IteratorUtils (Apache Commons Collections 4.0 API)

java.lang.Object
- org.apache.commons.collections4.IteratorUtils

```
public class IteratorUtils
extends Object
```
Provides static utility methods and decorators for Iterator instances. The implementations are provided in the iterators subpackage.
WARNING: Due to human error certain binary incompatibilities were introduced between Commons Collections 2.1 and 3.0. The class remained source and test compatible, so if you can recompile all your classes and dependencies everything is OK. Those methods which are binary incompatible are marked as such, together with alternate solutions that are binary compatible against versions 2.1.1 and 3.1.

Since:

2.1

Version:

$Id: IteratorUtils.java 1543964 2013-11-20 21:53:39Z tn $

Field Summary

Fields
Modifier and Type	Field and Description
`static ResettableIterator`	`EMPTY_ITERATOR` An iterator over no elements.
`static ResettableListIterator`	`EMPTY_LIST_ITERATOR` A list iterator over no elements.
`static MapIterator`	`EMPTY_MAP_ITERATOR` A map iterator over no elements.
`static OrderedIterator`	`EMPTY_ORDERED_ITERATOR` An ordered iterator over no elements.
`static OrderedMapIterator`	`EMPTY_ORDERED_MAP_ITERATOR` An ordered map iterator over no elements.

