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	/*
	* Copyright (c) 1997, 2021, Oracle and/or its affiliates. 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. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package java.util;

	import java.io.IOException;
	import java.io.ObjectInputStream;
	import java.io.ObjectOutputStream;
	import java.io.Serializable;
	import java.lang.reflect.Array;
	import java.util.function.BiConsumer;
	import java.util.function.BiFunction;
	import java.util.function.Consumer;
	import java.util.function.Function;
	import java.util.function.IntFunction;
	import java.util.function.Predicate;
	import java.util.function.UnaryOperator;
	import java.util.stream.IntStream;
	import java.util.stream.Stream;
	import java.util.stream.StreamSupport;
	import jdk.internal.access.SharedSecrets;

	/**
	* 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 {@code NullPointerException}
	* 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 {@code sort} 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 {@code UnsupportedOperationException} if the collection does not
	* support the appropriate mutation primitive(s), such as the {@code set}
	* 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 {@code sort} method on an unmodifiable list that is
	* already sorted may or may not throw {@code UnsupportedOperationException}.
	*
	* <p>This class is a member of the
	* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
	* 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
	* {@linkplain Comparable natural ordering} of its elements.
	* All elements in the list must implement the {@link Comparable}
	* interface. Furthermore, all elements in the list must be
	* <i>mutually comparable</i> (that is, {@code e1.compareTo(e2)}
	* must not throw a {@code ClassCastException} for any elements
	* {@code e1} and {@code e2} 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.
	*
	* @implNote
	* This implementation defers to the {@link List#sort(Comparator)}
	* method using the specified list and a {@code null} comparator.
	*
	* @param <T> the class of the objects in the list
	* @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 {@code set} operation.
	* @throws IllegalArgumentException (optional) if the implementation
	* detects that the natural ordering of the list elements is
	* found to violate the {@link Comparable} contract
	* @see List#sort(Comparator)
	*/
	@SuppressWarnings("unchecked")
	public static <T extends Comparable<? super T>> void sort(List<T> list) {
	list.sort(null);
	}

	/**
	* 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,
	* {@code c.compare(e1, e2)} must not throw a {@code ClassCastException}
	* for any elements {@code e1} and {@code e2} 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.
	*
	* @implNote
	* This implementation defers to the {@link List#sort(Comparator)}
	* method using the specified list and comparator.
	*
	* @param <T> the class of the objects in the list
	* @param list the list to be sorted.
	* @param c the comparator to determine the order of the list. A
	* {@code null} 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 {@code set} operation.
	* @throws IllegalArgumentException (optional) if the comparator is
	* found to violate the {@link Comparator} contract
	* @see List#sort(Comparator)
	*/
	@SuppressWarnings({"unchecked", "rawtypes"})
	public static <T> void sort(List<T> list, Comparator<? super T> c) {
	list.sort(c);
	}


	/**
	* 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 <T> the class of the objects in the list
	* @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, <code>(-(<i>insertion point</i>) - 1)</code>. 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 {@code list.size()} if all
	* elements in the list are less than the specified key. Note
	* that this guarantees that the return value will be >= 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 <T> the class of the objects in the list
	* @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 {@code null} 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, <code>(-(<i>insertion point</i>) - 1)</code>. 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 {@code list.size()} if all
	* elements in the list are less than the specified key. Note
	* that this guarantees that the return value will be >= 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.
	*/
	@SuppressWarnings("unchecked")
	public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) {
	if (c==null)
	return binarySearch((List<? extends Comparable<? super T>>) 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
	}

	/**
	* 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 {@code set} operation.
	*/
	@SuppressWarnings({"rawtypes", "unchecked"})
	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 {
	// instead of using a raw type here, it's possible to capture
	// the wildcard but it will require a call to a supplementary
	// private method
	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 {@code set} operation.
	*/
	public static void shuffle(List<?> list) {
	Random rnd = r;
	if (rnd == null)
	r = rnd = new Random(); // harmless race.
	shuffle(list, rnd);
	}

	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 {@code set} operation.
	*/
	@SuppressWarnings({"rawtypes", "unchecked"})
	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
	// instead of using a raw type here, it's possible to capture
	// the wildcard but it will require a call to a supplementary
	// private method
	ListIterator it = list.listIterator();
	for (Object e : arr) {
	it.next();
	it.set(e);
	}
	}
	}

	/**
	* 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 {@code i} or {@code j}
	* is out of range (i < 0 \|\| i >= list.size()
	* \|\| j < 0 \|\| j >= list.size()).
	* @since 1.4
	*/
	@SuppressWarnings({"rawtypes", "unchecked"})
	public static void swap(List<?> list, int i, int j) {
	// instead of using a raw type here, it's possible to capture
	// the wildcard but it will require a call to a supplementary
	// private method
	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 <T> the class of the objects in the list
	* @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 {@code set} 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's size must be greater than or equal to the source list's size.
	* If it is greater, the remaining elements in the destination list are
	* unaffected. <p>
	*
	* This method runs in linear time.
	*
	* @param <T> the class of the objects in the lists
	* @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 {@code set} 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 {@code Comparable} interface.
	* Furthermore, all elements in the collection must be <i>mutually
	* comparable</i> (that is, {@code e1.compareTo(e2)} must not throw a
	* {@code ClassCastException} for any elements {@code e1} and
	* {@code e2} in the collection).<p>
	*
	* This method iterates over the entire collection, hence it requires
	* time proportional to the size of the collection.
	*
	* @param <T> the class of the objects in 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, {@code comp.compare(e1, e2)} must not throw a
	* {@code ClassCastException} for any elements {@code e1} and
	* {@code e2} in the collection).<p>
	*
	* This method iterates over the entire collection, hence it requires
	* time proportional to the size of the collection.
	*
	* @param <T> the class of the objects in 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 {@code null} 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
	*/
	@SuppressWarnings({"unchecked", "rawtypes"})
	public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) {
	if (comp==null)
	return (T)min((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 {@code Comparable} interface.
	* Furthermore, all elements in the collection must be <i>mutually
	* comparable</i> (that is, {@code e1.compareTo(e2)} must not throw a
	* {@code ClassCastException} for any elements {@code e1} and
	* {@code e2} in the collection).<p>
	*
	* This method iterates over the entire collection, hence it requires
	* time proportional to the size of the collection.
	*
	* @param <T> the class of the objects in 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, {@code comp.compare(e1, e2)} must not throw a
	* {@code ClassCastException} for any elements {@code e1} and
	* {@code e2} in the collection).<p>
	*
	* This method iterates over the entire collection, hence it requires
	* time proportional to the size of the collection.
	*
	* @param <T> the class of the objects in 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 {@code null} 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
	*/
	@SuppressWarnings({"unchecked", "rawtypes"})
	public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) {
	if (comp==null)
	return (T)max((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 {@code i} will be
	* the element previously at index {@code (i - distance)} mod
	* {@code list.size()}, for all values of {@code i} between {@code 0}
	* and {@code list.size()-1}, inclusive. (This method has no effect on
	* the size of the list.)
	*
	* <p>For example, suppose {@code list} comprises{@code [t, a, n, k, s]}.
	* After invoking {@code Collections.rotate(list, 1)} (or
	* {@code Collections.rotate(list, -4)}), {@code list} will comprise
	* {@code [s, t, a, n, k]}.
	*
	* <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 {@code j} forward to position
	* {@code k} (which must be greater than or equal to {@code j}):
	* <pre>
	* Collections.rotate(list.subList(j, k+1), -1);
	* </pre>
	* To make this concrete, suppose {@code list} comprises
	* {@code [a, b, c, d, e]}. To move the element at index {@code 1}
	* ({@code b}) forward two positions, perform the following invocation:
	* <pre>
	* Collections.rotate(l.subList(1, 4), -1);
	* </pre>
	* The resulting list is {@code [a, c, d, b, e]}.
	*
	* <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
	* {@code RandomAccess} interface, this implementation breaks the
	* list into two sublist views around index {@code -distance mod size}.
	* 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 {@code list.size()}.
	* @throws UnsupportedOperationException if the specified list or
	* its list-iterator does not support the {@code set} 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 {@code newVal} each element {@code e}
	* in {@code list} such that
	* {@code (oldVal==null ? e==null : oldVal.equals(e))}.
	* (This method has no effect on the size of the list.)
	*
	* @param <T> the class of the objects in 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 {@code oldVal} is to be
	* replaced.
	* @return {@code true} if {@code list} contained one or more elements
	* {@code e} such that
	* {@code (oldVal==null ? e==null : oldVal.equals(e))}.
	* @throws UnsupportedOperationException if the specified list or
	* its list-iterator does not support the {@code set} 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 {@code i}
	* such that {@code source.subList(i, i+target.size()).equals(target)},
	* or -1 if there is no such index. (Returns -1 if
	* {@code target.size() > source.size()})
	*
	* <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 {@code target}.
	* @param target the list to search for as a subList of {@code source}.
	* @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 {@code i}
	* such that {@code source.subList(i, i+target.size()).equals(target)},
	* or -1 if there is no such index. (Returns -1 if
	* {@code target.size() > source.size()})
	*
	* <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 {@code target}.
	* @param target the list to search for as a subList of {@code source}.
	* @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 <a href="Collection.html#unmodview">unmodifiable view</a> of the
	* specified collection. 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
	* {@code UnsupportedOperationException}.<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.
	*
	* @implNote This method may return its argument if the argument is already unmodifiable.
	* @param <T> the class of the objects in the collection
	* @param c the collection for which an unmodifiable view is to be
	* returned.
	* @return an unmodifiable view of the specified collection.
	*/
	@SuppressWarnings("unchecked")
	public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) {
	if (c.getClass() == UnmodifiableCollection.class) {
	return (Collection<T>) c;
	}
	return new UnmodifiableCollection<>(c);
	}

	/**
	* @serial include
	*/
	static class UnmodifiableCollection<E> implements Collection<E>, Serializable {
	@java.io.Serial
	private static final long serialVersionUID = 1820017752578914078L;

	@SuppressWarnings("serial") // Conditionally serializable
	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 <T> T[] toArray(IntFunction<T[]> f) {return c.toArray(f);}
	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();
	}
	@Override
	public void forEachRemaining(Consumer<? super E> action) {
	// Use backing collection version
	i.forEachRemaining(action);
	}
	};
	}

	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();
	}

	// Override default methods in Collection
	@Override
	public void forEach(Consumer<? super E> action) {
	c.forEach(action);
	}
	@Override
	public boolean removeIf(Predicate<? super E> filter) {
	throw new UnsupportedOperationException();
	}
	@SuppressWarnings("unchecked")
	@Override
	public Spliterator<E> spliterator() {
	return (Spliterator<E>)c.spliterator();
	}
	@SuppressWarnings("unchecked")
	@Override
	public Stream<E> stream() {
	return (Stream<E>)c.stream();
	}
	@SuppressWarnings("unchecked")
	@Override
	public Stream<E> parallelStream() {
	return (Stream<E>)c.parallelStream();
	}
	}

	/**
	* Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the
	* specified set. 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 {@code UnsupportedOperationException}.<p>
	*
	* The returned set will be serializable if the specified set
	* is serializable.
	*
	* @implNote This method may return its argument if the argument is already unmodifiable.
	* @param <T> the class of the objects in the set
	* @param s the set for which an unmodifiable view is to be returned.
	* @return an unmodifiable view of the specified set.
	*/
	@SuppressWarnings("unchecked")
	public static <T> Set<T> unmodifiableSet(Set<? extends T> s) {
	// Not checking for subclasses because of heap pollution and information leakage.
	if (s.getClass() == UnmodifiableSet.class) {
	return (Set<T>) s;
	}
	return new UnmodifiableSet<>(s);
	}

