/*
    * 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 org.apache.commons.collections4;
  
  import java.lang.reflect.Array;
  import java.lang.reflect.Method;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Comparator;
  import java.util.Dictionary;
  import java.util.Enumeration;
  import java.util.HashSet;
  import java.util.Iterator;
  import java.util.List;
  import java.util.ListIterator;
  import java.util.Map;
  import java.util.Objects;
  import java.util.Set;
  import java.util.Spliterator;
  import java.util.Spliterators;
  import java.util.function.IntFunction;
  import java.util.stream.Stream;
  import java.util.stream.StreamSupport;
  
  import org.apache.commons.collections4.functors.EqualPredicate;
  import org.apache.commons.collections4.iterators.ArrayIterator;
  import org.apache.commons.collections4.iterators.ArrayListIterator;
  import org.apache.commons.collections4.iterators.BoundedIterator;
  import org.apache.commons.collections4.iterators.CollatingIterator;
  import org.apache.commons.collections4.iterators.EmptyIterator;
  import org.apache.commons.collections4.iterators.EmptyListIterator;
  import org.apache.commons.collections4.iterators.EmptyMapIterator;
  import org.apache.commons.collections4.iterators.EmptyOrderedIterator;
  import org.apache.commons.collections4.iterators.EmptyOrderedMapIterator;
  import org.apache.commons.collections4.iterators.EnumerationIterator;
  import org.apache.commons.collections4.iterators.FilterIterator;
  import org.apache.commons.collections4.iterators.FilterListIterator;
  import org.apache.commons.collections4.iterators.IteratorChain;
  import org.apache.commons.collections4.iterators.IteratorEnumeration;
  import org.apache.commons.collections4.iterators.IteratorIterable;
  import org.apache.commons.collections4.iterators.LazyIteratorChain;
  import org.apache.commons.collections4.iterators.ListIteratorWrapper;
  import org.apache.commons.collections4.iterators.LoopingIterator;
  import org.apache.commons.collections4.iterators.LoopingListIterator;
  import org.apache.commons.collections4.iterators.NodeListIterator;
  import org.apache.commons.collections4.iterators.ObjectArrayIterator;
  import org.apache.commons.collections4.iterators.ObjectArrayListIterator;
  import org.apache.commons.collections4.iterators.ObjectGraphIterator;
  import org.apache.commons.collections4.iterators.PeekingIterator;
  import org.apache.commons.collections4.iterators.PushbackIterator;
  import org.apache.commons.collections4.iterators.SingletonIterator;
  import org.apache.commons.collections4.iterators.SingletonListIterator;
  import org.apache.commons.collections4.iterators.SkippingIterator;
  import org.apache.commons.collections4.iterators.TransformIterator;
  import org.apache.commons.collections4.iterators.UnmodifiableIterator;
  import org.apache.commons.collections4.iterators.UnmodifiableListIterator;
  import org.apache.commons.collections4.iterators.UnmodifiableMapIterator;
  import org.apache.commons.collections4.iterators.ZippingIterator;
  import org.w3c.dom.Node;
  import org.w3c.dom.NodeList;
  
  /**
   * Provides static utility methods and decorators for {@link Iterator}
   * instances. The implementations are provided in the iterators subpackage.
   *
   * @since 2.1
   */
  public class IteratorUtils {
      // validation is done in this class in certain cases because the
      // public classes allow invalid states
  
      /**
       * An iterator over no elements.
       */
      @SuppressWarnings("rawtypes")
      public static final ResettableIterator EMPTY_ITERATOR = EmptyIterator.RESETTABLE_INSTANCE;
  
      /**
       * A list iterator over no elements.
       */
      @SuppressWarnings("rawtypes")
      public static final ResettableListIterator EMPTY_LIST_ITERATOR = EmptyListIterator.RESETTABLE_INSTANCE;
  
      /**
       * An ordered iterator over no elements.
      */
     @SuppressWarnings("rawtypes")
     public static final OrderedIterator EMPTY_ORDERED_ITERATOR = EmptyOrderedIterator.INSTANCE;
 
     /**
      * A map iterator over no elements.
      */
     @SuppressWarnings("rawtypes")
     public static final MapIterator EMPTY_MAP_ITERATOR = EmptyMapIterator.INSTANCE;
 
     /**
      * An ordered map iterator over no elements.
      */
     @SuppressWarnings("rawtypes")
     public static final OrderedMapIterator EMPTY_ORDERED_MAP_ITERATOR = EmptyOrderedMapIterator.INSTANCE;
     /**
      * Default delimiter used to delimit elements while converting an Iterator
      * to its String representation.
      */
     private static final String DEFAULT_TOSTRING_DELIMITER = ", ";
 
     private static <E, C extends Collection<E>> C addAll(final Iterator<? extends E> iterator, final C list) {
         Objects.requireNonNull(iterator, "iterator");
         while (iterator.hasNext()) {
             list.add(iterator.next());
         }
         return list;
     }
 
     /**
      * Gets an iterator over an object array.
      *
      * @param <E> the element type
      * @param array  the array over which to iterate
      * @return an iterator over the array
      * @throws NullPointerException if array is null
      */
     public static <E> ResettableIterator<E> arrayIterator(final E... array) {
         return new ObjectArrayIterator<>(array);
     }
 
     /**
      * Gets an iterator over the end part of an object array.
      *
      * @param <E> the element type
      * @param array  the array over which to iterate
      * @param start  the index to start iterating at
      * @return an iterator over part of the array
      * @throws IndexOutOfBoundsException if start is less than zero or greater
      *   than the length of the array
      * @throws NullPointerException if array is null
      */
     public static <E> ResettableIterator<E> arrayIterator(final E[] array, final int start) {
         return new ObjectArrayIterator<>(array, start);
     }
 
     /**
      * Gets an iterator over part of an object array.
      *
      * @param <E> the element type
      * @param array  the array over which to iterate
      * @param start  the index to start iterating at
      * @param end  the index to finish iterating at
      * @return an iterator over part of the array
      * @throws IndexOutOfBoundsException if array bounds are invalid
      * @throws IllegalArgumentException if end is before start
      * @throws NullPointerException if array is null
      */
     public static <E> ResettableIterator<E> arrayIterator(final E[] array, final int start, final int end) {
         return new ObjectArrayIterator<>(array, start, end);
     }
 
     /**
      * Gets an iterator over an object or primitive array.
      * <p>
      * This method will handle primitive arrays as well as object arrays.
      * The primitives will be wrapped in the appropriate wrapper class.
      * </p>
      *
      * @param <E> the element type
      * @param array  the array over which to iterate
      * @return an iterator over the array
      * @throws IllegalArgumentException if the array is not an array
      * @throws NullPointerException if array is null
      */
     public static <E> ResettableIterator<E> arrayIterator(final Object array) {
         return new ArrayIterator<>(array);
     }
 
