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() { return c.isEmpty(); }
2244 public boolean contains(Object o) { return c.contains(o); }
2245 public Object[] toArray() { return c.toArray(); }
2246 public <T> T[] toArray(T[] a) { return c.toArray(a); }
2247 public String toString() { return c.toString(); }
2248 public boolean remove(Object o) { return c.remove(o); }
2249 public void clear() { c.clear(); }
2250
2251 public boolean containsAll(Collection<?> coll) {
2252 return c.containsAll(coll);
2253 }
2254 public boolean removeAll(Collection<?> coll) {
2255 return c.removeAll(coll);
2256 }
2257 public boolean retainAll(Collection<?> coll) {
2258 return c.retainAll(coll);
2259 }
2260
2261 public Iterator<E> iterator() {
2262 final Iterator<E> it = c.iterator();
2263 return new Iterator<E>() {
2264 public boolean hasNext() { return it.hasNext(); }
2265 public E next() { return it.next(); }
2266 public void remove() { it.remove(); }};
2267 }
2268
2269 public boolean add(E e) {
2270 typeCheck(e);
2271 return c.add(e);
2272 }
2273
2274 private E[] zeroLengthElementArray = null; // Lazily initialized
2275
2276 private E[] zeroLengthElementArray() {
2277 return zeroLengthElementArray != null ? zeroLengthElementArray :
2278 (zeroLengthElementArray = zeroLengthArray(type));
2279 }
2280
2281 @SuppressWarnings("unchecked")
2282 Collection<E> checkedCopyOf(Collection<? extends E> coll) {
2283 Object[] a = null;
2284 try {
2285 E[] z = zeroLengthElementArray();
2286 a = coll.toArray(z);
2287 // Defend against coll violating the toArray contract
2288 if (a.getClass() != z.getClass())
2289 a = Arrays.copyOf(a, a.length, z.getClass());
2290 } catch (ArrayStoreException ignore) {
2291 // To get better and consistent diagnostics,
2292 // we call typeCheck explicitly on each element.
2293 // We call clone() to defend against coll retaining a
2294 // reference to the returned array and storing a bad
2295 // element into it after it has been type checked.
2296 a = coll.toArray().clone();
2297 for (Object o : a)
2298 typeCheck(o);
2299 }
2300 // A slight abuse of the type system, but safe here.
2301 return (Collection<E>) Arrays.asList(a);
2302 }
2303
2304 public boolean addAll(Collection<? extends E> coll) {
2305 // Doing things this way insulates us from concurrent changes
2306 // in the contents of coll and provides all-or-nothing
2307 // semantics (which we wouldn't get if we type-checked each
2308 // element as we added it)
2309 return c.addAll(checkedCopyOf(coll));
2310 }
2311 }
2312
2313 /**
2314 * Returns a dynamically typesafe view of the specified set.
2315 * Any attempt to insert an element of the wrong type will result in
2316 * an immediate {@link ClassCastException}. Assuming a set contains
2317 * no incorrectly typed elements prior to the time a dynamically typesafe
2318 * view is generated, and that all subsequent access to the set
2319 * takes place through the view, it is <i>guaranteed</i> that the
2320 * set cannot contain an incorrectly typed element.
2321 *
2322 * <p>A discussion of the use of dynamically typesafe views may be
2323 * found in the documentation for the {@link #checkedCollection
2324 * checkedCollection} method.
2325 *
2326 * <p>The returned set will be serializable if the specified set is
2327 * serializable.
2328 *
2329 * <p>Since {@code null} is considered to be a value of any reference
2330 * type, the returned set permits insertion of null elements whenever
2331 * the backing set does.
2332 *
2333 * @param s the set for which a dynamically typesafe view is to be
2334 * returned
2335 * @param type the type of element that {@code s} is permitted to hold
2336 * @return a dynamically typesafe view of the specified set
2337 * @since 1.5
2338 */
2339 public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) {
2340 return new CheckedSet<E>(s, type);
2341 }
2342
2343 /**
2344 * @serial include
2345 */
2346 static class CheckedSet<E> extends CheckedCollection<E>
2347 implements Set<E>, Serializable
2348 {
2349 private static final long serialVersionUID = 4694047833775013803L;
2350
2351 CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); }
2352
2353 public boolean equals(Object o) { return o == this || c.equals(o); }
2354 public int hashCode() { return c.hashCode(); }
2355 }
2356
2357 /**
2358 * Returns a dynamically typesafe view of the specified sorted set.
2359 * Any attempt to insert an element of the wrong type will result in an
2360 * immediate {@link ClassCastException}. Assuming a sorted set
2361 * contains no incorrectly typed elements prior to the time a
2362 * dynamically typesafe view is generated, and that all subsequent
2363 * access to the sorted set takes place through the view, it is
2364 * <i>guaranteed</i> that the sorted set cannot contain an incorrectly
2365 * typed element.
2366 *
2367 * <p>A discussion of the use of dynamically typesafe views may be
2368 * found in the documentation for the {@link #checkedCollection
2369 * checkedCollection} method.
2370 *
2371 * <p>The returned sorted set will be serializable if the specified sorted
2372 * set is serializable.
2373 *
2374 * <p>Since {@code null} is considered to be a value of any reference
2375 * type, the returned sorted set permits insertion of null elements
2376 * whenever the backing sorted set does.
2377 *
2378 * @param s the sorted set for which a dynamically typesafe view is to be
2379 * returned
2380 * @param type the type of element that {@code s} is permitted to hold
2381 * @return a dynamically typesafe view of the specified sorted set
2382 * @since 1.5
2383 */
2384 public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s,
2385 Class<E> type) {
2386 return new CheckedSortedSet<E>(s, type);
2387 }
2388
2389 /**
2390 * @serial include
2391 */
2392 static class CheckedSortedSet<E> extends CheckedSet<E>
2393 implements SortedSet<E>, Serializable
2394 {
2395 private static final long serialVersionUID = 1599911165492914959L;
2396 private final SortedSet<E> ss;
2397
2398 CheckedSortedSet(SortedSet<E> s, Class<E> type) {
2399 super(s, type);
2400 ss = s;
2401 }
2402
2403 public Comparator<? super E> comparator() { return ss.comparator(); }
2404 public E first() { return ss.first(); }
2405 public E last() { return ss.last(); }
2406
2407 public SortedSet<E> subSet(E fromElement, E toElement) {
2408 return checkedSortedSet(ss.subSet(fromElement,toElement), type);
2409 }
2410 public SortedSet<E> headSet(E toElement) {
2411 return checkedSortedSet(ss.headSet(toElement), type);
2412 }
2413 public SortedSet<E> tailSet(E fromElement) {
2414 return checkedSortedSet(ss.tailSet(fromElement), type);
2415 }
2416 }
2417
2418 /**
2419 * Returns a dynamically typesafe view of the specified list.
2420 * Any attempt to insert an element of the wrong type will result in
2421 * an immediate {@link ClassCastException}. Assuming a list contains
2422 * no incorrectly typed elements prior to the time a dynamically typesafe
2423 * view is generated, and that all subsequent access to the list
2424 * takes place through the view, it is <i>guaranteed</i> that the
2425 * list cannot contain an incorrectly typed element.
2426 *
2427 * <p>A discussion of the use of dynamically typesafe views may be
2428 * found in the documentation for the {@link #checkedCollection
2429 * checkedCollection} method.