	/**
	* @serial include
	*/
	static class UnmodifiableSet<E> extends UnmodifiableCollection<E>
	implements Set<E>, Serializable {
	@java.io.Serial
	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 <a href="Collection.html#unmodview">unmodifiable view</a> of the
	* specified sorted set. 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
	* {@code subSet}, {@code headSet}, or {@code tailSet} views, result in
	* an {@code UnsupportedOperationException}.<p>
	*
	* The returned sorted set will be serializable if the specified sorted set
	* is serializable.
	*
	* @implNote This method may return its argument if the argument is already unmodifiable.
	* @param <T> the class of the objects in the set
	* @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) {
	// Not checking for subclasses because of heap pollution and information leakage.
	if (s.getClass() == UnmodifiableSortedSet.class) {
	return s;
	}
	return new UnmodifiableSortedSet<>(s);
	}

	/**
	* @serial include
	*/
	static class UnmodifiableSortedSet<E>
	extends UnmodifiableSet<E>
	implements SortedSet<E>, Serializable {
	@java.io.Serial
	private static final long serialVersionUID = -4929149591599911165L;
	@SuppressWarnings("serial") // Conditionally serializable
	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<>(ss.subSet(fromElement,toElement));
	}
	public SortedSet<E> headSet(E toElement) {
	return new UnmodifiableSortedSet<>(ss.headSet(toElement));
	}
	public SortedSet<E> tailSet(E fromElement) {
	return new UnmodifiableSortedSet<>(ss.tailSet(fromElement));
	}

	public E first() {return ss.first();}
	public E last() {return ss.last();}
	}

	/**
	* Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the
	* specified navigable set. Query operations on the returned navigable set "read
	* through" to the specified navigable set. Attempts to modify the returned
	* navigable set, whether direct, via its iterator, or via its
	* {@code subSet}, {@code headSet}, or {@code tailSet} views, result in
	* an {@code UnsupportedOperationException}.<p>
	*
	* The returned navigable set will be serializable if the specified
	* navigable set is serializable.
	*
	* @implNote This method may return its argument if the argument is already unmodifiable.
	* @param <T> the class of the objects in the set
	* @param s the navigable set for which an unmodifiable view is to be
	* returned
	* @return an unmodifiable view of the specified navigable set
	* @since 1.8
	*/
	public static <T> NavigableSet<T> unmodifiableNavigableSet(NavigableSet<T> s) {
	if (s.getClass() == UnmodifiableNavigableSet.class) {
	return s;
	}
	return new UnmodifiableNavigableSet<>(s);
	}

	/**
	* Wraps a navigable set and disables all of the mutative operations.
	*
	* @param <E> type of elements
	* @serial include
	*/
	static class UnmodifiableNavigableSet<E>
	extends UnmodifiableSortedSet<E>
	implements NavigableSet<E>, Serializable {

	@java.io.Serial
	private static final long serialVersionUID = -6027448201786391929L;

	/**
	* A singleton empty unmodifiable navigable set used for
	* {@link #emptyNavigableSet()}.
	*
	* @param <E> type of elements, if there were any, and bounds
	*/
	private static class EmptyNavigableSet<E> extends UnmodifiableNavigableSet<E>
	implements Serializable {
	@java.io.Serial
	private static final long serialVersionUID = -6291252904449939134L;

	public EmptyNavigableSet() {
	super(new TreeSet<>());
	}

	@java.io.Serial
	private Object readResolve() { return EMPTY_NAVIGABLE_SET; }
	}

	@SuppressWarnings("rawtypes")
	private static final NavigableSet<?> EMPTY_NAVIGABLE_SET =
	new EmptyNavigableSet<>();

	/**
	* The instance we are protecting.
	*/
	@SuppressWarnings("serial") // Conditionally serializable
	private final NavigableSet<E> ns;

	UnmodifiableNavigableSet(NavigableSet<E> s) {super(s); ns = s;}

	public E lower(E e) { return ns.lower(e); }
	public E floor(E e) { return ns.floor(e); }
	public E ceiling(E e) { return ns.ceiling(e); }
	public E higher(E e) { return ns.higher(e); }
	public E pollFirst() { throw new UnsupportedOperationException(); }
	public E pollLast() { throw new UnsupportedOperationException(); }
	public NavigableSet<E> descendingSet()
	{ return new UnmodifiableNavigableSet<>(ns.descendingSet()); }
	public Iterator<E> descendingIterator()
	{ return descendingSet().iterator(); }

	public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
	return new UnmodifiableNavigableSet<>(
	ns.subSet(fromElement, fromInclusive, toElement, toInclusive));
	}

	public NavigableSet<E> headSet(E toElement, boolean inclusive) {
	return new UnmodifiableNavigableSet<>(
	ns.headSet(toElement, inclusive));
	}

	public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
	return new UnmodifiableNavigableSet<>(
	ns.tailSet(fromElement, inclusive));
	}
	}

	/**
	* Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the
	* specified list. 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
	* {@code UnsupportedOperationException}.<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.
	*
	* @implNote This method may return its argument if the argument is already unmodifiable.
	* @param <T> the class of the objects in the list
	* @param list the list for which an unmodifiable view is to be returned.
	* @return an unmodifiable view of the specified list.
	*/
	@SuppressWarnings("unchecked")
	public static <T> List<T> unmodifiableList(List<? extends T> list) {
	if (list.getClass() == UnmodifiableList.class \|\| list.getClass() == UnmodifiableRandomAccessList.class) {
	return (List<T>) list;
	}

	return (list instanceof RandomAccess ?
	new UnmodifiableRandomAccessList<>(list) :
	new UnmodifiableList<>(list));
	}

	/**
	* @serial include
	*/
	static class UnmodifiableList<E> extends UnmodifiableCollection<E>
	implements List<E> {
	@java.io.Serial
	private static final long serialVersionUID = -283967356065247728L;

	@SuppressWarnings("serial") // Conditionally serializable
	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();
	}

	@Override
	public void replaceAll(UnaryOperator<E> operator) {
	throw new UnsupportedOperationException();
	}
	@Override
	public void sort(Comparator<? super 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();
	}

	@Override
	public void forEachRemaining(Consumer<? super E> action) {
	i.forEachRemaining(action);
	}
	};
	}

	public List<E> subList(int fromIndex, int toIndex) {
	return new UnmodifiableList<>(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.
	*/
	@java.io.Serial
	private Object readResolve() {
	return (list instanceof RandomAccess
	? new UnmodifiableRandomAccessList<>(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<>(
	list.subList(fromIndex, toIndex));
	}

	@java.io.Serial
	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.
	*/
	@java.io.Serial
	private Object writeReplace() {
	return new UnmodifiableList<>(list);
	}
	}

	/**
	* Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the
	* specified map. 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
	* {@code UnsupportedOperationException}.<p>
	*
	* The returned map will be serializable if the specified map
	* is serializable.
	*
	* @implNote This method may return its argument if the argument is already unmodifiable.
	* @param <K> the class of the map keys
	* @param <V> the class of the map values
	* @param m the map for which an unmodifiable view is to be returned.
	* @return an unmodifiable view of the specified map.
	*/
	@SuppressWarnings("unchecked")
	public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) {
	// Not checking for subclasses because of heap pollution and information leakage.
	if (m.getClass() == UnmodifiableMap.class) {
	return (Map<K,V>) m;
	}
	return new UnmodifiableMap<>(m);
	}

	/**
	* @serial include
	*/
	private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable {
	@java.io.Serial
	private static final long serialVersionUID = -1034234728574286014L;

	@SuppressWarnings("serial") // Conditionally serializable
	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;
	private transient Set<Map.Entry<K,V>> entrySet;
	private transient Collection<V> values;

	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<>(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();}

	// Override default methods in Map
	@Override
	@SuppressWarnings("unchecked")
	public V getOrDefault(Object k, V defaultValue) {
	// Safe cast as we don't change the value
	return ((Map<K, V>)m).getOrDefault(k, defaultValue);
	}

	@Override
	public void forEach(BiConsumer<? super K, ? super V> action) {
	m.forEach(action);
	}

	@Override
	public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V putIfAbsent(K key, V value) {
	throw new UnsupportedOperationException();
	}

	@Override
	public boolean remove(Object key, Object value) {
	throw new UnsupportedOperationException();
	}

	@Override
	public boolean replace(K key, V oldValue, V newValue) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V replace(K key, V value) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V computeIfPresent(K key,
	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V compute(K key,
	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V merge(K key, V value,
	BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
	throw new UnsupportedOperationException();
	}

	/**
	* 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>> {
	@java.io.Serial
	private static final long serialVersionUID = 7854390611657943733L;

	@SuppressWarnings({"unchecked", "rawtypes"})
	UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) {
	// Need to cast to raw in order to work around a limitation in the type system
	super((Set)s);
	}

	static <K, V> Consumer<Map.Entry<? extends K, ? extends V>> entryConsumer(
	Consumer<? super Entry<K, V>> action) {
	return e -> action.accept(new UnmodifiableEntry<>(e));
	}

	public void forEach(Consumer<? super Entry<K, V>> action) {
	Objects.requireNonNull(action);
	c.forEach(entryConsumer(action));
	}

	static final class UnmodifiableEntrySetSpliterator<K, V>
	implements Spliterator<Entry<K,V>> {
	final Spliterator<Map.Entry<K, V>> s;

	UnmodifiableEntrySetSpliterator(Spliterator<Entry<K, V>> s) {
	this.s = s;
	}

	@Override
	public boolean tryAdvance(Consumer<? super Entry<K, V>> action) {
	Objects.requireNonNull(action);
	return s.tryAdvance(entryConsumer(action));
	}

	@Override
	public void forEachRemaining(Consumer<? super Entry<K, V>> action) {
	Objects.requireNonNull(action);
	s.forEachRemaining(entryConsumer(action));
	}

	@Override
	public Spliterator<Entry<K, V>> trySplit() {
	Spliterator<Entry<K, V>> split = s.trySplit();
	return split == null
	? null
	: new UnmodifiableEntrySetSpliterator<>(split);
	}

	@Override
	public long estimateSize() {
	return s.estimateSize();
	}

	@Override
	public long getExactSizeIfKnown() {
	return s.getExactSizeIfKnown();
	}

	@Override
	public int characteristics() {
	return s.characteristics();
	}

	@Override
	public boolean hasCharacteristics(int characteristics) {
	return s.hasCharacteristics(characteristics);
	}

	@Override
	public Comparator<? super Entry<K, V>> getComparator() {
	return s.getComparator();
	}
	}

	@SuppressWarnings("unchecked")
	public Spliterator<Entry<K,V>> spliterator() {
	return new UnmodifiableEntrySetSpliterator<>(
	(Spliterator<Map.Entry<K, V>>) c.spliterator());
	}

	@Override
	public Stream<Entry<K,V>> stream() {
	return StreamSupport.stream(spliterator(), false);
	}

	@Override
	public Stream<Entry<K,V>> parallelStream() {
	return StreamSupport.stream(spliterator(), true);
	}

	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<>(i.next());
	}
	public void remove() {
	throw new UnsupportedOperationException();
	}
	public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action) {
	i.forEachRemaining(entryConsumer(action));
	}
	};
	}

	@SuppressWarnings("unchecked")
	public Object[] toArray() {
	Object[] a = c.toArray();
	for (int i=0; i<a.length; i++)
	a[i] = new UnmodifiableEntry<>((Map.Entry<? extends K, ? extends V>)a[i]);
	return a;
	}

	@SuppressWarnings("unchecked")
	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<>((Map.Entry<? extends K, ? extends 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<>((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) {
	for (Object e : coll) {
	if (!contains(e)) // Invokes safe contains() above
	return false;
	}
	return true;
	}
	public boolean equals(Object o) {
	if (o == this)
	return true;

	return o instanceof Set<?> s
	&& s.size() == c.size()
	&& 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 = Objects.requireNonNull(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 (this == o)
	return true;
	return o instanceof Map.Entry<?, ?> t
	&& eq(e.getKey(), t.getKey())
	&& eq(e.getValue(), t.getValue());
	}
	public String toString() {return e.toString();}
	}
	}
	}

