gt:                 if (!(o instanceof Map.Entry))
context: /*
   * Copyright (c) 1997, 2012, 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.Serializable;
  import java.io.ObjectOutputStream;
  import java.io.IOException;
  import java.lang.reflect.Array;
  
  /**
   * This class consists exclusively of static methods that operate on or return
   * collections.  It contains polymorphic algorithms that operate on
   * collections, "wrappers", which return a new collection backed by a
   * specified collection, and a few other odds and ends.
   *
   * <p>The methods of this class all throw a <tt>NullPointerException</tt>
   * if the collections or class objects provided to them are null.
   *
   * <p>The documentation for the polymorphic algorithms contained in this class
   * generally includes a brief description of the <i>implementation</i>.  Such
   * descriptions should be regarded as <i>implementation notes</i>, rather than
   * parts of the <i>specification</i>.  Implementors should feel free to
   * substitute other algorithms, so long as the specification itself is adhered
   * to.  (For example, the algorithm used by <tt>sort</tt> does not have to be
   * a mergesort, but it does have to be <i>stable</i>.)
   *
   * <p>The "destructive" algorithms contained in this class, that is, the
   * algorithms that modify the collection on which they operate, are specified
   * to throw <tt>UnsupportedOperationException</tt> if the collection does not
   * support the appropriate mutation primitive(s), such as the <tt>set</tt>
   * method.  These algorithms may, but are not required to, throw this
   * exception if an invocation would have no effect on the collection.  For
   * example, invoking the <tt>sort</tt> method on an unmodifiable list that is
   * already sorted may or may not throw <tt>UnsupportedOperationException</tt>.
   *
   * <p>This class is a member of the
   * <a href="{@docRoot}/../technotes/guides/collections/index.html">
   * Java Collections Framework</a>.
   *
   * @author  Josh Bloch
   * @author  Neal Gafter
   * @see     Collection
   * @see     Set
   * @see     List
   * @see     Map
   * @since   1.2
   */
  
  public class Collections {
      // Suppresses default constructor, ensuring non-instantiability.
      private Collections() {
      }
  
      // Algorithms
  
      /*
       * Tuning parameters for algorithms - Many of the List algorithms have
       * two implementations, one of which is appropriate for RandomAccess
       * lists, the other for "sequential."  Often, the random access variant
       * yields better performance on small sequential access lists.  The
       * tuning parameters below determine the cutoff point for what constitutes
       * a "small" sequential access list for each algorithm.  The values below
       * were empirically determined to work well for LinkedList. Hopefully
       * they should be reasonable for other sequential access List
       * implementations.  Those doing performance work on this code would
       * do well to validate the values of these parameters from time to time.
       * (The first word of each tuning parameter name is the algorithm to which
       * it applies.)
       */
      private static final int BINARYSEARCH_THRESHOLD   = 5000;
      private static final int REVERSE_THRESHOLD        =   18;
      private static final int SHUFFLE_THRESHOLD        =    5;
      private static final int FILL_THRESHOLD           =   25;
      private static final int ROTATE_THRESHOLD         =  100;
      private static final int COPY_THRESHOLD           =   10;
      private static final int REPLACEALL_THRESHOLD     =   11;
      private static final int INDEXOFSUBLIST_THRESHOLD =   35;
  
      /**
       * Sorts the specified list into ascending order, according to the
       * {@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.
       *
       * <p>Implementation note: This implementation is a stable, adaptive,
       * iterative mergesort that requires far fewer than n lg(n) comparisons
       * when the input array is partially sorted, while offering the
       * performance of a traditional mergesort when the input array is
       * randomly ordered.  If the input array is nearly sorted, the
       * implementation requires approximately n comparisons.  Temporary
       * storage requirements vary from a small constant for nearly sorted
       * input arrays to n/2 object references for randomly ordered input
       * arrays.
       *
       * <p>The implementation takes equal advantage of ascending and
       * descending order in its input array, and can take advantage of
       * ascending and descending order in different parts of the same
       * input array.  It is well-suited to merging two or more sorted arrays:
       * simply concatenate the arrays and sort the resulting array.
       *
       * <p>The implementation was adapted from Tim Peters's list sort for Python
       * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt">
       * TimSort</a>).  It uses techiques from Peter McIlroy's "Optimistic
       * Sorting and Information Theoretic Complexity", in Proceedings of the
       * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474,
       * January 1993.
       *
       * <p>This implementation dumps the specified list into an array, sorts
       * the array, and iterates over the list resetting each element
       * from the corresponding position in the array.  This avoids the
       * n<sup>2</sup> log(n) performance that would result from attempting
       * to sort a linked list in place.
       *
       * @param  list the list to be sorted.
       * @throws ClassCastException if the list contains elements that are not
       *         <i>mutually comparable</i> (for example, strings and integers).
       * @throws UnsupportedOperationException if the specified list's
       *         list-iterator does not support the {@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
       */
      public static <T extends Comparable<? super T>> void sort(List<T> list) {
          Object[] a = list.toArray();
          Arrays.sort(a);
          ListIterator<T> i = list.listIterator();
          for (int j=0; j<a.length; j++) {
              i.next();
              i.set((T)a[j]);
          }
      }
  
      /**
       * Sorts the specified list according to the order induced by the
       * specified comparator.  All elements in the list must be <i>mutually
       * comparable</i> using the specified comparator (that is,
       * {@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.
       *
       * <p>Implementation note: This implementation is a stable, adaptive,
       * iterative mergesort that requires far fewer than n lg(n) comparisons
       * when the input array is partially sorted, while offering the
       * performance of a traditional mergesort when the input array is
       * randomly ordered.  If the input array is nearly sorted, the
       * implementation requires approximately n comparisons.  Temporary
       * storage requirements vary from a small constant for nearly sorted
       * input arrays to n/2 object references for randomly ordered input
       * arrays.
       *
       * <p>The implementation takes equal advantage of ascending and
       * descending order in its input array, and can take advantage of
       * ascending and descending order in different parts of the same
       * input array.  It is well-suited to merging two or more sorted arrays:
       * simply concatenate the arrays and sort the resulting array.
       *
       * <p>The implementation was adapted from Tim Peters's list sort for Python
       * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt">
       * TimSort</a>).  It uses techiques from Peter McIlroy's "Optimistic
       * Sorting and Information Theoretic Complexity", in Proceedings of the
       * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474,
       * January 1993.
       *
       * <p>This implementation dumps the specified list into an array, sorts
       * the array, and iterates over the list resetting each element
       * from the corresponding position in the array.  This avoids the
       * n<sup>2</sup> log(n) performance that would result from attempting
       * to sort a linked list in place.
       *
       * @param  list the list to be sorted.
       * @param  c the comparator to determine the order of the list.  A
       *        {@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
       */
      public static <T> void sort(List<T> list, Comparator<? super T> c) {
          Object[] a = list.toArray();
          Arrays.sort(a, (Comparator)c);
          ListIterator i = list.listIterator();
          for (int j=0; j<a.length; j++) {
              i.next();
              i.set(a[j]);
          }
      }
  
  
      /**
       * Searches the specified list for the specified object using the binary
       * search algorithm.  The list must be sorted into ascending order
       * according to the {@linkplain Comparable natural ordering} of its
       * elements (as by the {@link #sort(List)} method) prior to making this
       * call.  If it is not sorted, the results are undefined.  If the list
       * contains multiple elements equal to the specified object, there is no
       * guarantee which one will be found.
       *
       * <p>This method runs in log(n) time for a "random access" list (which
       * provides near-constant-time positional access).  If the specified list
       * does not implement the {@link RandomAccess} interface and is large,
       * this method will do an iterator-based binary search that performs
       * O(n) link traversals and O(log n) element comparisons.
       *
       * @param  list the list to be searched.
       * @param  key the key to be searched for.
       * @return the index of the search key, if it is contained in the list;
       *         otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>.  The
       *         <i>insertion point</i> is defined as the point at which the
       *         key would be inserted into the list: the index of the first
       *         element greater than the key, or <tt>list.size()</tt> if all
       *         elements in the list are less than the specified key.  Note
       *         that this guarantees that the return value will be &gt;= 0 if
       *         and only if the key is found.
       * @throws ClassCastException if the list contains elements that are not
       *         <i>mutually comparable</i> (for example, strings and
       *         integers), or the search key is not mutually comparable
       *         with the elements of the list.
       */
      public static <T>
      int binarySearch(List<? extends Comparable<? super T>> list, T key) {
          if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
              return Collections.indexedBinarySearch(list, key);
          else
              return Collections.iteratorBinarySearch(list, key);
      }
  
      private static <T>
      int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key)
      {
          int low = 0;
          int high = list.size()-1;
  
          while (low <= high) {
              int mid = (low + high) >>> 1;
              Comparable<? super T> midVal = list.get(mid);
              int cmp = midVal.compareTo(key);
  
              if (cmp < 0)
                  low = mid + 1;
              else if (cmp > 0)
                  high = mid - 1;
              else
                  return mid; // key found
          }
          return -(low + 1);  // key not found
      }
  
      private static <T>
      int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key)
      {
          int low = 0;
          int high = list.size()-1;
          ListIterator<? extends Comparable<? super T>> i = list.listIterator();
  
          while (low <= high) {
              int mid = (low + high) >>> 1;
              Comparable<? super T> midVal = get(i, mid);
              int cmp = midVal.compareTo(key);
  
              if (cmp < 0)
                  low = mid + 1;
              else if (cmp > 0)
                  high = mid - 1;
              else
                  return mid; // key found
          }
          return -(low + 1);  // key not found
      }
  
      /**
       * Gets the ith element from the given list by repositioning the specified
       * list listIterator.
       */
      private static <T> T get(ListIterator<? extends T> i, int index) {
          T obj = null;
          int pos = i.nextIndex();
          if (pos <= index) {
              do {
                  obj = i.next();
              } while (pos++ < index);
          } else {
              do {
                  obj = i.previous();
              } while (--pos > index);
          }
          return obj;
      }
  