2430 *
2431 * <p>The returned list will be serializable if the specified list
2432 * is serializable.
2433 *
2434 * <p>Since {@code null} is considered to be a value of any reference
2435 * type, the returned list permits insertion of null elements whenever
2436 * the backing list does.
2437 *
2438 * @param list the list for which a dynamically typesafe view is to be
2439 * returned
2440 * @param type the type of element that {@code list} is permitted to hold
2441 * @return a dynamically typesafe view of the specified list
2442 * @since 1.5
2443 */
2444 public static <E> List<E> checkedList(List<E> list, Class<E> type) {
2445 return (list instanceof RandomAccess ?
2446 new CheckedRandomAccessList<E>(list, type) :
2447 new CheckedList<E>(list, type));
2448 }
2449
2450 /**
2451 * @serial include
2452 */
2453 static class CheckedList<E>
2454 extends CheckedCollection<E>
2455 implements List<E>
2456 {
2457 private static final long serialVersionUID = 65247728283967356L;
2458 final List<E> list;
2459
2460 CheckedList(List<E> list, Class<E> type) {
2461 super(list, type);
2462 this.list = list;
2463 }
2464
2465 public boolean equals(Object o) { return o == this || list.equals(o); }
2466 public int hashCode() { return list.hashCode(); }
2467 public E get(int index) { return list.get(index); }
2468 public E remove(int index) { return list.remove(index); }
2469 public int indexOf(Object o) { return list.indexOf(o); }
2470 public int lastIndexOf(Object o) { return list.lastIndexOf(o); }
2471
2472 public E set(int index, E element) {
2473 typeCheck(element);
2474 return list.set(index, element);
2475 }
2476
2477 public void add(int index, E element) {
2478 typeCheck(element);
2479 list.add(index, element);
2480 }
2481
2482 public boolean addAll(int index, Collection<? extends E> c) {
2483 return list.addAll(index, checkedCopyOf(c));
2484 }
2485 public ListIterator<E> listIterator() { return listIterator(0); }
2486
2487 public ListIterator<E> listIterator(final int index) {
2488 final ListIterator<E> i = list.listIterator(index);
2489
2490 return new ListIterator<E>() {
2491 public boolean hasNext() { return i.hasNext(); }
2492 public E next() { return i.next(); }
2493 public boolean hasPrevious() { return i.hasPrevious(); }
2494 public E previous() { return i.previous(); }
2495 public int nextIndex() { return i.nextIndex(); }
2496 public int previousIndex() { return i.previousIndex(); }
2497 public void remove() { i.remove(); }
2498
2499 public void set(E e) {
2500 typeCheck(e);
2501 i.set(e);
2502 }
2503
2504 public void add(E e) {
2505 typeCheck(e);
2506 i.add(e);
2507 }
2508 };
2509 }
2510
2511 public List<E> subList(int fromIndex, int toIndex) {
2512 return new CheckedList<E>(list.subList(fromIndex, toIndex), type);
2513 }
2514 }
2515
2516 /**
2517 * @serial include
2518 */
2519 static class CheckedRandomAccessList<E> extends CheckedList<E>
2520 implements RandomAccess
2521 {
2522 private static final long serialVersionUID = 1638200125423088369L;
2523
2524 CheckedRandomAccessList(List<E> list, Class<E> type) {
2525 super(list, type);
2526 }
2527
2528 public List<E> subList(int fromIndex, int toIndex) {
2529 return new CheckedRandomAccessList<E>(
2530 list.subList(fromIndex, toIndex), type);
2531 }
2532 }
2533
2534 /**
2535 * Returns a dynamically typesafe view of the specified map.
2536 * Any attempt to insert a mapping whose key or value have the wrong
2537 * type will result in an immediate {@link ClassCastException}.
2538 * Similarly, any attempt to modify the value currently associated with
2539 * a key will result in an immediate {@link ClassCastException},
2540 * whether the modification is attempted directly through the map
2541 * itself, or through a {@link Map.Entry} instance obtained from the
2542 * map's {@link Map#entrySet() entry set} view.
2543 *
2544 * <p>Assuming a map contains no incorrectly typed keys or values
2545 * prior to the time a dynamically typesafe view is generated, and
2546 * that all subsequent access to the map takes place through the view
2547 * (or one of its collection views), it is <i>guaranteed</i> that the
2548 * map cannot contain an incorrectly typed key or value.
2549 *
2550 * <p>A discussion of the use of dynamically typesafe views may be
2551 * found in the documentation for the {@link #checkedCollection
2552 * checkedCollection} method.
2553 *
2554 * <p>The returned map will be serializable if the specified map is
2555 * serializable.
2556 *
2557 * <p>Since {@code null} is considered to be a value of any reference
2558 * type, the returned map permits insertion of null keys or values
2559 * whenever the backing map does.
2560 *
2561 * @param m the map for which a dynamically typesafe view is to be
2562 * returned
2563 * @param keyType the type of key that {@code m} is permitted to hold
2564 * @param valueType the type of value that {@code m} is permitted to hold
2565 * @return a dynamically typesafe view of the specified map
2566 * @since 1.5
2567 */
2568 public static <K, V> Map<K, V> checkedMap(Map<K, V> m,
2569 Class<K> keyType,
2570 Class<V> valueType) {
2571 return new CheckedMap<K,V>(m, keyType, valueType);
2572 }
2573
2574
2575 /**
2576 * @serial include
2577 */
2578 private static class CheckedMap<K,V>
2579 implements Map<K,V>, Serializable
2580 {
2581 private static final long serialVersionUID = 5742860141034234728L;
2582
2583 private final Map<K, V> m;
2584 final Class<K> keyType;
2585 final Class<V> valueType;
2586
2587 private void typeCheck(Object key, Object value) {
2588 if (key != null && !keyType.isInstance(key))
2589 throw new ClassCastException(badKeyMsg(key));
2590
2591 if (value != null && !valueType.isInstance(value))
2592 throw new ClassCastException(badValueMsg(value));
2593 }
2594
2595 private String badKeyMsg(Object key) {
2596 return "Attempt to insert " + key.getClass() +
2597 " key into map with key type " + keyType;
2598 }
2599
2600 private String badValueMsg(Object value) {
2601 return "Attempt to insert " + value.getClass() +
2602 " value into map with value type " + valueType;
2603 }
2604
2605 CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) {
2606 if (m == null || keyType == null || valueType == null)
2607 throw new NullPointerException();
2608 this.m = m;
2609 this.keyType = keyType;
2610 this.valueType = valueType;
2611 }
2612
2613 public int size() { return m.size(); }
2614 public boolean isEmpty() { return m.isEmpty(); }
2615 public boolean containsKey(Object key) { return m.containsKey(key); }
2616 public boolean containsValue(Object v) { return m.containsValue(v); }
2617 public V get(Object key) { return m.get(key); }
2618 public V remove(Object key) { return m.remove(key); }
2619 public void clear() { m.clear(); }
2620 public Set<K> keySet() { return m.keySet(); }
2621 public Collection<V> values() { return m.values(); }
2622 public boolean equals(Object o) { return o == this || m.equals(o); }
2623 public int hashCode() { return m.hashCode(); }
2624 public String toString() { return m.toString(); }
2625
2626 public V put(K key, V value) {
2627 typeCheck(key, value);
2628 return m.put(key, value);
2629 }
2630
2631 @SuppressWarnings("unchecked")
2632 public void putAll(Map<? extends K, ? extends V> t) {
2633 // Satisfy the following goals:
2634 // - good diagnostics in case of type mismatch
2635 // - all-or-nothing semantics
2636 // - protection from malicious t
2637 // - correct behavior if t is a concurrent map
2638 Object[] entries = t.entrySet().toArray();
2639 List<Map.Entry<K,V>> checked =
2640 new ArrayList<Map.Entry<K,V>>(entries.length);
2641 for (Object o : entries) {
2642 Map.Entry<?,?> e = (Map.Entry<?,?>) o;
2643 Object k = e.getKey();
2644 Object v = e.getValue();
2645 typeCheck(k, v);
2646 checked.add(
2647 new AbstractMap.SimpleImmutableEntry<K,V>((K) k, (V) v));
2648 }
2649 for (Map.Entry<K,V> e : checked)
2650 m.put(e.getKey(), e.getValue());
2651 }
2652
2653 private transient Set<Map.Entry<K,V>> entrySet = null;
2654
2655 public Set<Map.Entry<K,V>> entrySet() {
2656 if (entrySet==null)
2657 entrySet = new CheckedEntrySet<K,V>(m.entrySet(), valueType);
2658 return entrySet;
2659 }
2660
2661 /**
2662 * We need this class in addition to CheckedSet as Map.Entry permits
2663 * modification of the backing Map via the setValue operation. This
2664 * class is subtle: there are many possible attacks that must be
2665 * thwarted.