	/**
	* Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the
	* specified sorted map. 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
	* {@code subMap}, {@code headMap}, or {@code tailMap} views, result in
	* an {@code UnsupportedOperationException}.<p>
	*
	* The returned sorted map will be serializable if the specified sorted map
	* is serializable.
	*
	* @implNote This method may return its argument if the argument is already unmodifiable.
	* @param <K> the class of the map keys
	* @param <V> the class of the map values
	* @param m the sorted map for which an unmodifiable view is to be
	* returned.
	* @return an unmodifiable view of the specified sorted map.
	*/
	@SuppressWarnings("unchecked")
	public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) {
	// Not checking for subclasses because of heap pollution and information leakage.
	if (m.getClass() == UnmodifiableSortedMap.class) {
	return (SortedMap<K,V>) m;
	}
	return new UnmodifiableSortedMap<>(m);
	}

	/**
	* @serial include
	*/
	static class UnmodifiableSortedMap<K,V>
	extends UnmodifiableMap<K,V>
	implements SortedMap<K,V>, Serializable {
	@java.io.Serial
	private static final long serialVersionUID = -8806743815996713206L;

	@SuppressWarnings("serial") // Conditionally serializable
	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<>(sm.subMap(fromKey, toKey)); }
	public SortedMap<K,V> headMap(K toKey)
	{ return new UnmodifiableSortedMap<>(sm.headMap(toKey)); }
	public SortedMap<K,V> tailMap(K fromKey)
	{ return new UnmodifiableSortedMap<>(sm.tailMap(fromKey)); }
	public K firstKey() { return sm.firstKey(); }
	public K lastKey() { return sm.lastKey(); }
	}

	/**
	* Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the
	* specified navigable map. Query operations on the returned navigable map "read
	* through" to the specified navigable map. Attempts to modify the returned
	* navigable map, whether direct, via its collection views, or via its
	* {@code subMap}, {@code headMap}, or {@code tailMap} views, result in
	* an {@code UnsupportedOperationException}.<p>
	*
	* The returned navigable map will be serializable if the specified
	* navigable map is serializable.
	*
	* @implNote This method may return its argument if the argument is already unmodifiable.
	* @param <K> the class of the map keys
	* @param <V> the class of the map values
	* @param m the navigable map for which an unmodifiable view is to be
	* returned
	* @return an unmodifiable view of the specified navigable map
	* @since 1.8
	*/
	@SuppressWarnings("unchecked")
	public static <K,V> NavigableMap<K,V> unmodifiableNavigableMap(NavigableMap<K, ? extends V> m) {
	if (m.getClass() == UnmodifiableNavigableMap.class) {
	return (NavigableMap<K,V>) m;
	}
	return new UnmodifiableNavigableMap<>(m);
	}

	/**
	* @serial include
	*/
	static class UnmodifiableNavigableMap<K,V>
	extends UnmodifiableSortedMap<K,V>
	implements NavigableMap<K,V>, Serializable {
	@java.io.Serial
	private static final long serialVersionUID = -4858195264774772197L;

	/**
	* A class for the {@link EMPTY_NAVIGABLE_MAP} which needs readResolve
	* to preserve singleton property.
	*
	* @param <K> type of keys, if there were any, and of bounds
	* @param <V> type of values, if there were any
	*/
	private static class EmptyNavigableMap<K,V> extends UnmodifiableNavigableMap<K,V>
	implements Serializable {

	@java.io.Serial
	private static final long serialVersionUID = -2239321462712562324L;

	EmptyNavigableMap() { super(new TreeMap<>()); }

	@Override
	public NavigableSet<K> navigableKeySet()
	{ return emptyNavigableSet(); }

	@java.io.Serial
	private Object readResolve() { return EMPTY_NAVIGABLE_MAP; }
	}

	/**
	* Singleton for {@link emptyNavigableMap()} which is also immutable.
	*/
	private static final EmptyNavigableMap<?,?> EMPTY_NAVIGABLE_MAP =
	new EmptyNavigableMap<>();

	/**
	* The instance we wrap and protect.
	*/
	@SuppressWarnings("serial") // Conditionally serializable
	private final NavigableMap<K, ? extends V> nm;

	UnmodifiableNavigableMap(NavigableMap<K, ? extends V> m)
	{super(m); nm = m;}

	public K lowerKey(K key) { return nm.lowerKey(key); }
	public K floorKey(K key) { return nm.floorKey(key); }
	public K ceilingKey(K key) { return nm.ceilingKey(key); }
	public K higherKey(K key) { return nm.higherKey(key); }

	@SuppressWarnings("unchecked")
	public Entry<K, V> lowerEntry(K key) {
	Entry<K,V> lower = (Entry<K, V>) nm.lowerEntry(key);
	return (null != lower)
	? new UnmodifiableEntrySet.UnmodifiableEntry<>(lower)
	: null;
	}

	@SuppressWarnings("unchecked")
	public Entry<K, V> floorEntry(K key) {
	Entry<K,V> floor = (Entry<K, V>) nm.floorEntry(key);
	return (null != floor)
	? new UnmodifiableEntrySet.UnmodifiableEntry<>(floor)
	: null;
	}

	@SuppressWarnings("unchecked")
	public Entry<K, V> ceilingEntry(K key) {
	Entry<K,V> ceiling = (Entry<K, V>) nm.ceilingEntry(key);
	return (null != ceiling)
	? new UnmodifiableEntrySet.UnmodifiableEntry<>(ceiling)
	: null;
	}


	@SuppressWarnings("unchecked")
	public Entry<K, V> higherEntry(K key) {
	Entry<K,V> higher = (Entry<K, V>) nm.higherEntry(key);
	return (null != higher)
	? new UnmodifiableEntrySet.UnmodifiableEntry<>(higher)
	: null;
	}

	@SuppressWarnings("unchecked")
	public Entry<K, V> firstEntry() {
	Entry<K,V> first = (Entry<K, V>) nm.firstEntry();
	return (null != first)
	? new UnmodifiableEntrySet.UnmodifiableEntry<>(first)
	: null;
	}

	@SuppressWarnings("unchecked")
	public Entry<K, V> lastEntry() {
	Entry<K,V> last = (Entry<K, V>) nm.lastEntry();
	return (null != last)
	? new UnmodifiableEntrySet.UnmodifiableEntry<>(last)
	: null;
	}

	public Entry<K, V> pollFirstEntry()
	{ throw new UnsupportedOperationException(); }
	public Entry<K, V> pollLastEntry()
	{ throw new UnsupportedOperationException(); }
	public NavigableMap<K, V> descendingMap()
	{ return unmodifiableNavigableMap(nm.descendingMap()); }
	public NavigableSet<K> navigableKeySet()
	{ return unmodifiableNavigableSet(nm.navigableKeySet()); }
	public NavigableSet<K> descendingKeySet()
	{ return unmodifiableNavigableSet(nm.descendingKeySet()); }

	public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
	return unmodifiableNavigableMap(
	nm.subMap(fromKey, fromInclusive, toKey, toInclusive));
	}

	public NavigableMap<K, V> headMap(K toKey, boolean inclusive)
	{ return unmodifiableNavigableMap(nm.headMap(toKey, inclusive)); }
	public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive)
	{ return unmodifiableNavigableMap(nm.tailMap(fromKey, inclusive)); }
	}

	// 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 traversing it via {@link Iterator}, {@link Spliterator}
	* or {@link Stream}:
	* <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 {@code hashCode}
	* and {@code equals} operations through to the backing collection, but
	* relies on {@code Object}'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 <T> the class of the objects in the collection
	* @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<>(c);
	}

	static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) {
	return new SynchronizedCollection<>(c, mutex);
	}

	/**
	* @serial include
	*/
	static class SynchronizedCollection<E> implements Collection<E>, Serializable {
	@java.io.Serial
	private static final long serialVersionUID = 3053995032091335093L;

	@SuppressWarnings("serial") // Conditionally serializable
	final Collection<E> c; // Backing Collection
	@SuppressWarnings("serial") // Conditionally serializable
	final Object mutex; // Object on which to synchronize

	SynchronizedCollection(Collection<E> c) {
	this.c = Objects.requireNonNull(c);
	mutex = this;
	}

	SynchronizedCollection(Collection<E> c, Object mutex) {
	this.c = Objects.requireNonNull(c);
	this.mutex = Objects.requireNonNull(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 <T> T[] toArray(IntFunction<T[]> f) {
	synchronized (mutex) {return c.toArray(f);}
	}

	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();}
	}
	// Override default methods in Collection
	@Override
	public void forEach(Consumer<? super E> consumer) {
	synchronized (mutex) {c.forEach(consumer);}
	}
	@Override
	public boolean removeIf(Predicate<? super E> filter) {
	synchronized (mutex) {return c.removeIf(filter);}
	}
	@Override
	public Spliterator<E> spliterator() {
	return c.spliterator(); // Must be manually synched by user!
	}
	@Override
	public Stream<E> stream() {
	return c.stream(); // Must be manually synched by user!
	}
	@Override
	public Stream<E> parallelStream() {
	return c.parallelStream(); // Must be manually synched by user!
	}
	@java.io.Serial
	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
	* collection when traversing it via {@link Iterator}, {@link Spliterator}
	* or {@link Stream}:
	* <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 <T> the class of the objects in the set
	* @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<>(s);
	}

	static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) {
	return new SynchronizedSet<>(s, mutex);
	}

	/**
	* @serial include
	*/
	static class SynchronizedSet<E>
	extends SynchronizedCollection<E>
	implements Set<E> {
	@java.io.Serial
	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) {
	if (this == o)
	return true;
	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 traversing it or any of its {@code subSet},
	* {@code headSet}, or {@code tailSet} views via {@link Iterator},
	* {@link Spliterator} or {@link Stream}:
	* <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 <T> the class of the objects in the set
	* @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<>(s);
	}

	/**
	* @serial include
	*/
	static class SynchronizedSortedSet<E>
	extends SynchronizedSet<E>
	implements SortedSet<E>
	{
	@java.io.Serial
	private static final long serialVersionUID = 8695801310862127406L;

	@SuppressWarnings("serial") // Conditionally serializable
	private final 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<>(
	ss.subSet(fromElement, toElement), mutex);
	}
	}
	public SortedSet<E> headSet(E toElement) {
	synchronized (mutex) {
	return new SynchronizedSortedSet<>(ss.headSet(toElement), mutex);
	}
	}
	public SortedSet<E> tailSet(E fromElement) {
	synchronized (mutex) {
	return new SynchronizedSortedSet<>(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) navigable set backed by the
	* specified navigable set. In order to guarantee serial access, it is
	* critical that <strong>all</strong> access to the backing navigable set is
	* accomplished through the returned navigable set (or its views).<p>
	*
	* It is imperative that the user manually synchronize on the returned
	* navigable set when traversing it, or any of its {@code subSet},
	* {@code headSet}, or {@code tailSet} views, via {@link Iterator},
	* {@link Spliterator} or {@link Stream}:
	* <pre>
	* NavigableSet s = Collections.synchronizedNavigableSet(new TreeSet());
	* ...
	* synchronized (s) {
	* Iterator i = s.iterator(); // Must be in the synchronized block
	* while (i.hasNext())
	* foo(i.next());
	* }
	* </pre>
	* or:
	* <pre>
	* NavigableSet s = Collections.synchronizedNavigableSet(new TreeSet());
	* NavigableSet s2 = s.headSet(foo, true);
	* ...
	* 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 navigable set will be serializable if the specified
	* navigable set is serializable.
	*
	* @param <T> the class of the objects in the set
	* @param s the navigable set to be "wrapped" in a synchronized navigable
	* set
	* @return a synchronized view of the specified navigable set
	* @since 1.8
	*/
	public static <T> NavigableSet<T> synchronizedNavigableSet(NavigableSet<T> s) {
	return new SynchronizedNavigableSet<>(s);
	}

