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/*
 *  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 java.util;

import java.io.*;
import java.lang.reflect.Array;

/**
 * {@code Collections} contains static methods which operate on
 * {@code Collection} classes.
 *
 * @since 1.2
 */
public class Collections {

    private static final Iterator EMPTY_ITERATOR = new Iterator() {
        @Override public boolean hasNext() {
            return false;
        }

        @Override public Object next() {
            throw new NoSuchElementException();
        }

        @Override public void remove() {
            throw new IllegalStateException();
        }
    };

    private static final Enumeration EMPTY_ENUMERATION = new Enumeration() {
        @Override public boolean hasMoreElements() {
            return false;
        }

        @Override public Object nextElement() {
            throw new NoSuchElementException();
        }
    };

    private static final class CopiesList extends AbstractList implements Serializable {
        private final int n;
        private final E element;

        CopiesList(int length, E object) {
            if (length < 0) {
                throw new IllegalArgumentException("length < 0: " + length);
            }
            n = length;
            element = object;
        }

        @Override public boolean contains(Object object) {
            return element == null ? object == null : element.equals(object);
        }

        @Override public int size() {
            return n;
        }

        @Override public E get(int location) {
            if (location >= 0 && location < n) {
                return element;
            }
            throw new IndexOutOfBoundsException();
        }
    }

    @SuppressWarnings("unchecked")
    private static final class EmptyList extends AbstractList implements RandomAccess, Serializable {
        @Override public boolean contains(Object object) {
            return false;
        }

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

        @Override public Object get(int location) {
            throw new IndexOutOfBoundsException();
        }

        private Object readResolve() {
            return Collections.EMPTY_LIST;
        }
    }

    @SuppressWarnings("unchecked")
    private static final class EmptySet extends AbstractSet implements Serializable {
        @Override public boolean contains(Object object) {
            return false;
        }

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

        @Override public Iterator iterator() {
            return EMPTY_ITERATOR;
        }

        private Object readResolve() {
            return Collections.EMPTY_SET;
        }
    }

    @SuppressWarnings("unchecked")
    private static final class EmptyMap extends AbstractMap implements Serializable {
        @Override public boolean containsKey(Object key) {
            return false;
        }

        @Override public boolean containsValue(Object value) {
            return false;
        }

        @Override public Set entrySet() {
            return EMPTY_SET;
        }

        @Override public Object get(Object key) {
            return null;
        }

        @Override public Set keySet() {
            return EMPTY_SET;
        }

        @Override public Collection values() {
            return EMPTY_LIST;
        }

        private Object readResolve() {
            return Collections.EMPTY_MAP;
        }
    }

    /**
     * An empty immutable instance of {@link List}.
     */
    @SuppressWarnings("unchecked")
    public static final List EMPTY_LIST = new EmptyList();

    /**
     * An empty immutable instance of {@link Set}.
     */
    @SuppressWarnings("unchecked")
    public static final Set EMPTY_SET = new EmptySet();

    /**
     * An empty immutable instance of {@link Map}.
     */
    @SuppressWarnings("unchecked")
    public static final Map EMPTY_MAP = new EmptyMap();

    /**
     * This class is a singleton so that equals() and hashCode() work properly.
     */
    private static final class ReverseComparator implements Comparator, Serializable {
        private static final ReverseComparator INSTANCE = new ReverseComparator();

        @SuppressWarnings("unchecked")
        @Override public int compare(T o1, T o2) {
            Comparable c2 = (Comparable) o2;
            return c2.compareTo(o1);
        }

        private Object readResolve() throws ObjectStreamException {
            return INSTANCE;
        }
    }

    private static final class ReverseComparator2 implements Comparator, Serializable {
        private final Comparator cmp;

        ReverseComparator2(Comparator comparator) {
            this.cmp = comparator;
        }

        @Override public int compare(T o1, T o2) {
            return cmp.compare(o2, o1);
        }

        @Override public boolean equals(Object o) {
            return o instanceof ReverseComparator2
                    && ((ReverseComparator2) o).cmp.equals(cmp);
        }

        @Override public int hashCode() {
            return ~cmp.hashCode();
        }
    }

    private static final class SingletonSet extends AbstractSet implements Serializable {
        final E element;

        SingletonSet(E object) {
            element = object;
        }

        @Override public boolean contains(Object object) {
            return element == null ? object == null : element.equals(object);
        }

        @Override public int size() {
            return 1;
        }

        @Override public Iterator iterator() {
            return new Iterator() {
                boolean hasNext = true;

                @Override public boolean hasNext() {
                    return hasNext;
                }

                @Override public E next() {
                    if (hasNext) {
                        hasNext = false;
                        return element;
                    }
                    throw new NoSuchElementException();
                }

                @Override public void remove() {
                    throw new UnsupportedOperationException();
                }
            };
        }
    }

    private static final class SingletonList extends AbstractList implements Serializable {
        final E element;

        SingletonList(E object) {
            element = object;
        }

        @Override public boolean contains(Object object) {
            return element == null ? object == null : element.equals(object);
        }

        @Override public E get(int location) {
            if (location == 0) {
                return element;
            }
            throw new IndexOutOfBoundsException();
        }

        @Override public int size() {
            return 1;
        }
    }

    private static final class SingletonMap extends AbstractMap implements Serializable {
        final K k;
        final V v;

        SingletonMap(K key, V value) {
            k = key;
            v = value;
        }

        @Override public boolean containsKey(Object key) {
            return k == null ? key == null : k.equals(key);
        }

        @Override public boolean containsValue(Object value) {
            return v == null ? value == null : v.equals(value);
        }

        @Override public V get(Object key) {
            if (containsKey(key)) {
                return v;
            }
            return null;
        }

        @Override public int size() {
            return 1;
        }

        @Override public Set> entrySet() {
            return new AbstractSet>() {
                @Override public boolean contains(Object object) {
                    if (object instanceof Entry) {
                        Entry entry = (Entry) object;
                        return containsKey(entry.getKey())
                                && containsValue(entry.getValue());
                    }
                    return false;
                }

                @Override public int size() {
                    return 1;
                }

                @Override public Iterator> iterator() {
                    return new Iterator>() {
                        boolean hasNext = true;

                        @Override public boolean hasNext() {
                            return hasNext;
                        }

                        @Override public Entry next() {
                            if (!hasNext) {
                                throw new NoSuchElementException();
                            }

                            hasNext = false;
                            return new MapEntry(k, v) {
                                @Override public V setValue(V value) {
                                    throw new UnsupportedOperationException();
                                }
                            };
                        }

                        @Override public void remove() {
                            throw new UnsupportedOperationException();
                        }
                    };
                }
            };
        }
    }

    static class SynchronizedCollection implements Collection, Serializable {
        final Collection c;
        final Object mutex;

        SynchronizedCollection(Collection collection) {
            c = collection;
            mutex = this;
        }

        SynchronizedCollection(Collection collection, Object mutex) {
            c = collection;
            this.mutex = mutex;
        }

        @Override public boolean add(E object) {
            synchronized (mutex) {
                return c.add(object);
            }
        }

        @Override public boolean addAll(Collection collection) {
            synchronized (mutex) {
                return c.addAll(collection);
            }
        }

        @Override public void clear() {
            synchronized (mutex) {
                c.clear();
            }
        }

        @Override public boolean contains(Object object) {
            synchronized (mutex) {
                return c.contains(object);
            }
        }

        @Override public boolean containsAll(Collection collection) {
            synchronized (mutex) {
                return c.containsAll(collection);
            }
        }

        @Override public boolean isEmpty() {
            synchronized (mutex) {
                return c.isEmpty();
            }
        }

        @Override public Iterator iterator() {
            synchronized (mutex) {
                return c.iterator();
            }
        }

        @Override public boolean remove(Object object) {
            synchronized (mutex) {
                return c.remove(object);
            }
        }

        @Override public boolean removeAll(Collection collection) {
            synchronized (mutex) {
                return c.removeAll(collection);
            }
        }

        @Override public boolean retainAll(Collection collection) {
            synchronized (mutex) {
                return c.retainAll(collection);
            }
        }

        @Override public int size() {
            synchronized (mutex) {
                return c.size();
            }
        }

        @Override public Object[] toArray() {
            synchronized (mutex) {
                return c.toArray();
            }
        }

        @Override public String toString() {
            synchronized (mutex) {
                return c.toString();
            }
        }

        @Override public  T[] toArray(T[] array) {
            synchronized (mutex) {
                return c.toArray(array);
            }
        }

        private void writeObject(ObjectOutputStream stream) throws IOException {
            synchronized (mutex) {
                stream.defaultWriteObject();
            }
        }
    }

    static class SynchronizedRandomAccessList extends SynchronizedList implements RandomAccess {
        SynchronizedRandomAccessList(List l) {
            super(l);
        }

        SynchronizedRandomAccessList(List l, Object mutex) {
            super(l, mutex);
        }

        @Override public List subList(int start, int end) {
            synchronized (mutex) {
                return new SynchronizedRandomAccessList(list.subList(start, end), mutex);
            }
        }

        /**
         * Replaces this SynchronizedRandomAccessList with a SynchronizedList so
         * that JREs before 1.4 can deserialize this object without any
         * problems. This is necessary since RandomAccess API was introduced
         * only in 1.4.
         * 

         *
         * @return SynchronizedList
         *
         * @see SynchronizedList#readResolve()
         */
        private Object writeReplace() {
            return new SynchronizedList(list);
        }
    }

    static class SynchronizedList extends SynchronizedCollection implements List {
        final List list;

        SynchronizedList(List l) {
            super(l);
            list = l;
        }

        SynchronizedList(List l, Object mutex) {
            super(l, mutex);
            list = l;
        }

        @Override public void add(int location, E object) {
            synchronized (mutex) {
                list.add(location, object);
            }
        }

        @Override public boolean addAll(int location, Collection collection) {
            synchronized (mutex) {
                return list.addAll(location, collection);
            }
        }