2666 *
2667 * @serial exclude
2668 */
2669 static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> {
2670 private final Set<Map.Entry<K,V>> s;
2671 private final Class<V> valueType;
2672
2673 CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) {
2674 this.s = s;
2675 this.valueType = valueType;
2676 }
2677
2678 public int size() { return s.size(); }
2679 public boolean isEmpty() { return s.isEmpty(); }
2680 public String toString() { return s.toString(); }
2681 public int hashCode() { return s.hashCode(); }
2682 public void clear() { s.clear(); }
2683
2684 public boolean add(Map.Entry<K, V> e) {
2685 throw new UnsupportedOperationException();
2686 }
2687 public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) {
2688 throw new UnsupportedOperationException();
2689 }
2690
2691 public Iterator<Map.Entry<K,V>> iterator() {
2692 final Iterator<Map.Entry<K, V>> i = s.iterator();
2693 final Class<V> valueType = this.valueType;
2694
2695 return new Iterator<Map.Entry<K,V>>() {
2696 public boolean hasNext() { return i.hasNext(); }
2697 public void remove() { i.remove(); }
2698
2699 public Map.Entry<K,V> next() {
2700 return checkedEntry(i.next(), valueType);
2701 }
2702 };
2703 }
2704
2705 @SuppressWarnings("unchecked")
2706 public Object[] toArray() {
2707 Object[] source = s.toArray();
2708
2709 /*
2710 * Ensure that we don't get an ArrayStoreException even if
2711 * s.toArray returns an array of something other than Object
2712 */
2713 Object[] dest = (CheckedEntry.class.isInstance(
2714 source.getClass().getComponentType()) ? source :
2715 new Object[source.length]);
2716
2717 for (int i = 0; i < source.length; i++)
2718 dest[i] = checkedEntry((Map.Entry<K,V>)source[i],
2719 valueType);
2720 return dest;
2721 }
2722
2723 @SuppressWarnings("unchecked")
2724 public <T> T[] toArray(T[] a) {
2725 // We don't pass a to s.toArray, to avoid window of
2726 // vulnerability wherein an unscrupulous multithreaded client
2727 // could get his hands on raw (unwrapped) Entries from s.
2728 T[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
2729
2730 for (int i=0; i<arr.length; i++)
2731 arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i],
2732 valueType);
2733 if (arr.length > a.length)
2734 return arr;
2735
2736 System.arraycopy(arr, 0, a, 0, arr.length);
2737 if (a.length > arr.length)
2738 a[arr.length] = null;
2739 return a;
2740 }
2741
2742 /**
2743 * This method is overridden to protect the backing set against
2744 * an object with a nefarious equals function that senses
2745 * that the equality-candidate is Map.Entry and calls its
2746 * setValue method.
2747 */
2748 public boolean contains(Object o) {
2749 if (!(o instanceof Map.Entry))
2750 return false;
2751 Map.Entry<?,?> e = (Map.Entry<?,?>) o;
2752 return s.contains(
2753 (e instanceof CheckedEntry) ? e : checkedEntry(e, valueType));
2754 }
2755
2756 /**
2757 * The bulk collection methods are overridden to protect
2758 * against an unscrupulous collection whose contains(Object o)
2759 * method senses when o is a Map.Entry, and calls o.setValue.
2760 */
2761 public boolean containsAll(Collection<?> c) {
2762 for (Object o : c)
2763 if (!contains(o)) // Invokes safe contains() above
2764 return false;
2765 return true;
2766 }
2767
2768 public boolean remove(Object o) {
2769 if (!(o instanceof Map.Entry))
2770 return false;
2771 return s.remove(new AbstractMap.SimpleImmutableEntry
2772 <Object, Object>((Map.Entry<?,?>)o));
2773 }
2774
2775 public boolean removeAll(Collection<?> c) {
2776 return batchRemove(c, false);
2777 }
2778 public boolean retainAll(Collection<?> c) {
2779 return batchRemove(c, true);
2780 }
2781 private boolean batchRemove(Collection<?> c, boolean complement) {
2782 boolean modified = false;
2783 Iterator<Map.Entry<K,V>> it = iterator();
2784 while (it.hasNext()) {
2785 if (c.contains(it.next()) != complement) {
2786 it.remove();
2787 modified = true;
2788 }
2789 }
2790 return modified;
2791 }
2792
2793 public boolean equals(Object o) {
2794 if (o == this)
2795 return true;
2796 if (!(o instanceof Set))
2797 return false;
2798 Set<?> that = (Set<?>) o;
2799 return that.size() == s.size()
2800 && containsAll(that); // Invokes safe containsAll() above
2801 }
2802
2803 static <K,V,T> CheckedEntry<K,V,T> checkedEntry(Map.Entry<K,V> e,
2804 Class<T> valueType) {
2805 return new CheckedEntry<K,V,T>(e, valueType);
2806 }
2807
2808 /**
2809 * This "wrapper class" serves two purposes: it prevents
2810 * the client from modifying the backing Map, by short-circuiting
2811 * the setValue method, and it protects the backing Map against
2812 * an ill-behaved Map.Entry that attempts to modify another
2813 * Map.Entry when asked to perform an equality check.
