jdk-sandbox: comparison jdk/src/share/classes/java/util/Collections.java

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+/*
+* Copyright 1997-2007 Sun Microsystems, Inc.  All Rights Reserved.
+* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+*
+* This code is free software; you can redistribute it and/or modify it
+* under the terms of the GNU General Public License version 2 only, as
+* published by the Free Software Foundation.  Sun designates this
+* particular file as subject to the "Classpath" exception as provided
+* by Sun in the LICENSE file that accompanied this code.
+*
+* This code is distributed in the hope that it will be useful, but WITHOUT
+* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+* version 2 for more details (a copy is included in the LICENSE file that
+* accompanied this code).
+*
+* You should have received a copy of the GNU General Public License version
+* 2 along with this work; if not, write to the Free Software Foundation,
+* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+*
+* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+* CA 95054 USA or visit www.sun.com if you need additional information or
+* have any questions.
+*/
+package java.util;
+import java.io.Serializable;
+import java.io.ObjectOutputStream;
+import java.io.IOException;
+import java.lang.reflect.Array;
+/**
+* This class consists exclusively of static methods that operate on or return
+* collections.  It contains polymorphic algorithms that operate on
+* collections, "wrappers", which return a new collection backed by a
+* specified collection, and a few other odds and ends.
+*
+* <p>The methods of this class all throw a <tt>NullPointerException</tt>
+* if the collections or class objects provided to them are null.
+*
+* <p>The documentation for the polymorphic algorithms contained in this class
+* generally includes a brief description of the <i>implementation</i>.  Such
+* descriptions should be regarded as <i>implementation notes</i>, rather than
+* parts of the <i>specification</i>.  Implementors should feel free to
+* substitute other algorithms, so long as the specification itself is adhered
+* to.  (For example, the algorithm used by <tt>sort</tt> does not have to be
+* a mergesort, but it does have to be <i>stable</i>.)
+*
+* <p>The "destructive" algorithms contained in this class, that is, the
+* algorithms that modify the collection on which they operate, are specified
+* to throw <tt>UnsupportedOperationException</tt> if the collection does not
+* support the appropriate mutation primitive(s), such as the <tt>set</tt>
+* method.  These algorithms may, but are not required to, throw this
+* exception if an invocation would have no effect on the collection.  For
+* example, invoking the <tt>sort</tt> method on an unmodifiable list that is
+* already sorted may or may not throw <tt>UnsupportedOperationException</tt>.
+*
+* <p>This class is a member of the
+* <a href="{@docRoot}/../technotes/guides/collections/index.html">
+* Java Collections Framework</a>.
+*
+* @author  Josh Bloch
+* @author  Neal Gafter
+* @see     Collection
+* @see     Set
+* @see     List
+* @see     Map
+* @since   1.2
+*/
+public class Collections {
+// Suppresses default constructor, ensuring non-instantiability.
+private Collections() {
+}
+// Algorithms
+/*
+* Tuning parameters for algorithms - Many of the List algorithms have
+* two implementations, one of which is appropriate for RandomAccess
+* lists, the other for "sequential."  Often, the random access variant
+* yields better performance on small sequential access lists.  The
+* tuning parameters below determine the cutoff point for what constitutes
+* a "small" sequential access list for each algorithm.  The values below
+* were empirically determined to work well for LinkedList. Hopefully
+* they should be reasonable for other sequential access List
+* implementations.  Those doing performance work on this code would
+* do well to validate the values of these parameters from time to time.
+* (The first word of each tuning parameter name is the algorithm to which
+* it applies.)
+*/
+private static final int BINARYSEARCH_THRESHOLD   = 5000;
+private static final int REVERSE_THRESHOLD        =   18;
+private static final int SHUFFLE_THRESHOLD        =    5;
+private static final int FILL_THRESHOLD           =   25;
+private static final int ROTATE_THRESHOLD         =  100;
+private static final int COPY_THRESHOLD           =   10;
+private static final int REPLACEALL_THRESHOLD     =   11;
+private static final int INDEXOFSUBLIST_THRESHOLD =   35;
+/**
+* Sorts the specified list into ascending order, according to the
+* <i>natural ordering</i> of its elements.  All elements in the list must
+* implement the <tt>Comparable</tt> interface.  Furthermore, all elements
+* in the list must be <i>mutually comparable</i> (that is,
+* <tt>e1.compareTo(e2)</tt> must not throw a <tt>ClassCastException</tt>
+* for any elements <tt>e1</tt> and <tt>e2</tt> in the list).<p>
+*
+* This sort is guaranteed to be <i>stable</i>:  equal elements will
+* not be reordered as a result of the sort.<p>
+*
+* The specified list must be modifiable, but need not be resizable.<p>
+*
+* The sorting algorithm is a modified mergesort (in which the merge is
+* omitted if the highest element in the low sublist is less than the
+* lowest element in the high sublist).  This algorithm offers guaranteed
+* n log(n) performance.
+*
+* This implementation dumps the specified list into an array, sorts
+* the array, and iterates over the list resetting each element
+* from the corresponding position in the array.  This avoids the
+* n<sup>2</sup> log(n) performance that would result from attempting
+* to sort a linked list in place.
+*
+* @param  list the list to be sorted.
+* @throws ClassCastException if the list contains elements that are not
+*         <i>mutually comparable</i> (for example, strings and integers).
+* @throws UnsupportedOperationException if the specified list's
+*         list-iterator does not support the <tt>set</tt> operation.
+* @see Comparable
+*/
+public static <T extends Comparable<? super T>> void sort(List<T> list) {
+Object[] a = list.toArray();
+Arrays.sort(a);
+ListIterator<T> i = list.listIterator();
+for (int j=0; j<a.length; j++) {
+i.next();
+i.set((T)a[j]);
+}
+}
+/**
+* Sorts the specified list according to the order induced by the
+* specified comparator.  All elements in the list must be <i>mutually
+* comparable</i> using the specified comparator (that is,
+* <tt>c.compare(e1, e2)</tt> must not throw a <tt>ClassCastException</tt>
+* for any elements <tt>e1</tt> and <tt>e2</tt> in the list).<p>
+*
+* This sort is guaranteed to be <i>stable</i>:  equal elements will
+* not be reordered as a result of the sort.<p>
+*
+* The sorting algorithm is a modified mergesort (in which the merge is
+* omitted if the highest element in the low sublist is less than the
+* lowest element in the high sublist).  This algorithm offers guaranteed
+* n log(n) performance.
+*
+* The specified list must be modifiable, but need not be resizable.
+* This implementation dumps the specified list into an array, sorts
+* the array, and iterates over the list resetting each element
+* from the corresponding position in the array.  This avoids the
+* n<sup>2</sup> log(n) performance that would result from attempting
+* to sort a linked list in place.
+*
+* @param  list the list to be sorted.
+* @param  c the comparator to determine the order of the list.  A
+*        <tt>null</tt> value indicates that the elements' <i>natural
+*        ordering</i> should be used.
+* @throws ClassCastException if the list contains elements that are not
+*         <i>mutually comparable</i> using the specified comparator.
+* @throws UnsupportedOperationException if the specified list's
+*         list-iterator does not support the <tt>set</tt> operation.
+* @see Comparator
+*/
+public static <T> void sort(List<T> list, Comparator<? super T> c) {
+Object[] a = list.toArray();
+Arrays.sort(a, (Comparator)c);
+ListIterator i = list.listIterator();
+for (int j=0; j<a.length; j++) {
+i.next();
+i.set(a[j]);
+}
+}
+/**
+* Searches the specified list for the specified object using the binary
+* search algorithm.  The list must be sorted into ascending order
+* according to the {@linkplain Comparable natural ordering} of its
+* elements (as by the {@link #sort(List)} method) prior to making this
+* call.  If it is not sorted, the results are undefined.  If the list
+* contains multiple elements equal to the specified object, there is no
+* guarantee which one will be found.
+*
+* <p>This method runs in log(n) time for a "random access" list (which
+* provides near-constant-time positional access).  If the specified list
+* does not implement the {@link RandomAccess} interface and is large,
+* this method will do an iterator-based binary search that performs
+* O(n) link traversals and O(log n) element comparisons.
+*
+* @param  list the list to be searched.
+* @param  key the key to be searched for.
+* @return the index of the search key, if it is contained in the list;
+*         otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>.  The
+*         <i>insertion point</i> is defined as the point at which the
+*         key would be inserted into the list: the index of the first
+*         element greater than the key, or <tt>list.size()</tt> if all
+*         elements in the list are less than the specified key.  Note
+*         that this guarantees that the return value will be &gt;= 0 if
+*         and only if the key is found.
+* @throws ClassCastException if the list contains elements that are not
+*         <i>mutually comparable</i> (for example, strings and
+*         integers), or the search key is not mutually comparable
+*         with the elements of the list.
+*/
+public static <T>
+int binarySearch(List<? extends Comparable<? super T>> list, T key) {
+if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
+return Collections.indexedBinarySearch(list, key);
+else
+return Collections.iteratorBinarySearch(list, key);
+}
+private static <T>
+int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key)
+{
+int low = 0;
+int high = list.size()-1;
+while (low <= high) {
+int mid = (low + high) >>> 1;
+Comparable<? super T> midVal = list.get(mid);
+int cmp = midVal.compareTo(key);
+if (cmp < 0)
+low = mid + 1;
+else if (cmp > 0)
+high = mid - 1;
+else
+return mid; // key found
+}
+return -(low + 1);  // key not found
+}
+private static <T>
+int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key)
+{
+int low = 0;
+int high = list.size()-1;
+ListIterator<? extends Comparable<? super T>> i = list.listIterator();
+while (low <= high) {
+int mid = (low + high) >>> 1;
+Comparable<? super T> midVal = get(i, mid);
+int cmp = midVal.compareTo(key);
+if (cmp < 0)
+low = mid + 1;
+else if (cmp > 0)
+high = mid - 1;
+else
+return mid; // key found
+}
+return -(low + 1);  // key not found
+}
+/**
+* Gets the ith element from the given list by repositioning the specified
+* list listIterator.
+*/
+private static <T> T get(ListIterator<? extends T> i, int index) {
+T obj = null;
+int pos = i.nextIndex();
+if (pos <= index) {
+do {
+obj = i.next();
+} while (pos++ < index);
+} else {
+do {
+obj = i.previous();
+} while (--pos > index);
+}
+return obj;
+}
+/**
+* Searches the specified list for the specified object using the binary
+* search algorithm.  The list must be sorted into ascending order
+* according to the specified comparator (as by the
+* {@link #sort(List, Comparator) sort(List, Comparator)}
+* method), prior to making this call.  If it is
+* not sorted, the results are undefined.  If the list contains multiple
+* elements equal to the specified object, there is no guarantee which one
+* will be found.
+*
+* <p>This method runs in log(n) time for a "random access" list (which
+* provides near-constant-time positional access).  If the specified list
+* does not implement the {@link RandomAccess} interface and is large,
+* this method will do an iterator-based binary search that performs
+* O(n) link traversals and O(log n) element comparisons.
+*
+* @param  list the list to be searched.
+* @param  key the key to be searched for.
+* @param  c the comparator by which the list is ordered.
+*         A <tt>null</tt> value indicates that the elements'
+*         {@linkplain Comparable natural ordering} should be used.
+* @return the index of the search key, if it is contained in the list;
+*         otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>.  The
+*         <i>insertion point</i> is defined as the point at which the
+*         key would be inserted into the list: the index of the first
+*         element greater than the key, or <tt>list.size()</tt> if all
+*         elements in the list are less than the specified key.  Note
+*         that this guarantees that the return value will be &gt;= 0 if
+*         and only if the key is found.
+* @throws ClassCastException if the list contains elements that are not
+*         <i>mutually comparable</i> using the specified comparator,
+*         or the search key is not mutually comparable with the
+*         elements of the list using this comparator.
+*/
+public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) {
+if (c==null)
+return binarySearch((List) list, key);
+if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
+return Collections.indexedBinarySearch(list, key, c);
+else
+return Collections.iteratorBinarySearch(list, key, c);
+}
+private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
+int low = 0;
+int high = l.size()-1;
+while (low <= high) {
+int mid = (low + high) >>> 1;
+T midVal = l.get(mid);
+int cmp = c.compare(midVal, key);
+if (cmp < 0)
+low = mid + 1;
+else if (cmp > 0)
+high = mid - 1;
+else
+return mid; // key found
+}
+return -(low + 1);  // key not found
+}
+private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
+int low = 0;
+int high = l.size()-1;
+ListIterator<? extends T> i = l.listIterator();
+while (low <= high) {
+int mid = (low + high) >>> 1;
+T midVal = get(i, mid);
+int cmp = c.compare(midVal, key);
+if (cmp < 0)
+low = mid + 1;
+else if (cmp > 0)
+high = mid - 1;
+else
+return mid; // key found
+}
+return -(low + 1);  // key not found
+}
+private interface SelfComparable extends Comparable<SelfComparable> {}
+/**
+* Reverses the order of the elements in the specified list.<p>
+*
+* This method runs in linear time.
+*
+* @param  list the list whose elements are to be reversed.
+* @throws UnsupportedOperationException if the specified list or
+*         its list-iterator does not support the <tt>set</tt> operation.
+*/
+public static void reverse(List<?> list) {
+int size = list.size();
+if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) {
+for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--)
+swap(list, i, j);
+} else {
+ListIterator fwd = list.listIterator();
+ListIterator rev = list.listIterator(size);
+for (int i=0, mid=list.size()>>1; i<mid; i++) {
+Object tmp = fwd.next();
+fwd.set(rev.previous());
+rev.set(tmp);
+}
+}
+}
+/**
+* Randomly permutes the specified list using a default source of
+* randomness.  All permutations occur with approximately equal
+* likelihood.<p>
+*
+* The hedge "approximately" is used in the foregoing description because
+* default source of randomness is only approximately an unbiased source
+* of independently chosen bits. If it were a perfect source of randomly
+* chosen bits, then the algorithm would choose permutations with perfect
+* uniformity.<p>
+*
+* This implementation traverses the list backwards, from the last element
+* up to the second, repeatedly swapping a randomly selected element into
+* the "current position".  Elements are randomly selected from the
+* portion of the list that runs from the first element to the current
+* position, inclusive.<p>
+*
+* This method runs in linear time.  If the specified list does not
+* implement the {@link RandomAccess} interface and is large, this
+* implementation dumps the specified list into an array before shuffling
+* it, and dumps the shuffled array back into the list.  This avoids the
+* quadratic behavior that would result from shuffling a "sequential
+* access" list in place.
+*
+* @param  list the list to be shuffled.
+* @throws UnsupportedOperationException if the specified list or
+*         its list-iterator does not support the <tt>set</tt> operation.
+*/
+public static void shuffle(List<?> list) {
+if (r == null) {
+r = new Random();
+}
+shuffle(list, r);
+}
+private static Random r;
+/**
+* Randomly permute the specified list using the specified source of
+* randomness.  All permutations occur with equal likelihood
+* assuming that the source of randomness is fair.<p>
+*
+* This implementation traverses the list backwards, from the last element
+* up to the second, repeatedly swapping a randomly selected element into
+* the "current position".  Elements are randomly selected from the
+* portion of the list that runs from the first element to the current
+* position, inclusive.<p>
+*
+* This method runs in linear time.  If the specified list does not
+* implement the {@link RandomAccess} interface and is large, this
+* implementation dumps the specified list into an array before shuffling
+* it, and dumps the shuffled array back into the list.  This avoids the
+* quadratic behavior that would result from shuffling a "sequential
+* access" list in place.