        @Override public boolean equals(Object object) {
            synchronized (mutex) {
                return list.equals(object);
            }
        }

        @Override public E get(int location) {
            synchronized (mutex) {
                return list.get(location);
            }
        }

        @Override public int hashCode() {
            synchronized (mutex) {
                return list.hashCode();
            }
        }

        @Override public int indexOf(Object object) {
            final int size;
            final Object[] array;
            synchronized (mutex) {
                size = list.size();
                array = new Object[size];
                list.toArray(array);
            }
            if (object != null) {
                for (int i = 0; i < size; i++) {
                    if (object.equals(array[i])) {
                        return i;
                    }
                }
            } else {
                for (int i = 0; i < size; i++) {
                    if (array[i] == null) {
                        return i;
                    }
                }
            }
            return -1;
        }

        @Override public int lastIndexOf(Object object) {
            final int size;
            final Object[] array;
            synchronized (mutex) {
                size = list.size();
                array = new Object[size];
                list.toArray(array);
            }
            if (object != null) {
                for (int i = size - 1; i >= 0; i--) {
                    if (object.equals(array[i])) {
                        return i;
                    }
                }
            } else {
                for (int i = size - 1; i >= 0; i--) {
                    if (array[i] == null) {
                        return i;
                    }
                }
            }
            return -1;
        }

        @Override public ListIterator listIterator() {
            synchronized (mutex) {
                return list.listIterator();
            }
        }

        @Override public ListIterator listIterator(int location) {
            synchronized (mutex) {
                return list.listIterator(location);
            }
        }

        @Override public E remove(int location) {
            synchronized (mutex) {
                return list.remove(location);
            }
        }

        @Override public E set(int location, E object) {
            synchronized (mutex) {
                return list.set(location, object);
            }
        }

        @Override public List subList(int start, int end) {
            synchronized (mutex) {
                return new SynchronizedList(list.subList(start, end), mutex);
            }
        }

        private void writeObject(ObjectOutputStream stream) throws IOException {
            synchronized (mutex) {
                stream.defaultWriteObject();
            }
        }

        /**
         * Resolves SynchronizedList instances to SynchronizedRandomAccessList
         * instances if the underlying list is a Random Access list.
         * 

         * This is necessary since SynchronizedRandomAccessList instances are
         * replaced with SynchronizedList instances during serialization for
         * compliance with JREs before 1.4.
         * 

         *
         * @return a SynchronizedList instance if the underlying list implements
         *         RandomAccess interface, or this same object if not.
         *
         * @see SynchronizedRandomAccessList#writeReplace()
         */
        private Object readResolve() {
            if (list instanceof RandomAccess) {
                return new SynchronizedRandomAccessList(list, mutex);
            }
            return this;
        }
    }

    static class SynchronizedMap implements Map, Serializable {
        private final Map m;

        final Object mutex;

        SynchronizedMap(Map map) {
            m = map;
            mutex = this;
        }

        SynchronizedMap(Map map, Object mutex) {
            m = map;
            this.mutex = mutex;
        }

        @Override public void clear() {
            synchronized (mutex) {
                m.clear();
            }
        }

        @Override public boolean containsKey(Object key) {
            synchronized (mutex) {
                return m.containsKey(key);
            }
        }

        @Override public boolean containsValue(Object value) {
            synchronized (mutex) {
                return m.containsValue(value);
            }
        }

        @Override public Set> entrySet() {
            synchronized (mutex) {
                return new SynchronizedSet>(m.entrySet(), mutex);
            }
        }

        @Override public boolean equals(Object object) {
            synchronized (mutex) {
                return m.equals(object);
            }
        }

        @Override public V get(Object key) {
            synchronized (mutex) {
                return m.get(key);
            }
        }

        @Override public int hashCode() {
            synchronized (mutex) {
                return m.hashCode();
            }
        }

        @Override public boolean isEmpty() {
            synchronized (mutex) {
                return m.isEmpty();
            }
        }

        @Override public Set keySet() {
            synchronized (mutex) {
                return new SynchronizedSet(m.keySet(), mutex);
            }
        }

        @Override public V put(K key, V value) {
            synchronized (mutex) {
                return m.put(key, value);
            }
        }

        @Override public void putAll(Map map) {
            synchronized (mutex) {
                m.putAll(map);
            }
        }

        @Override public V remove(Object key) {
            synchronized (mutex) {
                return m.remove(key);
            }
        }

        @Override public int size() {
            synchronized (mutex) {
                return m.size();
            }
        }

        @Override public Collection values() {
            synchronized (mutex) {
                return new SynchronizedCollection(m.values(), mutex);
            }
        }

        @Override public String toString() {
            synchronized (mutex) {
                return m.toString();
            }
        }

        private void writeObject(ObjectOutputStream stream) throws IOException {
            synchronized (mutex) {
                stream.defaultWriteObject();
            }
        }
    }

    static class SynchronizedSet extends SynchronizedCollection implements Set {
        SynchronizedSet(Set set) {
            super(set);
        }

        SynchronizedSet(Set set, Object mutex) {
            super(set, mutex);
        }

        @Override public boolean equals(Object object) {
            synchronized (mutex) {
                return c.equals(object);
            }
        }

        @Override public int hashCode() {
            synchronized (mutex) {
                return c.hashCode();
            }
        }

        private void writeObject(ObjectOutputStream stream) throws IOException {
            synchronized (mutex) {
                stream.defaultWriteObject();
            }
        }
    }

    static class SynchronizedSortedMap extends SynchronizedMap implements SortedMap {
        private final SortedMap sm;

        SynchronizedSortedMap(SortedMap map) {
            super(map);
            sm = map;
        }

        SynchronizedSortedMap(SortedMap map, Object mutex) {
            super(map, mutex);
            sm = map;
        }

        @Override public Comparator comparator() {
            synchronized (mutex) {
                return sm.comparator();
            }
        }

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

        @Override public SortedMap headMap(K endKey) {
            synchronized (mutex) {
                return new SynchronizedSortedMap(sm.headMap(endKey),
                        mutex);
            }
        }

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

        @Override public SortedMap subMap(K startKey, K endKey) {
            synchronized (mutex) {
                return new SynchronizedSortedMap(sm.subMap(startKey,
                        endKey), mutex);
            }
        }

        @Override public SortedMap tailMap(K startKey) {
            synchronized (mutex) {
                return new SynchronizedSortedMap(sm.tailMap(startKey),
                        mutex);
            }
        }

        private void writeObject(ObjectOutputStream stream) throws IOException {
            synchronized (mutex) {
                stream.defaultWriteObject();
            }
        }
    }

    static class SynchronizedSortedSet extends SynchronizedSet implements SortedSet {
        private final SortedSet ss;

        SynchronizedSortedSet(SortedSet set) {
            super(set);
            ss = set;
        }

        SynchronizedSortedSet(SortedSet set, Object mutex) {
            super(set, mutex);
            ss = set;
        }

        @Override public Comparator comparator() {
            synchronized (mutex) {
                return ss.comparator();
            }
        }

        @Override public E first() {
            synchronized (mutex) {
                return ss.first();
            }
        }

        @Override public SortedSet headSet(E end) {
            synchronized (mutex) {
                return new SynchronizedSortedSet(ss.headSet(end), mutex);
            }
        }

        @Override public E last() {
            synchronized (mutex) {
                return ss.last();
            }
        }

        @Override public SortedSet subSet(E start, E end) {
            synchronized (mutex) {
                return new SynchronizedSortedSet(ss.subSet(start, end),
                        mutex);
            }
        }

        @Override public SortedSet tailSet(E start) {
            synchronized (mutex) {
                return new SynchronizedSortedSet(ss.tailSet(start), mutex);
            }
        }

        private void writeObject(ObjectOutputStream stream) throws IOException {
            synchronized (mutex) {
                stream.defaultWriteObject();
            }
        }
    }

    private static class UnmodifiableCollection implements Collection, Serializable {
        final Collection c;

        UnmodifiableCollection(Collection collection) {
            c = collection;
        }

        @Override public boolean add(E object) {
            throw new UnsupportedOperationException();
        }

        @Override public boolean addAll(Collection collection) {
            throw new UnsupportedOperationException();
        }

        @Override public void clear() {
            throw new UnsupportedOperationException();
        }

        @Override public boolean contains(Object object) {
            return c.contains(object);
        }

        @Override public boolean containsAll(Collection collection) {
            return c.containsAll(collection);
        }

        @Override public boolean isEmpty() {
            return c.isEmpty();
        }

        @Override public Iterator iterator() {
            return new Iterator() {
                Iterator iterator = c.iterator();

                @Override public boolean hasNext() {
                    return iterator.hasNext();
                }

                @Override public E next() {
                    return iterator.next();
                }

                @Override public void remove() {
                    throw new UnsupportedOperationException();
                }
            };
        }

        @Override public boolean remove(Object object) {
            throw new UnsupportedOperationException();
        }

        @Override public boolean removeAll(Collection collection) {
            throw new UnsupportedOperationException();
        }

        @Override public boolean retainAll(Collection collection) {
            throw new UnsupportedOperationException();
        }

        @Override public int size() {
            return c.size();
        }

        @Override public Object[] toArray() {
            return c.toArray();
        }

        @Override public  T[] toArray(T[] array) {
            return c.toArray(array);
        }

        @Override public String toString() {
            return c.toString();
        }
    }

    private static class UnmodifiableRandomAccessList extends UnmodifiableList implements RandomAccess {
        UnmodifiableRandomAccessList(List l) {
            super(l);
        }

        @Override public List subList(int start, int end) {
            return new UnmodifiableRandomAccessList(list.subList(start, end));
        }

        /**
         * Replaces this UnmodifiableRandomAccessList with an UnmodifiableList
         * so that JREs before 1.4 can deserialize this object without any
         * problems. This is necessary since RandomAccess API was introduced
         * only in 1.4.
         * 