2814 */
2815 private static class CheckedEntry<K,V,T> implements Map.Entry<K,V> {
2816 private final Map.Entry<K, V> e;
2817 private final Class<T> valueType;
2818
2819 CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) {
2820 this.e = e;
2821 this.valueType = valueType;
2822 }
2823
2824 public K getKey() { return e.getKey(); }
2825 public V getValue() { return e.getValue(); }
2826 public int hashCode() { return e.hashCode(); }
2827 public String toString() { return e.toString(); }
2828
2829 public V setValue(V value) {
2830 if (value != null && !valueType.isInstance(value))
2831 throw new ClassCastException(badValueMsg(value));
2832 return e.setValue(value);
2833 }
2834
2835 private String badValueMsg(Object value) {
2836 return "Attempt to insert " + value.getClass() +
2837 " value into map with value type " + valueType;
2838 }
2839
2840 public boolean equals(Object o) {
2841 if (o == this)
2842 return true;
2843 if (!(o instanceof Map.Entry))
2844 return false;
2845 return e.equals(new AbstractMap.SimpleImmutableEntry
2846 <Object, Object>((Map.Entry<?,?>)o));
2847 }
2848 }
2849 }
2850 }
2851
2852 /**
2853 * Returns a dynamically typesafe view of the specified sorted map.
2854 * Any attempt to insert a mapping whose key or value have the wrong
2855 * type will result in an immediate {@link ClassCastException}.
2856 * Similarly, any attempt to modify the value currently associated with
2857 * a key will result in an immediate {@link ClassCastException},
2858 * whether the modification is attempted directly through the map
2859 * itself, or through a {@link Map.Entry} instance obtained from the
2860 * map's {@link Map#entrySet() entry set} view.
2861 *
2862 * <p>Assuming a map contains no incorrectly typed keys or values
2863 * prior to the time a dynamically typesafe view is generated, and
2864 * that all subsequent access to the map takes place through the view
2865 * (or one of its collection views), it is <i>guaranteed</i> that the
2866 * map cannot contain an incorrectly typed key or value.
2867 *
2868 * <p>A discussion of the use of dynamically typesafe views may be
2869 * found in the documentation for the {@link #checkedCollection
2870 * checkedCollection} method.
2871 *
2872 * <p>The returned map will be serializable if the specified map is
2873 * serializable.
2874 *
2875 * <p>Since {@code null} is considered to be a value of any reference
2876 * type, the returned map permits insertion of null keys or values
2877 * whenever the backing map does.
2878 *
2879 * @param m the map for which a dynamically typesafe view is to be
2880 * returned
2881 * @param keyType the type of key that {@code m} is permitted to hold
2882 * @param valueType the type of value that {@code m} is permitted to hold
2883 * @return a dynamically typesafe view of the specified map
2884 * @since 1.5
2885 */
2886 public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m,
2887 Class<K> keyType,
2888 Class<V> valueType) {
2889 return new CheckedSortedMap<K,V>(m, keyType, valueType);
2890 }
2891
2892 /**
2893 * @serial include
2894 */
2895 static class CheckedSortedMap<K,V> extends CheckedMap<K,V>
2896 implements SortedMap<K,V>, Serializable
2897 {
2898 private static final long serialVersionUID = 1599671320688067438L;
2899
2900 private final SortedMap<K, V> sm;
2901
2902 CheckedSortedMap(SortedMap<K, V> m,
2903 Class<K> keyType, Class<V> valueType) {
2904 super(m, keyType, valueType);
2905 sm = m;
2906 }
2907
2908 public Comparator<? super K> comparator() { return sm.comparator(); }
2909 public K firstKey() { return sm.firstKey(); }
2910 public K lastKey() { return sm.lastKey(); }
2911
2912 public SortedMap<K,V> subMap(K fromKey, K toKey) {
2913 return checkedSortedMap(sm.subMap(fromKey, toKey),
2914 keyType, valueType);
2915 }
2916 public SortedMap<K,V> headMap(K toKey) {
2917 return checkedSortedMap(sm.headMap(toKey), keyType, valueType);
2918 }
2919 public SortedMap<K,V> tailMap(K fromKey) {
2920 return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType);
2921 }
2922 }
2923
2924 // Empty collections
2925
2926 /**
2927 * Returns an iterator that has no elements. More precisely,
2928 *
2929 * <ul compact>
2930 *
2931 * <li>{@link Iterator#hasNext hasNext} always returns {@code
2932 * false}.
2933 *
2934 * <li>{@link Iterator#next next} always throws {@link
2935 * NoSuchElementException}.
2936 *
2937 * <li>{@link Iterator#remove remove} always throws {@link
2938 * IllegalStateException}.
2939 *
2940 * </ul>
2941 *
2942 * <p>Implementations of this method are permitted, but not
2943 * required, to return the same object from multiple invocations.
2944 *
2945 * @return an empty iterator
2946 * @since 1.7
2947 */
2948 @SuppressWarnings("unchecked")
2949 public static <T> Iterator<T> emptyIterator() {
2950 return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR;
2951 }
2952
2953 private static class EmptyIterator<E> implements Iterator<E> {
2954 static final EmptyIterator<Object> EMPTY_ITERATOR
2955 = new EmptyIterator<Object>();
2956
2957 public boolean hasNext() { return false; }
2958 public E next() { throw new NoSuchElementException(); }
2959 public void remove() { throw new IllegalStateException(); }
2960 }
2961
2962 /**
2963 * Returns a list iterator that has no elements. More precisely,
2964 *
2965 * <ul compact>
2966 *
2967 * <li>{@link Iterator#hasNext hasNext} and {@link
2968 * ListIterator#hasPrevious hasPrevious} always return {@code
2969 * false}.
2970 *
2971 * <li>{@link Iterator#next next} and {@link ListIterator#previous
2972 * previous} always throw {@link NoSuchElementException}.
2973 *
2974 * <li>{@link Iterator#remove remove} and {@link ListIterator#set
2975 * set} always throw {@link IllegalStateException}.
2976 *
2977 * <li>{@link ListIterator#add add} always throws {@link
2978 * UnsupportedOperationException}.
2979 *
2980 * <li>{@link ListIterator#nextIndex nextIndex} always returns
2981 * {@code 0} .
2982 *
2983 * <li>{@link ListIterator#previousIndex previousIndex} always
2984 * returns {@code -1}.
2985 *
2986 * </ul>
2987 *
2988 * <p>Implementations of this method are permitted, but not
2989 * required, to return the same object from multiple invocations.
2990 *
2991 * @return an empty list iterator
2992 * @since 1.7
2993 */
2994 @SuppressWarnings("unchecked")
2995 public static <T> ListIterator<T> emptyListIterator() {
2996 return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR;
2997 }
2998
2999 private static class EmptyListIterator<E>
3000 extends EmptyIterator<E>
3001 implements ListIterator<E>
3002 {
3003 static final EmptyListIterator<Object> EMPTY_ITERATOR
3004 = new EmptyListIterator<Object>();
3005
3006 public boolean hasPrevious() { return false; }
3007 public E previous() { throw new NoSuchElementException(); }
3008 public int nextIndex() { return 0; }
3009 public int previousIndex() { return -1; }
3010 public void set(E e) { throw new IllegalStateException(); }
3011 public void add(E e) { throw new UnsupportedOperationException(); }
3012 }
3013
3014 /**
3015 * Returns an enumeration that has no elements. More precisely,
3016 *
3017 * <ul compact>
3018 *
3019 * <li>{@link Enumeration#hasMoreElements hasMoreElements} always
3020 * returns {@code false}.
3021 *
3022 * <li> {@link Enumeration#nextElement nextElement} always throws
3023 * {@link NoSuchElementException}.
3024 *
3025 * </ul>
3026 *
3027 * <p>Implementations of this method are permitted, but not
3028 * required, to return the same object from multiple invocations.
