content:  /*
   *  Copyright Beijing 58 Information Technology Co.,Ltd.
   *
   *  Licensed to the Apache Software Foundation (ASF) under one
   *  or more contributor license agreements.  See the NOTICE file
   *  distributed with this work for additional information
   *  regarding copyright ownership.  The ASF licenses this file
   *  to you under the Apache License, Version 2.0 (the
   *  "License"); you may not use this file except in compliance
   *  with the License.  You may obtain a copy of the License at
   *
   *        http://www.apache.org/licenses/LICENSE-2.0
   *
   *  Unless required by applicable law or agreed to in writing,
   *  software distributed under the License is distributed on an
   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   *  KIND, either express or implied.  See the License for the
   *  specific language governing permissions and limitations
   *  under the License.
   */
   package com.bj58.argo.thirdparty;
  
   import java.io.IOException;
   import java.io.ObjectOutputStream;
   import java.io.Serializable;
   import java.lang.reflect.Array;
   import java.util.*;
  
   /**
    *
    * 各种容器的封装
    *
    * @author Service Platform Architecture Team (spat@58.com)
    */
  
   public class Collections {
       // Suppresses default constructor, ensuring non-instantiability.
       private Collections() {
       }
  
       // Algorithms
  
       /*
        * Tuning parameters for algorithms - Many of the List algorithms have
        * two implementations, one of which is appropriate for RandomAccess
        * lists, the other for "sequential."  Often, the random access variant
        * yields better performance on small sequential access lists.  The
        * tuning parameters below determine the cutoff point for what constitutes
        * a "small" sequential access list for each algorithm.  The values below
        * were empirically determined to work well for LinkedList. Hopefully
        * they should be reasonable for other sequential access List
        * implementations.  Those doing performance work on this code would
        * do well to validate the values of these parameters from time to time.
        * (The first word of each tuning parameter name is the algorithm to which
        * it applies.)
        */
       private static final int BINARYSEARCH_THRESHOLD   = 5000;
       private static final int REVERSE_THRESHOLD        =   18;
       private static final int SHUFFLE_THRESHOLD        =    5;
       private static final int FILL_THRESHOLD           =   25;
       private static final int ROTATE_THRESHOLD         =  100;
       private static final int COPY_THRESHOLD           =   10;
       private static final int REPLACEALL_THRESHOLD     =   11;
       private static final int INDEXOFSUBLIST_THRESHOLD =   35;
  
       /**
        * Sorts the specified list into ascending order, according to the
        * <i>natural ordering</i> of its elements.  All elements in the list must
        * implement the <tt>Comparable</tt> interface.  Furthermore, all elements
        * in the list must be <i>mutually comparable</i> (that is,
        * <tt>e1.compareTo(e2)</tt> must not throw a <tt>ClassCastException</tt>
        * for any elements <tt>e1</tt> and <tt>e2</tt> in the list).<p>
        *
        * This sort is guaranteed to be <i>stable</i>:  equal elements will
        * not be reordered as a result of the sort.<p>
        *
        * The specified list must be modifiable, but need not be resizable.<p>
        *
        * The sorting algorithm is a modified mergesort (in which the merge is
        * omitted if the highest element in the low sublist is less than the
        * lowest element in the high sublist).  This algorithm offers guaranteed
        * n log(n) performance.
        *
        * This implementation dumps the specified list into an array, sorts
        * the array, and iterates over the list resetting each element
        * from the corresponding position in the array.  This avoids the
        * n<sup>2</sup> log(n) performance that would result from attempting
        * to sort a linked list in place.
        *
        * @param  list the list to be sorted.
        * @throws ClassCastException if the list contains elements that are not
        *	       <i>mutually comparable</i> (for example, strings and integers).
        * @throws UnsupportedOperationException if the specified list's
        *	       list-iterator does not support the <tt>set</tt> operation.
        * @see Comparable
        */
       public static <T extends Comparable<? super T>> void sort(List<T> list) {
       Object[] a = list.toArray();
       Arrays.sort(a);
       ListIterator<T> i = list.listIterator();
       for (int j=0; j<a.length; j++) {
           i.next();
           i.set((T)a[j]);
       }
       }
  
       /**
        * Sorts the specified list according to the order induced by the
        * specified comparator.  All elements in the list must be <i>mutually
        * comparable</i> using the specified comparator (that is,
        * <tt>c.compare(e1, e2)</tt> must not throw a <tt>ClassCastException</tt>
        * for any elements <tt>e1</tt> and <tt>e2</tt> in the list).<p>
        *
        * This sort is guaranteed to be <i>stable</i>:  equal elements will
        * not be reordered as a result of the sort.<p>
        *
        * The sorting algorithm is a modified mergesort (in which the merge is
        * omitted if the highest element in the low sublist is less than the
        * lowest element in the high sublist).  This algorithm offers guaranteed
        * n log(n) performance.
        *
        * The specified list must be modifiable, but need not be resizable.
        * This implementation dumps the specified list into an array, sorts
        * the array, and iterates over the list resetting each element
        * from the corresponding position in the array.  This avoids the
        * n<sup>2</sup> log(n) performance that would result from attempting
        * to sort a linked list in place.
        *
        * @param  list the list to be sorted.
        * @param  c the comparator to determine the order of the list.  A
        *        <tt>null</tt> value indicates that the elements' <i>natural
        *        ordering</i> should be used.
        * @throws ClassCastException if the list contains elements that are not
        *	       <i>mutually comparable</i> using the specified comparator.
        * @throws UnsupportedOperationException if the specified list's
        *	       list-iterator does not support the <tt>set</tt> operation.
        * @see java.util.Comparator
        */
       public static <T> void sort(List<T> list, Comparator<? super T> c) {
       Object[] a = list.toArray();
       Arrays.sort(a, (Comparator)c);
       ListIterator i = list.listIterator();
       for (int j=0; j<a.length; j++) {
           i.next();
           i.set(a[j]);
       }
       }
  
  
       /**
        * Searches the specified list for the specified object using the binary
        * search algorithm.  The list must be sorted into ascending order
        * according to the {@linkplain Comparable natural ordering} of its
        * elements (as by the {@link #sort(java.util.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 java.util.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(java.util.List, java.util.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 java.util.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 java.util.RandomAccess} interface and is large, this
        * implementation dumps the specified list into an array before shuffling
        * it, and dumps the shuffled array back into the list.  This avoids the
        * quadratic behavior that would result from shuffling a "sequential
        * access" list in place.
        *
        * @param  list the list to be shuffled.
        * @throws UnsupportedOperationException if the specified list or
        *         its list-iterator does not support the <tt>set</tt> operation.
        */
       public static void shuffle(List<?> list) {
           if (r == null) {
               r = new Random();
           }
           shuffle(list, r);
       }
       private static Random r;
  
       /**
        * Randomly permute the specified list using the specified source of
        * randomness.  All permutations occur with equal likelihood
        * assuming that the source of randomness is fair.<p>
        *
        * This implementation traverses the list backwards, from the last element
        * up to the second, repeatedly swapping a randomly selected element into
        * the "current position".  Elements are randomly selected from the
        * portion of the list that runs from the first element to the current
        * position, inclusive.<p>
        *
        * This method runs in linear time.  If the specified list does not
        * implement the {@link java.util.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 java.util.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 java.util.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 java.util.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 java.util.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
        * java.util.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(java.util.List)} method is invoked on each sublist create,
        * 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)list, distance);
           else
               rotate2((List)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 create 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 create is to be
        *	       returned.
        * @return an unmodifiable create of the specified collection.
        */
       public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) {
       return new UnmodifiableCollection<T>(c);
       }
  
       /**
        * @serial include
        */
       static class UnmodifiableCollection<E> implements Collection<E>, Serializable {
       // use serialVersionUID from JDK 1.2.2 for interoperability
       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>() {
           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 create 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 create is to be returned.
        * @return an unmodifiable create of the specified set.
        */
       public static <T> Set<T> unmodifiableSet(Set<? extends T> s) {
       return new UnmodifiableSet<T>(s);
       }
  
       /**
        * @serial include
        */
       static class UnmodifiableSet<E> extends UnmodifiableCollection<E>
                        implements Set<E>, Serializable {
       private static final long serialVersionUID = -9215047833775013803L;
  
       UnmodifiableSet(Set<? extends E> s)	{super(s);}
       public boolean equals(Object o) {return o == this || c.equals(o);}
       public int hashCode() 		{return c.hashCode();}
       }
  
       /**
        * Returns an unmodifiable create 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 create is to be
        *        returned.
        * @return an unmodifiable create of the specified sorted set.
        */
       public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) {
       return new UnmodifiableSortedSet<T>(s);
       }
  
       /**
        * @serial include
        */
       static class UnmodifiableSortedSet<E>
                            extends UnmodifiableSet<E>
                            implements SortedSet<E>, Serializable {
       private static final long serialVersionUID = -4929149591599911165L;
           private final SortedSet<E> ss;
  
       UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;}
  
           public Comparator<? super E> comparator() {return ss.comparator();}
  
           public SortedSet<E> subSet(E fromElement, E toElement) {
               return new UnmodifiableSortedSet<E>(ss.subSet(fromElement,toElement));
           }
           public SortedSet<E> headSet(E toElement) {
               return new UnmodifiableSortedSet<E>(ss.headSet(toElement));
           }
           public SortedSet<E> tailSet(E fromElement) {
               return new UnmodifiableSortedSet<E>(ss.tailSet(fromElement));
           }
  
           public E first() 	           {return ss.first();}
           public E last()  	           {return ss.last();}
       }
  
       /**
        * Returns an unmodifiable create 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 java.util.RandomAccess} if the specified list does.
        *
        * @param  list the list for which an unmodifiable create is to be returned.
        * @return an unmodifiable create of the specified list.
        */
       public static <T> List<T> unmodifiableList(List<? extends T> list) {
       return (list instanceof RandomAccess ?
                   new UnmodifiableRandomAccessList<T>(list) :
                   new UnmodifiableList<T>(list));
       }
  
       /**
        * @serial include
        */
       static class UnmodifiableList<E> extends UnmodifiableCollection<E>
                         implements List<E> {
           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>() {
           ListIterator<? extends E> i = list.listIterator(index);
  
           public boolean hasNext()     {return i.hasNext();}
           public E next()		     {return i.next();}
           public boolean hasPrevious() {return i.hasPrevious();}
           public E previous()	     {return i.previous();}
           public int nextIndex()       {return i.nextIndex();}
           public int previousIndex()   {return i.previousIndex();}
  
           public void remove() {
               throw new UnsupportedOperationException();
                   }
           public void set(E e) {
               throw new UnsupportedOperationException();
                   }
           public void add(E e) {
               throw new UnsupportedOperationException();
                   }
           };
       }
  
       public List<E> subList(int fromIndex, int toIndex) {
               return new UnmodifiableList<E>(list.subList(fromIndex, toIndex));
           }
  
           /**
            * UnmodifiableRandomAccessList instances are serialized as
            * UnmodifiableList instances to allow them to be deserialized
            * in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList).
            * This method inverts the transformation.  As a beneficial
            * side-effect, it also grafts the RandomAccess marker onto
            * UnmodifiableList instances that were serialized in pre-1.4 JREs.
            *
            * Note: Unfortunately, UnmodifiableRandomAccessList instances
            * serialized in 1.4.1 and deserialized in 1.4 will become
            * UnmodifiableList instances, as this method was missing in 1.4.
            */
           private Object readResolve() {
               return (list instanceof RandomAccess
               ? new UnmodifiableRandomAccessList<E>(list)
               : this);
           }
       }
  
       /**
        * @serial include
        */
       static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E>
                                                 implements RandomAccess
       {
           UnmodifiableRandomAccessList(List<? extends E> list) {
               super(list);
           }
  
       public List<E> subList(int fromIndex, int toIndex) {
               return new UnmodifiableRandomAccessList<E>(
                   list.subList(fromIndex, toIndex));
           }
  
           private static final long serialVersionUID = -2542308836966382001L;
  
           /**
            * Allows instances to be deserialized in pre-1.4 JREs (which do
            * not have UnmodifiableRandomAccessList).  UnmodifiableList has
            * a readResolve method that inverts this transformation upon
            * deserialization.
            */
           private Object writeReplace() {
               return new UnmodifiableList<E>(list);
           }
       }
  
       /**
        * Returns an unmodifiable create 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 create is to be returned.
        * @return an unmodifiable create of the specified map.
        */
       public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) {
       return new UnmodifiableMap<K,V>(m);
       }
  
       /**
        * @serial include
        */
       private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable {
       // use serialVersionUID from JDK 1.2.2 for interoperability
       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<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<Entry<K,V>> entrySet() {
           if (entrySet==null)
           entrySet = new UnmodifiableEntrySet<K,V>(m.entrySet());
           return entrySet;
       }
  
       public Collection<V> values() {
           if (values==null)
           values = unmodifiableCollection(m.values());
           return values;
       }
  
       public boolean equals(Object o) {return o == this || m.equals(o);}
       public int hashCode()           {return m.hashCode();}
           public String toString()        {return m.toString();}
  
           /**
            * We need this class in addition to UnmodifiableSet as
            * Map.Entries themselves permit modification of the backing Map
            * via their setValue operation.  This class is subtle: there are
            * many possible attacks that must be thwarted.
            *
            * @serial include
            */
           static class UnmodifiableEntrySet<K,V>
           extends UnmodifiableSet<Entry<K,V>> {
           private static final long serialVersionUID = 7854390611657943733L;
  
               UnmodifiableEntrySet(Set<? extends Entry<? extends K, ? extends V>> s) {
                   super((Set)s);
               }
               public Iterator<Entry<K,V>> iterator() {
                   return new Iterator<Entry<K,V>>() {
               Iterator<? extends Entry<? extends K, ? extends V>> i = c.iterator();
  
                       public boolean hasNext() {
                           return i.hasNext();
                       }
               public Entry<K,V> next() {
               return new UnmodifiableEntry<K,V>(i.next());
                       }
                       public void remove() {
                           throw new UnsupportedOperationException();
                       }
                   };
               }
  
               public Object[] toArray() {
                   Object[] a = c.toArray();
                   for (int i=0; i<a.length; i++)
                       a[i] = new UnmodifiableEntry<K,V>((Entry<K,V>)a[i]);
                   return a;
               }
  
               public <T> T[] toArray(T[] a) {
                   // We don't pass a to c.toArray, to avoid window of
                   // vulnerability wherein an unscrupulous multithreaded client
                   // could get his hands on raw (unwrapped) Entries from c.
           Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
  
                   for (int i=0; i<arr.length; i++)
                       arr[i] = new UnmodifiableEntry<K,V>((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 Entry))
                       return false;
                   return c.contains(new UnmodifiableEntry<K,V>((Entry<K,V>) o));
               }
  
               /**
                * The next two methods are overridden to protect against
                * an unscrupulous List whose contains(Object o) method senses
                * when o is a Map.Entry, and calls o.setValue.
                */
               public boolean containsAll(Collection<?> coll) {
                   Iterator<?> e = coll.iterator();
                   while (e.hasNext())
                       if (!contains(e.next())) // Invokes safe contains() above
                           return false;
                   return true;
               }
               public boolean equals(Object o) {
                   if (o == this)
                       return true;
  
                   if (!(o instanceof Set))
                       return false;
                   Set s = (Set) o;
                   if (s.size() != c.size())
                       return false;
                   return containsAll(s); // Invokes safe containsAll() above
               }
  
               /**
                * This "wrapper class" serves two purposes: it prevents
                * the client from modifying the backing Map, by short-circuiting
                * the setValue method, and it protects the backing Map against
                * an ill-behaved Map.Entry that attempts to modify another
                * Map Entry when asked to perform an equality check.
                */
               private static class UnmodifiableEntry<K,V> implements Entry<K,V> {
                   private Entry<? extends K, ? extends V> e;
  
                   UnmodifiableEntry(Entry<? extends K, ? extends V> e) {this.e = e;}
  
                   public K getKey()	  {return e.getKey();}
                   public V getValue()  {return e.getValue();}
                   public V setValue(V value) {
                       throw new UnsupportedOperationException();
                   }
                   public int hashCode()	  {return e.hashCode();}
                   public boolean equals(Object o) {
                       if (!(o instanceof Entry))
                           return false;
                       Entry t = (Entry)o;
                       return eq(e.getKey(),   t.getKey()) &&
                              eq(e.getValue(), t.getValue());
                   }
                   public String toString()  {return e.toString();}
               }
           }
       }
  
       /**
        * Returns an unmodifiable create 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 create is to be
        *        returned.
        * @return an unmodifiable create of the specified sorted map.
        */
       public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) {
       return new UnmodifiableSortedMap<K,V>(m);
       }
  
       /**
        * @serial include
        */
       static class UnmodifiableSortedMap<K,V>
         extends UnmodifiableMap<K,V>
         implements SortedMap<K,V>, Serializable {
       private static final long serialVersionUID = -8806743815996713206L;
  
           private final SortedMap<K, ? extends V> sm;
  
       UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m;}
  
           public Comparator<? super K> comparator() {return sm.comparator();}
  
           public SortedMap<K,V> subMap(K fromKey, K toKey) {
               return new UnmodifiableSortedMap<K,V>(sm.subMap(fromKey, toKey));
           }
           public SortedMap<K,V> headMap(K toKey) {
               return new UnmodifiableSortedMap<K,V>(sm.headMap(toKey));
           }
           public SortedMap<K,V> tailMap(K fromKey) {
               return new UnmodifiableSortedMap<K,V>(sm.tailMap(fromKey));
           }
  
           public K firstKey()           {return sm.firstKey();}
           public K lastKey()            {return sm.lastKey();}
       }
  
