/**
     * Returns a dynamically typesafe view of the specified sorted map.
     * Any attempt to insert a mapping whose key or value have the wrong
     * type will result in an immediate {@link ClassCastException}.
     * Similarly, any attempt to modify the value currently associated with
     * a key will result in an immediate {@link ClassCastException},
     * whether the modification is attempted directly through the map
     * itself, or through a {@link Map.Entry} instance obtained from the
     * map's {@link Map#entrySet() entry set} view.
     *
     * <p>Assuming a map contains no incorrectly typed keys or values
     * prior to the time a dynamically typesafe view is generated, and
     * that all subsequent access to the map takes place through the view
     * (or one of its collection views), it is <i>guaranteed</i> that the
     * map cannot contain an incorrectly typed key or value.
     *
     * <p>A discussion of the use of dynamically typesafe views may be
     * found in the documentation for the {@link #checkedCollection
     * checkedCollection} method.
     *
     * <p>The returned map will be serializable if the specified map is
     * serializable.
     *
     * <p>Since {@code null} is considered to be a value of any reference
     * type, the returned map permits insertion of null keys or values
     * whenever the backing map does.
     *
     * @param <K> the class of the map keys
     * @param <V> the class of the map values
     * @param m the map for which a dynamically typesafe view is to be
     *          returned
     * @param keyType the type of key that {@code m} is permitted to hold
     * @param valueType the type of value that {@code m} is permitted to hold
     * @return a dynamically typesafe view of the specified map
     * @since 1.5
     */
    public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m,
                                                        Class<K> keyType,
                                                        Class<V> valueType) {
        return new CheckedSortedMap<>(m, keyType, valueType);
    }

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

        private final SortedMap<K, V> sm;

        CheckedSortedMap(SortedMap<K, V> m,
                         Class<K> keyType, Class<V> valueType) {
            super(m, keyType, valueType);
            sm = m;
        }

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

        public SortedMap<K,V> subMap(K fromKey, K toKey) {
            return checkedSortedMap(sm.subMap(fromKey, toKey),
                                    keyType, valueType);
        }
        public SortedMap<K,V> headMap(K toKey) {
            return checkedSortedMap(sm.headMap(toKey), keyType, valueType);
        }
        public SortedMap<K,V> tailMap(K fromKey) {
            return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType);
        }
    }

    /**
     * Returns a dynamically typesafe view of the specified navigable map.
     * Any attempt to insert a mapping whose key or value have the wrong
     * type will result in an immediate {@link ClassCastException}.
     * Similarly, any attempt to modify the value currently associated with
     * a key will result in an immediate {@link ClassCastException},
     * whether the modification is attempted directly through the map
     * itself, or through a {@link Map.Entry} instance obtained from the
     * map's {@link Map#entrySet() entry set} view.
     *
     * <p>Assuming a map contains no incorrectly typed keys or values
     * prior to the time a dynamically typesafe view is generated, and
     * that all subsequent access to the map takes place through the view
     * (or one of its collection views), it is <em>guaranteed</em> that the
     * map cannot contain an incorrectly typed key or value.
     *
     * <p>A discussion of the use of dynamically typesafe views may be
     * found in the documentation for the {@link #checkedCollection
     * checkedCollection} method.
     *
     * <p>The returned map will be serializable if the specified map is
     * serializable.
     *
     * <p>Since {@code null} is considered to be a value of any reference
     * type, the returned map permits insertion of null keys or values
     * whenever the backing map does.
     *
     * @param <K> type of map keys
     * @param <V> type of map values
     * @param m the map for which a dynamically typesafe view is to be
     *          returned
     * @param keyType the type of key that {@code m} is permitted to hold
     * @param valueType the type of value that {@code m} is permitted to hold
     * @return a dynamically typesafe view of the specified map
     * @since 1.8
     */
    public static <K,V> NavigableMap<K,V> checkedNavigableMap(NavigableMap<K, V> m,
                                                        Class<K> keyType,
                                                        Class<V> valueType) {
        return new CheckedNavigableMap<>(m, keyType, valueType);
    }

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

        private final NavigableMap<K, V> nm;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    // Empty collections

