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Java Source Code / Java Documentation » 6.0 JDK Modules » j2me » java.util 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


0001:        /*
0002:         * @(#)Collections.java	1.52 06/10/10
0003:         *
0004:         * Copyright  1990-2006 Sun Microsystems, Inc. All Rights Reserved.  
0005:         * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
0006:         *   
0007:         * This program is free software; you can redistribute it and/or  
0008:         * modify it under the terms of the GNU General Public License version  
0009:         * 2 only, as published by the Free Software Foundation.   
0010:         *   
0011:         * This program is distributed in the hope that it will be useful, but  
0012:         * WITHOUT ANY WARRANTY; without even the implied warranty of  
0013:         * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU  
0014:         * General Public License version 2 for more details (a copy is  
0015:         * included at /legal/license.txt).   
0016:         *   
0017:         * You should have received a copy of the GNU General Public License  
0018:         * version 2 along with this work; if not, write to the Free Software  
0019:         * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  
0020:         * 02110-1301 USA   
0021:         *   
0022:         * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa  
0023:         * Clara, CA 95054 or visit www.sun.com if you need additional  
0024:         * information or have any questions. 
0025:         *
0026:         */
0027:
0028:        package java.util;
0029:
0030:        import java.io.Serializable;
0031:
0032:        /**
0033:         * This class consists exclusively of static methods that operate on or return
0034:         * collections.  It contains polymorphic algorithms that operate on
0035:         * collections, "wrappers", which return a new collection backed by a
0036:         * specified collection, and a few other odds and ends.
0037:         *
0038:         * <p>The methods of this class all throw a <tt>NullPointerException</tt>
0039:         * if the collections provided to them are null.
0040:         *
0041:         * <p>The documentation for the polymorphic algorithms contained in this class
0042:         * generally includes a brief description of the <i>implementation</i>.  Such
0043:         * descriptions should be regarded as <i>implementation notes</i>, rather than
0044:         * parts of the <i>specification</i>.  Implementors should feel free to
0045:         * substitute other algorithms, so long as the specification itself is adhered
0046:         * to.  (For example, the algorithm used by <tt>sort</tt> does not have to be
0047:         * a mergesort, but it does have to be <i>stable</i>.)
0048:         *
0049:         * <p>The "destructive" algorithms contained in this class, that is, the
0050:         * algorithms that modify the collection on which they operate, are specified
0051:         * to throw <tt>UnsupportedOperationException</tt> if the collection does not
0052:         * support the appropriate mutation primitive(s), such as the <tt>set</tt>
0053:         * method.  These algorithms may, but are not required to, throw this
0054:         * exception if an invocation would have no effect on the collection.  For
0055:         * example, invoking the <tt>sort</tt> method on an unmodifiable list that is
0056:         * already sorted may or may not throw <tt>UnsupportedOperationException</tt>.
0057:         *
0058:         * <p>This class is a member of the 
0059:         * <a href="{@docRoot}/../guide/collections/index.html">
0060:         * Java Collections Framework</a>.
0061:         *
0062:         * @author  Josh Bloch
0063:         * @version 1.45, 02/17/00
0064:         * @see	    Collection
0065:         * @see	    Set
0066:         * @see	    List
0067:         * @see	    Map
0068:         * @since   1.2
0069:         */
0070:
0071:        public class Collections {
0072:            // Suppresses default constructor, ensuring non-instantiability.
0073:            private Collections() {
0074:            }
0075:
0076:            // Algorithms
0077:
0078:            /*
0079:             * Tuning parameters for algorithms - Many of the List algorithms have
0080:             * two implementations, one of which is appropriate for RandomAccess
0081:             * lists, the other for "sequential."  Often, the random access variant
0082:             * yields better performance on small sequential access lists.  The
0083:             * tuning  parameters below determine the cutoff point for what constitutes
0084:             * a "small" sequential access list for each algorithm.  The values below
0085:             * were empirically determined to work well for LinkedList. Hopefully
0086:             * they should be reasonable for other sequential access List
0087:             * implementations.  Those doing performance work on this code would
0088:             * do well to validate the values of these parameters from time to time.
0089:             * (The first word of each tuning parameter name is the algorithm to which
0090:             * it applies.)
0091:             */
0092:            private static final int BINARYSEARCH_THRESHOLD = 5000;
0093:            private static final int REVERSE_THRESHOLD = 18;
0094:            private static final int SHUFFLE_THRESHOLD = 5;
0095:            private static final int FILL_THRESHOLD = 25;
0096:            private static final int ROTATE_THRESHOLD = 100;
0097:            private static final int COPY_THRESHOLD = 10;
0098:            private static final int REPLACEALL_THRESHOLD = 11;
0099:            private static final int INDEXOFSUBLIST_THRESHOLD = 35;
0100:
0101:            /**
0102:             * Sorts the specified list into ascending order, according to the
0103:             * <i>natural ordering</i> of its elements.  All elements in the list must
0104:             * implement the <tt>Comparable</tt> interface.  Furthermore, all elements
0105:             * in the list must be <i>mutually comparable</i> (that is,
0106:             * <tt>e1.compareTo(e2)</tt> must not throw a <tt>ClassCastException</tt>
0107:             * for any elements <tt>e1</tt> and <tt>e2</tt> in the list).<p>
0108:             *
0109:             * This sort is guaranteed to be <i>stable</i>:  equal elements will
0110:             * not be reordered as a result of the sort.<p>
0111:             *
0112:             * The specified list must be modifiable, but need not be resizable.<p>
0113:             *
0114:             * The sorting algorithm is a modified mergesort (in which the merge is
0115:             * omitted if the highest element in the low sublist is less than the
0116:             * lowest element in the high sublist).  This algorithm offers guaranteed
0117:             * n log(n) performance. 
0118:             *
0119:             * This implementation dumps the specified list into an array, sorts
0120:             * the array, and iterates over the list resetting each element
0121:             * from the corresponding position in the array.  This avoids the
0122:             * n<sup>2</sup> log(n) performance that would result from attempting
0123:             * to sort a linked list in place.
0124:             *
0125:             * @param  list the list to be sorted.
0126:             * @throws ClassCastException if the list contains elements that are not
0127:             *	       <i>mutually comparable</i> (for example, strings and integers).
0128:             * @throws UnsupportedOperationException if the specified list's
0129:             *	       list-iterator does not support the <tt>set</tt> operation.
0130:             * @see Comparable
0131:             */
0132:            public static void sort(List list) {
0133:                Object a[] = list.toArray();
0134:                Arrays.sort(a);
0135:                ListIterator i = list.listIterator();
0136:                for (int j = 0; j < a.length; j++) {
0137:                    i.next();
0138:                    i.set(a[j]);
0139:                }
0140:            }
0141:
0142:            /**
0143:             * Sorts the specified list according to the order induced by the
0144:             * specified comparator.  All elements in the list must be <i>mutually
0145:             * comparable</i> using the specified comparator (that is,
0146:             * <tt>c.compare(e1, e2)</tt> must not throw a <tt>ClassCastException</tt>
0147:             * for any elements <tt>e1</tt> and <tt>e2</tt> in the list).<p>
0148:             *
0149:             * This sort is guaranteed to be <i>stable</i>:  equal elements will
0150:             * not be reordered as a result of the sort.<p>
0151:             *
0152:             * The sorting algorithm is a modified mergesort (in which the merge is
0153:             * omitted if the highest element in the low sublist is less than the
0154:             * lowest element in the high sublist).  This algorithm offers guaranteed
0155:             * n log(n) performance. 
0156:             *
0157:             * The specified list must be modifiable, but need not be resizable.
0158:             * This implementation dumps the specified list into an array, sorts
0159:             * the array, and iterates over the list resetting each element
0160:             * from the corresponding position in the array.  This avoids the
0161:             * n<sup>2</sup> log(n) performance that would result from attempting
0162:             * to sort a linked list in place.
0163:             *
0164:             * @param  list the list to be sorted.
0165:             * @param  c the comparator to determine the order of the list.  A
0166:             *        <tt>null</tt> value indicates that the elements' <i>natural
0167:             *        ordering</i> should be used.
0168:             * @throws ClassCastException if the list contains elements that are not
0169:             *	       <i>mutually comparable</i> using the specified comparator.
0170:             * @throws UnsupportedOperationException if the specified list's
0171:             *	       list-iterator does not support the <tt>set</tt> operation.
0172:             * @see Comparator
0173:             */
0174:            public static void sort(List list, Comparator c) {
0175:                Object a[] = list.toArray();
0176:                Arrays.sort(a, c);
0177:                ListIterator i = list.listIterator();
0178:                for (int j = 0; j < a.length; j++) {
0179:                    i.next();
0180:                    i.set(a[j]);
0181:                }
0182:            }
0183:
0184:            /**
0185:             * Searches the specified list for the specified object using the binary
0186:             * search algorithm.  The list must be sorted into ascending order
0187:             * according to the <i>natural ordering</i> of its elements (as by the
0188:             * <tt>sort(List)</tt> method, above) prior to making this call.  If it is
0189:             * not sorted, the results are undefined.  If the list contains multiple
0190:             * elements equal to the specified object, there is no guarantee which one
0191:             * will be found.<p>
0192:             *
0193:             * This method runs in log(n) time for a "random access" list (which
0194:             * provides near-constant-time positional access).  If the specified list
0195:             * does not implement the {@link RandomAccess} and is large, this method
0196:             * will do an iterator-based binary search that performs O(n) link
0197:             * traversals and O(log n) element comparisons.
0198:             *
0199:             * @param  list the list to be searched.
0200:             * @param  key the key to be searched for.
0201:             * @return index of the search key, if it is contained in the list;
0202:             *	       otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>.  The
0203:             *	       <i>insertion point</i> is defined as the point at which the
0204:             *	       key would be inserted into the list: the index of the first
0205:             *	       element greater than the key, or <tt>list.size()</tt>, if all
0206:             *	       elements in the list are less than the specified key.  Note
0207:             *	       that this guarantees that the return value will be &gt;= 0 if
0208:             *	       and only if the key is found.
0209:             * @throws ClassCastException if the list contains elements that are not
0210:             *	       <i>mutually comparable</i> (for example, strings and
0211:             *	       integers), or the search key in not mutually comparable
0212:             *	       with the elements of the list.
0213:             * @see    Comparable
0214:             * @see #sort(List)
0215:             */
0216:            public static int binarySearch(List list, Object key) {
0217:                if (list instanceof  RandomAccess
0218:                        || list.size() < BINARYSEARCH_THRESHOLD)
0219:                    return indexedBinarySearch(list, key);
0220:                else
0221:                    return iteratorBinarySearch(list, key);
0222:            }
0223:
0224:            private static int indexedBinarySearch(List list, Object key) {
0225:                int low = 0;
0226:                int high = list.size() - 1;
0227:
0228:                while (low <= high) {
0229:                    int mid = (low + high) >> 1;
0230:                    Object midVal = list.get(mid);
0231:                    int cmp = ((Comparable) midVal).compareTo(key);
0232:
0233:                    if (cmp < 0)
0234:                        low = mid + 1;
0235:                    else if (cmp > 0)
0236:                        high = mid - 1;
0237:                    else
0238:                        return mid; // key found
0239:                }
0240:                return -(low + 1); // key not found
0241:            }
0242:
0243:            private static int iteratorBinarySearch(List list, Object key) {
0244:                int low = 0;
0245:                int high = list.size() - 1;
0246:                ListIterator i = list.listIterator();
0247:
0248:                while (low <= high) {
0249:                    int mid = (low + high) >> 1;
0250:                    Object midVal = get(i, mid);
0251:                    int cmp = ((Comparable) midVal).compareTo(key);
0252:
0253:                    if (cmp < 0)
0254:                        low = mid + 1;
0255:                    else if (cmp > 0)
0256:                        high = mid - 1;
0257:                    else
0258:                        return mid; // key found
0259:                }
0260:                return -(low + 1); // key not found
0261:            }
0262:
0263:            /**
0264:             * Gets the ith element from the given list by repositioning the specified
0265:             * list listIterator.
0266:             */
0267:            private static Object get(ListIterator i, int index) {
0268:                Object obj = null;
0269:                int pos = i.nextIndex();
0270:                if (pos <= index) {
0271:                    do {
0272:                        obj = i.next();
0273:                    } while (pos++ < index);
0274:                } else {
0275:                    do {
0276:                        obj = i.previous();
0277:                    } while (--pos > index);
0278:                }
0279:                return obj;
0280:            }
0281:
0282:            /**
0283:             * Searches the specified list for the specified object using the binary
0284:             * search algorithm.  The list must be sorted into ascending order
0285:             * according to the specified comparator (as by the <tt>Sort(List,
0286:             * Comparator)</tt> method, above), prior to making this call.  If it is
0287:             * not sorted, the results are undefined.  If the list contains multiple
0288:             * elements equal to the specified object, there is no guarantee which one
0289:             * will be found.<p>
0290:             *
0291:             * This method runs in log(n) time for a "random access" list (which
0292:             * provides near-constant-time positional access).  If the specified list
0293:             * does not implement the {@link RandomAccess} and is large, this
0294:             * this method will do an iterator-based binary search that performs
0295:             * O(n) link traversals and O(log n) element comparisons.