      /**
       * Searches the specified list for the specified object using the binary
       * search algorithm.  The list must be sorted into ascending order
       * according to the specified comparator (as by the
       * {@link #sort(List, Comparator) sort(List, Comparator)}
       * method), prior to making this call.  If it is
       * not sorted, the results are undefined.  If the list contains multiple
       * elements equal to the specified object, there is no guarantee which one
       * will be found.
       *
       * <p>This method runs in log(n) time for a "random access" list (which
       * provides near-constant-time positional access).  If the specified list
       * does not implement the {@link RandomAccess} interface and is large,
       * this method will do an iterator-based binary search that performs
       * O(n) link traversals and O(log n) element comparisons.
       *
       * @param  list the list to be searched.
       * @param  key the key to be searched for.
       * @param  c the comparator by which the list is ordered.
       *         A <tt>null</tt> value indicates that the elements'
       *         {@linkplain Comparable natural ordering} should be used.
       * @return the index of the search key, if it is contained in the list;
       *         otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>.  The
       *         <i>insertion point</i> is defined as the point at which the
       *         key would be inserted into the list: the index of the first
       *         element greater than the key, or <tt>list.size()</tt> if all
       *         elements in the list are less than the specified key.  Note
       *         that this guarantees that the return value will be &gt;= 0 if
       *         and only if the key is found.
       * @throws ClassCastException if the list contains elements that are not
       *         <i>mutually comparable</i> using the specified comparator,
       *         or the search key is not mutually comparable with the
       *         elements of the list using this comparator.
       */
      public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) {
          if (c==null)
              return binarySearch((List) list, key);
  
          if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
              return Collections.indexedBinarySearch(list, key, c);
          else
              return Collections.iteratorBinarySearch(list, key, c);
      }
  
      private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
          int low = 0;
          int high = l.size()-1;
  
          while (low <= high) {
              int mid = (low + high) >>> 1;
              T midVal = l.get(mid);
              int cmp = c.compare(midVal, key);
  
              if (cmp < 0)
                  low = mid + 1;
              else if (cmp > 0)
                  high = mid - 1;
              else
                  return mid; // key found
          }
          return -(low + 1);  // key not found
      }
  
      private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
          int low = 0;
          int high = l.size()-1;
          ListIterator<? extends T> i = l.listIterator();
  
          while (low <= high) {
              int mid = (low + high) >>> 1;
              T midVal = get(i, mid);
              int cmp = c.compare(midVal, key);
  
              if (cmp < 0)
                  low = mid + 1;
              else if (cmp > 0)
                  high = mid - 1;
              else
                  return mid; // key found
          }
          return -(low + 1);  // key not found
      }
  
      private interface SelfComparable extends Comparable<SelfComparable> {}
  
  
      /**
       * Reverses the order of the elements in the specified list.<p>
       *
       * This method runs in linear time.
       *
       * @param  list the list whose elements are to be reversed.
       * @throws UnsupportedOperationException if the specified list or
       *         its list-iterator does not support the <tt>set</tt> operation.
       */
      public static void reverse(List<?> list) {
          int size = list.size();
          if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) {
              for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--)
                  swap(list, i, j);
          } else {
              ListIterator fwd = list.listIterator();
              ListIterator rev = list.listIterator(size);
              for (int i=0, mid=list.size()>>1; i<mid; i++) {
                  Object tmp = fwd.next();
                  fwd.set(rev.previous());
                  rev.set(tmp);
              }
          }
      }
  
      /**
       * Randomly permutes the specified list using a default source of
       * randomness.  All permutations occur with approximately equal
       * likelihood.<p>
       *
       * The hedge "approximately" is used in the foregoing description because
       * default source of randomness is only approximately an unbiased source
       * of independently chosen bits. If it were a perfect source of randomly
       * chosen bits, then the algorithm would choose permutations with perfect
       * uniformity.<p>
       *
       * This implementation traverses the list backwards, from the last element
       * up to the second, repeatedly swapping a randomly selected element into
       * the "current position".  Elements are randomly selected from the
       * portion of the list that runs from the first element to the current
       * position, inclusive.<p>
       *
       * This method runs in linear time.  If the specified list does not
       * implement the {@link RandomAccess} interface and is large, this
       * implementation dumps the specified list into an array before shuffling
       * it, and dumps the shuffled array back into the list.  This avoids the
       * quadratic behavior that would result from shuffling a "sequential
       * access" list in place.
       *
       * @param  list the list to be shuffled.
       * @throws UnsupportedOperationException if the specified list or
       *         its list-iterator does not support the <tt>set</tt> operation.
       */
      public static void shuffle(List<?> list) {
          Random rnd = r;
          if (rnd == null)
              r = rnd = new Random();
          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 <tt>set</tt> operation.
       */
      public static void shuffle(List<?> list, Random rnd) {
          int size = list.size();
          if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) {
              for (int i=size; i>1; i--)
                  swap(list, i-1, rnd.nextInt(i));
          } else {
              Object arr[] = list.toArray();
  
              // Shuffle array
              for (int i=size; i>1; i--)
                  swap(arr, i-1, rnd.nextInt(i));
  
              // Dump array back into list
              ListIterator it = list.listIterator();
              for (int i=0; i<arr.length; i++) {
                  it.next();
                  it.set(arr[i]);
              }
          }
      }
  
      /**
       * Swaps the elements at the specified positions in the specified list.
       * (If the specified positions are equal, invoking this method leaves
       * the list unchanged.)
       *
       * @param list The list in which to swap elements.
       * @param i the index of one element to be swapped.
       * @param j the index of the other element to be swapped.
       * @throws IndexOutOfBoundsException if either <tt>i</tt> or <tt>j</tt>
       *         is out of range (i &lt; 0 || i &gt;= list.size()
       *         || j &lt; 0 || j &gt;= list.size()).
       * @since 1.4
       */
      public static void swap(List<?> list, int i, int j) {
          final List l = list;
          l.set(i, l.set(j, l.get(i)));
      }
  
      /**
       * Swaps the two specified elements in the specified array.
       */
      private static void swap(Object[] arr, int i, int j) {
          Object tmp = arr[i];
          arr[i] = arr[j];
          arr[j] = tmp;
      }
  
      /**
       * Replaces all of the elements of the specified list with the specified
       * element. <p>
       *
       * This method runs in linear time.
       *
       * @param  list the list to be filled with the specified element.
       * @param  obj The element with which to fill the specified list.
       * @throws UnsupportedOperationException if the specified list or its
       *         list-iterator does not support the <tt>set</tt> operation.
       */
      public static <T> void fill(List<? super T> list, T obj) {
          int size = list.size();
  
          if (size < FILL_THRESHOLD || list instanceof RandomAccess) {
              for (int i=0; i<size; i++)
                  list.set(i, obj);
          } else {
              ListIterator<? super T> itr = list.listIterator();
              for (int i=0; i<size; i++) {
                  itr.next();
                  itr.set(obj);
              }
          }
      }
  
      /**
       * Copies all of the elements from one list into another.  After the
       * operation, the index of each copied element in the destination list
       * will be identical to its index in the source list.  The destination
       * list must be at least as long as the source list.  If it is longer, the
       * remaining elements in the destination list are unaffected. <p>
       *
       * This method runs in linear time.
       *
       * @param  dest The destination list.
       * @param  src The source list.
       * @throws IndexOutOfBoundsException if the destination list is too small
       *         to contain the entire source List.
       * @throws UnsupportedOperationException if the destination list's
       *         list-iterator does not support the <tt>set</tt> operation.
       */
      public static <T> void copy(List<? super T> dest, List<? extends T> src) {
          int srcSize = src.size();
          if (srcSize > dest.size())
              throw new IndexOutOfBoundsException("Source does not fit in dest");
  
          if (srcSize < COPY_THRESHOLD ||
              (src instanceof RandomAccess && dest instanceof RandomAccess)) {
              for (int i=0; i<srcSize; i++)
                  dest.set(i, src.get(i));
          } else {
              ListIterator<? super T> di=dest.listIterator();
              ListIterator<? extends T> si=src.listIterator();
              for (int i=0; i<srcSize; i++) {
                  di.next();
                  di.set(si.next());
              }
          }
      }
  
      /**
       * Returns the minimum element of the given collection, according to the
       * <i>natural ordering</i> of its elements.  All elements in the
       * collection must implement the <tt>Comparable</tt> interface.
       * Furthermore, all elements in the collection must be <i>mutually
       * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
       * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
       * <tt>e2</tt> in the collection).<p>
       *
       * This method iterates over the entire collection, hence it requires
       * time proportional to the size of the collection.
       *
       * @param  coll the collection whose minimum element is to be determined.
       * @return the minimum element of the given collection, according
       *         to the <i>natural ordering</i> of its elements.
       * @throws ClassCastException if the collection contains elements that are
       *         not <i>mutually comparable</i> (for example, strings and
       *         integers).
       * @throws NoSuchElementException if the collection is empty.
       * @see Comparable
       */
      public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) {
          Iterator<? extends T> i = coll.iterator();
          T candidate = i.next();
  
          while (i.hasNext()) {
              T next = i.next();
              if (next.compareTo(candidate) < 0)
                  candidate = next;
          }
          return candidate;
      }
  
      /**
       * Returns the minimum element of the given collection, according to the
       * order induced by the specified comparator.  All elements in the
       * collection must be <i>mutually comparable</i> by the specified
       * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
       * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
       * <tt>e2</tt> in the collection).<p>
       *
       * This method iterates over the entire collection, hence it requires
       * time proportional to the size of the collection.
       *
       * @param  coll the collection whose minimum element is to be determined.
       * @param  comp the comparator with which to determine the minimum element.
       *         A <tt>null</tt> value indicates that the elements' <i>natural
       *         ordering</i> should be used.
       * @return the minimum element of the given collection, according
       *         to the specified comparator.
       * @throws ClassCastException if the collection contains elements that are
       *         not <i>mutually comparable</i> using the specified comparator.
       * @throws NoSuchElementException if the collection is empty.
       * @see Comparable
       */
      public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) {
          if (comp==null)
              return (T)min((Collection<SelfComparable>) (Collection) coll);
  