    /**
     * Returns an iterator that has no elements.  More precisely,
     *
     * <ul>
     * <li>{@link Iterator#hasNext hasNext} always returns {@code
     * false}.</li>
     * <li>{@link Iterator#next next} always throws {@link
     * NoSuchElementException}.</li>
     * <li>{@link Iterator#remove remove} always throws {@link
     * IllegalStateException}.</li>
     * </ul>
     *
     * <p>Implementations of this method are permitted, but not
     * required, to return the same object from multiple invocations.
     *
     * @param <T> type of elements, if there were any, in the iterator
     * @return an empty iterator
     * @since 1.7
     */
    @SuppressWarnings("unchecked")
    public static <T> Iterator<T> emptyIterator() {
        return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR;
    }

    private static class EmptyIterator<E> implements Iterator<E> {
        static final EmptyIterator<Object> EMPTY_ITERATOR
            = new EmptyIterator<>();

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

    /**
     * Returns a list iterator that has no elements.  More precisely,
     *
     * <ul>
     * <li>{@link Iterator#hasNext hasNext} and {@link
     * ListIterator#hasPrevious hasPrevious} always return {@code
     * false}.</li>
     * <li>{@link Iterator#next next} and {@link ListIterator#previous
     * previous} always throw {@link NoSuchElementException}.</li>
     * <li>{@link Iterator#remove remove} and {@link ListIterator#set
     * set} always throw {@link IllegalStateException}.</li>
     * <li>{@link ListIterator#add add} always throws {@link
     * UnsupportedOperationException}.</li>
     * <li>{@link ListIterator#nextIndex nextIndex} always returns
     * {@code 0}.</li>
     * <li>{@link ListIterator#previousIndex previousIndex} always
     * returns {@code -1}.</li>
     * </ul>
     *
     * <p>Implementations of this method are permitted, but not
     * required, to return the same object from multiple invocations.
     *
     * @param <T> type of elements, if there were any, in the iterator
     * @return an empty list iterator
     * @since 1.7
     */
    @SuppressWarnings("unchecked")
    public static <T> ListIterator<T> emptyListIterator() {
        return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR;
    }

    private static class EmptyListIterator<E>
        extends EmptyIterator<E>
        implements ListIterator<E>
    {
        static final EmptyListIterator<Object> EMPTY_ITERATOR
            = new EmptyListIterator<>();

        public boolean hasPrevious() { return false; }
        public E previous() { throw new NoSuchElementException(); }
        public int nextIndex()     { return 0; }
        public int previousIndex() { return -1; }
        public void set(E e) { throw new IllegalStateException(); }
        public void add(E e) { throw new UnsupportedOperationException(); }
    }

    /**
     * Returns an enumeration that has no elements.  More precisely,
     *
     * <ul>
     * <li>{@link Enumeration#hasMoreElements hasMoreElements} always
     * returns {@code false}.</li>
     * <li> {@link Enumeration#nextElement nextElement} always throws
     * {@link NoSuchElementException}.</li>
     * </ul>
     *
     * <p>Implementations of this method are permitted, but not
     * required, to return the same object from multiple invocations.
     *
     * @param  <T> the class of the objects in the enumeration
     * @return an empty enumeration
     * @since 1.7
     */
    @SuppressWarnings("unchecked")
    public static <T> Enumeration<T> emptyEnumeration() {
        return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION;
    }

    private static class EmptyEnumeration<E> implements Enumeration<E> {
        static final EmptyEnumeration<Object> EMPTY_ENUMERATION
            = new EmptyEnumeration<>();

        public boolean hasMoreElements() { return false; }
        public E nextElement() { throw new NoSuchElementException(); }
    }

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

    /**
     * Returns an empty set (immutable).  This set is serializable.
     * Unlike the like-named field, this method is parameterized.
     *
     * <p>This example illustrates the type-safe way to obtain an empty set:
     * <pre>
     *     Set&lt;String&gt; s = Collections.emptySet();
     * </pre>
     * @implNote Implementations of this method need not create a separate
     * {@code Set} object for each call.  Using this method is likely to have
     * comparable cost to using the like-named field.  (Unlike this method, the
     * field does not provide type safety.)
     *
     * @param  <T> the class of the objects in the set
     * @return the empty set
     *
     * @see #EMPTY_SET
     * @since 1.5
     */
    @SuppressWarnings("unchecked")
    public static final <T> Set<T> emptySet() {
        return (Set<T>) EMPTY_SET;
    }

    /**
     * @serial include
     */
    private static class EmptySet<E>
        extends AbstractSet<E>
        implements Serializable
    {
        private static final long serialVersionUID = 1582296315990362920L;