     /**
      * Gets an iterator over the end part of an object or primitive array.
      * <p>
      * This method will handle primitive arrays as well as object arrays.
      * The primitives will be wrapped in the appropriate wrapper class.
      * </p>
      *
      * @param <E> the element type
      * @param array  the array over which to iterate
      * @param start  the index to start iterating at
      * @return an iterator over part of the array
      * @throws IllegalArgumentException if the array is not an array
      * @throws IndexOutOfBoundsException if start is less than zero or greater
      *   than the length of the array
      * @throws NullPointerException if array is null
      */
     public static <E> ResettableIterator<E> arrayIterator(final Object array, final int start) {
         return new ArrayIterator<>(array, start);
     }
 
     /**
      * Gets an iterator over part of an object or primitive array.
      * <p>
      * This method will handle primitive arrays as well as object arrays.
      * The primitives will be wrapped in the appropriate wrapper class.
      * </p>
      *
      * @param <E> the element type
      * @param array  the array over which to iterate
      * @param start  the index to start iterating at
      * @param end  the index to finish iterating at
      * @return an iterator over part of the array
      * @throws IllegalArgumentException if the array is not an array or end is before start
      * @throws IndexOutOfBoundsException if array bounds are invalid
      * @throws NullPointerException if array is null
      */
     public static <E> ResettableIterator<E> arrayIterator(final Object array, final int start, final int end) {
         return new ArrayIterator<>(array, start, end);
     }
 
     /**
      * Gets a list iterator over an object array.
      *
      * @param <E> the element type
      * @param array  the array over which to iterate
      * @return a list iterator over the array
      * @throws NullPointerException if array is null
      */
     public static <E> ResettableListIterator<E> arrayListIterator(final E... array) {
         return new ObjectArrayListIterator<>(array);
     }
 
     /**
      * Gets a list iterator over the end part of an object array.
      *
      * @param <E> the element type
      * @param array  the array over which to iterate
      * @param start  the index to start iterating at
      * @return a list iterator over part of the array
      * @throws IndexOutOfBoundsException if start is less than zero
      * @throws NullPointerException if array is null
      */
     public static <E> ResettableListIterator<E> arrayListIterator(final E[] array, final int start) {
         return new ObjectArrayListIterator<>(array, start);
     }
 
     /**
      * Gets a list iterator over part of an object array.
      *
      * @param <E> the element type
      * @param array  the array over which to iterate
      * @param start  the index to start iterating at
      * @param end  the index to finish iterating at
      * @return a list iterator over part of the array
      * @throws IndexOutOfBoundsException if array bounds are invalid
      * @throws IllegalArgumentException if end is before start
      * @throws NullPointerException if array is null
      */
     public static <E> ResettableListIterator<E> arrayListIterator(final E[] array, final int start, final int end) {
         return new ObjectArrayListIterator<>(array, start, end);
     }
 
     /**
      * Gets a list iterator over an object or primitive array.
      * <p>
      * This method will handle primitive arrays as well as object arrays.
      * The primitives will be wrapped in the appropriate wrapper class.
      * </p>
      *
      * @param <E> the element type
      * @param array  the array over which to iterate
      * @return a list iterator over the array
      * @throws IllegalArgumentException if the array is not an array
      * @throws NullPointerException if array is null
      */
     public static <E> ResettableListIterator<E> arrayListIterator(final Object array) {
         return new ArrayListIterator<>(array);
     }
 
     /**
      * Gets a list iterator over the end part of an object or primitive array.
      * <p>
      * This method will handle primitive arrays as well as object arrays.
      * The primitives will be wrapped in the appropriate wrapper class.
      * </p>
      *
      * @param <E> the element type
      * @param array  the array over which to iterate
      * @param start  the index to start iterating at
      * @return a list iterator over part of the array
      * @throws IllegalArgumentException if the array is not an array
      * @throws IndexOutOfBoundsException if start is less than zero
      * @throws NullPointerException if array is null
      */
     public static <E> ResettableListIterator<E> arrayListIterator(final Object array, final int start) {
         return new ArrayListIterator<>(array, start);
     }
 
     /**
      * Gets a list iterator over part of an object or primitive array.
      * <p>
      * This method will handle primitive arrays as well as object arrays.
      * The primitives will be wrapped in the appropriate wrapper class.
      * </p>
      *
      * @param <E> the element type
      * @param array  the array over which to iterate
      * @param start  the index to start iterating at
      * @param end  the index to finish iterating at
      * @return a list iterator over part of the array
      * @throws IllegalArgumentException if the array is not an array or end is before start
      * @throws IndexOutOfBoundsException if array bounds are invalid
      * @throws NullPointerException if array is null
      */
     public static <E> ResettableListIterator<E> arrayListIterator(final Object array, final int start, final int end) {
         return new ArrayListIterator<>(array, start, end);
     }
 
     /**
      * Gets an enumeration that wraps an iterator.
      *
      * @param <E> the element type
      * @param iterator  the iterator to use, may not be null
      * @return a new enumeration
      * @throws NullPointerException if iterator is null
      */
     public static <E> Enumeration<E> asEnumeration(final Iterator<? extends E> iterator) {
         return new IteratorEnumeration<>(Objects.requireNonNull(iterator, "iterator"));
     }
 
     /**
      * Gets an {@link Iterable} that wraps an iterator.  The returned {@link Iterable} can be
      * used for a single iteration.
      *
      * @param <E> the element type
      * @param iterator  the iterator to use, may not be null
      * @return a new, single use {@link Iterable}
      * @throws NullPointerException if iterator is null
      */
     public static <E> Iterable<E> asIterable(final Iterator<? extends E> iterator) {
         Objects.requireNonNull(iterator, "iterator");
         return new IteratorIterable<>(iterator, false);
     }
 
     /**
      * Gets an iterator that provides an iterator view of the given enumeration.
      *
      * @param <E> the element type
      * @param enumeration  the enumeration to use, may not be null
      * @return a new iterator
      * @throws NullPointerException if enumeration is null
      */
     public static <E> Iterator<E> asIterator(final Enumeration<? extends E> enumeration) {
         return new EnumerationIterator<>(Objects.requireNonNull(enumeration, "enumeration"));
     }
 
     /**
      * Gets an iterator that provides an iterator view of the given enumeration
      * that will remove elements from the specified collection.
      *
      * @param <E> the element type
      * @param enumeration  the enumeration to use, may not be null
      * @param removeCollection  the collection to remove elements from, may not be null
      * @return a new iterator
      * @throws NullPointerException if enumeration or removeCollection is null
      */
     public static <E> Iterator<E> asIterator(final Enumeration<? extends E> enumeration,
                                              final Collection<? super E> removeCollection) {
         return new EnumerationIterator<>(Objects.requireNonNull(enumeration, "enumeration"),
                 Objects.requireNonNull(removeCollection, "removeCollection"));
     }
 
     /**
      * Gets an iterable that wraps an iterator.  The returned iterable can be
      * used for multiple iterations.
      *
      * @param <E> the element type
      * @param iterator  the iterator to use, may not be null
      * @return a new, multiple use iterable
      * @throws NullPointerException if iterator is null
      */
     public static <E> Iterable<E> asMultipleUseIterable(final Iterator<? extends E> iterator) {
         Objects.requireNonNull(iterator, "iterator");
         return new IteratorIterable<>(iterator, true);
     }
 