+*
+* @param  list the list to be shuffled.
+* @param  rnd the source of randomness to use to shuffle the list.
+* @throws UnsupportedOperationException if the specified list or its
+*         list-iterator does not support the <tt>set</tt> operation.
+*/
+public static void shuffle(List<?> list, Random rnd) {
+int size = list.size();
+if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) {
+for (int i=size; i>1; i--)
+swap(list, i-1, rnd.nextInt(i));
+} else {
+Object arr[] = list.toArray();
+// Shuffle array
+for (int i=size; i>1; i--)
+swap(arr, i-1, rnd.nextInt(i));
+// Dump array back into list
+ListIterator it = list.listIterator();
+for (int i=0; i<arr.length; i++) {
+it.next();
+it.set(arr[i]);
+}
+}
+}
+/**
+* Swaps the elements at the specified positions in the specified list.
+* (If the specified positions are equal, invoking this method leaves
+* the list unchanged.)
+*
+* @param list The list in which to swap elements.
+* @param i the index of one element to be swapped.
+* @param j the index of the other element to be swapped.
+* @throws IndexOutOfBoundsException if either <tt>i</tt> or <tt>j</tt>
+*         is out of range (i &lt; 0 || i &gt;= list.size()
+*         || j &lt; 0 || j &gt;= list.size()).
+* @since 1.4
+*/
+public static void swap(List<?> list, int i, int j) {
+final List l = list;
+l.set(i, l.set(j, l.get(i)));
+}
+/**
+* Swaps the two specified elements in the specified array.
+*/
+private static void swap(Object[] arr, int i, int j) {
+Object tmp = arr[i];
+arr[i] = arr[j];
+arr[j] = tmp;
+}
+/**
+* Replaces all of the elements of the specified list with the specified
+* element. <p>
+*
+* This method runs in linear time.
+*
+* @param  list the list to be filled with the specified element.
+* @param  obj The element with which to fill the specified list.
+* @throws UnsupportedOperationException if the specified list or its
+*         list-iterator does not support the <tt>set</tt> operation.
+*/
+public static <T> void fill(List<? super T> list, T obj) {
+int size = list.size();
+if (size < FILL_THRESHOLD || list instanceof RandomAccess) {
+for (int i=0; i<size; i++)
+list.set(i, obj);
+} else {
+ListIterator<? super T> itr = list.listIterator();
+for (int i=0; i<size; i++) {
+itr.next();
+itr.set(obj);
+}
+}
+}
+/**
+* Copies all of the elements from one list into another.  After the
+* operation, the index of each copied element in the destination list
+* will be identical to its index in the source list.  The destination
+* list must be at least as long as the source list.  If it is longer, the
+* remaining elements in the destination list are unaffected. <p>
+*
+* This method runs in linear time.
+*
+* @param  dest The destination list.
+* @param  src The source list.
+* @throws IndexOutOfBoundsException if the destination list is too small
+*         to contain the entire source List.
+* @throws UnsupportedOperationException if the destination list's
+*         list-iterator does not support the <tt>set</tt> operation.
+*/
+public static <T> void copy(List<? super T> dest, List<? extends T> src) {
+int srcSize = src.size();
+if (srcSize > dest.size())
+throw new IndexOutOfBoundsException("Source does not fit in dest");
+if (srcSize < COPY_THRESHOLD ||
+(src instanceof RandomAccess && dest instanceof RandomAccess)) {
+for (int i=0; i<srcSize; i++)
+dest.set(i, src.get(i));
+} else {
+ListIterator<? super T> di=dest.listIterator();
+ListIterator<? extends T> si=src.listIterator();
+for (int i=0; i<srcSize; i++) {
+di.next();
+di.set(si.next());
+}
+}
+}
+/**
+* Returns the minimum element of the given collection, according to the
+* <i>natural ordering</i> of its elements.  All elements in the
+* collection must implement the <tt>Comparable</tt> interface.
+* Furthermore, all elements in the collection must be <i>mutually
+* comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
+* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
+* <tt>e2</tt> in the collection).<p>
+*
+* This method iterates over the entire collection, hence it requires
+* time proportional to the size of the collection.
+*
+* @param  coll the collection whose minimum element is to be determined.
+* @return the minimum element of the given collection, according
+*         to the <i>natural ordering</i> of its elements.
+* @throws ClassCastException if the collection contains elements that are
+*         not <i>mutually comparable</i> (for example, strings and
+*         integers).
+* @throws NoSuchElementException if the collection is empty.
+* @see Comparable
+*/
+public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) {
+Iterator<? extends T> i = coll.iterator();
+T candidate = i.next();
+while (i.hasNext()) {
+T next = i.next();
+if (next.compareTo(candidate) < 0)
+candidate = next;
+}
+return candidate;
+}
+/**
+* Returns the minimum element of the given collection, according to the
+* order induced by the specified comparator.  All elements in the
+* collection must be <i>mutually comparable</i> by the specified
+* comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
+* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
+* <tt>e2</tt> in the collection).<p>
+*
+* This method iterates over the entire collection, hence it requires
+* time proportional to the size of the collection.
+*
+* @param  coll the collection whose minimum element is to be determined.
+* @param  comp the comparator with which to determine the minimum element.
+*         A <tt>null</tt> value indicates that the elements' <i>natural
+*         ordering</i> should be used.
+* @return the minimum element of the given collection, according
+*         to the specified comparator.
+* @throws ClassCastException if the collection contains elements that are
+*         not <i>mutually comparable</i> using the specified comparator.
+* @throws NoSuchElementException if the collection is empty.
+* @see Comparable
+*/
+public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) {
+if (comp==null)
+return (T)min((Collection<SelfComparable>) (Collection) coll);
+Iterator<? extends T> i = coll.iterator();
+T candidate = i.next();
+while (i.hasNext()) {
+T next = i.next();
+if (comp.compare(next, candidate) < 0)
+candidate = next;
+}
+return candidate;
+}
+/**
+* Returns the maximum element of the given collection, according to the
+* <i>natural ordering</i> of its elements.  All elements in the
+* collection must implement the <tt>Comparable</tt> interface.
+* Furthermore, all elements in the collection must be <i>mutually
+* comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
+* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
+* <tt>e2</tt> in the collection).<p>
+*
+* This method iterates over the entire collection, hence it requires
+* time proportional to the size of the collection.
+*
+* @param  coll the collection whose maximum element is to be determined.
+* @return the maximum element of the given collection, according
+*         to the <i>natural ordering</i> of its elements.
+* @throws ClassCastException if the collection contains elements that are
+*         not <i>mutually comparable</i> (for example, strings and
+*         integers).
+* @throws NoSuchElementException if the collection is empty.
+* @see Comparable
+*/
+public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) {
+Iterator<? extends T> i = coll.iterator();
+T candidate = i.next();
+while (i.hasNext()) {
+T next = i.next();
+if (next.compareTo(candidate) > 0)
+candidate = next;
+}
+return candidate;
+}
+/**
+* Returns the maximum element of the given collection, according to the
+* order induced by the specified comparator.  All elements in the
+* collection must be <i>mutually comparable</i> by the specified
+* comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
+* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
+* <tt>e2</tt> in the collection).<p>
+*
+* This method iterates over the entire collection, hence it requires
+* time proportional to the size of the collection.
+*
+* @param  coll the collection whose maximum element is to be determined.
+* @param  comp the comparator with which to determine the maximum element.
+*         A <tt>null</tt> value indicates that the elements' <i>natural
+*        ordering</i> should be used.
+* @return the maximum element of the given collection, according
+*         to the specified comparator.
+* @throws ClassCastException if the collection contains elements that are
+*         not <i>mutually comparable</i> using the specified comparator.
+* @throws NoSuchElementException if the collection is empty.
+* @see Comparable
+*/
+public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) {
+if (comp==null)
+return (T)max((Collection<SelfComparable>) (Collection) coll);
+Iterator<? extends T> i = coll.iterator();
+T candidate = i.next();
+while (i.hasNext()) {
+T next = i.next();
+if (comp.compare(next, candidate) > 0)
+candidate = next;
+}
+return candidate;
+}
+/**
+* Rotates the elements in the specified list by the specified distance.
+* After calling this method, the element at index <tt>i</tt> will be
+* the element previously at index <tt>(i - distance)</tt> mod
+* <tt>list.size()</tt>, for all values of <tt>i</tt> between <tt>0</tt>
+* and <tt>list.size()-1</tt>, inclusive.  (This method has no effect on
+* the size of the list.)
+*
+* <p>For example, suppose <tt>list</tt> comprises<tt> [t, a, n, k, s]</tt>.
+* After invoking <tt>Collections.rotate(list, 1)</tt> (or
+* <tt>Collections.rotate(list, -4)</tt>), <tt>list</tt> will comprise
+* <tt>[s, t, a, n, k]</tt>.
+*
+* <p>Note that this method can usefully be applied to sublists to
+* move one or more elements within a list while preserving the
+* order of the remaining elements.  For example, the following idiom
+* moves the element at index <tt>j</tt> forward to position
+* <tt>k</tt> (which must be greater than or equal to <tt>j</tt>):
+* <pre>
+*     Collections.rotate(list.subList(j, k+1), -1);
+* </pre>
+* To make this concrete, suppose <tt>list</tt> comprises
+* <tt>[a, b, c, d, e]</tt>.  To move the element at index <tt>1</tt>
+* (<tt>b</tt>) forward two positions, perform the following invocation:
+* <pre>
+*     Collections.rotate(l.subList(1, 4), -1);
+* </pre>
+* The resulting list is <tt>[a, c, d, b, e]</tt>.
+*
+* <p>To move more than one element forward, increase the absolute value
+* of the rotation distance.  To move elements backward, use a positive
+* shift distance.
+*
+* <p>If the specified list is small or implements the {@link
+* RandomAccess} interface, this implementation exchanges the first
+* element into the location it should go, and then repeatedly exchanges
+* the displaced element into the location it should go until a displaced
+* element is swapped into the first element.  If necessary, the process
+* is repeated on the second and successive elements, until the rotation
+* is complete.  If the specified list is large and doesn't implement the
+* <tt>RandomAccess</tt> interface, this implementation breaks the
+* list into two sublist views around index <tt>-distance mod size</tt>.
+* Then the {@link #reverse(List)} method is invoked on each sublist view,
+* and finally it is invoked on the entire list.  For a more complete
+* description of both algorithms, see Section 2.3 of Jon Bentley's
+* <i>Programming Pearls</i> (Addison-Wesley, 1986).
+*
+* @param list the list to be rotated.
+* @param distance the distance to rotate the list.  There are no
+*        constraints on this value; it may be zero, negative, or
+*        greater than <tt>list.size()</tt>.
+* @throws UnsupportedOperationException if the specified list or
+*         its list-iterator does not support the <tt>set</tt> operation.
+* @since 1.4
+*/
+public static void rotate(List<?> list, int distance) {
+if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD)
+rotate1(list, distance);
+else
+rotate2(list, distance);
+}
+private static <T> void rotate1(List<T> list, int distance) {
+int size = list.size();
+if (size == 0)
+return;
+distance = distance % size;
+if (distance < 0)
+distance += size;
+if (distance == 0)
+return;
+for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) {
+T displaced = list.get(cycleStart);
+int i = cycleStart;
+do {
+i += distance;
+if (i >= size)
+i -= size;
+displaced = list.set(i, displaced);
+nMoved ++;
+} while(i != cycleStart);
+}
+}
+private static void rotate2(List<?> list, int distance) {
+int size = list.size();
+if (size == 0)
+return;
+int mid =  -distance % size;
+if (mid < 0)
+mid += size;
+if (mid == 0)
+return;
+reverse(list.subList(0, mid));
+reverse(list.subList(mid, size));
+reverse(list);
+}
+/**
+* Replaces all occurrences of one specified value in a list with another.
+* More formally, replaces with <tt>newVal</tt> each element <tt>e</tt>
+* in <tt>list</tt> such that
+* <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
+* (This method has no effect on the size of the list.)
+*
+* @param list the list in which replacement is to occur.
+* @param oldVal the old value to be replaced.
+* @param newVal the new value with which <tt>oldVal</tt> is to be
+*        replaced.
+* @return <tt>true</tt> if <tt>list</tt> contained one or more elements
+*         <tt>e</tt> such that
+*         <tt>(oldVal==null ?  e==null : oldVal.equals(e))</tt>.
+* @throws UnsupportedOperationException if the specified list or
+*         its list-iterator does not support the <tt>set</tt> operation.
+* @since  1.4
+*/
+public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) {
+boolean result = false;
+int size = list.size();
+if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) {
+if (oldVal==null) {
+for (int i=0; i<size; i++) {
+if (list.get(i)==null) {
+list.set(i, newVal);
+result = true;
+}
+}
+} else {
+for (int i=0; i<size; i++) {
+if (oldVal.equals(list.get(i))) {
+list.set(i, newVal);
+result = true;
+}
+}
+}
+} else {
+ListIterator<T> itr=list.listIterator();
+if (oldVal==null) {
+for (int i=0; i<size; i++) {
+if (itr.next()==null) {
+itr.set(newVal);
+result = true;
+}
+}
+} else {
+for (int i=0; i<size; i++) {
+if (oldVal.equals(itr.next())) {
+itr.set(newVal);
+result = true;
+}
+}
+}
+}
+return result;
+}
+/**
+* Returns the starting position of the first occurrence of the specified
+* target list within the specified source list, or -1 if there is no
+* such occurrence.  More formally, returns the lowest index <tt>i</tt>
+* such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
+* or -1 if there is no such index.  (Returns -1 if
+* <tt>target.size() > source.size()</tt>.)
+*
+* <p>This implementation uses the "brute force" technique of scanning
+* over the source list, looking for a match with the target at each
+* location in turn.
+*
+* @param source the list in which to search for the first occurrence
+*        of <tt>target</tt>.
+* @param target the list to search for as a subList of <tt>source</tt>.
+* @return the starting position of the first occurrence of the specified
+*         target list within the specified source list, or -1 if there
+*         is no such occurrence.
+* @since  1.4
+*/
+public static int indexOfSubList(List<?> source, List<?> target) {
+int sourceSize = source.size();
+int targetSize = target.size();
+int maxCandidate = sourceSize - targetSize;
+if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
+(source instanceof RandomAccess&&target instanceof RandomAccess)) {
+nextCand:
+for (int candidate = 0; candidate <= maxCandidate; candidate++) {
+for (int i=0, j=candidate; i<targetSize; i++, j++)
+if (!eq(target.get(i), source.get(j)))
+continue nextCand;  // Element mismatch, try next cand
+return candidate;  // All elements of candidate matched target
+}
+} else {  // Iterator version of above algorithm
+ListIterator<?> si = source.listIterator();
+nextCand:
+for (int candidate = 0; candidate <= maxCandidate; candidate++) {
+ListIterator<?> ti = target.listIterator();
+for (int i=0; i<targetSize; i++) {
+if (!eq(ti.next(), si.next())) {
+// Back up source iterator to next candidate
+for (int j=0; j<i; j++)
+si.previous();
+continue nextCand;
+}
+}
+return candidate;
+}
+}
+return -1;  // No candidate matched the target
+}
+/**
+* Returns the starting position of the last occurrence of the specified
+* target list within the specified source list, or -1 if there is no such
+* occurrence.  More formally, returns the highest index <tt>i</tt>
+* such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
+* or -1 if there is no such index.  (Returns -1 if
+* <tt>target.size() > source.size()</tt>.)