  
       // Synch Wrappers
  
       /**
        * Returns a synchronized (thread-safe) collection backed by the specified
        * collection.  In order to guarantee serial access, it is critical that
        * <strong>all</strong> access to the backing collection is accomplished
        * through the returned collection.<p>
        *
        * It is imperative that the user manually synchronize on the returned
        * collection when iterating over it:
        * <pre>
        *  Collection c = Collections.synchronizedCollection(myCollection);
        *     ...
        *  synchronized(c) {
        *      Iterator i = c.iterator(); // Must be in the synchronized block
        *      while (i.hasNext())
        *         foo(i.next());
        *  }
        * </pre>
        * Failure to follow this advice may result in non-deterministic behavior.
        *
        * <p>The returned collection does <i>not</i> pass the <tt>hashCode</tt>
        * and <tt>equals</tt> operations through to the backing collection, but
        * relies on <tt>Object</tt>'s equals and hashCode methods.  This is
        * necessary to preserve the contracts of these operations in the case
        * that the backing collection is a set or a list.<p>
        *
        * The returned collection will be serializable if the specified collection
        * is serializable.
        *
        * @param  c the collection to be "wrapped" in a synchronized collection.
        * @return a synchronized create of the specified collection.
        */
       public static <T> Collection<T> synchronizedCollection(Collection<T> c) {
       return new SynchronizedCollection<T>(c);
       }
  
       static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) {
       return new SynchronizedCollection<T>(c, mutex);
       }
  
       /**
        * @serial include
        */
       static class SynchronizedCollection<E> implements Collection<E>, Serializable {
       // use serialVersionUID from JDK 1.2.2 for interoperability
       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 create of the specified set.
        */
       public static <T> Set<T> synchronizedSet(Set<T> s) {
       return new SynchronizedSet<T>(s);
       }
  
       static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) {
       return new SynchronizedSet<T>(s, mutex);
       }
  
       /**
        * @serial include
        */
       static class SynchronizedSet<E>
         extends SynchronizedCollection<E>
         implements Set<E> {
       private static final long serialVersionUID = 487447009682186044L;
  
       SynchronizedSet(Set<E> s) {
               super(s);
           }
       SynchronizedSet(Set<E> s, Object mutex) {
               super(s, mutex);
           }
  
       public boolean equals(Object o) {
           synchronized(mutex) {return c.equals(o);}
           }
       public int hashCode() {
           synchronized(mutex) {return c.hashCode();}
           }
       }
  
       /**
        * Returns a synchronized (thread-safe) sorted set backed by the specified
        * sorted set.  In order to guarantee serial access, it is critical that
        * <strong>all</strong> access to the backing sorted set is accomplished
        * through the returned sorted set (or its views).<p>
        *
        * It is imperative that the user manually synchronize on the returned
        * sorted set when iterating over it or any of its <tt>subSet</tt>,
        * <tt>headSet</tt>, or <tt>tailSet</tt> views.
        * <pre>
        *  SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
        *      ...
        *  synchronized(s) {
        *      Iterator i = s.iterator(); // Must be in the synchronized block
        *      while (i.hasNext())
        *          foo(i.next());
        *  }
        * </pre>
        * or:
        * <pre>
        *  SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
        *  SortedSet s2 = s.headSet(foo);
        *      ...
        *  synchronized(s) {  // Note: s, not s2!!!
        *      Iterator i = s2.iterator(); // Must be in the synchronized block
        *      while (i.hasNext())
        *          foo(i.next());
        *  }
        * </pre>
        * Failure to follow this advice may result in non-deterministic behavior.
        *
        * <p>The returned sorted set will be serializable if the specified
        * sorted set is serializable.
        *
        * @param  s the sorted set to be "wrapped" in a synchronized sorted set.
        * @return a synchronized create of the specified sorted set.
        */
       public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) {
       return new SynchronizedSortedSet<T>(s);
       }
  
       /**
        * @serial include
        */
       static class SynchronizedSortedSet<E>
       extends SynchronizedSet<E>
       implements SortedSet<E>
       {
       private static final long serialVersionUID = 8695801310862127406L;
  
           final private SortedSet<E> ss;
  
       SynchronizedSortedSet(SortedSet<E> s) {
               super(s);
               ss = s;
           }
       SynchronizedSortedSet(SortedSet<E> s, Object mutex) {
               super(s, mutex);
               ss = s;
           }
  
       public Comparator<? super E> comparator() {
           synchronized(mutex) {return ss.comparator();}
           }
  
           public SortedSet<E> subSet(E fromElement, E toElement) {
           synchronized(mutex) {
                   return new SynchronizedSortedSet<E>(
                       ss.subSet(fromElement, toElement), mutex);
               }
           }
           public SortedSet<E> headSet(E toElement) {
           synchronized(mutex) {
                   return new SynchronizedSortedSet<E>(ss.headSet(toElement), mutex);
               }
           }
           public SortedSet<E> tailSet(E fromElement) {
           synchronized(mutex) {
                  return new SynchronizedSortedSet<E>(ss.tailSet(fromElement),mutex);
               }
           }
  
           public E first() {
           synchronized(mutex) {return ss.first();}
           }
           public E last() {
           synchronized(mutex) {return ss.last();}
           }
       }
  
       /**
        * Returns a synchronized (thread-safe) list backed by the specified
        * list.  In order to guarantee serial access, it is critical that
        * <strong>all</strong> access to the backing list is accomplished
        * through the returned list.<p>
        *
        * It is imperative that the user manually synchronize on the returned
        * list when iterating over it:
        * <pre>
        *  List list = Collections.synchronizedList(new ArrayList());
        *      ...
        *  synchronized(list) {
        *      Iterator i = list.iterator(); // Must be in synchronized block
        *      while (i.hasNext())
        *          foo(i.next());
        *  }
        * </pre>
        * Failure to follow this advice may result in non-deterministic behavior.
        *
        * <p>The returned list will be serializable if the specified list is
        * serializable.
        *
        * @param  list the list to be "wrapped" in a synchronized list.
        * @return a synchronized create of the specified list.
        */
       public static <T> List<T> synchronizedList(List<T> list) {
       return (list instanceof RandomAccess ?
                   new SynchronizedRandomAccessList<T>(list) :
                   new SynchronizedList<T>(list));
       }
  
       static <T> List<T> synchronizedList(List<T> list, Object mutex) {
       return (list instanceof RandomAccess ?
                   new SynchronizedRandomAccessList<T>(list, mutex) :
                   new SynchronizedList<T>(list, mutex));
       }
  
       /**
        * @serial include
        */
       static class SynchronizedList<E>
       extends SynchronizedCollection<E>
       implements List<E> {
           static final long serialVersionUID = -7754090372962971524L;
  
       final List<E> list;
  
       SynchronizedList(List<E> list) {
           super(list);
           this.list = list;
       }
       SynchronizedList(List<E> list, Object mutex) {
               super(list, mutex);
           this.list = list;
           }
  
       public boolean equals(Object o) {
           synchronized(mutex) {return list.equals(o);}
           }
       public int hashCode() {
           synchronized(mutex) {return list.hashCode();}
           }
  
       public E get(int index) {
           synchronized(mutex) {return list.get(index);}
           }
       public E set(int index, E element) {
           synchronized(mutex) {return list.set(index, element);}
           }
       public void add(int index, E element) {
           synchronized(mutex) {list.add(index, element);}
           }
       public E remove(int index) {
           synchronized(mutex) {return list.remove(index);}
           }
  
       public int indexOf(Object o) {
           synchronized(mutex) {return list.indexOf(o);}
           }
       public int lastIndexOf(Object o) {
           synchronized(mutex) {return list.lastIndexOf(o);}
           }
  
       public boolean addAll(int index, Collection<? extends E> c) {
           synchronized(mutex) {return list.addAll(index, c);}
           }
  
       public ListIterator<E> listIterator() {
           return list.listIterator(); // Must be manually synched by user
           }
  
       public ListIterator<E> listIterator(int index) {
           return list.listIterator(index); // Must be manually synched by user
           }
  
       public List<E> subList(int fromIndex, int toIndex) {
           synchronized(mutex) {
                   return new SynchronizedList<E>(list.subList(fromIndex, toIndex),
                                               mutex);
               }
           }
  
           /**
            * SynchronizedRandomAccessList instances are serialized as
            * SynchronizedList instances to allow them to be deserialized
            * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList).
            * This method inverts the transformation.  As a beneficial
            * side-effect, it also grafts the RandomAccess marker onto
            * SynchronizedList instances that were serialized in pre-1.4 JREs.
            *
            * Note: Unfortunately, SynchronizedRandomAccessList instances
            * serialized in 1.4.1 and deserialized in 1.4 will become
            * SynchronizedList instances, as this method was missing in 1.4.
            */
           private Object readResolve() {
               return (list instanceof RandomAccess
               ? new SynchronizedRandomAccessList<E>(list)
               : this);
           }
       }
  
       /**
        * @serial include
        */
       static class SynchronizedRandomAccessList<E>
       extends SynchronizedList<E>
       implements RandomAccess {
  
           SynchronizedRandomAccessList(List<E> list) {
               super(list);
           }
  
       SynchronizedRandomAccessList(List<E> list, Object mutex) {
               super(list, mutex);
           }
  
       public List<E> subList(int fromIndex, int toIndex) {
           synchronized(mutex) {
                   return new SynchronizedRandomAccessList<E>(
                       list.subList(fromIndex, toIndex), mutex);
               }
           }
  
           static final long serialVersionUID = 1530674583602358482L;
  
           /**
            * Allows instances to be deserialized in pre-1.4 JREs (which do
            * not have SynchronizedRandomAccessList).  SynchronizedList has
            * a readResolve method that inverts this transformation upon
            * deserialization.
            */
           private Object writeReplace() {
               return new SynchronizedList<E>(list);
           }
       }
  