     // Bounded
     /**
      * Decorates the specified iterator to return at most the given number
      * of elements.
      *
      * @param <E> the element type
      * @param iterator  the iterator to decorate
      * @param max  the maximum number of elements returned by this iterator
      * @return a new bounded iterator
      * @throws NullPointerException if the iterator is null
      * @throws IllegalArgumentException if max is negative
      * @since 4.1
      */
     public static <E> BoundedIterator<E> boundedIterator(final Iterator<? extends E> iterator, final long max) {
         return boundedIterator(iterator, 0, max);
     }
 
     /**
      * Decorates the specified iterator to return at most the given number
      * of elements, skipping all elements until the iterator reaches the
      * position at {@code offset}.
      * <p>
      * The iterator is immediately advanced until it reaches the position at
      * {@code offset}, incurring O(n) time.
      * </p>
      *
      * @param <E> the element type
      * @param iterator  the iterator to decorate
      * @param offset  the index of the first element of the decorated iterator to return
      * @param max  the maximum number of elements returned by this iterator
      * @return a new bounded iterator
      * @throws NullPointerException if the iterator is null
      * @throws IllegalArgumentException if either offset or max is negative
      * @since 4.1
      */
     public static <E> BoundedIterator<E> boundedIterator(final Iterator<? extends E> iterator,
                                                          final long offset, final long max) {
         return new BoundedIterator<>(iterator, offset, max);
     }
 
     /**
      * Gets an iterator that iterates through a collections of {@link Iterator}s
      * one after another.
      *
      * @param <E> the element type
      * @param iterators  the iterators to use, not null or empty or contain nulls
      * @return a combination iterator over the iterators
      * @throws NullPointerException if iterators collection is null or contains a null
      * @throws ClassCastException if the iterators collection contains the wrong object type
      */
     public static <E> Iterator<E> chainedIterator(final Collection<? extends Iterator<? extends E>> iterators) {
         return new IteratorChain<>(iterators);
     }
 
     /**
      * Gets an iterator that iterates through an array of {@link Iterator}s
      * one after another.
      *
      * @param <E> the element type
      * @param iterators  the iterators to use, not null or empty or contain nulls
      * @return a combination iterator over the iterators
      * @throws NullPointerException if iterators array is null or contains a null
      */
     public static <E> Iterator<E> chainedIterator(final Iterator<? extends E>... iterators) {
         return new IteratorChain<>(iterators);
     }
 
     /**
      * Gets an iterator that iterates through two {@link Iterator}s
      * one after another.
      *
      * @param <E> the element type
      * @param iterator1  the first iterator to use, not null
      * @param iterator2  the second iterator to use, not null
      * @return a combination iterator over the iterators
      * @throws NullPointerException if either iterator is null
      */
     public static <E> Iterator<E> chainedIterator(final Iterator<? extends E> iterator1,
                                                   final Iterator<? extends E> iterator2) {
         // keep a version with two iterators to avoid the following warning in client code (Java 5 & 6)
         // "A generic array of E is created for a varargs parameter"
         return new IteratorChain<>(iterator1, iterator2);
     }
 
     /**
      * Gets an iterator that iterates through an {@link Iterator} of Iterators one after another.
      *
      * @param <E>       the element type
      * @param iterators the iterators to use, not null or empty or contain nulls
      * @return a combination iterator over the iterators
      * @throws NullPointerException if iterators collection is null or contains a null
      * @throws ClassCastException   if the iterators collection contains the wrong object type
      * @since 4.5.0-M3
      */
     public static <E> Iterator<E> chainedIterator(final Iterator<? extends Iterator<? extends E>> iterators) {
         return new LazyIteratorChain<E>() {
 
             @Override
             protected Iterator<? extends E> nextIterator(final int count) {
                 return iterators.hasNext() ? iterators.next() : null;
             }
 
         };
     }
 
     /**
      * Gets an iterator that provides an ordered iteration over the elements
      * contained in a collection of {@link Iterator}s.
      * <p>
      * Given two ordered {@link Iterator}s {@code A} and {@code B},
      * the {@link Iterator#next()} method will return the lesser of
      * {@code A.next()} and {@code B.next()} and so on.
      * </p>
      * <p>
      * The comparator is optional. If null is specified then natural order is used.
      * </p>
      *
      * @param <E> the element type
      * @param comparator  the comparator to use, may be null for natural order
      * @param iterators  the iterators to use, not null or empty or contain nulls
      * @return a combination iterator over the iterators
      * @throws NullPointerException if iterators collection is null or contains a null
      * @throws ClassCastException if the iterators collection contains the wrong object type
      */
     public static <E> Iterator<E> collatedIterator(final Comparator<? super E> comparator,
                                                    final Collection<Iterator<? extends E>> iterators) {
         @SuppressWarnings("unchecked")
         final Comparator<E> comp =
             comparator == null ? ComparatorUtils.NATURAL_COMPARATOR : (Comparator<E>) comparator;
         return new CollatingIterator<>(comp, iterators);
     }
 
     /**
      * Gets an iterator that provides an ordered iteration over the elements
      * contained in an array of {@link Iterator}s.
      * <p>
      * Given two ordered {@link Iterator}s {@code A} and {@code B},
      * the {@link Iterator#next()} method will return the lesser of
      * {@code A.next()} and {@code B.next()} and so on.
      * </p>
      * <p>
      * The comparator is optional. If null is specified then natural order is used.
      * </p>
      *
      * @param <E> the element type
      * @param comparator  the comparator to use, may be null for natural order
      * @param iterators  the iterators to use, not null or empty or contain nulls
      * @return a combination iterator over the iterators
      * @throws NullPointerException if iterators array is null or contains a null value
      */
     public static <E> Iterator<E> collatedIterator(final Comparator<? super E> comparator,
                                                    final Iterator<? extends E>... iterators) {
         @SuppressWarnings("unchecked")
         final Comparator<E> comp =
             comparator == null ? ComparatorUtils.NATURAL_COMPARATOR : (Comparator<E>) comparator;
         return new CollatingIterator<>(comp, iterators);
     }
 
     /**
      * Gets an iterator that provides an ordered iteration over the elements
      * contained in a collection of ordered {@link Iterator}s.
      * <p>
      * Given two ordered {@link Iterator}s {@code A} and {@code B},
      * the {@link Iterator#next()} method will return the lesser of
      * {@code A.next()} and {@code B.next()}.
      * </p>
      * <p>
      * The comparator is optional. If null is specified then natural order is used.
      * </p>
      *
      * @param <E> the element type
      * @param comparator  the comparator to use, may be null for natural order
      * @param iterator1  the first iterators to use, not null
      * @param iterator2  the first iterators to use, not null
      * @return a combination iterator over the iterators
      * @throws NullPointerException if either iterator is null
      */
     public static <E> Iterator<E> collatedIterator(final Comparator<? super E> comparator,
                                                    final Iterator<? extends E> iterator1,
                                                    final Iterator<? extends E> iterator2) {
         @SuppressWarnings("unchecked")
         final Comparator<E> comp =
             comparator == null ? ComparatorUtils.NATURAL_COMPARATOR : (Comparator<E>) comparator;
         return new CollatingIterator<>(comp, iterator1, iterator2);
     }
 