          Iterator<? extends T> i = coll.iterator();
          T candidate = i.next();
  
          while (i.hasNext()) {
              T next = i.next();
              if (comp.compare(next, candidate) < 0)
                  candidate = next;
          }
          return candidate;
      }
  
      /**
       * Returns the maximum element of the given collection, according to the
       * <i>natural ordering</i> of its elements.  All elements in the
       * collection must implement the <tt>Comparable</tt> interface.
       * Furthermore, all elements in the collection must be <i>mutually
       * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
       * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
       * <tt>e2</tt> in the collection).<p>
       *
       * This method iterates over the entire collection, hence it requires
       * time proportional to the size of the collection.
       *
       * @param  coll the collection whose maximum element is to be determined.
       * @return the maximum element of the given collection, according
       *         to the <i>natural ordering</i> of its elements.
       * @throws ClassCastException if the collection contains elements that are
       *         not <i>mutually comparable</i> (for example, strings and
       *         integers).
       * @throws NoSuchElementException if the collection is empty.
       * @see Comparable
       */
      public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) {
          Iterator<? extends T> i = coll.iterator();
          T candidate = i.next();
  
          while (i.hasNext()) {
              T next = i.next();
              if (next.compareTo(candidate) > 0)
                  candidate = next;
          }
          return candidate;
      }
  
      /**
       * Returns the maximum element of the given collection, according to the
       * order induced by the specified comparator.  All elements in the
       * collection must be <i>mutually comparable</i> by the specified
       * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
       * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
       * <tt>e2</tt> in the collection).<p>
       *
       * This method iterates over the entire collection, hence it requires
       * time proportional to the size of the collection.
       *
       * @param  coll the collection whose maximum element is to be determined.
       * @param  comp the comparator with which to determine the maximum element.
       *         A <tt>null</tt> value indicates that the elements' <i>natural
       *        ordering</i> should be used.
       * @return the maximum element of the given collection, according
       *         to the specified comparator.
       * @throws ClassCastException if the collection contains elements that are
       *         not <i>mutually comparable</i> using the specified comparator.
       * @throws NoSuchElementException if the collection is empty.
       * @see Comparable
       */
      public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) {
          if (comp==null)
              return (T)max((Collection<SelfComparable>) (Collection) coll);
  
          Iterator<? extends T> i = coll.iterator();
          T candidate = i.next();
  
          while (i.hasNext()) {
              T next = i.next();
              if (comp.compare(next, candidate) > 0)
                  candidate = next;
          }
          return candidate;
      }
  
      /**
       * Rotates the elements in the specified list by the specified distance.
       * After calling this method, the element at index <tt>i</tt> will be
       * the element previously at index <tt>(i - distance)</tt> mod
       * <tt>list.size()</tt>, for all values of <tt>i</tt> between <tt>0</tt>
       * and <tt>list.size()-1</tt>, inclusive.  (This method has no effect on
       * the size of the list.)
       *
       * <p>For example, suppose <tt>list</tt> comprises<tt> [t, a, n, k, s]</tt>.
       * After invoking <tt>Collections.rotate(list, 1)</tt> (or
       * <tt>Collections.rotate(list, -4)</tt>), <tt>list</tt> will comprise
       * <tt>[s, t, a, n, k]</tt>.
       *
       * <p>Note that this method can usefully be applied to sublists to
       * move one or more elements within a list while preserving the
       * order of the remaining elements.  For example, the following idiom
       * moves the element at index <tt>j</tt> forward to position
       * <tt>k</tt> (which must be greater than or equal to <tt>j</tt>):
       * <pre>
       *     Collections.rotate(list.subList(j, k+1), -1);
       * </pre>
       * To make this concrete, suppose <tt>list</tt> comprises
       * <tt>[a, b, c, d, e]</tt>.  To move the element at index <tt>1</tt>
       * (<tt>b</tt>) forward two positions, perform the following invocation:
       * <pre>
       *     Collections.rotate(l.subList(1, 4), -1);
       * </pre>
       * The resulting list is <tt>[a, c, d, b, e]</tt>.
       *
       * <p>To move more than one element forward, increase the absolute value
       * of the rotation distance.  To move elements backward, use a positive
       * shift distance.
       *
       * <p>If the specified list is small or implements the {@link
       * RandomAccess} interface, this implementation exchanges the first
       * element into the location it should go, and then repeatedly exchanges
       * the displaced element into the location it should go until a displaced
       * element is swapped into the first element.  If necessary, the process
       * is repeated on the second and successive elements, until the rotation
       * is complete.  If the specified list is large and doesn't implement the
       * <tt>RandomAccess</tt> interface, this implementation breaks the
       * list into two sublist views around index <tt>-distance mod size</tt>.
       * Then the {@link #reverse(List)} method is invoked on each sublist view,
       * and finally it is invoked on the entire list.  For a more complete
       * description of both algorithms, see Section 2.3 of Jon Bentley's
       * <i>Programming Pearls</i> (Addison-Wesley, 1986).
       *
       * @param list the list to be rotated.
       * @param distance the distance to rotate the list.  There are no
       *        constraints on this value; it may be zero, negative, or
       *        greater than <tt>list.size()</tt>.
       * @throws UnsupportedOperationException if the specified list or
       *         its list-iterator does not support the <tt>set</tt> operation.
       * @since 1.4
       */
      public static void rotate(List<?> list, int distance) {
          if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD)
              rotate1(list, distance);
          else
              rotate2(list, distance);
      }
  
      private static <T> void rotate1(List<T> list, int distance) {
          int size = list.size();
          if (size == 0)
              return;
          distance = distance % size;
          if (distance < 0)
              distance += size;
          if (distance == 0)
              return;
  
          for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) {
              T displaced = list.get(cycleStart);
              int i = cycleStart;
              do {
                  i += distance;
                  if (i >= size)
                      i -= size;
                  displaced = list.set(i, displaced);
                  nMoved ++;
              } while (i != cycleStart);
          }
      }
  
      private static void rotate2(List<?> list, int distance) {
          int size = list.size();
          if (size == 0)
              return;
          int mid =  -distance % size;
          if (mid < 0)
              mid += size;
          if (mid == 0)
              return;
  
          reverse(list.subList(0, mid));
          reverse(list.subList(mid, size));
          reverse(list);
      }
  
      /**
       * Replaces all occurrences of one specified value in a list with another.
       * More formally, replaces with <tt>newVal</tt> each element <tt>e</tt>
       * in <tt>list</tt> such that
       * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
       * (This method has no effect on the size of the list.)
       *
       * @param list the list in which replacement is to occur.
       * @param oldVal the old value to be replaced.
       * @param newVal the new value with which <tt>oldVal</tt> is to be
       *        replaced.
       * @return <tt>true</tt> if <tt>list</tt> contained one or more elements
       *         <tt>e</tt> such that
       *         <tt>(oldVal==null ?  e==null : oldVal.equals(e))</tt>.
       * @throws UnsupportedOperationException if the specified list or
       *         its list-iterator does not support the <tt>set</tt> operation.
       * @since  1.4
       */
      public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) {
          boolean result = false;
          int size = list.size();
          if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) {
              if (oldVal==null) {
                  for (int i=0; i<size; i++) {
                      if (list.get(i)==null) {
                          list.set(i, newVal);
                          result = true;
                      }
                  }
              } else {
                  for (int i=0; i<size; i++) {
                      if (oldVal.equals(list.get(i))) {
                          list.set(i, newVal);
                          result = true;
                      }
                  }
              }
          } else {
              ListIterator<T> itr=list.listIterator();
              if (oldVal==null) {
                  for (int i=0; i<size; i++) {
                      if (itr.next()==null) {
                          itr.set(newVal);
                          result = true;
                      }
                  }
              } else {
                  for (int i=0; i<size; i++) {
                      if (oldVal.equals(itr.next())) {
                          itr.set(newVal);
                          result = true;
                      }
                  }
              }
          }
          return result;
      }
  
      /**
       * Returns the starting position of the first occurrence of the specified
       * target list within the specified source list, or -1 if there is no
       * such occurrence.  More formally, returns the lowest index <tt>i</tt>
       * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
       * or -1 if there is no such index.  (Returns -1 if
       * <tt>target.size() > source.size()</tt>.)
       *
       * <p>This implementation uses the "brute force" technique of scanning
       * over the source list, looking for a match with the target at each
       * location in turn.
       *
       * @param source the list in which to search for the first occurrence
       *        of <tt>target</tt>.
       * @param target the list to search for as a subList of <tt>source</tt>.
       * @return the starting position of the first occurrence of the specified
       *         target list within the specified source list, or -1 if there
       *         is no such occurrence.
       * @since  1.4
       */
      public static int indexOfSubList(List<?> source, List<?> target) {
          int sourceSize = source.size();
          int targetSize = target.size();
          int maxCandidate = sourceSize - targetSize;
  
          if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
              (source instanceof RandomAccess&&target instanceof RandomAccess)) {
          nextCand:
              for (int candidate = 0; candidate <= maxCandidate; candidate++) {
                  for (int i=0, j=candidate; i<targetSize; i++, j++)
                      if (!eq(target.get(i), source.get(j)))
                          continue nextCand;  // Element mismatch, try next cand
                  return candidate;  // All elements of candidate matched target
              }
          } else {  // Iterator version of above algorithm
              ListIterator<?> si = source.listIterator();
          nextCand:
              for (int candidate = 0; candidate <= maxCandidate; candidate++) {
                  ListIterator<?> ti = target.listIterator();
                  for (int i=0; i<targetSize; i++) {
                      if (!eq(ti.next(), si.next())) {
                          // Back up source iterator to next candidate
                          for (int j=0; j<i; j++)
                              si.previous();
                          continue nextCand;
                      }
                  }
                  return candidate;
              }
          }
          return -1;  // No candidate matched the target
      }
  