       /**
        * Returns a synchronized (thread-safe) map backed by the specified
        * map.  In order to guarantee serial access, it is critical that
        * <strong>all</strong> access to the backing map is accomplished
        * through the returned map.<p>
        *
        * It is imperative that the user manually synchronize on the returned
        * map when iterating over any of its collection views:
        * <pre>
        *  Map m = Collections.synchronizedMap(new HashMap());
        *      ...
        *  Set s = m.keySet();  // Needn't be in synchronized block
        *      ...
        *  synchronized(m) {  // Synchronizing on m, not s!
        *      Iterator i = s.iterator(); // Must be in synchronized block
        *      while (i.hasNext())
        *          foo(i.next());
        *  }
        * </pre>
        * Failure to follow this advice may result in non-deterministic behavior.
        *
        * <p>The returned map will be serializable if the specified map is
        * serializable.
        *
        * @param  m the map to be "wrapped" in a synchronized map.
        * @return a synchronized create of the specified map.
        */
       public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) {
       return new SynchronizedMap<K,V>(m);
       }
  
       /**
        * @serial include
        */
       private static class SynchronizedMap<K,V>
       implements Map<K,V>, Serializable {
       // use serialVersionUID from JDK 1.2.2 for interoperability
       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<Entry<K,V>> entrySet = null;
       private transient Collection<V> values = null;
  
       public Set<K> keySet() {
               synchronized(mutex) {
                   if (keySet==null)
                       keySet = new SynchronizedSet<K>(m.keySet(), mutex);
                   return keySet;
               }
       }
  
       public Set<Entry<K,V>> entrySet() {
               synchronized(mutex) {
                   if (entrySet==null)
                       entrySet = new SynchronizedSet<Entry<K,V>>(m.entrySet(), mutex);
                   return entrySet;
               }
       }
  
       public Collection<V> values() {
               synchronized(mutex) {
                   if (values==null)
                       values = new SynchronizedCollection<V>(m.values(), mutex);
                   return values;
               }
           }
  
       public boolean equals(Object o) {
               synchronized(mutex) {return m.equals(o);}
           }
       public int hashCode() {
               synchronized(mutex) {return m.hashCode();}
           }
       public String toString() {
           synchronized(mutex) {return m.toString();}
           }
           private void writeObject(ObjectOutputStream s) throws IOException {
           synchronized(mutex) {s.defaultWriteObject();}
           }
       }
  
       /**
        * Returns a synchronized (thread-safe) sorted map backed by the specified
        * sorted map.  In order to guarantee serial access, it is critical that
        * <strong>all</strong> access to the backing sorted map is accomplished
        * through the returned sorted map (or its views).<p>
        *
        * It is imperative that the user manually synchronize on the returned
        * sorted map when iterating over any of its collection views, or the
        * collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or
        * <tt>tailMap</tt> views.
        * <pre>
        *  SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
        *      ...
        *  Set s = m.keySet();  // Needn't be in synchronized block
        *      ...
        *  synchronized(m) {  // Synchronizing on m, not s!
        *      Iterator i = s.iterator(); // Must be in synchronized block
        *      while (i.hasNext())
        *          foo(i.next());
        *  }
        * </pre>
        * or:
        * <pre>
        *  SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
        *  SortedMap m2 = m.subMap(foo, bar);
        *      ...
        *  Set s2 = m2.keySet();  // Needn't be in synchronized block
        *      ...
        *  synchronized(m) {  // Synchronizing on m, not m2 or s2!
        *      Iterator i = s.iterator(); // Must be in synchronized block
        *      while (i.hasNext())
        *          foo(i.next());
        *  }
        * </pre>
        * Failure to follow this advice may result in non-deterministic behavior.
        *
        * <p>The returned sorted map will be serializable if the specified
        * sorted map is serializable.
        *
        * @param  m the sorted map to be "wrapped" in a synchronized sorted map.
        * @return a synchronized create of the specified sorted map.
        */
       public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) {
       return new SynchronizedSortedMap<K,V>(m);
       }
  
  
       /**
        * @serial include
        */
       static class SynchronizedSortedMap<K,V>
       extends SynchronizedMap<K,V>
       implements SortedMap<K,V>
       {
       private static final long serialVersionUID = -8798146769416483793L;
  
           private final SortedMap<K,V> sm;
  
       SynchronizedSortedMap(SortedMap<K,V> m) {
               super(m);
               sm = m;
           }
       SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) {
               super(m, mutex);
               sm = m;
           }
  
       public Comparator<? super K> comparator() {
           synchronized(mutex) {return sm.comparator();}
           }
  
           public SortedMap<K,V> subMap(K fromKey, K toKey) {
           synchronized(mutex) {
                   return new SynchronizedSortedMap<K,V>(
                       sm.subMap(fromKey, toKey), mutex);
               }
           }
           public SortedMap<K,V> headMap(K toKey) {
           synchronized(mutex) {
                   return new SynchronizedSortedMap<K,V>(sm.headMap(toKey), mutex);
               }
           }
           public SortedMap<K,V> tailMap(K fromKey) {
           synchronized(mutex) {
                  return new SynchronizedSortedMap<K,V>(sm.tailMap(fromKey),mutex);
               }
           }
  
           public K firstKey() {
           synchronized(mutex) {return sm.firstKey();}
           }
           public K lastKey() {
           synchronized(mutex) {return sm.lastKey();}
           }
       }
  
       // Dynamically typesafe collection wrappers
  
       /**
        * Returns a dynamically typesafe create of the specified collection.  Any
        * attempt to insert an element of the wrong type will result in an
        * immediate <tt>ClassCastException</tt>.  Assuming a collection contains
        * no incorrectly typed elements prior to the time a dynamically typesafe
        * create is generated, and that all subsequent access to the collection
        * takes place through the create, 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 <tt>ClassCastException</tt>, 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 create.
        * For example, this declaration:
        * <pre>
        *     Collection&lt;String&gt; c = new HashSet&lt;String&gt;();
        * </pre>
        * may be replaced temporarily by this one:
        * <pre>
        *     Collection&lt;String&gt; c = Collections.checkedCollection(
        *         new HashSet&lt;String&gt;(), 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
        * <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 a dynamically typesafe create is to be
        *             returned
        * @param type the type of element that <tt>c</tt> is permitted to hold
        * @return a dynamically typesafe create of the specified collection
        * @since 1.5
        */
       public static <E> Collection<E> checkedCollection(Collection<E> c,
                                                         Class<E> type) {
           return new CheckedCollection<E>(c, type);
       }
  
       /**
        * @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 (!type.isInstance(o))
                   throw new ClassCastException("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 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 void clear() {
               c.clear();
           }
  
           public Iterator<E> iterator() {
           return new Iterator<E>() {
           private final Iterator<E> it = c.iterator();
           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);
           }
  
           public boolean addAll(Collection<? extends E> coll) {
               /*
                * Dump coll into an array of the required type.  This serves
                * three purposes: it insulates us from concurrent changes in
                * the contents of coll, it type-checks all of the elements in
                * coll, and it provides all-or-nothing semantics (which we
                * wouldn't get if we type-checked each element as we added it).
                */
               E[] a = null;
               try {
                   a = coll.toArray(zeroLengthElementArray());
               } catch (ArrayStoreException e) {
                   throw new ClassCastException();
               }
  
               boolean result = false;
               for (E e : a)
                   result |= c.add(e);
               return result;
           }
  
           private E[] zeroLengthElementArray = null; // Lazily initialized
  
           /*
            * We don't need locking or volatile, because it's OK if we getLogger
            * several zeroLengthElementArrays, and they're immutable.
            */
           E[] zeroLengthElementArray() {
               if (zeroLengthElementArray == null)
                   zeroLengthElementArray = (E[]) Array.newInstance(type, 0);
               return zeroLengthElementArray;
           }
       }
  
       /**
        * Returns a dynamically typesafe create of the specified set.
        * Any attempt to insert an element of the wrong type will result in
        * an immediate <tt>ClassCastException</tt>.  Assuming a set contains
        * no incorrectly typed elements prior to the time a dynamically typesafe
        * create is generated, and that all subsequent access to the set
        * takes place through the create, 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.
        *
        * @param s the set for which a dynamically typesafe create is to be
        *             returned
        * @param type the type of element that <tt>s</tt> is permitted to hold
        * @return a dynamically typesafe create of the specified set
        * @since 1.5
        */
       public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) {
           return new CheckedSet<E>(s, type);
       }
  
       /**
        * @serial include
        */
       static class CheckedSet<E> extends CheckedCollection<E>
                                    implements Set<E>, Serializable
       {
           private static final long serialVersionUID = 4694047833775013803L;
  
           CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); }
  
           public boolean equals(Object o) { return o == this || c.equals(o); }
           public int hashCode()           { return c.hashCode(); }
       }
  