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

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

        public boolean contains(Object obj) {return false;}
        public boolean containsAll(Collection<?> c) { return c.isEmpty(); }

        public Object[] toArray() { return new Object[0]; }

        public <T> T[] toArray(T[] a) {
            if (a.length > 0)
                a[0] = null;
            return a;
        }

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

        // Preserves singleton property
        private Object readResolve() {
            return EMPTY_SET;
        }
    }

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

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

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

    /**
     * Returns an empty list (immutable).  This list is serializable.
     *
     * <p>This example illustrates the type-safe way to obtain an empty list:
     * <pre>
     *     List&lt;String&gt; s = Collections.emptyList();
     * </pre>
     *
     * @implNote
     * Implementations of this method need not create a separate <tt>List</tt>
     * object for each call.   Using this method is likely to have comparable
     * cost to using the like-named field.  (Unlike this method, the field does
     * not provide type safety.)
     *
     * @param <T> type of elements, if there were any, in the list
     * @return an empty immutable list
     *
     * @see #EMPTY_LIST
     * @since 1.5
     */
    @SuppressWarnings("unchecked")
    public static final <T> List<T> emptyList() {
        return (List<T>) EMPTY_LIST;
    }

    /**
     * @serial include
     */
    private static class EmptyList<E>
        extends AbstractList<E>
        implements RandomAccess, Serializable {
        private static final long serialVersionUID = 8842843931221139166L;

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

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

        public boolean contains(Object obj) {return false;}
        public boolean containsAll(Collection<?> c) { return c.isEmpty(); }

        public Object[] toArray() { return new Object[0]; }

        public <T> T[] toArray(T[] a) {
            if (a.length > 0)
                a[0] = null;
            return a;
        }

        public E get(int index) {
            throw new IndexOutOfBoundsException("Index: "+index);
        }

        public boolean equals(Object o) {
            return (o instanceof List) && ((List<?>)o).isEmpty();
        }

        public int hashCode() { return 1; }

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

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

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

        // Preserves singleton property
        private Object readResolve() {
            return EMPTY_LIST;
        }
    }

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

    /**
     * Returns an empty map (immutable).  This map is serializable.
     *
     * <p>This example illustrates the type-safe way to obtain an empty map:
     * <pre>
     *     Map&lt;String, Date&gt; s = Collections.emptyMap();
     * </pre>
     * @implNote Implementations of this method need not create a separate
     * {@code Map} object for each call.  Using this method is likely to have
     * comparable cost to using the like-named field.  (Unlike this method, the
     * field does not provide type safety.)
     *
     * @param <K> the class of the map keys
     * @param <V> the class of the map values
     * @return an empty map
     * @see #EMPTY_MAP
     * @since 1.5
     */
    @SuppressWarnings("unchecked")
    public static final <K,V> Map<K,V> emptyMap() {
        return (Map<K,V>) EMPTY_MAP;
    }

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

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

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

        public int size()                          {return 0;}
        public boolean isEmpty()                   {return true;}
        public boolean containsKey(Object key)     {return false;}
        public boolean containsValue(Object value) {return false;}
        public V get(Object key)                   {return null;}
        public Set<K> keySet()                     {return emptySet();}
        public Collection<V> values()              {return emptySet();}
        public Set<Map.Entry<K,V>> entrySet()      {return emptySet();}

        public boolean equals(Object o) {
            return (o instanceof Map) && ((Map<?,?>)o).isEmpty();
        }

        public int hashCode()                      {return 0;}

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

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

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

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

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

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

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

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

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

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

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

        // Preserves singleton property
        private Object readResolve() {
            return EMPTY_MAP;
        }
    }

    // Singleton collections

    /**
     * Returns an immutable set containing only the specified object.
     * The returned set is serializable.
     *
     * @param  <T> the class of the objects in the set
     * @param o the sole object to be stored in the returned set.
     * @return an immutable set containing only the specified object.
     */
    public static <T> Set<T> singleton(T o) {
        return new SingletonSet<>(o);
    }

    static <E> Iterator<E> singletonIterator(final E e) {
        return new Iterator<E>() {
            private boolean hasNext = true;
            public boolean hasNext() {
                return hasNext;
            }
            public E next() {
                if (hasNext) {
                    hasNext = false;
                    return e;
                }
                throw new NoSuchElementException();
            }
            public void remove() {
                throw new UnsupportedOperationException();
            }
            @Override
            public void forEachRemaining(Consumer<? super E> action) {
                Objects.requireNonNull(action);
                if (hasNext) {
                    action.accept(e);
                    hasNext = false;
                }
            }
        };
    }