         *
         * @return UnmodifiableList
         *
         * @see UnmodifiableList#readResolve()
         */
        private Object writeReplace() {
            return new UnmodifiableList(list);
        }
    }

    private static class UnmodifiableList extends UnmodifiableCollection implements List {
        final List list;

        UnmodifiableList(List l) {
            super(l);
            list = l;
        }

        @Override public void add(int location, E object) {
            throw new UnsupportedOperationException();
        }

        @Override public boolean addAll(int location, Collection collection) {
            throw new UnsupportedOperationException();
        }

        @Override public boolean equals(Object object) {
            return list.equals(object);
        }

        @Override public E get(int location) {
            return list.get(location);
        }

        @Override public int hashCode() {
            return list.hashCode();
        }

        @Override public int indexOf(Object object) {
            return list.indexOf(object);
        }

        @Override public int lastIndexOf(Object object) {
            return list.lastIndexOf(object);
        }

        @Override public ListIterator listIterator() {
            return listIterator(0);
        }

        @Override public ListIterator listIterator(final int location) {
            return new ListIterator() {
                ListIterator iterator = list.listIterator(location);

                @Override public void add(E object) {
                    throw new UnsupportedOperationException();
                }

                @Override public boolean hasNext() {
                    return iterator.hasNext();
                }

                @Override public boolean hasPrevious() {
                    return iterator.hasPrevious();
                }

                @Override public E next() {
                    return iterator.next();
                }

                @Override public int nextIndex() {
                    return iterator.nextIndex();
                }

                @Override public E previous() {
                    return iterator.previous();
                }

                @Override public int previousIndex() {
                    return iterator.previousIndex();
                }

                @Override public void remove() {
                    throw new UnsupportedOperationException();
                }

                @Override public void set(E object) {
                    throw new UnsupportedOperationException();
                }
            };
        }

        @Override public E remove(int location) {
            throw new UnsupportedOperationException();
        }

        @Override public E set(int location, E object) {
            throw new UnsupportedOperationException();
        }

        @Override public List subList(int start, int end) {
            return new UnmodifiableList(list.subList(start, end));
        }

        /**
         * Resolves UnmodifiableList instances to UnmodifiableRandomAccessList
         * instances if the underlying list is a Random Access list.
         * 

         * This is necessary since UnmodifiableRandomAccessList instances are
         * replaced with UnmodifiableList instances during serialization for
         * compliance with JREs before 1.4.
         * 

         *
         * @return an UnmodifiableList instance if the underlying list
         *         implements RandomAccess interface, or this same object if
         *         not.
         *
         * @see UnmodifiableRandomAccessList#writeReplace()
         */
        private Object readResolve() {
            if (list instanceof RandomAccess) {
                return new UnmodifiableRandomAccessList(list);
            }
            return this;
        }
    }

    private static class UnmodifiableMap implements Map, Serializable {
        private final Map m;

        private static class UnmodifiableEntrySet extends UnmodifiableSet> {
            private static class UnmodifiableMapEntry implements Entry {
                Entry mapEntry;

                UnmodifiableMapEntry(Entry entry) {
                    mapEntry = entry;
                }

                @Override public boolean equals(Object object) {
                    return mapEntry.equals(object);
                }

                @Override public K getKey() {
                    return mapEntry.getKey();
                }

                @Override public V getValue() {
                    return mapEntry.getValue();
                }

                @Override public int hashCode() {
                    return mapEntry.hashCode();
                }

                @Override public V setValue(V object) {
                    throw new UnsupportedOperationException();
                }

                @Override public String toString() {
                    return mapEntry.toString();
                }
            }

            UnmodifiableEntrySet(Set> set) {
                super(set);
            }

            @Override public Iterator> iterator() {
                return new Iterator>() {
                    Iterator> iterator = c.iterator();

                    @Override public boolean hasNext() {
                        return iterator.hasNext();
                    }

                    @Override public Entry next() {
                        return new UnmodifiableMapEntry(iterator.next());
                    }

                    @Override public void remove() {
                        throw new UnsupportedOperationException();
                    }
                };
            }

            @Override public Object[] toArray() {
                int length = c.size();
                Object[] result = new Object[length];
                Iterator it = iterator();
                for (int i = length; --i >= 0;) {
                    result[i] = it.next();
                }
                return result;
            }

            @SuppressWarnings("unchecked")
            @Override public  T[] toArray(T[] contents) {
                int size = c.size(), index = 0;
                Iterator> it = iterator();
                if (size > contents.length) {
                    Class ct = contents.getClass().getComponentType();
                    contents = (T[]) Array.newInstance(ct, size);
                }
                while (index < size) {
                    contents[index++] = (T) it.next();
                }
                if (index < contents.length) {
                    contents[index] = null;
                }
                return contents;
            }
        }

        UnmodifiableMap(Map map) {
            m = map;
        }

        @Override public void clear() {
            throw new UnsupportedOperationException();
        }

        @Override public boolean containsKey(Object key) {
            return m.containsKey(key);
        }

        @Override public boolean containsValue(Object value) {
            return m.containsValue(value);
        }

        @Override public Set> entrySet() {
            return new UnmodifiableEntrySet(m.entrySet());
        }

        @Override public boolean equals(Object object) {
            return m.equals(object);
        }

        @Override public V get(Object key) {
            return m.get(key);
        }

        @Override public int hashCode() {
            return m.hashCode();
        }

        @Override public boolean isEmpty() {
            return m.isEmpty();
        }

        @Override public Set keySet() {
            return new UnmodifiableSet(m.keySet());
        }

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

        @Override public void putAll(Map map) {
            throw new UnsupportedOperationException();
        }

        @Override public V remove(Object key) {
            throw new UnsupportedOperationException();
        }

        @Override public int size() {
            return m.size();
        }

        @Override public Collection values() {
            return new UnmodifiableCollection(m.values());
        }

        @Override public String toString() {
            return m.toString();
        }
    }

    private static class UnmodifiableSet extends UnmodifiableCollection implements Set {
        UnmodifiableSet(Set set) {
            super(set);
        }

        @Override public boolean equals(Object object) {
            return c.equals(object);
        }

        @Override public int hashCode() {
            return c.hashCode();
        }
    }

    private static class UnmodifiableSortedMap extends UnmodifiableMap implements SortedMap {
        private final SortedMap sm;

        UnmodifiableSortedMap(SortedMap map) {
            super(map);
            sm = map;
        }

        @Override public Comparator comparator() {
            return sm.comparator();
        }

        @Override public K firstKey() {
            return sm.firstKey();
        }

        @Override public SortedMap headMap(K before) {
            return new UnmodifiableSortedMap(sm.headMap(before));
        }

        @Override public K lastKey() {
            return sm.lastKey();
        }

        @Override public SortedMap subMap(K start, K end) {
            return new UnmodifiableSortedMap(sm.subMap(start, end));
        }

        @Override public SortedMap tailMap(K after) {
            return new UnmodifiableSortedMap(sm.tailMap(after));
        }
    }

    private static class UnmodifiableSortedSet extends UnmodifiableSet implements SortedSet {
        private final SortedSet ss;

        UnmodifiableSortedSet(SortedSet set) {
            super(set);
            ss = set;
        }

        @Override public Comparator comparator() {
            return ss.comparator();
        }

        @Override public E first() {
            return ss.first();
        }

        @Override public SortedSet headSet(E before) {
            return new UnmodifiableSortedSet(ss.headSet(before));
        }

        @Override public E last() {
            return ss.last();
        }

        @Override public SortedSet subSet(E start, E end) {
            return new UnmodifiableSortedSet(ss.subSet(start, end));
        }

        @Override public SortedSet tailSet(E after) {
            return new UnmodifiableSortedSet(ss.tailSet(after));
        }
    }

    private Collections() {}

    /**
     * Performs a binary search for the specified element in the specified
     * sorted list. The list needs to be already sorted in natural sorting
     * order. Searching in an unsorted array has an undefined result. It's also
     * undefined which element is found if there are multiple occurrences of the
     * same element.
     *
     * @param list
     *            the sorted list to search.
     * @param object
     *            the element to find.
     * @return the non-negative index of the element, or a negative index which
     *         is the {@code -index - 1} where the element would be inserted
     * @throws ClassCastException
     *             if an element in the List or the search element does not
     *             implement Comparable, or cannot be compared to each other.
     */
    @SuppressWarnings("unchecked")
    public static  int binarySearch(List> list, T object) {
        if (list == null) {
            throw new NullPointerException("list == null");
        }
        if (list.isEmpty()) {
            return -1;
        }


        if (!(list instanceof RandomAccess)) {
            ListIterator> it = list.listIterator();
            while (it.hasNext()) {
                int result;
                if ((result = -it.next().compareTo(object)) <= 0) {
                    if (result == 0) {
                        return it.previousIndex();
                    }
                    return -it.previousIndex() - 1;
                }
            }
            return -list.size() - 1;
        }

        int low = 0, mid = list.size(), high = mid - 1, result = -1;
        while (low <= high) {
            mid = (low + high) >>> 1;
            if ((result = -list.get(mid).compareTo(object)) > 0) {
                low = mid + 1;
            } else if (result == 0) {
                return mid;
            } else {
                high = mid - 1;
            }
        }
        return -mid - (result < 0 ? 1 : 2);
    }