	/**
	* @serial include
	*/
	static class SynchronizedNavigableSet<E>
	extends SynchronizedSortedSet<E>
	implements NavigableSet<E>
	{
	@java.io.Serial
	private static final long serialVersionUID = -5505529816273629798L;

	@SuppressWarnings("serial") // Conditionally serializable
	private final NavigableSet<E> ns;

	SynchronizedNavigableSet(NavigableSet<E> s) {
	super(s);
	ns = s;
	}

	SynchronizedNavigableSet(NavigableSet<E> s, Object mutex) {
	super(s, mutex);
	ns = s;
	}
	public E lower(E e) { synchronized (mutex) {return ns.lower(e);} }
	public E floor(E e) { synchronized (mutex) {return ns.floor(e);} }
	public E ceiling(E e) { synchronized (mutex) {return ns.ceiling(e);} }
	public E higher(E e) { synchronized (mutex) {return ns.higher(e);} }
	public E pollFirst() { synchronized (mutex) {return ns.pollFirst();} }
	public E pollLast() { synchronized (mutex) {return ns.pollLast();} }

	public NavigableSet<E> descendingSet() {
	synchronized (mutex) {
	return new SynchronizedNavigableSet<>(ns.descendingSet(), mutex);
	}
	}

	public Iterator<E> descendingIterator()
	{ synchronized (mutex) { return descendingSet().iterator(); } }

	public NavigableSet<E> subSet(E fromElement, E toElement) {
	synchronized (mutex) {
	return new SynchronizedNavigableSet<>(ns.subSet(fromElement, true, toElement, false), mutex);
	}
	}
	public NavigableSet<E> headSet(E toElement) {
	synchronized (mutex) {
	return new SynchronizedNavigableSet<>(ns.headSet(toElement, false), mutex);
	}
	}
	public NavigableSet<E> tailSet(E fromElement) {
	synchronized (mutex) {
	return new SynchronizedNavigableSet<>(ns.tailSet(fromElement, true), mutex);
	}
	}

	public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
	synchronized (mutex) {
	return new SynchronizedNavigableSet<>(ns.subSet(fromElement, fromInclusive, toElement, toInclusive), mutex);
	}
	}

	public NavigableSet<E> headSet(E toElement, boolean inclusive) {
	synchronized (mutex) {
	return new SynchronizedNavigableSet<>(ns.headSet(toElement, inclusive), mutex);
	}
	}

	public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
	synchronized (mutex) {
	return new SynchronizedNavigableSet<>(ns.tailSet(fromElement, inclusive), mutex);
	}
	}
	}

	/**
	* 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 traversing it via {@link Iterator}, {@link Spliterator}
	* or {@link Stream}:
	* <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 <T> the class of the objects in the list
	* @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<>(list) :
	new SynchronizedList<>(list));
	}

	static <T> List<T> synchronizedList(List<T> list, Object mutex) {
	return (list instanceof RandomAccess ?
	new SynchronizedRandomAccessList<>(list, mutex) :
	new SynchronizedList<>(list, mutex));
	}

	/**
	* @serial include
	*/
	static class SynchronizedList<E>
	extends SynchronizedCollection<E>
	implements List<E> {
	@java.io.Serial
	private static final long serialVersionUID = -7754090372962971524L;

	@SuppressWarnings("serial") // Conditionally serializable
	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) {
	if (this == o)
	return true;
	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<>(list.subList(fromIndex, toIndex),
	mutex);
	}
	}

	@Override
	public void replaceAll(UnaryOperator<E> operator) {
	synchronized (mutex) {list.replaceAll(operator);}
	}
	@Override
	public void sort(Comparator<? super E> c) {
	synchronized (mutex) {list.sort(c);}
	}

	/**
	* 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.
	*/
	@java.io.Serial
	private Object readResolve() {
	return (list instanceof RandomAccess
	? new SynchronizedRandomAccessList<>(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<>(
	list.subList(fromIndex, toIndex), mutex);
	}
	}

	@java.io.Serial
	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.
	*/
	@java.io.Serial
	private Object writeReplace() {
	return new SynchronizedList<>(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 traversing any of its collection views via {@link Iterator},
	* {@link Spliterator} or {@link Stream}:
	* <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 <K> the class of the map keys
	* @param <V> the class of the map values
	* @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<>(m);
	}

	/**
	* @serial include
	*/
	private static class SynchronizedMap<K,V>
	implements Map<K,V>, Serializable {
	@java.io.Serial
	private static final long serialVersionUID = 1978198479659022715L;

	@SuppressWarnings("serial") // Conditionally serializable
	private final Map<K,V> m; // Backing Map
	@SuppressWarnings("serial") // Conditionally serializable
	final Object mutex; // Object on which to synchronize

	SynchronizedMap(Map<K,V> m) {
	this.m = Objects.requireNonNull(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;
	private transient Set<Map.Entry<K,V>> entrySet;
	private transient Collection<V> values;

	public Set<K> keySet() {
	synchronized (mutex) {
	if (keySet==null)
	keySet = new SynchronizedSet<>(m.keySet(), mutex);
	return keySet;
	}
	}

	public Set<Map.Entry<K,V>> entrySet() {
	synchronized (mutex) {
	if (entrySet==null)
	entrySet = new SynchronizedSet<>(m.entrySet(), mutex);
	return entrySet;
	}
	}

	public Collection<V> values() {
	synchronized (mutex) {
	if (values==null)
	values = new SynchronizedCollection<>(m.values(), mutex);
	return values;
	}
	}

	public boolean equals(Object o) {
	if (this == o)
	return true;
	synchronized (mutex) {return m.equals(o);}
	}
	public int hashCode() {
	synchronized (mutex) {return m.hashCode();}
	}
	public String toString() {
	synchronized (mutex) {return m.toString();}
	}

	// Override default methods in Map
	@Override
	public V getOrDefault(Object k, V defaultValue) {
	synchronized (mutex) {return m.getOrDefault(k, defaultValue);}
	}
	@Override
	public void forEach(BiConsumer<? super K, ? super V> action) {
	synchronized (mutex) {m.forEach(action);}
	}
	@Override
	public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
	synchronized (mutex) {m.replaceAll(function);}
	}
	@Override
	public V putIfAbsent(K key, V value) {
	synchronized (mutex) {return m.putIfAbsent(key, value);}
	}
	@Override
	public boolean remove(Object key, Object value) {
	synchronized (mutex) {return m.remove(key, value);}
	}
	@Override
	public boolean replace(K key, V oldValue, V newValue) {
	synchronized (mutex) {return m.replace(key, oldValue, newValue);}
	}
	@Override
	public V replace(K key, V value) {
	synchronized (mutex) {return m.replace(key, value);}
	}
	@Override
	public V computeIfAbsent(K key,
	Function<? super K, ? extends V> mappingFunction) {
	synchronized (mutex) {return m.computeIfAbsent(key, mappingFunction);}
	}
	@Override
	public V computeIfPresent(K key,
	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
	synchronized (mutex) {return m.computeIfPresent(key, remappingFunction);}
	}
	@Override
	public V compute(K key,
	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
	synchronized (mutex) {return m.compute(key, remappingFunction);}
	}
	@Override
	public V merge(K key, V value,
	BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
	synchronized (mutex) {return m.merge(key, value, remappingFunction);}
	}

	@java.io.Serial
	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 traversing any of its collection views, or the
	* collections views of any of its {@code subMap}, {@code headMap} or
	* {@code tailMap} views, via {@link Iterator}, {@link Spliterator} or
	* {@link Stream}:
	* <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 = s2.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 <K> the class of the map keys
	* @param <V> the class of the map values
	* @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<>(m);
	}

	/**
	* @serial include
	*/
	static class SynchronizedSortedMap<K,V>
	extends SynchronizedMap<K,V>
	implements SortedMap<K,V>
	{
	@java.io.Serial
	private static final long serialVersionUID = -8798146769416483793L;

	@SuppressWarnings("serial") // Conditionally serializable
	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<>(
	sm.subMap(fromKey, toKey), mutex);
	}
	}
	public SortedMap<K,V> headMap(K toKey) {
	synchronized (mutex) {
	return new SynchronizedSortedMap<>(sm.headMap(toKey), mutex);
	}
	}
	public SortedMap<K,V> tailMap(K fromKey) {
	synchronized (mutex) {
	return new SynchronizedSortedMap<>(sm.tailMap(fromKey),mutex);
	}
	}

	public K firstKey() {
	synchronized (mutex) {return sm.firstKey();}
	}
	public K lastKey() {
	synchronized (mutex) {return sm.lastKey();}
	}
	}

	/**
	* Returns a synchronized (thread-safe) navigable map backed by the
	* specified navigable map. In order to guarantee serial access, it is
	* critical that <strong>all</strong> access to the backing navigable map is
	* accomplished through the returned navigable map (or its views).<p>
	*
	* It is imperative that the user manually synchronize on the returned
	* navigable map when traversing any of its collection views, or the
	* collections views of any of its {@code subMap}, {@code headMap} or
	* {@code tailMap} views, via {@link Iterator}, {@link Spliterator} or
	* {@link Stream}:
	* <pre>
	* NavigableMap m = Collections.synchronizedNavigableMap(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>
	* NavigableMap m = Collections.synchronizedNavigableMap(new TreeMap());
	* NavigableMap m2 = m.subMap(foo, true, bar, false);
	* ...
	* 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 navigable map will be serializable if the specified
	* navigable map is serializable.
	*
	* @param <K> the class of the map keys
	* @param <V> the class of the map values
	* @param m the navigable map to be "wrapped" in a synchronized navigable
	* map
	* @return a synchronized view of the specified navigable map.
	* @since 1.8
	*/
	public static <K,V> NavigableMap<K,V> synchronizedNavigableMap(NavigableMap<K,V> m) {
	return new SynchronizedNavigableMap<>(m);
	}

	/**
	* A synchronized NavigableMap.
	*
	* @serial include
	*/
	static class SynchronizedNavigableMap<K,V>
	extends SynchronizedSortedMap<K,V>
	implements NavigableMap<K,V>
	{
	@java.io.Serial
	private static final long serialVersionUID = 699392247599746807L;

	@SuppressWarnings("serial") // Conditionally serializable
	private final NavigableMap<K,V> nm;