3029 *
3030 * @return an empty enumeration
3031 * @since 1.7
3032 */
3033 @SuppressWarnings("unchecked")
3034 public static <T> Enumeration<T> emptyEnumeration() {
3035 return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION;
3036 }
3037
3038 private static class EmptyEnumeration<E> implements Enumeration<E> {
3039 static final EmptyEnumeration<Object> EMPTY_ENUMERATION
3040 = new EmptyEnumeration<Object>();
3041
3042 public boolean hasMoreElements() { return false; }
3043 public E nextElement() { throw new NoSuchElementException(); }
3044 }
3045
3046 /**
3047 * The empty set (immutable). This set is serializable.
3048 *
3049 * @see #emptySet()
3050 */
3051 @SuppressWarnings("unchecked")
3052 public static final Set EMPTY_SET = new EmptySet<Object>();
3053
3054 /**
3055 * Returns the empty set (immutable). This set is serializable.
3056 * Unlike the like-named field, this method is parameterized.
3057 *
3058 * <p>This example illustrates the type-safe way to obtain an empty set:
3059 * <pre>
3060 * Set<String> s = Collections.emptySet();
3061 * </pre>
3062 * Implementation note: Implementations of this method need not
3063 * create a separate <tt>Set</tt> object for each call. Using this
3064 * method is likely to have comparable cost to using the like-named
3065 * field. (Unlike this method, the field does not provide type safety.)
3066 *
3067 * @see #EMPTY_SET
3068 * @since 1.5
3069 */
3070 @SuppressWarnings("unchecked")
3071 public static final <T> Set<T> emptySet() {
3072 return (Set<T>) EMPTY_SET;
3073 }
3074
3075 /**
3076 * @serial include
3077 */
3078 private static class EmptySet<E>
3079 extends AbstractSet<E>
3080 implements Serializable
3081 {
3082 private static final long serialVersionUID = 1582296315990362920L;
3083
3084 public Iterator<E> iterator() { return emptyIterator(); }
3085
3086 public int size() {return 0;}
3087 public boolean isEmpty() {return true;}
3088
3089 public boolean contains(Object obj) {return false;}
3090 public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
3091
3092 public Object[] toArray() { return new Object[0]; }
3093
3094 public <T> T[] toArray(T[] a) {
3095 if (a.length > 0)
3096 a[0] = null;
3097 return a;
3098 }
3099
3100 // Preserves singleton property
3101 private Object readResolve() {
3102 return EMPTY_SET;
3103 }
3104 }
3105
3106 /**
3107 * The empty list (immutable). This list is serializable.
3108 *
3109 * @see #emptyList()
3110 */
3111 @SuppressWarnings("unchecked")
3112 public static final List EMPTY_LIST = new EmptyList<Object>();
3113
3114 /**
3115 * Returns the empty list (immutable). This list is serializable.
3116 *
3117 * <p>This example illustrates the type-safe way to obtain an empty list:
3118 * <pre>
3119 * List<String> s = Collections.emptyList();
3120 * </pre>
3121 * Implementation note: Implementations of this method need not
3122 * create a separate <tt>List</tt> object for each call. Using this
3123 * method is likely to have comparable cost to using the like-named
3124 * field. (Unlike this method, the field does not provide type safety.)
3125 *
3126 * @see #EMPTY_LIST
3127 * @since 1.5
3128 */
3129 @SuppressWarnings("unchecked")
3130 public static final <T> List<T> emptyList() {
3131 return (List<T>) EMPTY_LIST;
3132 }
3133
3134 /**
3135 * @serial include
3136 */
3137 private static class EmptyList<E>
3138 extends AbstractList<E>
3139 implements RandomAccess, Serializable {
3140 private static final long serialVersionUID = 8842843931221139166L;
3141
3142 public Iterator<E> iterator() {
3143 return emptyIterator();
3144 }
3145 public ListIterator<E> listIterator() {
3146 return emptyListIterator();
3147 }
3148
3149 public int size() {return 0;}
3150 public boolean isEmpty() {return true;}
3151
3152 public boolean contains(Object obj) {return false;}
3153 public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
3154
3155 public Object[] toArray() { return new Object[0]; }
3156
3157 public <T> T[] toArray(T[] a) {
3158 if (a.length > 0)
3159 a[0] = null;
3160 return a;
3161 }
3162
3163 public E get(int index) {
3164 throw new IndexOutOfBoundsException("Index: "+index);
3165 }
3166
3167 public boolean equals(Object o) {
3168 return (o instanceof List) && ((List<?>)o).isEmpty();
3169 }
3170
3171 public int hashCode() { return 1; }
3172
3173 // Preserves singleton property
3174 private Object readResolve() {
3175 return EMPTY_LIST;
3176 }
3177 }
3178
3179 /**
3180 * The empty map (immutable). This map is serializable.
3181 *
3182 * @see #emptyMap()
3183 * @since 1.3
3184 */
3185 @SuppressWarnings("unchecked")
3186 public static final Map EMPTY_MAP = new EmptyMap<Object,Object>();
3187
3188 /**
3189 * Returns the empty map (immutable). This map is serializable.
3190 *
3191 * <p>This example illustrates the type-safe way to obtain an empty set:
3192 * <pre>
3193 * Map<String, Date> s = Collections.emptyMap();
3194 * </pre>
3195 * Implementation note: Implementations of this method need not
3196 * create a separate <tt>Map</tt> object for each call. Using this
3197 * method is likely to have comparable cost to using the like-named
3198 * field. (Unlike this method, the field does not provide type safety.)
3199 *
3200 * @see #EMPTY_MAP
3201 * @since 1.5
3202 */
3203 @SuppressWarnings("unchecked")
3204 public static final <K,V> Map<K,V> emptyMap() {
3205 return (Map<K,V>) EMPTY_MAP;
3206 }
3207
3208 /**
3209 * @serial include
3210 */
3211 private static class EmptyMap<K,V>
3212 extends AbstractMap<K,V>
3213 implements Serializable
3214 {
3215 private static final long serialVersionUID = 6428348081105594320L;
3216
3217 public int size() {return 0;}
3218 public boolean isEmpty() {return true;}
3219 public boolean containsKey(Object key) {return false;}
3220 public boolean containsValue(Object value) {return false;}
3221 public V get(Object key) {return null;}
3222 public Set<K> keySet() {return emptySet();}
3223 public Collection<V> values() {return emptySet();}
3224 public Set<Map.Entry<K,V>> entrySet() {return emptySet();}
3225
3226 public boolean equals(Object o) {
3227 return (o instanceof Map) && ((Map<?,?>)o).isEmpty();
3228 }
3229
3230 public int hashCode() {return 0;}
3231
3232 // Preserves singleton property
3233 private Object readResolve() {
3234 return EMPTY_MAP;
3235 }
3236 }
3237
3238 // Singleton collections
3239
3240 /**
3241 * Returns an immutable set containing only the specified object.
3242 * The returned set is serializable.
3243 *
3244 * @param o the sole object to be stored in the returned set.
3245 * @return an immutable set containing only the specified object.