      /**
       * Returns the starting position of the last occurrence of the specified
       * target list within the specified source list, or -1 if there is no such
       * occurrence.  More formally, returns the highest index <tt>i</tt>
       * such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
       * or -1 if there is no such index.  (Returns -1 if
       * <tt>target.size() > source.size()</tt>.)
       *
       * <p>This implementation uses the "brute force" technique of iterating
       * over the source list, looking for a match with the target at each
       * location in turn.
       *
       * @param source the list in which to search for the last occurrence
       *        of <tt>target</tt>.
       * @param target the list to search for as a subList of <tt>source</tt>.
       * @return the starting position of the last occurrence of the specified
       *         target list within the specified source list, or -1 if there
       *         is no such occurrence.
       * @since  1.4
       */
      public static int lastIndexOfSubList(List<?> source, List<?> target) {
          int sourceSize = source.size();
          int targetSize = target.size();
          int maxCandidate = sourceSize - targetSize;
  
          if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
              source instanceof RandomAccess) {   // Index access version
          nextCand:
              for (int candidate = maxCandidate; candidate >= 0; candidate--) {
                  for (int i=0, j=candidate; i<targetSize; i++, j++)
                      if (!eq(target.get(i), source.get(j)))
                          continue nextCand;  // Element mismatch, try next cand
                  return candidate;  // All elements of candidate matched target
              }
          } else {  // Iterator version of above algorithm
              if (maxCandidate < 0)
                  return -1;
              ListIterator<?> si = source.listIterator(maxCandidate);
          nextCand:
              for (int candidate = maxCandidate; candidate >= 0; candidate--) {
                  ListIterator<?> ti = target.listIterator();
                  for (int i=0; i<targetSize; i++) {
                      if (!eq(ti.next(), si.next())) {
                          if (candidate != 0) {
                              // Back up source iterator to next candidate
                              for (int j=0; j<=i+1; j++)
                                  si.previous();
                          }
                          continue nextCand;
                      }
                  }
                  return candidate;
              }
          }
          return -1;  // No candidate matched the target
      }
  
  
      // Unmodifiable Wrappers
  
      /**
       * Returns an unmodifiable view of the specified collection.  This method
       * allows modules to provide users with "read-only" access to internal
       * collections.  Query operations on the returned collection "read through"
       * to the specified collection, and attempts to modify the returned
       * collection, whether direct or via its iterator, result in an
       * <tt>UnsupportedOperationException</tt>.<p>
       *
       * The returned collection does <i>not</i> pass the hashCode and equals
       * operations through to the backing collection, but relies on
       * <tt>Object</tt>'s <tt>equals</tt> and <tt>hashCode</tt> methods.  This
       * is necessary to preserve the contracts of these operations in the case
       * that the backing collection is a set or a list.<p>
       *
       * The returned collection will be serializable if the specified collection
       * is serializable.
       *
       * @param  c the collection for which an unmodifiable view is to be
       *         returned.
       * @return an unmodifiable view of the specified collection.
       */
      public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) {
          return new UnmodifiableCollection<>(c);
      }
  
      /**
       * @serial include
       */
      static class UnmodifiableCollection<E> implements Collection<E>, Serializable {
          private static final long serialVersionUID = 1820017752578914078L;
  
          final Collection<? extends E> c;
  
          UnmodifiableCollection(Collection<? extends E> c) {
              if (c==null)
                  throw new NullPointerException();
              this.c = c;
          }
  
          public int size()                   {return c.size();}
          public boolean isEmpty()            {return c.isEmpty();}
          public boolean contains(Object o)   {return c.contains(o);}
          public Object[] toArray()           {return c.toArray();}
          public <T> T[] toArray(T[] a)       {return c.toArray(a);}
          public String toString()            {return c.toString();}
  
          public Iterator<E> iterator() {
              return new Iterator<E>() {
                  private final Iterator<? extends E> i = c.iterator();
  
                  public boolean hasNext() {return i.hasNext();}
                  public E next()          {return i.next();}
                  public void remove() {
                      throw new UnsupportedOperationException();
                  }
              };
          }
  
          public boolean add(E e) {
              throw new UnsupportedOperationException();
          }
          public boolean remove(Object o) {
              throw new UnsupportedOperationException();
          }
  
          public boolean containsAll(Collection<?> coll) {
              return c.containsAll(coll);
          }
          public boolean addAll(Collection<? extends E> coll) {
              throw new UnsupportedOperationException();
          }
          public boolean removeAll(Collection<?> coll) {
              throw new UnsupportedOperationException();
          }
          public boolean retainAll(Collection<?> coll) {
              throw new UnsupportedOperationException();
          }
          public void clear() {
              throw new UnsupportedOperationException();
          }
      }
  
      /**
       * Returns an unmodifiable view of the specified set.  This method allows
       * modules to provide users with "read-only" access to internal sets.
       * Query operations on the returned set "read through" to the specified
       * set, and attempts to modify the returned set, whether direct or via its
       * iterator, result in an <tt>UnsupportedOperationException</tt>.<p>
       *
       * The returned set will be serializable if the specified set
       * is serializable.
       *
       * @param  s the set for which an unmodifiable view is to be returned.
       * @return an unmodifiable view of the specified set.
       */
      public static <T> Set<T> unmodifiableSet(Set<? extends T> s) {
          return new UnmodifiableSet<>(s);
      }
  
      /**
       * @serial include
       */
      static class UnmodifiableSet<E> extends UnmodifiableCollection<E>
                                   implements Set<E>, Serializable {
          private static final long serialVersionUID = -9215047833775013803L;
  
          UnmodifiableSet(Set<? extends E> s)     {super(s);}
          public boolean equals(Object o) {return o == this || c.equals(o);}
          public int hashCode()           {return c.hashCode();}
      }
  
      /**
       * Returns an unmodifiable view of the specified sorted set.  This method
       * allows modules to provide users with "read-only" access to internal
       * sorted sets.  Query operations on the returned sorted set "read
       * through" to the specified sorted set.  Attempts to modify the returned
       * sorted set, whether direct, via its iterator, or via its
       * <tt>subSet</tt>, <tt>headSet</tt>, or <tt>tailSet</tt> views, result in
       * an <tt>UnsupportedOperationException</tt>.<p>
       *
       * The returned sorted set will be serializable if the specified sorted set
       * is serializable.
       *
       * @param s the sorted set for which an unmodifiable view is to be
       *        returned.
       * @return an unmodifiable view of the specified sorted set.
       */
      public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) {
          return new UnmodifiableSortedSet<>(s);
      }
  
      /**
       * @serial include
       */
      static class UnmodifiableSortedSet<E>
                               extends UnmodifiableSet<E>
                               implements SortedSet<E>, Serializable {
          private static final long serialVersionUID = -4929149591599911165L;
          private final SortedSet<E> ss;
  
          UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;}
  
          public Comparator<? super E> comparator() {return ss.comparator();}
  
          public SortedSet<E> subSet(E fromElement, E toElement) {
              return new UnmodifiableSortedSet<>(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 unmodifiable view of the specified list.  This method allows
       * modules to provide users with "read-only" access to internal
       * lists.  Query operations on the returned list "read through" to the
       * specified list, and attempts to modify the returned list, whether
       * direct or via its iterator, result in an
       * <tt>UnsupportedOperationException</tt>.<p>
       *
       * The returned list will be serializable if the specified list
       * is serializable. Similarly, the returned list will implement
       * {@link RandomAccess} if the specified list does.
       *
       * @param  list the list for which an unmodifiable view is to be returned.
       * @return an unmodifiable view of the specified list.
       */
      public static <T> List<T> unmodifiableList(List<? extends T> list) {
          return (list instanceof RandomAccess ?
                  new UnmodifiableRandomAccessList<>(list) :
                  new UnmodifiableList<>(list));
      }
  
      /**
       * @serial include
       */
      static class UnmodifiableList<E> extends UnmodifiableCollection<E>
                                    implements List<E> {
          private static final long serialVersionUID = -283967356065247728L;
          final List<? extends E> list;
  
          UnmodifiableList(List<? extends E> list) {
              super(list);
              this.list = list;
          }
  
          public boolean equals(Object o) {return o == this || list.equals(o);}
          public int hashCode()           {return list.hashCode();}
  
          public E get(int index) {return list.get(index);}
          public E set(int index, E element) {
              throw new UnsupportedOperationException();
          }
          public void add(int index, E element) {
              throw new UnsupportedOperationException();
          }
          public E remove(int index) {
              throw new UnsupportedOperationException();
          }
          public int indexOf(Object o)            {return list.indexOf(o);}
          public int lastIndexOf(Object o)        {return list.lastIndexOf(o);}
          public boolean addAll(int index, Collection<? extends E> c) {
              throw new UnsupportedOperationException();
          }
          public ListIterator<E> listIterator()   {return listIterator(0);}
  
          public ListIterator<E> listIterator(final int index) {
              return new ListIterator<E>() {
                  private final ListIterator<? extends E> i
                      = list.listIterator(index);
  
                  public boolean hasNext()     {return i.hasNext();}
                  public E next()              {return i.next();}
                  public boolean hasPrevious() {return i.hasPrevious();}
                  public E previous()          {return i.previous();}
                  public int nextIndex()       {return i.nextIndex();}
                  public int previousIndex()   {return i.previousIndex();}
  
                  public void remove() {
                      throw new UnsupportedOperationException();
                  }
                  public void set(E e) {
                      throw new UnsupportedOperationException();
                  }
                  public void add(E e) {
                      throw new UnsupportedOperationException();
                  }
              };
          }
  
          public List<E> subList(int fromIndex, int toIndex) {
              return new UnmodifiableList<>(list.subList(fromIndex, toIndex));
          }
  
          /**
           * UnmodifiableRandomAccessList instances are serialized as
           * UnmodifiableList instances to allow them to be deserialized
           * in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList).
           * This method inverts the transformation.  As a beneficial
           * side-effect, it also grafts the RandomAccess marker onto
           * UnmodifiableList instances that were serialized in pre-1.4 JREs.
           *
           * Note: Unfortunately, UnmodifiableRandomAccessList instances
           * serialized in 1.4.1 and deserialized in 1.4 will become
           * UnmodifiableList instances, as this method was missing in 1.4.
           */
          private Object readResolve() {
              return (list instanceof RandomAccess
                      ? new UnmodifiableRandomAccessList<>(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));
          }
  
          private static final long serialVersionUID = -2542308836966382001L;
  