+*
+* <p>This implementation uses the "brute force" technique of iterating
+* over the source list, looking for a match with the target at each
+* location in turn.
+*
+* @param source the list in which to search for the last occurrence
+*        of <tt>target</tt>.
+* @param target the list to search for as a subList of <tt>source</tt>.
+* @return the starting position of the last occurrence of the specified
+*         target list within the specified source list, or -1 if there
+*         is no such occurrence.
+* @since  1.4
+*/
+public static int lastIndexOfSubList(List<?> source, List<?> target) {
+int sourceSize = source.size();
+int targetSize = target.size();
+int maxCandidate = sourceSize - targetSize;
+if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
+source instanceof RandomAccess) {   // Index access version
+nextCand:
+for (int candidate = maxCandidate; candidate >= 0; candidate--) {
+for (int i=0, j=candidate; i<targetSize; i++, j++)
+if (!eq(target.get(i), source.get(j)))
+continue nextCand;  // Element mismatch, try next cand
+return candidate;  // All elements of candidate matched target
+}
+} else {  // Iterator version of above algorithm
+if (maxCandidate < 0)
+return -1;
+ListIterator<?> si = source.listIterator(maxCandidate);
+nextCand:
+for (int candidate = maxCandidate; candidate >= 0; candidate--) {
+ListIterator<?> ti = target.listIterator();
+for (int i=0; i<targetSize; i++) {
+if (!eq(ti.next(), si.next())) {
+if (candidate != 0) {
+// Back up source iterator to next candidate
+for (int j=0; j<=i+1; j++)
+si.previous();
+}
+continue nextCand;
+}
+}
+return candidate;
+}
+}
+return -1;  // No candidate matched the target
+}
+// Unmodifiable Wrappers
+/**
+* Returns an unmodifiable view of the specified collection.  This method
+* allows modules to provide users with "read-only" access to internal
+* collections.  Query operations on the returned collection "read through"
+* to the specified collection, and attempts to modify the returned
+* collection, whether direct or via its iterator, result in an
+* <tt>UnsupportedOperationException</tt>.<p>
+*
+* The returned collection does <i>not</i> pass the hashCode and equals
+* operations through to the backing collection, but relies on
+* <tt>Object</tt>'s <tt>equals</tt> and <tt>hashCode</tt> methods.  This
+* is necessary to preserve the contracts of these operations in the case
+* that the backing collection is a set or a list.<p>
+*
+* The returned collection will be serializable if the specified collection
+* is serializable.
+*
+* @param  c the collection for which an unmodifiable view is to be
+*         returned.
+* @return an unmodifiable view of the specified collection.
+*/
+public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) {
+return new UnmodifiableCollection<T>(c);
+}
+/**
+* @serial include
+*/
+static class UnmodifiableCollection<E> implements Collection<E>, Serializable {
+private static final long serialVersionUID = 1820017752578914078L;
+final Collection<? extends E> c;
+UnmodifiableCollection(Collection<? extends E> c) {
+if (c==null)
+throw new NullPointerException();
+this.c = c;
+}
+public int size()                   {return c.size();}
+public boolean isEmpty()            {return c.isEmpty();}
+public boolean contains(Object o)   {return c.contains(o);}
+public Object[] toArray()           {return c.toArray();}
+public <T> T[] toArray(T[] a)       {return c.toArray(a);}
+public String toString()            {return c.toString();}
+public Iterator<E> iterator() {
+return new Iterator<E>() {
+private final Iterator<? extends E> i = c.iterator();
+public boolean hasNext() {return i.hasNext();}
+public E next()          {return i.next();}
+public void remove() {
+throw new UnsupportedOperationException();
+}
+};
+}
+public boolean add(E e) {
+throw new UnsupportedOperationException();
+}
+public boolean remove(Object o) {
+throw new UnsupportedOperationException();
+}
+public boolean containsAll(Collection<?> coll) {
+return c.containsAll(coll);
+}
+public boolean addAll(Collection<? extends E> coll) {
+throw new UnsupportedOperationException();
+}
+public boolean removeAll(Collection<?> coll) {
+throw new UnsupportedOperationException();
+}
+public boolean retainAll(Collection<?> coll) {
+throw new UnsupportedOperationException();
+}
+public void clear() {
+throw new UnsupportedOperationException();
+}
+}
+/**
+* Returns an unmodifiable view of the specified set.  This method allows
+* modules to provide users with "read-only" access to internal sets.
+* Query operations on the returned set "read through" to the specified
+* set, and attempts to modify the returned set, whether direct or via its
+* iterator, result in an <tt>UnsupportedOperationException</tt>.<p>
+*
+* The returned set will be serializable if the specified set
+* is serializable.
+*
+* @param  s the set for which an unmodifiable view is to be returned.
+* @return an unmodifiable view of the specified set.
+*/
+public static <T> Set<T> unmodifiableSet(Set<? extends T> s) {
+return new UnmodifiableSet<T>(s);
+}
+/**
+* @serial include
+*/
+static class UnmodifiableSet<E> extends UnmodifiableCollection<E>
+implements Set<E>, Serializable {
+private static final long serialVersionUID = -9215047833775013803L;
+UnmodifiableSet(Set<? extends E> s)     {super(s);}
+public boolean equals(Object o) {return o == this || c.equals(o);}
+public int hashCode()           {return c.hashCode();}
+}
+/**
+* Returns an unmodifiable view of the specified sorted set.  This method
+* allows modules to provide users with "read-only" access to internal
+* sorted sets.  Query operations on the returned sorted set "read
+* through" to the specified sorted set.  Attempts to modify the returned
+* sorted set, whether direct, via its iterator, or via its
+* <tt>subSet</tt>, <tt>headSet</tt>, or <tt>tailSet</tt> views, result in
+* an <tt>UnsupportedOperationException</tt>.<p>
+*
+* The returned sorted set will be serializable if the specified sorted set
+* is serializable.
+*
+* @param s the sorted set for which an unmodifiable view is to be
+*        returned.
+* @return an unmodifiable view of the specified sorted set.
+*/
+public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) {
+return new UnmodifiableSortedSet<T>(s);
+}
+/**
+* @serial include
+*/
+static class UnmodifiableSortedSet<E>
+extends UnmodifiableSet<E>
+implements SortedSet<E>, Serializable {
+private static final long serialVersionUID = -4929149591599911165L;
+private final SortedSet<E> ss;
+UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;}
+public Comparator<? super E> comparator() {return ss.comparator();}
+public SortedSet<E> subSet(E fromElement, E toElement) {
+return new UnmodifiableSortedSet<E>(ss.subSet(fromElement,toElement));
+}
+public SortedSet<E> headSet(E toElement) {
+return new UnmodifiableSortedSet<E>(ss.headSet(toElement));
+}
+public SortedSet<E> tailSet(E fromElement) {
+return new UnmodifiableSortedSet<E>(ss.tailSet(fromElement));
+}
+public E first()                   {return ss.first();}
+public E last()                    {return ss.last();}
+}
+/**
+* Returns an unmodifiable view of the specified list.  This method allows
+* modules to provide users with "read-only" access to internal
+* lists.  Query operations on the returned list "read through" to the
+* specified list, and attempts to modify the returned list, whether
+* direct or via its iterator, result in an
+* <tt>UnsupportedOperationException</tt>.<p>
+*
+* The returned list will be serializable if the specified list
+* is serializable. Similarly, the returned list will implement
+* {@link RandomAccess} if the specified list does.
+*
+* @param  list the list for which an unmodifiable view is to be returned.
+* @return an unmodifiable view of the specified list.
+*/
+public static <T> List<T> unmodifiableList(List<? extends T> list) {
+return (list instanceof RandomAccess ?
+new UnmodifiableRandomAccessList<T>(list) :
+new UnmodifiableList<T>(list));
+}
+/**
+* @serial include
+*/
+static class UnmodifiableList<E> extends UnmodifiableCollection<E>
+implements List<E> {
+private static final long serialVersionUID = -283967356065247728L;
+final List<? extends E> list;
+UnmodifiableList(List<? extends E> list) {
+super(list);
+this.list = list;
+}
+public boolean equals(Object o) {return o == this || list.equals(o);}
+public int hashCode()           {return list.hashCode();}
+public E get(int index) {return list.get(index);}
+public E set(int index, E element) {
+throw new UnsupportedOperationException();
+}
+public void add(int index, E element) {
+throw new UnsupportedOperationException();
+}
+public E remove(int index) {
+throw new UnsupportedOperationException();
+}
+public int indexOf(Object o)            {return list.indexOf(o);}
+public int lastIndexOf(Object o)        {return list.lastIndexOf(o);}
+public boolean addAll(int index, Collection<? extends E> c) {
+throw new UnsupportedOperationException();
+}
+public ListIterator<E> listIterator()   {return listIterator(0);}
+public ListIterator<E> listIterator(final int index) {
+return new ListIterator<E>() {
+private final ListIterator<? extends E> i
+= list.listIterator(index);
+public boolean hasNext()     {return i.hasNext();}
+public E next()              {return i.next();}
+public boolean hasPrevious() {return i.hasPrevious();}
+public E previous()          {return i.previous();}
+public int nextIndex()       {return i.nextIndex();}
+public int previousIndex()   {return i.previousIndex();}
+public void remove() {
+throw new UnsupportedOperationException();
+}
+public void set(E e) {
+throw new UnsupportedOperationException();
+}
+public void add(E e) {
+throw new UnsupportedOperationException();
+}
+};
+}
+public List<E> subList(int fromIndex, int toIndex) {
+return new UnmodifiableList<E>(list.subList(fromIndex, toIndex));
+}
+/**
+* UnmodifiableRandomAccessList instances are serialized as
+* UnmodifiableList instances to allow them to be deserialized
+* in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList).
+* This method inverts the transformation.  As a beneficial
+* side-effect, it also grafts the RandomAccess marker onto
+* UnmodifiableList instances that were serialized in pre-1.4 JREs.
+*
+* Note: Unfortunately, UnmodifiableRandomAccessList instances
+* serialized in 1.4.1 and deserialized in 1.4 will become
+* UnmodifiableList instances, as this method was missing in 1.4.
+*/
+private Object readResolve() {
+return (list instanceof RandomAccess
+? new UnmodifiableRandomAccessList<E>(list)
+: this);
+}
+}
+/**
+* @serial include
+*/
+static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E>
+implements RandomAccess
+{
+UnmodifiableRandomAccessList(List<? extends E> list) {
+super(list);
+}
+public List<E> subList(int fromIndex, int toIndex) {
+return new UnmodifiableRandomAccessList<E>(
+list.subList(fromIndex, toIndex));
+}
+private static final long serialVersionUID = -2542308836966382001L;
+/**
+* Allows instances to be deserialized in pre-1.4 JREs (which do
+* not have UnmodifiableRandomAccessList).  UnmodifiableList has
+* a readResolve method that inverts this transformation upon
+* deserialization.
+*/
+private Object writeReplace() {
+return new UnmodifiableList<E>(list);
+}
+}
+/**
+* Returns an unmodifiable view of the specified map.  This method
+* allows modules to provide users with "read-only" access to internal
+* maps.  Query operations on the returned map "read through"
+* to the specified map, and attempts to modify the returned
+* map, whether direct or via its collection views, result in an
+* <tt>UnsupportedOperationException</tt>.<p>
+*
+* The returned map will be serializable if the specified map
+* is serializable.
+*
+* @param  m the map for which an unmodifiable view is to be returned.
+* @return an unmodifiable view of the specified map.
+*/
+public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) {
+return new UnmodifiableMap<K,V>(m);
+}
+/**
+* @serial include
+*/
+private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable {
+private static final long serialVersionUID = -1034234728574286014L;
+private final Map<? extends K, ? extends V> m;
+UnmodifiableMap(Map<? extends K, ? extends V> m) {
+if (m==null)
+throw new NullPointerException();
+this.m = m;
+}
+public int size()                        {return m.size();}
+public boolean isEmpty()                 {return m.isEmpty();}
+public boolean containsKey(Object key)   {return m.containsKey(key);}
+public boolean containsValue(Object val) {return m.containsValue(val);}
+public V get(Object key)                 {return m.get(key);}
+public V put(K key, V value) {
+throw new UnsupportedOperationException();
+}
+public V remove(Object key) {
+throw new UnsupportedOperationException();
+}
+public void putAll(Map<? extends K, ? extends V> m) {
+throw new UnsupportedOperationException();
+}
+public void clear() {
+throw new UnsupportedOperationException();
+}
+private transient Set<K> keySet = null;
+private transient Set<Map.Entry<K,V>> entrySet = null;
+private transient Collection<V> values = null;
+public Set<K> keySet() {
+if (keySet==null)
+keySet = unmodifiableSet(m.keySet());
+return keySet;
+}
+public Set<Map.Entry<K,V>> entrySet() {
+if (entrySet==null)
+entrySet = new UnmodifiableEntrySet<K,V>(m.entrySet());
+return entrySet;
+}
+public Collection<V> values() {
+if (values==null)
+values = unmodifiableCollection(m.values());
+return values;
+}
+public boolean equals(Object o) {return o == this || m.equals(o);}
+public int hashCode()           {return m.hashCode();}
+public String toString()        {return m.toString();}
+/**
+* We need this class in addition to UnmodifiableSet as
+* Map.Entries themselves permit modification of the backing Map
+* via their setValue operation.  This class is subtle: there are
+* many possible attacks that must be thwarted.
+*
+* @serial include
+*/
+static class UnmodifiableEntrySet<K,V>
+extends UnmodifiableSet<Map.Entry<K,V>> {
+private static final long serialVersionUID = 7854390611657943733L;
+UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) {
+super((Set)s);
+}
+public Iterator<Map.Entry<K,V>> iterator() {
+return new Iterator<Map.Entry<K,V>>() {
+private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator();
+public boolean hasNext() {
+return i.hasNext();
+}
+public Map.Entry<K,V> next() {
+return new UnmodifiableEntry<K,V>(i.next());
+}
+public void remove() {
+throw new UnsupportedOperationException();
+}
+};
+}
+public Object[] toArray() {
+Object[] a = c.toArray();
+for (int i=0; i<a.length; i++)
+a[i] = new UnmodifiableEntry<K,V>((Map.Entry<K,V>)a[i]);
+return a;
+}
+public <T> T[] toArray(T[] a) {
+// We don't pass a to c.toArray, to avoid window of
+// vulnerability wherein an unscrupulous multithreaded client
+// could get his hands on raw (unwrapped) Entries from c.
+Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
+for (int i=0; i<arr.length; i++)
+arr[i] = new UnmodifiableEntry<K,V>((Map.Entry<K,V>)arr[i]);
+if (arr.length > a.length)
+return (T[])arr;
+System.arraycopy(arr, 0, a, 0, arr.length);
+if (a.length > arr.length)
+a[arr.length] = null;
+return a;
+}
+/**
+* This method is overridden to protect the backing set against
+* an object with a nefarious equals function that senses
+* that the equality-candidate is Map.Entry and calls its
+* setValue method.
+*/
+public boolean contains(Object o) {
+if (!(o instanceof Map.Entry))
+return false;
+return c.contains(
+new UnmodifiableEntry<Object,Object>((Map.Entry<?,?>) o));
+}
+/**
+* The next two methods are overridden to protect against
+* an unscrupulous List whose contains(Object o) method senses
+* when o is a Map.Entry, and calls o.setValue.
+*/
+public boolean containsAll(Collection<?> coll) {
+Iterator<?> e = coll.iterator();
+while (e.hasNext())
+if (!contains(e.next())) // Invokes safe contains() above
+return false;
+return true;
+}
+public boolean equals(Object o) {
+if (o == this)
+return true;
+if (!(o instanceof Set))
+return false;
+Set s = (Set) o;
+if (s.size() != c.size())
+return false;
+return containsAll(s); // Invokes safe containsAll() above
+}
+/**
+* This "wrapper class" serves two purposes: it prevents
+* the client from modifying the backing Map, by short-circuiting
+* the setValue method, and it protects the backing Map against
+* an ill-behaved Map.Entry that attempts to modify another
+* Map Entry when asked to perform an equality check.
+*/
+private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> {
+private Map.Entry<? extends K, ? extends V> e;
+UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) {this.e = e;}
+public K getKey()         {return e.getKey();}
+public V getValue()  {return e.getValue();}
+public V setValue(V value) {
+throw new UnsupportedOperationException();
+}
+public int hashCode()     {return e.hashCode();}
+public boolean equals(Object o) {
+if (!(o instanceof Map.Entry))
+return false;
+Map.Entry t = (Map.Entry)o;
+return eq(e.getKey(),   t.getKey()) &&
+eq(e.getValue(), t.getValue());
+}
+public String toString()  {return e.toString();}
+}
+}
+}
+/**
+* Returns an unmodifiable view of the specified sorted map.  This method
+* allows modules to provide users with "read-only" access to internal
+* sorted maps.  Query operations on the returned sorted map "read through"
+* to the specified sorted map.  Attempts to modify the returned
+* sorted map, whether direct, via its collection views, or via its
+* <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in
+* an <tt>UnsupportedOperationException</tt>.<p>
+*
+* The returned sorted map will be serializable if the specified sorted map
+* is serializable.
+*
+* @param m the sorted map for which an unmodifiable view is to be
+*        returned.
+* @return an unmodifiable view of the specified sorted map.
+*/
+public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) {
+return new UnmodifiableSortedMap<K,V>(m);
+}
+/**
+* @serial include
+*/
+static class UnmodifiableSortedMap<K,V>
+extends UnmodifiableMap<K,V>
+implements SortedMap<K,V>, Serializable {
+private static final long serialVersionUID = -8806743815996713206L;
+private final SortedMap<K, ? extends V> sm;
+UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m;}
+public Comparator<? super K> comparator() {return sm.comparator();}
+public SortedMap<K,V> subMap(K fromKey, K toKey) {
+return new UnmodifiableSortedMap<K,V>(sm.subMap(fromKey, toKey));
+}
+public SortedMap<K,V> headMap(K toKey) {
+return new UnmodifiableSortedMap<K,V>(sm.headMap(toKey));
+}
+public SortedMap<K,V> tailMap(K fromKey) {
+return new UnmodifiableSortedMap<K,V>(sm.tailMap(fromKey));
+}
+public K firstKey()           {return sm.firstKey();}
+public K lastKey()            {return sm.lastKey();}
+}
+// Synch Wrappers
+/**
+* Returns a synchronized (thread-safe) collection backed by the specified
+* collection.  In order to guarantee serial access, it is critical that
+* <strong>all</strong> access to the backing collection is accomplished
+* through the returned collection.<p>
+*
+* It is imperative that the user manually synchronize on the returned
+* collection when iterating over it:
+* <pre>
+*  Collection c = Collections.synchronizedCollection(myCollection);
+*     ...
+*  synchronized(c) {
+*      Iterator i = c.iterator(); // Must be in the synchronized block
+*      while (i.hasNext())
+*         foo(i.next());
+*  }
+* </pre>
+* Failure to follow this advice may result in non-deterministic behavior.
+*
+* <p>The returned collection does <i>not</i> pass the <tt>hashCode</tt>
+* and <tt>equals</tt> operations through to the backing collection, but
+* relies on <tt>Object</tt>'s equals and hashCode methods.  This is
+* necessary to preserve the contracts of these operations in the case
+* that the backing collection is a set or a list.<p>
+*
+* The returned collection will be serializable if the specified collection
+* is serializable.
+*
+* @param  c the collection to be "wrapped" in a synchronized collection.
+* @return a synchronized view of the specified collection.
+*/
+public static <T> Collection<T> synchronizedCollection(Collection<T> c) {
+return new SynchronizedCollection<T>(c);
+}
+static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) {
+return new SynchronizedCollection<T>(c, mutex);
+}
+/**
+* @serial include
+*/
+static class SynchronizedCollection<E> implements Collection<E>, Serializable {
+private static final long serialVersionUID = 3053995032091335093L;
+final Collection<E> c;  // Backing Collection
+final Object mutex;     // Object on which to synchronize
+SynchronizedCollection(Collection<E> c) {
+if (c==null)
+throw new NullPointerException();
+this.c = c;
+mutex = this;
+}
+SynchronizedCollection(Collection<E> c, Object mutex) {
+this.c = c;
+this.mutex = mutex;
+}
+public int size() {
+synchronized(mutex) {return c.size();}
+}
+public boolean isEmpty() {
+synchronized(mutex) {return c.isEmpty();}
+}
+public boolean contains(Object o) {
+synchronized(mutex) {return c.contains(o);}
+}
+public Object[] toArray() {
+synchronized(mutex) {return c.toArray();}
+}
+public <T> T[] toArray(T[] a) {
+synchronized(mutex) {return c.toArray(a);}
+}
+public Iterator<E> iterator() {
+return c.iterator(); // Must be manually synched by user!
+}
+public boolean add(E e) {
+synchronized(mutex) {return c.add(e);}
+}
+public boolean remove(Object o) {
+synchronized(mutex) {return c.remove(o);}
+}
+public boolean containsAll(Collection<?> coll) {
+synchronized(mutex) {return c.containsAll(coll);}
+}
+public boolean addAll(Collection<? extends E> coll) {
+synchronized(mutex) {return c.addAll(coll);}
+}
+public boolean removeAll(Collection<?> coll) {
+synchronized(mutex) {return c.removeAll(coll);}
+}
+public boolean retainAll(Collection<?> coll) {
+synchronized(mutex) {return c.retainAll(coll);}
+}
+public void clear() {
+synchronized(mutex) {c.clear();}
+}
+public String toString() {
+synchronized(mutex) {return c.toString();}
+}
+private void writeObject(ObjectOutputStream s) throws IOException {
+synchronized(mutex) {s.defaultWriteObject();}
+}
+}
+/**
+* Returns a synchronized (thread-safe) set backed by the specified
+* set.  In order to guarantee serial access, it is critical that
+* <strong>all</strong> access to the backing set is accomplished
+* through the returned set.<p>
+*
+* It is imperative that the user manually synchronize on the returned
+* set when iterating over it:
+* <pre>
+*  Set s = Collections.synchronizedSet(new HashSet());
+*      ...
+*  synchronized(s) {
+*      Iterator i = s.iterator(); // Must be in the synchronized block
+*      while (i.hasNext())
+*          foo(i.next());
+*  }
+* </pre>
+* Failure to follow this advice may result in non-deterministic behavior.
+*
+* <p>The returned set will be serializable if the specified set is
+* serializable.
+*
+* @param  s the set to be "wrapped" in a synchronized set.
+* @return a synchronized view of the specified set.
+*/
+public static <T> Set<T> synchronizedSet(Set<T> s) {
+return new SynchronizedSet<T>(s);
+}
+static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) {
+return new SynchronizedSet<T>(s, mutex);
+}
+/**
+* @serial include
+*/
+static class SynchronizedSet<E>
+extends SynchronizedCollection<E>
+implements Set<E> {
+private static final long serialVersionUID = 487447009682186044L;
+SynchronizedSet(Set<E> s) {
+super(s);
+}
+SynchronizedSet(Set<E> s, Object mutex) {
+super(s, mutex);
+}
+public boolean equals(Object o) {
+synchronized(mutex) {return c.equals(o);}
+}
+public int hashCode() {
+synchronized(mutex) {return c.hashCode();}
+}
+}
+/**
+* Returns a synchronized (thread-safe) sorted set backed by the specified
+* sorted set.  In order to guarantee serial access, it is critical that
+* <strong>all</strong> access to the backing sorted set is accomplished
+* through the returned sorted set (or its views).<p>
+*
+* It is imperative that the user manually synchronize on the returned
+* sorted set when iterating over it or any of its <tt>subSet</tt>,
+* <tt>headSet</tt>, or <tt>tailSet</tt> views.
+* <pre>
+*  SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
+*      ...
+*  synchronized(s) {
+*      Iterator i = s.iterator(); // Must be in the synchronized block
+*      while (i.hasNext())
+*          foo(i.next());
+*  }
+* </pre>
+* or:
+* <pre>
+*  SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
+*  SortedSet s2 = s.headSet(foo);
+*      ...
+*  synchronized(s) {  // Note: s, not s2!!!
+*      Iterator i = s2.iterator(); // Must be in the synchronized block
+*      while (i.hasNext())
+*          foo(i.next());
+*  }
+* </pre>
+* Failure to follow this advice may result in non-deterministic behavior.
+*
+* <p>The returned sorted set will be serializable if the specified
+* sorted set is serializable.
+*
+* @param  s the sorted set to be "wrapped" in a synchronized sorted set.
+* @return a synchronized view of the specified sorted set.
+*/
+public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) {
+return new SynchronizedSortedSet<T>(s);
+}
+/**
+* @serial include
+*/
+static class SynchronizedSortedSet<E>
+extends SynchronizedSet<E>
+implements SortedSet<E>
+{
+private static final long serialVersionUID = 8695801310862127406L;
+final private SortedSet<E> ss;
+SynchronizedSortedSet(SortedSet<E> s) {
+super(s);
+ss = s;
+}
+SynchronizedSortedSet(SortedSet<E> s, Object mutex) {
+super(s, mutex);
+ss = s;
+}
+public Comparator<? super E> comparator() {
+synchronized(mutex) {return ss.comparator();}
+}
+public SortedSet<E> subSet(E fromElement, E toElement) {
+synchronized(mutex) {
+return new SynchronizedSortedSet<E>(
+ss.subSet(fromElement, toElement), mutex);
+}
+}
+public SortedSet<E> headSet(E toElement) {
+synchronized(mutex) {
+return new SynchronizedSortedSet<E>(ss.headSet(toElement), mutex);
+}
+}
+public SortedSet<E> tailSet(E fromElement) {
+synchronized(mutex) {
+return new SynchronizedSortedSet<E>(ss.tailSet(fromElement),mutex);
+}
+}
+public E first() {
+synchronized(mutex) {return ss.first();}
+}
+public E last() {
+synchronized(mutex) {return ss.last();}
+}
+}
+/**
+* Returns a synchronized (thread-safe) list backed by the specified
+* list.  In order to guarantee serial access, it is critical that
+* <strong>all</strong> access to the backing list is accomplished
+* through the returned list.<p>
+*
+* It is imperative that the user manually synchronize on the returned
+* list when iterating over it:
+* <pre>
+*  List list = Collections.synchronizedList(new ArrayList());
+*      ...
+*  synchronized(list) {
+*      Iterator i = list.iterator(); // Must be in synchronized block
+*      while (i.hasNext())
+*          foo(i.next());
+*  }
+* </pre>
+* Failure to follow this advice may result in non-deterministic behavior.
+*
+* <p>The returned list will be serializable if the specified list is
+* serializable.
+*
+* @param  list the list to be "wrapped" in a synchronized list.
+* @return a synchronized view of the specified list.
+*/
+public static <T> List<T> synchronizedList(List<T> list) {
+return (list instanceof RandomAccess ?
+new SynchronizedRandomAccessList<T>(list) :
+new SynchronizedList<T>(list));
+}
+static <T> List<T> synchronizedList(List<T> list, Object mutex) {
+return (list instanceof RandomAccess ?
+new SynchronizedRandomAccessList<T>(list, mutex) :
+new SynchronizedList<T>(list, mutex));
+}
+/**
+* @serial include
+*/
+static class SynchronizedList<E>
+extends SynchronizedCollection<E>
+implements List<E> {
+private static final long serialVersionUID = -7754090372962971524L;
+final List<E> list;
+SynchronizedList(List<E> list) {
+super(list);
+this.list = list;
+}
+SynchronizedList(List<E> list, Object mutex) {
+super(list, mutex);
+this.list = list;
+}
+public boolean equals(Object o) {
+synchronized(mutex) {return list.equals(o);}
+}
+public int hashCode() {
+synchronized(mutex) {return list.hashCode();}
+}
+public E get(int index) {
+synchronized(mutex) {return list.get(index);}
+}
+public E set(int index, E element) {
+synchronized(mutex) {return list.set(index, element);}
+}
+public void add(int index, E element) {
+synchronized(mutex) {list.add(index, element);}
+}
+public E remove(int index) {
+synchronized(mutex) {return list.remove(index);}
+}
+public int indexOf(Object o) {
+synchronized(mutex) {return list.indexOf(o);}
+}
+public int lastIndexOf(Object o) {
+synchronized(mutex) {return list.lastIndexOf(o);}
+}
+public boolean addAll(int index, Collection<? extends E> c) {
+synchronized(mutex) {return list.addAll(index, c);}
+}
+public ListIterator<E> listIterator() {
+return list.listIterator(); // Must be manually synched by user
+}
+public ListIterator<E> listIterator(int index) {
+return list.listIterator(index); // Must be manually synched by user
+}
+public List<E> subList(int fromIndex, int toIndex) {
+synchronized(mutex) {
+return new SynchronizedList<E>(list.subList(fromIndex, toIndex),
+mutex);
+}
+}
+/**
+* SynchronizedRandomAccessList instances are serialized as
+* SynchronizedList instances to allow them to be deserialized
+* in pre-1.4 JREs (which do not have SynchronizedRandomAccessList).
+* This method inverts the transformation.  As a beneficial
+* side-effect, it also grafts the RandomAccess marker onto
+* SynchronizedList instances that were serialized in pre-1.4 JREs.
+*
+* Note: Unfortunately, SynchronizedRandomAccessList instances
+* serialized in 1.4.1 and deserialized in 1.4 will become
+* SynchronizedList instances, as this method was missing in 1.4.