0296:             *
0297:             * @param  list the list to be searched.
0298:             * @param  key the key to be searched for.
0299:             * @param  c the comparator by which the list is ordered.  A
0300:             *        <tt>null</tt> value indicates that the elements' <i>natural
0301:             *        ordering</i> should be used.
0302:             * @return index of the search key, if it is contained in the list;
0303:             *	       otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>.  The
0304:             *	       <i>insertion point</i> is defined as the point at which the
0305:             *	       key would be inserted into the list: the index of the first
0306:             *	       element greater than the key, or <tt>list.size()</tt>, if all
0307:             *	       elements in the list are less than the specified key.  Note
0308:             *	       that this guarantees that the return value will be &gt;= 0 if
0309:             *	       and only if the key is found.
0310:             * @throws ClassCastException if the list contains elements that are not
0311:             *	       <i>mutually comparable</i> using the specified comparator,
0312:             *	       or the search key in not mutually comparable with the
0313:             *	       elements of the list using this comparator.
0314:             * @see    Comparable
0315:             * @see #sort(List, Comparator)
0316:             */
0317:            public static int binarySearch(List list, Object key, Comparator c) {
0318:                if (c == null)
0319:                    return binarySearch(list, key);
0320:
0321:                if (list instanceof  RandomAccess
0322:                        || list.size() < BINARYSEARCH_THRESHOLD)
0323:                    return indexedBinarySearch(list, key, c);
0324:                else
0325:                    return iteratorBinarySearch(list, key, c);
0326:            }
0327:
0328:            private static int indexedBinarySearch(List l, Object key,
0329:                    Comparator c) {
0330:                int low = 0;
0331:                int high = l.size() - 1;
0332:
0333:                while (low <= high) {
0334:                    int mid = (low + high) >> 1;
0335:                    Object midVal = l.get(mid);
0336:                    int cmp = c.compare(midVal, key);
0337:
0338:                    if (cmp < 0)
0339:                        low = mid + 1;
0340:                    else if (cmp > 0)
0341:                        high = mid - 1;
0342:                    else
0343:                        return mid; // key found
0344:                }
0345:                return -(low + 1); // key not found
0346:            }
0347:
0348:            private static int iteratorBinarySearch(List l, Object key,
0349:                    Comparator c) {
0350:                int low = 0;
0351:                int high = l.size() - 1;
0352:                ListIterator i = l.listIterator();
0353:
0354:                while (low <= high) {
0355:                    int mid = (low + high) >> 1;
0356:                    Object midVal = get(i, mid);
0357:                    int cmp = c.compare(midVal, key);
0358:
0359:                    if (cmp < 0)
0360:                        low = mid + 1;
0361:                    else if (cmp > 0)
0362:                        high = mid - 1;
0363:                    else
0364:                        return mid; // key found
0365:                }
0366:                return -(low + 1); // key not found
0367:            }
0368:
0369:            /**
0370:             * Reverses the order of the elements in the specified list.<p>
0371:             *
0372:             * This method runs in linear time.
0373:             *
0374:             * @param  list the list whose elements are to be reversed.
0375:             * @throws UnsupportedOperationException if the specified list or
0376:             *         its list-iterator does not support the <tt>set</tt> method.
0377:             */
0378:            public static void reverse(List list) {
0379:                int size = list.size();
0380:                if (size < REVERSE_THRESHOLD || list instanceof  RandomAccess) {
0381:                    for (int i = 0, mid = size >> 1, j = size - 1; i < mid; i++, j--)
0382:                        swap(list, i, j);
0383:                } else {
0384:                    ListIterator fwd = list.listIterator();
0385:                    ListIterator rev = list.listIterator(size);
0386:                    for (int i = 0, mid = list.size() >> 1; i < mid; i++) {
0387:                        Object tmp = fwd.next();
0388:                        fwd.set(rev.previous());
0389:                        rev.set(tmp);
0390:                    }
0391:                }
0392:            }
0393:
0394:            /**
0395:             * Randomly permutes the specified list using a default source of
0396:             * randomness.  All permutations occur with approximately equal
0397:             * likelihood.<p>
0398:             *
0399:             * The hedge "approximately" is used in the foregoing description because
0400:             * default source of randomenss is only approximately an unbiased source
0401:             * of independently chosen bits. If it were a perfect source of randomly
0402:             * chosen bits, then the algorithm would choose permutations with perfect
0403:             * uniformity.<p>
0404:             *
0405:             * This implementation traverses the list backwards, from the last element
0406:             * up to the second, repeatedly swapping a randomly selected element into
0407:             * the "current position".  Elements are randomly selected from the
0408:             * portion of the list that runs from the first element to the current
0409:             * position, inclusive.<p>
0410:             *
0411:             * This method runs in linear time.  If the specified list does not
0412:             * implement the {@link RandomAccess} interface and is large, this
0413:             * implementation dumps the specified list into an array before shuffling
0414:             * it, and dumps the shuffled array back into the list.  This avoids the
0415:             * quadratic behavior that would result from shuffling a "sequential
0416:             * access" list in place.
0417:             *
0418:             * @param  list the list to be shuffled.
0419:             * @throws UnsupportedOperationException if the specified list or
0420:             *         its list-iterator does not support the <tt>set</tt> method.
0421:             */
0422:            public static void shuffle(List list) {
0423:                shuffle(list, r);
0424:            }
0425:
0426:            private static Random r = new Random();
0427:
0428:            /**
0429:             * Randomly permute the specified list using the specified source of
0430:             * randomness.  All permutations occur with equal likelihood
0431:             * assuming that the source of randomness is fair.<p>
0432:             *
0433:             * This implementation traverses the list backwards, from the last element
0434:             * up to the second, repeatedly swapping a randomly selected element into
0435:             * the "current position".  Elements are randomly selected from the
0436:             * portion of the list that runs from the first element to the current
0437:             * position, inclusive.<p>
0438:             *
0439:             * This method runs in linear time.  If the specified list does not
0440:             * implement the {@link RandomAccess} interface and is large, this
0441:             * implementation dumps the specified list into an array before shuffling
0442:             * it, and dumps the shuffled array back into the list.  This avoids the
0443:             * quadratic behavior that would result from shuffling a "sequential
0444:             * access" list in place.
0445:             *
0446:             * @param  list the list to be shuffled.
0447:             * @param  rnd the source of randomness to use to shuffle the list.
0448:             * @throws UnsupportedOperationException if the specified list or its
0449:             *         list-iterator does not support the <tt>set</tt> operation.
0450:             */
0451:            public static void shuffle(List list, Random rnd) {
0452:                int size = list.size();
0453:                if (size < SHUFFLE_THRESHOLD || list instanceof  RandomAccess) {
0454:                    for (int i = size; i > 1; i--)
0455:                        swap(list, i - 1, rnd.nextInt(i));
0456:                } else {
0457:                    Object arr[] = list.toArray();
0458:
0459:                    // Shuffle array
0460:                    for (int i = size; i > 1; i--)
0461:                        swap(arr, i - 1, rnd.nextInt(i));
0462:
0463:                    // Dump array back into list
0464:                    ListIterator it = list.listIterator();
0465:                    for (int i = 0; i < arr.length; i++) {
0466:                        it.next();
0467:                        it.set(arr[i]);
0468:                    }
0469:                }
0470:            }
0471:
0472:            /**
0473:             * Swaps the elements at the specified positions in the specified list.
0474:             * (If the specified positions are equal, invoking this method leaves
0475:             * the list unchanged.)
0476:             *
0477:             * @param list The list in which to swap elements.
0478:             * @param i the index of one element to be swapped.
0479:             * @param j the index of the other element to be swapped.
0480:             * @throws IndexOutOfBoundsException if either <tt>i</tt> or <tt>j</tt>
0481:             *         is out of range (i &lt; 0 || i &gt;= list.size()
0482:             *         || j &lt; 0 || j &gt;= list.size()).
0483:             * @since 1.4
0484:             */
0485:            public static void swap(List list, int i, int j) {
0486:                list.set(i, list.set(j, list.get(i)));
0487:            }
0488:
0489:            /**
0490:             * Swaps the two specified elements in the specified array.
0491:             */
0492:            private static void swap(Object[] arr, int i, int j) {
0493:                Object tmp = arr[i];
0494:                arr[i] = arr[j];
0495:                arr[j] = tmp;
0496:            }
0497:
0498:            /**
0499:             * Replaces all of the elements of the specified list with the specified
0500:             * element. <p>
0501:             *
0502:             * This method runs in linear time.
0503:             *
0504:             * @param  list the list to be filled with the specified element.
0505:             * @param  obj The element with which to fill the specified list.
0506:             * @throws UnsupportedOperationException if the specified list or its
0507:             *	       list-iterator does not support the <tt>set</tt> operation.
0508:             */
0509:            public static void fill(List list, Object obj) {
0510:                int size = list.size();
0511:
0512:                if (size < FILL_THRESHOLD || list instanceof  RandomAccess) {
0513:                    for (int i = 0; i < size; i++)
0514:                        list.set(i, obj);
0515:                } else {
0516:                    ListIterator itr = list.listIterator();
0517:                    for (int i = 0; i < size; i++) {
0518:                        itr.next();
0519:                        itr.set(obj);
0520:                    }
0521:                }
0522:            }
0523:
0524:            /**
0525:             * Copies all of the elements from one list into another.  After the
0526:             * operation, the index of each copied element in the destination list
0527:             * will be identical to its index in the source list.  The destination
0528:             * list must be at least as long as the source list.  If it is longer, the
0529:             * remaining elements in the destination list are unaffected. <p>
0530:             *
0531:             * This method runs in linear time.
0532:             *
0533:             * @param  dest The destination list.
0534:             * @param  src The source list.
0535:             * @throws IndexOutOfBoundsException if the destination list is too small
0536:             *         to contain the entire source List.
0537:             * @throws UnsupportedOperationException if the destination list's
0538:             *         list-iterator does not support the <tt>set</tt> operation.
0539:             */
0540:            public static void copy(List dest, List src) {
0541:                int srcSize = src.size();
0542:                if (srcSize > dest.size())
0543:                    throw new IndexOutOfBoundsException(
0544:                            "Source does not fit in dest");
0545:
0546:                if (srcSize < COPY_THRESHOLD
0547:                        || (src instanceof  RandomAccess && dest instanceof  RandomAccess)) {
0548:                    for (int i = 0; i < srcSize; i++)
0549:                        dest.set(i, src.get(i));
0550:                } else {
0551:                    ListIterator di = dest.listIterator(), si = src
0552:                            .listIterator();
0553:                    for (int i = 0; i < srcSize; i++) {
0554:                        di.next();
0555:                        di.set(si.next());
0556:                    }
0557:                }
0558:            }
0559:
0560:            /**
0561:             * Returns the minimum element of the given collection, according to the
0562:             * <i>natural ordering</i> of its elements.  All elements in the
0563:             * collection must implement the <tt>Comparable</tt> interface.
0564:             * Furthermore, all elements in the collection must be <i>mutually
0565:             * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
0566:             * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
0567:             * <tt>e2</tt> in the collection).<p>
0568:             *
0569:             * This method iterates over the entire collection, hence it requires
0570:             * time proportional to the size of the collection.
0571:             *
0572:             * @param  coll the collection whose minimum element is to be determined.
0573:             * @return the minimum element of the given collection, according
0574:             *         to the <i>natural ordering</i> of its elements.
0575:             * @throws ClassCastException if the collection contains elements that are
0576:             *	       not <i>mutually comparable</i> (for example, strings and
0577:             *	       integers).
0578:             * @throws NoSuchElementException if the collection is empty.
0579:             * @see Comparable
0580:             */
0581:            public static Object min(Collection coll) {
0582:                Iterator i = coll.iterator();
0583:                Comparable candidate = (Comparable) (i.next());
0584:
0585:                while (i.hasNext()) {
0586:                    Comparable next = (Comparable) (i.next());
0587:                    if (next.compareTo(candidate) < 0)
0588:                        candidate = next;
0589:                }
0590:                return candidate;
0591:            }
0592:
0593:            /**
0594:             * Returns the minimum element of the given collection, according to the
0595:             * order induced by the specified comparator.  All elements in the
0596:             * collection must be <i>mutually comparable</i> by the specified
0597:             * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
0598:             * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
0599:             * <tt>e2</tt> in the collection).<p>
0600:             *
0601:             * This method iterates over the entire collection, hence it requires
0602:             * time proportional to the size of the collection.
0603:             *
0604:             * @param  coll the collection whose minimum element is to be determined.
0605:             * @param  comp the comparator with which to determine the minimum element.