    /**
     * Performs a binary search for the specified element in the specified
     * sorted list using the specified comparator. The list needs to be already
     * sorted according to the comparator passed. Searching in an unsorted array
     * has an undefined result. It's also undefined which element is found if
     * there are multiple occurrences of the same element.
     *
     * @param list
     *            the sorted List to search.
     * @param object
     *            the element to find.
     * @param comparator
     *            the comparator. If the comparator is {@code null} then the
     *            search uses the objects' natural ordering.
     * @return the non-negative index of the element, or a negative index which
     *         is the {@code -index - 1} where the element would be inserted.
     * @throws ClassCastException
     *             when an element in the list and the searched element cannot
     *             be compared to each other using the comparator.
     */
    @SuppressWarnings("unchecked")
    public static  int binarySearch(List list, T object,
            Comparator comparator) {
        if (comparator == null) {
            return Collections.binarySearch(
                    (List>) list, object);
        }
        if (!(list instanceof RandomAccess)) {
            ListIterator it = list.listIterator();
            while (it.hasNext()) {
                int result;
                if ((result = -comparator.compare(it.next(), object)) <= 0) {
                    if (result == 0) {
                        return it.previousIndex();
                    }
                    return -it.previousIndex() - 1;
                }
            }
            return -list.size() - 1;
        }

        int low = 0, mid = list.size(), high = mid - 1, result = -1;
        while (low <= high) {
            mid = (low + high) >>> 1;
            if ((result = -comparator.compare(list.get(mid), object)) > 0) {
                low = mid + 1;
            } else if (result == 0) {
                return mid;
            } else {
                high = mid - 1;
            }
        }
        return -mid - (result < 0 ? 1 : 2);
    }

    /**
     * Copies the elements from the source list to the destination list. At the
     * end both lists will have the same objects at the same index. If the
     * destination array is larger than the source list, the elements in the
     * destination list with {@code index >= source.size()} will be unchanged.
     *
     * @param destination
     *            the list whose elements are set from the source list.
     * @param source
     *            the list with the elements to be copied into the destination.
     * @throws IndexOutOfBoundsException
     *             when the destination list is smaller than the source list.
     * @throws UnsupportedOperationException
     *             when replacing an element in the destination list is not
     *             supported.
     */
    public static  void copy(List destination, List source) {
        if (destination.size() < source.size()) {
            throw new IndexOutOfBoundsException("destination.size() < source.size(): " +
                    destination.size() + " < " + source.size());
        }
        Iterator srcIt = source.iterator();
        ListIterator destIt = destination.listIterator();
        while (srcIt.hasNext()) {
            try {
                destIt.next();
            } catch (NoSuchElementException e) {
                // TODO: AssertionError?
                throw new IndexOutOfBoundsException("Source size " + source.size() +
                        " does not fit into destination");
            }
            destIt.set(srcIt.next());
        }
    }

    /**
     * Returns an {@code Enumeration} on the specified collection.
     *
     * @param collection
     *            the collection to enumerate.
     * @return an Enumeration.
     */
    public static  Enumeration enumeration(Collection collection) {
        final Collection c = collection;
        return new Enumeration() {
            Iterator it = c.iterator();

            @Override public boolean hasMoreElements() {
                return it.hasNext();
            }

            @Override public T nextElement() {
                return it.next();
            }
        };
    }

    /**
     * Fills the specified list with the specified element.
     *
     * @param list
     *            the list to fill.
     * @param object
     *            the element to fill the list with.
     * @throws UnsupportedOperationException
     *             when replacing an element in the List is not supported.
     */
    public static  void fill(List list, T object) {
        ListIterator it = list.listIterator();
        while (it.hasNext()) {
            it.next();
            it.set(object);
        }
    }

    /**
     * Searches the specified collection for the maximum element.
     *
     * @param collection
     *            the collection to search.
     * @return the maximum element in the Collection.
     * @throws ClassCastException
     *             when an element in the collection does not implement
     *             {@code Comparable} or elements cannot be compared to each
     *             other.
     */
    public static > T max(
            Collection collection) {
        Iterator it = collection.iterator();
        T max = it.next();
        while (it.hasNext()) {
            T next = it.next();
            if (max.compareTo(next) < 0) {
                max = next;
            }
        }
        return max;
    }

    /**
     * Searches the specified collection for the maximum element using the
     * specified comparator.
     *
     * @param collection
     *            the collection to search.
     * @param comparator
     *            the comparator.
     * @return the maximum element in the Collection.
     * @throws ClassCastException
     *             when elements in the collection cannot be compared to each
     *             other using the {@code Comparator}.
     */
    public static  T max(Collection collection,
            Comparator comparator) {
        if (comparator == null) {
            @SuppressWarnings("unchecked") // null comparator? T is comparable
            T result = (T) max((Collection) collection);
            return result;
        }

        Iterator it = collection.iterator();
        T max = it.next();
        while (it.hasNext()) {
            T next = it.next();
            if (comparator.compare(max, next) < 0) {
                max = next;
            }
        }
        return max;
    }

    /**
     * Searches the specified collection for the minimum element.
     *
     * @param collection
     *            the collection to search.
     * @return the minimum element in the collection.
     * @throws ClassCastException
     *             when an element in the collection does not implement
     *             {@code Comparable} or elements cannot be compared to each
     *             other.
     */
    public static > T min(
            Collection collection) {
        Iterator it = collection.iterator();
        T min = it.next();
        while (it.hasNext()) {
            T next = it.next();
            if (min.compareTo(next) > 0) {
                min = next;
            }
        }
        return min;
    }

    /**
     * Searches the specified collection for the minimum element using the
     * specified comparator.
     *
     * @param collection
     *            the collection to search.
     * @param comparator
     *            the comparator.
     * @return the minimum element in the collection.
     * @throws ClassCastException
     *             when elements in the collection cannot be compared to each
     *             other using the {@code Comparator}.
     */
    public static  T min(Collection collection,
            Comparator comparator) {
        if (comparator == null) {
            @SuppressWarnings("unchecked") // null comparator? T is comparable
            T result = (T) min((Collection) collection);
            return result;
        }

        Iterator it = collection.iterator();
        T min = it.next();
        while (it.hasNext()) {
            T next = it.next();
            if (comparator.compare(min, next) > 0) {
                min = next;
            }
        }
        return min;
    }

    /**
     * Returns a list containing the specified number of the specified element.
     * The list cannot be modified. The list is serializable.
     *
     * @param length
     *            the size of the returned list.
     * @param object
     *            the element to be added {@code length} times to a list.
     * @return a list containing {@code length} copies of the element.
     * @throws IllegalArgumentException
     *             when {@code length < 0}.
     */
    public static  List nCopies(final int length, T object) {
        return new CopiesList(length, object);
    }

    /**
     * Modifies the specified {@code List} by reversing the order of the
     * elements.
     *
     * @param list
     *            the list to reverse.
     * @throws UnsupportedOperationException
     *             when replacing an element in the List is not supported.
     */
    @SuppressWarnings("unchecked")
    public static void reverse(List list) {
        int size = list.size();
        ListIterator front = (ListIterator) list.listIterator();
        ListIterator back = (ListIterator) list.listIterator(size);
        for (int i = 0; i < size / 2; i++) {
            Object frontNext = front.next();
            Object backPrev = back.previous();
            front.set(backPrev);
            back.set(frontNext);
        }
    }

    /**
     * A comparator which reverses the natural order of the elements. The
     * {@code Comparator} that's returned is {@link Serializable}.
     *
     * @return a {@code Comparator} instance.
     */
    @SuppressWarnings("unchecked")
    public static  Comparator reverseOrder() {
        return (Comparator) ReverseComparator.INSTANCE;
    }

    /**
     * Returns a {@link Comparator} that reverses the order of the
     * {@code Comparator} passed. If the {@code Comparator} passed is
     * {@code null}, then this method is equivalent to {@link #reverseOrder()}.
     * 

     * The {@code Comparator} that's returned is {@link Serializable} if the
     * {@code Comparator} passed is serializable or {@code null}.
     *
     * @param c
     *            the {@code Comparator} to reverse or {@code null}.
     * @return a {@code Comparator} instance.
     * @since 1.5
     */
    public static  Comparator reverseOrder(Comparator c) {
        if (c == null) {
            return reverseOrder();
        }
        if (c instanceof ReverseComparator2) {
            return ((ReverseComparator2) c).cmp;
        }
        return new ReverseComparator2(c);
    }

    /**
     * Moves every element of the list to a random new position in the list.
     *
     * @param list
     *            the List to shuffle.
     *
     * @throws UnsupportedOperationException
     *             when replacing an element in the List is not supported.
     */
    public static void shuffle(List list) {
        shuffle(list, new Random());
    }

    /**
     * Moves every element of the list to a random new position in the list
     * using the specified random number generator.
     *
     * @param list
     *            the list to shuffle.
     * @param random
     *            the random number generator.
     * @throws UnsupportedOperationException
     *             when replacing an element in the list is not supported.
     */
    public static void shuffle(List list, Random random) {
        @SuppressWarnings("unchecked") // we won't put foreign objects in
        final List objectList = (List) list;

        if (list instanceof RandomAccess) {
            for (int i = objectList.size() - 1; i > 0; i--) {
                int index = random.nextInt(i + 1);
                objectList.set(index, objectList.set(i, objectList.get(index)));
            }
        } else {
            Object[] array = objectList.toArray();
            for (int i = array.length - 1; i > 0; i--) {
                int index = random.nextInt(i + 1);
                Object temp = array[i];
                array[i] = array[index];
                array[index] = temp;
            }

            int i = 0;
            ListIterator it = objectList.listIterator();
            while (it.hasNext()) {
                it.next();
                it.set(array[i++]);
            }
        }
    }

    /**
     * Returns a set containing the specified element. The set cannot be
     * modified. The set is serializable.
     *
     * @param object
     *            the element.
     * @return a set containing the element.
     */
    public static  Set singleton(E object) {
        return new SingletonSet(object);
    }

    /**
     * Returns a list containing the specified element. The list cannot be
     * modified. The list is serializable.
     *
     * @param object
     *            the element.
     * @return a list containing the element.
     */
    public static  List singletonList(E object) {
        return new SingletonList(object);
    }

    /**
     * Returns a Map containing the specified key and value. The map cannot be
     * modified. The map is serializable.
     *
     * @param key
     *            the key.
     * @param value
     *            the value.
     * @return a Map containing the key and value.
     */
    public static  Map singletonMap(K key, V value) {
        return new SingletonMap(key, value);
    }