3246 */
3247 public static <T> Set<T> singleton(T o) {
3248 return new SingletonSet<T>(o);
3249 }
3250
3251 static <E> Iterator<E> singletonIterator(final E e) {
3252 return new Iterator<E>() {
3253 private boolean hasNext = true;
3254 public boolean hasNext() {
3255 return hasNext;
3256 }
3257 public E next() {
3258 if (hasNext) {
3259 hasNext = false;
3260 return e;
3261 }
3262 throw new NoSuchElementException();
3263 }
3264 public void remove() {
3265 throw new UnsupportedOperationException();
3266 }
3267 };
3268 }
3269
3270 /**
3271 * @serial include
3272 */
3273 private static class SingletonSet<E>
3274 extends AbstractSet<E>
3275 implements Serializable
3276 {
3277 private static final long serialVersionUID = 3193687207550431679L;
3278
3279 final private E element;
3280
3281 SingletonSet(E e) {element = e;}
3282
3283 public Iterator<E> iterator() {
3284 return singletonIterator(element);
3285 }
3286
3287 public int size() {return 1;}
3288
3289 public boolean contains(Object o) {return eq(o, element);}
3290 }
3291
3292 /**
3293 * Returns an immutable list containing only the specified object.
3294 * The returned list is serializable.
3295 *
3296 * @param o the sole object to be stored in the returned list.
3297 * @return an immutable list containing only the specified object.
3298 * @since 1.3
3299 */
3300 public static <T> List<T> singletonList(T o) {
3301 return new SingletonList<T>(o);
3302 }
3303
3304 /**
3305 * @serial include
3306 */
3307 private static class SingletonList<E>
3308 extends AbstractList<E>
3309 implements RandomAccess, Serializable {
3310
3311 private static final long serialVersionUID = 3093736618740652951L;
3312
3313 private final E element;
3314
3315 SingletonList(E obj) {element = obj;}
3316
3317 public Iterator<E> iterator() {
3318 return singletonIterator(element);
3319 }
3320
3321 public int size() {return 1;}
3322
3323 public boolean contains(Object obj) {return eq(obj, element);}
3324
3325 public E get(int index) {
3326 if (index != 0)
3327 throw new IndexOutOfBoundsException("Index: "+index+", Size: 1");
3328 return element;
3329 }
3330 }
3331
3332 /**
3333 * Returns an immutable map, mapping only the specified key to the
3334 * specified value. The returned map is serializable.
3335 *
3336 * @param key the sole key to be stored in the returned map.
3337 * @param value the value to which the returned map maps <tt>key</tt>.
3338 * @return an immutable map containing only the specified key-value
3339 * mapping.
3340 * @since 1.3
3341 */
3342 public static <K,V> Map<K,V> singletonMap(K key, V value) {
3343 return new SingletonMap<K,V>(key, value);
3344 }
3345
3346 /**
3347 * @serial include
3348 */
3349 private static class SingletonMap<K,V>
3350 extends AbstractMap<K,V>
3351 implements Serializable {
3352 private static final long serialVersionUID = -6979724477215052911L;
3353
3354 private final K k;
3355 private final V v;
3356
3357 SingletonMap(K key, V value) {
3358 k = key;
3359 v = value;
3360 }
3361
3362 public int size() {return 1;}
3363
3364 public boolean isEmpty() {return false;}
3365
3366 public boolean containsKey(Object key) {return eq(key, k);}
3367
3368 public boolean containsValue(Object value) {return eq(value, v);}
3369
3370 public V get(Object key) {return (eq(key, k) ? v : null);}
3371
3372 private transient Set<K> keySet = null;
3373 private transient Set<Map.Entry<K,V>> entrySet = null;
3374 private transient Collection<V> values = null;
3375
3376 public Set<K> keySet() {
3377 if (keySet==null)
3378 keySet = singleton(k);
3379 return keySet;
3380 }
3381
3382 public Set<Map.Entry<K,V>> entrySet() {
3383 if (entrySet==null)
3384 entrySet = Collections.<Map.Entry<K,V>>singleton(
3385 new SimpleImmutableEntry<K,V>(k, v));
3386 return entrySet;
3387 }
3388
3389 public Collection<V> values() {
3390 if (values==null)
3391 values = singleton(v);
3392 return values;
3393 }
3394
3395 }
3396
3397 // Miscellaneous
3398
3399 /**
3400 * Returns an immutable list consisting of <tt>n</tt> copies of the
3401 * specified object. The newly allocated data object is tiny (it contains
3402 * a single reference to the data object). This method is useful in
3403 * combination with the <tt>List.addAll</tt> method to grow lists.
3404 * The returned list is serializable.
3405 *
3406 * @param n the number of elements in the returned list.
3407 * @param o the element to appear repeatedly in the returned list.
3408 * @return an immutable list consisting of <tt>n</tt> copies of the
3409 * specified object.
3410 * @throws IllegalArgumentException if n < 0.
3411 * @see List#addAll(Collection)
3412 * @see List#addAll(int, Collection)
3413 */
3414 public static <T> List<T> nCopies(int n, T o) {
3415 if (n < 0)
3416 throw new IllegalArgumentException("List length = " + n);
3417 return new CopiesList<T>(n, o);
3418 }
3419
3420 /**
3421 * @serial include
3422 */
3423 private static class CopiesList<E>
3424 extends AbstractList<E>
3425 implements RandomAccess, Serializable
3426 {
3427 private static final long serialVersionUID = 2739099268398711800L;
3428
3429 final int n;
3430 final E element;
3431
3432 CopiesList(int n, E e) {
3433 assert n >= 0;
3434 this.n = n;
3435 element = e;
3436 }
3437
3438 public int size() {
3439 return n;
3440 }
3441
3442 public boolean contains(Object obj) {
3443 return n != 0 && eq(obj, element);
3444 }
3445
3446 public int indexOf(Object o) {
3447 return contains(o) ? 0 : -1;
3448 }
3449
3450 public int lastIndexOf(Object o) {
3451 return contains(o) ? n - 1 : -1;
3452 }
3453
3454 public E get(int index) {
3455 if (index < 0 || index >= n)
3456 throw new IndexOutOfBoundsException("Index: "+index+
3457 ", Size: "+n);
3458 return element;
3459 }
3460
3461 public Object[] toArray() {
3462 final Object[] a = new Object[n];
3463 if (element != null)
3464 Arrays.fill(a, 0, n, element);
3465 return a;
3466 }
3467
3468 public <T> T[] toArray(T[] a) {
3469 final int n = this.n;
3470 if (a.length < n) {
3471 a = (T[])java.lang.reflect.Array
3472 .newInstance(a.getClass().getComponentType(), n);
3473 if (element != null)
3474 Arrays.fill(a, 0, n, element);
3475 } else {
3476 Arrays.fill(a, 0, n, element);
3477 if (a.length > n)
3478 a[n] = null;
3479 }
3480 return a;
3481 }
3482
3483 public List<E> subList(int fromIndex, int toIndex) {
3484 if (fromIndex < 0)
3485 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
3486 if (toIndex > n)
3487 throw new IndexOutOfBoundsException("toIndex = " + toIndex);
3488 if (fromIndex > toIndex)
3489 throw new IllegalArgumentException("fromIndex(" + fromIndex +
3490 ") > toIndex(" + toIndex + ")");
3491 return new CopiesList<E>(toIndex - fromIndex, element);
3492 }
3493 }
3494
3495 /**
3496 * Returns a comparator that imposes the reverse of the <i>natural
3497 * ordering</i> on a collection of objects that implement the
3498 * <tt>Comparable</tt> interface. (The natural ordering is the ordering
3499 * imposed by the objects' own <tt>compareTo</tt> method.) This enables a
3500 * simple idiom for sorting (or maintaining) collections (or arrays) of
3501 * objects that implement the <tt>Comparable</tt> interface in
3502 * reverse-natural-order. For example, suppose a is an array of
3503 * strings. Then: <pre>
3504 * Arrays.sort(a, Collections.reverseOrder());
3505 * </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p>
3506 *
3507 * The returned comparator is serializable.