       /**
        * Returns a dynamically typesafe create of the specified sorted set.  Any
        * attempt to insert an element of the wrong type will result in an
        * immediate <tt>ClassCastException</tt>.  Assuming a sorted set contains
        * no incorrectly typed elements prior to the time a dynamically typesafe
        * create is generated, and that all subsequent access to the sorted set
        * takes place through the create, 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.
        *
        * @param s the sorted set for which a dynamically typesafe create is to be
        *             returned
        * @param type the type of element that <tt>s</tt> is permitted to hold
        * @return a dynamically typesafe create of the specified sorted set
        * @since 1.5
        */
       public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s,
                                                       Class<E> type) {
           return new CheckedSortedSet<E>(s, type);
       }
  
       /**
        * @serial include
        */
       static class CheckedSortedSet<E> extends CheckedSet<E>
           implements SortedSet<E>, Serializable
       {
           private static final long serialVersionUID = 1599911165492914959L;
           private final SortedSet<E> ss;
  
           CheckedSortedSet(SortedSet<E> s, Class<E> type) {
               super(s, type);
               ss = s;
           }
  
           public Comparator<? super E> comparator() { return ss.comparator(); }
           public E first()                   { return ss.first(); }
           public E last()                    { return ss.last(); }
  
           public SortedSet<E> subSet(E fromElement, E toElement) {
               return new CheckedSortedSet<E>(ss.subSet(fromElement,toElement),
                                              type);
           }
           public SortedSet<E> headSet(E toElement) {
               return new CheckedSortedSet<E>(ss.headSet(toElement), type);
           }
           public SortedSet<E> tailSet(E fromElement) {
               return new CheckedSortedSet<E>(ss.tailSet(fromElement), type);
           }
       }
  
       /**
        * Returns a dynamically typesafe create of the specified list.
        * Any attempt to insert an element of the wrong type will result in
        * an immediate <tt>ClassCastException</tt>.  Assuming a list contains
        * no incorrectly typed elements prior to the time a dynamically typesafe
        * create is generated, and that all subsequent access to the list
        * takes place through the create, 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.
        *
        * @param list the list for which a dynamically typesafe create is to be
        *             returned
        * @param type the type of element that <tt>list</tt> is permitted to hold
        * @return a dynamically typesafe create of the specified list
        * @since 1.5
        */
       public static <E> List<E> checkedList(List<E> list, Class<E> type) {
           return (list instanceof RandomAccess ?
                   new CheckedRandomAccessList<E>(list, type) :
                   new CheckedList<E>(list, type));
       }
  
       /**
        * @serial include
        */
       static class CheckedList<E> extends CheckedCollection<E>
                                   implements List<E>
       {
           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) {
               // See CheckCollection.addAll, above, for an explanation
               E[] a = null;
               try {
                   a = c.toArray(zeroLengthElementArray());
               } catch (ArrayStoreException e) {
                   throw new ClassCastException();
               }
  
               return list.addAll(index, Arrays.asList(a));
           }
           public ListIterator<E> listIterator()   { return listIterator(0); }
  
           public ListIterator<E> listIterator(final int index) {
               return new ListIterator<E>() {
                   ListIterator<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()         { i.remove(); }
  
                   public void set(E e) {
                       typeCheck(e);
                       i.set(e);
                   }
  
                   public void add(E e) {
                       typeCheck(e);
                       i.add(e);
                   }
               };
           }
  
           public List<E> subList(int fromIndex, int toIndex) {
               return new CheckedList<E>(list.subList(fromIndex, toIndex), type);
           }
       }
  
       /**
        * @serial include
        */
       static class CheckedRandomAccessList<E> extends CheckedList<E>
                                               implements RandomAccess
       {
           private static final long serialVersionUID = 1638200125423088369L;
  
           CheckedRandomAccessList(List<E> list, Class<E> type) {
               super(list, type);
           }
  
           public List<E> subList(int fromIndex, int toIndex) {
               return new CheckedRandomAccessList<E>(
                   list.subList(fromIndex, toIndex), type);
           }
       }
  
       /**
        * Returns a dynamically typesafe create of the specified map.  Any attempt
        * to insert a mapping whose key or value have the wrong type will result
        * in an immediate <tt>ClassCastException</tt>.  Similarly, any attempt to
        * modify the value currently associated with a key will result in an
        * immediate <tt>ClassCastException</tt>, whether the modification is
        * attempted directly through the map itself, or through a {@link
        * java.util.Map.Entry} instance obtained from the map's {@link java.util.Map#entrySet()
        * entry set} create.
        *
        * <p>Assuming a map contains no incorrectly typed keys or values
        * prior to the time a dynamically typesafe create is generated, and
        * that all subsequent access to the map takes place through the create
        * (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.
        *
        * @param m the map for which a dynamically typesafe create is to be
        *             returned
        * @param keyType the type of key that <tt>m</tt> is permitted to hold
        * @param valueType the type of value that <tt>m</tt> is permitted to hold
        * @return a dynamically typesafe create of the specified map
        * @since 1.5
        */
       public static <K, V> Map<K, V> checkedMap(Map<K, V> m, Class<K> keyType,
                                                 Class<V> valueType) {
           return new CheckedMap<K,V>(m, keyType, valueType);
       }
  
  
       /**
        * @serial include
        */
       private static class CheckedMap<K,V> implements Map<K,V>,
                                                            Serializable
       {
           private static final long serialVersionUID = 5742860141034234728L;
  
           private final Map<K, V> m;
           final Class<K> keyType;
           final Class<V> valueType;
  
           private void typeCheck(Object key, Object value) {
               if (!keyType.isInstance(key))
                   throw new ClassCastException("Attempt to insert " +
                       key.getClass() + " key into collection with key type "
                       + keyType);
  
               if (!valueType.isInstance(value))
                   throw new ClassCastException("Attempt to insert " +
                       value.getClass() +" value into collection 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);
           }
  
           public void putAll(Map<? extends K, ? extends V> t) {
               // See CheckCollection.addAll, above, for an explanation
               K[] keys = null;
               try {
                   keys = t.keySet().toArray(zeroLengthKeyArray());
               } catch (ArrayStoreException e) {
                   throw new ClassCastException();
               }
               V[] values = null;
               try {
                   values = t.values().toArray(zeroLengthValueArray());
               } catch (ArrayStoreException e) {
                   throw new ClassCastException();
               }
  
               if (keys.length != values.length)
                   throw new ConcurrentModificationException();
  
               for (int i = 0; i < keys.length; i++)
                   m.put(keys[i], values[i]);
           }
  
           // Lazily initialized
           private K[] zeroLengthKeyArray   = null;
           private V[] zeroLengthValueArray = null;
  
           /*
            * We don't need locking or volatile, because it's OK if we getLogger
            * several zeroLengthValueArrays, and they're immutable.
            */
           private K[] zeroLengthKeyArray() {
               if (zeroLengthKeyArray == null)
                   zeroLengthKeyArray = (K[]) Array.newInstance(keyType, 0);
               return zeroLengthKeyArray;
           }
           private V[] zeroLengthValueArray() {
               if (zeroLengthValueArray == null)
                   zeroLengthValueArray = (V[]) Array.newInstance(valueType, 0);
               return zeroLengthValueArray;
           }
  
           private transient Set<Entry<K,V>> entrySet = null;
  
           public Set<Entry<K,V>> entrySet() {
               if (entrySet==null)
                   entrySet = new CheckedEntrySet<K,V>(m.entrySet(), valueType);
               return entrySet;
           }
  
           /**
            * We need this class in addition to CheckedSet as Map.Entry permits
            * modification of the backing Map via the setValue operation.  This
            * class is subtle: there are many possible attacks that must be
            * thwarted.
            *
            * @serial exclude
            */
           static class CheckedEntrySet<K,V> implements Set<Entry<K,V>> {
               Set<Entry<K,V>> s;
               Class<V> valueType;
  
               CheckedEntrySet(Set<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 boolean remove(Object o)     { return s.remove(o); }
               public boolean removeAll(Collection<?> coll) {
                   return s.removeAll(coll);
               }
               public boolean retainAll(Collection<?> coll) {
                   return s.retainAll(coll);
               }
               public void clear() {
                   s.clear();
               }
  
               public boolean add(Entry<K, V> e){
                   throw new UnsupportedOperationException();
               }
               public boolean addAll(Collection<? extends Entry<K, V>> coll) {
                   throw new UnsupportedOperationException();
               }
  
  
               public Iterator<Entry<K,V>> iterator() {
                   return new Iterator<Entry<K,V>>() {
                       Iterator<Entry<K, V>> i = s.iterator();
  
                       public boolean hasNext() { return i.hasNext(); }
                       public void remove()     { i.remove(); }
  
                       public Entry<K,V> next() {
                           return new CheckedEntry<K,V>(i.next(), valueType);
                       }
                   };
               }
  
               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] = new CheckedEntry<K,V>((Entry<K,V>)source[i],
                                                       valueType);
                   return dest;
               }
  
               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.
                   Object[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
  
                   for (int i=0; i<arr.length; i++)
                       arr[i] = new CheckedEntry<K,V>((Entry<K,V>)arr[i],
                                                      valueType);
                   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 Entry))
                       return false;
                   return s.contains(
                       new CheckedEntry<K,V>((Entry<K,V>) o, valueType));
               }
  