    /**
     * Sorts the given list in ascending natural order. The algorithm is
     * stable which means equal elements don't get reordered.
     *
     * @throws ClassCastException if any element does not implement {@code Comparable},
     *     or if {@code compareTo} throws for any pair of elements.
     */
    @SuppressWarnings("unchecked")
    public static > void sort(List list) {
        Object[] array = list.toArray();
        Arrays.sort(array);
        int i = 0;
        ListIterator it = list.listIterator();
        while (it.hasNext()) {
            it.next();
            it.set((T) array[i++]);
        }
    }

    /**
     * Sorts the given list using the given comparator. The algorithm is
     * stable which means equal elements don't get reordered.
     *
     * @throws ClassCastException if any element does not implement {@code Comparable},
     *     or if {@code compareTo} throws for any pair of elements.
     */
    @SuppressWarnings("unchecked")
    public static  void sort(List list, Comparator comparator) {
        T[] array = list.toArray((T[]) new Object[list.size()]);
        Arrays.sort(array, comparator);
        int i = 0;
        ListIterator it = list.listIterator();
        while (it.hasNext()) {
            it.next();
            it.set(array[i++]);
        }
    }

    /**
     * Swaps the elements of list {@code list} at indices {@code index1} and
     * {@code index2}.
     *
     * @param list
     *            the list to manipulate.
     * @param index1
     *            position of the first element to swap with the element in
     *            index2.
     * @param index2
     *            position of the other element.
     *
     * @throws IndexOutOfBoundsException
     *             if index1 or index2 is out of range of this list.
     * @since 1.4
     */
    @SuppressWarnings("unchecked")
    public static void swap(List list, int index1, int index2) {
        if (list == null) {
            throw new NullPointerException("list == null");
        }
        final int size = list.size();
        if (index1 < 0 || index1 >= size || index2 < 0 || index2 >= size) {
            throw new IndexOutOfBoundsException();
        }
        if (index1 == index2) {
            return;
        }
        List rawList = (List) list;
        rawList.set(index2, rawList.set(index1, rawList.get(index2)));
    }

    /**
     * Replaces all occurrences of Object {@code obj} in {@code list} with
     * {@code newObj}. If the {@code obj} is {@code null}, then all
     * occurrences of {@code null} are replaced with {@code newObj}.
     *
     * @param list
     *            the list to modify.
     * @param obj
     *            the object to find and replace occurrences of.
     * @param obj2
     *            the object to replace all occurrences of {@code obj} in
     *            {@code list}.
     * @return true, if at least one occurrence of {@code obj} has been found in
     *         {@code list}.
     * @throws UnsupportedOperationException
     *             if the list does not support setting elements.
     */
    public static  boolean replaceAll(List list, T obj, T obj2) {
        int index;
        boolean found = false;

        while ((index = list.indexOf(obj)) > -1) {
            found = true;
            list.set(index, obj2);
        }
        return found;
    }

    /**
     * Rotates the elements in {@code list} by the distance {@code dist}
     * 

     * e.g. for a given list with elements [1, 2, 3, 4, 5, 6, 7, 8, 9, 0],
     * calling rotate(list, 3) or rotate(list, -7) would modify the list to look
     * like this: [8, 9, 0, 1, 2, 3, 4, 5, 6, 7]
     *
     * @param lst
     *            the list whose elements are to be rotated.
     * @param dist
     *            is the distance the list is rotated. This can be any valid
     *            integer. Negative values rotate the list backwards.
     */
    @SuppressWarnings("unchecked")
    public static void rotate(List lst, int dist) {
        List list = (List) lst;
        int size = list.size();

        // Can't sensibly rotate an empty collection
        if (size == 0) {
            return;
        }

        // normalize the distance
        int normdist;
        if (dist > 0) {
            normdist = dist % size;
        } else {
            normdist = size - ((dist % size) * (-1));
        }

        if (normdist == 0 || normdist == size) {
            return;
        }

        if (list instanceof RandomAccess) {
            // make sure each element gets juggled
            // with the element in the position it is supposed to go to
            Object temp = list.get(0);
            int index = 0, beginIndex = 0;
            for (int i = 0; i < size; i++) {
                index = (index + normdist) % size;
                temp = list.set(index, temp);
                if (index == beginIndex) {
                    index = ++beginIndex;
                    temp = list.get(beginIndex);
                }
            }
        } else {
            int divideIndex = (size - normdist) % size;
            List sublist1 = list.subList(0, divideIndex);
            List sublist2 = list.subList(divideIndex, size);
            reverse(sublist1);
            reverse(sublist2);
            reverse(list);
        }
    }

    /**
     * Searches the {@code list} for {@code sublist} and returns the beginning
     * index of the first occurrence.
     * 

     * -1 is returned if the {@code sublist} does not exist in {@code list}.
     *
     * @param list
     *            the List to search {@code sublist} in.
     * @param sublist
     *            the List to search in {@code list}.
     * @return the beginning index of the first occurrence of {@code sublist} in
     *         {@code list}, or -1.
     */
    public static int indexOfSubList(List list, List sublist) {
        int size = list.size();
        int sublistSize = sublist.size();

        if (sublistSize > size) {
            return -1;
        }

        if (sublistSize == 0) {
            return 0;
        }

        // find the first element of sublist in the list to get a head start
        Object firstObj = sublist.get(0);
        int index = list.indexOf(firstObj);
        if (index == -1) {
            return -1;
        }

        while (index < size && (size - index >= sublistSize)) {
            ListIterator listIt = list.listIterator(index);

            if ((firstObj == null) ? listIt.next() == null : firstObj
                    .equals(listIt.next())) {

                // iterate through the elements in sublist to see
                // if they are included in the same order in the list
                ListIterator sublistIt = sublist.listIterator(1);
                boolean difFound = false;
                while (sublistIt.hasNext()) {
                    Object element = sublistIt.next();
                    if (!listIt.hasNext()) {
                        return -1;
                    }
                    if ((element == null) ? listIt.next() != null : !element
                            .equals(listIt.next())) {
                        difFound = true;
                        break;
                    }
                }
                // All elements of sublist are found in main list
                // starting from index.
                if (!difFound) {
                    return index;
                }
            }
            // This was not the sequence we were looking for,
            // continue search for the firstObj in main list
            // at the position after index.
            index++;
        }
        return -1;
    }

    /**
     * Searches the {@code list} for {@code sublist} and returns the beginning
     * index of the last occurrence.
     * 

     * -1 is returned if the {@code sublist} does not exist in {@code list}.
     *
     * @param list
     *            the list to search {@code sublist} in.
     * @param sublist
     *            the list to search in {@code list}.
     * @return the beginning index of the last occurrence of {@code sublist} in
     *         {@code list}, or -1.
     */
    public static int lastIndexOfSubList(List list, List sublist) {
        int sublistSize = sublist.size();
        int size = list.size();

        if (sublistSize > size) {
            return -1;
        }

        if (sublistSize == 0) {
            return size;
        }

        // find the last element of sublist in the list to get a head start
        Object lastObj = sublist.get(sublistSize - 1);
        int index = list.lastIndexOf(lastObj);

        while ((index > -1) && (index + 1 >= sublistSize)) {
            ListIterator listIt = list.listIterator(index + 1);

            if ((lastObj == null) ? listIt.previous() == null : lastObj
                    .equals(listIt.previous())) {
                // iterate through the elements in sublist to see
                // if they are included in the same order in the list
                ListIterator sublistIt = sublist
                        .listIterator(sublistSize - 1);
                boolean difFound = false;
                while (sublistIt.hasPrevious()) {
                    Object element = sublistIt.previous();
                    if (!listIt.hasPrevious()) {
                        return -1;
                    }
                    if ((element == null) ? listIt.previous() != null
                            : !element.equals(listIt.previous())) {
                        difFound = true;
                        break;
                    }
                }
                // All elements of sublist are found in main list
                // starting from listIt.nextIndex().
                if (!difFound) {
                    return listIt.nextIndex();
                }
            }
            // This was not the sequence we were looking for,
            // continue search for the lastObj in main list
            // at the position before index.
            index--;
        }
        return -1;
    }

    /**
     * Returns an {@code ArrayList} with all the elements in the {@code
     * enumeration}. The elements in the returned {@code ArrayList} are in the
     * same order as in the {@code enumeration}.
     *
     * @param enumeration
     *            the source {@link Enumeration}.
     * @return an {@code ArrayList} from {@code enumeration}.
     */
    public static  ArrayList list(Enumeration enumeration) {
        ArrayList list = new ArrayList();
        while (enumeration.hasMoreElements()) {
            list.add(enumeration.nextElement());
        }
        return list;
    }

    /**
     * Returns a wrapper on the specified collection which synchronizes all
     * access to the collection.
     *
     * @param collection
     *            the Collection to wrap in a synchronized collection.
     * @return a synchronized Collection.
     */
    public static  Collection synchronizedCollection(
            Collection collection) {
        if (collection == null) {
            throw new NullPointerException("collection == null");
        }
        return new SynchronizedCollection(collection);
    }

    /**
     * Returns a wrapper on the specified List which synchronizes all access to
     * the List.
     *
     * @param list
     *            the List to wrap in a synchronized list.
     * @return a synchronized List.
     */
    public static  List synchronizedList(List list) {
        if (list == null) {
            throw new NullPointerException("list == null");
        }
        if (list instanceof RandomAccess) {
            return new SynchronizedRandomAccessList(list);
        }
        return new SynchronizedList(list);
    }

    /**
     * Returns a wrapper on the specified map which synchronizes all access to
     * the map.
     *
     * @param map
     *            the map to wrap in a synchronized map.
     * @return a synchronized Map.
     */
    public static  Map synchronizedMap(Map map) {
        if (map == null) {
            throw new NullPointerException("map == null");
        }
        return new SynchronizedMap(map);
    }