     /**
      * Checks if the object is contained in the given iterator.
      * <p>
      * A {@code null} or empty iterator returns false.
      * </p>
      *
      * @param <E> the type of object the {@link Iterator} contains
      * @param iterator  the iterator to check, may be null
      * @param object  the object to check
      * @return true if the object is contained in the iterator, false otherwise
      * @since 4.1
      */
     public static <E> boolean contains(final Iterator<E> iterator, final Object object) {
         return matchesAny(iterator, EqualPredicate.equalPredicate(object));
     }
 
     /**
      * Gets an empty iterator.
      * <p>
      * This iterator is a valid iterator object that will iterate over nothing.
      * </p>
      *
      * @param <E> the element type
      * @return an iterator over nothing
      */
     public static <E> ResettableIterator<E> emptyIterator() {
         return EmptyIterator.<E>resettableEmptyIterator();
     }
 
     /**
      * Gets an empty list iterator.
      * <p>
      * This iterator is a valid list iterator object that will iterate
      * over nothing.
      * </p>
      *
      * @param <E> the element type
      * @return a list iterator over nothing
      */
     public static <E> ResettableListIterator<E> emptyListIterator() {
         return EmptyListIterator.<E>resettableEmptyListIterator();
     }
 
     /**
      * Gets an empty map iterator.
      * <p>
      * This iterator is a valid map iterator object that will iterate
      * over nothing.
      * </p>
      *
      * @param <K> the key type
      * @param <V> the value type
      * @return a map iterator over nothing
      */
     public static <K, V> MapIterator<K, V> emptyMapIterator() {
         return EmptyMapIterator.<K, V>emptyMapIterator();
     }
 
     /**
      * Gets an empty ordered iterator.
      * <p>
      * This iterator is a valid iterator object that will iterate
      * over nothing.
      * </p>
      *
      * @param <E> the element type
      * @return an ordered iterator over nothing
      */
     public static <E> OrderedIterator<E> emptyOrderedIterator() {
         return EmptyOrderedIterator.<E>emptyOrderedIterator();
     }
 
     /**
      * Gets an empty ordered map iterator.
      * <p>
      * This iterator is a valid map iterator object that will iterate
      * over nothing.
      * </p>
      *
      * @param <K> the key type
      * @param <V> the value type
      * @return a map iterator over nothing
      */
     public static <K, V> OrderedMapIterator<K, V> emptyOrderedMapIterator() {
         return EmptyOrderedMapIterator.<K, V>emptyOrderedMapIterator();
     }
 
     /**
      * Gets an iterator that filters another iterator.
      * <p>
      * The returned iterator will only return objects that match the specified
      * filtering predicate.
      * </p>
      *
      * @param <E> the element type
      * @param iterator  the iterator to use, not null
      * @param predicate  the predicate to use as a filter, not null
      * @return a new filtered iterator
      * @throws NullPointerException if either parameter is null
      */
     public static <E> Iterator<E> filteredIterator(final Iterator<? extends E> iterator,
                                                    final Predicate<? super E> predicate) {
         Objects.requireNonNull(iterator, "iterator");
         Objects.requireNonNull(predicate, "predicate");
         return new FilterIterator<>(iterator, predicate);
     }
 
     /**
      * Gets a list iterator that filters another list iterator.
      * <p>
      * The returned iterator will only return objects that match the specified
      * filtering predicate.
      * </p>
      *
      * @param <E> the element type
      * @param listIterator  the list iterator to use, not null
      * @param predicate  the predicate to use as a filter, not null
      * @return a new filtered iterator
      * @throws NullPointerException if either parameter is null
      */
     public static <E> ListIterator<E> filteredListIterator(final ListIterator<? extends E> listIterator,
             final Predicate<? super E> predicate) {
 
         Objects.requireNonNull(listIterator, "listIterator");
         Objects.requireNonNull(predicate, "predicate");
         return new FilterListIterator<>(listIterator, predicate);
     }
 
     /**
      * Finds the first element in the given iterator which matches the given predicate.
      * <p>
      * A {@code null} or empty iterator returns null.
      * </p>
      *
      * @param <E> the element type
      * @param iterator  the iterator to search, may be null
      * @param predicate  the predicate to use, must not be null
      * @return the first element of the iterator which matches the predicate or null if none could be found
      * @throws NullPointerException if predicate is null
      * @since 4.1
      */
     public static <E> E find(final Iterator<E> iterator, final Predicate<? super E> predicate) {
         return find(iterator, predicate, null);
     }
 
     /**
      * Finds the first element in the given iterator which matches the given predicate.
      * <p>
      * A {@code null} or empty iterator returns {@code defaultValue}.
      * </p>
      *
      * @param <E>          the element type.
      * @param iterator     the iterator to search, may be null.
      * @param predicate    the predicate to use, must not be null.
      * @param defaultValue the default value, may be null.
      * @return the first element of the iterator which matches the predicate or null if none could be found.
      * @throws NullPointerException if predicate is null.
      */
     private static <E> E find(final Iterator<E> iterator, final Predicate<? super E> predicate, final E defaultValue) {
         Objects.requireNonNull(predicate, "predicate");
         if (iterator != null) {
             while (iterator.hasNext()) {
                 final E element = iterator.next();
                 if (predicate.test(element)) {
                     return element;
                 }
             }
         }
         return defaultValue;
     }
 
     /**
      * Shortcut for {@code get(iterator, 0)}.
      * <p>
      * Returns the {@code first} value in {@link Iterator}, throwing
      * {@code IndexOutOfBoundsException} if there is no such element.
      * </p>
      * <p>
      * The Iterator is advanced to {@code 0} (or to the end, if
      * {@code 0} exceeds the number of entries) as a side effect of this method.
      * </p>
      * @param <E> the type of object in the {@link Iterator}
      * @param iterator the iterator to get a value from
      * @return the first object
      * @throws IndexOutOfBoundsException if the request is invalid
      * @since 4.2
      */
     public static <E> E first(final Iterator<E> iterator) {
         return get(iterator, 0);
     }
 
     /**
      * Applies the closure to each element of the provided iterator.
      *
      * @param <E> the element type
      * @param iterator  the iterator to use, may be null
      * @param closure  the closure to apply to each element, may not be null
      * @throws NullPointerException if closure is null
      * @since 4.1
      */
     public static <E> void forEach(final Iterator<E> iterator, final Closure<? super E> closure) {
         Objects.requireNonNull(closure, "closure");
         if (iterator != null) {
             while (iterator.hasNext()) {
                 closure.accept(iterator.next());
             }
         }
     }
 