               /**
                * The next two methods are overridden to protect against
                * an unscrupulous collection whose contains(Object o) method
                * senses when o is a Map.Entry, and calls o.setValue.
                */
               public boolean containsAll(Collection<?> coll) {
                   Iterator<?> e = coll.iterator();
                   while (e.hasNext())
                       if (!contains(e.next())) // Invokes safe contains() above
                           return false;
                   return true;
               }
  
               public boolean equals(Object o) {
                   if (o == this)
                       return true;
                   if (!(o instanceof Set))
                       return false;
                   Set<?> that = (Set<?>) o;
                   if (that.size() != s.size())
                       return false;
                   return containsAll(that); // 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 CheckedEntry<K,V> implements Entry<K,V> {
                   private Entry<K, V> e;
                   private Class<V> valueType;
  
                   CheckedEntry(Entry<K, V> e, Class<V> valueType) {
                       this.e = e;
                       this.valueType = valueType;
                   }
  
                   public K getKey()        { return e.getKey(); }
                   public V getValue()      { return e.getValue(); }
                   public int hashCode()    { return e.hashCode(); }
                   public String toString() { return e.toString(); }
  
  
                   public V setValue(V value) {
                       if (!valueType.isInstance(value))
                           throw new ClassCastException("Attempt to insert " +
                           value.getClass() +
                           " value into collection with value type " + valueType);
                       return e.setValue(value);
                   }
  
                   public boolean equals(Object o) {
                       if (!(o instanceof Entry))
                           return false;
                       Entry t = (Entry)o;
                       return eq(e.getKey(),   t.getKey()) &&
                              eq(e.getValue(), t.getValue());
                   }
               }
           }
       }
  
       /**
        * Returns a dynamically typesafe create of the specified sorted map.  Any
        * attempt to insert a mapping whose key or value have the wrong type will
        * result in an immediate <tt>ClassCastException</tt>.  Similarly, any
        * attempt to modify the value currently associated with a key will result
        * in an immediate <tt>ClassCastException</tt>, whether the modification
        * is attempted directly through the map itself, or through a {@link
        * java.util.Map.Entry} instance obtained from the map's {@link java.util.Map#entrySet() entry
        * set} create.
        *
        * <p>Assuming a map contains no incorrectly typed keys or values
        * prior to the time a dynamically typesafe create is generated, and
        * that all subsequent access to the map takes place through the create
        * (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.
        *
        * @param m the map for which a dynamically typesafe create is to be
        *             returned
        * @param keyType the type of key that <tt>m</tt> is permitted to hold
        * @param valueType the type of value that <tt>m</tt> is permitted to hold
        * @return a dynamically typesafe create of the specified map
        * @since 1.5
        */
       public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m,
                                                           Class<K> keyType,
                                                           Class<V> valueType) {
           return new CheckedSortedMap<K,V>(m, keyType, valueType);
       }
  
       /**
        * @serial include
        */
       static class CheckedSortedMap<K,V> extends CheckedMap<K,V>
           implements SortedMap<K,V>, Serializable
       {
           private static final long serialVersionUID = 1599671320688067438L;
  
           private final SortedMap<K, V> sm;
  
           CheckedSortedMap(SortedMap<K, V> m,
                            Class<K> keyType, Class<V> valueType) {
               super(m, keyType, valueType);
               sm = m;
           }
  
           public Comparator<? super K> comparator() { return sm.comparator(); }
           public K firstKey()                       { return sm.firstKey(); }
           public K lastKey()                        { return sm.lastKey(); }
  
           public SortedMap<K,V> subMap(K fromKey, K toKey) {
               return new CheckedSortedMap<K,V>(sm.subMap(fromKey, toKey),
                                                keyType, valueType);
           }
  
           public SortedMap<K,V> headMap(K toKey) {
               return new CheckedSortedMap<K,V>(sm.headMap(toKey),
                                                keyType, valueType);
           }
  
           public SortedMap<K,V> tailMap(K fromKey) {
               return new CheckedSortedMap<K,V>(sm.tailMap(fromKey),
                                                keyType, valueType);
           }
       }
  
       // Miscellaneous
  
       /**
        * The empty set (immutable).  This set is serializable.
        *
        * @see #emptySet()
        */
       public static final Set EMPTY_SET = new EmptySet();
  
       /**
        * Returns the empty set (immutable).  This set is serializable.
        * Unlike the like-named field, this method is parameterized.
        *
        * <p>This example illustrates the type-safe way to obtain an empty set:
        * <pre>
        *     Set&lt;String&gt; s = Collections.emptySet();
        * </pre>
        * Implementation note:  Implementations of this method need not
        * getLogger a separate <tt>Set</tt> object for each call.   Using this
        * method is likely to have comparable cost to using the like-named
        * field.  (Unlike this method, the field does not provide type safety.)
        *
        * @see #EMPTY_SET
        * @since 1.5
        */
       public static final <T> Set<T> emptySet() {
       return (Set<T>) EMPTY_SET;
       }
  
       /**
        * @serial include
        */
       private static class EmptySet extends AbstractSet<Object> implements Serializable {
       // use serialVersionUID from JDK 1.2.2 for interoperability
       private static final long serialVersionUID = 1582296315990362920L;
  
           public Iterator<Object> iterator() {
               return new Iterator<Object>() {
                   public boolean hasNext() {
                       return false;
                   }
                   public Object next() {
                       throw new NoSuchElementException();
                   }
                   public void remove() {
                       throw new UnsupportedOperationException();
                   }
               };
           }
  
           public int size() {return 0;}
  
           public boolean contains(Object obj) {return false;}
  
           // Preserves singleton property
           private Object readResolve() {
               return EMPTY_SET;
           }
       }
  
       /**
        * The empty list (immutable).  This list is serializable.
        *
        * @see #emptyList()
        */
       public static final List EMPTY_LIST = new EmptyList();
  
       /**
        * Returns the empty list (immutable).  This list is serializable.
        *
        * <p>This example illustrates the type-safe way to obtain an empty list:
        * <pre>
        *     List&lt;String&gt; s = Collections.emptyList();
        * </pre>
        * Implementation note:  Implementations of this method need not
        * getLogger a separate <tt>List</tt> object for each call.   Using this
        * method is likely to have comparable cost to using the like-named
        * field.  (Unlike this method, the field does not provide type safety.)
        *
        * @see #EMPTY_LIST
        * @since 1.5
        */
       public static final <T> List<T> emptyList() {
       return (List<T>) EMPTY_LIST;
       }
  
       /**
        * @serial include
        */
       private static class EmptyList
       extends AbstractList<Object>
       implements RandomAccess, Serializable {
       // use serialVersionUID from JDK 1.2.2 for interoperability
       private static final long serialVersionUID = 8842843931221139166L;
  
           public int size() {return 0;}
  
           public boolean contains(Object obj) {return false;}
  
           public Object get(int index) {
               throw new IndexOutOfBoundsException("Index: "+index);
           }
  
           // Preserves singleton property
           private Object readResolve() {
               return EMPTY_LIST;
           }
       }
  
       /**
        * The empty map (immutable).  This map is serializable.
        *
        * @see #emptyMap()
        * @since 1.3
        */
       public static final Map EMPTY_MAP = new EmptyMap();
  
       /**
        * Returns the empty map (immutable).  This map is serializable.
        *
        * <p>This example illustrates the type-safe way to obtain an empty set:
        * <pre>
        *     Map&lt;String, Date&gt; s = Collections.emptyMap();
        * </pre>
        * Implementation note:  Implementations of this method need not
        * getLogger a separate <tt>Map</tt> object for each call.   Using this
        * method is likely to have comparable cost to using the like-named
        * field.  (Unlike this method, the field does not provide type safety.)
        *
        * @see #EMPTY_MAP
        * @since 1.5
        */
       public static final <K,V> Map<K,V> emptyMap() {
       return (Map<K,V>) EMPTY_MAP;
       }
  
       private static class EmptyMap
       extends AbstractMap<Object,Object>
       implements Serializable {
  
           private static final long serialVersionUID = 6428348081105594320L;
  
           public int size()                          {return 0;}
  
           public boolean isEmpty()                   {return true;}
  
           public boolean containsKey(Object key)     {return false;}
  
           public boolean containsValue(Object value) {return false;}
  
       public Object get(Object key)              {return null;}
  
           public Set<Object> keySet()                {return Collections.<Object>emptySet();}
  
           public Collection<Object> values()         {return Collections.<Object>emptySet();}
  
           public Set<Entry<Object,Object>> entrySet() {
           return Collections.emptySet();
       }
  
           public boolean equals(Object o) {
               return (o instanceof Map) && ((Map)o).size()==0;
           }
  
           public int hashCode()                      {return 0;}
  
           // Preserves singleton property
           private Object readResolve() {
               return EMPTY_MAP;
           }
       }
  
       /**
        * Returns an immutable set containing only the specified object.
        * The returned set is serializable.
        *
        * @param o the sole object to be stored in the returned set.
        * @return an immutable set containing only the specified object.
        */
       public static <T> Set<T> singleton(T o) {
       return new SingletonSet<T>(o);
       }
  
       /**
        * @serial include
        */
       private static class SingletonSet<E>
       extends AbstractSet<E>
       implements Serializable
       {
       // use serialVersionUID from JDK 1.2.2 for interoperability
       private static final long serialVersionUID = 3193687207550431679L;
  
           final private E element;
  