    /**
     * Returns a wrapper on the specified set which synchronizes all access to
     * the set.
     *
     * @param set
     *            the set to wrap in a synchronized set.
     * @return a synchronized set.
     */
    public static  Set synchronizedSet(Set set) {
        if (set == null) {
            throw new NullPointerException("set == null");
        }
        return new SynchronizedSet(set);
    }

    /**
     * Returns a wrapper on the specified sorted map which synchronizes all
     * access to the sorted map.
     *
     * @param map
     *            the sorted map to wrap in a synchronized sorted map.
     * @return a synchronized sorted map.
     */
    public static  SortedMap synchronizedSortedMap(
            SortedMap map) {
        if (map == null) {
            throw new NullPointerException("map == null");
        }
        return new SynchronizedSortedMap(map);
    }

    /**
     * Returns a wrapper on the specified sorted set which synchronizes all
     * access to the sorted set.
     *
     * @param set
     *            the sorted set to wrap in a synchronized sorted set.
     * @return a synchronized sorted set.
     */
    public static  SortedSet synchronizedSortedSet(SortedSet set) {
        if (set == null) {
            throw new NullPointerException("set == null");
        }
        return new SynchronizedSortedSet(set);
    }

    /**
     * Returns a wrapper on the specified collection which throws an
     * {@code UnsupportedOperationException} whenever an attempt is made to
     * modify the collection.
     *
     * @param collection
     *            the collection to wrap in an unmodifiable collection.
     * @return an unmodifiable collection.
     */
    @SuppressWarnings("unchecked")
    public static  Collection unmodifiableCollection(
            Collection collection) {
        if (collection == null) {
            throw new NullPointerException("collection == null");
        }
        return new UnmodifiableCollection((Collection) collection);
    }

    /**
     * Returns a wrapper on the specified list which throws an
     * {@code UnsupportedOperationException} whenever an attempt is made to
     * modify the list.
     *
     * @param list
     *            the list to wrap in an unmodifiable list.
     * @return an unmodifiable List.
     */
    @SuppressWarnings("unchecked")
    public static  List unmodifiableList(List list) {
        if (list == null) {
            throw new NullPointerException("list == null");
        }
        if (list instanceof RandomAccess) {
            return new UnmodifiableRandomAccessList((List) list);
        }
        return new UnmodifiableList((List) list);
    }

    /**
     * Returns a wrapper on the specified map which throws an
     * {@code UnsupportedOperationException} whenever an attempt is made to
     * modify the map.
     *
     * @param map
     *            the map to wrap in an unmodifiable map.
     * @return a unmodifiable map.
     */
    @SuppressWarnings("unchecked")
    public static  Map unmodifiableMap(
            Map map) {
        if (map == null) {
            throw new NullPointerException("map == null");
        }
        return new UnmodifiableMap((Map) map);
    }

    /**
     * Returns a wrapper on the specified set which throws an
     * {@code UnsupportedOperationException} whenever an attempt is made to
     * modify the set.
     *
     * @param set
     *            the set to wrap in an unmodifiable set.
     * @return a unmodifiable set
     */
    @SuppressWarnings("unchecked")
    public static  Set unmodifiableSet(Set set) {
        if (set == null) {
            throw new NullPointerException("set == null");
        }
        return new UnmodifiableSet((Set) set);
    }

    /**
     * Returns a wrapper on the specified sorted map which throws an
     * {@code UnsupportedOperationException} whenever an attempt is made to
     * modify the sorted map.
     *
     * @param map
     *            the sorted map to wrap in an unmodifiable sorted map.
     * @return a unmodifiable sorted map
     */
    @SuppressWarnings("unchecked")
    public static  SortedMap unmodifiableSortedMap(
            SortedMap map) {
        if (map == null) {
            throw new NullPointerException("map == null");
        }
        return new UnmodifiableSortedMap((SortedMap) map);
    }

    /**
     * Returns a wrapper on the specified sorted set which throws an
     * {@code UnsupportedOperationException} whenever an attempt is made to
     * modify the sorted set.
     *
     * @param set
     *            the sorted set to wrap in an unmodifiable sorted set.
     * @return a unmodifiable sorted set.
     */
    public static  SortedSet unmodifiableSortedSet(SortedSet set) {
        if (set == null) {
            throw new NullPointerException("set == null");
        }
        return new UnmodifiableSortedSet(set);
    }

    /**
     * Returns the number of elements in the {@code Collection} that match the
     * {@code Object} passed. If the {@code Object} is {@code null}, then the
     * number of {@code null} elements is returned.
     *
     * @param c
     *            the {@code Collection} to search.
     * @param o
     *            the {@code Object} to search for.
     * @return the number of matching elements.
     * @throws NullPointerException
     *             if the {@code Collection} parameter is {@code null}.
     * @since 1.5
     */
    public static int frequency(Collection c, Object o) {
        if (c == null) {
            throw new NullPointerException("c == null");
        }
        if (c.isEmpty()) {
            return 0;
        }
        int result = 0;
        Iterator itr = c.iterator();
        while (itr.hasNext()) {
            Object e = itr.next();
            if (o == null ? e == null : o.equals(e)) {
                result++;
            }
        }
        return result;
    }

    /**
     * Returns a type-safe empty, immutable {@link List}.
     *
     * @return an empty {@link List}.
     * @since 1.5
     * @see #EMPTY_LIST
     */
    @SuppressWarnings("unchecked")
    public static final  List emptyList() {
        return EMPTY_LIST;
    }

    /**
     * Returns a type-safe empty, immutable {@link Set}.
     *
     * @return an empty {@link Set}.
     * @since 1.5
     * @see #EMPTY_SET
     */
    @SuppressWarnings("unchecked")
    public static final  Set emptySet() {
        return EMPTY_SET;
    }

    /**
     * Returns a type-safe empty, immutable {@link Map}.
     *
     * @return an empty {@link Map}.
     * @since 1.5
     * @see #EMPTY_MAP
     */
    @SuppressWarnings("unchecked")
    public static final  Map emptyMap() {
        return EMPTY_MAP;
    }

    /**
     * Returns an enumeration containing no elements.
     * @since 1.7
     */
    @SuppressWarnings("unchecked")
    public static  Enumeration emptyEnumeration() {
        return (Enumeration) EMPTY_ENUMERATION;
    }

    /**
     * Returns an iterator containing no elements.
     * @since 1.7
     */
    @SuppressWarnings("unchecked")
    public static  Iterator emptyIterator() {
        return (Iterator) EMPTY_ITERATOR;
    }

    /**
     * Returns a list iterator containing no elements.
     * @since 1.7
     */
    public static  ListIterator emptyListIterator() {
        return Collections.emptyList().listIterator();
    }

    /**
     * Returns a dynamically typesafe view of the specified collection. Trying
     * to insert an element of the wrong type into this collection throws a
     * {@code ClassCastException}. At creation time the types in {@code c} are
     * not checked for correct type.
     *
     * @param c
     *            the collection to be wrapped in a typesafe collection.
     * @param type
     *            the type of the elements permitted to insert.
     * @return a typesafe collection.
     */
    public static  Collection checkedCollection(Collection c,
            Class type) {
        return new CheckedCollection(c, type);
    }

    /**
     * Returns a dynamically typesafe view of the specified map. Trying to
     * insert an element of the wrong type into this map throws a
     * {@code ClassCastException}. At creation time the types in {@code m} are
     * not checked for correct type.
     *
     * @param m
     *            the map to be wrapped in a typesafe map.
     * @param keyType
     *            the type of the keys permitted to insert.
     * @param valueType
     *            the type of the values permitted to insert.
     * @return a typesafe map.
     */
    public static  Map checkedMap(Map m, Class keyType,
            Class valueType) {
        return new CheckedMap(m, keyType, valueType);
    }

    /**
     * Returns a dynamically typesafe view of the specified list. Trying to
     * insert an element of the wrong type into this list throws a
     * {@code ClassCastException}. At creation time the types in {@code list}
     * are not checked for correct type.
     *
     * @param list
     *            the list to be wrapped in a typesafe list.
     * @param type
     *            the type of the elements permitted to insert.
     * @return a typesafe list.
     */
    public static  List checkedList(List list, Class type) {
        if (list instanceof RandomAccess) {
            return new CheckedRandomAccessList(list, type);
        }
        return new CheckedList(list, type);
    }

    /**
     * Returns a dynamically typesafe view of the specified set. Trying to
     * insert an element of the wrong type into this set throws a
     * {@code ClassCastException}. At creation time the types in {@code s} are
     * not checked for correct type.
     *
     * @param s
     *            the set to be wrapped in a typesafe set.
     * @param type
     *            the type of the elements permitted to insert.
     * @return a typesafe set.
     */
    public static  Set checkedSet(Set s, Class type) {
        return new CheckedSet(s, type);
    }

    /**
     * Returns a dynamically typesafe view of the specified sorted map. Trying
     * to insert an element of the wrong type into this sorted map throws a
     * {@code ClassCastException}. At creation time the types in {@code m} are
     * not checked for correct type.
     *
     * @param m
     *            the sorted map to be wrapped in a typesafe sorted map.
     * @param keyType
     *            the type of the keys permitted to insert.
     * @param valueType
     *            the type of the values permitted to insert.
     * @return a typesafe sorted map.
     */
    public static  SortedMap checkedSortedMap(SortedMap m,
            Class keyType, Class valueType) {
        return new CheckedSortedMap(m, keyType, valueType);
    }

    /**
     * Returns a dynamically typesafe view of the specified sorted set. Trying
     * to insert an element of the wrong type into this sorted set throws a
     * {@code ClassCastException}. At creation time the types in {@code s} are
     * not checked for correct type.
     *
     * @param s
     *            the sorted set to be wrapped in a typesafe sorted set.
     * @param type
     *            the type of the elements permitted to insert.
     * @return a typesafe sorted set.
     */
    public static  SortedSet checkedSortedSet(SortedSet s,
            Class type) {
        return new CheckedSortedSet(s, type);
    }