0606:             *         A <tt>null</tt> value indicates that the elements' <i>natural
0607:             *         ordering</i> should be used.
0608:             * @return the minimum element of the given collection, according
0609:             *         to the specified comparator.
0610:             * @throws ClassCastException if the collection contains elements that are
0611:             *	       not <i>mutually comparable</i> using the specified comparator.
0612:             * @throws NoSuchElementException if the collection is empty.
0613:             * @see Comparable
0614:             */
0615:            public static Object min(Collection coll, Comparator comp) {
0616:                if (comp == null)
0617:                    return min(coll);
0618:
0619:                Iterator i = coll.iterator();
0620:                Object candidate = i.next();
0621:
0622:                while (i.hasNext()) {
0623:                    Object next = i.next();
0624:                    if (comp.compare(next, candidate) < 0)
0625:                        candidate = next;
0626:                }
0627:                return candidate;
0628:            }
0629:
0630:            /**
0631:             * Returns the maximum element of the given collection, according to the
0632:             * <i>natural ordering</i> of its elements.  All elements in the
0633:             * collection must implement the <tt>Comparable</tt> interface.
0634:             * Furthermore, all elements in the collection must be <i>mutually
0635:             * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
0636:             * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
0637:             * <tt>e2</tt> in the collection).<p>
0638:             *
0639:             * This method iterates over the entire collection, hence it requires
0640:             * time proportional to the size of the collection.
0641:             *
0642:             * @param  coll the collection whose maximum element is to be determined.
0643:             * @return the maximum element of the given collection, according
0644:             *         to the <i>natural ordering</i> of its elements.
0645:             * @throws ClassCastException if the collection contains elements that are
0646:             *	       not <i>mutually comparable</i> (for example, strings and
0647:             *         integers).
0648:             * @throws NoSuchElementException if the collection is empty.
0649:             * @see Comparable
0650:             */
0651:            public static Object max(Collection coll) {
0652:                Iterator i = coll.iterator();
0653:                Comparable candidate = (Comparable) (i.next());
0654:
0655:                while (i.hasNext()) {
0656:                    Comparable next = (Comparable) (i.next());
0657:                    if (next.compareTo(candidate) > 0)
0658:                        candidate = next;
0659:                }
0660:                return candidate;
0661:            }
0662:
0663:            /**
0664:             * Returns the maximum element of the given collection, according to the
0665:             * order induced by the specified comparator.  All elements in the
0666:             * collection must be <i>mutually comparable</i> by the specified
0667:             * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
0668:             * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
0669:             * <tt>e2</tt> in the collection).<p>
0670:             *
0671:             * This method iterates over the entire collection, hence it requires
0672:             * time proportional to the size of the collection.
0673:             *
0674:             * @param  coll the collection whose maximum element is to be determined.
0675:             * @param  comp the comparator with which to determine the maximum element.
0676:             *         A <tt>null</tt> value indicates that the elements' <i>natural
0677:             *        ordering</i> should be used.
0678:             * @return the maximum element of the given collection, according
0679:             *         to the specified comparator.
0680:             * @throws ClassCastException if the collection contains elements that are
0681:             *	       not <i>mutually comparable</i> using the specified comparator.
0682:             * @throws NoSuchElementException if the collection is empty.
0683:             * @see Comparable
0684:             */
0685:            public static Object max(Collection coll, Comparator comp) {
0686:                if (comp == null)
0687:                    return max(coll);
0688:
0689:                Iterator i = coll.iterator();
0690:                Object candidate = i.next();
0691:
0692:                while (i.hasNext()) {
0693:                    Object next = i.next();
0694:                    if (comp.compare(next, candidate) > 0)
0695:                        candidate = next;
0696:                }
0697:                return candidate;
0698:            }
0699:
0700:            /**
0701:             * Rotates the elements in the specified list by the specified distance.
0702:             * After calling this method, the element at index <tt>i</tt> will be
0703:             * the element previously at index <tt>(i - distance)</tt> mod
0704:             * <tt>list.size()</tt>, for all values of <tt>i</tt> between <tt>0</tt>
0705:             * and <tt>list.size()-1</tt>, inclusive.  (This method has no effect on
0706:             * the size of the list.)
0707:             *
0708:             * <p>For example, suppose <tt>list</tt> comprises<tt> [t, a, n, k, s]</tt>.
0709:             * After invoking <tt>Collections.rotate(list, 1)</tt> (or
0710:             * <tt>Collections.rotate(list, -4)</tt>), <tt>list</tt> will comprise
0711:             * <tt>[s, t, a, n, k]</tt>.
0712:             *
0713:             * <p>Note that this method can usefully be applied to sublists to
0714:             * move one or more elements within a list while preserving the
0715:             * order of the remaining elements.  For example, the following idiom
0716:             * moves the element at index <tt>j</tt> forward to position
0717:             * <tt>k</tt> (which must be greater than or equal to <tt>j</tt>):
0718:             * <pre>
0719:             *     Collections.rotate(list.subList(j, k+1), -1);
0720:             * </pre>
0721:             * To make this concrete, suppose <tt>list</tt> comprises
0722:             * <tt>[a, b, c, d, e]</tt>.  To move the element at index <tt>1</tt>
0723:             * (<tt>b</tt>) forward two positions, perform the following invocation:
0724:             * <pre>
0725:             *     Collections.rotate(l.subList(1, 4), -1);
0726:             * </pre>
0727:             * The resulting list is <tt>[a, c, d, b, e]</tt>.
0728:             * 
0729:             * <p>To move more than one element forward, increase the absolute value
0730:             * of the rotation distance.  To move elements backward, use a positive
0731:             * shift distance.
0732:             *
0733:             * <p>If the specified list is small or implements the {@link
0734:             * RandomAccess} interface, this implementation exchanges the first
0735:             * element into the location it should go, and then repeatedly exchanges
0736:             * the displaced element into the location it should go until a displaced
0737:             * element is swapped into the first element.  If necessary, the process
0738:             * is repeated on the second and successive elements, until the rotation
0739:             * is complete.  If the specified list is large and doesn't implement the
0740:             * <tt>RandomAccess</tt> interface, this implementation breaks the
0741:             * list into two sublist views around index <tt>-distance mod size</tt>.
0742:             * Then the {@link #reverse(List)} method is invoked on each sublist view,
0743:             * and finally it is invoked on the entire list.  For a more complete
0744:             * description of both algorithms, see Section 2.3 of Jon Bentley's
0745:             * <i>Programming Pearls</i> (Addison-Wesley, 1986).
0746:             *
0747:             * @param list the list to be rotated.
0748:             * @param distance the distance to rotate the list.  There are no
0749:             *        constraints on this value; it may be zero, negative, or
0750:             *        greater than <tt>list.size()</tt>.
0751:             * @throws UnsupportedOperationException if the specified list or
0752:             *         its list-iterator does not support the <tt>set</tt> method.
0753:             * @since 1.4
0754:             */
0755:            public static void rotate(List list, int distance) {
0756:                if (list instanceof  RandomAccess
0757:                        || list.size() < ROTATE_THRESHOLD)
0758:                    rotate1(list, distance);
0759:                else
0760:                    rotate2(list, distance);
0761:            }
0762:
0763:            private static void rotate1(List list, int distance) {
0764:                int size = list.size();
0765:                if (size == 0)
0766:                    return;
0767:                distance = distance % size;
0768:                if (distance < 0)
0769:                    distance += size;
0770:                if (distance == 0)
0771:                    return;
0772:
0773:                for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) {
0774:                    Object displaced = list.get(cycleStart);
0775:                    int i = cycleStart;
0776:                    do {
0777:                        i += distance;
0778:                        if (i >= size)
0779:                            i -= size;
0780:                        displaced = list.set(i, displaced);
0781:                        nMoved++;
0782:                    } while (i != cycleStart);
0783:                }
0784:            }
0785:
0786:            private static void rotate2(List list, int distance) {
0787:                int size = list.size();
0788:                if (size == 0)
0789:                    return;
0790:                int mid = -distance % size;
0791:                if (mid < 0)
0792:                    mid += size;
0793:                if (mid == 0)
0794:                    return;
0795:
0796:                Collections.reverse(list.subList(0, mid));
0797:                Collections.reverse(list.subList(mid, size));
0798:                Collections.reverse(list);
0799:            }
0800:
0801:            /**
0802:             * Replaces all occurrences of one specified value in a list with another.
0803:             * More formally, replaces with <tt>newVal</tt> each element <tt>e</tt>
0804:             * in <tt>list</tt> such that
0805:             * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
0806:             * (This method has no effect on the size of the list.)
0807:             *
0808:             * @param list the list in which replacement is to occur.
0809:             * @param oldVal the old value to be replaced.
0810:             * @param newVal the new value with which <tt>oldVal</tt> is to be
0811:             *        replaced.
0812:             * @return <tt>true</tt> if <tt>list</tt> contained one or more elements
0813:             *         <tt>e</tt> such that
0814:             *         <tt>(oldVal==null ?  e==null : oldVal.equals(e))</tt>.
0815:             * @throws UnsupportedOperationException if the specified list or
0816:             *         its list-iterator does not support the <tt>set</tt> method.
0817:             * @since  1.4
0818:             */
0819:            public static boolean replaceAll(List list, Object oldVal,
0820:                    Object newVal) {
0821:                boolean result = false;
0822:                int size = list.size();
0823:                if (size < REPLACEALL_THRESHOLD || list instanceof  RandomAccess) {
0824:                    if (oldVal == null) {
0825:                        for (int i = 0; i < size; i++) {
0826:                            if (list.get(i) == null) {
0827:                                list.set(i, newVal);
0828:                                result = true;
0829:                            }
0830:                        }
0831:                    } else {
0832:                        for (int i = 0; i < size; i++) {
0833:                            if (oldVal.equals(list.get(i))) {
0834:                                list.set(i, newVal);
0835:                                result = true;
0836:                            }
0837:                        }
0838:                    }
0839:                } else {
0840:                    ListIterator itr = list.listIterator();
0841:                    if (oldVal == null) {
0842:                        for (int i = 0; i < size; i++) {
0843:                            if (itr.next() == null) {
0844:                                itr.set(newVal);
0845:                                result = true;
0846:                            }
0847:                        }
0848:                    } else {
0849:                        for (int i = 0; i < size; i++) {
0850:                            if (oldVal.equals(itr.next())) {
0851:                                itr.set(newVal);
0852:                                result = true;
0853:                            }
0854:                        }
0855:                    }
0856:                }
0857:                return result;
0858:            }
0859:
0860:            /**
0861:             * Returns the starting position of the first occurrence of the specified
0862:             * target list within the specified source list, or -1 if there is no
0863:             * such occurrence.  More formally, returns the the lowest index <tt>i</tt>
0864:             * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
0865:             * or -1 if there is no such index.  (Returns -1 if
0866:             * <tt>target.size() > source.size()</tt>.)
0867:             *
0868:             * <p>This implementation uses the "brute force" technique of scanning
0869:             * over the source list, looking for a match with the target at each
0870:             * location in turn.
0871:             *
0872:             * @param source the list in which to search for the first occurrence
0873:             *        of <tt>target</tt>.
0874:             * @param target the list to search for as a subList of <tt>source</tt>.
0875:             * @return the starting position of the first occurrence of the specified
0876:             *         target list within the specified source list, or -1 if there
0877:             *         is no such occurrence.
0878:             * @since  1.4
0879:             */
0880:            public static int indexOfSubList(List source, List target) {
0881:                int sourceSize = source.size();
0882:                int targetSize = target.size();
0883:                int maxCandidate = sourceSize - targetSize;
0884:
0885:                if (sourceSize < INDEXOFSUBLIST_THRESHOLD
0886:                        || (source instanceof  RandomAccess && target instanceof  RandomAccess)) {
0887:                    nextCand: for (int candidate = 0; candidate <= maxCandidate; candidate++) {
0888:                        for (int i = 0, j = candidate; i < targetSize; i++, j++)
0889:                            if (!eq(target.get(i), source.get(j)))
0890:                                continue nextCand; // Element mismatch, try next cand
0891:                        return candidate; // All elements of candidate matched target
0892:                    }
0893:                } else { // Iterator version of above algorithm
0894:                    ListIterator si = source.listIterator();
0895:                    nextCand: for (int candidate = 0; candidate <= maxCandidate; candidate++) {
0896:                        ListIterator ti = target.listIterator();
0897:                        for (int i = 0; i < targetSize; i++) {
0898:                            if (!eq(ti.next(), si.next())) {
0899:                                // Back up source iterator to next candidate
0900:                                for (int j = 0; j < i; j++)
0901:                                    si.previous();
0902:                                continue nextCand;
0903:                            }
0904:                        }
0905:                        return candidate;
0906:                    }
0907:                }
0908:                return -1; // No candidate matched the target
0909:            }
0910:
0911:            /**
0912:             * Returns the starting position of the last occurrence of the specified
0913:             * target list within the specified source list, or -1 if there is no such
0914:             * occurrence.  More formally, returns the the highest index <tt>i</tt>
0915:             * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
0916:             * or -1 if there is no such index.  (Returns -1 if
0917:             * <tt>target.size() > source.size()</tt>.)