	SynchronizedNavigableMap(NavigableMap<K,V> m) {
	super(m);
	nm = m;
	}
	SynchronizedNavigableMap(NavigableMap<K,V> m, Object mutex) {
	super(m, mutex);
	nm = m;
	}

	public Entry<K, V> lowerEntry(K key)
	{ synchronized (mutex) { return nm.lowerEntry(key); } }
	public K lowerKey(K key)
	{ synchronized (mutex) { return nm.lowerKey(key); } }
	public Entry<K, V> floorEntry(K key)
	{ synchronized (mutex) { return nm.floorEntry(key); } }
	public K floorKey(K key)
	{ synchronized (mutex) { return nm.floorKey(key); } }
	public Entry<K, V> ceilingEntry(K key)
	{ synchronized (mutex) { return nm.ceilingEntry(key); } }
	public K ceilingKey(K key)
	{ synchronized (mutex) { return nm.ceilingKey(key); } }
	public Entry<K, V> higherEntry(K key)
	{ synchronized (mutex) { return nm.higherEntry(key); } }
	public K higherKey(K key)
	{ synchronized (mutex) { return nm.higherKey(key); } }
	public Entry<K, V> firstEntry()
	{ synchronized (mutex) { return nm.firstEntry(); } }
	public Entry<K, V> lastEntry()
	{ synchronized (mutex) { return nm.lastEntry(); } }
	public Entry<K, V> pollFirstEntry()
	{ synchronized (mutex) { return nm.pollFirstEntry(); } }
	public Entry<K, V> pollLastEntry()
	{ synchronized (mutex) { return nm.pollLastEntry(); } }

	public NavigableMap<K, V> descendingMap() {
	synchronized (mutex) {
	return
	new SynchronizedNavigableMap<>(nm.descendingMap(), mutex);
	}
	}

	public NavigableSet<K> keySet() {
	return navigableKeySet();
	}

	public NavigableSet<K> navigableKeySet() {
	synchronized (mutex) {
	return new SynchronizedNavigableSet<>(nm.navigableKeySet(), mutex);
	}
	}

	public NavigableSet<K> descendingKeySet() {
	synchronized (mutex) {
	return new SynchronizedNavigableSet<>(nm.descendingKeySet(), mutex);
	}
	}


	public SortedMap<K,V> subMap(K fromKey, K toKey) {
	synchronized (mutex) {
	return new SynchronizedNavigableMap<>(
	nm.subMap(fromKey, true, toKey, false), mutex);
	}
	}
	public SortedMap<K,V> headMap(K toKey) {
	synchronized (mutex) {
	return new SynchronizedNavigableMap<>(nm.headMap(toKey, false), mutex);
	}
	}
	public SortedMap<K,V> tailMap(K fromKey) {
	synchronized (mutex) {
	return new SynchronizedNavigableMap<>(nm.tailMap(fromKey, true),mutex);
	}
	}

	public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
	synchronized (mutex) {
	return new SynchronizedNavigableMap<>(
	nm.subMap(fromKey, fromInclusive, toKey, toInclusive), mutex);
	}
	}

	public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
	synchronized (mutex) {
	return new SynchronizedNavigableMap<>(
	nm.headMap(toKey, inclusive), mutex);
	}
	}

	public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) {
	synchronized (mutex) {
	return new SynchronizedNavigableMap<>(
	nm.tailMap(fromKey, inclusive), mutex);
	}
	}
	}

	// 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<>();
	* }</pre>
	* may be replaced temporarily by this one:
	* <pre> {@code
	* Collection<String> c = Collections.checkedCollection(
	* new HashSet<>(), 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 <E> the class of the objects in the collection
	* @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<>(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 {
	@java.io.Serial
	private static final long serialVersionUID = 1578914078182001775L;

	@SuppressWarnings("serial") // Conditionally serializable
	final Collection<E> c;
	@SuppressWarnings("serial") // Conditionally serializable
	final Class<E> type;

	@SuppressWarnings("unchecked")
	E typeCheck(Object o) {
	if (o != null && !type.isInstance(o))
	throw new ClassCastException(badElementMsg(o));
	return (E) 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) {
	this.c = Objects.requireNonNull(c, "c");
	this.type = Objects.requireNonNull(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 <T> T[] toArray(IntFunction<T[]> f) { return c.toArray(f); }
	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() {
	// JDK-6363904 - unwrapped iterator could be typecast to
	// ListIterator with unsafe set()
	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 void forEachRemaining(Consumer<? super E> action) {
	it.forEachRemaining(action);
	}
	};
	}

	public boolean add(E e) { return c.add(typeCheck(e)); }

	@SuppressWarnings("serial") // Conditionally serializable
	private E[] zeroLengthElementArray; // Lazily initialized

	private E[] zeroLengthElementArray() {
	return zeroLengthElementArray != null ? zeroLengthElementArray :
	(zeroLengthElementArray = zeroLengthArray(type));
	}

	@SuppressWarnings("unchecked")
	Collection<E> checkedCopyOf(Collection<? extends E> coll) {
	Object[] a;
	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));
	}

	// Override default methods in Collection
	@Override
	public void forEach(Consumer<? super E> action) {c.forEach(action);}
	@Override
	public boolean removeIf(Predicate<? super E> filter) {
	return c.removeIf(filter);
	}
	@Override
	public Spliterator<E> spliterator() {return c.spliterator();}
	@Override
	public Stream<E> stream() {return c.stream();}
	@Override
	public Stream<E> parallelStream() {return c.parallelStream();}
	}

	/**
	* Returns a dynamically typesafe view of the specified queue.
	* Any attempt to insert an element of the wrong type will result in
	* an immediate {@link ClassCastException}. Assuming a queue contains
	* no incorrectly typed elements prior to the time a dynamically typesafe
	* view is generated, and that all subsequent access to the queue
	* takes place through the view, it is <i>guaranteed</i> that the
	* queue 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 queue will be serializable if the specified queue
	* is serializable.
	*
	* <p>Since {@code null} is considered to be a value of any reference
	* type, the returned queue permits insertion of {@code null} elements
	* whenever the backing queue does.
	*
	* @param <E> the class of the objects in the queue
	* @param queue the queue for which a dynamically typesafe view is to be
	* returned
	* @param type the type of element that {@code queue} is permitted to hold
	* @return a dynamically typesafe view of the specified queue
	* @since 1.8
	*/
	public static <E> Queue<E> checkedQueue(Queue<E> queue, Class<E> type) {
	return new CheckedQueue<>(queue, type);
	}

	/**
	* @serial include
	*/
	static class CheckedQueue<E>
	extends CheckedCollection<E>
	implements Queue<E>, Serializable
	{
	@java.io.Serial
	private static final long serialVersionUID = 1433151992604707767L;
	@SuppressWarnings("serial") // Conditionally serializable
	final Queue<E> queue;

	CheckedQueue(Queue<E> queue, Class<E> elementType) {
	super(queue, elementType);
	this.queue = queue;
	}

	public E element() {return queue.element();}
	public boolean equals(Object o) {return o == this \|\| c.equals(o);}
	public int hashCode() {return c.hashCode();}
	public E peek() {return queue.peek();}
	public E poll() {return queue.poll();}
	public E remove() {return queue.remove();}
	public boolean offer(E e) {return queue.offer(typeCheck(e));}
	}

	/**
	* 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 <E> the class of the objects in the set
	* @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<>(s, type);
	}

	/**
	* @serial include
	*/
	static class CheckedSet<E> extends CheckedCollection<E>
	implements Set<E>, Serializable
	{
	@java.io.Serial
	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 <E> the class of the objects in the set
	* @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<>(s, type);
	}

	/**
	* @serial include
	*/
	static class CheckedSortedSet<E> extends CheckedSet<E>
	implements SortedSet<E>, Serializable
	{
	@java.io.Serial
	private static final long serialVersionUID = 1599911165492914959L;

	@SuppressWarnings("serial") // Conditionally serializable
	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 navigable set.
	* Any attempt to insert an element of the wrong type will result in an
	* immediate {@link ClassCastException}. Assuming a navigable set
	* contains no incorrectly typed elements prior to the time a
	* dynamically typesafe view is generated, and that all subsequent
	* access to the navigable set takes place through the view, it is
	* <em>guaranteed</em> that the navigable 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 navigable set will be serializable if the specified
	* navigable set is serializable.
	*
	* <p>Since {@code null} is considered to be a value of any reference
	* type, the returned navigable set permits insertion of null elements
	* whenever the backing sorted set does.
	*
	* @param <E> the class of the objects in the set
	* @param s the navigable 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 navigable set
	* @since 1.8
	*/
	public static <E> NavigableSet<E> checkedNavigableSet(NavigableSet<E> s,
	Class<E> type) {
	return new CheckedNavigableSet<>(s, type);
	}

	/**
	* @serial include
	*/
	static class CheckedNavigableSet<E> extends CheckedSortedSet<E>
	implements NavigableSet<E>, Serializable
	{
	@java.io.Serial
	private static final long serialVersionUID = -5429120189805438922L;

	@SuppressWarnings("serial") // Conditionally serializable
	private final NavigableSet<E> ns;

	CheckedNavigableSet(NavigableSet<E> s, Class<E> type) {
	super(s, type);
	ns = s;
	}

	public E lower(E e) { return ns.lower(e); }
	public E floor(E e) { return ns.floor(e); }
	public E ceiling(E e) { return ns.ceiling(e); }
	public E higher(E e) { return ns.higher(e); }
	public E pollFirst() { return ns.pollFirst(); }
	public E pollLast() {return ns.pollLast(); }
	public NavigableSet<E> descendingSet()
	{ return checkedNavigableSet(ns.descendingSet(), type); }
	public Iterator<E> descendingIterator()
	{return checkedNavigableSet(ns.descendingSet(), type).iterator(); }

	public NavigableSet<E> subSet(E fromElement, E toElement) {
	return checkedNavigableSet(ns.subSet(fromElement, true, toElement, false), type);
	}
	public NavigableSet<E> headSet(E toElement) {
	return checkedNavigableSet(ns.headSet(toElement, false), type);
	}
	public NavigableSet<E> tailSet(E fromElement) {
	return checkedNavigableSet(ns.tailSet(fromElement, true), type);
	}

	public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
	return checkedNavigableSet(ns.subSet(fromElement, fromInclusive, toElement, toInclusive), type);
	}

	public NavigableSet<E> headSet(E toElement, boolean inclusive) {
	return checkedNavigableSet(ns.headSet(toElement, inclusive), type);
	}

	public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
	return checkedNavigableSet(ns.tailSet(fromElement, inclusive), 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 <E> the class of the objects in the list
	* @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<>(list, type) :
	new CheckedList<>(list, type));
	}

	/**
	* @serial include
	*/
	static class CheckedList<E>
	extends CheckedCollection<E>
	implements List<E>
	{
	@java.io.Serial
	private static final long serialVersionUID = 65247728283967356L;
	@SuppressWarnings("serial") // Conditionally serializable
	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) {
	return list.set(index, typeCheck(element));
	}

	public void add(int index, E element) {
	list.add(index, typeCheck(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) {
	i.set(typeCheck(e));
	}

	public void add(E e) {
	i.add(typeCheck(e));
	}

	@Override
	public void forEachRemaining(Consumer<? super E> action) {
	i.forEachRemaining(action);
	}
	};
	}

	public List<E> subList(int fromIndex, int toIndex) {
	return new CheckedList<>(list.subList(fromIndex, toIndex), type);
	}

	/**
	* {@inheritDoc}
	*
	* @throws ClassCastException if the class of an element returned by the
	* operator prevents it from being added to this collection. The
	* exception may be thrown after some elements of the list have
	* already been replaced.
	*/
	@Override
	public void replaceAll(UnaryOperator<E> operator) {
	Objects.requireNonNull(operator);
	list.replaceAll(e -> typeCheck(operator.apply(e)));
	}

	@Override
	public void sort(Comparator<? super E> c) {
	list.sort(c);
	}
	}

	/**
	* @serial include
	*/
	static class CheckedRandomAccessList<E> extends CheckedList<E>
	implements RandomAccess
	{
	@java.io.Serial
	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<>(
	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 <K> the class of the map keys
	* @param <V> the class of the map values
	* @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<>(m, keyType, valueType);
	}


	/**
	* @serial include
	*/
	private static class CheckedMap<K,V>
	implements Map<K,V>, Serializable
	{
	@java.io.Serial
	private static final long serialVersionUID = 5742860141034234728L;

	@SuppressWarnings("serial") // Conditionally serializable
	private final Map<K, V> m;
	@SuppressWarnings("serial") // Conditionally serializable
	final Class<K> keyType;
	@SuppressWarnings("serial") // Conditionally serializable
	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 BiFunction<? super K, ? super V, ? extends V> typeCheck(
	BiFunction<? super K, ? super V, ? extends V> func) {
	Objects.requireNonNull(func);
	return (k, v) -> {
	V newValue = func.apply(k, v);
	typeCheck(k, newValue);
	return newValue;
	};
	}

	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) {
	this.m = Objects.requireNonNull(m);
	this.keyType = Objects.requireNonNull(keyType);
	this.valueType = Objects.requireNonNull(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<>(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)k, (V)v));
	}
	for (Map.Entry<K,V> e : checked)
	m.put(e.getKey(), e.getValue());
	}

	private transient Set<Map.Entry<K,V>> entrySet;

	public Set<Map.Entry<K,V>> entrySet() {
	if (entrySet==null)
	entrySet = new CheckedEntrySet<>(m.entrySet(), valueType);
	return entrySet;
	}