           SingletonSet(E e) {element = e;}
  
           public Iterator<E> iterator() {
               return new Iterator<E>() {
                   private boolean hasNext = true;
                   public boolean hasNext() {
                       return hasNext;
                   }
                   public E next() {
                       if (hasNext) {
                           hasNext = false;
                           return element;
                       }
                       throw new NoSuchElementException();
                   }
                   public void remove() {
                       throw new UnsupportedOperationException();
                   }
               };
           }
  
           public int size() {return 1;}
  
           public boolean contains(Object o) {return eq(o, element);}
       }
  
       /**
        * Returns an immutable list containing only the specified object.
        * The returned list is serializable.
        *
        * @param o the sole object to be stored in the returned list.
        * @return an immutable list containing only the specified object.
        * @since 1.3
        */
       public static <T> List<T> singletonList(T o) {
       return new SingletonList<T>(o);
       }
  
       private static class SingletonList<E>
       extends AbstractList<E>
       implements RandomAccess, Serializable {
  
           static final long serialVersionUID = 3093736618740652951L;
  
           private final E element;
  
           SingletonList(E obj)                {element = obj;}
  
           public int size()                   {return 1;}
  
           public boolean contains(Object obj) {return eq(obj, element);}
  
           public E get(int index) {
               if (index != 0)
                 throw new IndexOutOfBoundsException("Index: "+index+", Size: 1");
               return element;
           }
       }
  
       /**
        * Returns an immutable map, mapping only the specified key to the
        * specified value.  The returned map is serializable.
        *
        * @param key the sole key to be stored in the returned map.
        * @param value the value to which the returned map maps <tt>key</tt>.
        * @return an immutable map containing only the specified key-value
        *         mapping.
        * @since 1.3
        */
       public static <K,V> Map<K,V> singletonMap(K key, V value) {
       return new SingletonMap<K,V>(key, value);
       }
  
       private static class SingletonMap<K,V>
         extends AbstractMap<K,V>
         implements Serializable {
       private static final long serialVersionUID = -6979724477215052911L;
  
           private final K k;
       private final V v;
  
           SingletonMap(K key, V value) {
               k = key;
               v = value;
           }
  
           public int size()                          {return 1;}
  
           public boolean isEmpty()                   {return false;}
  
           public boolean containsKey(Object key)     {return eq(key, k);}
  
           public boolean containsValue(Object value) {return eq(value, v);}
  
           public V get(Object key)                   {return (eq(key, k) ? v : null);}
  
           private transient Set<K> keySet = null;
           private transient Set<Entry<K,V>> entrySet = null;
           private transient Collection<V> values = null;
  
       public Set<K> keySet() {
           if (keySet==null)
           keySet = singleton(k);
           return keySet;
       }
  
       public Set<Entry<K,V>> entrySet() {
           if (entrySet==null)
           entrySet = Collections.<Entry<K,V>>singleton(
                   new SimpleImmutableEntry<K, V>(k, v));
           return entrySet;
       }
  
       public Collection<V> values() {
           if (values==null)
           values = singleton(v);
           return values;
       }
  
       }
  
       /**
        * Returns an immutable list consisting of <tt>n</tt> copies of the
        * specified object.  The newly allocated data object is tiny (it contains
        * a single reference to the data object).  This method is useful in
        * combination with the <tt>List.addAll</tt> method to grow lists.
        * The returned list is serializable.
        *
        * @param  n the number of elements in the returned list.
        * @param  o the element to appear repeatedly in the returned list.
        * @return an immutable list consisting of <tt>n</tt> copies of the
        * 	       specified object.
        * @throws IllegalArgumentException if n &lt; 0.
        * @see    java.util.List#addAll(java.util.Collection)
        * @see    java.util.List#addAll(int, java.util.Collection)
        */
       public static <T> List<T> nCopies(int n, T o) {
       if (n < 0)
           throw new IllegalArgumentException("List length = " + n);
           return new CopiesList<T>(n, o);
       }
  
       /**
        * @serial include
        */
       private static class CopiesList<E>
       extends AbstractList<E>
       implements RandomAccess, Serializable
       {
           static final long serialVersionUID = 2739099268398711800L;
  
           final int n;
           final E element;
  
           CopiesList(int n, E e) {
           assert n >= 0;
               this.n = n;
               element = e;
           }
  
           public int size() {
               return n;
           }
  
           public boolean contains(Object obj) {
               return n != 0 && eq(obj, element);
           }
  
       public int indexOf(Object o) {
           return contains(o) ? 0 : -1;
       }
  
       public int lastIndexOf(Object o) {
           return contains(o) ? n - 1 : -1;
       }
  
           public E get(int index) {
               if (index < 0 || index >= n)
                   throw new IndexOutOfBoundsException("Index: "+index+
                                                       ", Size: "+n);
               return element;
           }
  
       public Object[] toArray() {
           final Object[] a = new Object[n];
           if (element != null)
           Arrays.fill(a, 0, n, element);
           return a;
       }
  
       public <T> T[] toArray(T[] a) {
           final int n = this.n;
           if (a.length < n) {
           a = (T[]) Array
               .newInstance(a.getClass().getComponentType(), n);
           if (element != null)
               Arrays.fill(a, 0, n, element);
           } else {
           Arrays.fill(a, 0, n, element);
           if (a.length > n)
               a[n] = null;
           }
           return a;
       }
  
       public List<E> subList(int fromIndex, int toIndex) {
           if (fromIndex < 0)
           throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
           if (toIndex > n)
           throw new IndexOutOfBoundsException("toIndex = " + toIndex);
           if (fromIndex > toIndex)
           throw new IllegalArgumentException("fromIndex(" + fromIndex +
                              ") > toIndex(" + toIndex + ")");
           return new CopiesList(toIndex - fromIndex, element);
       }
       }
  
       /**
        * Returns a comparator that imposes the reverse of the <i>natural
        * ordering</i> on a collection of objects that implement the
        * <tt>Comparable</tt> interface.  (The natural ordering is the ordering
        * imposed by the objects' own <tt>compareTo</tt> method.)  This enables a
        * simple idiom for sorting (or maintaining) collections (or arrays) of
        * objects that implement the <tt>Comparable</tt> interface in
        * reverse-natural-order.  For example, suppose a is an array of
        * strings. Then: <pre>
        * 		Arrays.sort(a, Collections.reverseOrder());
        * </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p>
        *
        * The returned comparator is serializable.
        *
        * @return a comparator that imposes the reverse of the <i>natural
        * 	       ordering</i> on a collection of objects that implement
        *	       the <tt>Comparable</tt> interface.
        * @see Comparable
        */
       public static <T> Comparator<T> reverseOrder() {
           return (Comparator<T>) REVERSE_ORDER;
       }
  
       private static final Comparator REVERSE_ORDER = new ReverseComparator();
  
       /**
        * @serial include
        */
       private static class ReverseComparator<T>
       implements Comparator<Comparable<Object>>, Serializable {
  
       // use serialVersionUID from JDK 1.2.2 for interoperability
       private static final long serialVersionUID = 7207038068494060240L;
  
           public int compare(Comparable<Object> c1, Comparable<Object> c2) {
               return c2.compareTo(c1);
           }
  
           private Object readResolve() { return reverseOrder(); }
       }
  
       /**
        * Returns a comparator that imposes the reverse ordering of the specified
        * comparator.  If the specified comparator is null, this method is
        * equivalent to {@link #reverseOrder()} (in other words, it returns a
        * comparator that imposes the reverse of the <i>natural ordering</i> on a
        * collection of objects that implement the Comparable interface).
        *
        * <p>The returned comparator is serializable (assuming the specified
        * comparator is also serializable or null).
        *
        * @return a comparator that imposes the reverse ordering of the
        *     specified comparator.
        * @since 1.5
        */
       public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) {
           if (cmp == null)
               return reverseOrder();
  
           return new ReverseComparator2<T>(cmp);
       }
  
       /**
        * @serial include
        */
       private static class ReverseComparator2<T> implements Comparator<T>,
           Serializable
       {
           private static final long serialVersionUID = 4374092139857L;
  
           /**
            * The comparator specified in the static factory.  This will never
            * be null, as the static factory returns a ReverseComparator
            * instance if its argument is null.
            *
            * @serial
            */
           private Comparator<T> cmp;
  
           ReverseComparator2(Comparator<T> cmp) {
               assert cmp != null;
               this.cmp = cmp;
           }
  
           public int compare(T t1, T t2) {
               return cmp.compare(t2, t1);
           }
       }
  
       /**
        * Returns an enumeration over the specified collection.  This provides
        * interoperability with legacy APIs that require an enumeration
        * as input.
        *
        * @param c the collection for which an enumeration is to be returned.
        * @return an enumeration over the specified collection.
        * @see java.util.Enumeration
        */
       public static <T> Enumeration<T> enumeration(final Collection<T> c) {
       return new Enumeration<T>() {
           Iterator<T> i = c.iterator();
  
           public boolean hasMoreElements() {
           return i.hasNext();
           }
  
           public T nextElement() {
           return i.next();
           }
           };
       }
  