0918:             *
0919:             * <p>This implementation uses the "brute force" technique of iterating
0920:             * over the source list, looking for a match with the target at each
0921:             * location in turn.
0922:             *
0923:             * @param source the list in which to search for the last occurrence
0924:             *        of <tt>target</tt>.
0925:             * @param target the list to search for as a subList of <tt>source</tt>.
0926:             * @return the starting position of the last occurrence of the specified
0927:             *         target list within the specified source list, or -1 if there
0928:             *         is no such occurrence.
0929:             * @since  1.4
0930:             */
0931:            public static int lastIndexOfSubList(List source, List target) {
0932:                int sourceSize = source.size();
0933:                int targetSize = target.size();
0934:                int maxCandidate = sourceSize - targetSize;
0935:
0936:                if (sourceSize < INDEXOFSUBLIST_THRESHOLD
0937:                        || source instanceof  RandomAccess) { // Index access version
0938:                    nextCand: for (int candidate = maxCandidate; candidate >= 0; candidate--) {
0939:                        for (int i = 0, j = candidate; i < targetSize; i++, j++)
0940:                            if (!eq(target.get(i), source.get(j)))
0941:                                continue nextCand; // Element mismatch, try next cand
0942:                        return candidate; // All elements of candidate matched target
0943:                    }
0944:                } else { // Iterator version of above algorithm
0945:                    if (maxCandidate < 0)
0946:                        return -1;
0947:                    ListIterator si = source.listIterator(maxCandidate);
0948:                    nextCand: for (int candidate = maxCandidate; candidate >= 0; candidate--) {
0949:                        ListIterator ti = target.listIterator();
0950:                        for (int i = 0; i < targetSize; i++) {
0951:                            if (!eq(ti.next(), si.next())) {
0952:                                if (candidate != 0) {
0953:                                    // Back up source iterator to next candidate
0954:                                    for (int j = 0; j <= i + 1; j++)
0955:                                        si.previous();
0956:                                }
0957:                                continue nextCand;
0958:                            }
0959:                        }
0960:                        return candidate;
0961:                    }
0962:                }
0963:                return -1; // No candidate matched the target
0964:            }
0965:
0966:            // Unmodifiable Wrappers
0967:
0968:            /**
0969:             * Returns an unmodifiable view of the specified collection.  This method
0970:             * allows modules to provide users with "read-only" access to internal
0971:             * collections.  Query operations on the returned collection "read through"
0972:             * to the specified collection, and attempts to modify the returned
0973:             * collection, whether direct or via its iterator, result in an
0974:             * <tt>UnsupportedOperationException</tt>.<p>
0975:             *
0976:             * The returned collection does <i>not</i> pass the hashCode and equals
0977:             * operations through to the backing collection, but relies on
0978:             * <tt>Object</tt>'s <tt>equals</tt> and <tt>hashCode</tt> methods.  This
0979:             * is necessary to preserve the contracts of these operations in the case
0980:             * that the backing collection is a set or a list.<p>
0981:             *
0982:             * The returned collection will be serializable if the specified collection
0983:             * is serializable. 
0984:             *
0985:             * @param  c the collection for which an unmodifiable view is to be
0986:             *	       returned.
0987:             * @return an unmodifiable view of the specified collection.
0988:             */
0989:            public static Collection unmodifiableCollection(Collection c) {
0990:                return new UnmodifiableCollection(c);
0991:            }
0992:
0993:            /**
0994:             * @serial include
0995:             */
0996:            static class UnmodifiableCollection implements  Collection,
0997:                    Serializable {
0998:                // use serialVersionUID from JDK 1.2.2 for interoperability
0999:                private static final long serialVersionUID = 1820017752578914078L;
1000:
1001:                Collection c;
1002:
1003:                UnmodifiableCollection(Collection c) {
1004:                    if (c == null)
1005:                        throw new NullPointerException();
1006:                    this .c = c;
1007:                }
1008:
1009:                public int size() {
1010:                    return c.size();
1011:                }
1012:
1013:                public boolean isEmpty() {
1014:                    return c.isEmpty();
1015:                }
1016:
1017:                public boolean contains(Object o) {
1018:                    return c.contains(o);
1019:                }
1020:
1021:                public Object[] toArray() {
1022:                    return c.toArray();
1023:                }
1024:
1025:                public Object[] toArray(Object[] a) {
1026:                    return c.toArray(a);
1027:                }
1028:
1029:                public String toString() {
1030:                    return c.toString();
1031:                }
1032:
1033:                public Iterator iterator() {
1034:                    return new Iterator() {
1035:                        Iterator i = c.iterator();
1036:
1037:                        public boolean hasNext() {
1038:                            return i.hasNext();
1039:                        }
1040:
1041:                        public Object next() {
1042:                            return i.next();
1043:                        }
1044:
1045:                        public void remove() {
1046:                            throw new UnsupportedOperationException();
1047:                        }
1048:                    };
1049:                }
1050:
1051:                public boolean add(Object o) {
1052:                    throw new UnsupportedOperationException();
1053:                }
1054:
1055:                public boolean remove(Object o) {
1056:                    throw new UnsupportedOperationException();
1057:                }
1058:
1059:                public boolean containsAll(Collection coll) {
1060:                    return c.containsAll(coll);
1061:                }
1062:
1063:                public boolean addAll(Collection coll) {
1064:                    throw new UnsupportedOperationException();
1065:                }
1066:
1067:                public boolean removeAll(Collection coll) {
1068:                    throw new UnsupportedOperationException();
1069:                }
1070:
1071:                public boolean retainAll(Collection coll) {
1072:                    throw new UnsupportedOperationException();
1073:                }
1074:
1075:                public void clear() {
1076:                    throw new UnsupportedOperationException();
1077:                }
1078:            }
1079:
1080:            /**
1081:             * Returns an unmodifiable view of the specified set.  This method allows
1082:             * modules to provide users with "read-only" access to internal sets.
1083:             * Query operations on the returned set "read through" to the specified
1084:             * set, and attempts to modify the returned set, whether direct or via its
1085:             * iterator, result in an <tt>UnsupportedOperationException</tt>.<p>
1086:             *
1087:             * The returned set will be serializable if the specified set
1088:             * is serializable. 
1089:             *
1090:             * @param  s the set for which an unmodifiable view is to be returned.
1091:             * @return an unmodifiable view of the specified set.
1092:             */
1093:
1094:            public static Set unmodifiableSet(Set s) {
1095:                return new UnmodifiableSet(s);
1096:            }
1097:
1098:            /**
1099:             * @serial include
1100:             */
1101:            static class UnmodifiableSet extends UnmodifiableCollection
1102:                    implements  Set, Serializable {
1103:                UnmodifiableSet(Set s) {
1104:                    super (s);
1105:                }
1106:
1107:                public boolean equals(Object o) {
1108:                    return c.equals(o);
1109:                }
1110:
1111:                public int hashCode() {
1112:                    return c.hashCode();
1113:                }
1114:            }
1115:
1116:            /**
1117:             * Returns an unmodifiable view of the specified sorted set.  This method
1118:             * allows modules to provide users with "read-only" access to internal
1119:             * sorted sets.  Query operations on the returned sorted set "read
1120:             * through" to the specified sorted set.  Attempts to modify the returned
1121:             * sorted set, whether direct, via its iterator, or via its
1122:             * <tt>subSet</tt>, <tt>headSet</tt>, or <tt>tailSet</tt> views, result in
1123:             * an <tt>UnsupportedOperationException</tt>.<p>
1124:             *
1125:             * The returned sorted set will be serializable if the specified sorted set
1126:             * is serializable. 
1127:             *
1128:             * @param s the sorted set for which an unmodifiable view is to be
1129:             *        returned. 
1130:             * @return an unmodifiable view of the specified sorted set.
1131:             */
1132:            public static SortedSet unmodifiableSortedSet(SortedSet s) {
1133:                return new UnmodifiableSortedSet(s);
1134:            }
1135:
1136:            /**
1137:             * @serial include
1138:             */
1139:            static class UnmodifiableSortedSet extends UnmodifiableSet
1140:                    implements  SortedSet, Serializable {
1141:                private SortedSet ss;
1142:
1143:                UnmodifiableSortedSet(SortedSet s) {
1144:                    super (s);
1145:                    ss = s;
1146:                }
1147:
1148:                public Comparator comparator() {
1149:                    return ss.comparator();
1150:                }
1151:
1152:                public SortedSet subSet(Object fromElement, Object toElement) {
1153:                    return new UnmodifiableSortedSet(ss.subSet(fromElement,
1154:                            toElement));
1155:                }
1156:
1157:                public SortedSet headSet(Object toElement) {
1158:                    return new UnmodifiableSortedSet(ss.headSet(toElement));
1159:                }
1160:
1161:                public SortedSet tailSet(Object fromElement) {
1162:                    return new UnmodifiableSortedSet(ss.tailSet(fromElement));
1163:                }
1164:
1165:                public Object first() {
1166:                    return ss.first();
1167:                }
1168:
1169:                public Object last() {
1170:                    return ss.last();
1171:                }
1172:            }
1173:
1174:            /**
1175:             * Returns an unmodifiable view of the specified list.  This method allows
1176:             * modules to provide users with "read-only" access to internal
1177:             * lists.  Query operations on the returned list "read through" to the
1178:             * specified list, and attempts to modify the returned list, whether
1179:             * direct or via its iterator, result in an
1180:             * <tt>UnsupportedOperationException</tt>.<p>
1181:             *
1182:             * The returned list will be serializable if the specified list
1183:             * is serializable. Similarly, the returned list will implement
1184:             * {@link RandomAccess} if the specified list does.
1185:             * the 
1186:             *
1187:             * @param  list the list for which an unmodifiable view is to be returned.
1188:             * @return an unmodifiable view of the specified list.
1189:             */
1190:            public static List unmodifiableList(List list) {
1191:                return (list instanceof  RandomAccess ? new UnmodifiableRandomAccessList(
1192:                        list)
1193:                        : new UnmodifiableList(list));
1194:            }
1195:
1196:            /**
1197:             * @serial include
1198:             */
1199:            static class UnmodifiableList extends UnmodifiableCollection
1200:                    implements  List {
1201:                static final long serialVersionUID = -283967356065247728L;
1202:                List list;
1203:
1204:                UnmodifiableList(List list) {
1205:                    super (list);
1206:                    this .list = list;
1207:                }
1208:
1209:                public boolean equals(Object o) {
1210:                    return list.equals(o);
1211:                }
1212:
1213:                public int hashCode() {
1214:                    return list.hashCode();
1215:                }
1216:
1217:                public Object get(int index) {
1218:                    return list.get(index);
1219:                }
1220:
1221:                public Object set(int index, Object element) {
1222:                    throw new UnsupportedOperationException();
1223:                }
1224:
1225:                public void add(int index, Object element) {
1226:                    throw new UnsupportedOperationException();
1227:                }
1228:
1229:                public Object remove(int index) {
1230:                    throw new UnsupportedOperationException();
1231:                }
1232:
1233:                public int indexOf(Object o) {
1234:                    return list.indexOf(o);
1235:                }
1236:
1237:                public int lastIndexOf(Object o) {
1238:                    return list.lastIndexOf(o);
1239:                }
1240:
1241:                public boolean addAll(int index, Collection c) {
1242:                    throw new UnsupportedOperationException();
1243:                }
1244:
1245:                public ListIterator listIterator() {
1246:                    return listIterator(0);
1247:                }
1248:
1249:                public ListIterator listIterator(final int index) {
1250:                    return new ListIterator() {
1251:                        ListIterator i = list.listIterator(index);
1252:
1253:                        public boolean hasNext() {
1254:                            return i.hasNext();
1255:                        }
1256:
1257:                        public Object next() {
1258:                            return i.next();
1259:                        }
1260:
1261:                        public boolean hasPrevious() {
1262:                            return i.hasPrevious();
1263:                        }
1264:
1265:                        public Object previous() {
1266:                            return i.previous();
1267:                        }
1268:
1269:                        public int nextIndex() {
1270:                            return i.nextIndex();
1271:                        }
1272:
1273:                        public int previousIndex() {
1274:                            return i.previousIndex();
1275:                        }
1276:
1277:                        public void remove() {
1278:                            throw new UnsupportedOperationException();
1279:                        }
1280:
1281:                        public void set(Object o) {
1282:                            throw new UnsupportedOperationException();
1283:                        }
1284:
1285:                        public void add(Object o) {
1286:                            throw new UnsupportedOperationException();
1287:                        }
1288:                    };
1289:                }
1290:
1291:                public List subList(int fromIndex, int toIndex) {
1292:                    return new UnmodifiableList(list
1293:                            .subList(fromIndex, toIndex));
1294:                }
1295:
1296:                /**
1297:                 * UnmodifiableRandomAccessList instances are serialized as
1298:                 * UnmodifiableList instances to allow them to be deserialized
1299:                 * in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList).