          /**
           * Allows instances to be deserialized in pre-1.4 JREs (which do
           * not have UnmodifiableRandomAccessList).  UnmodifiableList has
           * a readResolve method that inverts this transformation upon
           * deserialization.
           */
          private Object writeReplace() {
              return new UnmodifiableList<>(list);
          }
      }
  
      /**
       * Returns an unmodifiable view of the specified map.  This method
       * allows modules to provide users with "read-only" access to internal
       * maps.  Query operations on the returned map "read through"
       * to the specified map, and attempts to modify the returned
       * map, whether direct or via its collection views, result in an
       * <tt>UnsupportedOperationException</tt>.<p>
       *
       * The returned map will be serializable if the specified map
       * is serializable.
       *
       * @param  m the map for which an unmodifiable view is to be returned.
       * @return an unmodifiable view of the specified map.
       */
      public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) {
          return new UnmodifiableMap<>(m);
      }
  
      /**
       * @serial include
       */
      private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable {
          private static final long serialVersionUID = -1034234728574286014L;
  
          private final Map<? extends K, ? extends V> m;
  
          UnmodifiableMap(Map<? extends K, ? extends V> m) {
              if (m==null)
                  throw new NullPointerException();
              this.m = m;
          }
  
          public int size()                        {return m.size();}
          public boolean isEmpty()                 {return m.isEmpty();}
          public boolean containsKey(Object key)   {return m.containsKey(key);}
          public boolean containsValue(Object val) {return m.containsValue(val);}
          public V get(Object key)                 {return m.get(key);}
  
          public V put(K key, V value) {
              throw new UnsupportedOperationException();
          }
          public V remove(Object key) {
              throw new UnsupportedOperationException();
          }
          public void putAll(Map<? extends K, ? extends V> m) {
              throw new UnsupportedOperationException();
          }
          public void clear() {
              throw new UnsupportedOperationException();
          }
  
          private transient Set<K> keySet = null;
          private transient Set<Map.Entry<K,V>> entrySet = null;
          private transient Collection<V> values = null;
  
          public Set<K> keySet() {
              if (keySet==null)
                  keySet = unmodifiableSet(m.keySet());
              return keySet;
          }
  
          public Set<Map.Entry<K,V>> entrySet() {
              if (entrySet==null)
                  entrySet = new UnmodifiableEntrySet<>(m.entrySet());
              return entrySet;
          }
  
          public Collection<V> values() {
              if (values==null)
                  values = unmodifiableCollection(m.values());
              return values;
          }
  
          public boolean equals(Object o) {return o == this || m.equals(o);}
          public int hashCode()           {return m.hashCode();}
          public String toString()        {return m.toString();}
  
          /**
           * We need this class in addition to UnmodifiableSet as
           * Map.Entries themselves permit modification of the backing Map
           * via their setValue operation.  This class is subtle: there are
           * many possible attacks that must be thwarted.
           *
           * @serial include
           */
          static class UnmodifiableEntrySet<K,V>
              extends UnmodifiableSet<Map.Entry<K,V>> {
              private static final long serialVersionUID = 7854390611657943733L;
  
              UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) {
                  super((Set)s);
              }
              public Iterator<Map.Entry<K,V>> iterator() {
                  return new Iterator<Map.Entry<K,V>>() {
                      private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator();
  
                      public boolean hasNext() {
                          return i.hasNext();
                      }
                      public Map.Entry<K,V> next() {
                          return new UnmodifiableEntry<>(i.next());
                      }
                      public void remove() {
                          throw new UnsupportedOperationException();
                      }
                  };
              }
  
              public Object[] toArray() {
                  Object[] a = c.toArray();
                  for (int i=0; i<a.length; i++)
                      a[i] = new UnmodifiableEntry<>((Map.Entry<K,V>)a[i]);
                  return a;
              }
  
              public <T> T[] toArray(T[] a) {
                  // We don't pass a to c.toArray, to avoid window of
                  // vulnerability wherein an unscrupulous multithreaded client
                  // could get his hands on raw (unwrapped) Entries from c.
                  Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
  
                  for (int i=0; i<arr.length; i++)
                      arr[i] = new UnmodifiableEntry<>((Map.Entry<K,V>)arr[i]);
  
                  if (arr.length > a.length)
                      return (T[])arr;
  
                  System.arraycopy(arr, 0, a, 0, arr.length);
                  if (a.length > arr.length)
                      a[arr.length] = null;
                  return a;
              }
  
              /**
               * This method is overridden to protect the backing set against
               * an object with a nefarious equals function that senses
               * that the equality-candidate is Map.Entry and calls its
               * setValue method.
               */
              public boolean contains(Object o) {
                  if (!(o instanceof Map.Entry))
                      return false;
                  return c.contains(
                      new UnmodifiableEntry<>((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;
  
                  if (!(o instanceof Set))
                      return false;
                  Set s = (Set) o;
                  if (s.size() != c.size())
                      return false;
                  return containsAll(s); // Invokes safe containsAll() above
              }
  
              /**
               * This "wrapper class" serves two purposes: it prevents
               * the client from modifying the backing Map, by short-circuiting
               * the setValue method, and it protects the backing Map against
               * an ill-behaved Map.Entry that attempts to modify another
               * Map Entry when asked to perform an equality check.
               */
              private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> {
                  private Map.Entry<? extends K, ? extends V> e;
  
                  UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) {this.e = e;}
  
                  public K getKey()        {return e.getKey();}
                  public V getValue()      {return e.getValue();}
                  public V setValue(V value) {
                      throw new UnsupportedOperationException();
                  }
                  public int hashCode()    {return e.hashCode();}
                  public boolean equals(Object o) {
                      if (this == o)
                          return true;
                      if (!(o instanceof Map.Entry))
                          return false;
                      Map.Entry t = (Map.Entry)o;
                      return eq(e.getKey(),   t.getKey()) &&
                             eq(e.getValue(), t.getValue());
                  }
                  public String toString() {return e.toString();}
              }
          }
      }
  
      /**
       * Returns an unmodifiable view of the specified sorted map.  This method
       * allows modules to provide users with "read-only" access to internal
       * sorted maps.  Query operations on the returned sorted map "read through"
       * to the specified sorted map.  Attempts to modify the returned
       * sorted map, whether direct, via its collection views, or via its
       * <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in
       * an <tt>UnsupportedOperationException</tt>.<p>
       *
       * The returned sorted map will be serializable if the specified sorted map
       * is serializable.
       *
       * @param m the sorted map for which an unmodifiable view is to be
       *        returned.
       * @return an unmodifiable view of the specified sorted map.
       */
      public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) {
          return new UnmodifiableSortedMap<>(m);
      }
  
      /**
       * @serial include
       */
      static class UnmodifiableSortedMap<K,V>
            extends UnmodifiableMap<K,V>
            implements SortedMap<K,V>, Serializable {
          private static final long serialVersionUID = -8806743815996713206L;
  
          private final SortedMap<K, ? extends V> sm;
  
          UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m;}
  
          public Comparator<? super K> comparator() {return sm.comparator();}
  
          public SortedMap<K,V> subMap(K fromKey, K toKey) {
              return new UnmodifiableSortedMap<>(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();}
      }
  
  
      // Synch Wrappers
  
      /**
       * Returns a synchronized (thread-safe) collection backed by the specified
       * collection.  In order to guarantee serial access, it is critical that
       * <strong>all</strong> access to the backing collection is accomplished
       * through the returned collection.<p>
       *
       * It is imperative that the user manually synchronize on the returned
       * collection when iterating over it:
       * <pre>
       *  Collection c = Collections.synchronizedCollection(myCollection);
       *     ...
       *  synchronized (c) {
       *      Iterator i = c.iterator(); // Must be in the synchronized block
       *      while (i.hasNext())
       *         foo(i.next());
       *  }
       * </pre>
       * Failure to follow this advice may result in non-deterministic behavior.
       *
       * <p>The returned collection does <i>not</i> pass the <tt>hashCode</tt>
       * and <tt>equals</tt> operations through to the backing collection, but
       * relies on <tt>Object</tt>'s equals and hashCode methods.  This is
       * necessary to preserve the contracts of these operations in the case
       * that the backing collection is a set or a list.<p>
       *
       * The returned collection will be serializable if the specified collection
       * is serializable.
       *
       * @param  c the collection to be "wrapped" in a synchronized collection.
       * @return a synchronized view of the specified collection.
       */
      public static <T> Collection<T> synchronizedCollection(Collection<T> c) {
          return new SynchronizedCollection<>(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 {
          private static final long serialVersionUID = 3053995032091335093L;
  
          final Collection<E> c;  // Backing Collection
          final Object mutex;     // Object on which to synchronize
  
          SynchronizedCollection(Collection<E> c) {
              if (c==null)
                  throw new NullPointerException();
              this.c = c;
              mutex = this;
          }
          SynchronizedCollection(Collection<E> c, Object mutex) {
              this.c = c;
              this.mutex = mutex;
          }
  
          public int size() {
              synchronized (mutex) {return c.size();}
          }
          public boolean isEmpty() {
              synchronized (mutex) {return c.isEmpty();}
          }
          public boolean contains(Object o) {
              synchronized (mutex) {return c.contains(o);}
          }
          public Object[] toArray() {
              synchronized (mutex) {return c.toArray();}
          }
          public <T> T[] toArray(T[] a) {
              synchronized (mutex) {return c.toArray(a);}
          }
  
          public Iterator<E> iterator() {
              return c.iterator(); // Must be manually synched by user!
          }
  
          public boolean add(E e) {
              synchronized (mutex) {return c.add(e);}
          }
          public boolean remove(Object o) {
              synchronized (mutex) {return c.remove(o);}
          }
  
          public boolean containsAll(Collection<?> coll) {
              synchronized (mutex) {return c.containsAll(coll);}
          }
          public boolean addAll(Collection<? extends E> coll) {
              synchronized (mutex) {return c.addAll(coll);}
          }
          public boolean removeAll(Collection<?> coll) {
              synchronized (mutex) {return c.removeAll(coll);}
          }
          public boolean retainAll(Collection<?> coll) {
              synchronized (mutex) {return c.retainAll(coll);}
          }
          public void clear() {
              synchronized (mutex) {c.clear();}
          }
          public String toString() {
              synchronized (mutex) {return c.toString();}
          }
          private void writeObject(ObjectOutputStream s) throws IOException {
              synchronized (mutex) {s.defaultWriteObject();}
          }
      }
  