	// Override default methods in Map
	@Override
	public void forEach(BiConsumer<? super K, ? super V> action) {
	m.forEach(action);
	}

	@Override
	public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
	m.replaceAll(typeCheck(function));
	}

	@Override
	public V putIfAbsent(K key, V value) {
	typeCheck(key, value);
	return m.putIfAbsent(key, value);
	}

	@Override
	public boolean remove(Object key, Object value) {
	return m.remove(key, value);
	}

	@Override
	public boolean replace(K key, V oldValue, V newValue) {
	typeCheck(key, newValue);
	return m.replace(key, oldValue, newValue);
	}

	@Override
	public V replace(K key, V value) {
	typeCheck(key, value);
	return m.replace(key, value);
	}

	@Override
	public V computeIfAbsent(K key,
	Function<? super K, ? extends V> mappingFunction) {
	Objects.requireNonNull(mappingFunction);
	return m.computeIfAbsent(key, k -> {
	V value = mappingFunction.apply(k);
	typeCheck(k, value);
	return value;
	});
	}

	@Override
	public V computeIfPresent(K key,
	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
	return m.computeIfPresent(key, typeCheck(remappingFunction));
	}

	@Override
	public V compute(K key,
	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
	return m.compute(key, typeCheck(remappingFunction));
	}

	@Override
	public V merge(K key, V value,
	BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
	Objects.requireNonNull(remappingFunction);
	return m.merge(key, value, (v1, v2) -> {
	V newValue = remappingFunction.apply(v1, v2);
	typeCheck(null, newValue);
	return newValue;
	});
	}

	/**
	* 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();

	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);
	}

	public void forEachRemaining(Consumer<? super Entry<K, V>> action) {
	i.forEachRemaining(
	e -> action.accept(checkedEntry(e, 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 = (source.getClass() == Object[].class)
	? 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) {
	return o instanceof Map.Entry<?, ?> e
	&& 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
	<>((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) {
	Objects.requireNonNull(c);
	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;
	return o instanceof Set<?> that
	&& 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<>(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 = Objects.requireNonNull(e);
	this.valueType = Objects.requireNonNull(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
	<>((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 <K> the class of the map keys
	* @param <V> the class of the map values
	* @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<>(m, keyType, valueType);
	}

	/**
	* @serial include
	*/
	static class CheckedSortedMap<K,V> extends CheckedMap<K,V>
	implements SortedMap<K,V>, Serializable
	{
	@java.io.Serial
	private static final long serialVersionUID = 1599671320688067438L;

	@SuppressWarnings("serial") // Conditionally serializable
	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);
	}
	}

	/**
	* Returns a dynamically typesafe view of the specified navigable 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 <em>guaranteed</em> 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 <K> type of map keys
	* @param <V> type of map values
	* @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 1.8
	*/
	public static <K,V> NavigableMap<K,V> checkedNavigableMap(NavigableMap<K, V> m,
	Class<K> keyType,
	Class<V> valueType) {
	return new CheckedNavigableMap<>(m, keyType, valueType);
	}

	/**
	* @serial include
	*/
	static class CheckedNavigableMap<K,V> extends CheckedSortedMap<K,V>
	implements NavigableMap<K,V>, Serializable
	{
	@java.io.Serial
	private static final long serialVersionUID = -4852462692372534096L;

	@SuppressWarnings("serial") // Conditionally serializable
	private final NavigableMap<K, V> nm;

	CheckedNavigableMap(NavigableMap<K, V> m,
	Class<K> keyType, Class<V> valueType) {
	super(m, keyType, valueType);
	nm = m;
	}

	public Comparator<? super K> comparator() { return nm.comparator(); }
	public K firstKey() { return nm.firstKey(); }
	public K lastKey() { return nm.lastKey(); }

	public Entry<K, V> lowerEntry(K key) {
	Entry<K,V> lower = nm.lowerEntry(key);
	return (null != lower)
	? new CheckedMap.CheckedEntrySet.CheckedEntry<>(lower, valueType)
	: null;
	}

	public K lowerKey(K key) { return nm.lowerKey(key); }

	public Entry<K, V> floorEntry(K key) {
	Entry<K,V> floor = nm.floorEntry(key);
	return (null != floor)
	? new CheckedMap.CheckedEntrySet.CheckedEntry<>(floor, valueType)
	: null;
	}

	public K floorKey(K key) { return nm.floorKey(key); }

	public Entry<K, V> ceilingEntry(K key) {
	Entry<K,V> ceiling = nm.ceilingEntry(key);
	return (null != ceiling)
	? new CheckedMap.CheckedEntrySet.CheckedEntry<>(ceiling, valueType)
	: null;
	}

	public K ceilingKey(K key) { return nm.ceilingKey(key); }

	public Entry<K, V> higherEntry(K key) {
	Entry<K,V> higher = nm.higherEntry(key);
	return (null != higher)
	? new CheckedMap.CheckedEntrySet.CheckedEntry<>(higher, valueType)
	: null;
	}

	public K higherKey(K key) { return nm.higherKey(key); }

	public Entry<K, V> firstEntry() {
	Entry<K,V> first = nm.firstEntry();
	return (null != first)
	? new CheckedMap.CheckedEntrySet.CheckedEntry<>(first, valueType)
	: null;
	}

	public Entry<K, V> lastEntry() {
	Entry<K,V> last = nm.lastEntry();
	return (null != last)
	? new CheckedMap.CheckedEntrySet.CheckedEntry<>(last, valueType)
	: null;
	}

	public Entry<K, V> pollFirstEntry() {
	Entry<K,V> entry = nm.pollFirstEntry();
	return (null == entry)
	? null
	: new CheckedMap.CheckedEntrySet.CheckedEntry<>(entry, valueType);
	}

	public Entry<K, V> pollLastEntry() {
	Entry<K,V> entry = nm.pollLastEntry();
	return (null == entry)
	? null
	: new CheckedMap.CheckedEntrySet.CheckedEntry<>(entry, valueType);
	}

	public NavigableMap<K, V> descendingMap() {
	return checkedNavigableMap(nm.descendingMap(), keyType, valueType);
	}

	public NavigableSet<K> keySet() {
	return navigableKeySet();
	}

	public NavigableSet<K> navigableKeySet() {
	return checkedNavigableSet(nm.navigableKeySet(), keyType);
	}

	public NavigableSet<K> descendingKeySet() {
	return checkedNavigableSet(nm.descendingKeySet(), keyType);
	}

	@Override
	public NavigableMap<K,V> subMap(K fromKey, K toKey) {
	return checkedNavigableMap(nm.subMap(fromKey, true, toKey, false),
	keyType, valueType);
	}

	@Override
	public NavigableMap<K,V> headMap(K toKey) {
	return checkedNavigableMap(nm.headMap(toKey, false), keyType, valueType);
	}

	@Override
	public NavigableMap<K,V> tailMap(K fromKey) {
	return checkedNavigableMap(nm.tailMap(fromKey, true), keyType, valueType);
	}

	public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
	return checkedNavigableMap(nm.subMap(fromKey, fromInclusive, toKey, toInclusive), keyType, valueType);
	}

	public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
	return checkedNavigableMap(nm.headMap(toKey, inclusive), keyType, valueType);
	}

	public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) {
	return checkedNavigableMap(nm.tailMap(fromKey, inclusive), keyType, valueType);
	}
	}

	// Empty collections

	/**
	* Returns an iterator that has no elements. More precisely,
	*
	* <ul>
	* <li>{@link Iterator#hasNext hasNext} always returns {@code
	* false}.</li>
	* <li>{@link Iterator#next next} always throws {@link
	* NoSuchElementException}.</li>
	* <li>{@link Iterator#remove remove} always throws {@link
	* IllegalStateException}.</li>
	* </ul>
	*
	* <p>Implementations of this method are permitted, but not
	* required, to return the same object from multiple invocations.
	*
	* @param <T> type of elements, if there were any, in the iterator
	* @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<>();

	public boolean hasNext() { return false; }
	public E next() { throw new NoSuchElementException(); }
	public void remove() { throw new IllegalStateException(); }
	@Override
	public void forEachRemaining(Consumer<? super E> action) {
	Objects.requireNonNull(action);
	}
	}

	/**
	* Returns a list iterator that has no elements. More precisely,
	*
	* <ul>
	* <li>{@link Iterator#hasNext hasNext} and {@link
	* ListIterator#hasPrevious hasPrevious} always return {@code
	* false}.</li>
	* <li>{@link Iterator#next next} and {@link ListIterator#previous
	* previous} always throw {@link NoSuchElementException}.</li>
	* <li>{@link Iterator#remove remove} and {@link ListIterator#set
	* set} always throw {@link IllegalStateException}.</li>
	* <li>{@link ListIterator#add add} always throws {@link
	* UnsupportedOperationException}.</li>
	* <li>{@link ListIterator#nextIndex nextIndex} always returns
	* {@code 0}.</li>
	* <li>{@link ListIterator#previousIndex previousIndex} always
	* returns {@code -1}.</li>
	* </ul>
	*
	* <p>Implementations of this method are permitted, but not
	* required, to return the same object from multiple invocations.
	*
	* @param <T> type of elements, if there were any, in the iterator
	* @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<>();

	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>
	* <li>{@link Enumeration#hasMoreElements hasMoreElements} always
	* returns {@code false}.</li>
	* <li> {@link Enumeration#nextElement nextElement} always throws
	* {@link NoSuchElementException}.</li>
	* </ul>
	*
	* <p>Implementations of this method are permitted, but not
	* required, to return the same object from multiple invocations.
	*
	* @param <T> the class of the objects in the enumeration
	* @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<>();

	public boolean hasMoreElements() { return false; }
	public E nextElement() { throw new NoSuchElementException(); }
	public Iterator<E> asIterator() { return emptyIterator(); }
	}

	/**
	* The empty set (immutable). This set is serializable.
	*
	* @see #emptySet()
	*/
	@SuppressWarnings("rawtypes")
	public static final Set EMPTY_SET = new EmptySet<>();

	/**
	* Returns an 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<String> s = Collections.emptySet();
	* </pre>
	* @implNote Implementations of this method need not create a separate
	* {@code Set} 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.)
	*
	* @param <T> the class of the objects in the set
	* @return the empty set
	*
	* @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
	{
	@java.io.Serial
	private static final long serialVersionUID = 1582296315990362920L;

	public Iterator<E> iterator() { return emptyIterator(); }

	public int size() {return 0;}
	public boolean isEmpty() {return true;}
	public void clear() {}

	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;
	}

	// Override default methods in Collection
	@Override
	public void forEach(Consumer<? super E> action) {
	Objects.requireNonNull(action);
	}
	@Override
	public boolean removeIf(Predicate<? super E> filter) {
	Objects.requireNonNull(filter);
	return false;
	}
	@Override
	public Spliterator<E> spliterator() { return Spliterators.emptySpliterator(); }

	// Preserves singleton property
	@java.io.Serial
	private Object readResolve() {
	return EMPTY_SET;
	}

	@Override
	public int hashCode() {
	return 0;
	}
	}

	/**
	* Returns an empty sorted set (immutable). This set is serializable.
	*
	* <p>This example illustrates the type-safe way to obtain an empty
	* sorted set:
	* <pre> {@code
	* SortedSet<String> s = Collections.emptySortedSet();
	* }</pre>
	*
	* @implNote Implementations of this method need not create a separate
	* {@code SortedSet} object for each call.
	*
	* @param <E> type of elements, if there were any, in the set
	* @return the empty sorted set
	* @since 1.8
	*/
	@SuppressWarnings("unchecked")
	public static <E> SortedSet<E> emptySortedSet() {
	return (SortedSet<E>) UnmodifiableNavigableSet.EMPTY_NAVIGABLE_SET;
	}