     /**
      * Executes the given closure on each but the last element in the iterator.
      * <p>
      * If the input iterator is null no change is made.
      * </p>
      *
      * @param <E> the type of object the {@link Iterator} contains
      * @param iterator  the iterator to get the input from, may be null
      * @param closure  the closure to perform, may not be null
      * @return the last element in the iterator, or null if iterator is null or empty
      * @throws NullPointerException if closure is null
      * @since 4.1
      */
     public static <E> E forEachButLast(final Iterator<E> iterator, final Closure<? super E> closure) {
         Objects.requireNonNull(closure, "closure");
 
         if (iterator != null) {
             while (iterator.hasNext()) {
                 final E element = iterator.next();
                 if (!iterator.hasNext()) {
                     return element;
                 }
                 closure.accept(element);
             }
         }
         return null;
     }
 
     /**
      * Gets the {@code index}-th value in {@link Iterator}, throwing {@code IndexOutOfBoundsException} if there is no such element.
      * <p>
      * The Iterator is advanced to {@code index} (or to the end, if {@code index} exceeds the number of entries) as a side effect of this method.
      * </p>
      *
      * @param <E>      the type of object in the {@link Iterator}.
      * @param iterator the iterator to get a value from.
      * @param index    the index to get, 0-based.
      * @return the object at the specified index.
      * @throws IndexOutOfBoundsException if the index is invalid.
      * @since 4.1
      */
     public static <E> E get(final Iterator<E> iterator, final int index) {
         return get(iterator, index, ioob -> {
             throw new IndexOutOfBoundsException("Entry does not exist: " + ioob);
         });
     }
 
     /**
      * Gets the {@code index}-th value in {@link Iterator}, throwing {@code IndexOutOfBoundsException} if there is no such element.
      * <p>
      * The Iterator is advanced to {@code index} (or to the end, if {@code index} exceeds the number of entries) as a side effect of this method.
      * </p>
      *
      * @param <E>             the type of object in the {@link Iterator}
      * @param iterator        the iterator to get a value from
      * @param index           the index to get, 0-based.
      * @param defaultSupplier supplies a default value at an index.
      * @return the object at the specified index
      * @throws IndexOutOfBoundsException if the index is invalid
      */
     static <E> E get(final Iterator<E> iterator, final int index, final IntFunction<E> defaultSupplier) {
         int i = index;
         CollectionUtils.checkIndexBounds(i);
         while (iterator.hasNext()) {
             i--;
             if (i == -1) {
                 return iterator.next();
             }
             iterator.next();
         }
         return defaultSupplier.apply(i);
     }
 
     /**
      * Gets a suitable Iterator for the given object.
      * <p>
      * This method can handle objects as follows
      * </p>
      * <ul>
      * <li>null - empty iterator
      * <li>Iterator - returned directly
      * <li>Enumeration - wrapped
      * <li>Collection - iterator from collection returned
      * <li>Map - values iterator returned
      * <li>Dictionary - values (elements) enumeration returned as iterator
      * <li>array - iterator over array returned
      * <li>object with iterator() public method accessed by reflection
      * <li>object - singleton iterator
      * <li>NodeList - iterator over the list
      * <li>Node - iterator over the child nodes
      * </ul>
      *
      * @param obj  the object to convert to an iterator
      * @return a suitable iterator, never null
      */
     public static Iterator<?> getIterator(final Object obj) {
         if (obj == null) {
             return emptyIterator();
         }
         if (obj instanceof Iterator) {
             return (Iterator<?>) obj;
         }
         if (obj instanceof Iterable) {
             return ((Iterable<?>) obj).iterator();
         }
         if (obj instanceof Object[]) {
             return new ObjectArrayIterator<>((Object[]) obj);
         }
         if (obj instanceof Enumeration) {
             return new EnumerationIterator<>((Enumeration<?>) obj);
         }
         if (obj instanceof Map) {
             return ((Map<?, ?>) obj).values().iterator();
         }
         if (obj instanceof NodeList) {
             return new NodeListIterator((NodeList) obj);
         }
         if (obj instanceof Node) {
             return new NodeListIterator((Node) obj);
         }
         if (obj instanceof Dictionary) {
             return new EnumerationIterator<>(((Dictionary<?, ?>) obj).elements());
         }
         if (obj.getClass().isArray()) {
             return new ArrayIterator<>(obj);
         }
         try {
             final Method method = obj.getClass().getMethod("iterator", (Class[]) null);
             if (Iterator.class.isAssignableFrom(method.getReturnType())) {
                 final Iterator<?> it = (Iterator<?>) method.invoke(obj, (Object[]) null);
                 if (it != null) {
                     return it;
                 }
             }
         } catch (final RuntimeException | ReflectiveOperationException ignore) { // NOPMD
             // ignore
         }
         return singletonIterator(obj);
     }
 
     /**
      * Returns the index of the first element in the specified iterator that
      * matches the given predicate.
      * <p>
      * A {@code null} or empty iterator returns -1.
      * </p>
      *
      * @param <E> the element type
      * @param iterator  the iterator to search, may be null
      * @param predicate  the predicate to use, may not be null
      * @return the index of the first element which matches the predicate or -1 if none matches
      * @throws NullPointerException if predicate is null
      * @since 4.1
      */
     public static <E> int indexOf(final Iterator<E> iterator, final Predicate<? super E> predicate) {
         Objects.requireNonNull(predicate, "predicate");
 
         if (iterator != null) {
             for (int index = 0; iterator.hasNext(); index++) {
                 final E element = iterator.next();
                 if (predicate.test(element)) {
                     return index;
                 }
             }
         }
         return CollectionUtils.INDEX_NOT_FOUND;
     }
 
     /**
      * Checks if the given iterator is empty.
      * <p>
      * A {@code null} or empty iterator returns true.
      * </p>
      *
      * @param iterator  the {@link Iterator} to use, may be null
      * @return true if the iterator is exhausted or null, false otherwise
      * @since 4.1
      */
     public static boolean isEmpty(final Iterator<?> iterator) {
         return iterator == null || !iterator.hasNext();
     }
 
     /**
      * Gets an iterator that loops continuously over the supplied collection.
      * <p>
      * The iterator will only stop looping if the remove method is called
      * enough times to empty the collection, or if the collection is empty
      * to start with.
      * </p>
      *
      * @param <E> the element type
      * @param collection  the collection to iterate over, not null
      * @return a new looping iterator
      * @throws NullPointerException if the collection is null
      */
     public static <E> ResettableIterator<E> loopingIterator(final Collection<? extends E> collection) {
         return new LoopingIterator<>(Objects.requireNonNull(collection, "collection"));
     }
 
     /**
      * Gets an iterator that loops continuously over the supplied list.
      * <p>
      * The iterator will only stop looping if the remove method is called
      * enough times to empty the list, or if the list is empty to start with.
      * </p>
      *
      * @param <E> the element type
      * @param list  the list to iterate over, not null
      * @return a new looping iterator
      * @throws NullPointerException if the list is null
      * @since 3.2
      */
     public static <E> ResettableListIterator<E> loopingListIterator(final List<E> list) {
         return new LoopingListIterator<>(Objects.requireNonNull(list, "list"));
     }
 