3508 *
3509 * @return a comparator that imposes the reverse of the <i>natural
3510 * ordering</i> on a collection of objects that implement
3511 * the <tt>Comparable</tt> interface.
3512 * @see Comparable
3513 */
3514 public static <T> Comparator<T> reverseOrder() {
3515 return (Comparator<T>) ReverseComparator.REVERSE_ORDER;
3516 }
3517
3518 /**
3519 * @serial include
3520 */
3521 private static class ReverseComparator
3522 implements Comparator<Comparable<Object>>, Serializable {
3523
3524 private static final long serialVersionUID = 7207038068494060240L;
3525
3526 static final ReverseComparator REVERSE_ORDER
3527 = new ReverseComparator();
3528
3529 public int compare(Comparable<Object> c1, Comparable<Object> c2) {
3530 return c2.compareTo(c1);
3531 }
3532
3533 private Object readResolve() { return reverseOrder(); }
3534 }
3535
3536 /**
3537 * Returns a comparator that imposes the reverse ordering of the specified
3538 * comparator. If the specified comparator is null, this method is
3539 * equivalent to {@link #reverseOrder()} (in other words, it returns a
3540 * comparator that imposes the reverse of the <i>natural ordering</i> on a
3541 * collection of objects that implement the Comparable interface).
3542 *
3543 * <p>The returned comparator is serializable (assuming the specified
3544 * comparator is also serializable or null).
3545 *
3546 * @return a comparator that imposes the reverse ordering of the
3547 * specified comparator
3548 * @since 1.5
3549 */
3550 public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) {
3551 if (cmp == null)
3552 return reverseOrder();
3553
3554 if (cmp instanceof ReverseComparator2)
3555 return ((ReverseComparator2<T>)cmp).cmp;
3556
3557 return new ReverseComparator2<T>(cmp);
3558 }
3559
3560 /**
3561 * @serial include
3562 */
3563 private static class ReverseComparator2<T> implements Comparator<T>,
3564 Serializable
3565 {
3566 private static final long serialVersionUID = 4374092139857L;
3567
3568 /**
3569 * The comparator specified in the static factory. This will never
3570 * be null, as the static factory returns a ReverseComparator
3571 * instance if its argument is null.
3572 *
3573 * @serial
3574 */
3575 final Comparator<T> cmp;
3576
3577 ReverseComparator2(Comparator<T> cmp) {
3578 assert cmp != null;
3579 this.cmp = cmp;
3580 }
3581
3582 public int compare(T t1, T t2) {
3583 return cmp.compare(t2, t1);
3584 }
3585
3586 public boolean equals(Object o) {
3587 return (o == this) ||
3588 (o instanceof ReverseComparator2 &&
3589 cmp.equals(((ReverseComparator2)o).cmp));
3590 }
3591
3592 public int hashCode() {
3593 return cmp.hashCode() ^ Integer.MIN_VALUE;
3594 }
3595 }
3596
3597 /**
3598 * Returns an enumeration over the specified collection. This provides
3599 * interoperability with legacy APIs that require an enumeration
3600 * as input.
3601 *
3602 * @param c the collection for which an enumeration is to be returned.
3603 * @return an enumeration over the specified collection.
3604 * @see Enumeration
3605 */
3606 public static <T> Enumeration<T> enumeration(final Collection<T> c) {
3607 return new Enumeration<T>() {
3608 private final Iterator<T> i = c.iterator();
3609
3610 public boolean hasMoreElements() {
3611 return i.hasNext();
3612 }
3613
3614 public T nextElement() {
3615 return i.next();
3616 }
3617 };
3618 }
3619
3620 /**
3621 * Returns an array list containing the elements returned by the
3622 * specified enumeration in the order they are returned by the
3623 * enumeration. This method provides interoperability between
3624 * legacy APIs that return enumerations and new APIs that require
3625 * collections.
3626 *
3627 * @param e enumeration providing elements for the returned
3628 * array list
3629 * @return an array list containing the elements returned
3630 * by the specified enumeration.
3631 * @since 1.4
3632 * @see Enumeration
3633 * @see ArrayList
3634 */
3635 public static <T> ArrayList<T> list(Enumeration<T> e) {
3636 ArrayList<T> l = new ArrayList<T>();
3637 while (e.hasMoreElements())
3638 l.add(e.nextElement());
3639 return l;
3640 }
3641
3642 /**
3643 * Returns true if the specified arguments are equal, or both null.
3644 */
3645 static boolean eq(Object o1, Object o2) {
3646 return o1==null ? o2==null : o1.equals(o2);
3647 }
3648
3649 /**
3650 * Returns the number of elements in the specified collection equal to the
3651 * specified object. More formally, returns the number of elements
3652 * <tt>e</tt> in the collection such that
3653 * <tt>(o == null ? e == null : o.equals(e))</tt>.
3654 *
3655 * @param c the collection in which to determine the frequency
3656 * of <tt>o</tt>
3657 * @param o the object whose frequency is to be determined
3658 * @throws NullPointerException if <tt>c</tt> is null
3659 * @since 1.5
3660 */
3661 public static int frequency(Collection<?> c, Object o) {
3662 int result = 0;
3663 if (o == null) {
3664 for (Object e : c)
3665 if (e == null)
3666 result++;
3667 } else {
3668 for (Object e : c)
3669 if (o.equals(e))
3670 result++;
3671 }
3672 return result;
3673 }
3674
3675 /**
3676 * Returns <tt>true</tt> if the two specified collections have no
3677 * elements in common.
3678 *
3679 * <p>Care must be exercised if this method is used on collections that
3680 * do not comply with the general contract for <tt>Collection</tt>.
3681 * Implementations may elect to iterate over either collection and test
3682 * for containment in the other collection (or to perform any equivalent
3683 * computation). If either collection uses a nonstandard equality test
3684 * (as does a {@link SortedSet} whose ordering is not <i>compatible with
3685 * equals</i>, or the key set of an {@link IdentityHashMap}), both
3686 * collections must use the same nonstandard equality test, or the
3687 * result of this method is undefined.
3688 *
3689 * <p>Note that it is permissible to pass the same collection in both
3690 * parameters, in which case the method will return true if and only if
3691 * the collection is empty.
3692 *
3693 * @param c1 a collection
3694 * @param c2 a collection
3695 * @throws NullPointerException if either collection is null
3696 * @since 1.5
3697 */
3698 public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
3699 /*
3700 * We're going to iterate through c1 and test for inclusion in c2.
3701 * If c1 is a Set and c2 isn't, swap the collections. Otherwise,
3702 * place the shorter collection in c1. Hopefully this heuristic
3703 * will minimize the cost of the operation.