      /**
       * Returns a synchronized (thread-safe) set backed by the specified
       * set.  In order to guarantee serial access, it is critical that
       * <strong>all</strong> access to the backing set is accomplished
       * through the returned set.<p>
       *
       * It is imperative that the user manually synchronize on the returned
       * set when iterating over it:
       * <pre>
       *  Set s = Collections.synchronizedSet(new HashSet());
       *      ...
       *  synchronized (s) {
       *      Iterator i = s.iterator(); // Must be in the synchronized block
       *      while (i.hasNext())
       *          foo(i.next());
       *  }
       * </pre>
       * Failure to follow this advice may result in non-deterministic behavior.
       *
       * <p>The returned set will be serializable if the specified set is
       * serializable.
       *
       * @param  s the set to be "wrapped" in a synchronized set.
       * @return a synchronized view of the specified set.
       */
      public static <T> Set<T> synchronizedSet(Set<T> s) {
          return new SynchronizedSet<>(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> {
          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 iterating over it or any of its <tt>subSet</tt>,
       * <tt>headSet</tt>, or <tt>tailSet</tt> views.
       * <pre>
       *  SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
       *      ...
       *  synchronized (s) {
       *      Iterator i = s.iterator(); // Must be in the synchronized block
       *      while (i.hasNext())
       *          foo(i.next());
       *  }
       * </pre>
       * or:
       * <pre>
       *  SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
       *  SortedSet s2 = s.headSet(foo);
       *      ...
       *  synchronized (s) {  // Note: s, not s2!!!
       *      Iterator i = s2.iterator(); // Must be in the synchronized block
       *      while (i.hasNext())
       *          foo(i.next());
       *  }
       * </pre>
       * Failure to follow this advice may result in non-deterministic behavior.
       *
       * <p>The returned sorted set will be serializable if the specified
       * sorted set is serializable.
       *
       * @param  s the sorted set to be "wrapped" in a synchronized sorted set.
       * @return a synchronized view of the specified sorted set.
       */
      public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) {
          return new SynchronizedSortedSet<>(s);
      }
  
      /**
       * @serial include
       */
      static class SynchronizedSortedSet<E>
          extends SynchronizedSet<E>
          implements SortedSet<E>
      {
          private static final long serialVersionUID = 8695801310862127406L;
  
          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) list backed by the specified
       * list.  In order to guarantee serial access, it is critical that
       * <strong>all</strong> access to the backing list is accomplished
       * through the returned list.<p>
       *
       * It is imperative that the user manually synchronize on the returned
       * list when iterating over it:
       * <pre>
       *  List list = Collections.synchronizedList(new ArrayList());
       *      ...
       *  synchronized (list) {
       *      Iterator i = list.iterator(); // Must be in synchronized block
       *      while (i.hasNext())
       *          foo(i.next());
       *  }
       * </pre>
       * Failure to follow this advice may result in non-deterministic behavior.
       *
       * <p>The returned list will be serializable if the specified list is
       * serializable.
       *
       * @param  list the list to be "wrapped" in a synchronized list.
       * @return a synchronized view of the specified list.
       */
      public static <T> List<T> synchronizedList(List<T> list) {
          return (list instanceof RandomAccess ?
                  new SynchronizedRandomAccessList<>(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> {
          private static final long serialVersionUID = -7754090372962971524L;
  
          final List<E> list;
  
          SynchronizedList(List<E> list) {
              super(list);
              this.list = list;
          }
          SynchronizedList(List<E> list, Object mutex) {
              super(list, mutex);
              this.list = list;
          }
  
          public boolean equals(Object o) {
              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);
              }
          }
  
          /**
           * SynchronizedRandomAccessList instances are serialized as
           * SynchronizedList instances to allow them to be deserialized
           * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList).
           * This method inverts the transformation.  As a beneficial
           * side-effect, it also grafts the RandomAccess marker onto
           * SynchronizedList instances that were serialized in pre-1.4 JREs.
           *
           * Note: Unfortunately, SynchronizedRandomAccessList instances
           * serialized in 1.4.1 and deserialized in 1.4 will become
           * SynchronizedList instances, as this method was missing in 1.4.
           */
          private Object readResolve() {
              return (list instanceof RandomAccess
                      ? new SynchronizedRandomAccessList<>(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);
              }
          }
  
          private static final long serialVersionUID = 1530674583602358482L;
  
          /**
           * Allows instances to be deserialized in pre-1.4 JREs (which do
           * not have SynchronizedRandomAccessList).  SynchronizedList has
           * a readResolve method that inverts this transformation upon
           * deserialization.
           */
          private Object writeReplace() {
              return new SynchronizedList<>(list);
          }
      }
  
      /**
       * Returns a synchronized (thread-safe) map backed by the specified
       * map.  In order to guarantee serial access, it is critical that
       * <strong>all</strong> access to the backing map is accomplished
       * through the returned map.<p>
       *
       * It is imperative that the user manually synchronize on the returned
       * map when iterating over any of its collection views:
       * <pre>
       *  Map m = Collections.synchronizedMap(new HashMap());
       *      ...
       *  Set s = m.keySet();  // Needn't be in synchronized block
       *      ...
       *  synchronized (m) {  // Synchronizing on m, not s!
       *      Iterator i = s.iterator(); // Must be in synchronized block
       *      while (i.hasNext())
       *          foo(i.next());
       *  }
       * </pre>
       * Failure to follow this advice may result in non-deterministic behavior.
       *
       * <p>The returned map will be serializable if the specified map is
       * serializable.
       *
       * @param  m the map to be "wrapped" in a synchronized map.
       * @return a synchronized view of the specified map.
       */
      public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) {
          return new SynchronizedMap<>(m);
      }
  
      /**
       * @serial include
       */
      private static class SynchronizedMap<K,V>
          implements Map<K,V>, Serializable {
          private static final long serialVersionUID = 1978198479659022715L;
  
          private final Map<K,V> m;     // Backing Map
          final Object      mutex;        // Object on which to synchronize
  
          SynchronizedMap(Map<K,V> m) {
              if (m==null)
                  throw new NullPointerException();
              this.m = m;
              mutex = this;
          }
  
          SynchronizedMap(Map<K,V> m, Object mutex) {
              this.m = m;
              this.mutex = mutex;
          }
  
          public int size() {
              synchronized (mutex) {return m.size();}
          }
          public boolean isEmpty() {
              synchronized (mutex) {return m.isEmpty();}
          }
          public boolean containsKey(Object key) {
              synchronized (mutex) {return m.containsKey(key);}
          }
          public boolean containsValue(Object value) {
              synchronized (mutex) {return m.containsValue(value);}
          }
          public V get(Object key) {
              synchronized (mutex) {return m.get(key);}
          }
  
          public V put(K key, V value) {
              synchronized (mutex) {return m.put(key, value);}
          }
          public V remove(Object key) {
              synchronized (mutex) {return m.remove(key);}
          }
          public void putAll(Map<? extends K, ? extends V> map) {
              synchronized (mutex) {m.putAll(map);}
          }
          public void clear() {
              synchronized (mutex) {m.clear();}
          }
  
          private transient Set<K> keySet = null;
          private transient Set<Map.Entry<K,V>> entrySet = null;
          private transient Collection<V> values = null;
  
          public Set<K> keySet() {
              synchronized (mutex) {
                  if (keySet==null)
                      keySet = new SynchronizedSet<>(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();}
          }
          private void writeObject(ObjectOutputStream s) throws IOException {
              synchronized (mutex) {s.defaultWriteObject();}
          }
      }
  
      /**
       * Returns a synchronized (thread-safe) sorted map backed by the specified
       * sorted map.  In order to guarantee serial access, it is critical that
       * <strong>all</strong> access to the backing sorted map is accomplished
       * through the returned sorted map (or its views).<p>
       *
       * It is imperative that the user manually synchronize on the returned
       * sorted map when iterating over any of its collection views, or the
       * collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or
       * <tt>tailMap</tt> views.
       * <pre>
       *  SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
       *      ...
       *  Set s = m.keySet();  // Needn't be in synchronized block
       *      ...
       *  synchronized (m) {  // Synchronizing on m, not s!
       *      Iterator i = s.iterator(); // Must be in synchronized block
       *      while (i.hasNext())
       *          foo(i.next());
       *  }
       * </pre>
       * or:
       * <pre>
       *  SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
       *  SortedMap m2 = m.subMap(foo, bar);
       *      ...
       *  Set s2 = m2.keySet();  // Needn't be in synchronized block
       *      ...
       *  synchronized (m) {  // Synchronizing on m, not m2 or s2!
       *      Iterator i = s.iterator(); // Must be in synchronized block
       *      while (i.hasNext())
       *          foo(i.next());
       *  }
       * </pre>
       * Failure to follow this advice may result in non-deterministic behavior.
       *
       * <p>The returned sorted map will be serializable if the specified
       * sorted map is serializable.
       *
       * @param  m the sorted map to be "wrapped" in a synchronized sorted map.
       * @return a synchronized view of the specified sorted map.
       */
      public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) {
          return new SynchronizedSortedMap<>(m);
      }
  
  
      /**
       * @serial include
       */
      static class SynchronizedSortedMap<K,V>
          extends SynchronizedMap<K,V>
          implements SortedMap<K,V>
      {
          private static final long serialVersionUID = -8798146769416483793L;
  
          private final SortedMap<K,V> sm;
  
          SynchronizedSortedMap(SortedMap<K,V> m) {
              super(m);
              sm = m;
          }
          SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) {
              super(m, mutex);
              sm = m;
          }
  
          public Comparator<? super K> comparator() {
              synchronized (mutex) {return sm.comparator();}
          }
  
          public SortedMap<K,V> subMap(K fromKey, K toKey) {
              synchronized (mutex) {
                  return new SynchronizedSortedMap<>(
                      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();}
          }
      }
  