1300:                 * This method inverts the transformation.  As a beneficial
1301:                 * side-effect, it also grafts the RandomAccess marker onto
1302:                 * UnmodifiableList instances that were serialized in pre-1.4 JREs.
1303:                 *
1304:                 * Note: Unfortunately, UnmodifiableRandomAccessList instances
1305:                 * serialized in 1.4.1 and deserialized in 1.4 will become
1306:                 * UnmodifiableList instances, as this method was missing in 1.4.
1307:                 */
1308:                private Object readResolve() {
1309:                    return (list instanceof  RandomAccess ? new UnmodifiableRandomAccessList(
1310:                            list)
1311:                            : this );
1312:                }
1313:            }
1314:
1315:            /**
1316:             * @serial include
1317:             */
1318:            static class UnmodifiableRandomAccessList extends UnmodifiableList
1319:                    implements  RandomAccess {
1320:                UnmodifiableRandomAccessList(List list) {
1321:                    super (list);
1322:                }
1323:
1324:                public List subList(int fromIndex, int toIndex) {
1325:                    return new UnmodifiableRandomAccessList(list.subList(
1326:                            fromIndex, toIndex));
1327:                }
1328:
1329:                private static final long serialVersionUID = -2542308836966382001L;
1330:
1331:                /**
1332:                 * Allows instances to be deserialized in pre-1.4 JREs (which do
1333:                 * not have UnmodifiableRandomAccessList).  UnmodifiableList has
1334:                 * a readResolve method that inverts this transformation upon
1335:                 * deserialization.
1336:                 */
1337:                private Object writeReplace() {
1338:                    return new UnmodifiableList(list);
1339:                }
1340:            }
1341:
1342:            /**
1343:             * Returns an unmodifiable view of the specified map.  This method
1344:             * allows modules to provide users with "read-only" access to internal
1345:             * maps.  Query operations on the returned map "read through"
1346:             * to the specified map, and attempts to modify the returned
1347:             * map, whether direct or via its collection views, result in an
1348:             * <tt>UnsupportedOperationException</tt>.<p>
1349:             *
1350:             * The returned map will be serializable if the specified map
1351:             * is serializable. 
1352:             *
1353:             * @param  m the map for which an unmodifiable view is to be returned.
1354:             * @return an unmodifiable view of the specified map.
1355:             */
1356:            public static Map unmodifiableMap(Map m) {
1357:                return new UnmodifiableMap(m);
1358:            }
1359:
1360:            /**
1361:             * @serial include
1362:             */
1363:            private static class UnmodifiableMap implements  Map, Serializable {
1364:                // use serialVersionUID from JDK 1.2.2 for interoperability
1365:                private static final long serialVersionUID = -1034234728574286014L;
1366:
1367:                private final Map m;
1368:
1369:                UnmodifiableMap(Map m) {
1370:                    if (m == null)
1371:                        throw new NullPointerException();
1372:                    this .m = m;
1373:                }
1374:
1375:                public int size() {
1376:                    return m.size();
1377:                }
1378:
1379:                public boolean isEmpty() {
1380:                    return m.isEmpty();
1381:                }
1382:
1383:                public boolean containsKey(Object key) {
1384:                    return m.containsKey(key);
1385:                }
1386:
1387:                public boolean containsValue(Object val) {
1388:                    return m.containsValue(val);
1389:                }
1390:
1391:                public Object get(Object key) {
1392:                    return m.get(key);
1393:                }
1394:
1395:                public Object put(Object key, Object value) {
1396:                    throw new UnsupportedOperationException();
1397:                }
1398:
1399:                public Object remove(Object key) {
1400:                    throw new UnsupportedOperationException();
1401:                }
1402:
1403:                public void putAll(Map t) {
1404:                    throw new UnsupportedOperationException();
1405:                }
1406:
1407:                public void clear() {
1408:                    throw new UnsupportedOperationException();
1409:                }
1410:
1411:                private transient Set keySet = null;
1412:                private transient Set entrySet = null;
1413:                private transient Collection values = null;
1414:
1415:                public Set keySet() {
1416:                    if (keySet == null)
1417:                        keySet = unmodifiableSet(m.keySet());
1418:                    return keySet;
1419:                }
1420:
1421:                public Set entrySet() {
1422:                    if (entrySet == null)
1423:                        entrySet = new UnmodifiableEntrySet(m.entrySet());
1424:                    return entrySet;
1425:                }
1426:
1427:                public Collection values() {
1428:                    if (values == null)
1429:                        values = unmodifiableCollection(m.values());
1430:                    return values;
1431:                }
1432:
1433:                public boolean equals(Object o) {
1434:                    return m.equals(o);
1435:                }
1436:
1437:                public int hashCode() {
1438:                    return m.hashCode();
1439:                }
1440:
1441:                public String toString() {
1442:                    return m.toString();
1443:                }
1444:
1445:                /**
1446:                 * We need this class in addition to UnmodifiableSet as
1447:                 * Map.Entries themselves permit modification of the backing Map
1448:                 * via their setValue operation.  This class is subtle: there are
1449:                 * many possible attacks that must be thwarted.
1450:                 *
1451:                 * @serial include
1452:                 */
1453:                static class UnmodifiableEntrySet extends UnmodifiableSet {
1454:                    UnmodifiableEntrySet(Set s) {
1455:                        super (s);
1456:                    }
1457:
1458:                    public Iterator iterator() {
1459:                        return new Iterator() {
1460:                            Iterator i = c.iterator();
1461:
1462:                            public boolean hasNext() {
1463:                                return i.hasNext();
1464:                            }
1465:
1466:                            public Object next() {
1467:                                return new UnmodifiableEntry((Map.Entry) i
1468:                                        .next());
1469:                            }
1470:
1471:                            public void remove() {
1472:                                throw new UnsupportedOperationException();
1473:                            }
1474:                        };
1475:                    }
1476:
1477:                    public Object[] toArray() {
1478:                        Object[] a = c.toArray();
1479:                        for (int i = 0; i < a.length; i++)
1480:                            a[i] = new UnmodifiableEntry((Map.Entry) a[i]);
1481:                        return a;
1482:                    }
1483:
1484:                    public Object[] toArray(Object a[]) {
1485:                        // We don't pass a to c.toArray, to avoid window of
1486:                        // vulnerability wherein an unscrupulous multithreaded client
1487:                        // could get his hands on raw (unwrapped) Entries from c.
1488:                        Object[] arr = c.toArray(a.length == 0 ? a
1489:                                : (Object[]) java.lang.reflect.Array
1490:                                        .newInstance(a.getClass()
1491:                                                .getComponentType(), 0));
1492:                        for (int i = 0; i < arr.length; i++)
1493:                            arr[i] = new UnmodifiableEntry((Map.Entry) arr[i]);
1494:
1495:                        if (arr.length > a.length)
1496:                            return arr;
1497:
1498:                        System.arraycopy(arr, 0, a, 0, arr.length);
1499:                        if (a.length > arr.length)
1500:                            a[arr.length] = null;
1501:                        return a;
1502:                    }
1503:
1504:                    /**
1505:                     * This method is overridden to protect the backing set against
1506:                     * an object with a nefarious equals function that senses
1507:                     * that the equality-candidate is Map.Entry and calls its
1508:                     * setValue method.
1509:                     */
1510:                    public boolean contains(Object o) {
1511:                        if (!(o instanceof  Map.Entry))
1512:                            return false;
1513:                        return c.contains(new UnmodifiableEntry((Map.Entry) o));
1514:                    }
1515:
1516:                    /**
1517:                     * The next two methods are overridden to protect against
1518:                     * an unscrupulous List whose contains(Object o) method senses
1519:                     * when o is a Map.Entry, and calls o.setValue.
1520:                     */
1521:                    public boolean containsAll(Collection coll) {
1522:                        Iterator e = coll.iterator();
1523:                        while (e.hasNext())
1524:                            if (!contains(e.next())) // Invokes safe contains() above
1525:                                return false;
1526:                        return true;
1527:                    }
1528:
1529:                    public boolean equals(Object o) {
1530:                        if (o == this )
1531:                            return true;
1532:
1533:                        if (!(o instanceof  Set))
1534:                            return false;
1535:                        Set s = (Set) o;
1536:                        if (s.size() != c.size())
1537:                            return false;
1538:                        return containsAll(s); // Invokes safe containsAll() above
1539:                    }
1540:
1541:                    /**
1542:                     * This "wrapper class" serves two purposes: it prevents
1543:                     * the client from modifying the backing Map, by short-circuiting
1544:                     * the setValue method, and it protects the backing Map against
1545:                     * an ill-behaved Map.Entry that attempts to modify another
1546:                     * Map Entry when asked to perform an equality check.
1547:                     */
1548:                    private static class UnmodifiableEntry implements  Map.Entry {
1549:                        private Map.Entry e;
1550:
1551:                        UnmodifiableEntry(Map.Entry e) {
1552:                            this .e = e;
1553:                        }
1554:
1555:                        public Object getKey() {
1556:                            return e.getKey();
1557:                        }
1558:
1559:                        public Object getValue() {
1560:                            return e.getValue();
1561:                        }
1562:
1563:                        public Object setValue(Object value) {
1564:                            throw new UnsupportedOperationException();
1565:                        }
1566:
1567:                        public int hashCode() {
1568:                            return e.hashCode();
1569:                        }
1570:
1571:                        public boolean equals(Object o) {
1572:                            if (!(o instanceof  Map.Entry))
1573:                                return false;
1574:                            Map.Entry t = (Map.Entry) o;
1575:                            return eq(e.getKey(), t.getKey())
1576:                                    && eq(e.getValue(), t.getValue());
1577:                        }
1578:
1579:                        public String toString() {
1580:                            return e.toString();
1581:                        }
1582:                    }
1583:                }
1584:            }
1585:
1586:            /**
1587:             * Returns an unmodifiable view of the specified sorted map.  This method
1588:             * allows modules to provide users with "read-only" access to internal
1589:             * sorted maps.  Query operations on the returned sorted map "read through"
1590:             * to the specified sorted map.  Attempts to modify the returned
1591:             * sorted map, whether direct, via its collection views, or via its
1592:             * <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in
1593:             * an <tt>UnsupportedOperationException</tt>.<p>
1594:             *
1595:             * The returned sorted map will be serializable if the specified sorted map
1596:             * is serializable. 
1597:             *
1598:             * @param m the sorted map for which an unmodifiable view is to be
1599:             *        returned. 
1600:             * @return an unmodifiable view of the specified sorted map.
1601:             */
1602:            public static SortedMap unmodifiableSortedMap(SortedMap m) {
1603:                return new UnmodifiableSortedMap(m);
1604:            }
1605:
1606:            /**
1607:             * @serial include
1608:             */
1609:            static class UnmodifiableSortedMap extends UnmodifiableMap
1610:                    implements  SortedMap, Serializable {
1611:                private SortedMap sm;
1612:
1613:                UnmodifiableSortedMap(SortedMap m) {
1614:                    super (m);
1615:                    sm = m;
1616:                }
1617:
1618:                public Comparator comparator() {
1619:                    return sm.comparator();
1620:                }
1621:
1622:                public SortedMap subMap(Object fromKey, Object toKey) {
1623:                    return new UnmodifiableSortedMap(sm.subMap(fromKey, toKey));
1624:                }
1625:
1626:                public SortedMap headMap(Object toKey) {
1627:                    return new UnmodifiableSortedMap(sm.headMap(toKey));
1628:                }
1629:
1630:                public SortedMap tailMap(Object fromKey) {
1631:                    return new UnmodifiableSortedMap(sm.tailMap(fromKey));
1632:                }
1633:
1634:                public Object firstKey() {
1635:                    return sm.firstKey();
1636:                }
1637:
1638:                public Object lastKey() {
1639:                    return sm.lastKey();
1640:                }
1641:            }
1642:
1643:            // Synch Wrappers
1644:
1645:            /**
1646:             * Returns a synchronized (thread-safe) collection backed by the specified
1647:             * collection.  In order to guarantee serial access, it is critical that
1648:             * <strong>all</strong> access to the backing collection is accomplished
1649:             * through the returned collection.<p>
1650:             *
1651:             * It is imperative that the user manually synchronize on the returned
1652:             * collection when iterating over it:
1653:             * <pre>
1654:             *  Collection c = Collections.synchronizedCollection(myCollection);
1655:             *     ...
1656:             *  synchronized(c) {
1657:             *      Iterator i = c.iterator(); // Must be in the synchronized block
1658:             *      while (i.hasNext())
1659:             *         foo(i.next());
1660:             *  }
1661:             * </pre>
1662:             * Failure to follow this advice may result in non-deterministic behavior.
