super T> itr = list.listIterator();
522 for (int i=0; i<size; i++) {
523 itr.next();
524 itr.set(obj);
525 }
526 }
527 }
528
529 /**
530 * Copies all of the elements from one list into another. After the
531 * operation, the index of each copied element in the destination list
532 * will be identical to its index in the source list. The destination
533 * list must be at least as long as the source list. If it is longer, the
534 * remaining elements in the destination list are unaffected. <p>
535 *
536 * This method runs in linear time.
537 *
538 * @param dest The destination list.
539 * @param src The source list.
540 * @throws IndexOutOfBoundsException if the destination list is too small
541 * to contain the entire source List.
542 * @throws UnsupportedOperationException if the destination list's
543 * list-iterator does not support the <tt>set</tt> operation.
544 */
545 public static <T> void copy(List<? super T> dest, List<? extends T> src) {
546 int srcSize = src.size();
547 if (srcSize > dest.size())
548 throw new IndexOutOfBoundsException("Source does not fit in dest");
549
550 if (srcSize < COPY_THRESHOLD ||
551 (src instanceof RandomAccess && dest instanceof RandomAccess)) {
552 for (int i=0; i<srcSize; i++)
553 dest.set(i, src.get(i));
554 } else {
555 ListIterator<? super T> di=dest.listIterator();
556 ListIterator<? extends T> si=src.listIterator();
557 for (int i=0; i<srcSize; i++) {
558 di.next();
559 di.set(si.next());
560 }
561 }
562 }
563
564 /**
565 * Returns the minimum element of the given collection, according to the
566 * <i>natural ordering</i> of its elements. All elements in the
567 * collection must implement the <tt>Comparable</tt> interface.
568 * Furthermore, all elements in the collection must be <i>mutually
569 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
570 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
571 * <tt>e2</tt> in the collection).<p>
572 *
573 * This method iterates over the entire collection, hence it requires
574 * time proportional to the size of the collection.
575 *
576 * @param coll the collection whose minimum element is to be determined.
577 * @return the minimum element of the given collection, according
578 * to the <i>natural ordering</i> of its elements.
579 * @throws ClassCastException if the collection contains elements that are
580 * not <i>mutually comparable</i> (for example, strings and
581 * integers).
582 * @throws NoSuchElementException if the collection is empty.
583 * @see Comparable
584 */
585 public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) {
586 Iterator<? extends T> i = coll.iterator();
587 T candidate = i.next();
588
589 while (i.hasNext()) {
590 T next = i.next();
591 if (next.compareTo(candidate) < 0)
592 candidate = next;
593 }
594 return candidate;
595 }
596
597 /**
598 * Returns the minimum element of the given collection, according to the
599 * order induced by the specified comparator. All elements in the
600 * collection must be <i>mutually comparable</i> by the specified
601 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
602 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
603 * <tt>e2</tt> in the collection).<p>
604 *
605 * This method iterates over the entire collection, hence it requires
606 * time proportional to the size of the collection.
607 *
608 * @param coll the collection whose minimum element is to be determined.
609 * @param comp the comparator with which to determine the minimum element.
610 * A <tt>null</tt> value indicates that the elements' <i>natural
611 * ordering</i> should be used.
612 * @return the minimum element of the given collection, according
613 * to the specified comparator.
614 * @throws ClassCastException if the collection contains elements that are
615 * not <i>mutually comparable</i> using the specified comparator.
616 * @throws NoSuchElementException if the collection is empty.
617 * @see Comparable
618 */
619 public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) {
620 if (comp==null)
621 return (T)min((Collection<SelfComparable>) (Collection) coll);
622
623 Iterator<? extends T> i = coll.iterator();
624 T candidate = i.next();
625
626 while (i.hasNext()) {
627 T next = i.next();
628 if (comp.compare(next, candidate) < 0)
629 candidate = next;
630 }
631 return candidate;
632 }
633
634 /**
635 * Returns the maximum element of the given collection, according to the
636 * <i>natural ordering</i> of its elements. All elements in the
637 * collection must implement the <tt>Comparable</tt> interface.
638 * Furthermore, all elements in the collection must be <i>mutually
639 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
640 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
641 * <tt>e2</tt> in the collection).<p>
642 *
643 * This method iterates over the entire collection, hence it requires
644 * time proportional to the size of the collection.
645 *
646 * @param coll the collection whose maximum element is to be determined.
647 * @return the maximum element of the given collection, according
648 * to the <i>natural ordering</i> of its elements.
649 * @throws ClassCastException if the collection contains elements that are
650 * not <i>mutually comparable</i> (for example, strings and
651 * integers).
652 * @throws NoSuchElementException if the collection is empty.
653 * @see Comparable
654 */
655 public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) {
656 Iterator<? extends T> i = coll.iterator();
657 T candidate = i.next();
658
659 while (i.hasNext()) {
660 T next = i.next();
661 if (next.compareTo(candidate) > 0)
662 candidate = next;
663 }
664 return candidate;
665 }
666
667 /**
668 * Returns the maximum element of the given collection, according to the
669 * order induced by the specified comparator. All elements in the
670 * collection must be <i>mutually comparable</i> by the specified
671 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
672 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
673 * <tt>e2</tt> in the collection).<p>
674 *
675 * This method iterates over the entire collection, hence it requires
676 * time proportional to the size of the collection.
677 *
678 * @param coll the collection whose maximum element is to be determined.
679 * @param comp the comparator with which to determine the maximum element.
680 * A <tt>null</tt> value indicates that the elements' <i>natural
681 * ordering</i> should be used.
682 * @return the maximum element of the given collection, according
683 * to the specified comparator.
684 * @throws ClassCastException if the collection contains elements that are
685 * not <i>mutually comparable</i> using the specified comparator.
686 * @throws NoSuchElementException if the collection is empty.
687 * @see Comparable
688 */
689 public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) {
690 if (comp==null)
691 return (T)max((Collection<SelfComparable>) (Collection) coll);
692
693 Iterator<? extends T> i = coll.iterator();
694 T candidate = i.next();
695
696 while (i.hasNext()) {
697 T next = i.next();
698 if (comp.compare(next, candidate) > 0)
699 candidate = next;
700 }
701 return candidate;
702 }
703
704 /**
705 * Rotates the elements in the specified list by the specified distance.
706 * After calling this method, the element at index <tt>i</tt> will be
707 * the element previously at index <tt>(i - distance)</tt> mod
708 * <tt>list.size()</tt>, for all values of <tt>i</tt> between <tt>0</tt>
709 * and <tt>list.size()-1</tt>, inclusive. (This method has no effect on
710 * the size of the list.)
711 *
712 * <p>For example, suppose <tt>list</tt> comprises<tt> [t, a, n, k, s]</tt>.
713 * After invoking <tt>Collections.rotate(list, 1)</tt> (or
714 * <tt>Collections.rotate(list, -4)</tt>), <tt>list</tt> will comprise
715 * <tt>[s, t, a, n, k]</tt>.
716 *
717 * <p>Note that this method can usefully be applied to sublists to
718 * move one or more elements within a list while preserving the
719 * order of the remaining elements. For example, the following idiom
720 * moves the element at index <tt>j</tt> forward to position
721 * <tt>k</tt> (which must be greater than or equal to <tt>j</tt>):
722 * <pre>
723 * Collections.rotate(list.subList(j, k+1), -1);
724 * </pre>
725 * To make this concrete, suppose <tt>list</tt> comprises
726 * <tt>[a, b, c, d, e]</tt>. To move the element at index <tt>1</tt>
727 * (<tt>b</tt>) forward two positions, perform the following invocation:
728 * <pre>
729 * Collections.rotate(l.subList(1, 4), -1);
730 * </pre>
731 * The resulting list is <tt>[a, c, d, b, e]</tt>.