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

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

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

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

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

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

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

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

        private final E element;

        SingletonSet(E e) {element = e;}

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

        public int size() {return 1;}

        public boolean contains(Object o) {return eq(o, element);}

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

    /**
     * Returns an immutable list containing only the specified object.
     * The returned list is serializable.
     *
     * @param  <T> the class of the objects in the list
     * @param o the sole object to be stored in the returned list.
     * @return an immutable list containing only the specified object.
     * @since 1.3
     */
    public static <T> List<T> singletonList(T o) {
        return new SingletonList<>(o);
    }

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

        private static final long serialVersionUID = 3093736618740652951L;

        private final E element;

        SingletonList(E obj)                {element = obj;}

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

        public int size()                   {return 1;}

        public boolean contains(Object obj) {return eq(obj, element);}

        public E get(int index) {
            if (index != 0)
              throw new IndexOutOfBoundsException("Index: "+index+", Size: 1");
            return element;
        }

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

    /**
     * Returns an immutable map, mapping only the specified key to the
     * specified value.  The returned map is serializable.
     *
     * @param <K> the class of the map keys
     * @param <V> the class of the map values
     * @param key the sole key to be stored in the returned map.
     * @param value the value to which the returned map maps <tt>key</tt>.
     * @return an immutable map containing only the specified key-value
     *         mapping.
     * @since 1.3
     */
    public static <K,V> Map<K,V> singletonMap(K key, V value) {
        return new SingletonMap<>(key, value);
    }

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

        private final K k;
        private final V v;

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

        public int size()                                           {return 1;}
        public boolean isEmpty()                                {return false;}
        public boolean containsKey(Object key)             {return eq(key, k);}
        public boolean containsValue(Object value)       {return eq(value, v);}
        public V get(Object key)              {return (eq(key, k) ? v : null);}

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

        public Set<K> keySet() {
            if (keySet==null)
                keySet = singleton(k);
            return keySet;
        }

        public Set<Map.Entry<K,V>> entrySet() {
            if (entrySet==null)
                entrySet = Collections.<Map.Entry<K,V>>singleton(
                    new SimpleImmutableEntry<>(k, v));
            return entrySet;
        }

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

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

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

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

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

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

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

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

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

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

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

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

    // Miscellaneous

    /**
     * Returns an immutable list consisting of <tt>n</tt> copies of the
     * specified object.  The newly allocated data object is tiny (it contains
     * a single reference to the data object).  This method is useful in
     * combination with the <tt>List.addAll</tt> method to grow lists.
     * The returned list is serializable.
     *
     * @param  <T> the class of the object to copy and of the objects
     *         in the returned list.
     * @param  n the number of elements in the returned list.
     * @param  o the element to appear repeatedly in the returned list.
     * @return an immutable list consisting of <tt>n</tt> copies of the
     *         specified object.
     * @throws IllegalArgumentException if {@code n < 0}
     * @see    List#addAll(Collection)
     * @see    List#addAll(int, Collection)
     */
    public static <T> List<T> nCopies(int n, T o) {
        if (n < 0)
            throw new IllegalArgumentException("List length = " + n);
        return new CopiesList<>(n, o);
    }

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

        final int n;
        final E element;

        CopiesList(int n, E e) {
            assert n >= 0;
            this.n = n;
            element = e;
        }

        public int size() {
            return n;
        }

        public boolean contains(Object obj) {
            return n != 0 && eq(obj, element);
        }

        public int indexOf(Object o) {
            return contains(o) ? 0 : -1;
        }

        public int lastIndexOf(Object o) {
            return contains(o) ? n - 1 : -1;
        }

        public E get(int index) {
            if (index < 0 || index >= n)
                throw new IndexOutOfBoundsException("Index: "+index+
                                                    ", Size: "+n);
            return element;
        }

        public Object[] toArray() {
            final Object[] a = new Object[n];
            if (element != null)
                Arrays.fill(a, 0, n, element);
            return a;
        }