1663:             *
1664:             * <p>The returned collection does <i>not</i> pass the <tt>hashCode</tt>
1665:             * and <tt>equals</tt> operations through to the backing collection, but
1666:             * relies on <tt>Object</tt>'s equals and hashCode methods.  This is
1667:             * necessary to preserve the contracts of these operations in the case
1668:             * that the backing collection is a set or a list.<p>
1669:             *
1670:             * The returned collection will be serializable if the specified collection
1671:             * is serializable. 
1672:             *
1673:             * @param  c the collection to be "wrapped" in a synchronized collection.
1674:             * @return a synchronized view of the specified collection.
1675:             */
1676:            public static Collection synchronizedCollection(Collection c) {
1677:                return new SynchronizedCollection(c);
1678:            }
1679:
1680:            static Collection synchronizedCollection(Collection c, Object mutex) {
1681:                return new SynchronizedCollection(c, mutex);
1682:            }
1683:
1684:            /**
1685:             * @serial include
1686:             */
1687:            static class SynchronizedCollection implements  Collection,
1688:                    Serializable {
1689:                // use serialVersionUID from JDK 1.2.2 for interoperability
1690:                private static final long serialVersionUID = 3053995032091335093L;
1691:
1692:                Collection c; // Backing Collection
1693:                Object mutex; // Object on which to synchronize
1694:
1695:                SynchronizedCollection(Collection c) {
1696:                    if (c == null)
1697:                        throw new NullPointerException();
1698:                    this .c = c;
1699:                    mutex = this ;
1700:                }
1701:
1702:                SynchronizedCollection(Collection c, Object mutex) {
1703:                    this .c = c;
1704:                    this .mutex = mutex;
1705:                }
1706:
1707:                public int size() {
1708:                    synchronized (mutex) {
1709:                        return c.size();
1710:                    }
1711:                }
1712:
1713:                public boolean isEmpty() {
1714:                    synchronized (mutex) {
1715:                        return c.isEmpty();
1716:                    }
1717:                }
1718:
1719:                public boolean contains(Object o) {
1720:                    synchronized (mutex) {
1721:                        return c.contains(o);
1722:                    }
1723:                }
1724:
1725:                public Object[] toArray() {
1726:                    synchronized (mutex) {
1727:                        return c.toArray();
1728:                    }
1729:                }
1730:
1731:                public Object[] toArray(Object[] a) {
1732:                    synchronized (mutex) {
1733:                        return c.toArray(a);
1734:                    }
1735:                }
1736:
1737:                public Iterator iterator() {
1738:                    return c.iterator(); // Must be manually synched by user!
1739:                }
1740:
1741:                public boolean add(Object o) {
1742:                    synchronized (mutex) {
1743:                        return c.add(o);
1744:                    }
1745:                }
1746:
1747:                public boolean remove(Object o) {
1748:                    synchronized (mutex) {
1749:                        return c.remove(o);
1750:                    }
1751:                }
1752:
1753:                public boolean containsAll(Collection coll) {
1754:                    synchronized (mutex) {
1755:                        return c.containsAll(coll);
1756:                    }
1757:                }
1758:
1759:                public boolean addAll(Collection coll) {
1760:                    synchronized (mutex) {
1761:                        return c.addAll(coll);
1762:                    }
1763:                }
1764:
1765:                public boolean removeAll(Collection coll) {
1766:                    synchronized (mutex) {
1767:                        return c.removeAll(coll);
1768:                    }
1769:                }
1770:
1771:                public boolean retainAll(Collection coll) {
1772:                    synchronized (mutex) {
1773:                        return c.retainAll(coll);
1774:                    }
1775:                }
1776:
1777:                public void clear() {
1778:                    synchronized (mutex) {
1779:                        c.clear();
1780:                    }
1781:                }
1782:
1783:                public String toString() {
1784:                    synchronized (mutex) {
1785:                        return c.toString();
1786:                    }
1787:                }
1788:            }
1789:
1790:            /**
1791:             * Returns a synchronized (thread-safe) set backed by the specified
1792:             * set.  In order to guarantee serial access, it is critical that
1793:             * <strong>all</strong> access to the backing set is accomplished
1794:             * through the returned set.<p>
1795:             *
1796:             * It is imperative that the user manually synchronize on the returned
1797:             * set when iterating over it:
1798:             * <pre>
1799:             *  Set s = Collections.synchronizedSet(new HashSet());
1800:             *      ...
1801:             *  synchronized(s) {
1802:             *      Iterator i = s.iterator(); // Must be in the synchronized block
1803:             *      while (i.hasNext())
1804:             *          foo(i.next());
1805:             *  }
1806:             * </pre>
1807:             * Failure to follow this advice may result in non-deterministic behavior.
1808:             *
1809:             * <p>The returned set will be serializable if the specified set is
1810:             * serializable.
1811:             *
1812:             * @param  s the set to be "wrapped" in a synchronized set.
1813:             * @return a synchronized view of the specified set.
1814:             */
1815:            public static Set synchronizedSet(Set s) {
1816:                return new SynchronizedSet(s);
1817:            }
1818:
1819:            static Set synchronizedSet(Set s, Object mutex) {
1820:                return new SynchronizedSet(s, mutex);
1821:            }
1822:
1823:            /**
1824:             * @serial include
1825:             */
1826:            static class SynchronizedSet extends SynchronizedCollection
1827:                    implements  Set {
1828:                SynchronizedSet(Set s) {
1829:                    super (s);
1830:                }
1831:
1832:                SynchronizedSet(Set s, Object mutex) {
1833:                    super (s, mutex);
1834:                }
1835:
1836:                public boolean equals(Object o) {
1837:                    synchronized (mutex) {
1838:                        return c.equals(o);
1839:                    }
1840:                }
1841:
1842:                public int hashCode() {
1843:                    synchronized (mutex) {
1844:                        return c.hashCode();
1845:                    }
1846:                }
1847:            }
1848:
1849:            /**
1850:             * Returns a synchronized (thread-safe) sorted set backed by the specified
1851:             * sorted set.  In order to guarantee serial access, it is critical that
1852:             * <strong>all</strong> access to the backing sorted set is accomplished
1853:             * through the returned sorted set (or its views).<p>
1854:             *
1855:             * It is imperative that the user manually synchronize on the returned
1856:             * sorted set when iterating over it or any of its <tt>subSet</tt>,
1857:             * <tt>headSet</tt>, or <tt>tailSet</tt> views.
1858:             * <pre>
1859:             *  SortedSet s = Collections.synchronizedSortedSet(new HashSortedSet());
1860:             *      ...
1861:             *  synchronized(s) {
1862:             *      Iterator i = s.iterator(); // Must be in the synchronized block
1863:             *      while (i.hasNext())
1864:             *          foo(i.next());
1865:             *  }
1866:             * </pre>
1867:             * or:
1868:             * <pre>
1869:             *  SortedSet s = Collections.synchronizedSortedSet(new HashSortedSet());
1870:             *  SortedSet s2 = s.headSet(foo);
1871:             *      ...
1872:             *  synchronized(s) {  // Note: s, not s2!!!
1873:             *      Iterator i = s2.iterator(); // Must be in the synchronized block
1874:             *      while (i.hasNext())
1875:             *          foo(i.next());
1876:             *  }
1877:             * </pre>
1878:             * Failure to follow this advice may result in non-deterministic behavior.
1879:             *
1880:             * <p>The returned sorted set will be serializable if the specified
1881:             * sorted set is serializable.
1882:             *
1883:             * @param  s the sorted set to be "wrapped" in a synchronized sorted set.
1884:             * @return a synchronized view of the specified sorted set.
1885:             */
1886:            public static SortedSet synchronizedSortedSet(SortedSet s) {
1887:                return new SynchronizedSortedSet(s);
1888:            }
1889:
1890:            /**
1891:             * @serial include
1892:             */
1893:            static class SynchronizedSortedSet extends SynchronizedSet
1894:                    implements  SortedSet {
1895:                private SortedSet ss;
1896:
1897:                SynchronizedSortedSet(SortedSet s) {
1898:                    super (s);
1899:                    ss = s;
1900:                }
1901:
1902:                SynchronizedSortedSet(SortedSet s, Object mutex) {
1903:                    super (s, mutex);
1904:                    ss = s;
1905:                }
1906:
1907:                public Comparator comparator() {
1908:                    synchronized (mutex) {
1909:                        return ss.comparator();
1910:                    }
1911:                }
1912:
1913:                public SortedSet subSet(Object fromElement, Object toElement) {
1914:                    synchronized (mutex) {
1915:                        return new SynchronizedSortedSet(ss.subSet(fromElement,
1916:                                toElement), mutex);
1917:                    }
1918:                }
1919:
1920:                public SortedSet headSet(Object toElement) {
1921:                    synchronized (mutex) {
1922:                        return new SynchronizedSortedSet(ss.headSet(toElement),
1923:                                mutex);
1924:                    }
1925:                }
1926:
1927:                public SortedSet tailSet(Object fromElement) {
1928:                    synchronized (mutex) {
1929:                        return new SynchronizedSortedSet(ss
1930:                                .tailSet(fromElement), mutex);
1931:                    }
1932:                }
1933:
1934:                public Object first() {
1935:                    synchronized (mutex) {
1936:                        return ss.first();
1937:                    }
1938:                }
1939:
1940:                public Object last() {
1941:                    synchronized (mutex) {
1942:                        return ss.last();
1943:                    }
1944:                }
1945:            }
1946:
1947:            /**
1948:             * Returns a synchronized (thread-safe) list backed by the specified
1949:             * list.  In order to guarantee serial access, it is critical that
1950:             * <strong>all</strong> access to the backing list is accomplished
1951:             * through the returned list.<p>
1952:             *
1953:             * It is imperative that the user manually synchronize on the returned
1954:             * list when iterating over it:
1955:             * <pre>
1956:             *  List list = Collections.synchronizedList(new ArrayList());
1957:             *      ...
1958:             *  synchronized(list) {
1959:             *      Iterator i = list.iterator(); // Must be in synchronized block
1960:             *      while (i.hasNext())
1961:             *          foo(i.next());
1962:             *  }
1963:             * </pre>
1964:             * Failure to follow this advice may result in non-deterministic behavior.
1965:             *
1966:             * <p>The returned list will be serializable if the specified list is
1967:             * serializable.
1968:             *
1969:             * @param  list the list to be "wrapped" in a synchronized list.
1970:             * @return a synchronized view of the specified list.
1971:             */
1972:            public static List synchronizedList(List list) {
1973:                return (list instanceof  RandomAccess ? new SynchronizedRandomAccessList(
1974:                        list)
1975:                        : new SynchronizedList(list));
1976:            }
1977:
1978:            static List synchronizedList(List list, Object mutex) {
1979:                return (list instanceof  RandomAccess ? new SynchronizedRandomAccessList(
1980:                        list, mutex)
1981:                        : new SynchronizedList(list, mutex));
1982:            }
1983:
1984:            /**
1985:             * @serial include
1986:             */
1987:            static class SynchronizedList extends SynchronizedCollection
1988:                    implements  List {
1989:                static final long serialVersionUID = -7754090372962971524L;
1990:
1991:                List list;
1992:
1993:                SynchronizedList(List list) {
1994:                    super (list);
1995:                    this .list = list;
1996:                }
1997:
1998:                SynchronizedList(List list, Object mutex) {
1999:                    super (list, mutex);
2000:                    this .list = list;
2001:                }
2002:
2003:                public boolean equals(Object o) {
2004:                    synchronized (mutex) {
2005:                        return list.equals(o);
2006:                    }
2007:                }
2008:
2009:                public int hashCode() {
2010:                    synchronized (mutex) {
2011:                        return list.hashCode();
2012:                    }
2013:                }
2014:
2015:                public Object get(int index) {
2016:                    synchronized (mutex) {
2017:                        return list.get(index);
2018:                    }
2019:                }
2020:
2021:                public Object set(int index, Object element) {
2022:                    synchronized (mutex) {
2023:                        return list.set(index, element);
2024:                    }
2025:                }
2026:
2027:                public void add(int index, Object element) {
2028:                    synchronized (mutex) {
2029:                        list.add(index, element);
2030:                    }
2031:                }
2032:
2033:                public Object remove(int index) {
2034:                    synchronized (mutex) {
2035:                        return list.remove(index);
2036:                    }
2037:                }
2038:
2039:                public int indexOf(Object o) {
2040:                    synchronized (mutex) {
2041:                        return list.indexOf(o);
2042:                    }
2043:                }
2044:
2045:                public int lastIndexOf(Object o) {
2046:                    synchronized (mutex) {
2047:                        return list.lastIndexOf(o);
2048:                    }
2049:                }
2050:
2051:                public boolean addAll(int index, Collection c) {
2052:                    synchronized (mutex) {
2053:                        return list.addAll(index, c);
2054:                    }
2055:                }
2056:
2057:                public ListIterator listIterator() {
2058:                    return list.listIterator(); // Must be manually synched by user
2059:                }
2060:
2061:                public ListIterator listIterator(int index) {
2062:                    return list.listIterator(index); // Must be manually synched by usr
2063:                }
2064:
2065:                public List subList(int fromIndex, int toIndex) {
2066:                    synchronized (mutex) {
2067:                        return new SynchronizedList(list.subList(fromIndex,
2068:                                toIndex), mutex);
2069:                    }
2070:                }
2071:
2072:                /**
2073:                 * SynchronizedRandomAccessList instances are serialized as
2074:                 * SynchronizedList instances to allow them to be deserialized
2075:                 * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList).