732 *
733 * <p>To move more than one element forward, increase the absolute value
734 * of the rotation distance. To move elements backward, use a positive
735 * shift distance.
736 *
737 * <p>If the specified list is small or implements the {@link
738 * RandomAccess} interface, this implementation exchanges the first
739 * element into the location it should go, and then repeatedly exchanges
740 * the displaced element into the location it should go until a displaced
741 * element is swapped into the first element. If necessary, the process
742 * is repeated on the second and successive elements, until the rotation
743 * is complete. If the specified list is large and doesn't implement the
744 * <tt>RandomAccess</tt> interface, this implementation breaks the
745 * list into two sublist views around index <tt>-distance mod size</tt>.
746 * Then the {@link #reverse(List)} method is invoked on each sublist view,
747 * and finally it is invoked on the entire list. For a more complete
748 * description of both algorithms, see Section 2.3 of Jon Bentley's
749 * <i>Programming Pearls</i> (Addison-Wesley, 1986).
750 *
751 * @param list the list to be rotated.
752 * @param distance the distance to rotate the list. There are no
753 * constraints on this value; it may be zero, negative, or
754 * greater than <tt>list.size()</tt>.
755 * @throws UnsupportedOperationException if the specified list or
756 * its list-iterator does not support the <tt>set</tt> operation.
757 * @since 1.4
758 */
759 public static void rotate(List<?> list, int distance) {
760 if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD)
761 rotate1(list, distance);
762 else
763 rotate2(list, distance);
764 }
765
766 private static <T> void rotate1(List<T> list, int distance) {
767 int size = list.size();
768 if (size == 0)
769 return;
770 distance = distance % size;
771 if (distance < 0)
772 distance += size;
773 if (distance == 0)
774 return;
775
776 for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) {
777 T displaced = list.get(cycleStart);
778 int i = cycleStart;
779 do {
780 i += distance;
781 if (i >= size)
782 i -= size;
783 displaced = list.set(i, displaced);
784 nMoved ++;
785 } while(i != cycleStart);
786 }
787 }
788
789 private static void rotate2(List<?> list, int distance) {
790 int size = list.size();
791 if (size == 0)
792 return;
793 int mid = -distance % size;
794 if (mid < 0)
795 mid += size;
796 if (mid == 0)
797 return;
798
799 reverse(list.subList(0, mid));
800 reverse(list.subList(mid, size));
801 reverse(list);
802 }
803
804 /**
805 * Replaces all occurrences of one specified value in a list with another.
806 * More formally, replaces with <tt>newVal</tt> each element <tt>e</tt>
807 * in <tt>list</tt> such that
808 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
809 * (This method has no effect on the size of the list.)
810 *
811 * @param list the list in which replacement is to occur.
812 * @param oldVal the old value to be replaced.
813 * @param newVal the new value with which <tt>oldVal</tt> is to be
814 * replaced.
815 * @return <tt>true</tt> if <tt>list</tt> contained one or more elements
816 * <tt>e</tt> such that
817 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
818 * @throws UnsupportedOperationException if the specified list or
819 * its list-iterator does not support the <tt>set</tt> operation.
820 * @since 1.4
821 */
822 public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) {
823 boolean result = false;
824 int size = list.size();
825 if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) {
826 if (oldVal==null) {
827 for (int i=0; i<size; i++) {
828 if (list.get(i)==null) {
829 list.set(i, newVal);
830 result = true;
831 }
832 }
833 } else {
834 for (int i=0; i<size; i++) {
835 if (oldVal.equals(list.get(i))) {
836 list.set(i, newVal);
837 result = true;
838 }
839 }
840 }
841 } else {
842 ListIterator<T> itr=list.listIterator();
843 if (oldVal==null) {
844 for (int i=0; i<size; i++) {
845 if (itr.next()==null) {
846 itr.set(newVal);
847 result = true;
848 }
849 }
850 } else {
851 for (int i=0; i<size; i++) {
852 if (oldVal.equals(itr.next())) {
853 itr.set(newVal);
854 result = true;
855 }
856 }
857 }
858 }
859 return result;
860 }
861
862 /**
863 * Returns the starting position of the first occurrence of the specified
864 * target list within the specified source list, or -1 if there is no
865 * such occurrence. More formally, returns the lowest index <tt>i</tt>
866 * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
867 * or -1 if there is no such index. (Returns -1 if
868 * <tt>target.size() > source.size()</tt>.)
869 *
870 * <p>This implementation uses the "brute force" technique of scanning
871 * over the source list, looking for a match with the target at each
872 * location in turn.
873 *
874 * @param source the list in which to search for the first occurrence
875 * of <tt>target</tt>.
876 * @param target the list to search for as a subList of <tt>source</tt>.
877 * @return the starting position of the first occurrence of the specified
878 * target list within the specified source list, or -1 if there
879 * is no such occurrence.
880 * @since 1.4
881 */
882 public static int indexOfSubList(List<?> source, List<?> target) {
883 int sourceSize = source.size();
884 int targetSize = target.size();
885 int maxCandidate = sourceSize - targetSize;
886
887 if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
888 (source instanceof RandomAccess&&target instanceof RandomAccess)) {
889 nextCand:
890 for (int candidate = 0; candidate <= maxCandidate; candidate++) {
891 for (int i=0, j=candidate; i<targetSize; i++, j++)
892 if (!eq(target.get(i), source.get(j)))
893 continue nextCand; // Element mismatch, try next cand
894 return candidate; // All elements of candidate matched target
895 }
896 } else { // Iterator version of above algorithm
897 ListIterator<?> si = source.listIterator();
898 nextCand:
899 for (int candidate = 0; candidate <= maxCandidate; candidate++) {
900 ListIterator<?> ti = target.listIterator();
901 for (int i=0; i<targetSize; i++) {
902 if (!eq(ti.next(), si.next())) {
903 // Back up source iterator to next candidate
904 for (int j=0; j<i; j++)
905 si.previous();
906 continue nextCand;
907 }
908 }
909 return candidate;
910 }
911 }
912 return -1; // No candidate matched the target
913 }
914
915 /**
916 * Returns the starting position of the last occurrence of the specified
917 * target list within the specified source list, or -1 if there is no such
918 * occurrence. More formally, returns the highest index <tt>i</tt>
919 * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
920 * or -1 if there is no such index. (Returns -1 if
921 * <tt>target.size() > source.size()</tt>.)
922 *
923 * <p>This implementation uses the "brute force" technique of iterating
924 * over the source list, looking for a match with the target at each
925 * location in turn.
926 *
927 * @param source the list in which to search for the last occurrence
928 * of <tt>target</tt>.
929 * @param target the list to search for as a subList of <tt>source</tt>.
930 * @return the starting position of the last occurrence of the specified
931 * target list within the specified source list, or -1 if there
932 * is no such occurrence.