+*/
+private Object readResolve() {
+return (list instanceof RandomAccess
+? new SynchronizedRandomAccessList<E>(list)
+: this);
+}
+}
+/**
+* @serial include
+*/
+static class SynchronizedRandomAccessList<E>
+extends SynchronizedList<E>
+implements RandomAccess {
+SynchronizedRandomAccessList(List<E> list) {
+super(list);
+}
+SynchronizedRandomAccessList(List<E> list, Object mutex) {
+super(list, mutex);
+}
+public List<E> subList(int fromIndex, int toIndex) {
+synchronized(mutex) {
+return new SynchronizedRandomAccessList<E>(
+list.subList(fromIndex, toIndex), mutex);
+}
+}
+private static final long serialVersionUID = 1530674583602358482L;
+/**
+* Allows instances to be deserialized in pre-1.4 JREs (which do
+* not have SynchronizedRandomAccessList).  SynchronizedList has
+* a readResolve method that inverts this transformation upon
+* deserialization.
+*/
+private Object writeReplace() {
+return new SynchronizedList<E>(list);
+}
+}
+/**
+* Returns a synchronized (thread-safe) map backed by the specified
+* map.  In order to guarantee serial access, it is critical that
+* <strong>all</strong> access to the backing map is accomplished
+* through the returned map.<p>
+*
+* It is imperative that the user manually synchronize on the returned
+* map when iterating over any of its collection views:
+* <pre>
+*  Map m = Collections.synchronizedMap(new HashMap());
+*      ...
+*  Set s = m.keySet();  // Needn't be in synchronized block
+*      ...
+*  synchronized(m) {  // Synchronizing on m, not s!
+*      Iterator i = s.iterator(); // Must be in synchronized block
+*      while (i.hasNext())
+*          foo(i.next());
+*  }
+* </pre>
+* Failure to follow this advice may result in non-deterministic behavior.
+*
+* <p>The returned map will be serializable if the specified map is
+* serializable.
+*
+* @param  m the map to be "wrapped" in a synchronized map.
+* @return a synchronized view of the specified map.
+*/
+public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) {
+return new SynchronizedMap<K,V>(m);
+}
+/**
+* @serial include
+*/
+private static class SynchronizedMap<K,V>
+implements Map<K,V>, Serializable {
+private static final long serialVersionUID = 1978198479659022715L;
+private final Map<K,V> m;     // Backing Map
+final Object      mutex;        // Object on which to synchronize
+SynchronizedMap(Map<K,V> m) {
+if (m==null)
+throw new NullPointerException();
+this.m = m;
+mutex = this;
+}
+SynchronizedMap(Map<K,V> m, Object mutex) {
+this.m = m;
+this.mutex = mutex;
+}
+public int size() {
+synchronized(mutex) {return m.size();}
+}
+public boolean isEmpty() {
+synchronized(mutex) {return m.isEmpty();}
+}
+public boolean containsKey(Object key) {
+synchronized(mutex) {return m.containsKey(key);}
+}
+public boolean containsValue(Object value) {
+synchronized(mutex) {return m.containsValue(value);}
+}
+public V get(Object key) {
+synchronized(mutex) {return m.get(key);}
+}
+public V put(K key, V value) {
+synchronized(mutex) {return m.put(key, value);}
+}
+public V remove(Object key) {
+synchronized(mutex) {return m.remove(key);}
+}
+public void putAll(Map<? extends K, ? extends V> map) {
+synchronized(mutex) {m.putAll(map);}
+}
+public void clear() {
+synchronized(mutex) {m.clear();}
+}
+private transient Set<K> keySet = null;
+private transient Set<Map.Entry<K,V>> entrySet = null;
+private transient Collection<V> values = null;
+public Set<K> keySet() {
+synchronized(mutex) {
+if (keySet==null)
+keySet = new SynchronizedSet<K>(m.keySet(), mutex);
+return keySet;
+}
+}
+public Set<Map.Entry<K,V>> entrySet() {
+synchronized(mutex) {
+if (entrySet==null)
+entrySet = new SynchronizedSet<Map.Entry<K,V>>(m.entrySet(), mutex);
+return entrySet;
+}
+}
+public Collection<V> values() {
+synchronized(mutex) {
+if (values==null)
+values = new SynchronizedCollection<V>(m.values(), mutex);
+return values;
+}
+}
+public boolean equals(Object o) {
+synchronized(mutex) {return m.equals(o);}
+}
+public int hashCode() {
+synchronized(mutex) {return m.hashCode();}
+}
+public String toString() {
+synchronized(mutex) {return m.toString();}
+}
+private void writeObject(ObjectOutputStream s) throws IOException {
+synchronized(mutex) {s.defaultWriteObject();}
+}
+}
+/**
+* Returns a synchronized (thread-safe) sorted map backed by the specified
+* sorted map.  In order to guarantee serial access, it is critical that
+* <strong>all</strong> access to the backing sorted map is accomplished
+* through the returned sorted map (or its views).<p>
+*
+* It is imperative that the user manually synchronize on the returned
+* sorted map when iterating over any of its collection views, or the
+* collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or
+* <tt>tailMap</tt> views.
+* <pre>
+*  SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
+*      ...
+*  Set s = m.keySet();  // Needn't be in synchronized block
+*      ...
+*  synchronized(m) {  // Synchronizing on m, not s!
+*      Iterator i = s.iterator(); // Must be in synchronized block
+*      while (i.hasNext())
+*          foo(i.next());
+*  }
+* </pre>
+* or:
+* <pre>
+*  SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
+*  SortedMap m2 = m.subMap(foo, bar);
+*      ...
+*  Set s2 = m2.keySet();  // Needn't be in synchronized block
+*      ...
+*  synchronized(m) {  // Synchronizing on m, not m2 or s2!
+*      Iterator i = s.iterator(); // Must be in synchronized block
+*      while (i.hasNext())
+*          foo(i.next());
+*  }
+* </pre>
+* Failure to follow this advice may result in non-deterministic behavior.
+*
+* <p>The returned sorted map will be serializable if the specified
+* sorted map is serializable.
+*
+* @param  m the sorted map to be "wrapped" in a synchronized sorted map.
+* @return a synchronized view of the specified sorted map.
+*/
+public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) {
+return new SynchronizedSortedMap<K,V>(m);
+}
+/**
+* @serial include
+*/
+static class SynchronizedSortedMap<K,V>
+extends SynchronizedMap<K,V>
+implements SortedMap<K,V>
+{
+private static final long serialVersionUID = -8798146769416483793L;
+private final SortedMap<K,V> sm;
+SynchronizedSortedMap(SortedMap<K,V> m) {
+super(m);
+sm = m;
+}
+SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) {
+super(m, mutex);
+sm = m;
+}
+public Comparator<? super K> comparator() {
+synchronized(mutex) {return sm.comparator();}
+}
+public SortedMap<K,V> subMap(K fromKey, K toKey) {
+synchronized(mutex) {
+return new SynchronizedSortedMap<K,V>(
+sm.subMap(fromKey, toKey), mutex);
+}
+}
+public SortedMap<K,V> headMap(K toKey) {
+synchronized(mutex) {
+return new SynchronizedSortedMap<K,V>(sm.headMap(toKey), mutex);
+}
+}
+public SortedMap<K,V> tailMap(K fromKey) {
+synchronized(mutex) {
+return new SynchronizedSortedMap<K,V>(sm.tailMap(fromKey),mutex);
+}
+}
+public K firstKey() {
+synchronized(mutex) {return sm.firstKey();}
+}
+public K lastKey() {
+synchronized(mutex) {return sm.lastKey();}
+}
+}
+// Dynamically typesafe collection wrappers
+/**
+* Returns a dynamically typesafe view of the specified collection.
+* Any attempt to insert an element of the wrong type will result in an
+* immediate {@link ClassCastException}.  Assuming a collection
+* contains no incorrectly typed elements prior to the time a
+* dynamically typesafe view is generated, and that all subsequent
+* access to the collection takes place through the view, it is
+* <i>guaranteed</i> that the collection cannot contain an incorrectly
+* typed element.
+*
+* <p>The generics mechanism in the language provides compile-time
+* (static) type checking, but it is possible to defeat this mechanism
+* with unchecked casts.  Usually this is not a problem, as the compiler
+* issues warnings on all such unchecked operations.  There are, however,
+* times when static type checking alone is not sufficient.  For example,
+* suppose a collection is passed to a third-party library and it is
+* imperative that the library code not corrupt the collection by
+* inserting an element of the wrong type.
+*
+* <p>Another use of dynamically typesafe views is debugging.  Suppose a
+* program fails with a {@code ClassCastException}, indicating that an
+* incorrectly typed element was put into a parameterized collection.
+* Unfortunately, the exception can occur at any time after the erroneous
+* element is inserted, so it typically provides little or no information
+* as to the real source of the problem.  If the problem is reproducible,
+* one can quickly determine its source by temporarily modifying the
+* program to wrap the collection with a dynamically typesafe view.
+* For example, this declaration:
+*  <pre> {@code
+*     Collection<String> c = new HashSet<String>();
+* }</pre>
+* may be replaced temporarily by this one:
+*  <pre> {@code
+*     Collection<String> c = Collections.checkedCollection(
+*         new HashSet<String>(), String.class);
+* }</pre>
+* Running the program again will cause it to fail at the point where
+* an incorrectly typed element is inserted into the collection, clearly
+* identifying the source of the problem.  Once the problem is fixed, the
+* modified declaration may be reverted back to the original.
+*
+* <p>The returned collection does <i>not</i> pass the hashCode and equals
+* operations through to the backing collection, but relies on
+* {@code Object}'s {@code equals} and {@code hashCode} methods.  This
+* is necessary to preserve the contracts of these operations in the case
+* that the backing collection is a set or a list.
+*
+* <p>The returned collection will be serializable if the specified
+* collection is serializable.
+*
+* <p>Since {@code null} is considered to be a value of any reference
+* type, the returned collection permits insertion of null elements
+* whenever the backing collection does.
+*
+* @param c the collection for which a dynamically typesafe view is to be
+*          returned
+* @param type the type of element that {@code c} is permitted to hold
+* @return a dynamically typesafe view of the specified collection
+* @since 1.5
+*/
+public static <E> Collection<E> checkedCollection(Collection<E> c,
+Class<E> type) {
+return new CheckedCollection<E>(c, type);
+}
+@SuppressWarnings("unchecked")
+static <T> T[] zeroLengthArray(Class<T> type) {
+return (T[]) Array.newInstance(type, 0);
+}
+/**
+* @serial include
+*/
+static class CheckedCollection<E> implements Collection<E>, Serializable {
+private static final long serialVersionUID = 1578914078182001775L;
+final Collection<E> c;
+final Class<E> type;
+void typeCheck(Object o) {
+if (o != null && !type.isInstance(o))
+throw new ClassCastException(badElementMsg(o));
+}
+private String badElementMsg(Object o) {
+return "Attempt to insert " + o.getClass() +
+" element into collection with element type " + type;
+}
+CheckedCollection(Collection<E> c, Class<E> type) {
+if (c==null || type == null)
+throw new NullPointerException();
+this.c = c;
+this.type = type;
+}
+public int size()                 { return c.size(); }
+public boolean isEmpty()          { return c.isEmpty(); }
+public boolean contains(Object o) { return c.contains(o); }
+public Object[] toArray()         { return c.toArray(); }
+public <T> T[] toArray(T[] a)     { return c.toArray(a); }
+public String toString()          { return c.toString(); }
+public boolean remove(Object o)   { return c.remove(o); }
+public void clear()               {        c.clear(); }
+public boolean containsAll(Collection<?> coll) {
+return c.containsAll(coll);
+}
+public boolean removeAll(Collection<?> coll) {
+return c.removeAll(coll);
+}
+public boolean retainAll(Collection<?> coll) {
+return c.retainAll(coll);
+}
+public Iterator<E> iterator() {
+final Iterator<E> it = c.iterator();
+return new Iterator<E>() {
+public boolean hasNext() { return it.hasNext(); }
+public E next()          { return it.next(); }
+public void remove()     {        it.remove(); }};
+}
+public boolean add(E e) {
+typeCheck(e);
+return c.add(e);
+}
+private E[] zeroLengthElementArray = null; // Lazily initialized
+private E[] zeroLengthElementArray() {
+return zeroLengthElementArray != null ? zeroLengthElementArray :
+(zeroLengthElementArray = zeroLengthArray(type));
+}
+@SuppressWarnings("unchecked")
+Collection<E> checkedCopyOf(Collection<? extends E> coll) {
+Object[] a = null;
+try {
+E[] z = zeroLengthElementArray();
+a = coll.toArray(z);
+// Defend against coll violating the toArray contract
+if (a.getClass() != z.getClass())
+a = Arrays.copyOf(a, a.length, z.getClass());
+} catch (ArrayStoreException ignore) {
+// To get better and consistent diagnostics,
+// we call typeCheck explicitly on each element.
+// We call clone() to defend against coll retaining a
+// reference to the returned array and storing a bad
+// element into it after it has been type checked.
+a = coll.toArray().clone();
+for (Object o : a)
+typeCheck(o);
+}
+// A slight abuse of the type system, but safe here.
+return (Collection<E>) Arrays.asList(a);
+}
+public boolean addAll(Collection<? extends E> coll) {
+// Doing things this way insulates us from concurrent changes
+// in the contents of coll and provides all-or-nothing
+// semantics (which we wouldn't get if we type-checked each
+// element as we added it)
+return c.addAll(checkedCopyOf(coll));
+}
+}
+/**
+* Returns a dynamically typesafe view of the specified set.
+* Any attempt to insert an element of the wrong type will result in
+* an immediate {@link ClassCastException}.  Assuming a set contains
+* no incorrectly typed elements prior to the time a dynamically typesafe
+* view is generated, and that all subsequent access to the set
+* takes place through the view, it is <i>guaranteed</i> that the
+* set cannot contain an incorrectly typed element.
+*
+* <p>A discussion of the use of dynamically typesafe views may be
+* found in the documentation for the {@link #checkedCollection
+* checkedCollection} method.
+*
+* <p>The returned set will be serializable if the specified set is
+* serializable.
+*
+* <p>Since {@code null} is considered to be a value of any reference
+* type, the returned set permits insertion of null elements whenever
+* the backing set does.
+*
+* @param s the set for which a dynamically typesafe view is to be
+*          returned
+* @param type the type of element that {@code s} is permitted to hold
+* @return a dynamically typesafe view of the specified set
+* @since 1.5
+*/
+public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) {
+return new CheckedSet<E>(s, type);
+}
+/**
+* @serial include
+*/
+static class CheckedSet<E> extends CheckedCollection<E>
+implements Set<E>, Serializable
+{
+private static final long serialVersionUID = 4694047833775013803L;
+CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); }
+public boolean equals(Object o) { return o == this || c.equals(o); }
+public int hashCode()           { return c.hashCode(); }
+}
+/**
+* Returns a dynamically typesafe view of the specified sorted set.
+* Any attempt to insert an element of the wrong type will result in an
+* immediate {@link ClassCastException}.  Assuming a sorted set
+* contains no incorrectly typed elements prior to the time a
+* dynamically typesafe view is generated, and that all subsequent
+* access to the sorted set takes place through the view, it is
+* <i>guaranteed</i> that the sorted set cannot contain an incorrectly
+* typed element.