2076:                 * This method inverts the transformation.  As a beneficial
2077:                 * side-effect, it also grafts the RandomAccess marker onto
2078:                 * SynchronizedList instances that were serialized in pre-1.4 JREs.
2079:                 *
2080:                 * Note: Unfortunately, SynchronizedRandomAccessList instances
2081:                 * serialized in 1.4.1 and deserialized in 1.4 will become
2082:                 * SynchronizedList instances, as this method was missing in 1.4.
2083:                 */
2084:                private Object readResolve() {
2085:                    return (list instanceof  RandomAccess ? new SynchronizedRandomAccessList(
2086:                            list)
2087:                            : this );
2088:                }
2089:            }
2090:
2091:            /**
2092:             * @serial include
2093:             */
2094:            static class SynchronizedRandomAccessList extends SynchronizedList
2095:                    implements  RandomAccess {
2096:                SynchronizedRandomAccessList(List list) {
2097:                    super (list);
2098:                }
2099:
2100:                SynchronizedRandomAccessList(List list, Object mutex) {
2101:                    super (list, mutex);
2102:                }
2103:
2104:                public List subList(int fromIndex, int toIndex) {
2105:                    synchronized (mutex) {
2106:                        return new SynchronizedRandomAccessList(list.subList(
2107:                                fromIndex, toIndex), mutex);
2108:                    }
2109:                }
2110:
2111:                static final long serialVersionUID = 1530674583602358482L;
2112:
2113:                /**
2114:                 * Allows instances to be deserialized in pre-1.4 JREs (which do
2115:                 * not have SynchronizedRandomAccessList).  SynchronizedList has
2116:                 * a readResolve method that inverts this transformation upon
2117:                 * deserialization.
2118:                 */
2119:                private Object writeReplace() {
2120:                    return new SynchronizedList(list);
2121:                }
2122:            }
2123:
2124:            /**
2125:             * Returns a synchronized (thread-safe) map backed by the specified
2126:             * map.  In order to guarantee serial access, it is critical that
2127:             * <strong>all</strong> access to the backing map is accomplished
2128:             * through the returned map.<p>
2129:             *
2130:             * It is imperative that the user manually synchronize on the returned
2131:             * map when iterating over any of its collection views:
2132:             * <pre>
2133:             *  Map m = Collections.synchronizedMap(new HashMap());
2134:             *      ...
2135:             *  Set s = m.keySet();  // Needn't be in synchronized block
2136:             *      ...
2137:             *  synchronized(m) {  // Synchronizing on m, not s!
2138:             *      Iterator i = s.iterator(); // Must be in synchronized block
2139:             *      while (i.hasNext())
2140:             *          foo(i.next());
2141:             *  }
2142:             * </pre>
2143:             * Failure to follow this advice may result in non-deterministic behavior.
2144:             *
2145:             * <p>The returned map will be serializable if the specified map is
2146:             * serializable.
2147:             *
2148:             * @param  m the map to be "wrapped" in a synchronized map.
2149:             * @return a synchronized view of the specified map.
2150:             */
2151:            public static Map synchronizedMap(Map m) {
2152:                return new SynchronizedMap(m);
2153:            }
2154:
2155:            /**
2156:             * @serial include
2157:             */
2158:            private static class SynchronizedMap implements  Map, Serializable {
2159:                // use serialVersionUID from JDK 1.2.2 for interoperability
2160:                private static final long serialVersionUID = 1978198479659022715L;
2161:
2162:                private Map m; // Backing Map
2163:                Object mutex; // Object on which to synchronize
2164:
2165:                SynchronizedMap(Map m) {
2166:                    if (m == null)
2167:                        throw new NullPointerException();
2168:                    this .m = m;
2169:                    mutex = this ;
2170:                }
2171:
2172:                SynchronizedMap(Map m, Object mutex) {
2173:                    this .m = m;
2174:                    this .mutex = mutex;
2175:                }
2176:
2177:                public int size() {
2178:                    synchronized (mutex) {
2179:                        return m.size();
2180:                    }
2181:                }
2182:
2183:                public boolean isEmpty() {
2184:                    synchronized (mutex) {
2185:                        return m.isEmpty();
2186:                    }
2187:                }
2188:
2189:                public boolean containsKey(Object key) {
2190:                    synchronized (mutex) {
2191:                        return m.containsKey(key);
2192:                    }
2193:                }
2194:
2195:                public boolean containsValue(Object value) {
2196:                    synchronized (mutex) {
2197:                        return m.containsValue(value);
2198:                    }
2199:                }
2200:
2201:                public Object get(Object key) {
2202:                    synchronized (mutex) {
2203:                        return m.get(key);
2204:                    }
2205:                }
2206:
2207:                public Object put(Object key, Object value) {
2208:                    synchronized (mutex) {
2209:                        return m.put(key, value);
2210:                    }
2211:                }
2212:
2213:                public Object remove(Object key) {
2214:                    synchronized (mutex) {
2215:                        return m.remove(key);
2216:                    }
2217:                }
2218:
2219:                public void putAll(Map map) {
2220:                    synchronized (mutex) {
2221:                        m.putAll(map);
2222:                    }
2223:                }
2224:
2225:                public void clear() {
2226:                    synchronized (mutex) {
2227:                        m.clear();
2228:                    }
2229:                }
2230:
2231:                private transient Set keySet = null;
2232:                private transient Set entrySet = null;
2233:                private transient Collection values = null;
2234:
2235:                public Set keySet() {
2236:                    synchronized (mutex) {
2237:                        if (keySet == null)
2238:                            keySet = new SynchronizedSet(m.keySet(), mutex);
2239:                        return keySet;
2240:                    }
2241:                }
2242:
2243:                public Set entrySet() {
2244:                    synchronized (mutex) {
2245:                        if (entrySet == null)
2246:                            entrySet = new SynchronizedSet(m.entrySet(), mutex);
2247:                        return entrySet;
2248:                    }
2249:                }
2250:
2251:                public Collection values() {
2252:                    synchronized (mutex) {
2253:                        if (values == null)
2254:                            values = new SynchronizedCollection(m.values(),
2255:                                    mutex);
2256:                        return values;
2257:                    }
2258:                }
2259:
2260:                public boolean equals(Object o) {
2261:                    synchronized (mutex) {
2262:                        return m.equals(o);
2263:                    }
2264:                }
2265:
2266:                public int hashCode() {
2267:                    synchronized (mutex) {
2268:                        return m.hashCode();
2269:                    }
2270:                }
2271:
2272:                public String toString() {
2273:                    synchronized (mutex) {
2274:                        return m.toString();
2275:                    }
2276:                }
2277:            }
2278:
2279:            /**
2280:             * Returns a synchronized (thread-safe) sorted map backed by the specified
2281:             * sorted map.  In order to guarantee serial access, it is critical that
2282:             * <strong>all</strong> access to the backing sorted map is accomplished
2283:             * through the returned sorted map (or its views).<p>
2284:             *
2285:             * It is imperative that the user manually synchronize on the returned
2286:             * sorted map when iterating over any of its collection views, or the
2287:             * collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or
2288:             * <tt>tailMap</tt> views.
2289:             * <pre>
2290:             *  SortedMap m = Collections.synchronizedSortedMap(new HashSortedMap());
2291:             *      ...
2292:             *  Set s = m.keySet();  // Needn't be in synchronized block
2293:             *      ...
2294:             *  synchronized(m) {  // Synchronizing on m, not s!
2295:             *      Iterator i = s.iterator(); // Must be in synchronized block
2296:             *      while (i.hasNext())
2297:             *          foo(i.next());
2298:             *  }
2299:             * </pre>
2300:             * or:
2301:             * <pre>
2302:             *  SortedMap m = Collections.synchronizedSortedMap(new HashSortedMap());
2303:             *  SortedMap m2 = m.subMap(foo, bar);
2304:             *      ...
2305:             *  Set s2 = m2.keySet();  // Needn't be in synchronized block
2306:             *      ...
2307:             *  synchronized(m) {  // Synchronizing on m, not m2 or s2!
2308:             *      Iterator i = s.iterator(); // Must be in synchronized block
2309:             *      while (i.hasNext())
2310:             *          foo(i.next());
2311:             *  }
2312:             * </pre>
2313:             * Failure to follow this advice may result in non-deterministic behavior.
2314:             *
2315:             * <p>The returned sorted map will be serializable if the specified
2316:             * sorted map is serializable.
2317:             *
2318:             * @param  m the sorted map to be "wrapped" in a synchronized sorted map.
2319:             * @return a synchronized view of the specified sorted map.
2320:             */
2321:            public static SortedMap synchronizedSortedMap(SortedMap m) {
2322:                return new SynchronizedSortedMap(m);
2323:            }
2324:
2325:            /**
2326:             * @serial include
2327:             */
2328:            static class SynchronizedSortedMap extends SynchronizedMap
2329:                    implements  SortedMap {
2330:                private SortedMap sm;
2331:
2332:                SynchronizedSortedMap(SortedMap m) {
2333:                    super (m);
2334:                    sm = m;
2335:                }
2336:
2337:                SynchronizedSortedMap(SortedMap m, Object mutex) {
2338:                    super (m, mutex);
2339:                    sm = m;
2340:                }
2341:
2342:                public Comparator comparator() {
2343:                    synchronized (mutex) {
2344:                        return sm.comparator();
2345:                    }
2346:                }
2347:
2348:                public SortedMap subMap(Object fromKey, Object toKey) {
2349:                    synchronized (mutex) {
2350:                        return new SynchronizedSortedMap(sm.subMap(fromKey,
2351:                                toKey), mutex);
2352:                    }
2353:                }
2354:
2355:                public SortedMap headMap(Object toKey) {
2356:                    synchronized (mutex) {
2357:                        return new SynchronizedSortedMap(sm.headMap(toKey),
2358:                                mutex);
2359:                    }
2360:                }
2361:
2362:                public SortedMap tailMap(Object fromKey) {
2363:                    synchronized (mutex) {
2364:                        return new SynchronizedSortedMap(sm.tailMap(fromKey),
2365:                                mutex);
2366:                    }
2367:                }
2368:
2369:                public Object firstKey() {
2370:                    synchronized (mutex) {
2371:                        return sm.firstKey();
2372:                    }
2373:                }
2374:
2375:                public Object lastKey() {
2376:                    synchronized (mutex) {
2377:                        return sm.lastKey();
2378:                    }
2379:                }
2380:            }
2381:
2382:            // Miscellaneous
2383:
2384:            /**
2385:             * The empty set (immutable).  This set is serializable.
2386:             */
2387:            public static final Set EMPTY_SET = new EmptySet();
2388:
2389:            /**
2390:             * @serial include
2391:             */
2392:            private static class EmptySet extends AbstractSet implements 
2393:                    Serializable {
2394:                // use serialVersionUID from JDK 1.2.2 for interoperability
2395:                private static final long serialVersionUID = 1582296315990362920L;
2396:
2397:                public Iterator iterator() {
2398:                    return new Iterator() {
2399:                        public boolean hasNext() {
2400:                            return false;
2401:                        }
2402:
2403:                        public Object next() {
2404:                            throw new NoSuchElementException();
2405:                        }
2406:
2407:                        public void remove() {
2408:                            throw new UnsupportedOperationException();
2409:                        }
2410:                    };
2411:                }
2412:
2413:                public int size() {
2414:                    return 0;
2415:                }
2416:
2417:                public boolean contains(Object obj) {
2418:                    return false;
2419:                }
2420:
2421:                // Preserves singleton property
2422:                private Object readResolve() {
2423:                    return EMPTY_SET;
2424:                }
2425:            }
2426:
2427:            /**
2428:             * The empty list (immutable).  This list is serializable.
2429:             */
2430:            public static final List EMPTY_LIST = new EmptyList();
2431:
2432:            /**
2433:             * @serial include
2434:             */
2435:            private static class EmptyList extends AbstractList implements 
2436:                    RandomAccess, Serializable {
2437:                // use serialVersionUID from JDK 1.2.2 for interoperability
2438:                private static final long serialVersionUID = 8842843931221139166L;
2439:
2440:                public int size() {
2441:                    return 0;
2442:                }
2443:
2444:                public boolean contains(Object obj) {
2445:                    return false;
2446:                }
2447:
2448:                public Object get(int index) {
2449:                    throw new IndexOutOfBoundsException("Index: " + index);
2450:                }
2451:
2452:                // Preserves singleton property
2453:                private Object readResolve() {
2454:                    return EMPTY_LIST;
2455:                }
2456:            }
2457:
2458:            /**
2459:             * The empty map (immutable).  This map is serializable.