     /**
      * Answers true if a predicate is true for every element of an iterator.
      * <p>
      * A {@code null} or empty iterator returns true.
      * </p>
      *
      * @param <E> the type of object the {@link Iterator} contains
      * @param iterator  the {@link Iterator} to use, may be null
      * @param predicate  the predicate to use, may not be null
      * @return true if every element of the collection matches the predicate or if the
      *   collection is empty, false otherwise
      * @throws NullPointerException if predicate is null
      * @since 4.1
      */
     public static <E> boolean matchesAll(final Iterator<E> iterator, final Predicate<? super E> predicate) {
         Objects.requireNonNull(predicate, "predicate");
 
         if (iterator != null) {
             while (iterator.hasNext()) {
                 final E element = iterator.next();
                 if (!predicate.test(element)) {
                     return false;
                 }
             }
         }
         return true;
     }
 
     /**
      * Answers true if a predicate is true for any element of the iterator.
      * <p>
      * A {@code null} or empty iterator returns false.
      * </p>
      *
      * @param <E> the type of object the {@link Iterator} contains
      * @param iterator  the {@link Iterator} to use, may be null
      * @param predicate  the predicate to use, may not be null
      * @return true if any element of the collection matches the predicate, false otherwise
      * @throws NullPointerException if predicate is null
      * @since 4.1
      */
     public static <E> boolean matchesAny(final Iterator<E> iterator, final Predicate<? super E> predicate) {
         return indexOf(iterator, predicate) != -1;
     }
 
     /**
      * Gets an {@link Iterator} that wraps the specified node's childNodes.
      * The returned {@link Iterator} can be used for a single iteration.
      * <p>
      * Convenience method, allows easy iteration over NodeLists:
      * </p>
      * <pre>
      *   Iterator&lt;Node&gt; iterator = IteratorUtils.nodeListIterator(node);
      *   for (Node childNode : IteratorUtils.asIterable(iterator)) {
      *     ...
      *   }
      * </pre>
      *
      * @param node  the node to use, may not be null
      * @return a new, single use {@link Iterator}
      * @throws NullPointerException if node is null
      * @since 4.0
      */
     public static NodeListIterator nodeListIterator(final Node node) {
         return new NodeListIterator(Objects.requireNonNull(node, "node"));
     }
 
     /**
      * Gets an {@link Iterator} that wraps the specified {@link NodeList}.
      * The returned {@link Iterator} can be used for a single iteration.
      *
      * @param nodeList  the node list to use, may not be null
      * @return a new, single use {@link Iterator}
      * @throws NullPointerException if nodeList is null
      * @since 4.0
      */
     public static NodeListIterator nodeListIterator(final NodeList nodeList) {
         return new NodeListIterator(Objects.requireNonNull(nodeList, "nodeList"));
     }
 
     /**
      * Gets an iterator that operates over an object graph.
      * <p>
      * This iterator can extract multiple objects from a complex tree-like object graph.
      * The iteration starts from a single root object.
      * It uses a {@code Transformer} to extract the iterators and elements.
      * Its main benefit is that no intermediate {@code List} is created.
      * </p>
      * <p>
      * For example, consider an object graph:
      * </p>
      * <pre>
      *                 |- Branch -- Leaf
      *                 |         \- Leaf
      *         |- Tree |         /- Leaf
      *         |       |- Branch -- Leaf
      *  Forest |                 \- Leaf
      *         |       |- Branch -- Leaf
      *         |       |         \- Leaf
      *         |- Tree |         /- Leaf
      *                 |- Branch -- Leaf
      *                 |- Branch -- Leaf</pre>
      * <p>
      * The following {@code Transformer}, used in this class, will extract all
      * the Leaf objects without creating a combined intermediate list:
      * </p>
      * <pre>
      * public Object transform(Object input) {
      *   if (input instanceof Forest) {
      *     return ((Forest) input).treeIterator();
      *   }
      *   if (input instanceof Tree) {
      *     return ((Tree) input).branchIterator();
      *   }
      *   if (input instanceof Branch) {
      *     return ((Branch) input).leafIterator();
      *   }
      *   if (input instanceof Leaf) {
      *     return input;
      *   }
      *   throw new ClassCastException();
      * }</pre>
      * <p>
      * Internally, iteration starts from the root object. When next is called,
      * the transformer is called to examine the object. The transformer will return
      * either an iterator or an object. If the object is an Iterator, the next element
      * from that iterator is obtained and the process repeats. If the element is an object
      * it is returned.
      * </p>
      * <p>
      * Under many circumstances, linking Iterators together in this manner is
      * more efficient (and convenient) than using nested for loops to extract a list.
      * </p>
      *
      * @param <E> the element type
      * @param root  the root object to start iterating from, null results in an empty iterator
      * @param transformer  the transformer to use, see above, null uses no effect transformer
      * @return a new object graph iterator
      * @since 3.1
      */
     public static <E> Iterator<E> objectGraphIterator(final E root,
             final Transformer<? super E, ? extends E> transformer) {
         return new ObjectGraphIterator<>(root, transformer);
     }
 
     /**
      * Gets an iterator that supports one-element lookahead.
      *
      * @param <E> the element type
      * @param iterator  the iterator to decorate, not null
      * @return a peeking iterator
      * @throws NullPointerException if the iterator is null
      * @since 4.0
      */
     public static <E> Iterator<E> peekingIterator(final Iterator<? extends E> iterator) {
         return PeekingIterator.peekingIterator(iterator);
     }
 
     /**
      * Gets an iterator that supports pushback of elements.
      *
      * @param <E> the element type
      * @param iterator  the iterator to decorate, not null
      * @return a pushback iterator
      * @throws NullPointerException if the iterator is null
      * @since 4.0
      */
     public static <E> Iterator<E> pushbackIterator(final Iterator<? extends E> iterator) {
         return PushbackIterator.pushbackIterator(iterator);
     }
 
     /**
      * Gets a singleton iterator.
      * <p>
      * This iterator is a valid iterator object that will iterate over
      * the specified object.
      * </p>
      *
      * @param <E> the element type
      * @param object  the single object over which to iterate
      * @return a singleton iterator over the object
      */
     public static <E> ResettableIterator<E> singletonIterator(final E object) {
         return new SingletonIterator<>(object);
     }
 
     /**
      * Gets a singleton list iterator.
      * <p>
      * This iterator is a valid list iterator object that will iterate over
      * the specified object.
      * </p>
      *
      * @param <E> the element type
      * @param object  the single object over which to iterate
      * @return a singleton list iterator over the object
      */
     public static <E> ListIterator<E> singletonListIterator(final E object) {
         return new SingletonListIterator<>(object);
     }
 