	/**
	* Returns an empty navigable set (immutable). This set is serializable.
	*
	* <p>This example illustrates the type-safe way to obtain an empty
	* navigable set:
	* <pre> {@code
	* NavigableSet<String> s = Collections.emptyNavigableSet();
	* }</pre>
	*
	* @implNote Implementations of this method need not
	* create a separate {@code NavigableSet} object for each call.
	*
	* @param <E> type of elements, if there were any, in the set
	* @return the empty navigable set
	* @since 1.8
	*/
	@SuppressWarnings("unchecked")
	public static <E> NavigableSet<E> emptyNavigableSet() {
	return (NavigableSet<E>) UnmodifiableNavigableSet.EMPTY_NAVIGABLE_SET;
	}

	/**
	* The empty list (immutable). This list is serializable.
	*
	* @see #emptyList()
	*/
	@SuppressWarnings("rawtypes")
	public static final List EMPTY_LIST = new EmptyList<>();

	/**
	* Returns an empty list (immutable). This list is serializable.
	*
	* <p>This example illustrates the type-safe way to obtain an empty list:
	* <pre>
	* List<String> s = Collections.emptyList();
	* </pre>
	*
	* @implNote
	* Implementations of this method need not create a separate {@code List}
	* 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.)
	*
	* @param <T> type of elements, if there were any, in the list
	* @return an empty immutable list
	*
	* @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 {
	@java.io.Serial
	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 void clear() {}

	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; }

	@Override
	public boolean removeIf(Predicate<? super E> filter) {
	Objects.requireNonNull(filter);
	return false;
	}
	@Override
	public void replaceAll(UnaryOperator<E> operator) {
	Objects.requireNonNull(operator);
	}
	@Override
	public void sort(Comparator<? super E> c) {
	}

	// Override default methods in Collection
	@Override
	public void forEach(Consumer<? super E> action) {
	Objects.requireNonNull(action);
	}

	@Override
	public Spliterator<E> spliterator() { return Spliterators.emptySpliterator(); }

	// Preserves singleton property
	@java.io.Serial
	private Object readResolve() {
	return EMPTY_LIST;
	}
	}

	/**
	* The empty map (immutable). This map is serializable.
	*
	* @see #emptyMap()
	* @since 1.3
	*/
	@SuppressWarnings("rawtypes")
	public static final Map EMPTY_MAP = new EmptyMap<>();

	/**
	* Returns an empty map (immutable). This map is serializable.
	*
	* <p>This example illustrates the type-safe way to obtain an empty map:
	* <pre>
	* Map<String, Date> s = Collections.emptyMap();
	* </pre>
	* @implNote Implementations of this method need not create a separate
	* {@code Map} 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.)
	*
	* @param <K> the class of the map keys
	* @param <V> the class of the map values
	* @return an empty map
	* @see #EMPTY_MAP
	* @since 1.5
	*/
	@SuppressWarnings("unchecked")
	public static final <K,V> Map<K,V> emptyMap() {
	return (Map<K,V>) EMPTY_MAP;
	}

	/**
	* Returns an empty sorted map (immutable). This map is serializable.
	*
	* <p>This example illustrates the type-safe way to obtain an empty map:
	* <pre> {@code
	* SortedMap<String, Date> s = Collections.emptySortedMap();
	* }</pre>
	*
	* @implNote Implementations of this method need not create a separate
	* {@code SortedMap} object for each call.
	*
	* @param <K> the class of the map keys
	* @param <V> the class of the map values
	* @return an empty sorted map
	* @since 1.8
	*/
	@SuppressWarnings("unchecked")
	public static final <K,V> SortedMap<K,V> emptySortedMap() {
	return (SortedMap<K,V>) UnmodifiableNavigableMap.EMPTY_NAVIGABLE_MAP;
	}

	/**
	* Returns an empty navigable map (immutable). This map is serializable.
	*
	* <p>This example illustrates the type-safe way to obtain an empty map:
	* <pre> {@code
	* NavigableMap<String, Date> s = Collections.emptyNavigableMap();
	* }</pre>
	*
	* @implNote Implementations of this method need not create a separate
	* {@code NavigableMap} object for each call.
	*
	* @param <K> the class of the map keys
	* @param <V> the class of the map values
	* @return an empty navigable map
	* @since 1.8
	*/
	@SuppressWarnings("unchecked")
	public static final <K,V> NavigableMap<K,V> emptyNavigableMap() {
	return (NavigableMap<K,V>) UnmodifiableNavigableMap.EMPTY_NAVIGABLE_MAP;
	}

	/**
	* @serial include
	*/
	private static class EmptyMap<K,V>
	extends AbstractMap<K,V>
	implements Serializable
	{
	@java.io.Serial
	private static final long serialVersionUID = 6428348081105594320L;

	public int size() {return 0;}
	public boolean isEmpty() {return true;}
	public void clear() {}
	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;}

	// Override default methods in Map
	@Override
	@SuppressWarnings("unchecked")
	public V getOrDefault(Object k, V defaultValue) {
	return defaultValue;
	}

	@Override
	public void forEach(BiConsumer<? super K, ? super V> action) {
	Objects.requireNonNull(action);
	}

	@Override
	public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
	Objects.requireNonNull(function);
	}

	@Override
	public V putIfAbsent(K key, V value) {
	throw new UnsupportedOperationException();
	}

	@Override
	public boolean remove(Object key, Object value) {
	throw new UnsupportedOperationException();
	}

	@Override
	public boolean replace(K key, V oldValue, V newValue) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V replace(K key, V value) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V computeIfAbsent(K key,
	Function<? super K, ? extends V> mappingFunction) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V computeIfPresent(K key,
	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V compute(K key,
	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V merge(K key, V value,
	BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
	throw new UnsupportedOperationException();
	}

	// Preserves singleton property
	@java.io.Serial
	private Object readResolve() {
	return EMPTY_MAP;
	}
	}

	// Singleton collections

	/**
	* Returns an immutable set containing only the specified object.
	* The returned set is serializable.
	*
	* @param <T> the class of the objects in the set
	* @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<>(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();
	}
	@Override
	public void forEachRemaining(Consumer<? super E> action) {
	Objects.requireNonNull(action);
	if (hasNext) {
	hasNext = false;
	action.accept(e);
	}
	}
	};
	}

	/**
	* Creates a {@code Spliterator} with only the specified element
	*
	* @param <T> Type of elements
	* @return A singleton {@code Spliterator}
	*/
	static <T> Spliterator<T> singletonSpliterator(final T element) {
	return new Spliterator<T>() {
	long est = 1;

	@Override
	public Spliterator<T> trySplit() {
	return null;
	}

	@Override
	public boolean tryAdvance(Consumer<? super T> consumer) {
	Objects.requireNonNull(consumer);
	if (est > 0) {
	est--;
	consumer.accept(element);
	return true;
	}
	return false;
	}

	@Override
	public void forEachRemaining(Consumer<? super T> consumer) {
	tryAdvance(consumer);
	}

	@Override
	public long estimateSize() {
	return est;
	}

	@Override
	public int characteristics() {
	int value = (element != null) ? Spliterator.NONNULL : 0;

	return value \| Spliterator.SIZED \| Spliterator.SUBSIZED \| Spliterator.IMMUTABLE \|
	Spliterator.DISTINCT \| Spliterator.ORDERED;
	}
	};
	}

	/**
	* @serial include
	*/
	private static class SingletonSet<E>
	extends AbstractSet<E>
	implements Serializable
	{
	@java.io.Serial
	private static final long serialVersionUID = 3193687207550431679L;

	@SuppressWarnings("serial") // Conditionally serializable
	private final 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);}

	// Override default methods for Collection
	@Override
	public void forEach(Consumer<? super E> action) {
	action.accept(element);
	}
	@Override
	public Spliterator<E> spliterator() {
	return singletonSpliterator(element);
	}
	@Override
	public boolean removeIf(Predicate<? super E> filter) {
	throw new UnsupportedOperationException();
	}
	@Override
	public int hashCode() {
	return Objects.hashCode(element);
	}
	}

	/**
	* Returns an immutable list containing only the specified object.
	* The returned list is serializable.
	*
	* @param <T> the class of the objects in the list
	* @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<>(o);
	}

	/**
	* @serial include
	*/
	private static class SingletonList<E>
	extends AbstractList<E>
	implements RandomAccess, Serializable {

	@java.io.Serial
	private static final long serialVersionUID = 3093736618740652951L;

	@SuppressWarnings("serial") // Conditionally serializable
	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;
	}

	// Override default methods for Collection
	@Override
	public void forEach(Consumer<? super E> action) {
	action.accept(element);
	}
	@Override
	public boolean removeIf(Predicate<? super E> filter) {
	throw new UnsupportedOperationException();
	}
	@Override
	public void replaceAll(UnaryOperator<E> operator) {
	throw new UnsupportedOperationException();
	}
	@Override
	public void sort(Comparator<? super E> c) {
	}
	@Override
	public Spliterator<E> spliterator() {
	return singletonSpliterator(element);
	}
	@Override
	public int hashCode() {
	return 31 + Objects.hashCode(element);
	}
	}

	/**
	* Returns an immutable map, mapping only the specified key to the
	* specified value. The returned map is serializable.
	*
	* @param <K> the class of the map keys
	* @param <V> the class of the map values
	* @param key the sole key to be stored in the returned map.
	* @param value the value to which the returned map maps {@code key}.
	* @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<>(key, value);
	}

	/**
	* @serial include
	*/
	private static class SingletonMap<K,V>
	extends AbstractMap<K,V>
	implements Serializable {
	@java.io.Serial
	private static final long serialVersionUID = -6979724477215052911L;

	@SuppressWarnings("serial") // Conditionally serializable
	private final K k;
	@SuppressWarnings("serial") // Conditionally serializable
	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;
	private transient Set<Map.Entry<K,V>> entrySet;
	private transient Collection<V> values;

	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));
	return entrySet;
	}

	public Collection<V> values() {
	if (values==null)
	values = singleton(v);
	return values;
	}

	// Override default methods in Map
	@Override
	public V getOrDefault(Object key, V defaultValue) {
	return eq(key, k) ? v : defaultValue;
	}

	@Override
	public void forEach(BiConsumer<? super K, ? super V> action) {
	action.accept(k, v);
	}

	@Override
	public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V putIfAbsent(K key, V value) {
	throw new UnsupportedOperationException();
	}

	@Override
	public boolean remove(Object key, Object value) {
	throw new UnsupportedOperationException();
	}

	@Override
	public boolean replace(K key, V oldValue, V newValue) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V replace(K key, V value) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V computeIfAbsent(K key,
	Function<? super K, ? extends V> mappingFunction) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V computeIfPresent(K key,
	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V compute(K key,
	BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
	throw new UnsupportedOperationException();
	}

	@Override
	public V merge(K key, V value,
	BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
	throw new UnsupportedOperationException();
	}

	@Override
	public int hashCode() {
	return Objects.hashCode(k) ^ Objects.hashCode(v);
	}
	}

	// Miscellaneous

	/**
	* Returns an immutable list consisting of {@code n} 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 {@code List.addAll} method to grow lists.
	* The returned list is serializable.
	*
	* @param <T> the class of the object to copy and of the objects
	* in the returned list.
	* @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 {@code n} copies of the
	* specified object.
	* @throws IllegalArgumentException if {@code n < 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<>(n, o);
	}

	/**
	* @serial include
	*/
	private static class CopiesList<E>
	extends AbstractList<E>
	implements RandomAccess, Serializable
	{
	@java.io.Serial
	private static final long serialVersionUID = 2739099268398711800L;

	final int n;
	@SuppressWarnings("serial") // Conditionally serializable
	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;
	}

	@SuppressWarnings("unchecked")
	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<>(toIndex - fromIndex, element);
	}