       /**
        * Returns an array list containing the elements returned by the
        * specified enumeration in the order they are returned by the
        * enumeration.  This method provides interoperability between
        * legacy APIs that return enumerations and new APIs that require
        * collections.
        *
        * @param e enumeration providing elements for the returned
        *          array list
        * @return an array list containing the elements returned
        *         by the specified enumeration.
        * @since 1.4
        * @see java.util.Enumeration
        * @see java.util.ArrayList
        */
       public static <T> ArrayList<T> list(Enumeration<T> e) {
           ArrayList<T> l = new ArrayList<T>();
           while (e.hasMoreElements())
               l.add(e.nextElement());
           return l;
       }
  
       /**
        * Returns true if the specified arguments are equal, or both null.
        */
       private static boolean eq(Object o1, Object o2) {
           return (o1==null ? o2==null : o1.equals(o2));
       }
  
       /**
        * Returns the number of elements in the specified collection equal to the
        * specified object.  More formally, returns the number of elements
        * <tt>e</tt> in the collection such that
        * <tt>(o == null ? e == null : o.equals(e))</tt>.
        *
        * @param c the collection in which to determine the frequency
        *     of <tt>o</tt>
        * @param o the object whose frequency is to be determined
        * @throws NullPointerException if <tt>c</tt> is null
        * @since 1.5
        */
       public static int frequency(Collection<?> c, Object o) {
           int result = 0;
           if (o == null) {
               for (Object e : c)
                   if (e == null)
                       result++;
           } else {
               for (Object e : c)
                   if (o.equals(e))
                       result++;
           }
           return result;
       }
  
       /**
        * Returns <tt>true</tt> if the two specified collections have no
        * elements in common.
        *
        * <p>Care must be exercised if this method is used on collections that
        * do not comply with the general contract for <tt>Collection</tt>.
        * Implementations may elect to iterate over either collection and test
        * for containment in the other collection (or to perform any equivalent
        * computation).  If either collection uses a nonstandard equality test
        * (as does a {@link java.util.SortedSet} whose ordering is not <i>compatible with
        * equals</i>, or the key set of an {@link java.util.IdentityHashMap}), both
        * collections must use the same nonstandard equality test, or the
        * result of this method is undefined.
        *
        * <p>Note that it is permissible to pass the same collection in both
        * parameters, in which case the method will return true if and only if
        * the collection is empty.
        *
        * @param c1 a collection
        * @param c2 a collection
        * @throws NullPointerException if either collection is null
        * @since 1.5
        */
       public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
           /*
            * We're going to iterate through c1 and test for inclusion in c2.
            * If c1 is a Set and c2 isn't, swap the collections.  Otherwise,
            * place the shorter collection in c1.  Hopefully this heuristic
            * will minimize the cost of the operation.
            */
           if ((c1 instanceof Set) && !(c2 instanceof Set) ||
               (c1.size() > c2.size())) {
               Collection<?> tmp = c1;
               c1 = c2;
               c2 = tmp;
           }
  
           for (Object e : c1)
               if (c2.contains(e))
                   return false;
           return true;
       }
  
       /**
        * Adds all of the specified elements to the specified collection.
        * Elements to be added may be specified individually or as an array.
        * The behavior of this convenience method is identical to that of
        * <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely
        * to run significantly faster under most implementations.
        *
        * <p>When elements are specified individually, this method provides a
        * convenient way to add a few elements to an existing collection:
        * <pre>
        *     Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon");
        * </pre>
        *
        * @param c the collection into which <tt>elements</tt> are to be inserted
        * @param elements the elements to insert into <tt>c</tt>
        * @return <tt>true</tt> if the collection changed as a result of the call
        * @throws UnsupportedOperationException if <tt>c</tt> does not support
        *         the <tt>add</tt> operation
        * @throws NullPointerException if <tt>elements</tt> contains one or more
        *         null values and <tt>c</tt> does not permit null elements, or
        *         if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt>
        * @throws IllegalArgumentException if some property of a value in
        *         <tt>elements</tt> prevents it from being added to <tt>c</tt>
        * @see java.util.Collection#addAll(java.util.Collection)
        * @since 1.5
        */
       public static <T> boolean addAll(Collection<? super T> c, T... elements) {
           boolean result = false;
           for (T element : elements)
               result |= c.add(element);
           return result;
       }
  
       /**
        * Returns a set backed by the specified map.  The resulting set displays
        * the same ordering, concurrency, and performance characteristics as the
        * backing map.  In essence, this factory method provides a {@link java.util.Set}
        * implementation corresponding to any {@link java.util.Map} implementation.  There
        * is no need to use this method on a {@link java.util.Map} implementation that
        * already has a corresponding {@link java.util.Set} implementation (such as {@link
        * java.util.HashMap} or {@link java.util.TreeMap}).
        *
        * <p>Each method invocation on the set returned by this method results in
        * exactly one method invocation on the backing map or its <tt>keySet</tt>
        * create, with one exception.  The <tt>addAll</tt> method is implemented
        * as a sequence of <tt>put</tt> invocations on the backing map.
        *
        * <p>The specified map must be empty at the time this method is invoked,
        * and should not be accessed directly after this method returns.  These
        * conditions are ensured if the map is created empty, passed directly
        * to this method, and no reference to the map is retained, as illustrated
        * in the following code fragment:
        * <pre>
        *    Set&lt;Object&gt; weakHashSet = Collections.newSetFromMap(
        *        new WeakHashMap&lt;Object, Boolean&gt;());
        * </pre>
        *
        * @param map the backing map
        * @return the set backed by the map
        * @throws IllegalArgumentException if <tt>map</tt> is not empty
        * @since 1.6
        */
       public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
           return new SetFromMap<E>(map);
       }
  
       private static class SetFromMap<E> extends AbstractSet<E>
           implements Set<E>, Serializable
       {
           private final Map<E, Boolean> m;  // The backing map
           private transient Set<E> s;       // Its keySet
  
           SetFromMap(Map<E, Boolean> map) {
               if (!map.isEmpty())
                   throw new IllegalArgumentException("Map is non-empty");
               m = map;
               s = map.keySet();
           }
  
           public void clear()               {        m.clear(); }
           public int size()                 { return m.size(); }
           public boolean isEmpty()          { return m.isEmpty(); }
           public boolean contains(Object o) { return m.containsKey(o); }
           public boolean remove(Object o)   { return m.remove(o) != null; }
           public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; }
           public Iterator<E> iterator()     { return s.iterator(); }
           public Object[] toArray()         { return s.toArray(); }
           public <T> T[] toArray(T[] a)     { return s.toArray(a); }
           public String toString()          { return s.toString(); }
           public int hashCode()             { return s.hashCode(); }
           public boolean equals(Object o)   { return o == this || s.equals(o); }
           public boolean containsAll(Collection<?> c) {return s.containsAll(c);}
           public boolean removeAll(Collection<?> c)   {return s.removeAll(c);}
           public boolean retainAll(Collection<?> c)   {return s.retainAll(c);}
       // addAll is the only inherited implementation
  
           private static final long serialVersionUID = 2454657854757543876L;
  
           private void readObject(java.io.ObjectInputStream stream)
               throws IOException, ClassNotFoundException
           {
               stream.defaultReadObject();
               s = m.keySet();
           }
       }
  
       /**
        * Returns a create of a {@link java.util.Deque} as a Last-in-first-out (Lifo)
        * {@link java.util.Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>,
        * <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This
        * create can be useful when you would like to use a method
        * requiring a <tt>Queue</tt> but you need Lifo ordering.
        *
        * <p>Each method invocation on the queue returned by this method
        * results in exactly one method invocation on the backing deque, with
        * one exception.  The {@link java.util.Queue#addAll addAll} method is
        * implemented as a sequence of {@link java.util.Deque#addFirst addFirst}
        * invocations on the backing deque.
        *
        * @param deque the deque
        * @return the queue
        * @since  1.6
        */
       public static <T> Queue<T> asLifoQueue(Deque<T> deque) {
           return new AsLIFOQueue<T>(deque);
       }
  
       static class AsLIFOQueue<E> extends AbstractQueue<E>
           implements Queue<E>, Serializable {
       private static final long serialVersionUID = 1802017725587941708L;
           private final Deque<E> q;
           AsLIFOQueue(Deque<E> q)           { this.q = q; }
           public boolean add(E e)           { q.addFirst(e); return true; }
           public boolean offer(E e)         { return q.offerFirst(e); }
           public E poll()                   { return q.pollFirst(); }
           public E remove()                 { return q.removeFirst(); }
           public E peek()                   { return q.peekFirst(); }
           public E element()                { return q.getFirst(); }
           public void clear()               {        q.clear(); }
           public int size()                 { return q.size(); }
           public boolean isEmpty()          { return q.isEmpty(); }
           public boolean contains(Object o) { return q.contains(o); }
           public boolean remove(Object o)   { return q.remove(o); }
           public Iterator<E> iterator()     { return q.iterator(); }
           public Object[] toArray()         { return q.toArray(); }
           public <T> T[] toArray(T[] a)     { return q.toArray(a); }
           public String toString()          { return q.toString(); }
       public boolean containsAll(Collection<?> c) {return q.containsAll(c);}
       public boolean removeAll(Collection<?> c)   {return q.removeAll(c);}
       public boolean retainAll(Collection<?> c)   {return q.retainAll(c);}
       // We use inherited addAll; forwarding addAll would be wrong
       }
   }
  
  