+*
+* <p>A discussion of the use of dynamically typesafe views may be
+* found in the documentation for the {@link #checkedCollection
+* checkedCollection} method.
+*
+* <p>The returned sorted set will be serializable if the specified sorted
+* set is serializable.
+*
+* <p>Since {@code null} is considered to be a value of any reference
+* type, the returned sorted set permits insertion of null elements
+* whenever the backing sorted set does.
+*
+* @param s the sorted set for which a dynamically typesafe view is to be
+*          returned
+* @param type the type of element that {@code s} is permitted to hold
+* @return a dynamically typesafe view of the specified sorted set
+* @since 1.5
+*/
+public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s,
+Class<E> type) {
+return new CheckedSortedSet<E>(s, type);
+}
+/**
+* @serial include
+*/
+static class CheckedSortedSet<E> extends CheckedSet<E>
+implements SortedSet<E>, Serializable
+{
+private static final long serialVersionUID = 1599911165492914959L;
+private final SortedSet<E> ss;
+CheckedSortedSet(SortedSet<E> s, Class<E> type) {
+super(s, type);
+ss = s;
+}
+public Comparator<? super E> comparator() { return ss.comparator(); }
+public E first()                   { return ss.first(); }
+public E last()                    { return ss.last(); }
+public SortedSet<E> subSet(E fromElement, E toElement) {
+return checkedSortedSet(ss.subSet(fromElement,toElement), type);
+}
+public SortedSet<E> headSet(E toElement) {
+return checkedSortedSet(ss.headSet(toElement), type);
+}
+public SortedSet<E> tailSet(E fromElement) {
+return checkedSortedSet(ss.tailSet(fromElement), type);
+}
+}
+/**
+* Returns a dynamically typesafe view of the specified list.
+* Any attempt to insert an element of the wrong type will result in
+* an immediate {@link ClassCastException}.  Assuming a list contains
+* no incorrectly typed elements prior to the time a dynamically typesafe
+* view is generated, and that all subsequent access to the list
+* takes place through the view, it is <i>guaranteed</i> that the
+* list cannot contain an incorrectly typed element.
+*
+* <p>A discussion of the use of dynamically typesafe views may be
+* found in the documentation for the {@link #checkedCollection
+* checkedCollection} method.
+*
+* <p>The returned list will be serializable if the specified list
+* is serializable.
+*
+* <p>Since {@code null} is considered to be a value of any reference
+* type, the returned list permits insertion of null elements whenever
+* the backing list does.
+*
+* @param list the list for which a dynamically typesafe view is to be
+*             returned
+* @param type the type of element that {@code list} is permitted to hold
+* @return a dynamically typesafe view of the specified list
+* @since 1.5
+*/
+public static <E> List<E> checkedList(List<E> list, Class<E> type) {
+return (list instanceof RandomAccess ?
+new CheckedRandomAccessList<E>(list, type) :
+new CheckedList<E>(list, type));
+}
+/**
+* @serial include
+*/
+static class CheckedList<E>
+extends CheckedCollection<E>
+implements List<E>
+{
+private static final long serialVersionUID = 65247728283967356L;
+final List<E> list;
+CheckedList(List<E> list, Class<E> type) {
+super(list, type);
+this.list = list;
+}
+public boolean equals(Object o)  { return o == this || list.equals(o); }
+public int hashCode()            { return list.hashCode(); }
+public E get(int index)          { return list.get(index); }
+public E remove(int index)       { return list.remove(index); }
+public int indexOf(Object o)     { return list.indexOf(o); }
+public int lastIndexOf(Object o) { return list.lastIndexOf(o); }
+public E set(int index, E element) {
+typeCheck(element);
+return list.set(index, element);
+}
+public void add(int index, E element) {
+typeCheck(element);
+list.add(index, element);
+}
+public boolean addAll(int index, Collection<? extends E> c) {
+return list.addAll(index, checkedCopyOf(c));
+}
+public ListIterator<E> listIterator()   { return listIterator(0); }
+public ListIterator<E> listIterator(final int index) {
+final ListIterator<E> i = list.listIterator(index);
+return new ListIterator<E>() {
+public boolean hasNext()     { return i.hasNext(); }
+public E next()              { return i.next(); }
+public boolean hasPrevious() { return i.hasPrevious(); }
+public E previous()          { return i.previous(); }
+public int nextIndex()       { return i.nextIndex(); }
+public int previousIndex()   { return i.previousIndex(); }
+public void remove()         {        i.remove(); }
+public void set(E e) {
+typeCheck(e);
+i.set(e);
+}
+public void add(E e) {
+typeCheck(e);
+i.add(e);
+}
+};
+}
+public List<E> subList(int fromIndex, int toIndex) {
+return new CheckedList<E>(list.subList(fromIndex, toIndex), type);
+}
+}
+/**
+* @serial include
+*/
+static class CheckedRandomAccessList<E> extends CheckedList<E>
+implements RandomAccess
+{
+private static final long serialVersionUID = 1638200125423088369L;
+CheckedRandomAccessList(List<E> list, Class<E> type) {
+super(list, type);
+}
+public List<E> subList(int fromIndex, int toIndex) {
+return new CheckedRandomAccessList<E>(
+list.subList(fromIndex, toIndex), type);
+}
+}
+/**
+* Returns a dynamically typesafe view of the specified map.
+* Any attempt to insert a mapping whose key or value have the wrong
+* type will result in an immediate {@link ClassCastException}.
+* Similarly, any attempt to modify the value currently associated with
+* a key will result in an immediate {@link ClassCastException},
+* whether the modification is attempted directly through the map
+* itself, or through a {@link Map.Entry} instance obtained from the
+* map's {@link Map#entrySet() entry set} view.
+*
+* <p>Assuming a map contains no incorrectly typed keys or values
+* prior to the time a dynamically typesafe view is generated, and
+* that all subsequent access to the map takes place through the view
+* (or one of its collection views), it is <i>guaranteed</i> that the
+* map cannot contain an incorrectly typed key or value.
+*
+* <p>A discussion of the use of dynamically typesafe views may be
+* found in the documentation for the {@link #checkedCollection
+* checkedCollection} method.
+*
+* <p>The returned map will be serializable if the specified map is
+* serializable.
+*
+* <p>Since {@code null} is considered to be a value of any reference
+* type, the returned map permits insertion of null keys or values
+* whenever the backing map does.
+*
+* @param m the map for which a dynamically typesafe view is to be
+*          returned
+* @param keyType the type of key that {@code m} is permitted to hold
+* @param valueType the type of value that {@code m} is permitted to hold
+* @return a dynamically typesafe view of the specified map
+* @since 1.5
+*/
+public static <K, V> Map<K, V> checkedMap(Map<K, V> m,
+Class<K> keyType,
+Class<V> valueType) {
+return new CheckedMap<K,V>(m, keyType, valueType);
+}
+/**
+* @serial include
+*/
+private static class CheckedMap<K,V>
+implements Map<K,V>, Serializable
+{
+private static final long serialVersionUID = 5742860141034234728L;
+private final Map<K, V> m;
+final Class<K> keyType;
+final Class<V> valueType;
+private void typeCheck(Object key, Object value) {
+if (key != null && !keyType.isInstance(key))
+throw new ClassCastException(badKeyMsg(key));
+if (value != null && !valueType.isInstance(value))
+throw new ClassCastException(badValueMsg(value));
+}
+private String badKeyMsg(Object key) {
+return "Attempt to insert " + key.getClass() +
+" key into map with key type " + keyType;
+}
+private String badValueMsg(Object value) {
+return "Attempt to insert " + value.getClass() +
+" value into map with value type " + valueType;
+}
+CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) {
+if (m == null || keyType == null || valueType == null)
+throw new NullPointerException();
+this.m = m;
+this.keyType = keyType;
+this.valueType = valueType;
+}
+public int size()                      { return m.size(); }
+public boolean isEmpty()               { return m.isEmpty(); }
+public boolean containsKey(Object key) { return m.containsKey(key); }
+public boolean containsValue(Object v) { return m.containsValue(v); }
+public V get(Object key)               { return m.get(key); }
+public V remove(Object key)            { return m.remove(key); }
+public void clear()                    { m.clear(); }
+public Set<K> keySet()                 { return m.keySet(); }
+public Collection<V> values()          { return m.values(); }
+public boolean equals(Object o)        { return o == this || m.equals(o); }
+public int hashCode()                  { return m.hashCode(); }
+public String toString()               { return m.toString(); }
+public V put(K key, V value) {
+typeCheck(key, value);
+return m.put(key, value);
+}
+@SuppressWarnings("unchecked")
+public void putAll(Map<? extends K, ? extends V> t) {
+// Satisfy the following goals:
+// - good diagnostics in case of type mismatch
+// - all-or-nothing semantics
+// - protection from malicious t
+// - correct behavior if t is a concurrent map
+Object[] entries = t.entrySet().toArray();
+List<Map.Entry<K,V>> checked =
+new ArrayList<Map.Entry<K,V>>(entries.length);
+for (Object o : entries) {
+Map.Entry<?,?> e = (Map.Entry<?,?>) o;
+Object k = e.getKey();
+Object v = e.getValue();
+typeCheck(k, v);
+checked.add(
+new AbstractMap.SimpleImmutableEntry<K,V>((K) k, (V) v));
+}
+for (Map.Entry<K,V> e : checked)
+m.put(e.getKey(), e.getValue());
+}
+private transient Set<Map.Entry<K,V>> entrySet = null;
+public Set<Map.Entry<K,V>> entrySet() {
+if (entrySet==null)
+entrySet = new CheckedEntrySet<K,V>(m.entrySet(), valueType);
+return entrySet;
+}
+/**
+* We need this class in addition to CheckedSet as Map.Entry permits
+* modification of the backing Map via the setValue operation.  This
+* class is subtle: there are many possible attacks that must be
+* thwarted.
+*
+* @serial exclude
+*/
+static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> {
+private final Set<Map.Entry<K,V>> s;
+private final Class<V> valueType;
+CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) {
+this.s = s;
+this.valueType = valueType;
+}
+public int size()        { return s.size(); }
+public boolean isEmpty() { return s.isEmpty(); }
+public String toString() { return s.toString(); }
+public int hashCode()    { return s.hashCode(); }
+public void clear()      {        s.clear(); }
+public boolean add(Map.Entry<K, V> e) {
+throw new UnsupportedOperationException();
+}
+public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) {
+throw new UnsupportedOperationException();
+}
+public Iterator<Map.Entry<K,V>> iterator() {
+final Iterator<Map.Entry<K, V>> i = s.iterator();
+final Class<V> valueType = this.valueType;
+return new Iterator<Map.Entry<K,V>>() {
+public boolean hasNext() { return i.hasNext(); }
+public void remove()     { i.remove(); }
+public Map.Entry<K,V> next() {
+return checkedEntry(i.next(), valueType);
+}
+};
+}
+@SuppressWarnings("unchecked")
+public Object[] toArray() {
+Object[] source = s.toArray();
+/*
+* Ensure that we don't get an ArrayStoreException even if
+* s.toArray returns an array of something other than Object
+*/
+Object[] dest = (CheckedEntry.class.isInstance(
+source.getClass().getComponentType()) ? source :
+new Object[source.length]);
+for (int i = 0; i < source.length; i++)
+dest[i] = checkedEntry((Map.Entry<K,V>)source[i],
+valueType);
+return dest;
+}
+@SuppressWarnings("unchecked")
+public <T> T[] toArray(T[] a) {
+// We don't pass a to s.toArray, to avoid window of
+// vulnerability wherein an unscrupulous multithreaded client
+// could get his hands on raw (unwrapped) Entries from s.
+T[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
+for (int i=0; i<arr.length; i++)
+arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i],
+valueType);
+if (arr.length > a.length)
+return arr;
+System.arraycopy(arr, 0, a, 0, arr.length);
+if (a.length > arr.length)
+a[arr.length] = null;
+return a;
+}
+/**
+* This method is overridden to protect the backing set against
+* an object with a nefarious equals function that senses
+* that the equality-candidate is Map.Entry and calls its
+* setValue method.
+*/
+public boolean contains(Object o) {
+if (!(o instanceof Map.Entry))
+return false;
+Map.Entry<?,?> e = (Map.Entry<?,?>) o;
+return s.contains(
+(e instanceof CheckedEntry) ? e : checkedEntry(e, valueType));
+}
+/**
+* The bulk collection methods are overridden to protect
+* against an unscrupulous collection whose contains(Object o)
+* method senses when o is a Map.Entry, and calls o.setValue.
+*/
+public boolean containsAll(Collection<?> c) {
+for (Object o : c)
+if (!contains(o)) // Invokes safe contains() above
+return false;
+return true;
+}
+public boolean remove(Object o) {
+if (!(o instanceof Map.Entry))
+return false;
+return s.remove(new AbstractMap.SimpleImmutableEntry
+<Object, Object>((Map.Entry<?,?>)o));
+}
+public boolean removeAll(Collection<?> c) {
+return batchRemove(c, false);
+}
+public boolean retainAll(Collection<?> c) {
+return batchRemove(c, true);
+}
+private boolean batchRemove(Collection<?> c, boolean complement) {
+boolean modified = false;
+Iterator<Map.Entry<K,V>> it = iterator();
+while (it.hasNext()) {
+if (c.contains(it.next()) != complement) {
+it.remove();
+modified = true;
+}
+}
+return modified;
+}
+public boolean equals(Object o) {
+if (o == this)
+return true;
+if (!(o instanceof Set))
+return false;
+Set<?> that = (Set<?>) o;
+return that.size() == s.size()
+&& containsAll(that); // Invokes safe containsAll() above
+}
+static <K,V,T> CheckedEntry<K,V,T> checkedEntry(Map.Entry<K,V> e,
+Class<T> valueType) {
+return new CheckedEntry<K,V,T>(e, valueType);
+}
+/**
+* This "wrapper class" serves two purposes: it prevents
+* the client from modifying the backing Map, by short-circuiting
+* the setValue method, and it protects the backing Map against
+* an ill-behaved Map.Entry that attempts to modify another
+* Map.Entry when asked to perform an equality check.
+*/
+private static class CheckedEntry<K,V,T> implements Map.Entry<K,V> {
+private final Map.Entry<K, V> e;
+private final Class<T> valueType;
+CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) {
+this.e = e;
+this.valueType = valueType;
+}
+public K getKey()        { return e.getKey(); }
+public V getValue()      { return e.getValue(); }
+public int hashCode()    { return e.hashCode(); }
+public String toString() { return e.toString(); }
+public V setValue(V value) {
+if (value != null && !valueType.isInstance(value))
+throw new ClassCastException(badValueMsg(value));
+return e.setValue(value);
+}
+private String badValueMsg(Object value) {
+return "Attempt to insert " + value.getClass() +
+" value into map with value type " + valueType;
+}
+public boolean equals(Object o) {
+if (o == this)
+return true;
+if (!(o instanceof Map.Entry))
+return false;
+return e.equals(new AbstractMap.SimpleImmutableEntry
+<Object, Object>((Map.Entry<?,?>)o));
+}
+}
+}
+}
+/**
+* Returns a dynamically typesafe view of the specified sorted map.
+* Any attempt to insert a mapping whose key or value have the wrong
+* type will result in an immediate {@link ClassCastException}.