3704 */
3705 if ((c1 instanceof Set) && !(c2 instanceof Set) ||
3706 (c1.size() > c2.size())) {
3707 Collection<?> tmp = c1;
3708 c1 = c2;
3709 c2 = tmp;
3710 }
3711
3712 for (Object e : c1)
3713 if (c2.contains(e))
3714 return false;
3715 return true;
3716 }
3717
3718 /**
3719 * Adds all of the specified elements to the specified collection.
3720 * Elements to be added may be specified individually or as an array.
3721 * The behavior of this convenience method is identical to that of
3722 * <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely
3723 * to run significantly faster under most implementations.
3724 *
3725 * <p>When elements are specified individually, this method provides a
3726 * convenient way to add a few elements to an existing collection:
3727 * <pre>
3728 * Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon");
3729 * </pre>
3730 *
3731 * @param c the collection into which <tt>elements</tt> are to be inserted
3732 * @param elements the elements to insert into <tt>c</tt>
3733 * @return <tt>true</tt> if the collection changed as a result of the call
3734 * @throws UnsupportedOperationException if <tt>c</tt> does not support
3735 * the <tt>add</tt> operation
3736 * @throws NullPointerException if <tt>elements</tt> contains one or more
3737 * null values and <tt>c</tt> does not permit null elements, or
3738 * if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt>
3739 * @throws IllegalArgumentException if some property of a value in
3740 * <tt>elements</tt> prevents it from being added to <tt>c</tt>
3741 * @see Collection#addAll(Collection)
3742 * @since 1.5
3743 */
3744 public static <T> boolean addAll(Collection<? super T> c, T... elements) {
3745 boolean result = false;
3746 for (T element : elements)
3747 result |= c.add(element);
3748 return result;
3749 }
3750
3751 /**
3752 * Returns a set backed by the specified map. The resulting set displays
3753 * the same ordering, concurrency, and performance characteristics as the
3754 * backing map. In essence, this factory method provides a {@link Set}
3755 * implementation corresponding to any {@link Map} implementation. There
3756 * is no need to use this method on a {@link Map} implementation that
3757 * already has a corresponding {@link Set} implementation (such as {@link
3758 * HashMap} or {@link TreeMap}).
3759 *
3760 * <p>Each method invocation on the set returned by this method results in
3761 * exactly one method invocation on the backing map or its <tt>keySet</tt>
3762 * view, with one exception. The <tt>addAll</tt> method is implemented
3763 * as a sequence of <tt>put</tt> invocations on the backing map.
3764 *
3765 * <p>The specified map must be empty at the time this method is invoked,
3766 * and should not be accessed directly after this method returns. These
3767 * conditions are ensured if the map is created empty, passed directly
3768 * to this method, and no reference to the map is retained, as illustrated
3769 * in the following code fragment:
3770 * <pre>
3771 * Set<Object> weakHashSet = Collections.newSetFromMap(
3772 * new WeakHashMap<Object, Boolean>());
3773 * </pre>
3774 *
3775 * @param map the backing map
3776 * @return the set backed by the map
3777 * @throws IllegalArgumentException if <tt>map</tt> is not empty
3778 * @since 1.6
3779 */
3780 public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
3781 return new SetFromMap<E>(map);
3782 }
3783
3784 /**
3785 * @serial include
3786 */
3787 private static class SetFromMap<E> extends AbstractSet<E>
3788 implements Set<E>, Serializable
3789 {
3790 private final Map<E, Boolean> m; // The backing map
3791 private transient Set<E> s; // Its keySet
3792
3793 SetFromMap(Map<E, Boolean> map) {
3794 if (!map.isEmpty())
3795 throw new IllegalArgumentException("Map is non-empty");
3796 m = map;
3797 s = map.keySet();
3798 }
3799
3800 public void clear() { m.clear(); }
3801 public int size() { return m.size(); }
3802 public boolean isEmpty() { return m.isEmpty(); }
3803 public boolean contains(Object o) { return m.containsKey(o); }
3804 public boolean remove(Object o) { return m.remove(o) != null; }
3805 public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; }
3806 public Iterator<E> iterator() { return s.iterator(); }
3807 public Object[] toArray() { return s.toArray(); }
3808 public <T> T[] toArray(T[] a) { return s.toArray(a); }
3809 public String toString() { return s.toString(); }
3810 public int hashCode() { return s.hashCode(); }
3811 public boolean equals(Object o) { return o == this || s.equals(o); }
3812 public boolean containsAll(Collection<?> c) {return s.containsAll(c);}
3813 public boolean removeAll(Collection<?> c) {return s.removeAll(c);}
3814 public boolean retainAll(Collection<?> c) {return s.retainAll(c);}
3815 // addAll is the only inherited implementation
3816
3817 private static final long serialVersionUID = 2454657854757543876L;
3818
3819 private void readObject(java.io.ObjectInputStream stream)
3820 throws IOException, ClassNotFoundException
3821 {
3822 stream.defaultReadObject();
3823 s = m.keySet();
3824 }
3825 }
3826
3827 /**
3828 * Returns a view of a {@link Deque} as a Last-in-first-out (Lifo)
3829 * {@link Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>,
3830 * <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This
3831 * view can be useful when you would like to use a method
3832 * requiring a <tt>Queue</tt> but you need Lifo ordering.
3833 *
3834 * <p>Each method invocation on the queue returned by this method
3835 * results in exactly one method invocation on the backing deque, with
3836 * one exception. The {@link Queue#addAll addAll} method is
3837 * implemented as a sequence of {@link Deque#addFirst addFirst}
3838 * invocations on the backing deque.
3839 *
3840 * @param deque the deque
3841 * @return the queue
3842 * @since 1.6
3843 */
3844 public static <T> Queue<T> asLifoQueue(Deque<T> deque) {
3845 return new AsLIFOQueue<T>(deque);
3846 }
3847
3848 /**
3849 * @serial include
3850 */
3851 static class AsLIFOQueue<E> extends AbstractQueue<E>
3852 implements Queue<E>, Serializable {
3853 private static final long serialVersionUID = 1802017725587941708L;
3854 private final Deque<E> q;
3855 AsLIFOQueue(Deque<E> q) { this.q = q; }
3856 public boolean add(E e) { q.addFirst(e); return true; }
3857 public boolean offer(E e) { return q.offerFirst(e); }
3858 public E poll() { return q.pollFirst(); }
3859 public E remove() { return q.removeFirst(); }
3860 public E peek() { return q.peekFirst(); }
3861 public E element() { return q.getFirst(); }
3862 public void clear() { q.clear(); }
3863 public int size() { return q.size(); }
3864 public boolean isEmpty() { return q.isEmpty(); }
3865 public boolean contains(Object o) { return q.contains(o); }
3866 public boolean remove(Object o) { return q.remove(o); }
3867 public Iterator<E> iterator() { return q.iterator(); }
3868 public Object[] toArray() { return q.toArray(); }
3869 public <T> T[] toArray(T[] a) { return q.toArray(a); }
3870 public String toString() { return q.toString(); }
3871 public boolean containsAll(Collection<?> c) {return q.containsAll(c);}
3872 public boolean removeAll(Collection<?> c) {return q.removeAll(c);}
3873 public boolean retainAll(Collection<?> c) {return q.retainAll(c);}
3874 // We use inherited addAll; forwarding addAll would be wrong
3875 }
3876 }
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