933 * @since 1.4
934 */
935 public static int lastIndexOfSubList(List<?> source, List<?> target) {
936 int sourceSize = source.size();
937 int targetSize = target.size();
938 int maxCandidate = sourceSize - targetSize;
939
940 if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
941 source instanceof RandomAccess) { // Index access version
942 nextCand:
943 for (int candidate = maxCandidate; candidate >= 0; candidate--) {
944 for (int i=0, j=candidate; i<targetSize; i++, j++)
945 if (!eq(target.get(i), source.get(j)))
946 continue nextCand; // Element mismatch, try next cand
947 return candidate; // All elements of candidate matched target
948 }
949 } else { // Iterator version of above algorithm
950 if (maxCandidate < 0)
951 return -1;
952 ListIterator<?> si = source.listIterator(maxCandidate);
953 nextCand:
954 for (int candidate = maxCandidate; candidate >= 0; candidate--) {
955 ListIterator<?> ti = target.listIterator();
956 for (int i=0; i<targetSize; i++) {
957 if (!eq(ti.next(), si.next())) {
958 if (candidate != 0) {
959 // Back up source iterator to next candidate
960 for (int j=0; j<=i+1; j++)
961 si.previous();
962 }
963 continue nextCand;
964 }
965 }
966 return candidate;
967 }
968 }
969 return -1; // No candidate matched the target
970 }
971
972
973 // Unmodifiable Wrappers
974
975 /**
976 * Returns an unmodifiable view of the specified collection. This method
977 * allows modules to provide users with "read-only" access to internal
978 * collections. Query operations on the returned collection "read through"
979 * to the specified collection, and attempts to modify the returned
980 * collection, whether direct or via its iterator, result in an
981 * <tt>UnsupportedOperationException</tt>.<p>
982 *
983 * The returned collection does <i>not</i> pass the hashCode and equals
984 * operations through to the backing collection, but relies on
985 * <tt>Object</tt>'s <tt>equals</tt> and <tt>hashCode</tt> methods. This
986 * is necessary to preserve the contracts of these operations in the case
987 * that the backing collection is a set or a list.<p>
988 *
989 * The returned collection will be serializable if the specified collection
990 * is serializable.
991 *
992 * @param c the collection for which an unmodifiable view is to be
993 * returned.
994 * @return an unmodifiable view of the specified collection.
995 */
996 public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) {
997 return new UnmodifiableCollection<T>(c);
998 }
999
1000 /**
1001 * @serial include
1002 */
1003 static class UnmodifiableCollection<E> implements Collection<E>, Serializable {
1004 private static final long serialVersionUID = 1820017752578914078L;
1005
1006 final Collection<? extends E> c;
1007
1008 UnmodifiableCollection(Collection<? extends E> c) {
1009 if (c==null)
1010 throw new NullPointerException();
1011 this.c = c;
1012 }
1013
1014 public int size() {return c.size();}
1015 public boolean isEmpty() {return c.isEmpty();}
1016 public boolean contains(Object o) {return c.contains(o);}
1017 public Object[] toArray() {return c.toArray();}
1018 public <T> T[] toArray(T[] a) {return c.toArray(a);}
1019 public String toString() {return c.toString();}
1020
1021 public Iterator<E> iterator() {
1022 return new Iterator<E>() {
1023 private final Iterator<? extends E> i = c.iterator();
1024
1025 public boolean hasNext() {return i.hasNext();}
1026 public E next() {return i.next();}
1027 public void remove() {
1028 throw new UnsupportedOperationException();
1029 }
1030 };
1031 }
1032
1033 public boolean add(E e) {
1034 throw new UnsupportedOperationException();
1035 }
1036 public boolean remove(Object o) {
1037 throw new UnsupportedOperationException();
1038 }
1039
1040 public boolean containsAll(Collection<?> coll) {
1041 return c.containsAll(coll);
1042 }
1043 public boolean addAll(Collection<? extends E> coll) {
1044 throw new UnsupportedOperationException();
1045 }
1046 public boolean removeAll(Collection<?> coll) {
1047 throw new UnsupportedOperationException();
1048 }
1049 public boolean retainAll(Collection<?> coll) {
1050 throw new UnsupportedOperationException();
1051 }
1052 public void clear() {
1053 throw new UnsupportedOperationException();
1054 }
1055 }
1056
1057 /**
1058 * Returns an unmodifiable view of the specified set. This method allows
1059 * modules to provide users with "read-only" access to internal sets.
1060 * Query operations on the returned set "read through" to the specified
1061 * set, and attempts to modify the returned set, whether direct or via its
1062 * iterator, result in an <tt>UnsupportedOperationException</tt>.<p>
1063 *
1064 * The returned set will be serializable if the specified set
1065 * is serializable.
1066 *
1067 * @param s the set for which an unmodifiable view is to be returned.
1068 * @return an unmodifiable view of the specified set.
1069 */
1070 public static <T> Set<T> unmodifiableSet(Set<? extends T> s) {
1071 return new UnmodifiableSet<T>(s);
1072 }
1073
1074 /**
1075 * @serial include
1076 */
1077 static class UnmodifiableSet<E> extends UnmodifiableCollection<E>
1078 implements Set<E>, Serializable {
1079 private static final long serialVersionUID = -9215047833775013803L;
1080
1081 UnmodifiableSet(Set<? extends E> s) {super(s);}
1082 public boolean equals(Object o) {return o == this || c.equals(o);}
1083 public int hashCode() {return c.hashCode();}
1084 }
1085
1086 /**
1087 * Returns an unmodifiable view of the specified sorted set. This method
1088 * allows modules to provide users with "read-only" access to internal
1089 * sorted sets. Query operations on the returned sorted set "read
1090 * through" to the specified sorted set. Attempts to modify the returned
1091 * sorted set, whether direct, via its iterator, or via its
1092 * <tt>subSet</tt>, <tt>headSet</tt>, or <tt>tailSet</tt> views, result in
1093 * an <tt>UnsupportedOperationException</tt>.<p>
1094 *
1095 * The returned sorted set will be serializable if the specified sorted set
1096 * is serializable.
1097 *
1098 * @param s the sorted set for which an unmodifiable view is to be
1099 * returned.
1100 * @return an unmodifiable view of the specified sorted set.
1101 */
1102 public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) {
1103 return new UnmodifiableSortedSet<T>(s);
1104 }
1105
1106 /**
1107 * @serial include
1108 */
1109 static class UnmodifiableSortedSet<E>
1110 extends UnmodifiableSet<E>
1111 implements SortedSet<E>, Serializable {
1112 private static final long serialVersionUID = -4929149591599911165L;
1113 private final SortedSet<E> ss;
1114
1115 UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;}
1116
1117 public Comparator<? super E> comparator() {return ss.comparator();}
1118
1119 public SortedSet<E> subSet(E fromElement, E toElement) {
1120 return new UnmodifiableSortedSet<E>(ss.subSet(fromElement,toElement));
1121 }
1122 public SortedSet<E> headSet(E toElement) {
1123 return new UnmodifiableSortedSet<E>(ss.headSet(toElement));
1124 }
1125 public SortedSet<E> tailSet(E fromElement) {
1126 return new UnmodifiableSortedSet<E>(ss.tailSet(fromElement));
1127 }
1128
1129 public E first() {return ss.first();}
1130 public E last() {return ss.last();}
1131 }
1132
1133 /**
1134 * Returns an unmodifiable view of the specified list. This method allows
1135 * modules to provide users with "read-only" access to internal
1136 * lists. Query operations on the returned list "read through" to the
1137 * specified list, and attempts to modify the returned list, whether
1138 * direct or via its iterator, result in an
1139 * <tt>UnsupportedOperationException</tt>.<p>
1140 *
1141 * The returned list will be serializable if the specified list
1142 * is serializable. Similarly, the returned list will implement
1143 * {@link RandomAccess} if the specified list does.
1144 *
1145 * @param list the list for which an unmodifiable view is to be returned.
1146 * @return an unmodifiable view of the specified list.
1147 */
1148 public static <T> List<T> unmodifiableList(List<? extends T> list) {
1149 return (list instanceof RandomAccess ?