     /**
      * Returns the number of elements contained in the given iterator.
      * <p>
      * A {@code null} or empty iterator returns {@code 0}.
      * </p>
      *
      * @param iterator  the iterator to check, may be null
      * @return the number of elements contained in the iterator
      * @since 4.1
      */
     public static int size(final Iterator<?> iterator) {
         int size = 0;
         if (iterator != null) {
             while (iterator.hasNext()) {
                 iterator.next();
                 size++;
             }
         }
         return size;
     }
 
     /**
      * Decorates the specified iterator to skip the first N elements.
      *
      * @param <E> the element type
      * @param iterator  the iterator to decorate
      * @param offset  the first number of elements to skip
      * @return a new skipping iterator
      * @throws NullPointerException if the iterator is null
      * @throws IllegalArgumentException if offset is negative
      * @since 4.1
      */
     public static <E> SkippingIterator<E> skippingIterator(final Iterator<E> iterator, final long offset) {
         return new SkippingIterator<>(iterator, offset);
     }
 
     /**
      * Creates a stream on the given Iterable.
      *
      * @param <E> the type of elements in the Iterable.
      * @param iterable the Iterable to stream or null.
      * @return a new Stream or {@link Stream#empty()} if the Iterable is null.
      * @since 4.5.0-M3
      */
     public static <E> Stream<E> stream(final Iterable<E> iterable) {
         return iterable == null ? Stream.empty() : StreamSupport.stream(iterable.spliterator(), false);
     }
 
     /**
      * Creates a stream on the given Iterator.
      *
      * @param <E> the type of elements in the Iterator.
      * @param iterator the Iterator to stream or null.
      * @return a new Stream or {@link Stream#empty()} if the Iterator is null.
      * @since 4.5.0-M3
      */
     public static <E> Stream<E> stream(final Iterator<E> iterator) {
         return iterator == null ? Stream.empty() : StreamSupport.stream(Spliterators.spliteratorUnknownSize(iterator, Spliterator.ORDERED), false);
     }
 
     /**
      * Gets an array based on an iterator.
      * <p>
      * As the wrapped Iterator is traversed, an ArrayList of its values is
      * created. At the end, this is converted to an array.
      * </p>
      *
      * @param iterator  the iterator to use, not null
      * @return an array of the iterator contents
      * @throws NullPointerException if iterator parameter is null
      */
     public static Object[] toArray(final Iterator<?> iterator) {
         Objects.requireNonNull(iterator, "iterator");
         final List<?> list = toList(iterator, 100);
         return list.toArray();
     }
 
     /**
      * Gets an array based on an iterator.
      * <p>
      * As the wrapped Iterator is traversed, an ArrayList of its values is
      * created. At the end, this is converted to an array.
      * </p>
      *
      * @param <E> the element type
      * @param iterator  the iterator to use, not null
      * @param arrayClass  the class of array to create
      * @return an array of the iterator contents
      * @throws NullPointerException if iterator parameter or arrayClass is null
      * @throws ArrayStoreException if the arrayClass is invalid
      */
     public static <E> E[] toArray(final Iterator<? extends E> iterator, final Class<E> arrayClass) {
         Objects.requireNonNull(iterator, "iterator");
         Objects.requireNonNull(arrayClass, "arrayClass");
         final List<E> list = toList(iterator, 100);
         @SuppressWarnings("unchecked")
         final E[] array = (E[]) Array.newInstance(arrayClass, list.size());
         return list.toArray(array);
     }
 
     /**
      * Gets a list based on an iterator.
      * <p>
      * As the wrapped Iterator is traversed, an ArrayList of its values is
      * created. At the end, the list is returned.
      * </p>
      *
      * @param <E> the element type
      * @param iterator  the iterator to use, not null
      * @return a list of the iterator contents
      * @throws NullPointerException if iterator parameter is null
      */
     public static <E> List<E> toList(final Iterator<? extends E> iterator) {
         return toList(iterator, 10);
     }
 
     /**
      * Gets a list based on an iterator.
      * <p>
      * As the wrapped Iterator is traversed, an ArrayList of its values is
      * created. At the end, the list is returned.
      * </p>
      *
      * @param <E> the element type
      * @param iterator  the iterator to use, not null
      * @param estimatedSize  the initial size of the ArrayList
      * @return a list of the iterator contents
      * @throws NullPointerException if iterator parameter is null
      * @throws IllegalArgumentException if the size is less than 1
      */
     public static <E> List<E> toList(final Iterator<? extends E> iterator, final int estimatedSize) {
         if (estimatedSize < 1) {
             throw new IllegalArgumentException("Estimated size must be greater than 0");
         }
         return addAll(iterator, new ArrayList<>(estimatedSize));
     }
 
     /**
      * Gets a list iterator based on a simple iterator.
      * <p>
      * As the wrapped Iterator is traversed, a LinkedList of its values is
      * cached, permitting all required operations of ListIterator.
      * </p>
      *
      * @param <E> the element type
      * @param iterator  the iterator to use, may not be null
      * @return a new iterator
      * @throws NullPointerException if iterator parameter is null
      */
     public static <E> ListIterator<E> toListIterator(final Iterator<? extends E> iterator) {
         Objects.requireNonNull(iterator, "iterator");
         return new ListIteratorWrapper<>(iterator);
     }
 
     /**
      * Gets a set based on an iterator.
      * <p>
      * As the wrapped Iterator is traversed, a HashSet of its values is
      * created. At the end, the set is returned.
      * </p>
      *
      * @param <E> the element type
      * @param iterator  the iterator to use, not null
      * @return a set of the iterator contents
      * @throws NullPointerException if iterator parameter is null
      * @since 4.5.0-M4
      */
     public static <E> Set<E> toSet(final Iterator<? extends E> iterator) {
         return toSet(iterator, 10);
     }
 
     /**
      * Gets a set based on an iterator.
      * <p>
      * As the wrapped Iterator is traversed, a HashSet of its values is
      * created. At the end, the set is returned.
      * </p>
      *
      * @param <E> the element type
      * @param iterator  the iterator to use, not null
      * @param estimatedSize  the initial size of the HashSet
      * @return a list of the iterator contents
      * @throws NullPointerException if iterator parameter is null
      * @throws IllegalArgumentException if the size is less than 1
      * @since 4.5.0-M4
      */
     public static <E> Set<E> toSet(final Iterator<? extends E> iterator, final int estimatedSize) {
         if (estimatedSize < 1) {
             throw new IllegalArgumentException("Estimated size must be greater than 0");
         }
         return addAll(iterator, new HashSet<>(estimatedSize));
     }
 
     /**
      * Returns a string representation of the elements of the specified iterator.
      * <p>
      * The string representation consists of a list of the iterator's elements,
      * enclosed in square brackets ({@code "[]"}). Adjacent elements are separated
      * by the characters {@code ", "} (a comma followed by a space). Elements are
      * converted to strings as by {@code String.valueOf(Object)}.
      * </p>
      *
      * @param <E> the element type
      * @param iterator  the iterator to convert to a string, may be null
      * @return a string representation of {@code iterator}
      * @since 4.1
      */
     public static <E> String toString(final Iterator<E> iterator) {
         return toString(iterator, TransformerUtils.stringValueTransformer(),
                         DEFAULT_TOSTRING_DELIMITER, CollectionUtils.DEFAULT_TOSTRING_PREFIX,
                 CollectionUtils.DEFAULT_TOSTRING_SUFFIX);
     }
 