        @SuppressWarnings("unchecked")
        public <T> T[] toArray(T[] a) {
            final int n = this.n;
            if (a.length < n) {
                a = (T[])java.lang.reflect.Array
                    .newInstance(a.getClass().getComponentType(), n);
                if (element != null)
                    Arrays.fill(a, 0, n, element);
            } else {
                Arrays.fill(a, 0, n, element);
                if (a.length > n)
                    a[n] = null;
            }
            return a;
        }

        public List<E> subList(int fromIndex, int toIndex) {
            if (fromIndex < 0)
                throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
            if (toIndex > n)
                throw new IndexOutOfBoundsException("toIndex = " + toIndex);
            if (fromIndex > toIndex)
                throw new IllegalArgumentException("fromIndex(" + fromIndex +
                                                   ") > toIndex(" + toIndex + ")");
            return new CopiesList<>(toIndex - fromIndex, element);
        }

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

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

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

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

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

        private static final long serialVersionUID = 7207038068494060240L;

        static final ReverseComparator REVERSE_ORDER
            = new ReverseComparator();

        public int compare(Comparable<Object> c1, Comparable<Object> c2) {
            return c2.compareTo(c1);
        }

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

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

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

        if (cmp instanceof ReverseComparator2)
            return ((ReverseComparator2<T>)cmp).cmp;

        return new ReverseComparator2<>(cmp);
    }

    /**
     * @serial include
     */
    private static class ReverseComparator2<T> implements Comparator<T>,
        Serializable
    {
        private static final long serialVersionUID = 4374092139857L;

        /**
         * The comparator specified in the static factory.  This will never
         * be null, as the static factory returns a ReverseComparator
         * instance if its argument is null.
         *
         * @serial
         */
        final Comparator<T> cmp;

        ReverseComparator2(Comparator<T> cmp) {
            assert cmp != null;
            this.cmp = cmp;
        }

        public int compare(T t1, T t2) {
            return cmp.compare(t2, t1);
        }

        public boolean equals(Object o) {
            return (o == this) ||
                (o instanceof ReverseComparator2 &&
                 cmp.equals(((ReverseComparator2)o).cmp));
        }

        public int hashCode() {
            return cmp.hashCode() ^ Integer.MIN_VALUE;
        }

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

    /**
     * Returns an enumeration over the specified collection.  This provides
     * interoperability with legacy APIs that require an enumeration
     * as input.
     *
     * @param  <T> the class of the objects in the collection
     * @param c the collection for which an enumeration is to be returned.
     * @return an enumeration over the specified collection.
     * @see Enumeration
     */
    public static <T> Enumeration<T> enumeration(final Collection<T> c) {
        return new Enumeration<T>() {
            private final Iterator<T> i = c.iterator();

            public boolean hasMoreElements() {
                return i.hasNext();
            }

            public T nextElement() {
                return i.next();
            }
        };
    }

    /**
     * Returns an array list containing the elements returned by the
     * specified enumeration in the order they are returned by the
     * enumeration.  This method provides interoperability between
     * legacy APIs that return enumerations and new APIs that require
     * collections.
     *
     * @param <T> the class of the objects returned by the enumeration
     * @param e enumeration providing elements for the returned
     *          array list
     * @return an array list containing the elements returned
     *         by the specified enumeration.
     * @since 1.4
     * @see Enumeration
     * @see ArrayList
     */
    public static <T> ArrayList<T> list(Enumeration<T> e) {
        ArrayList<T> l = new ArrayList<>();
        while (e.hasMoreElements())
            l.add(e.nextElement());
        return l;
    }

    /**
     * Returns true if the specified arguments are equal, or both null.
     *
     * NB: Do not replace with Object.equals until JDK-8015417 is resolved.
     */
    static boolean eq(Object o1, Object o2) {
        return o1==null ? o2==null : o1.equals(o2);
    }

    /**
     * Returns the number of elements in the specified collection equal to the
     * specified object.  More formally, returns the number of elements
     * <tt>e</tt> in the collection such that
     * <tt>(o == null ? e == null : o.equals(e))</tt>.
     *
     * @param c the collection in which to determine the frequency
     *     of <tt>o</tt>
     * @param o the object whose frequency is to be determined
     * @return the number of elements in {@code c} equal to {@code o}
     * @throws NullPointerException if <tt>c</tt> is null
     * @since 1.5
     */
    public static int frequency(Collection<?> c, Object o) {
        int result = 0;
        if (o == null) {
            for (Object e : c)
                if (e == null)
                    result++;
        } else {
            for (Object e : c)
                if (o.equals(e))
                    result++;
        }
        return result;
    }