      // Dynamically typesafe collection wrappers
  
      /**
       * Returns a dynamically typesafe view of the specified collection.
       * Any attempt to insert an element of the wrong type will result in an
       * immediate {@link ClassCastException}.  Assuming a collection
       * contains no incorrectly typed elements prior to the time a
       * dynamically typesafe view is generated, and that all subsequent
       * access to the collection takes place through the view, it is
       * <i>guaranteed</i> that the collection cannot contain an incorrectly
       * typed element.
       *
       * <p>The generics mechanism in the language provides compile-time
       * (static) type checking, but it is possible to defeat this mechanism
       * with unchecked casts.  Usually this is not a problem, as the compiler
       * issues warnings on all such unchecked operations.  There are, however,
       * times when static type checking alone is not sufficient.  For example,
       * suppose a collection is passed to a third-party library and it is
       * imperative that the library code not corrupt the collection by
       * inserting an element of the wrong type.
       *
       * <p>Another use of dynamically typesafe views is debugging.  Suppose a
       * program fails with a {@code ClassCastException}, indicating that an
       * incorrectly typed element was put into a parameterized collection.
       * Unfortunately, the exception can occur at any time after the erroneous
       * element is inserted, so it typically provides little or no information
       * as to the real source of the problem.  If the problem is reproducible,
       * one can quickly determine its source by temporarily modifying the
       * program to wrap the collection with a dynamically typesafe view.
       * For example, this declaration:
       *  <pre> {@code
       *     Collection<String> c = new HashSet<String>();
       * }</pre>
       * may be replaced temporarily by this one:
       *  <pre> {@code
       *     Collection<String> c = Collections.checkedCollection(
       *         new HashSet<String>(), String.class);
       * }</pre>
       * Running the program again will cause it to fail at the point where
       * an incorrectly typed element is inserted into the collection, clearly
       * identifying the source of the problem.  Once the problem is fixed, the
       * modified declaration may be reverted back to the original.
       *
       * <p>The returned collection does <i>not</i> pass the hashCode and equals
       * operations through to the backing collection, but relies on
       * {@code Object}'s {@code equals} and {@code hashCode} methods.  This
       * is necessary to preserve the contracts of these operations in the case
       * that the backing collection is a set or a list.
       *
       * <p>The returned collection will be serializable if the specified
       * collection is serializable.
       *
       * <p>Since {@code null} is considered to be a value of any reference
       * type, the returned collection permits insertion of null elements
       * whenever the backing collection does.
       *
       * @param c the collection for which a dynamically typesafe view is to be
       *          returned
       * @param type the type of element that {@code c} is permitted to hold
       * @return a dynamically typesafe view of the specified collection
       * @since 1.5
       */
      public static <E> Collection<E> checkedCollection(Collection<E> c,
                                                        Class<E> type) {
          return new CheckedCollection<>(c, type);
      }
  
      @SuppressWarnings("unchecked")
      static <T> T[] zeroLengthArray(Class<T> type) {
          return (T[]) Array.newInstance(type, 0);
      }
  
      /**
       * @serial include
       */
      static class CheckedCollection<E> implements Collection<E>, Serializable {
          private static final long serialVersionUID = 1578914078182001775L;
  
          final Collection<E> c;
          final Class<E> type;
  
          void typeCheck(Object o) {
              if (o != null && !type.isInstance(o))
                  throw new ClassCastException(badElementMsg(o));
          }
  
          private String badElementMsg(Object o) {
              return "Attempt to insert " + o.getClass() +
                  " element into collection with element type " + type;
          }
  
          CheckedCollection(Collection<E> c, Class<E> type) {
              if (c==null || type == null)
                  throw new NullPointerException();
              this.c = c;
              this.type = type;
          }
  
          public int size()                 { return c.size(); }
          public boolean isEmpty()          { return c.isEmpty(); }
          public boolean contains(Object o) { return c.contains(o); }
          public Object[] toArray()         { return c.toArray(); }
          public <T> T[] toArray(T[] a)     { return c.toArray(a); }
          public String toString()          { return c.toString(); }
          public boolean remove(Object o)   { return c.remove(o); }
          public void clear()               {        c.clear(); }
  
          public boolean containsAll(Collection<?> coll) {
              return c.containsAll(coll);
          }
          public boolean removeAll(Collection<?> coll) {
              return c.removeAll(coll);
          }
          public boolean retainAll(Collection<?> coll) {
              return c.retainAll(coll);
          }
  
          public Iterator<E> iterator() {
              final Iterator<E> it = c.iterator();
              return new Iterator<E>() {
                  public boolean hasNext() { return it.hasNext(); }
                  public E next()          { return it.next(); }
                  public void remove()     {        it.remove(); }};
          }
  
          public boolean add(E e) {
              typeCheck(e);
              return c.add(e);
          }
  
          private E[] zeroLengthElementArray = null; // Lazily initialized
  
          private E[] zeroLengthElementArray() {
              return zeroLengthElementArray != null ? zeroLengthElementArray :
                  (zeroLengthElementArray = zeroLengthArray(type));
          }
  
          @SuppressWarnings("unchecked")
          Collection<E> checkedCopyOf(Collection<? extends E> coll) {
              Object[] a = null;
              try {
                  E[] z = zeroLengthElementArray();
                  a = coll.toArray(z);
                  // Defend against coll violating the toArray contract
                  if (a.getClass() != z.getClass())
                      a = Arrays.copyOf(a, a.length, z.getClass());
              } catch (ArrayStoreException ignore) {
                  // To get better and consistent diagnostics,
                  // we call typeCheck explicitly on each element.
                  // We call clone() to defend against coll retaining a
                  // reference to the returned array and storing a bad
                  // element into it after it has been type checked.
                  a = coll.toArray().clone();
                  for (Object o : a)
                      typeCheck(o);
              }
              // A slight abuse of the type system, but safe here.
              return (Collection<E>) Arrays.asList(a);
          }
  
          public boolean addAll(Collection<? extends E> coll) {
              // Doing things this way insulates us from concurrent changes
              // in the contents of coll and provides all-or-nothing
              // semantics (which we wouldn't get if we type-checked each
              // element as we added it)
              return c.addAll(checkedCopyOf(coll));
          }
      }
  
      /**
       * Returns a dynamically typesafe view of the specified set.
       * Any attempt to insert an element of the wrong type will result in
       * an immediate {@link ClassCastException}.  Assuming a set contains
       * no incorrectly typed elements prior to the time a dynamically typesafe
       * view is generated, and that all subsequent access to the set
       * takes place through the view, it is <i>guaranteed</i> that the
       * set cannot contain an incorrectly typed element.
       *
       * <p>A discussion of the use of dynamically typesafe views may be
       * found in the documentation for the {@link #checkedCollection
       * checkedCollection} method.
       *
       * <p>The returned set will be serializable if the specified set is
       * serializable.
       *
       * <p>Since {@code null} is considered to be a value of any reference
       * type, the returned set permits insertion of null elements whenever
       * the backing set does.
       *
       * @param s the set for which a dynamically typesafe view is to be
       *          returned
       * @param type the type of element that {@code s} is permitted to hold
       * @return a dynamically typesafe view of the specified set
       * @since 1.5
       */
      public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) {
          return new CheckedSet<>(s, type);
      }
  
      /**
       * @serial include
       */
      static class CheckedSet<E> extends CheckedCollection<E>
                                   implements Set<E>, Serializable
      {
          private static final long serialVersionUID = 4694047833775013803L;
  
          CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); }
  
          public boolean equals(Object o) { return o == this || c.equals(o); }
          public int hashCode()           { return c.hashCode(); }
      }
  
      /**
       * Returns a dynamically typesafe view of the specified sorted set.
       * Any attempt to insert an element of the wrong type will result in an
       * immediate {@link ClassCastException}.  Assuming a sorted set
       * contains no incorrectly typed elements prior to the time a
       * dynamically typesafe view is generated, and that all subsequent
       * access to the sorted set takes place through the view, it is
       * <i>guaranteed</i> that the sorted set cannot contain an incorrectly
       * typed element.
       *
       * <p>A discussion of the use of dynamically typesafe views may be
       * found in the documentation for the {@link #checkedCollection
       * checkedCollection} method.
       *
       * <p>The returned sorted set will be serializable if the specified sorted
       * set is serializable.
       *
       * <p>Since {@code null} is considered to be a value of any reference
       * type, the returned sorted set permits insertion of null elements
       * whenever the backing sorted set does.
       *
       * @param s the sorted set for which a dynamically typesafe view is to be
       *          returned
       * @param type the type of element that {@code s} is permitted to hold
       * @return a dynamically typesafe view of the specified sorted set
       * @since 1.5
       */
      public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s,
                                                      Class<E> type) {
          return new CheckedSortedSet<>(s, type);
      }
  
      /**
       * @serial include
       */
      static class CheckedSortedSet<E> extends CheckedSet<E>
          implements SortedSet<E>, Serializable
      {
          private static final long serialVersionUID = 1599911165492914959L;
          private final SortedSet<E> ss;
  
          CheckedSortedSet(SortedSet<E> s, Class<E> type) {
              super(s, type);
              ss = s;
          }
  
          public Comparator<? super E> comparator() { return ss.comparator(); }
          public E first()                   { return ss.first(); }
          public E last()                    { return ss.last(); }
  
          public SortedSet<E> subSet(E fromElement, E toElement) {
              return checkedSortedSet(ss.subSet(fromElement,toElement), type);
          }
          public SortedSet<E> headSet(E toElement) {
              return checkedSortedSet(ss.headSet(toElement), type);
          }
          public SortedSet<E> tailSet(E fromElement) {
              return checkedSortedSet(ss.tailSet(fromElement), type);
          }
      }
  