1150 new UnmodifiableRandomAccessList<T>(list) :
1151 new UnmodifiableList<T>(list));
1152 }
1153
1154 /**
1155 * @serial include
1156 */
1157 static class UnmodifiableList<E> extends UnmodifiableCollection<E>
1158 implements List<E> {
1159 private static final long serialVersionUID = -283967356065247728L;
1160 final List<? extends E> list;
1161
1162 UnmodifiableList(List<? extends E> list) {
1163 super(list);
1164 this.list = list;
1165 }
1166
1167 public boolean equals(Object o) {return o == this || list.equals(o);}
1168 public int hashCode() {return list.hashCode();}
1169
1170 public E get(int index) {return list.get(index);}
1171 public E set(int index, E element) {
1172 throw new UnsupportedOperationException();
1173 }
1174 public void add(int index, E element) {
1175 throw new UnsupportedOperationException();
1176 }
1177 public E remove(int index) {
1178 throw new UnsupportedOperationException();
1179 }
1180 public int indexOf(Object o) {return list.indexOf(o);}
1181 public int lastIndexOf(Object o) {return list.lastIndexOf(o);}
1182 public boolean addAll(int index, Collection<? extends E> c) {
1183 throw new UnsupportedOperationException();
1184 }
1185 public ListIterator<E> listIterator() {return listIterator(0);}
1186
1187 public ListIterator<E> listIterator(final int index) {
1188 return new ListIterator<E>() {
1189 private final ListIterator<? extends E> i
1190 = list.listIterator(index);
1191
1192 public boolean hasNext() {return i.hasNext();}
1193 public E next() {return i.next();}
1194 public boolean hasPrevious() {return i.hasPrevious();}
1195 public E previous() {return i.previous();}
1196 public int nextIndex() {return i.nextIndex();}
1197 public int previousIndex() {return i.previousIndex();}
1198
1199 public void remove() {
1200 throw new UnsupportedOperationException();
1201 }
1202 public void set(E e) {
1203 throw new UnsupportedOperationException();
1204 }
1205 public void add(E e) {
1206 throw new UnsupportedOperationException();
1207 }
1208 };
1209 }
1210
1211 public List<E> subList(int fromIndex, int toIndex) {
1212 return new UnmodifiableList<E>(list.subList(fromIndex, toIndex));
1213 }
1214
1215 /**
1216 * UnmodifiableRandomAccessList instances are serialized as
1217 * UnmodifiableList instances to allow them to be deserialized
1218 * in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList).
1219 * This method inverts the transformation. As a beneficial
1220 * side-effect, it also grafts the RandomAccess marker onto
1221 * UnmodifiableList instances that were serialized in pre-1.4 JREs.
1222 *
1223 * Note: Unfortunately, UnmodifiableRandomAccessList instances
1224 * serialized in 1.4.1 and deserialized in 1.4 will become
1225 * UnmodifiableList instances, as this method was missing in 1.4.
1226 */
1227 private Object readResolve() {
1228 return (list instanceof RandomAccess
1229 ? new UnmodifiableRandomAccessList<E>(list)
1230 : this);
1231 }
1232 }
1233
1234 /**
1235 * @serial include
1236 */
1237 static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E>
1238 implements RandomAccess
1239 {
1240 UnmodifiableRandomAccessList(List<? extends E> list) {
1241 super(list);
1242 }
1243
1244 public List<E> subList(int fromIndex, int toIndex) {
1245 return new UnmodifiableRandomAccessList<E>(
1246 list.subList(fromIndex, toIndex));
1247 }
1248
1249 private static final long serialVersionUID = -2542308836966382001L;
1250
1251 /**
1252 * Allows instances to be deserialized in pre-1.4 JREs (which do
1253 * not have UnmodifiableRandomAccessList). UnmodifiableList has
1254 * a readResolve method that inverts this transformation upon
1255 * deserialization.
1256 */
1257 private Object writeReplace() {
1258 return new UnmodifiableList<E>(list);
1259 }
1260 }
1261
1262 /**
1263 * Returns an unmodifiable view of the specified map. This method
1264 * allows modules to provide users with "read-only" access to internal
1265 * maps. Query operations on the returned map "read through"
1266 * to the specified map, and attempts to modify the returned
1267 * map, whether direct or via its collection views, result in an
1268 * <tt>UnsupportedOperationException</tt>.<p>
1269 *
1270 * The returned map will be serializable if the specified map
1271 * is serializable.
1272 *
1273 * @param m the map for which an unmodifiable view is to be returned.
1274 * @return an unmodifiable view of the specified map.
1275 */
1276 public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) {
1277 return new UnmodifiableMap<K,V>(m);
1278 }
1279
1280 /**
1281 * @serial include
1282 */
1283 private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable {
1284 private static final long serialVersionUID = -1034234728574286014L;
1285
1286 private final Map<? extends K, ? extends V> m;
1287
1288 UnmodifiableMap(Map<? extends K, ? extends V> m) {
1289 if (m==null)
1290 throw new NullPointerException();
1291 this.m = m;
1292 }
1293
1294 public int size() {return m.size();}
1295 public boolean isEmpty() {return m.isEmpty();}
1296 public boolean containsKey(Object key) {return m.containsKey(key);}
1297 public boolean containsValue(Object val) {return m.containsValue(val);}
1298 public V get(Object key) {return m.get(key);}
1299
1300 public V put(K key, V value) {
1301 throw new UnsupportedOperationException();
1302 }
1303 public V remove(Object key) {
1304 throw new UnsupportedOperationException();
1305 }
1306 public void putAll(Map<? extends K, ? extends V> m) {
1307 throw new UnsupportedOperationException();
1308 }
1309 public void clear() {
1310 throw new UnsupportedOperationException();
1311 }
1312
1313 private transient Set<K> keySet = null;
1314 private transient Set<Map.Entry<K,V>> entrySet = null;
1315 private transient Collection<V> values = null;
1316
1317 public Set<K> keySet() {
1318 if (keySet==null)
1319 keySet = unmodifiableSet(m.keySet());
1320 return keySet;
1321 }
1322
1323 public Set<Map.Entry<K,V>> entrySet() {
1324 if (entrySet==null)
1325 entrySet = new UnmodifiableEntrySet<K,V>(m.entrySet());
1326 return entrySet;
1327 }
1328
1329 public Collection<V> values() {
1330 if (values==null)
1331 values = unmodifiableCollection(m.values());
1332 return values;
1333 }
1334
1335 public boolean equals(Object o) {return o == this || m.equals(o);}
1336 public int hashCode() {return m.hashCode();}
1337 public String toString() {return m.toString();}
1338
1339 /**
1340 * We need this class in addition to UnmodifiableSet as
1341 * Map.Entries themselves permit modification of the backing Map
1342 * via their setValue operation. This class is subtle: there are
1343 * many possible attacks that must be thwarted.
1344 *
1345 * @serial include
1346 */
1347 static class UnmodifiableEntrySet<K,V>
1348 extends UnmodifiableSet<Map.Entry<K,V>> {
1349 private static final long serialVersionUID = 7854390611657943733L;
1350
1351 UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) {
1352 super((Set)s);
1353 }
1354 public Iterator<Map.Entry<K,V>> iterator() {
1355 return new Iterator<Map.Entry<K,V>>() {
1356 private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator();
1357
1358 public boolean hasNext() {
1359 return i.hasNext();
1360 }
1361 public Map.Entry<K,V> next() {
1362 return new UnmodifiableEntry<K,V>(i.next());
1363 }
1364 public void remove() {
1365 throw new UnsupportedOperationException();
1366 }
1367 };
1368 }
1369
1370 public Object[] toArray() {
1371 Object[] a = c.toArray();
1372 for (int i=0; i<a.length; i++)
1373 a[i] = new UnmodifiableEntry<K,V>((Map.Entry<K,V>)a[i]);
1374 return a;
1375 }
1376
1377 public <T> T[] toArray(T[] a) {
1378 // We don't pass a to c.toArray, to avoid window of
1379 // vulnerability wherein an unscrupulous multithreaded client
1380 // could get his hands on raw (unwrapped) Entries from c.