	@Override
	public int hashCode() {
	if (n == 0) return 1;
	// hashCode of n repeating elements is 31^n + elementHash * Sum(31^k, k = 0..n-1)
	// this implementation completes in O(log(n)) steps taking advantage of
	// 31^(2n) = (31^n)^2 and Sum(31^k, k = 0..(2n-1)) = Sum(31^k, k = 0..n-1) * (31^n + 1)
	int pow = 31;
	int sum = 1;
	for (int i = Integer.numberOfLeadingZeros(n) + 1; i < Integer.SIZE; i++) {
	sum *= pow + 1;
	pow *= pow;
	if ((n << i) < 0) {
	pow *= 31;
	sum = sum * 31 + 1;
	}
	}
	return pow + sum * (element == null ? 0 : element.hashCode());
	}

	@Override
	public boolean equals(Object o) {
	if (o == this)
	return true;
	if (o instanceof CopiesList<?> other) {
	return n == other.n && (n == 0 \|\| eq(element, other.element));
	}
	if (!(o instanceof List))
	return false;

	int remaining = n;
	E e = element;
	Iterator<?> itr = ((List<?>) o).iterator();
	if (e == null) {
	while (itr.hasNext() && remaining-- > 0) {
	if (itr.next() != null)
	return false;
	}
	} else {
	while (itr.hasNext() && remaining-- > 0) {
	if (!e.equals(itr.next()))
	return false;
	}
	}
	return remaining == 0 && !itr.hasNext();
	}

	// Override default methods in Collection
	@Override
	public Stream<E> stream() {
	return IntStream.range(0, n).mapToObj(i -> element);
	}

	@Override
	public Stream<E> parallelStream() {
	return IntStream.range(0, n).parallel().mapToObj(i -> element);
	}

	@Override
	public Spliterator<E> spliterator() {
	return stream().spliterator();
	}

	@java.io.Serial
	private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
	ois.defaultReadObject();
	SharedSecrets.getJavaObjectInputStreamAccess().checkArray(ois, Object[].class, n);
	}
	}

	/**
	* Returns a comparator that imposes the reverse of the <em>natural
	* ordering</em> on a collection of objects that implement the
	* {@code Comparable} interface. (The natural ordering is the ordering
	* imposed by the objects' own {@code compareTo} method.) This enables a
	* simple idiom for sorting (or maintaining) collections (or arrays) of
	* objects that implement the {@code Comparable} interface in
	* reverse-natural-order. For example, suppose {@code 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.
	*
	* @param <T> the class of the objects compared by the comparator
	* @return A comparator that imposes the reverse of the <i>natural
	* ordering</i> on a collection of objects that implement
	* the {@code Comparable} interface.
	* @see Comparable
	*/
	@SuppressWarnings("unchecked")
	public static <T> Comparator<T> reverseOrder() {
	return (Comparator<T>) ReverseComparator.REVERSE_ORDER;
	}

	/**
	* @serial include
	*/
	private static class ReverseComparator
	implements Comparator<Comparable<Object>>, Serializable {

	@java.io.Serial
	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);
	}

	@java.io.Serial
	private Object readResolve() { return Collections.reverseOrder(); }

	@Override
	public Comparator<Comparable<Object>> reversed() {
	return Comparator.naturalOrder();
	}
	}

	/**
	* Returns a comparator that imposes the reverse ordering of the specified
	* comparator. If the specified comparator is {@code null}, this method is
	* equivalent to {@link #reverseOrder()} (in other words, it returns a
	* comparator that imposes the reverse of the <em>natural ordering</em> on
	* a collection of objects that implement the Comparable interface).
	*
	* <p>The returned comparator is serializable (assuming the specified
	* comparator is also serializable or {@code null}).
	*
	* @param <T> the class of the objects compared by the comparator
	* @param cmp a comparator who's ordering is to be reversed by the returned
	* comparator or {@code null}
	* @return A comparator that imposes the reverse ordering of the
	* specified comparator.
	* @since 1.5
	*/
	@SuppressWarnings("unchecked")
	public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) {
	if (cmp == null) {
	return (Comparator<T>) ReverseComparator.REVERSE_ORDER;
	} else if (cmp == ReverseComparator.REVERSE_ORDER) {
	return (Comparator<T>) Comparators.NaturalOrderComparator.INSTANCE;
	} else if (cmp == Comparators.NaturalOrderComparator.INSTANCE) {
	return (Comparator<T>) ReverseComparator.REVERSE_ORDER;
	} else if (cmp instanceof ReverseComparator2) {
	return ((ReverseComparator2<T>) cmp).cmp;
	} else {
	return new ReverseComparator2<>(cmp);
	}
	}

	/**
	* @serial include
	*/
	private static class ReverseComparator2<T> implements Comparator<T>,
	Serializable
	{
	@java.io.Serial
	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
	*/
	@SuppressWarnings("serial") // Conditionally serializable
	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;
	}

	@Override
	public Comparator<T> reversed() {
	return cmp;
	}
	}

	/**
	* Returns an enumeration over the specified collection. This provides
	* interoperability with legacy APIs that require an enumeration
	* as input.
	*
	* <p>The iterator returned from a call to {@link Enumeration#asIterator()}
	* does not support removal of elements from the specified collection. This
	* is necessary to avoid unintentionally increasing the capabilities of the
	* returned enumeration.
	*
	* @param <T> the class of the objects in the collection
	* @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 <T> the class of the objects returned by the enumeration
	* @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<>();
	while (e.hasMoreElements())
	l.add(e.nextElement());
	return l;
	}

	/**
	* Returns true if the specified arguments are equal, or both null.
	*
	* NB: Do not replace with Object.equals until JDK-8015417 is resolved.
	*/
	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
	* {@code e} in the collection such that
	* {@code Objects.equals(o, e)}.
	*
	* @param c the collection in which to determine the frequency
	* of {@code o}
	* @param o the object whose frequency is to be determined
	* @return the number of elements in {@code c} equal to {@code o}
	* @throws NullPointerException if {@code c} 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 {@code true} 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 {@code Collection}.
	* 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 <em>compatible with
	* equals</em>, 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>Care must also be exercised when using collections that have
	* restrictions on the elements that they may contain. Collection
	* implementations are allowed to throw exceptions for any operation
	* involving elements they deem ineligible. For absolute safety the
	* specified collections should contain only elements which are
	* eligible elements for both collections.
	*
	* <p>Note that it is permissible to pass the same collection in both
	* parameters, in which case the method will return {@code true} if and
	* only if the collection is empty.
	*
	* @param c1 a collection
	* @param c2 a collection
	* @return {@code true} if the two specified collections have no
	* elements in common.
	* @throws NullPointerException if either collection is {@code null}.
	* @throws NullPointerException if one collection contains a {@code null}
	* element and {@code null} is not an eligible element for the other collection.
	* (<a href="Collection.html#optional-restrictions">optional</a>)
	* @throws ClassCastException if one collection contains an element that is
	* of a type which is ineligible for the other collection.
	* (<a href="Collection.html#optional-restrictions">optional</a>)
	* @since 1.5
	*/
	public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
	// The collection to be used for contains(). Preference is given to
	// the collection who's contains() has lower O() complexity.
	Collection<?> contains = c2;
	// The collection to be iterated. If the collections' contains() impl
	// are of different O() complexity, the collection with slower
	// contains() will be used for iteration. For collections who's
	// contains() are of the same complexity then best performance is
	// achieved by iterating the smaller collection.
	Collection<?> iterate = c1;

	// Performance optimization cases. The heuristics:
	// 1. Generally iterate over c1.
	// 2. If c1 is a Set then iterate over c2.
	// 3. If either collection is empty then result is always true.
	// 4. Iterate over the smaller Collection.
	if (c1 instanceof Set) {
	// Use c1 for contains as a Set's contains() is expected to perform
	// better than O(N/2)
	iterate = c2;
	contains = c1;
	} else if (!(c2 instanceof Set)) {
	// Both are mere Collections. Iterate over smaller collection.
	// Example: If c1 contains 3 elements and c2 contains 50 elements and
	// assuming contains() requires ceiling(N/2) comparisons then
	// checking for all c1 elements in c2 would require 75 comparisons
	// (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring
	// 100 comparisons (50 * ceiling(3/2)).
	int c1size = c1.size();
	int c2size = c2.size();
	if (c1size == 0 \|\| c2size == 0) {
	// At least one collection is empty. Nothing will match.
	return true;
	}

	if (c1size > c2size) {
	iterate = c2;
	contains = c1;
	}
	}

	for (Object e : iterate) {
	if (contains.contains(e)) {
	// Found a common element. Collections are not disjoint.
	return false;
	}
	}

	// No common elements were found.
	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 behaviour of this convenience method is similar to that of
	* {@code cc.addAll(Collections.unmodifiableList(Arrays.asList(elements)))}.
	*
	* <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 <T> the class of the elements to add and of the collection
	* @param c the collection into which {@code elements} are to be inserted
	* @param elements the elements to insert into {@code c}
	* @return {@code true} if the collection changed as a result of the call
	* @throws UnsupportedOperationException if {@code c} does not support
	* the {@code add} operation
	* @throws NullPointerException if {@code elements} contains one or more
	* null values and {@code c} does not permit null elements, or
	* if {@code c} or {@code elements} are {@code null}
	* @throws IllegalArgumentException if some property of a value in
	* {@code elements} prevents it from being added to {@code c}
	* @see Collection#addAll(Collection)
	* @since 1.5
	*/
	@SafeVarargs
	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 {@code keySet}
	* view, with one exception. The {@code addAll} method is implemented
	* as a sequence of {@code put} 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<Object> weakHashSet = Collections.newSetFromMap(
	* new WeakHashMap<Object, Boolean>());
	* </pre>
	*
	* @param <E> the class of the map keys and of the objects in the
	* returned set
	* @param map the backing map
	* @return the set backed by the map
	* @throws IllegalArgumentException if {@code map} is not empty
	* @since 1.6
	*/
	public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
	return new SetFromMap<>(map);
	}

	/**
	* @serial include
	*/
	private static class SetFromMap<E> extends AbstractSet<E>
	implements Set<E>, Serializable
	{
	@SuppressWarnings("serial") // Conditionally 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

	// Override default methods in Collection
	@Override
	public void forEach(Consumer<? super E> action) {
	s.forEach(action);
	}
	@Override
	public boolean removeIf(Predicate<? super E> filter) {
	return s.removeIf(filter);
	}

	@Override
	public Spliterator<E> spliterator() {return s.spliterator();}
	@Override
	public Stream<E> stream() {return s.stream();}
	@Override
	public Stream<E> parallelStream() {return s.parallelStream();}

	@java.io.Serial
	private static final long serialVersionUID = 2454657854757543876L;

	@java.io.Serial
	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 {@code add} is mapped to {@code push},
	* {@code remove} is mapped to {@code pop} and so on. This
	* view can be useful when you would like to use a method
	* requiring a {@code Queue} 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 <T> the class of the objects in the deque
	* @param deque the deque
	* @return the queue
	* @since 1.6
	*/
	public static <T> Queue<T> asLifoQueue(Deque<T> deque) {
	return new AsLIFOQueue<>(Objects.requireNonNull(deque));
	}

	/**
	* @serial include
	*/
	static class AsLIFOQueue<E> extends AbstractQueue<E>
	implements Queue<E>, Serializable {
	@java.io.Serial
	private static final long serialVersionUID = 1802017725587941708L;
	@SuppressWarnings("serial") // Conditionally serializable
	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 <T> T[] toArray(IntFunction<T[]> f) { return q.toArray(f); }
	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

	// Override default methods in Collection
	@Override
	public void forEach(Consumer<? super E> action) {q.forEach(action);}
	@Override
	public boolean removeIf(Predicate<? super E> filter) {
	return q.removeIf(filter);
	}
	@Override
	public Spliterator<E> spliterator() {return q.spliterator();}
	@Override
	public Stream<E> stream() {return q.stream();}
	@Override
	public Stream<E> parallelStream() {return q.parallelStream();}
	}
	}

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