    /**
     * Adds all the specified elements to the specified collection.
     *
     * @param c
     *            the collection the elements are to be inserted into.
     * @param a
     *            the elements to insert.
     * @return true if the collection changed during insertion.
     * @throws UnsupportedOperationException
     *             when the method is not supported.
     * @throws NullPointerException
     *             when {@code c} or {@code a} is {@code null}, or {@code a}
     *             contains one or more {@code null} elements and {@code c}
     *             doesn't support {@code null} elements.
     * @throws IllegalArgumentException
     *             if at least one of the elements can't be inserted into the
     *             collection.
     */
    @SafeVarargs
    public static  boolean addAll(Collection c, T... a) {
        boolean modified = false;
        for (int i = 0; i < a.length; i++) {
            modified |= c.add(a[i]);
        }
        return modified;
    }

    /**
     * Returns whether the specified collections have no elements in common.
     *
     * @param c1
     *            the first collection.
     * @param c2
     *            the second collection.
     * @return {@code true} if the collections have no elements in common,
     *         {@code false} otherwise.
     * @throws NullPointerException
     *             if one of the collections is {@code null}.
     */
    public static boolean disjoint(Collection c1, Collection c2) {
        if ((c1 instanceof Set) && !(c2 instanceof Set)
                || (c2.size()) > c1.size()) {
            Collection tmp = c1;
            c1 = c2;
            c2 = tmp;
        }
        Iterator it = c1.iterator();
        while (it.hasNext()) {
            if (c2.contains(it.next())) {
                return false;
            }
        }
        return true;
    }

    /**
     * Checks if specified object is instance of specified class. Used for a
     * dynamically typesafe view of the collections.
     *
     * @param obj -
     *            object is to be checked
     * @param type -
     *            class of object that should be
     * @return specified object
     */
    static  E checkType(E obj, Class type) {
        if (obj != null && !type.isInstance(obj)) {
            throw new ClassCastException("Attempt to insert element of type " + obj.getClass() +
                    " into collection of type " + type);
        }
        return obj;
    }

    /**
     * Returns a set backed by {@code map}.
     *
     * @throws IllegalArgumentException if the map is not empty
     * @since 1.6
     */
    public static  Set newSetFromMap(Map map) {
        if (map.isEmpty()) {
            return new SetFromMap(map);
        }
        throw new IllegalArgumentException("map not empty");
    }

    /**
     * Returns a last-in, first-out queue as a view of {@code deque}.
     *
     * @since 1.6
     */
    public static  Queue asLifoQueue(Deque deque) {
        return new AsLIFOQueue(deque);
    }

    private static class SetFromMap extends AbstractSet implements Serializable {
        // Must be named as is, to pass serialization compatibility test.
        private final Map m;

        private transient Set backingSet;

        SetFromMap(final Map map) {
            m = map;
            backingSet = map.keySet();
        }

        @Override public boolean equals(Object object) {
            return backingSet.equals(object);
        }

        @Override public int hashCode() {
            return backingSet.hashCode();
        }

        @Override public boolean add(E object) {
            return m.put(object, Boolean.TRUE) == null;
        }

        @Override public void clear() {
            m.clear();
        }

        @Override public String toString() {
            return backingSet.toString();
        }

        @Override public boolean contains(Object object) {
            return backingSet.contains(object);
        }

        @Override public boolean containsAll(Collection collection) {
            return backingSet.containsAll(collection);
        }

        @Override public boolean isEmpty() {
            return m.isEmpty();
        }

        @Override public boolean remove(Object object) {
            return m.remove(object) != null;
        }

        @Override public boolean retainAll(Collection collection) {
            return backingSet.retainAll(collection);
        }

        @Override public Object[] toArray() {
            return backingSet.toArray();
        }

        @Override
        public  T[] toArray(T[] contents) {
            return backingSet.toArray(contents);
        }

        @Override public Iterator iterator() {
            return backingSet.iterator();
        }

        @Override public int size() {
            return m.size();
        }

        @SuppressWarnings("unchecked")
        private void readObject(ObjectInputStream stream)
                throws IOException, ClassNotFoundException {
            stream.defaultReadObject();
            backingSet = m.keySet();
        }
    }

    private static class AsLIFOQueue extends AbstractQueue implements Serializable {
        // Must be named as is, to pass serialization compatibility test.
        private final Deque q;

        AsLIFOQueue(final Deque deque) {
            this.q = deque;
        }

        @Override public Iterator iterator() {
            return q.iterator();
        }

        @Override public int size() {
            return q.size();
        }

        @Override public boolean offer(E o) {
            return q.offerFirst(o);
        }

        @Override public E peek() {
            return q.peekFirst();
        }

        @Override public E poll() {
            return q.pollFirst();
        }

        @Override public boolean add(E o) {
            q.push(o);
            return true;
        }

        @Override public void clear() {
            q.clear();
        }

        @Override public E element() {
            return q.getFirst();
        }

        @Override public E remove() {
            return q.pop();
        }

        @Override public boolean contains(Object object) {
            return q.contains(object);
        }

        @Override public boolean containsAll(Collection collection) {
            return q.containsAll(collection);
        }

        @Override public boolean isEmpty() {
            return q.isEmpty();
        }

        @Override public boolean remove(Object object) {
            return q.remove(object);
        }

        @Override public boolean removeAll(Collection collection) {
            return q.removeAll(collection);
        }

        @Override public boolean retainAll(Collection collection) {
            return q.retainAll(collection);
        }

        @Override public Object[] toArray() {
            return q.toArray();
        }

        @Override public  T[] toArray(T[] contents) {
            return q.toArray(contents);
        }

        @Override public String toString() {
            return q.toString();
        }
    }

    /**
     * A dynamically typesafe view of a Collection.
     */
    private static class CheckedCollection implements Collection, Serializable {
        final Collection c;

        final Class type;

        public CheckedCollection(Collection c, Class type) {
            if (c == null) {
                throw new NullPointerException("c == null");
            } else if (type == null) {
                throw new NullPointerException("type == null");
            }
            this.c = c;
            this.type = type;
        }

        @Override public int size() {
            return c.size();
        }

        @Override public boolean isEmpty() {
            return c.isEmpty();
        }

        @Override public boolean contains(Object obj) {
            return c.contains(obj);
        }

        @Override public Iterator iterator() {
            Iterator i = c.iterator();
            if (i instanceof ListIterator) {
                i = new CheckedListIterator((ListIterator) i, type);
            }
            return i;
        }

        @Override public Object[] toArray() {
            return c.toArray();
        }

        @Override public  T[] toArray(T[] arr) {
            return c.toArray(arr);
        }

        @Override public boolean add(E obj) {
            return c.add(checkType(obj, type));
        }

        @Override public boolean remove(Object obj) {
            return c.remove(obj);
        }

        @Override public boolean containsAll(Collection c1) {
            return c.containsAll(c1);
        }

        @SuppressWarnings("unchecked")
        @Override public boolean addAll(Collection c1) {
            Object[] array = c1.toArray();
            for (Object o : array) {
                checkType(o, type);
            }
            return c.addAll((List) Arrays.asList(array));
        }

        @Override public boolean removeAll(Collection c1) {
            return c.removeAll(c1);
        }

        @Override public boolean retainAll(Collection c1) {
            return c.retainAll(c1);
        }

        @Override public void clear() {
            c.clear();
        }

        @Override public String toString() {
            return c.toString();
        }
    }

    /**
     * Class represents a dynamically typesafe view of the specified
     * ListIterator.
     */
    private static class CheckedListIterator implements ListIterator {

        private final ListIterator i;

        private final Class type;

        /**
         * Constructs a dynamically typesafe view of the specified ListIterator.
         *
         * @param i -
         *            the listIterator for which a dynamically typesafe view to
         *            be constructed.
         */
        public CheckedListIterator(ListIterator i, Class type) {
            this.i = i;
            this.type = type;
        }

        @Override public boolean hasNext() {
            return i.hasNext();
        }

        @Override public E next() {
            return i.next();
        }

        @Override public void remove() {
            i.remove();
        }

        @Override public boolean hasPrevious() {
            return i.hasPrevious();
        }

        @Override public E previous() {
            return i.previous();
        }

        @Override public int nextIndex() {
            return i.nextIndex();
        }

        @Override public int previousIndex() {
            return i.previousIndex();
        }

        @Override public void set(E obj) {
            i.set(checkType(obj, type));
        }

        @Override public void add(E obj) {
            i.add(checkType(obj, type));
        }
    }

    /**
     * Class represents a dynamically typesafe view of a List.
     */
    private static class CheckedList extends CheckedCollection implements List {
        final List l;

        public CheckedList(List l, Class type) {
            super(l, type);
            this.l = l;
        }

        @SuppressWarnings("unchecked")
        @Override public boolean addAll(int index, Collection c1) {
            Object[] array = c1.toArray();
            for (Object o : array) {
                checkType(o, type);
            }
            return l.addAll(index, (List) Arrays.asList(array));
        }

        @Override public E get(int index) {
            return l.get(index);
        }

        @Override public E set(int index, E obj) {
            return l.set(index, checkType(obj, type));
        }

        @Override public void add(int index, E obj) {
            l.add(index, checkType(obj, type));
        }

        @Override public E remove(int index) {
            return l.remove(index);
        }

        @Override public int indexOf(Object obj) {
            return l.indexOf(obj);
        }

        @Override public int lastIndexOf(Object obj) {
            return l.lastIndexOf(obj);
        }

        @Override public ListIterator listIterator() {
            return new CheckedListIterator(l.listIterator(), type);
        }

        @Override public ListIterator listIterator(int index) {
            return new CheckedListIterator(l.listIterator(index), type);
        }

        @Override public List subList(int fromIndex, int toIndex) {
            return checkedList(l.subList(fromIndex, toIndex), type);
        }