    /**
     * Returns {@code true} if the two specified collections have no
     * elements in common.
     *
     * <p>Care must be exercised if this method is used on collections that
     * do not comply with the general contract for {@code Collection}.
     * Implementations may elect to iterate over either collection and test
     * for containment in the other collection (or to perform any equivalent
     * computation).  If either collection uses a nonstandard equality test
     * (as does a {@link SortedSet} whose ordering is not <em>compatible with
     * equals</em>, or the key set of an {@link IdentityHashMap}), both
     * collections must use the same nonstandard equality test, or the
     * result of this method is undefined.
     *
     * <p>Care must also be exercised when using collections that have
     * restrictions on the elements that they may contain. Collection
     * implementations are allowed to throw exceptions for any operation
     * involving elements they deem ineligible. For absolute safety the
     * specified collections should contain only elements which are
     * eligible elements for both collections.
     *
     * <p>Note that it is permissible to pass the same collection in both
     * parameters, in which case the method will return {@code true} if and
     * only if the collection is empty.
     *
     * @param c1 a collection
     * @param c2 a collection
     * @return {@code true} if the two specified collections have no
     * elements in common.
     * @throws NullPointerException if either collection is {@code null}.
     * @throws NullPointerException if one collection contains a {@code null}
     * element and {@code null} is not an eligible element for the other collection.
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws ClassCastException if one collection contains an element that is
     * of a type which is ineligible for the other collection.
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @since 1.5
     */
    public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
        // The collection to be used for contains(). Preference is given to
        // the collection who's contains() has lower O() complexity.
        Collection<?> contains = c2;
        // The collection to be iterated. If the collections' contains() impl
        // are of different O() complexity, the collection with slower
        // contains() will be used for iteration. For collections who's
        // contains() are of the same complexity then best performance is
        // achieved by iterating the smaller collection.
        Collection<?> iterate = c1;

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

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

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

        // No common elements were found.
        return true;
    }

    /**
     * Adds all of the specified elements to the specified collection.
     * Elements to be added may be specified individually or as an array.
     * The behavior of this convenience method is identical to that of
     * <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely
     * to run significantly faster under most implementations.
     *
     * <p>When elements are specified individually, this method provides a
     * convenient way to add a few elements to an existing collection:
     * <pre>
     *     Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon");
     * </pre>
     *
     * @param  <T> the class of the elements to add and of the collection
     * @param c the collection into which <tt>elements</tt> are to be inserted
     * @param elements the elements to insert into <tt>c</tt>
     * @return <tt>true</tt> if the collection changed as a result of the call
     * @throws UnsupportedOperationException if <tt>c</tt> does not support
     *         the <tt>add</tt> operation
     * @throws NullPointerException if <tt>elements</tt> contains one or more
     *         null values and <tt>c</tt> does not permit null elements, or
     *         if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt>
     * @throws IllegalArgumentException if some property of a value in
     *         <tt>elements</tt> prevents it from being added to <tt>c</tt>
     * @see Collection#addAll(Collection)
     * @since 1.5
     */
    @SafeVarargs
    public static <T> boolean addAll(Collection<? super T> c, T... elements) {
        boolean result = false;
        for (T element : elements)
            result |= c.add(element);
        return result;
    }

    /**
     * Returns a set backed by the specified map.  The resulting set displays
     * the same ordering, concurrency, and performance characteristics as the
     * backing map.  In essence, this factory method provides a {@link Set}
     * implementation corresponding to any {@link Map} implementation.  There
     * is no need to use this method on a {@link Map} implementation that
     * already has a corresponding {@link Set} implementation (such as {@link
     * HashMap} or {@link TreeMap}).
     *
     * <p>Each method invocation on the set returned by this method results in
     * exactly one method invocation on the backing map or its <tt>keySet</tt>
     * view, with one exception.  The <tt>addAll</tt> method is implemented
     * as a sequence of <tt>put</tt> invocations on the backing map.
     *
     * <p>The specified map must be empty at the time this method is invoked,
     * and should not be accessed directly after this method returns.  These
     * conditions are ensured if the map is created empty, passed directly
     * to this method, and no reference to the map is retained, as illustrated
     * in the following code fragment:
     * <pre>
     *    Set&lt;Object&gt; weakHashSet = Collections.newSetFromMap(
     *        new WeakHashMap&lt;Object, Boolean&gt;());
     * </pre>
     *
     * @param <E> the class of the map keys and of the objects in the
     *        returned set
     * @param map the backing map
     * @return the set backed by the map
     * @throws IllegalArgumentException if <tt>map</tt> is not empty
     * @since 1.6
     */
    public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
        return new SetFromMap<>(map);
    }