1381 Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
1382
1383 for (int i=0; i<arr.length; i++)
1384 arr[i] = new UnmodifiableEntry<K,V>((Map.Entry<K,V>)arr[i]);
1385
1386 if (arr.length > a.length)
1387 return (T[])arr;
1388
1389 System.arraycopy(arr, 0, a, 0, arr.length);
1390 if (a.length > arr.length)
1391 a[arr.length] = null;
1392 return a;
1393 }
1394
1395 /**
1396 * This method is overridden to protect the backing set against
1397 * an object with a nefarious equals function that senses
1398 * that the equality-candidate is Map.Entry and calls its
1399 * setValue method.
1400 */
1401 public boolean contains(Object o) {
1402 if (!(o instanceof Map.Entry))
1403 return false;
1404 return c.contains(
1405 new UnmodifiableEntry<Object,Object>((Map.Entry<?,?>) o));
1406 }
1407
1408 /**
1409 * The next two methods are overridden to protect against
1410 * an unscrupulous List whose contains(Object o) method senses
1411 * when o is a Map.Entry, and calls o.setValue.
1412 */
1413 public boolean containsAll(Collection<?> coll) {
1414 Iterator<?> e = coll.iterator();
1415 while (e.hasNext())
1416 if (!contains(e.next())) // Invokes safe contains() above
1417 return false;
1418 return true;
1419 }
1420 public boolean equals(Object o) {
1421 if (o == this)
1422 return true;
1423
1424 if (!(o instanceof Set))
1425 return false;
1426 Set s = (Set) o;
1427 if (s.size() != c.size())
1428 return false;
1429 return containsAll(s); // Invokes safe containsAll() above
1430 }
1431
1432 /**
1433 * This "wrapper class" serves two purposes: it prevents
1434 * the client from modifying the backing Map, by short-circuiting
1435 * the setValue method, and it protects the backing Map against
1436 * an ill-behaved Map.Entry that attempts to modify another
1437 * Map Entry when asked to perform an equality check.
1438 */
1439 private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> {
1440 private Map.Entry<? extends K, ? extends V> e;
1441
1442 UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) {this.e = e;}
1443
1444 public K getKey() {return e.getKey();}
1445 public V getValue() {return e.getValue();}
1446 public V setValue(V value) {
1447 throw new UnsupportedOperationException();
1448 }
1449 public int hashCode() {return e.hashCode();}
1450 public boolean equals(Object o) {
1451 if (!(o instanceof Map.Entry))
1452 return false;
1453 Map.Entry t = (Map.Entry)o;
1454 return eq(e.getKey(), t.getKey()) &&
1455 eq(e.getValue(), t.getValue());
1456 }
1457 public String toString() {return e.toString();}
1458 }
1459 }
1460 }
1461
1462 /**
1463 * Returns an unmodifiable view of the specified sorted map. This method
1464 * allows modules to provide users with "read-only" access to internal
1465 * sorted maps. Query operations on the returned sorted map "read through"
1466 * to the specified sorted map. Attempts to modify the returned
1467 * sorted map, whether direct, via its collection views, or via its
1468 * <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in
1469 * an <tt>UnsupportedOperationException</tt>.<p>
1470 *
1471 * The returned sorted map will be serializable if the specified sorted map
1472 * is serializable.
1473 *
1474 * @param m the sorted map for which an unmodifiable view is to be
1475 * returned.
1476 * @return an unmodifiable view of the specified sorted map.
1477 */
1478 public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) {
1479 return new UnmodifiableSortedMap<K,V>(m);
1480 }
1481
1482 /**
1483 * @serial include
1484 */
1485 static class UnmodifiableSortedMap<K,V>
1486 extends UnmodifiableMap<K,V>
1487 implements SortedMap<K,V>, Serializable {
1488 private static final long serialVersionUID = -8806743815996713206L;
1489
1490 private final SortedMap<K, ? extends V> sm;
1491
1492 UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m;}
1493
1494 public Comparator<? super K> comparator() {return sm.comparator();}
1495
1496 public SortedMap<K,V> subMap(K fromKey, K toKey) {
1497 return new UnmodifiableSortedMap<K,V>(sm.subMap(fromKey, toKey));
1498 }
1499 public SortedMap<K,V> headMap(K toKey) {
1500 return new UnmodifiableSortedMap<K,V>(sm.headMap(toKey));
1501 }
1502 public SortedMap<K,V> tailMap(K fromKey) {
1503 return new UnmodifiableSortedMap<K,V>(sm.tailMap(fromKey));
1504 }
1505
1506 public K firstKey() {return sm.firstKey();}
1507 public K lastKey() {return sm.lastKey();}
1508 }
1509
1510
1511 // Synch Wrappers
1512
1513 /**
1514 * Returns a synchronized (thread-safe) collection backed by the specified
1515 * collection. In order to guarantee serial access, it is critical that
1516 * <strong>all</strong> access to the backing collection is accomplished
1517 * through the returned collection.<p>
1518 *
1519 * It is imperative that the user manually synchronize on the returned
1520 * collection when iterating over it:
1521 * <pre>
1522 * Collection c = Collections.synchronizedCollection(myCollection);
1523 * ...
1524 * synchronized(c) {
1525 * Iterator i = c.iterator(); // Must be in the synchronized block
1526 * while (i.hasNext())
1527 * foo(i.next());
1528 * }
1529 * </pre>
1530 * Failure to follow this advice may result in non-deterministic behavior.
1531 *
1532 * <p>The returned collection does <i>not</i> pass the <tt>hashCode</tt>
1533 * and <tt>equals</tt> operations through to the backing collection, but
1534 * relies on <tt>Object</tt>'s equals and hashCode methods. This is
1535 * necessary to preserve the contracts of these operations in the case
1536 * that the backing collection is a set or a list.<p>
1537 *
1538 * The returned collection will be serializable if the specified collection
1539 * is serializable.
1540 *
1541 * @param c the collection to be "wrapped" in a synchronized collection.
1542 * @return a synchronized view of the specified collection.
1543 */
1544 public static <T> Collection<T> synchronizedCollection(Collection<T> c) {
1545 return new SynchronizedCollection<T>(c);
1546 }
1547
1548 static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) {
1549 return new SynchronizedCollection<T>(c, mutex);
1550 }
1551
1552 /**
1553 * @serial include
1554 */
1555 static class SynchronizedCollection<E> implements Collection<E>, Serializable {
1556 private static final long serialVersionUID = 3053995032091335093L;
1557
1558 final Collection<E> c; // Backing Collection
1559 final Object mutex; // Object on which to synchronize
1560
1561 SynchronizedCollection(Collection<E> c) {
1562 if (c==null)
1563 throw new NullPointerException();
1564 this.c = c;
1565 mutex = this;
1566 }
1567 SynchronizedCollection(Collection<E> c, Object mutex) {
1568 this.c = c;
1569 this.mutex = mutex;
1570 }
1571
1572 public int size() {
1573 synchronized(mutex) {return c.size();}
1574 }
1575 public boolean isEmpty() {
1576 synchronized(mutex) {return c.isEmpty();}
1577 }
1578 public boolean contains(Object o) {
1579 synchronized(mutex) {return c.contains(o);}
1580 }
1581 public Object[] toArray() {
1582 synchronized(mutex) {return c.toArray();}
1583 }
1584 public <T> T[] toArray(T[] a) {
1585 synchronized(mutex) {return c.toArray(a);}
1586 }
1587
1588 public Iterator<E> iterator() {
1589 return c.iterator(); // Must be manually synched by user!