2460:             *
2461:             * @since 1.3
2462:             */
2463:            public static final Map EMPTY_MAP = new EmptyMap();
2464:
2465:            private static class EmptyMap extends AbstractMap implements 
2466:                    Serializable {
2467:                private static final long serialVersionUID = 6428348081105594320L;
2468:
2469:                public int size() {
2470:                    return 0;
2471:                }
2472:
2473:                public boolean isEmpty() {
2474:                    return true;
2475:                }
2476:
2477:                public boolean containsKey(Object key) {
2478:                    return false;
2479:                }
2480:
2481:                public boolean containsValue(Object value) {
2482:                    return false;
2483:                }
2484:
2485:                public Object get(Object key) {
2486:                    return null;
2487:                }
2488:
2489:                public Set keySet() {
2490:                    return EMPTY_SET;
2491:                }
2492:
2493:                public Collection values() {
2494:                    return EMPTY_SET;
2495:                }
2496:
2497:                public Set entrySet() {
2498:                    return EMPTY_SET;
2499:                }
2500:
2501:                public boolean equals(Object o) {
2502:                    return (o instanceof  Map) && ((Map) o).size() == 0;
2503:                }
2504:
2505:                public int hashCode() {
2506:                    return 0;
2507:                }
2508:
2509:                // Preserves singleton property
2510:                private Object readResolve() {
2511:                    return EMPTY_MAP;
2512:                }
2513:            }
2514:
2515:            /**
2516:             * Returns an immutable set containing only the specified object.
2517:             * The returned set is serializable.
2518:             *
2519:             * @param o the sole object to be stored in the returned set.
2520:             * @return an immutable set containing only the specified object.
2521:             */
2522:            public static Set singleton(Object o) {
2523:                return new SingletonSet(o);
2524:            }
2525:
2526:            /**
2527:             * @serial include
2528:             */
2529:            private static class SingletonSet extends AbstractSet implements 
2530:                    Serializable {
2531:                // use serialVersionUID from JDK 1.2.2 for interoperability
2532:                private static final long serialVersionUID = 3193687207550431679L;
2533:
2534:                private Object element;
2535:
2536:                SingletonSet(Object o) {
2537:                    element = o;
2538:                }
2539:
2540:                public Iterator iterator() {
2541:                    return new Iterator() {
2542:                        private boolean hasNext = true;
2543:
2544:                        public boolean hasNext() {
2545:                            return hasNext;
2546:                        }
2547:
2548:                        public Object next() {
2549:                            if (hasNext) {
2550:                                hasNext = false;
2551:                                return element;
2552:                            }
2553:                            throw new NoSuchElementException();
2554:                        }
2555:
2556:                        public void remove() {
2557:                            throw new UnsupportedOperationException();
2558:                        }
2559:                    };
2560:                }
2561:
2562:                public int size() {
2563:                    return 1;
2564:                }
2565:
2566:                public boolean contains(Object o) {
2567:                    return eq(o, element);
2568:                }
2569:            }
2570:
2571:            /**
2572:             * Returns an immutable list containing only the specified object.
2573:             * The returned list is serializable.
2574:             *
2575:             * @param o the sole object to be stored in the returned list.
2576:             * @return an immutable list containing only the specified object.
2577:             * @since 1.3
2578:             */
2579:            public static List singletonList(Object o) {
2580:                return new SingletonList(o);
2581:            }
2582:
2583:            private static class SingletonList extends AbstractList implements 
2584:                    RandomAccess, Serializable {
2585:                static final long serialVersionUID = 3093736618740652951L;
2586:
2587:                private final Object element;
2588:
2589:                SingletonList(Object obj) {
2590:                    element = obj;
2591:                }
2592:
2593:                public int size() {
2594:                    return 1;
2595:                }
2596:
2597:                public boolean contains(Object obj) {
2598:                    return eq(obj, element);
2599:                }
2600:
2601:                public Object get(int index) {
2602:                    if (index != 0)
2603:                        throw new IndexOutOfBoundsException("Index: " + index
2604:                                + ", Size: 1");
2605:                    return element;
2606:                }
2607:            }
2608:
2609:            /**
2610:             * Returns an immutable map, mapping only the specified key to the
2611:             * specified value.  The returned map is serializable.
2612:             *
2613:             * @param key the sole key to be stored in the returned map.
2614:             * @param value the value to which the returned map maps <tt>key</tt>.
2615:             * @return an immutable map containing only the specified key-value
2616:             *         mapping.
2617:             * @since 1.3
2618:             */
2619:            public static Map singletonMap(Object key, Object value) {
2620:                return new SingletonMap(key, value);
2621:            }
2622:
2623:            private static class SingletonMap extends AbstractMap implements 
2624:                    Serializable {
2625:                private final Object k, v;
2626:
2627:                SingletonMap(Object key, Object value) {
2628:                    k = key;
2629:                    v = value;
2630:                }
2631:
2632:                public int size() {
2633:                    return 1;
2634:                }
2635:
2636:                public boolean isEmpty() {
2637:                    return false;
2638:                }
2639:
2640:                public boolean containsKey(Object key) {
2641:                    return eq(key, k);
2642:                }
2643:
2644:                public boolean containsValue(Object value) {
2645:                    return eq(value, v);
2646:                }
2647:
2648:                public Object get(Object key) {
2649:                    return (eq(key, k) ? v : null);
2650:                }
2651:
2652:                private transient Set keySet = null;
2653:                private transient Set entrySet = null;
2654:                private transient Collection values = null;
2655:
2656:                public Set keySet() {
2657:                    if (keySet == null)
2658:                        keySet = singleton(k);
2659:                    return keySet;
2660:                }
2661:
2662:                public Set entrySet() {
2663:                    if (entrySet == null)
2664:                        entrySet = singleton(new ImmutableEntry(k, v));
2665:                    return entrySet;
2666:                }
2667:
2668:                public Collection values() {
2669:                    if (values == null)
2670:                        values = singleton(v);
2671:                    return values;
2672:                }
2673:
2674:                private static class ImmutableEntry implements  Map.Entry {
2675:                    final Object k;
2676:                    final Object v;
2677:
2678:                    ImmutableEntry(Object key, Object value) {
2679:                        k = key;
2680:                        v = value;
2681:                    }
2682:
2683:                    public Object getKey() {
2684:                        return k;
2685:                    }
2686:
2687:                    public Object getValue() {
2688:                        return v;
2689:                    }
2690:
2691:                    public Object setValue(Object value) {
2692:                        throw new UnsupportedOperationException();
2693:                    }
2694:
2695:                    public boolean equals(Object o) {
2696:                        if (!(o instanceof  Map.Entry))
2697:                            return false;
2698:                        Map.Entry e = (Map.Entry) o;
2699:                        return eq(e.getKey(), k) && eq(e.getValue(), v);
2700:                    }
2701:
2702:                    public int hashCode() {
2703:                        return ((k == null ? 0 : k.hashCode()) ^ (v == null ? 0
2704:                                : v.hashCode()));
2705:                    }
2706:
2707:                    public String toString() {
2708:                        return k + "=" + v;
2709:                    }
2710:                }
2711:            }
2712:
2713:            /**
2714:             * Returns an immutable list consisting of <tt>n</tt> copies of the
2715:             * specified object.  The newly allocated data object is tiny (it contains
2716:             * a single reference to the data object).  This method is useful in
2717:             * combination with the <tt>List.addAll</tt> method to grow lists.
2718:             * The returned list is serializable.
2719:             *
2720:             * @param  n the number of elements in the returned list.
2721:             * @param  o the element to appear repeatedly in the returned list.
2722:             * @return an immutable list consisting of <tt>n</tt> copies of the
2723:             * 	       specified object.
2724:             * @throws IllegalArgumentException if n &lt; 0.
2725:             * @see    List#addAll(Collection)
2726:             * @see    List#addAll(int, Collection)
2727:             */
2728:            public static List nCopies(int n, Object o) {
2729:                return new CopiesList(n, o);
2730:            }
2731:
2732:            /**
2733:             * @serial include
2734:             */
2735:            private static class CopiesList extends AbstractList implements 
2736:                    RandomAccess, Serializable {
2737:                static final long serialVersionUID = 2739099268398711800L;
2738:
2739:                int n;
2740:                Object element;
2741:
2742:                CopiesList(int n, Object o) {
2743:                    if (n < 0)
2744:                        throw new IllegalArgumentException("List length = " + n);
2745:                    this .n = n;
2746:                    element = o;
2747:                }
2748:
2749:                public int size() {
2750:                    return n;
2751:                }
2752:
2753:                public boolean contains(Object obj) {
2754:                    return n != 0 && eq(obj, element);
2755:                }
2756:
2757:                public Object get(int index) {
2758:                    if (index < 0 || index >= n)
2759:                        throw new IndexOutOfBoundsException("Index: " + index
2760:                                + ", Size: " + n);
2761:                    return element;
2762:                }
2763:            }
2764:
2765:            /**
2766:             * Returns a comparator that imposes the reverse of the <i>natural
2767:             * ordering</i> on a collection of objects that implement the
2768:             * <tt>Comparable</tt> interface.  (The natural ordering is the ordering
2769:             * imposed by the objects' own <tt>compareTo</tt> method.)  This enables a
2770:             * simple idiom for sorting (or maintaining) collections (or arrays) of
2771:             * objects that implement the <tt>Comparable</tt> interface in
2772:             * reverse-natural-order.  For example, suppose a is an array of
2773:             * strings. Then: <pre>
2774:             * 		Arrays.sort(a, Collections.reverseOrder());
2775:             * </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p>
2776:             *
2777:             * The returned comparator is serializable.
2778:             *
2779:             * @return a comparator that imposes the reverse of the <i>natural
2780:             * 	       ordering</i> on a collection of objects that implement
2781:             *	       the <tt>Comparable</tt> interface.
2782:             * @see Comparable
2783:             */
2784:            public static Comparator reverseOrder() {
2785:                return REVERSE_ORDER;
2786:            }
2787:
2788:            private static final Comparator REVERSE_ORDER = new ReverseComparator();
2789:
2790:            /**
2791:             * @serial include
2792:             */
2793:            private static class ReverseComparator implements  Comparator,
2794:                    Serializable {
2795:                // use serialVersionUID from JDK 1.2.2 for interoperability
2796:                private static final long serialVersionUID = 7207038068494060240L;
2797:
2798:                public int compare(Object o1, Object o2) {
2799:                    Comparable c1 = (Comparable) o1;
2800:                    Comparable c2 = (Comparable) o2;
2801:
2802:                    int cmp = c1.compareTo(c2);
2803:                    /*
2804:                     * We can't simply return -cmp, as -Integer.MIN_VALUE == 
2805:                     * Integer.MIN_VALUE.
2806:                     */
2807:                    return -(cmp | (cmp >>> 1));
2808:                }
2809:            }
2810:
2811:            /**
2812:             * Returns an enumeration over the specified collection.  This provides
2813:             * interoperatbility with legacy APIs that require an enumeration
2814:             * as input.
2815:             *
2816:             * @param c the collection for which an enumeration is to be returned.
2817:             * @return an enumeration over the specified collection.
2818:             * @see Enumeration
2819:             */
2820:            public static Enumeration enumeration(final Collection c) {
2821:                return new Enumeration() {
2822:                    Iterator i = c.iterator();
2823:
2824:                    public boolean hasMoreElements() {
2825:                        return i.hasNext();
2826:                    }
2827:
2828:                    public Object nextElement() {
2829:                        return i.next();
2830:                    }
2831:                };
2832:            }
2833:
2834:            /**
2835:             * Returns an array list containing the elements returned by the
2836:             * specified enumeration in the order they are returned by the
2837:             * enumeration.  This method provides interoperatbility between
2838:             * legacy APIs that return enumerations and new APIs that require
2839:             * collections.
2840:             *
2841:             * @param e enumeration providing elements for the returned
2842:             *          array list
2843:             * @return an array list containing the elements returned
2844:             *         by the specified enumeration.
2845:             * @since 1.4
2846:             * @see Enumeration
2847:             * @see ArrayList
2848:             */
2849:            public static ArrayList list(Enumeration e) {
2850:                ArrayList l = new ArrayList();
2851:                while (e.hasMoreElements())
2852:                    l.add(e.nextElement());
2853:                return l;
2854:            }
2855:
2856:            /**
2857:             * Returns true if the specified arguments are equal, or both null.
2858:             */
2859:            private static boolean eq(Object o1, Object o2) {
2860:                return (o1 == null ? o2 == null : o1.equals(o2));
2861:            }
2862:        }
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