     /**
      * Returns a string representation of the elements of the specified iterator.
      * <p>
      * The string representation consists of a list of the iterable's elements,
      * enclosed in square brackets ({@code "[]"}). Adjacent elements are separated
      * by the characters {@code ", "} (a comma followed by a space). Elements are
      * converted to strings as by using the provided {@code transformer}.
      * </p>
      *
      * @param <E> the element type
      * @param iterator  the iterator to convert to a string, may be null
      * @param transformer  the transformer used to get a string representation of an element
      * @return a string representation of {@code iterator}
      * @throws NullPointerException if {@code transformer} is null
      * @since 4.1
      */
     public static <E> String toString(final Iterator<E> iterator,
                                       final Transformer<? super E, String> transformer) {
         return toString(iterator, transformer, DEFAULT_TOSTRING_DELIMITER,
                 CollectionUtils.DEFAULT_TOSTRING_PREFIX, CollectionUtils.DEFAULT_TOSTRING_SUFFIX);
     }
 
     /**
      * Returns a string representation of the elements of the specified iterator.
      * <p>
      * The string representation consists of a list of the iterator's elements,
      * enclosed by the provided {@code prefix} and {@code suffix}. Adjacent elements
      * are separated by the provided {@code delimiter}. Elements are converted to
      * strings as by using the provided {@code transformer}.
      * </p>
      *
      * @param <E> the element type
      * @param iterator  the iterator to convert to a string, may be null
      * @param transformer  the transformer used to get a string representation of an element
      * @param delimiter  the string to delimit elements
      * @param prefix  the prefix, prepended to the string representation
      * @param suffix  the suffix, appended to the string representation
      * @return a string representation of {@code iterator}
      * @throws NullPointerException if either transformer, delimiter, prefix or suffix is null
      * @since 4.1
      */
     public static <E> String toString(final Iterator<E> iterator,
                                       final Transformer<? super E, String> transformer,
                                       final String delimiter,
                                       final String prefix,
                                       final String suffix) {
         Objects.requireNonNull(transformer, "transformer");
         Objects.requireNonNull(delimiter, "delimiter");
         Objects.requireNonNull(prefix, "prefix");
         Objects.requireNonNull(suffix, "suffix");
         final StringBuilder stringBuilder = new StringBuilder(prefix);
         if (iterator != null) {
             while (iterator.hasNext()) {
                 final E element = iterator.next();
                 stringBuilder.append(transformer.apply(element));
                 stringBuilder.append(delimiter);
             }
             if (stringBuilder.length() > prefix.length()) {
                 stringBuilder.setLength(stringBuilder.length() - delimiter.length());
             }
         }
         stringBuilder.append(suffix);
         return stringBuilder.toString();
     }
 
     /**
      * Gets an iterator that transforms the elements of another iterator.
      * <p>
      * The transformation occurs during the next() method and the underlying
      * iterator is unaffected by the transformation.
      * </p>
      *
      * @param <I> the input type
      * @param <O> the output type
      * @param iterator  the iterator to use, not null
      * @param transformer  the transform to use, not null
      * @return a new transforming iterator
      * @throws NullPointerException if either parameter is null
      */
     public static <I, O> Iterator<O> transformedIterator(final Iterator<? extends I> iterator,
             final Transformer<? super I, ? extends O> transformer) {
 
         Objects.requireNonNull(iterator, "iterator");
         Objects.requireNonNull(transformer, "transformer");
         return new TransformIterator<>(iterator, transformer);
     }
 
     /**
      * Gets an immutable version of an {@link Iterator}. The returned object
      * will always throw an {@link UnsupportedOperationException} for
      * the {@link Iterator#remove} method.
      *
      * @param <E> the element type
      * @param iterator  the iterator to make immutable
      * @return an immutable version of the iterator
      */
     public static <E> Iterator<E> unmodifiableIterator(final Iterator<E> iterator) {
         return UnmodifiableIterator.unmodifiableIterator(iterator);
     }
 
     /**
      * Gets an immutable version of a {@link ListIterator}. The returned object
      * will always throw an {@link UnsupportedOperationException} for
      * the {@link Iterator#remove}, {@link ListIterator#add} and
      * {@link ListIterator#set} methods.
      *
      * @param <E> the element type
      * @param listIterator  the iterator to make immutable
      * @return an immutable version of the iterator
      */
     public static <E> ListIterator<E> unmodifiableListIterator(final ListIterator<E> listIterator) {
         return UnmodifiableListIterator.unmodifiableListIterator(listIterator);
     }
 
     /**
      * Gets an immutable version of a {@link MapIterator}. The returned object
      * will always throw an {@link UnsupportedOperationException} for
      * the {@link Iterator#remove}, {@link MapIterator#setValue(Object)} methods.
      *
      * @param <K> the key type
      * @param <V> the value type
      * @param mapIterator  the iterator to make immutable
      * @return an immutable version of the iterator
      */
     public static <K, V> MapIterator<K, V> unmodifiableMapIterator(final MapIterator<K, V> mapIterator) {
         return UnmodifiableMapIterator.unmodifiableMapIterator(mapIterator);
     }
 
     /**
      * Returns an iterator that interleaves elements from the decorated iterators.
      *
      * @param <E> the element type
      * @param iterators  the array of iterators to interleave
      * @return an iterator, interleaving the decorated iterators
      * @throws NullPointerException if any iterator is null
      * @since 4.1
      */
     public static <E> ZippingIterator<E> zippingIterator(final Iterator<? extends E>... iterators) {
         return new ZippingIterator<>(iterators);
     }
 
     /**
      * Returns an iterator that interleaves elements from the decorated iterators.
      *
      * @param <E> the element type
      * @param a  the first iterator to interleave
      * @param b  the second iterator to interleave
      * @return an iterator, interleaving the decorated iterators
      * @throws NullPointerException if any iterator is null
      * @since 4.1
      */
     public static <E> ZippingIterator<E> zippingIterator(final Iterator<? extends E> a,
                                                          final Iterator<? extends E> b) {
         return new ZippingIterator<>(a, b);
     }
 
     /**
      * Returns an iterator that interleaves elements from the decorated iterators.
      *
      * @param <E> the element type
      * @param a  the first iterator to interleave
      * @param b  the second iterator to interleave
      * @param c  the third iterator to interleave
      * @return an iterator, interleaving the decorated iterators
      * @throws NullPointerException if any iterator is null
      * @since 4.1
      */
     public static <E> ZippingIterator<E> zippingIterator(final Iterator<? extends E> a,
                                                          final Iterator<? extends E> b,
                                                          final Iterator<? extends E> c) {
         return new ZippingIterator<>(a, b, c);
     }
 
     /**
      * Don't allow instances.
      */
     private IteratorUtils() {
         // empty
     }
 
 }