1590 }
1591
1592 public boolean add(E e) {
1593 synchronized(mutex) {return c.add(e);}
1594 }
1595 public boolean remove(Object o) {
1596 synchronized(mutex) {return c.remove(o);}
1597 }
1598
1599 public boolean containsAll(Collection<?> coll) {
1600 synchronized(mutex) {return c.containsAll(coll);}
1601 }
1602 public boolean addAll(Collection<? extends E> coll) {
1603 synchronized(mutex) {return c.addAll(coll);}
1604 }
1605 public boolean removeAll(Collection<?> coll) {
1606 synchronized(mutex) {return c.removeAll(coll);}
1607 }
1608 public boolean retainAll(Collection<?> coll) {
1609 synchronized(mutex) {return c.retainAll(coll);}
1610 }
1611 public void clear() {
1612 synchronized(mutex) {c.clear();}
1613 }
1614 public String toString() {
1615 synchronized(mutex) {return c.toString();}
1616 }
1617 private void writeObject(ObjectOutputStream s) throws IOException {
1618 synchronized(mutex) {s.defaultWriteObject();}
1619 }
1620 }
1621
1622 /**
1623 * Returns a synchronized (thread-safe) set backed by the specified
1624 * set. In order to guarantee serial access, it is critical that
1625 * <strong>all</strong> access to the backing set is accomplished
1626 * through the returned set.<p>
1627 *
1628 * It is imperative that the user manually synchronize on the returned
1629 * set when iterating over it:
1630 * <pre>
1631 * Set s = Collections.synchronizedSet(new HashSet());
1632 * ...
1633 * synchronized(s) {
1634 * Iterator i = s.iterator(); // Must be in the synchronized block
1635 * while (i.hasNext())
1636 * foo(i.next());
1637 * }
1638 * </pre>
1639 * Failure to follow this advice may result in non-deterministic behavior.
1640 *
1641 * <p>The returned set will be serializable if the specified set is
1642 * serializable.
1643 *
1644 * @param s the set to be "wrapped" in a synchronized set.
1645 * @return a synchronized view of the specified set.
1646 */
1647 public static <T> Set<T> synchronizedSet(Set<T> s) {
1648 return new SynchronizedSet<T>(s);
1649 }
1650
1651 static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) {
1652 return new SynchronizedSet<T>(s, mutex);
1653 }
1654
1655 /**
1656 * @serial include
1657 */
1658 static class SynchronizedSet<E>
1659 extends SynchronizedCollection<E>
1660 implements Set<E> {
1661 private static final long serialVersionUID = 487447009682186044L;
1662
1663 SynchronizedSet(Set<E> s) {
1664 super(s);
1665 }
1666 SynchronizedSet(Set<E> s, Object mutex) {
1667 super(s, mutex);
1668 }
1669
1670 public boolean equals(Object o) {
1671 synchronized(mutex) {return c.equals(o);}
1672 }
1673 public int hashCode() {
1674 synchronized(mutex) {return c.hashCode();}
1675 }
1676 }
1677
1678 /**
1679 * Returns a synchronized (thread-safe) sorted set backed by the specified
1680 * sorted set. In order to guarantee serial access, it is critical that
1681 * <strong>all</strong> access to the backing sorted set is accomplished
1682 * through the returned sorted set (or its views).<p>
1683 *
1684 * It is imperative that the user manually synchronize on the returned
1685 * sorted set when iterating over it or any of its <tt>subSet</tt>,
1686 * <tt>headSet</tt>, or <tt>tailSet</tt> views.
1687 * <pre>
1688 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
1689 * ...
1690 * synchronized(s) {
1691 * Iterator i = s.iterator(); // Must be in the synchronized block
1692 * while (i.hasNext())
1693 * foo(i.next());
1694 * }
1695 * </pre>
1696 * or:
1697 * <pre>
1698 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
1699 * SortedSet s2 = s.headSet(foo);
1700 * ...
1701 * synchronized(s) { // Note: s, not s2!!!
1702 * Iterator i = s2.iterator(); // Must be in the synchronized block
1703 * while (i.hasNext())
1704 * foo(i.next());
1705 * }
1706 * </pre>
1707 * Failure to follow this advice may result in non-deterministic behavior.
1708 *
1709 * <p>The returned sorted set will be serializable if the specified
1710 * sorted set is serializable.
1711 *
1712 * @param s the sorted set to be "wrapped" in a synchronized sorted set.
1713 * @return a synchronized view of the specified sorted set.
1714 */
1715 public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) {
1716 return new SynchronizedSortedSet<T>(s);
1717 }
1718
1719 /**
1720 * @serial include
1721 */
1722 static class SynchronizedSortedSet<E>
1723 extends SynchronizedSet<E>
1724 implements SortedSet<E>
1725 {
1726 private static final long serialVersionUID = 8695801310862127406L;
1727
1728 final private SortedSet<E> ss;
1729
1730 SynchronizedSortedSet(SortedSet<E> s) {
1731 super(s);
1732 ss = s;
1733 }
1734 SynchronizedSortedSet(SortedSet<E> s, Object mutex) {
1735 super(s, mutex);
1736 ss = s;
1737 }
1738
1739 public Comparator<? super E> comparator() {
1740 synchronized(mutex) {return ss.comparator();}
1741 }
1742
1743 public SortedSet<E> subSet(E fromElement, E toElement) {
1744 synchronized(mutex) {
1745 return new SynchronizedSortedSet<E>(
1746 ss.subSet(fromElement, toElement), mutex);
1747 }
1748 }
1749 public SortedSet<E> headSet(E toElement) {
1750 synchronized(mutex) {
1751 return new SynchronizedSortedSet<E>(ss.headSet(toElement), mutex);
1752 }
1753 }
1754 public SortedSet<E> tailSet(E fromElement) {
1755 synchronized(mutex) {
1756 return new SynchronizedSortedSet<E>(ss.tailSet(fromElement),mutex);
1757 }
1758 }
1759
1760 public E first() {
1761 synchronized(mutex) {return ss.first();}
1762 }
1763 public E last() {
1764 synchronized(mutex) {return ss.last();}
1765 }
1766 }
1767
1768 /**
1769 * Returns a synchronized (thread-safe) list backed by the specified
1770 * list. In order to guarantee serial access, it is critical that
1771 * <strong>all</strong> access to the backing list is accomplished
1772 * through the returned list.<p>
1773 *
1774 * It is imperative that the user manually synchronize on the returned
1775 * list when iterating over it:
1776 * <pre>
1777 * List list = Collections.synchronizedList(new ArrayList());
1778 * ...
1779 * synchronized(list) {
1780 * Iterator i = list.iterator(); // Must be in synchronized block
1781 * while (i.hasNext())
1782 * foo(i.next());
1783 * }
1784 * </pre>
1785 * Failure to follow this advice may result in non-deterministic behavior.
1786 *
1787 * <p>The returned list will be serializable if the specified list is
1788 * serializable.
1789 *
1790 * @param list the list to be "wrapped" in a synchronized list.
1791 * @return a synchronized view of the specified list.
1792 */
1793 public static <T> List<T> synchronizedList(List<T> list) {
1794 return (list instanceof RandomAccess ?
1795 new SynchronizedRandomAccessList<T>(list) :
1796 new SynchronizedList<T>(list));
1797 }
1798
1799 static <T> List<T> synchronizedList(List<T> list, Object mutex) {
1800 return (list instanceof RandomAccess ?