    /**
     * @serial include
     */
    private static class SetFromMap<E> extends AbstractSet<E>
        implements Set<E>, Serializable
    {
        private final Map<E, Boolean> m;  // The backing map
        private transient Set<E> s;       // Its keySet

        SetFromMap(Map<E, Boolean> map) {
            if (!map.isEmpty())
                throw new IllegalArgumentException("Map is non-empty");
            m = map;
            s = map.keySet();
        }

        public void clear()               {        m.clear(); }
        public int size()                 { return m.size(); }
        public boolean isEmpty()          { return m.isEmpty(); }
        public boolean contains(Object o) { return m.containsKey(o); }
        public boolean remove(Object o)   { return m.remove(o) != null; }
        public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; }
        public Iterator<E> iterator()     { return s.iterator(); }
        public Object[] toArray()         { return s.toArray(); }
        public <T> T[] toArray(T[] a)     { return s.toArray(a); }
        public String toString()          { return s.toString(); }
        public int hashCode()             { return s.hashCode(); }
        public boolean equals(Object o)   { return o == this || s.equals(o); }
        public boolean containsAll(Collection<?> c) {return s.containsAll(c);}
        public boolean removeAll(Collection<?> c)   {return s.removeAll(c);}
        public boolean retainAll(Collection<?> c)   {return s.retainAll(c);}
        // addAll is the only inherited implementation

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

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

        private static final long serialVersionUID = 2454657854757543876L;

        private void readObject(java.io.ObjectInputStream stream)
            throws IOException, ClassNotFoundException
        {
            stream.defaultReadObject();
            s = m.keySet();
        }
    }

    /**
     * Returns a view of a {@link Deque} as a Last-in-first-out (Lifo)
     * {@link Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>,
     * <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This
     * view can be useful when you would like to use a method
     * requiring a <tt>Queue</tt> but you need Lifo ordering.
     *
     * <p>Each method invocation on the queue returned by this method
     * results in exactly one method invocation on the backing deque, with
     * one exception.  The {@link Queue#addAll addAll} method is
     * implemented as a sequence of {@link Deque#addFirst addFirst}
     * invocations on the backing deque.
     *
     * @param  <T> the class of the objects in the deque
     * @param deque the deque
     * @return the queue
     * @since  1.6
     */
    public static <T> Queue<T> asLifoQueue(Deque<T> deque) {
        return new AsLIFOQueue<>(deque);
    }

    /**
     * @serial include
     */
    static class AsLIFOQueue<E> extends AbstractQueue<E>
        implements Queue<E>, Serializable {
        private static final long serialVersionUID = 1802017725587941708L;
        private final Deque<E> q;
        AsLIFOQueue(Deque<E> q)           { this.q = q; }
        public boolean add(E e)           { q.addFirst(e); return true; }
        public boolean offer(E e)         { return q.offerFirst(e); }
        public E poll()                   { return q.pollFirst(); }
        public E remove()                 { return q.removeFirst(); }
        public E peek()                   { return q.peekFirst(); }
        public E element()                { return q.getFirst(); }
        public void clear()               {        q.clear(); }
        public int size()                 { return q.size(); }
        public boolean isEmpty()          { return q.isEmpty(); }
        public boolean contains(Object o) { return q.contains(o); }
        public boolean remove(Object o)   { return q.remove(o); }
        public Iterator<E> iterator()     { return q.iterator(); }
        public Object[] toArray()         { return q.toArray(); }
        public <T> T[] toArray(T[] a)     { return q.toArray(a); }
        public String toString()          { return q.toString(); }
        public boolean containsAll(Collection<?> c) {return q.containsAll(c);}
        public boolean removeAll(Collection<?> c)   {return q.removeAll(c);}
        public boolean retainAll(Collection<?> c)   {return q.retainAll(c);}
        // We use inherited addAll; forwarding addAll would be wrong

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