Method Summary

Methods
Modifier and Type	Method and Description
`static <E> ResettableIterator<E>`	`arrayIterator(E... array)` Gets an iterator over an object array.
`static <E> ResettableIterator<E>`	`arrayIterator(E[] array, int start)` Gets an iterator over the end part of an object array.
`static <E> ResettableIterator<E>`	`arrayIterator(E[] array, int start, int end)` Gets an iterator over part of an object array.
`static <E> ResettableIterator<E>`	`arrayIterator(Object array)` Gets an iterator over an object or primitive array.
`static <E> ResettableIterator<E>`	`arrayIterator(Object array, int start)` Gets an iterator over the end part of an object or primitive array.
`static <E> ResettableIterator<E>`	`arrayIterator(Object array, int start, int end)` Gets an iterator over part of an object or primitive array.
`static <E> ResettableListIterator<E>`	`arrayListIterator(E... array)` Gets a list iterator over an object array.
`static <E> ResettableListIterator<E>`	`arrayListIterator(E[] array, int start)` Gets a list iterator over the end part of an object array.
`static <E> ResettableListIterator<E>`	`arrayListIterator(E[] array, int start, int end)` Gets a list iterator over part of an object array.
`static <E> ResettableListIterator<E>`	`arrayListIterator(Object array)` Gets a list iterator over an object or primitive array.
`static <E> ResettableListIterator<E>`	`arrayListIterator(Object array, int start)` Gets a list iterator over the end part of an object or primitive array.
`static <E> ResettableListIterator<E>`	`arrayListIterator(Object array, int start, int end)` Gets a list iterator over part of an object or primitive array.
`static <E> Enumeration<E>`	`asEnumeration(Iterator<? extends E> iterator)` Gets an enumeration that wraps an iterator.
`static <E> Iterable<E>`	`asIterable(Iterator<? extends E> iterator)` Gets an `Iterable` that wraps an iterator.
`static <E> Iterator<E>`	`asIterator(Enumeration<? extends E> enumeration)` Gets an iterator that provides an iterator view of the given enumeration.
`static <E> Iterator<E>`	`asIterator(Enumeration<? extends E> enumeration, Collection<? super E> removeCollection)` Gets an iterator that provides an iterator view of the given enumeration that will remove elements from the specified collection.
`static <E> Iterable<E>`	`asMultipleUseIterable(Iterator<? extends E> iterator)` Gets an iterable that wraps an iterator.
`static <E> Iterator<E>`	`chainedIterator(Collection<Iterator<? extends E>> iterators)` Gets an iterator that iterates through a collections of `Iterator`s one after another.
`static <E> Iterator<E>`	`chainedIterator(Iterator<? extends E>... iterators)` Gets an iterator that iterates through an array of `Iterator`s one after another.
`static <E> Iterator<E>`	`chainedIterator(Iterator<? extends E> iterator1, Iterator<? extends E> iterator2)` Gets an iterator that iterates through two `Iterator`s one after another.
`static <E> Iterator<E>`	`collatedIterator(Comparator<? super E> comparator, Collection<Iterator<? extends E>> iterators)` Gets an iterator that provides an ordered iteration over the elements contained in a collection of `Iterator`s.
`static <E> Iterator<E>`	`collatedIterator(Comparator<? super E> comparator, Iterator<? extends E>... iterators)` Gets an iterator that provides an ordered iteration over the elements contained in an array of `Iterator`s.
`static <E> Iterator<E>`	`collatedIterator(Comparator<? super E> comparator, Iterator<? extends E> iterator1, Iterator<? extends E> iterator2)` Gets an iterator that provides an ordered iteration over the elements contained in a collection of ordered `Iterator`s.
`static <E> ResettableIterator<E>`	`emptyIterator()` Gets an empty iterator.
`static <E> ResettableListIterator<E>`	`emptyListIterator()` Gets an empty list iterator.
`static <K,V> MapIterator<K,V>`	`emptyMapIterator()` Gets an empty map iterator.
`static <E> OrderedIterator<E>`	`emptyOrderedIterator()` Gets an empty ordered iterator.
`static <K,V> OrderedMapIterator<K,V>`	`emptyOrderedMapIterator()` Gets an empty ordered map iterator.
`static <E> Iterator<E>`	`filteredIterator(Iterator<? extends E> iterator, Predicate<? super E> predicate)` Gets an iterator that filters another iterator.
`static <E> ListIterator<E>`	`filteredListIterator(ListIterator<? extends E> listIterator, Predicate<? super E> predicate)` Gets a list iterator that filters another list iterator.
`static Iterator<?>`	`getIterator(Object obj)` Gets a suitable Iterator for the given object.
`static <E> ResettableIterator<E>`	`loopingIterator(Collection<? extends E> coll)` Gets an iterator that loops continuously over the supplied collection.
`static <E> ResettableListIterator<E>`	`loopingListIterator(List<E> list)` Gets an iterator that loops continuously over the supplied list.
`static NodeListIterator`	`nodeListIterator(Node node)` Gets an `Iterator` that wraps the specified node's childNodes.
`static NodeListIterator`	`nodeListIterator(NodeList nodeList)` Gets an `Iterator` that wraps the specified `NodeList`.
`static <E> Iterator<E>`	`objectGraphIterator(E root, Transformer<? super E,? extends E> transformer)` Gets an iterator that operates over an object graph.
`static <E> Iterator<E>`	`peekingIterator(Iterator<? extends E> iterator)` Gets an iterator that supports one-element lookahead.
`static <E> Iterator<E>`	`pushbackIterator(Iterator<? extends E> iterator)` Gets an iterator that supports pushback of elements.
`static <E> ResettableIterator<E>`	`singletonIterator(E object)` Gets a singleton iterator.
`static <E> ListIterator<E>`	`singletonListIterator(E object)` Gets a singleton list iterator.
`static Object[]`	`toArray(Iterator<?> iterator)` Gets an array based on an iterator.
`static <E> E[]`	`toArray(Iterator<? extends E> iterator, Class<E> arrayClass)` Gets an array based on an iterator.
`static <E> List<E>`	`toList(Iterator<? extends E> iterator)` Gets a list based on an iterator.
`static <E> List<E>`	`toList(Iterator<? extends E> iterator, int estimatedSize)` Gets a list based on an iterator.
`static <E> ListIterator<E>`	`toListIterator(Iterator<? extends E> iterator)` Gets a list iterator based on a simple iterator.
`static <I,O> Iterator<O>`	`transformedIterator(Iterator<? extends I> iterator, Transformer<? super I,? extends O> transform)` Gets an iterator that transforms the elements of another iterator.
`static <E> Iterator<E>`	`unmodifiableIterator(Iterator<E> iterator)` Gets an immutable version of an `Iterator`.
`static <E> ListIterator<E>`	`unmodifiableListIterator(ListIterator<E> listIterator)` Gets an immutable version of a `ListIterator`.
`static <K,V> MapIterator<K,V>`	`unmodifiableMapIterator(MapIterator<K,V> mapIterator)` Gets an immutable version of a `MapIterator`.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - EMPTY_ITERATOR
```
public static final ResettableIterator EMPTY_ITERATOR
```
    An iterator over no elements.
    WARNING: This constant is binary incompatible with Commons Collections 2.1 and 2.1.1. Use EmptyIterator.INSTANCE for compatibility with Commons Collections 2.1.1.
  - EMPTY_LIST_ITERATOR
```
public static final ResettableListIterator EMPTY_LIST_ITERATOR
```
    A list iterator over no elements.
    WARNING: This constant is binary incompatible with Commons Collections 2.1 and 2.1.1. Use EmptyListIterator.INSTANCE for compatibility with Commons Collections 2.1.1.
  - EMPTY_ORDERED_ITERATOR
```
public static final OrderedIterator EMPTY_ORDERED_ITERATOR
```
    An ordered iterator over no elements.
  - EMPTY_MAP_ITERATOR
```
public static final MapIterator EMPTY_MAP_ITERATOR
```
    A map iterator over no elements.
  - EMPTY_ORDERED_MAP_ITERATOR
```
public static final OrderedMapIterator EMPTY_ORDERED_MAP_ITERATOR
```
    An ordered map iterator over no elements.
- Method Detail
  - emptyIterator
```
public static <E> ResettableIterator<E> emptyIterator()
```
    Gets an empty iterator.
    This iterator is a valid iterator object that will iterate over nothing.
    WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1. Use EmptyIterator.INSTANCE for compatibility with Commons Collections 2.1.1.
    