        @Override public boolean equals(Object obj) {
            return l.equals(obj);
        }

        @Override public int hashCode() {
            return l.hashCode();
        }
    }

    /**
     * A dynamically typesafe view of a RandomAccessList.
     */
    private static class CheckedRandomAccessList extends CheckedList implements RandomAccess {
        public CheckedRandomAccessList(List l, Class type) {
            super(l, type);
        }
    }

    /**
     * A dynamically typesafe view of a Set.
     */
    private static class CheckedSet extends CheckedCollection implements Set {
        public CheckedSet(Set s, Class type) {
            super(s, type);
        }

        @Override public boolean equals(Object obj) {
            return c.equals(obj);
        }

        @Override public int hashCode() {
            return c.hashCode();
        }
    }

    /**
     * A dynamically typesafe view of a Map.
     */
    private static class CheckedMap implements Map, Serializable {
        final Map m;
        final Class keyType;
        final Class valueType;

        private CheckedMap(Map m, Class keyType, Class valueType) {
            if (m == null) {
                throw new NullPointerException("m == null");
            } else if (keyType == null) {
                throw new NullPointerException("keyType == null");
            } else if (valueType == null) {
                throw new NullPointerException("valueType == null");
            }
            this.m = m;
            this.keyType = keyType;
            this.valueType = valueType;
        }

        @Override public int size() {
            return m.size();
        }

        @Override public boolean isEmpty() {
            return m.isEmpty();
        }

        @Override public boolean containsKey(Object key) {
            return m.containsKey(key);
        }

        @Override public boolean containsValue(Object value) {
            return m.containsValue(value);
        }

        @Override public V get(Object key) {
            return m.get(key);
        }

        @Override public V put(K key, V value) {
            return m.put(checkType(key, keyType), checkType(value, valueType));
        }

        @Override public V remove(Object key) {
            return m.remove(key);
        }

        @SuppressWarnings("unchecked")
        @Override public void putAll(Map map) {
            int size = map.size();
            if (size == 0) {
                return;
            }
            Entry[] entries = new Entry[size];
            Iterator> it = map
                    .entrySet().iterator();
            for (int i = 0; i < size; i++) {
                Entry e = it.next();
                checkType(e.getKey(), keyType);
                checkType(e.getValue(), valueType);
                entries[i] = e;
            }
            for (int i = 0; i < size; i++) {
                m.put(entries[i].getKey(), entries[i].getValue());
            }
        }

        @Override public void clear() {
            m.clear();
        }

        @Override public Set keySet() {
            return m.keySet();
        }

        @Override public Collection values() {
            return m.values();
        }

        @Override public Set> entrySet() {
            return new CheckedEntrySet(m.entrySet(), valueType);
        }

        @Override public boolean equals(Object obj) {
            return m.equals(obj);
        }

        @Override public int hashCode() {
            return m.hashCode();
        }

        @Override public String toString() {
            return m.toString();
        }

        /**
         * A dynamically typesafe view of a Map.Entry.
         */
        private static class CheckedEntry implements Entry {
            final Entry e;
            final Class valueType;

            public CheckedEntry(Entry e, Class valueType) {
                if (e == null) {
                    throw new NullPointerException("e == null");
                }
                this.e = e;
                this.valueType = valueType;
            }

            @Override public K getKey() {
                return e.getKey();
            }

            @Override public V getValue() {
                return e.getValue();
            }

            @Override public V setValue(V obj) {
                return e.setValue(checkType(obj, valueType));
            }

            @Override public boolean equals(Object obj) {
                return e.equals(obj);
            }

            @Override public int hashCode() {
                return e.hashCode();
            }
        }

        /**
         * A dynamically typesafe view of an entry set.
         */
        private static class CheckedEntrySet implements Set> {
            final Set> s;
            final Class valueType;

            public CheckedEntrySet(Set> s, Class valueType) {
                this.s = s;
                this.valueType = valueType;
            }

            @Override public Iterator> iterator() {
                return new CheckedEntryIterator(s.iterator(), valueType);
            }

            @Override public Object[] toArray() {
                int thisSize = size();
                Object[] array = new Object[thisSize];
                Iterator it = iterator();
                for (int i = 0; i < thisSize; i++) {
                    array[i] = it.next();
                }
                return array;
            }

            @SuppressWarnings("unchecked")
            @Override public  T[] toArray(T[] array) {
                int thisSize = size();
                if (array.length < thisSize) {
                    Class ct = array.getClass().getComponentType();
                    array = (T[]) Array.newInstance(ct, thisSize);
                }
                Iterator it = iterator();
                for (int i = 0; i < thisSize; i++) {
                    array[i] = (T) it.next();
                }
                if (thisSize < array.length) {
                    array[thisSize] = null;
                }
                return array;
            }

            @Override public boolean retainAll(Collection c) {
                return s.retainAll(c);
            }

            @Override public boolean removeAll(Collection c) {
                return s.removeAll(c);
            }

            @Override public boolean containsAll(Collection c) {
                return s.containsAll(c);
            }

            @Override public boolean addAll(Collection> c) {
                throw new UnsupportedOperationException();
            }

            @Override public boolean remove(Object o) {
                return s.remove(o);
            }

            @Override public boolean contains(Object o) {
                return s.contains(o);
            }

            @Override public boolean add(Entry o) {
                throw new UnsupportedOperationException();
            }

            @Override public boolean isEmpty() {
                return s.isEmpty();
            }

            @Override public void clear() {
                s.clear();
            }

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

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

            @Override public boolean equals(Object object) {
                return s.equals(object);
            }

            /**
             * A dynamically typesafe view of an entry iterator.
             */
            private static class CheckedEntryIterator implements Iterator> {
                Iterator> i;
                Class valueType;

                public CheckedEntryIterator(Iterator> i,
                        Class valueType) {
                    this.i = i;
                    this.valueType = valueType;
                }

                @Override public boolean hasNext() {
                    return i.hasNext();
                }

                @Override public void remove() {
                    i.remove();
                }

                @Override public Entry next() {
                    return new CheckedEntry(i.next(), valueType);
                }
            }
        }
    }

    /**
     * A dynamically typesafe view of a SortedSet.
     */
    private static class CheckedSortedSet extends CheckedSet implements SortedSet {
        private final SortedSet ss;

        public CheckedSortedSet(SortedSet s, Class type) {
            super(s, type);
            this.ss = s;
        }

        @Override public Comparator comparator() {
            return ss.comparator();
        }

        @Override public SortedSet subSet(E fromElement, E toElement) {
            return new CheckedSortedSet(ss.subSet(fromElement, toElement),
                    type);
        }

        @Override public SortedSet headSet(E toElement) {
            return new CheckedSortedSet(ss.headSet(toElement), type);
        }

        @Override public SortedSet tailSet(E fromElement) {
            return new CheckedSortedSet(ss.tailSet(fromElement), type);
        }

        @Override public E first() {
            return ss.first();
        }

        @Override public E last() {
            return ss.last();
        }
    }

    /**
     * A dynamically typesafe view of a SortedMap.
     */
    private static class CheckedSortedMap extends CheckedMap implements SortedMap {
        final SortedMap sm;

        CheckedSortedMap(SortedMap m, Class keyType, Class valueType) {
            super(m, keyType, valueType);
            this.sm = m;
        }

        @Override public Comparator comparator() {
            return sm.comparator();
        }

        @Override public SortedMap subMap(K fromKey, K toKey) {
            return new CheckedSortedMap(sm.subMap(fromKey, toKey), keyType, valueType);
        }

        @Override public SortedMap headMap(K toKey) {
            return new CheckedSortedMap(sm.headMap(toKey), keyType, valueType);
        }

        @Override public SortedMap tailMap(K fromKey) {
            return new CheckedSortedMap(sm.tailMap(fromKey), keyType, valueType);
        }

        @Override public K firstKey() {
            return sm.firstKey();
        }

        @Override public K lastKey() {
            return sm.lastKey();
        }
    }

    /**
     * Computes a hash code and applies a supplemental hash function to defend
     * against poor quality hash functions. This is critical because HashMap
     * uses power-of-two length hash tables, that otherwise encounter collisions
     * for hash codes that do not differ in lower or upper bits.
     * Routine taken from java.util.concurrent.ConcurrentHashMap.hash(int).
     * @hide
     */
    public static int secondaryHash(Object key) {
        return secondaryHash(key.hashCode());
    }

    /**
     * Computes an identity hash code and applies a supplemental hash function to defend
     * against poor quality hash functions. This is critical because identity hash codes
     * are currently implemented as object addresses, which will have been aligned by the
     * underlying memory allocator causing all hash codes to have the same bottom bits.
     * @hide
     */
    public static int secondaryIdentityHash(Object key) {
        return secondaryHash(SystemInt.identityHashCode(key));
    }

    private static int secondaryHash(int h) {
        // Spread bits to regularize both segment and index locations,
        // using variant of single-word Wang/Jenkins hash.
        h += (h <<  15) ^ 0xffffcd7d;
        h ^= (h >>> 10);
        h += (h <<   3);
        h ^= (h >>>  6);
        h += (h <<   2) + (h << 14);
        return h ^ (h >>> 16);
    }

    /**
     * Returns the smallest power of two >= its argument, with several caveats:
     * If the argument is negative but not Integer.MIN_VALUE, the method returns
     * zero. If the argument is > 2^30 or equal to Integer.MIN_VALUE, the method
     * returns Integer.MIN_VALUE. If the argument is zero, the method returns
     * zero.
     * @hide
     */
    public static int roundUpToPowerOfTwo(int i) {
        i--; // If input is a power of two, shift its high-order bit right.

        // "Smear" the high-order bit all the way to the right.
        i |= i >>>  1;
        i |= i >>>  2;
        i |= i >>>  4;
        i |= i >>>  8;
        i |= i >>> 16;

        return i + 1;
    }
}
    

    

    

            

    

            



    
    






    
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