1801 new SynchronizedRandomAccessList<T>(list, mutex) :
1802 new SynchronizedList<T>(list, mutex));
1803 }
1804
1805 /**
1806 * @serial include
1807 */
1808 static class SynchronizedList<E>
1809 extends SynchronizedCollection<E>
1810 implements List<E> {
1811 private static final long serialVersionUID = -7754090372962971524L;
1812
1813 final List<E> list;
1814
1815 SynchronizedList(List<E> list) {
1816 super(list);
1817 this.list = list;
1818 }
1819 SynchronizedList(List<E> list, Object mutex) {
1820 super(list, mutex);
1821 this.list = list;
1822 }
1823
1824 public boolean equals(Object o) {
1825 synchronized(mutex) {return list.equals(o);}
1826 }
1827 public int hashCode() {
1828 synchronized(mutex) {return list.hashCode();}
1829 }
1830
1831 public E get(int index) {
1832 synchronized(mutex) {return list.get(index);}
1833 }
1834 public E set(int index, E element) {
1835 synchronized(mutex) {return list.set(index, element);}
1836 }
1837 public void add(int index, E element) {
1838 synchronized(mutex) {list.add(index, element);}
1839 }
1840 public E remove(int index) {
1841 synchronized(mutex) {return list.remove(index);}
1842 }
1843
1844 public int indexOf(Object o) {
1845 synchronized(mutex) {return list.indexOf(o);}
1846 }
1847 public int lastIndexOf(Object o) {
1848 synchronized(mutex) {return list.lastIndexOf(o);}
1849 }
1850
1851 public boolean addAll(int index, Collection<? extends E> c) {
1852 synchronized(mutex) {return list.addAll(index, c);}
1853 }
1854
1855 public ListIterator<E> listIterator() {
1856 return list.listIterator(); // Must be manually synched by user
1857 }
1858
1859 public ListIterator<E> listIterator(int index) {
1860 return list.listIterator(index); // Must be manually synched by user
1861 }
1862
1863 public List<E> subList(int fromIndex, int toIndex) {
1864 synchronized(mutex) {
1865 return new SynchronizedList<E>(list.subList(fromIndex, toIndex),
1866 mutex);
1867 }
1868 }
1869
1870 /**
1871 * SynchronizedRandomAccessList instances are serialized as
1872 * SynchronizedList instances to allow them to be deserialized
1873 * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList).
1874 * This method inverts the transformation. As a beneficial
1875 * side-effect, it also grafts the RandomAccess marker onto
1876 * SynchronizedList instances that were serialized in pre-1.4 JREs.
1877 *
1878 * Note: Unfortunately, SynchronizedRandomAccessList instances
1879 * serialized in 1.4.1 and deserialized in 1.4 will become
1880 * SynchronizedList instances, as this method was missing in 1.4.
1881 */
1882 private Object readResolve() {
1883 return (list instanceof RandomAccess
1884 ? new SynchronizedRandomAccessList<E>(list)
1885 : this);
1886 }
1887 }
1888
1889 /**
1890 * @serial include
1891 */
1892 static class SynchronizedRandomAccessList<E>
1893 extends SynchronizedList<E>
1894 implements RandomAccess {
1895
1896 SynchronizedRandomAccessList(List<E> list) {
1897 super(list);
1898 }
1899
1900 SynchronizedRandomAccessList(List<E> list, Object mutex) {
1901 super(list, mutex);
1902 }
1903
1904 public List<E> subList(int fromIndex, int toIndex) {
1905 synchronized(mutex) {
1906 return new SynchronizedRandomAccessList<E>(
1907 list.subList(fromIndex, toIndex), mutex);
1908 }
1909 }
1910
1911 private static final long serialVersionUID = 1530674583602358482L;
1912
1913 /**
1914 * Allows instances to be deserialized in pre-1.4 JREs (which do
1915 * not have SynchronizedRandomAccessList). SynchronizedList has
1916 * a readResolve method that inverts this transformation upon
1917 * deserialization.
1918 */
1919 private Object writeReplace() {
1920 return new SynchronizedList<E>(list);
1921 }
1922 }
1923
1924 /**
1925 * Returns a synchronized (thread-safe) map backed by the specified
1926 * map. In order to guarantee serial access, it is critical that
1927 * <strong>all</strong> access to the backing map is accomplished
1928 * through the returned map.<p>
1929 *
1930 * It is imperative that the user manually synchronize on the returned
1931 * map when iterating over any of its collection views:
1932 * <pre>
1933 * Map m = Collections.synchronizedMap(new HashMap());
1934 * ...
1935 * Set s = m.keySet(); // Needn't be in synchronized block
1936 * ...
1937 * synchronized(m) { // Synchronizing on m, not s!
1938 * Iterator i = s.iterator(); // Must be in synchronized block
1939 * while (i.hasNext())
1940 * foo(i.next());
1941 * }
1942 * </pre>
1943 * Failure to follow this advice may result in non-deterministic behavior.
1944 *
1945 * <p>The returned map will be serializable if the specified map is
1946 * serializable.
1947 *
1948 * @param m the map to be "wrapped" in a synchronized map.
1949 * @return a synchronized view of the specified map.
1950 */
1951 public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) {
1952 return new SynchronizedMap<K,V>(m);
1953 }
1954
1955 /**
1956 * @serial include
1957 */
1958 private static class SynchronizedMap<K,V>
1959 implements Map<K,V>, Serializable {
1960 private static final long serialVersionUID = 1978198479659022715L;
1961
1962 private final Map<K,V> m; // Backing Map
1963 final Object mutex; // Object on which to synchronize
1964
1965 SynchronizedMap(Map<K,V> m) {
1966 if (m==null)
1967 throw new NullPointerException();
1968 this.m = m;
1969 mutex = this;
1970 }
1971
1972 SynchronizedMap(Map<K,V> m, Object mutex) {
1973 this.m = m;
1974 this.mutex = mutex;
1975 }
1976
1977 public int size() {
1978 synchronized(mutex) {return m.size();}
1979 }
1980 public boolean isEmpty() {
1981 synchronized(mutex) {return m.isEmpty();}
1982 }
1983 public boolean containsKey(Object key) {
1984 synchronized(mutex) {return m.containsKey(key);}
1985 }
1986 public boolean containsValue(Object value) {
1987 synchronized(mutex) {return m.containsValue(value);}
1988 }
1989 public V get(Object key) {
1990 synchronized(mutex) {return m.get(key);}
1991 }
1992
1993 public V put(K key, V value) {
1994 synchronized(mutex) {return m.put(key, value);}
1995 }
1996 public V remove(Object key) {
1997 synchronized(mutex) {return m.remove(key);}
1998 }
1999 public void putAll(Map<? extends K, ? extends V> map) {
2000 synchronized(mutex) {m.putAll(map);}
2001 }
2002 public void clear() {
2003 synchronized(mutex) {m.clear();}
2004 }
2005
2006 private transient Set<K> keySet = null;
2007 private transient Set<Map.Entry<K,V>> entrySet = null;
2008 private transient Collection<V> values = null;
2009
2010 public Set<K> keySet() {
2011 synchronized(mutex) {
2012 if (keySet==null)
2013 keySet = new SynchronizedSet<K>(m.keySet(), mutex);
2014 return keySet;
2015 }
2016 }
2017
2018 public Set<Map.Entry<K,V>> entrySet() {
2019 synchronized(mutex) {
2020 if (entrySet==null)
2021 entrySet = new SynchronizedSet<Map.Entry<K,V>>(m.entrySet(), mutex);
2022 return entrySet;
2023 }
2024 }
2025
2026 public Collection<V> values() {
2027 synchronized(mutex) {
2028 if (values==null)
2029 values = new SynchronizedCollection<V>(m.values(), mutex);
2030 return values;
2031 }
2032 }
2033
2034 public boolean equals(Object o) {
2035 synchronized(mutex) {return m.equals(o);}
2036 }
2037 public int hashCode() {
2038 synchronized(mutex) {return m.hashCode();}
2039 }
2040 public String toString() {
2041 synchronized(mutex) {return m.toString();}
2042 }
2043 private void writeObject(ObjectOutputStream s) throws IOException {
2044 synchronized(mutex) {s.defaultWriteObject();}
2045 }
2046 }
2047
2048 /**
2049 * Returns a synchronized (thread-safe) sorted map backed by the specified
2050 * sorted map. In order to guarantee serial access, it is critical that
2051 * <strong>all</strong> access to the backing sorted map is accomplished
2052 * through the returned sorted map (or its views).<p>
2053 *
2054 * It is imperative that the user manually synchronize on the returned
2055 * sorted map when iterating over any of its collection views, or the
2056 * collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or
2057 * <tt>tailMap</tt> views.