+* Similarly, any attempt to modify the value currently associated with
+* a key will result in an immediate {@link ClassCastException},
+* whether the modification is attempted directly through the map
+* itself, or through a {@link Map.Entry} instance obtained from the
+* map's {@link Map#entrySet() entry set} view.
+*
+* <p>Assuming a map contains no incorrectly typed keys or values
+* prior to the time a dynamically typesafe view is generated, and
+* that all subsequent access to the map takes place through the view
+* (or one of its collection views), it is <i>guaranteed</i> that the
+* map cannot contain an incorrectly typed key or value.
+*
+* <p>A discussion of the use of dynamically typesafe views may be
+* found in the documentation for the {@link #checkedCollection
+* checkedCollection} method.
+*
+* <p>The returned map will be serializable if the specified map is
+* serializable.
+*
+* <p>Since {@code null} is considered to be a value of any reference
+* type, the returned map permits insertion of null keys or values
+* whenever the backing map does.
+*
+* @param m the map for which a dynamically typesafe view is to be
+*          returned
+* @param keyType the type of key that {@code m} is permitted to hold
+* @param valueType the type of value that {@code m} is permitted to hold
+* @return a dynamically typesafe view of the specified map
+* @since 1.5
+*/
+public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m,
+Class<K> keyType,
+Class<V> valueType) {
+return new CheckedSortedMap<K,V>(m, keyType, valueType);
+}
+/**
+* @serial include
+*/
+static class CheckedSortedMap<K,V> extends CheckedMap<K,V>
+implements SortedMap<K,V>, Serializable
+{
+private static final long serialVersionUID = 1599671320688067438L;
+private final SortedMap<K, V> sm;
+CheckedSortedMap(SortedMap<K, V> m,
+Class<K> keyType, Class<V> valueType) {
+super(m, keyType, valueType);
+sm = m;
+}
+public Comparator<? super K> comparator() { return sm.comparator(); }
+public K firstKey()                       { return sm.firstKey(); }
+public K lastKey()                        { return sm.lastKey(); }
+public SortedMap<K,V> subMap(K fromKey, K toKey) {
+return checkedSortedMap(sm.subMap(fromKey, toKey),
+keyType, valueType);
+}
+public SortedMap<K,V> headMap(K toKey) {
+return checkedSortedMap(sm.headMap(toKey), keyType, valueType);
+}
+public SortedMap<K,V> tailMap(K fromKey) {
+return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType);
+}
+}
+// Empty collections
+/**
+* Returns an iterator that has no elements.  More precisely,
+*
+* <ul compact>
+*
+* <li>{@link Iterator#hasNext hasNext} always returns {@code
+* false}.
+*
+* <li>{@link Iterator#next next} always throws {@link
+* NoSuchElementException}.
+*
+* <li>{@link Iterator#remove remove} always throws {@link
+* IllegalStateException}.
+*
+* </ul>
+*
+* <p>Implementations of this method are permitted, but not
+* required, to return the same object from multiple invocations.
+*
+* @return an empty iterator
+* @since 1.7
+*/
+@SuppressWarnings("unchecked")
+public static <T> Iterator<T> emptyIterator() {
+return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR;
+}
+private static class EmptyIterator<E> implements Iterator<E> {
+static final EmptyIterator<Object> EMPTY_ITERATOR
+= new EmptyIterator<Object>();
+public boolean hasNext() { return false; }
+public E next() { throw new NoSuchElementException(); }
+public void remove() { throw new IllegalStateException(); }
+}
+/**
+* Returns a list iterator that has no elements.  More precisely,
+*
+* <ul compact>
+*
+* <li>{@link Iterator#hasNext hasNext} and {@link
+* ListIterator#hasPrevious hasPrevious} always return {@code
+* false}.
+*
+* <li>{@link Iterator#next next} and {@link ListIterator#previous
+* previous} always throw {@link NoSuchElementException}.
+*
+* <li>{@link Iterator#remove remove} and {@link ListIterator#set
+* set} always throw {@link IllegalStateException}.
+*
+* <li>{@link ListIterator#add add} always throws {@link
+* UnsupportedOperationException}.
+*
+* <li>{@link ListIterator#nextIndex nextIndex} always returns
+* {@code 0} .
+*
+* <li>{@link ListIterator#previousIndex previousIndex} always
+* returns {@code -1}.
+*
+* </ul>
+*
+* <p>Implementations of this method are permitted, but not
+* required, to return the same object from multiple invocations.
+*
+* @return an empty list iterator
+* @since 1.7
+*/
+@SuppressWarnings("unchecked")
+public static <T> ListIterator<T> emptyListIterator() {
+return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR;
+}
+private static class EmptyListIterator<E>
+extends EmptyIterator<E>
+implements ListIterator<E>
+{
+static final EmptyListIterator<Object> EMPTY_ITERATOR
+= new EmptyListIterator<Object>();
+public boolean hasPrevious() { return false; }
+public E previous() { throw new NoSuchElementException(); }
+public int nextIndex()     { return 0; }
+public int previousIndex() { return -1; }
+public void set(E e) { throw new IllegalStateException(); }
+public void add(E e) { throw new UnsupportedOperationException(); }
+}
+/**
+* Returns an enumeration that has no elements.  More precisely,
+*
+* <ul compact>
+*
+* <li>{@link Enumeration#hasMoreElements hasMoreElements} always
+* returns {@code false}.
+*
+* <li> {@link Enumeration#nextElement nextElement} always throws
+* {@link NoSuchElementException}.
+*
+* </ul>
+*
+* <p>Implementations of this method are permitted, but not
+* required, to return the same object from multiple invocations.
+*
+* @return an empty enumeration
+* @since 1.7
+*/
+@SuppressWarnings("unchecked")
+public static <T> Enumeration<T> emptyEnumeration() {
+return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION;
+}
+private static class EmptyEnumeration<E> implements Enumeration<E> {
+static final EmptyEnumeration<Object> EMPTY_ENUMERATION
+= new EmptyEnumeration<Object>();
+public boolean hasMoreElements() { return false; }
+public E nextElement() { throw new NoSuchElementException(); }
+}
+/**
+* The empty set (immutable).  This set is serializable.
+*
+* @see #emptySet()
+*/
+@SuppressWarnings("unchecked")
+public static final Set EMPTY_SET = new EmptySet<Object>();
+/**
+* Returns the empty set (immutable).  This set is serializable.
+* Unlike the like-named field, this method is parameterized.
+*
+* <p>This example illustrates the type-safe way to obtain an empty set:
+* <pre>
+*     Set&lt;String&gt; s = Collections.emptySet();
+* </pre>
+* Implementation note:  Implementations of this method need not
+* create a separate <tt>Set</tt> object for each call.   Using this
+* method is likely to have comparable cost to using the like-named
+* field.  (Unlike this method, the field does not provide type safety.)
+*
+* @see #EMPTY_SET
+* @since 1.5
+*/
+@SuppressWarnings("unchecked")
+public static final <T> Set<T> emptySet() {
+return (Set<T>) EMPTY_SET;
+}
+/**
+* @serial include
+*/
+private static class EmptySet<E>
+extends AbstractSet<E>
+implements Serializable
+{
+private static final long serialVersionUID = 1582296315990362920L;
+public Iterator<E> iterator() { return emptyIterator(); }
+public int size() {return 0;}
+public boolean isEmpty() {return true;}
+public boolean contains(Object obj) {return false;}
+public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
+public Object[] toArray() { return new Object[0]; }
+public <T> T[] toArray(T[] a) {
+if (a.length > 0)
+a[0] = null;
+return a;
+}
+// Preserves singleton property
+private Object readResolve() {
+return EMPTY_SET;
+}
+}
+/**
+* The empty list (immutable).  This list is serializable.
+*
+* @see #emptyList()
+*/
+@SuppressWarnings("unchecked")
+public static final List EMPTY_LIST = new EmptyList<Object>();
+/**
+* Returns the empty list (immutable).  This list is serializable.
+*
+* <p>This example illustrates the type-safe way to obtain an empty list:
+* <pre>
+*     List&lt;String&gt; s = Collections.emptyList();
+* </pre>
+* Implementation note:  Implementations of this method need not
+* create a separate <tt>List</tt> object for each call.   Using this
+* method is likely to have comparable cost to using the like-named
+* field.  (Unlike this method, the field does not provide type safety.)
+*
+* @see #EMPTY_LIST
+* @since 1.5
+*/
+@SuppressWarnings("unchecked")
+public static final <T> List<T> emptyList() {
+return (List<T>) EMPTY_LIST;
+}
+/**
+* @serial include
+*/
+private static class EmptyList<E>
+extends AbstractList<E>
+implements RandomAccess, Serializable {
+private static final long serialVersionUID = 8842843931221139166L;
+public Iterator<E> iterator() {
+return emptyIterator();
+}
+public ListIterator<E> listIterator() {
+return emptyListIterator();
+}
+public int size() {return 0;}
+public boolean isEmpty() {return true;}
+public boolean contains(Object obj) {return false;}
+public boolean containsAll(Collection<?> c) { return c.isEmpty(); }
+public Object[] toArray() { return new Object[0]; }
+public <T> T[] toArray(T[] a) {
+if (a.length > 0)
+a[0] = null;
+return a;
+}
+public E get(int index) {
+throw new IndexOutOfBoundsException("Index: "+index);
+}
+public boolean equals(Object o) {
+return (o instanceof List) && ((List<?>)o).isEmpty();
+}
+public int hashCode() { return 1; }
+// Preserves singleton property
+private Object readResolve() {
+return EMPTY_LIST;
+}
+}
+/**
+* The empty map (immutable).  This map is serializable.
+*
+* @see #emptyMap()
+* @since 1.3
+*/
+@SuppressWarnings("unchecked")
+public static final Map EMPTY_MAP = new EmptyMap<Object,Object>();
+/**
+* Returns the empty map (immutable).  This map is serializable.
+*
+* <p>This example illustrates the type-safe way to obtain an empty set:
+* <pre>
+*     Map&lt;String, Date&gt; s = Collections.emptyMap();
+* </pre>
+* Implementation note:  Implementations of this method need not
+* create a separate <tt>Map</tt> object for each call.   Using this
+* method is likely to have comparable cost to using the like-named
+* field.  (Unlike this method, the field does not provide type safety.)
+*
+* @see #EMPTY_MAP
+* @since 1.5
+*/
+@SuppressWarnings("unchecked")
+public static final <K,V> Map<K,V> emptyMap() {
+return (Map<K,V>) EMPTY_MAP;
+}
+/**
+* @serial include
+*/
+private static class EmptyMap<K,V>
+extends AbstractMap<K,V>
+implements Serializable
+{
+private static final long serialVersionUID = 6428348081105594320L;
+public int size()                          {return 0;}
+public boolean isEmpty()                   {return true;}
+public boolean containsKey(Object key)     {return false;}
+public boolean containsValue(Object value) {return false;}
+public V get(Object key)                   {return null;}
+public Set<K> keySet()                     {return emptySet();}
+public Collection<V> values()              {return emptySet();}
+public Set<Map.Entry<K,V>> entrySet()      {return emptySet();}
+public boolean equals(Object o) {
+return (o instanceof Map) && ((Map<?,?>)o).isEmpty();
+}
+public int hashCode()                      {return 0;}
+// Preserves singleton property
+private Object readResolve() {
+return EMPTY_MAP;
+}
+}
+// Singleton collections
+/**
+* Returns an immutable set containing only the specified object.
+* The returned set is serializable.
+*
+* @param o the sole object to be stored in the returned set.
+* @return an immutable set containing only the specified object.
+*/
+public static <T> Set<T> singleton(T o) {
+return new SingletonSet<T>(o);
+}
+static <E> Iterator<E> singletonIterator(final E e) {
+return new Iterator<E>() {
+private boolean hasNext = true;
+public boolean hasNext() {
+return hasNext;
+}
+public E next() {
+if (hasNext) {
+hasNext = false;
+return e;
+}
+throw new NoSuchElementException();
+}
+public void remove() {
+throw new UnsupportedOperationException();
+}
+};
+}
+/**
+* @serial include
+*/
+private static class SingletonSet<E>
+extends AbstractSet<E>
+implements Serializable
+{
+private static final long serialVersionUID = 3193687207550431679L;
+final private E element;
+SingletonSet(E e) {element = e;}
+public Iterator<E> iterator() {
+return singletonIterator(element);
+}
+public int size() {return 1;}
+public boolean contains(Object o) {return eq(o, element);}
+}
+/**
+* Returns an immutable list containing only the specified object.
+* The returned list is serializable.
+*
+* @param o the sole object to be stored in the returned list.
+* @return an immutable list containing only the specified object.
+* @since 1.3
+*/
+public static <T> List<T> singletonList(T o) {
+return new SingletonList<T>(o);
+}
+/**
+* @serial include
+*/
+private static class SingletonList<E>
+extends AbstractList<E>
+implements RandomAccess, Serializable {
+private static final long serialVersionUID = 3093736618740652951L;
+private final E element;
+SingletonList(E obj)                {element = obj;}
+public Iterator<E> iterator() {
+return singletonIterator(element);
+}
+public int size()                   {return 1;}
+public boolean contains(Object obj) {return eq(obj, element);}
+public E get(int index) {
+if (index != 0)
+throw new IndexOutOfBoundsException("Index: "+index+", Size: 1");
+return element;
+}
+}
+/**
+* Returns an immutable map, mapping only the specified key to the
+* specified value.  The returned map is serializable.
+*
+* @param key the sole key to be stored in the returned map.
+* @param value the value to which the returned map maps <tt>key</tt>.
+* @return an immutable map containing only the specified key-value
+*         mapping.
+* @since 1.3
+*/
+public static <K,V> Map<K,V> singletonMap(K key, V value) {
+return new SingletonMap<K,V>(key, value);
+}
+/**
+* @serial include
+*/
+private static class SingletonMap<K,V>
+extends AbstractMap<K,V>
+implements Serializable {
+private static final long serialVersionUID = -6979724477215052911L;
+private final K k;
+private final V v;
+SingletonMap(K key, V value) {
+k = key;
+v = value;
+}
+public int size()                          {return 1;}
+public boolean isEmpty()                   {return false;}
+public boolean containsKey(Object key)     {return eq(key, k);}
+public boolean containsValue(Object value) {return eq(value, v);}
+public V get(Object key)                   {return (eq(key, k) ? v : null);}
+private transient Set<K> keySet = null;
+private transient Set<Map.Entry<K,V>> entrySet = null;
+private transient Collection<V> values = null;
+public Set<K> keySet() {
+if (keySet==null)
+keySet = singleton(k);
+return keySet;
+}
+public Set<Map.Entry<K,V>> entrySet() {
+if (entrySet==null)
+entrySet = Collections.<Map.Entry<K,V>>singleton(
+new SimpleImmutableEntry<K,V>(k, v));
+return entrySet;
+}
+public Collection<V> values() {
+if (values==null)
+values = singleton(v);
+return values;
+}
+}
+// Miscellaneous
+/**
+* Returns an immutable list consisting of <tt>n</tt> copies of the
+* specified object.  The newly allocated data object is tiny (it contains
+* a single reference to the data object).  This method is useful in
+* combination with the <tt>List.addAll</tt> method to grow lists.