      /**
       * Returns a dynamically typesafe view of the specified list.
       * Any attempt to insert an element of the wrong type will result in
       * an immediate {@link ClassCastException}.  Assuming a list contains
       * no incorrectly typed elements prior to the time a dynamically typesafe
       * view is generated, and that all subsequent access to the list
       * takes place through the view, it is <i>guaranteed</i> that the
       * list cannot contain an incorrectly typed element.
       *
       * <p>A discussion of the use of dynamically typesafe views may be
       * found in the documentation for the {@link #checkedCollection
       * checkedCollection} method.
       *
       * <p>The returned list will be serializable if the specified list
       * is serializable.
       *
       * <p>Since {@code null} is considered to be a value of any reference
       * type, the returned list permits insertion of null elements whenever
       * the backing list does.
       *
       * @param list the list for which a dynamically typesafe view is to be
       *             returned
       * @param type the type of element that {@code list} is permitted to hold
       * @return a dynamically typesafe view of the specified list
       * @since 1.5
       */
      public static <E> List<E> checkedList(List<E> list, Class<E> type) {
          return (list instanceof RandomAccess ?
                  new CheckedRandomAccessList<>(list, type) :
                  new CheckedList<>(list, type));
      }
  
      /**
       * @serial include
       */
      static class CheckedList<E>
          extends CheckedCollection<E>
          implements List<E>
      {
          private static final long serialVersionUID = 65247728283967356L;
          final List<E> list;
  
          CheckedList(List<E> list, Class<E> type) {
              super(list, type);
              this.list = list;
          }
  
          public boolean equals(Object o)  { return o == this || list.equals(o); }
          public int hashCode()            { return list.hashCode(); }
          public E get(int index)          { return list.get(index); }
          public E remove(int index)       { return list.remove(index); }
          public int indexOf(Object o)     { return list.indexOf(o); }
          public int lastIndexOf(Object o) { return list.lastIndexOf(o); }
  
          public E set(int index, E element) {
              typeCheck(element);
              return list.set(index, element);
          }
  
          public void add(int index, E element) {
              typeCheck(element);
              list.add(index, element);
          }
  
          public boolean addAll(int index, Collection<? extends E> c) {
              return list.addAll(index, checkedCopyOf(c));
          }
          public ListIterator<E> listIterator()   { return listIterator(0); }
  
          public ListIterator<E> listIterator(final int index) {
              final ListIterator<E> i = list.listIterator(index);
  
              return new ListIterator<E>() {
                  public boolean hasNext()     { return i.hasNext(); }
                  public E next()              { return i.next(); }
                  public boolean hasPrevious() { return i.hasPrevious(); }
                  public E previous()          { return i.previous(); }
                  public int nextIndex()       { return i.nextIndex(); }
                  public int previousIndex()   { return i.previousIndex(); }
                  public void remove()         {        i.remove(); }
  
                  public void set(E e) {
                      typeCheck(e);
                      i.set(e);
                  }
  
                  public void add(E e) {
                      typeCheck(e);
                      i.add(e);
                  }
              };
          }
  
          public List<E> subList(int fromIndex, int toIndex) {
              return new CheckedList<>(list.subList(fromIndex, toIndex), type);
          }
      }
  
      /**
       * @serial include
       */
      static class CheckedRandomAccessList<E> extends CheckedList<E>
                                              implements RandomAccess
      {
          private static final long serialVersionUID = 1638200125423088369L;
  
          CheckedRandomAccessList(List<E> list, Class<E> type) {
              super(list, type);
          }
  
          public List<E> subList(int fromIndex, int toIndex) {
              return new CheckedRandomAccessList<>(
                  list.subList(fromIndex, toIndex), type);
          }
      }
  
      /**
       * Returns a dynamically typesafe view of the specified map.
       * Any attempt to insert a mapping whose key or value have the wrong
       * type will result in an immediate {@link ClassCastException}.
       * Similarly, any attempt to modify the value currently associated with
       * a key will result in an immediate {@link ClassCastException},
       * whether the modification is attempted directly through the map
       * itself, or through a {@link Map.Entry} instance obtained from the
       * map's {@link Map#entrySet() entry set} view.
       *
       * <p>Assuming a map contains no incorrectly typed keys or values
       * prior to the time a dynamically typesafe view is generated, and
       * that all subsequent access to the map takes place through the view
       * (or one of its collection views), it is <i>guaranteed</i> that the
       * map cannot contain an incorrectly typed key or value.
       *
       * <p>A discussion of the use of dynamically typesafe views may be
       * found in the documentation for the {@link #checkedCollection
       * checkedCollection} method.
       *
       * <p>The returned map will be serializable if the specified map is
       * serializable.
       *
       * <p>Since {@code null} is considered to be a value of any reference
       * type, the returned map permits insertion of null keys or values
       * whenever the backing map does.
       *
       * @param m the map for which a dynamically typesafe view is to be
       *          returned
       * @param keyType the type of key that {@code m} is permitted to hold
       * @param valueType the type of value that {@code m} is permitted to hold
       * @return a dynamically typesafe view of the specified map
       * @since 1.5
       */
      public static <K, V> Map<K, V> checkedMap(Map<K, V> m,
                                                Class<K> keyType,
                                                Class<V> valueType) {
          return new CheckedMap<>(m, keyType, valueType);
      }
  
  
      /**
       * @serial include
       */
      private static class CheckedMap<K,V>
          implements Map<K,V>, Serializable
      {
          private static final long serialVersionUID = 5742860141034234728L;
  
          private final Map<K, V> m;
          final Class<K> keyType;
          final Class<V> valueType;
  
          private void typeCheck(Object key, Object value) {
              if (key != null && !keyType.isInstance(key))
                  throw new ClassCastException(badKeyMsg(key));
  
              if (value != null && !valueType.isInstance(value))
                  throw new ClassCastException(badValueMsg(value));
          }
  
          private String badKeyMsg(Object key) {
              return "Attempt to insert " + key.getClass() +
                  " key into map with key type " + keyType;
          }
  
          private String badValueMsg(Object value) {
              return "Attempt to insert " + value.getClass() +
                  " value into map with value type " + valueType;
          }
  
          CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) {
              if (m == null || keyType == null || valueType == null)
                  throw new NullPointerException();
              this.m = m;
              this.keyType = keyType;
              this.valueType = valueType;
          }
  
          public int size()                      { return m.size(); }
          public boolean isEmpty()               { return m.isEmpty(); }
          public boolean containsKey(Object key) { return m.containsKey(key); }
          public boolean containsValue(Object v) { return m.containsValue(v); }
          public V get(Object key)               { return m.get(key); }
          public V remove(Object key)            { return m.remove(key); }
          public void clear()                    { m.clear(); }
          public Set<K> keySet()                 { return m.keySet(); }
          public Collection<V> values()          { return m.values(); }
          public boolean equals(Object o)        { return o == this || m.equals(o); }
          public int hashCode()                  { return m.hashCode(); }
          public String toString()               { return m.toString(); }
  
          public V put(K key, V value) {
              typeCheck(key, value);
              return m.put(key, value);
          }
  
          @SuppressWarnings("unchecked")
          public void putAll(Map<? extends K, ? extends V> t) {
              // Satisfy the following goals:
              // - good diagnostics in case of type mismatch
              // - all-or-nothing semantics
              // - protection from malicious t
              // - correct behavior if t is a concurrent map
              Object[] entries = t.entrySet().toArray();
              List<Map.Entry<K,V>> checked = new ArrayList<>(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 = null;
  
          public Set<Map.Entry<K,V>> entrySet() {
              if (entrySet==null)
                  entrySet = new CheckedEntrySet<>(m.entrySet(), valueType);
              return entrySet;
          }
  
          /**
           * We need this class in addition to CheckedSet as Map.Entry permits
           * modification of the backing Map via the setValue operation.  This
           * class is subtle: there are many possible attacks that must be
           * thwarted.
           *
           * @serial exclude
           */
          static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> {
              private final Set<Map.Entry<K,V>> s;
              private final Class<V> valueType;
  
              CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) {
                  this.s = s;
                  this.valueType = valueType;
              }
  
              public int size()        { return s.size(); }
              public boolean isEmpty() { return s.isEmpty(); }
              public String toString() { return s.toString(); }
              public int hashCode()    { return s.hashCode(); }
              public void clear()      {        s.clear(); }
  
              public boolean add(Map.Entry<K, V> e) {
                  throw new UnsupportedOperationException();
              }
              public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) {
                  throw new UnsupportedOperationException();
              }
  
              public Iterator<Map.Entry<K,V>> iterator() {
                  final Iterator<Map.Entry<K, V>> i = s.iterator();
                  final Class<V> valueType = this.valueType;
  
                  return new Iterator<Map.Entry<K,V>>() {
                      public boolean hasNext() { return i.hasNext(); }
                      public void remove()     { i.remove(); }
  
                      public Map.Entry<K,V> next() {
                          return checkedEntry(i.next(), valueType);
                      }
                  };
              }
  
              @SuppressWarnings("unchecked")
              public Object[] toArray() {
                  Object[] source = s.toArray();
  
                  /*
                   * Ensure that we don't get an ArrayStoreException even if
                   * s.toArray returns an array of something other than Object
                   */
                  Object[] dest = (CheckedEntry.class.isInstance(
                      source.getClass().getComponentType()) ? source :
                                   new Object[source.length]);
  
                  for (int i = 0; i < source.length; i++)
                      dest[i] = checkedEntry((Map.Entry<K,V>)source[i],
                                             valueType);
                  return dest;
              }
  
              @SuppressWarnings("unchecked")
              public <T> T[] toArray(T[] a) {
                  // We don't pass a to s.toArray, to avoid window of
                  // vulnerability wherein an unscrupulous multithreaded client
                  // could get his hands on raw (unwrapped) Entries from s.
                  T[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
  
                  for (int i=0; i<arr.length; i++)
                      arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i],
                                                valueType);
                  if (arr.length > a.length)
                      return arr;
  
                  System.arraycopy(arr, 0, a, 0, arr.length);
                  if (a.length > arr.length)
                      a[arr.length] = null;
                  return a;
              }
  
              /**
               * This method is overridden to protect the backing set against
               * an object with a nefarious equals function that senses
               * that the equality-candidate is Map.Entry and calls its
               * setValue method.
               */
              public boolean contains(Object o) {
  