2058 * <pre>
2059 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
2060 * ...
2061 * Set s = m.keySet(); // Needn't be in synchronized block
2062 * ...
2063 * synchronized(m) { // Synchronizing on m, not s!
2064 * Iterator i = s.iterator(); // Must be in synchronized block
2065 * while (i.hasNext())
2066 * foo(i.next());
2067 * }
2068 * </pre>
2069 * or:
2070 * <pre>
2071 * SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
2072 * SortedMap m2 = m.subMap(foo, bar);
2073 * ...
2074 * Set s2 = m2.keySet(); // Needn't be in synchronized block
2075 * ...
2076 * synchronized(m) { // Synchronizing on m, not m2 or s2!
2077 * Iterator i = s.iterator(); // Must be in synchronized block
2078 * while (i.hasNext())
2079 * foo(i.next());
2080 * }
2081 * </pre>
2082 * Failure to follow this advice may result in non-deterministic behavior.
2083 *
2084 * <p>The returned sorted map will be serializable if the specified
2085 * sorted map is serializable.
2086 *
2087 * @param m the sorted map to be "wrapped" in a synchronized sorted map.
2088 * @return a synchronized view of the specified sorted map.
2089 */
2090 public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) {
2091 return new SynchronizedSortedMap<K,V>(m);
2092 }
2093
2094
2095 /**
2096 * @serial include
2097 */
2098 static class SynchronizedSortedMap<K,V>
2099 extends SynchronizedMap<K,V>
2100 implements SortedMap<K,V>
2101 {
2102 private static final long serialVersionUID = -8798146769416483793L;
2103
2104 private final SortedMap<K,V> sm;
2105
2106 SynchronizedSortedMap(SortedMap<K,V> m) {
2107 super(m);
2108 sm = m;
2109 }
2110 SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) {
2111 super(m, mutex);
2112 sm = m;
2113 }
2114
2115 public Comparator<? super K> comparator() {
2116 synchronized(mutex) {return sm.comparator();}
2117 }
2118
2119 public SortedMap<K,V> subMap(K fromKey, K toKey) {
2120 synchronized(mutex) {
2121 return new SynchronizedSortedMap<K,V>(
2122 sm.subMap(fromKey, toKey), mutex);
2123 }
2124 }
2125 public SortedMap<K,V> headMap(K toKey) {
2126 synchronized(mutex) {
2127 return new SynchronizedSortedMap<K,V>(sm.headMap(toKey), mutex);
2128 }
2129 }
2130 public SortedMap<K,V> tailMap(K fromKey) {
2131 synchronized(mutex) {
2132 return new SynchronizedSortedMap<K,V>(sm.tailMap(fromKey),mutex);
2133 }
2134 }
2135
2136 public K firstKey() {
2137 synchronized(mutex) {return sm.firstKey();}
2138 }
2139 public K lastKey() {
2140 synchronized(mutex) {return sm.lastKey();}
2141 }
2142 }
2143
2144 // Dynamically typesafe collection wrappers
2145
2146 /**
2147 * Returns a dynamically typesafe view of the specified collection.
2148 * Any attempt to insert an element of the wrong type will result in an
2149 * immediate {@link ClassCastException}. Assuming a collection
2150 * contains no incorrectly typed elements prior to the time a
2151 * dynamically typesafe view is generated, and that all subsequent
2152 * access to the collection takes place through the view, it is
2153 * <i>guaranteed</i> that the collection cannot contain an incorrectly
2154 * typed element.
2155 *
2156 * <p>The generics mechanism in the language provides compile-time
2157 * (static) type checking, but it is possible to defeat this mechanism
2158 * with unchecked casts. Usually this is not a problem, as the compiler
2159 * issues warnings on all such unchecked operations. There are, however,
2160 * times when static type checking alone is not sufficient. For example,
2161 * suppose a collection is passed to a third-party library and it is
2162 * imperative that the library code not corrupt the collection by
2163 * inserting an element of the wrong type.
2164 *
2165 * <p>Another use of dynamically typesafe views is debugging. Suppose a
2166 * program fails with a {@code ClassCastException}, indicating that an
2167 * incorrectly typed element was put into a parameterized collection.
2168 * Unfortunately, the exception can occur at any time after the erroneous
2169 * element is inserted, so it typically provides little or no information
2170 * as to the real source of the problem. If the problem is reproducible,
2171 * one can quickly determine its source by temporarily modifying the
2172 * program to wrap the collection with a dynamically typesafe view.
2173 * For example, this declaration:
2174 * <pre> {@code
2175 * Collection<String> c = new HashSet<String>();
2176 * }</pre>
2177 * may be replaced temporarily by this one:
2178 * <pre> {@code
2179 * Collection<String> c = Collections.checkedCollection(
2180 * new HashSet<String>(), String.class);
2181 * }</pre>
2182 * Running the program again will cause it to fail at the point where
2183 * an incorrectly typed element is inserted into the collection, clearly
2184 * identifying the source of the problem. Once the problem is fixed, the
2185 * modified declaration may be reverted back to the original.
2186 *
2187 * <p>The returned collection does <i>not</i> pass the hashCode and equals
2188 * operations through to the backing collection, but relies on
2189 * {@code Object}'s {@code equals} and {@code hashCode} methods. This
2190 * is necessary to preserve the contracts of these operations in the case
2191 * that the backing collection is a set or a list.
2192 *
2193 * <p>The returned collection will be serializable if the specified
2194 * collection is serializable.
2195 *
2196 * <p>Since {@code null} is considered to be a value of any reference
2197 * type, the returned collection permits insertion of null elements
2198 * whenever the backing collection does.
2199 *
2200 * @param c the collection for which a dynamically typesafe view is to be
2201 * returned
2202 * @param type the type of element that {@code c} is permitted to hold
2203 * @return a dynamically typesafe view of the specified collection
2204 * @since 1.5
2205 */
2206 public static <E> Collection<E> checkedCollection(Collection<E> c,
2207 Class<E> type) {
2208 return new CheckedCollection<E>(c, type);
2209 }
2210
2211 @SuppressWarnings("unchecked")
2212 static <T> T[] zeroLengthArray(Class<T> type) {
2213 return (T[]) Array.newInstance(type, 0);
2214 }
2215
2216 /**
2217 * @serial include
2218 */
2219 static class CheckedCollection<E> implements Collection<E>, Serializable {
2220 private static final long serialVersionUID = 1578914078182001775L;
2221
2222 final Collection<E> c;
2223 final Class<E> type;
2224
2225 void typeCheck(Object o) {
2226 if (o != null && !type.isInstance(o))
2227 throw new ClassCastException(badElementMsg(o));
2228 }
2229
2230 private String badElementMsg(Object o) {
2231 return "Attempt to insert " + o.getClass() +
2232 " element into collection with element type " + type;
2233 }
2234
2235 CheckedCollection(Collection<E> c, Class<E> type) {
2236 if (c==null || type == null)
2237 throw new NullPointerException();
2238 this.c = c;
2239 this.type = type;
2240 }
2241
2242 public int size() { return c.size(); }
2243 public boolean isEmpty() { retu
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