+* The returned list is serializable.
+*
+* @param  n the number of elements in the returned list.
+* @param  o the element to appear repeatedly in the returned list.
+* @return an immutable list consisting of <tt>n</tt> copies of the
+*         specified object.
+* @throws IllegalArgumentException if n &lt; 0.
+* @see    List#addAll(Collection)
+* @see    List#addAll(int, Collection)
+*/
+public static <T> List<T> nCopies(int n, T o) {
+if (n < 0)
+throw new IllegalArgumentException("List length = " + n);
+return new CopiesList<T>(n, o);
+}
+/**
+* @serial include
+*/
+private static class CopiesList<E>
+extends AbstractList<E>
+implements RandomAccess, Serializable
+{
+private static final long serialVersionUID = 2739099268398711800L;
+final int n;
+final E element;
+CopiesList(int n, E e) {
+assert n >= 0;
+this.n = n;
+element = e;
+}
+public int size() {
+return n;
+}
+public boolean contains(Object obj) {
+return n != 0 && eq(obj, element);
+}
+public int indexOf(Object o) {
+return contains(o) ? 0 : -1;
+}
+public int lastIndexOf(Object o) {
+return contains(o) ? n - 1 : -1;
+}
+public E get(int index) {
+if (index < 0 || index >= n)
+throw new IndexOutOfBoundsException("Index: "+index+
+", Size: "+n);
+return element;
+}
+public Object[] toArray() {
+final Object[] a = new Object[n];
+if (element != null)
+Arrays.fill(a, 0, n, element);
+return a;
+}
+public <T> T[] toArray(T[] a) {
+final int n = this.n;
+if (a.length < n) {
+a = (T[])java.lang.reflect.Array
+.newInstance(a.getClass().getComponentType(), n);
+if (element != null)
+Arrays.fill(a, 0, n, element);
+} else {
+Arrays.fill(a, 0, n, element);
+if (a.length > n)
+a[n] = null;
+}
+return a;
+}
+public List<E> subList(int fromIndex, int toIndex) {
+if (fromIndex < 0)
+throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
+if (toIndex > n)
+throw new IndexOutOfBoundsException("toIndex = " + toIndex);
+if (fromIndex > toIndex)
+throw new IllegalArgumentException("fromIndex(" + fromIndex +
+") > toIndex(" + toIndex + ")");
+return new CopiesList<E>(toIndex - fromIndex, element);
+}
+}
+/**
+* Returns a comparator that imposes the reverse of the <i>natural
+* ordering</i> on a collection of objects that implement the
+* <tt>Comparable</tt> interface.  (The natural ordering is the ordering
+* imposed by the objects' own <tt>compareTo</tt> method.)  This enables a
+* simple idiom for sorting (or maintaining) collections (or arrays) of
+* objects that implement the <tt>Comparable</tt> interface in
+* reverse-natural-order.  For example, suppose a is an array of
+* strings. Then: <pre>
+*          Arrays.sort(a, Collections.reverseOrder());
+* </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p>
+*
+* The returned comparator is serializable.
+*
+* @return a comparator that imposes the reverse of the <i>natural
+*         ordering</i> on a collection of objects that implement
+*         the <tt>Comparable</tt> interface.
+* @see Comparable
+*/
+public static <T> Comparator<T> reverseOrder() {
+return (Comparator<T>) ReverseComparator.REVERSE_ORDER;
+}
+/**
+* @serial include
+*/
+private static class ReverseComparator
+implements Comparator<Comparable<Object>>, Serializable {
+private static final long serialVersionUID = 7207038068494060240L;
+static final ReverseComparator REVERSE_ORDER
+= new ReverseComparator();
+public int compare(Comparable<Object> c1, Comparable<Object> c2) {
+return c2.compareTo(c1);
+}
+private Object readResolve() { return reverseOrder(); }
+}
+/**
+* Returns a comparator that imposes the reverse ordering of the specified
+* comparator.  If the specified comparator is null, this method is
+* equivalent to {@link #reverseOrder()} (in other words, it returns a
+* comparator that imposes the reverse of the <i>natural ordering</i> on a
+* collection of objects that implement the Comparable interface).
+*
+* <p>The returned comparator is serializable (assuming the specified
+* comparator is also serializable or null).
+*
+* @return a comparator that imposes the reverse ordering of the
+*         specified comparator
+* @since 1.5
+*/
+public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) {
+if (cmp == null)
+return reverseOrder();
+if (cmp instanceof ReverseComparator2)
+return ((ReverseComparator2<T>)cmp).cmp;
+return new ReverseComparator2<T>(cmp);
+}
+/**
+* @serial include
+*/
+private static class ReverseComparator2<T> implements Comparator<T>,
+Serializable
+{
+private static final long serialVersionUID = 4374092139857L;
+/**
+* The comparator specified in the static factory.  This will never
+* be null, as the static factory returns a ReverseComparator
+* instance if its argument is null.
+*
+* @serial
+*/
+final Comparator<T> cmp;
+ReverseComparator2(Comparator<T> cmp) {
+assert cmp != null;
+this.cmp = cmp;
+}
+public int compare(T t1, T t2) {
+return cmp.compare(t2, t1);
+}
+public boolean equals(Object o) {
+return (o == this) ||
+(o instanceof ReverseComparator2 &&
+cmp.equals(((ReverseComparator2)o).cmp));
+}
+public int hashCode() {
+return cmp.hashCode() ^ Integer.MIN_VALUE;
+}
+}
+/**
+* Returns an enumeration over the specified collection.  This provides
+* interoperability with legacy APIs that require an enumeration
+* as input.
+*
+* @param c the collection for which an enumeration is to be returned.
+* @return an enumeration over the specified collection.
+* @see Enumeration
+*/
+public static <T> Enumeration<T> enumeration(final Collection<T> c) {
+return new Enumeration<T>() {
+private final Iterator<T> i = c.iterator();
+public boolean hasMoreElements() {
+return i.hasNext();
+}
+public T nextElement() {
+return i.next();
+}
+};
+}
+/**
+* Returns an array list containing the elements returned by the
+* specified enumeration in the order they are returned by the
+* enumeration.  This method provides interoperability between
+* legacy APIs that return enumerations and new APIs that require
+* collections.
+*
+* @param e enumeration providing elements for the returned
+*          array list
+* @return an array list containing the elements returned
+*         by the specified enumeration.
+* @since 1.4
+* @see Enumeration
+* @see ArrayList
+*/
+public static <T> ArrayList<T> list(Enumeration<T> e) {
+ArrayList<T> l = new ArrayList<T>();
+while (e.hasMoreElements())
+l.add(e.nextElement());
+return l;
+}
+/**
+* Returns true if the specified arguments are equal, or both null.
+*/
+static boolean eq(Object o1, Object o2) {
+return o1==null ? o2==null : o1.equals(o2);
+}
+/**
+* Returns the number of elements in the specified collection equal to the
+* specified object.  More formally, returns the number of elements
+* <tt>e</tt> in the collection such that
+* <tt>(o == null ? e == null : o.equals(e))</tt>.
+*
+* @param c the collection in which to determine the frequency
+*     of <tt>o</tt>
+* @param o the object whose frequency is to be determined
+* @throws NullPointerException if <tt>c</tt> is null
+* @since 1.5
+*/
+public static int frequency(Collection<?> c, Object o) {
+int result = 0;
+if (o == null) {
+for (Object e : c)
+if (e == null)
+result++;
+} else {
+for (Object e : c)
+if (o.equals(e))
+result++;
+}
+return result;
+}
+/**
+* Returns <tt>true</tt> if the two specified collections have no
+* elements in common.
+*
+* <p>Care must be exercised if this method is used on collections that
+* do not comply with the general contract for <tt>Collection</tt>.
+* Implementations may elect to iterate over either collection and test
+* for containment in the other collection (or to perform any equivalent
+* computation).  If either collection uses a nonstandard equality test
+* (as does a {@link SortedSet} whose ordering is not <i>compatible with
+* equals</i>, or the key set of an {@link IdentityHashMap}), both
+* collections must use the same nonstandard equality test, or the
+* result of this method is undefined.
+*
+* <p>Note that it is permissible to pass the same collection in both
+* parameters, in which case the method will return true if and only if
+* the collection is empty.
+*
+* @param c1 a collection
+* @param c2 a collection
+* @throws NullPointerException if either collection is null
+* @since 1.5
+*/
+public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
+/*
+* We're going to iterate through c1 and test for inclusion in c2.
+* If c1 is a Set and c2 isn't, swap the collections.  Otherwise,
+* place the shorter collection in c1.  Hopefully this heuristic
+* will minimize the cost of the operation.
+*/
+if ((c1 instanceof Set) && !(c2 instanceof Set) ||
+(c1.size() > c2.size())) {
+Collection<?> tmp = c1;
+c1 = c2;
+c2 = tmp;
+}
+for (Object e : c1)
+if (c2.contains(e))
+return false;
+return true;
+}
+/**
+* Adds all of the specified elements to the specified collection.
+* Elements to be added may be specified individually or as an array.
+* The behavior of this convenience method is identical to that of
+* <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely
+* to run significantly faster under most implementations.
+*
+* <p>When elements are specified individually, this method provides a
+* convenient way to add a few elements to an existing collection:
+* <pre>
+*     Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon");
+* </pre>
+*
+* @param c the collection into which <tt>elements</tt> are to be inserted
+* @param elements the elements to insert into <tt>c</tt>
+* @return <tt>true</tt> if the collection changed as a result of the call
+* @throws UnsupportedOperationException if <tt>c</tt> does not support
+*         the <tt>add</tt> operation
+* @throws NullPointerException if <tt>elements</tt> contains one or more
+*         null values and <tt>c</tt> does not permit null elements, or
+*         if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt>
+* @throws IllegalArgumentException if some property of a value in
+*         <tt>elements</tt> prevents it from being added to <tt>c</tt>
+* @see Collection#addAll(Collection)
+* @since 1.5
+*/
+public static <T> boolean addAll(Collection<? super T> c, T... elements) {
+boolean result = false;
+for (T element : elements)
+result |= c.add(element);
+return result;
+}
+/**
+* Returns a set backed by the specified map.  The resulting set displays
+* the same ordering, concurrency, and performance characteristics as the
+* backing map.  In essence, this factory method provides a {@link Set}
+* implementation corresponding to any {@link Map} implementation.  There
+* is no need to use this method on a {@link Map} implementation that
+* already has a corresponding {@link Set} implementation (such as {@link
+* HashMap} or {@link TreeMap}).
+*
+* <p>Each method invocation on the set returned by this method results in
+* exactly one method invocation on the backing map or its <tt>keySet</tt>
+* view, with one exception.  The <tt>addAll</tt> method is implemented
+* as a sequence of <tt>put</tt> invocations on the backing map.
+*
+* <p>The specified map must be empty at the time this method is invoked,
+* and should not be accessed directly after this method returns.  These
+* conditions are ensured if the map is created empty, passed directly
+* to this method, and no reference to the map is retained, as illustrated
+* in the following code fragment:
+* <pre>
+*    Set&lt;Object&gt; weakHashSet = Collections.newSetFromMap(
+*        new WeakHashMap&lt;Object, Boolean&gt;());
+* </pre>
+*
+* @param map the backing map
+* @return the set backed by the map
+* @throws IllegalArgumentException if <tt>map</tt> is not empty
+* @since 1.6
+*/
+public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
+return new SetFromMap<E>(map);
+}
+/**
+* @serial include
+*/
+private static class SetFromMap<E> extends AbstractSet<E>
+implements Set<E>, Serializable
+{
+private final Map<E, Boolean> m;  // The backing map
+private transient Set<E> s;       // Its keySet
+SetFromMap(Map<E, Boolean> map) {
+if (!map.isEmpty())
+throw new IllegalArgumentException("Map is non-empty");
+m = map;
+s = map.keySet();
+}
+public void clear()               {        m.clear(); }
+public int size()                 { return m.size(); }
+public boolean isEmpty()          { return m.isEmpty(); }
+public boolean contains(Object o) { return m.containsKey(o); }
+public boolean remove(Object o)   { return m.remove(o) != null; }
+public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; }
+public Iterator<E> iterator()     { return s.iterator(); }
+public Object[] toArray()         { return s.toArray(); }
+public <T> T[] toArray(T[] a)     { return s.toArray(a); }
+public String toString()          { return s.toString(); }
+public int hashCode()             { return s.hashCode(); }
+public boolean equals(Object o)   { return o == this || s.equals(o); }
+public boolean containsAll(Collection<?> c) {return s.containsAll(c);}
+public boolean removeAll(Collection<?> c)   {return s.removeAll(c);}
+public boolean retainAll(Collection<?> c)   {return s.retainAll(c);}
+// addAll is the only inherited implementation
+private static final long serialVersionUID = 2454657854757543876L;
+private void readObject(java.io.ObjectInputStream stream)
+throws IOException, ClassNotFoundException
+{
+stream.defaultReadObject();
+s = m.keySet();
+}
+}
+/**
+* Returns a view of a {@link Deque} as a Last-in-first-out (Lifo)
+* {@link Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>,
+* <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This
+* view can be useful when you would like to use a method
+* requiring a <tt>Queue</tt> but you need Lifo ordering.
+*
+* <p>Each method invocation on the queue returned by this method
+* results in exactly one method invocation on the backing deque, with
+* one exception.  The {@link Queue#addAll addAll} method is
+* implemented as a sequence of {@link Deque#addFirst addFirst}
+* invocations on the backing deque.
+*
+* @param deque the deque
+* @return the queue
+* @since  1.6
+*/
+public static <T> Queue<T> asLifoQueue(Deque<T> deque) {
+return new AsLIFOQueue<T>(deque);
+}
+/**
+* @serial include
+*/
+static class AsLIFOQueue<E> extends AbstractQueue<E>
+implements Queue<E>, Serializable {
+private static final long serialVersionUID = 1802017725587941708L;
+private final Deque<E> q;
+AsLIFOQueue(Deque<E> q)           { this.q = q; }
+public boolean add(E e)           { q.addFirst(e); return true; }
+public boolean offer(E e)         { return q.offerFirst(e); }
+public E poll()                   { return q.pollFirst(); }
+public E remove()                 { return q.removeFirst(); }
+public E peek()                   { return q.peekFirst(); }
+public E element()                { return q.getFirst(); }
+public void clear()               {        q.clear(); }
+public int size()                 { return q.size(); }
+public boolean isEmpty()          { return q.isEmpty(); }
+public boolean contains(Object o) { return q.contains(o); }
+public boolean remove(Object o)   { return q.remove(o); }
+public Iterator<E> iterator()     { return q.iterator(); }
+public Object[] toArray()         { return q.toArray(); }
+public <T> T[] toArray(T[] a)     { return q.toArray(a); }
+public String toString()          { return q.toString(); }
+public boolean containsAll(Collection<?> c) {return q.containsAll(c);}
+public boolean removeAll(Collection<?> c)   {return q.removeAll(c);}
+public boolean retainAll(Collection<?> c)   {return q.retainAll(c);}
+// We use inherited addAll; forwarding addAll would be wrong
+}
+}

changeset 2	90ce3da70b43
child 3420	bba8035eebfa