    Type Parameters:
    E - the element type
    
    Returns:
    an iterator over nothing
  - emptyListIterator
```
public static <E> ResettableListIterator<E> emptyListIterator()
```
    Gets an empty list iterator.
    This iterator is a valid list iterator object that will iterate over nothing.
    WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1. Use EmptyListIterator.INSTANCE for compatibility with Commons Collections 2.1.1.
    
    Type Parameters:
    E - the element type
    
    Returns:
    a list iterator over nothing
  - emptyOrderedIterator
```
public static <E> OrderedIterator<E> emptyOrderedIterator()
```
    Gets an empty ordered iterator.
    This iterator is a valid iterator object that will iterate over nothing.
    
    Type Parameters:
    E - the element type
    
    Returns:
    an ordered iterator over nothing
  - emptyMapIterator
```
public static <K,V> MapIterator<K,V> emptyMapIterator()
```
    Gets an empty map iterator.
    This iterator is a valid map iterator object that will iterate over nothing.
    
    Type Parameters:
    K - the key type
    V - the value type
    
    Returns:
    a map iterator over nothing
  - emptyOrderedMapIterator
```
public static <K,V> OrderedMapIterator<K,V> emptyOrderedMapIterator()
```
    Gets an empty ordered map iterator.
    This iterator is a valid map iterator object that will iterate over nothing.
    
    Type Parameters:
    K - the key type
    V - the value type
    
    Returns:
    a map iterator over nothing
  - singletonIterator
```
public static <E> ResettableIterator<E> singletonIterator(E object)
```
    Gets a singleton iterator.
    This iterator is a valid iterator object that will iterate over the specified object.
    WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1. Use new SingletonIterator(object) for compatibility.
    
    Type Parameters:
    E - the element type
    Parameters:
    object - the single object over which to iterate
    
    Returns:
    a singleton iterator over the object
  - singletonListIterator
```
public static <E> ListIterator<E> singletonListIterator(E object)
```
    Gets a singleton list iterator.
    This iterator is a valid list iterator object that will iterate over the specified object.
    
    Type Parameters:
    E - the element type
    Parameters:
    object - the single object over which to iterate
    
    Returns:
    a singleton list iterator over the object
  - arrayIterator
```
public static <E> ResettableIterator<E> arrayIterator(E... array)
```
    Gets an iterator over an object array.
    WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1. Use new ArrayIterator(array) for compatibility.
    
    Type Parameters:
    E - the element type
    Parameters:
    array - the array over which to iterate
    
    Returns:
    an iterator over the array
    
    Throws:
    
    NullPointerException - if array is null
  - arrayIterator
```
public static <E> ResettableIterator<E> arrayIterator(Object array)
```
    Gets an iterator over an object or primitive array.
    This method will handle primitive arrays as well as object arrays. The primitives will be wrapped in the appropriate wrapper class.
    
    Type Parameters:
    E - the element type
    Parameters:
    array - the array over which to iterate
    
    Returns:
    an iterator over the array
    
    Throws:
    
    IllegalArgumentException - if the array is not an array
    
    NullPointerException - if array is null
  - arrayIterator
```
public static <E> ResettableIterator<E> arrayIterator(E[] array,
                                      int start)
```
    Gets an iterator over the end part of an object array.
    WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1. Use new ArrayIterator(array,start) for compatibility.
    
    Type Parameters:
    E - the element type
    Parameters:
    array - the array over which to iterate
    start - the index to start iterating at
    
    Returns:
    an iterator over part of the array
    
    Throws:
    
    IndexOutOfBoundsException - if start is less than zero or greater than the length of the array
    
    NullPointerException - if array is null
  - arrayIterator
```
public static <E> ResettableIterator<E> arrayIterator(Object array,
                                      int start)
```
    Gets an iterator over the end part of an object or primitive array.
    This method will handle primitive arrays as well as object arrays. The primitives will be wrapped in the appropriate wrapper class.
    
    Type Parameters:
    E - the element type
    Parameters:
    array - the array over which to iterate
    start - the index to start iterating at
    
    Returns:
    an iterator over part of the array
    
    Throws:
    
    IllegalArgumentException - if the array is not an array
    
    IndexOutOfBoundsException - if start is less than zero or greater than the length of the array
    
    NullPointerException - if array is null
  - arrayIterator
```
public static <E> ResettableIterator<E> arrayIterator(E[] array,
                                      int start,
                                      int end)
```
    Gets an iterator over part of an object array.
    WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1. Use new ArrayIterator(array,start,end) for compatibility.
    
    Type Parameters:
    E - the element type
    Parameters:
    array - the array over which to iterate
    start - the index to start iterating at
    end - the index to finish iterating at
    
    Returns:
    an iterator over part of the array
    
    Throws:
    
    IndexOutOfBoundsException - if array bounds are invalid
    
    IllegalArgumentException - if end is before start
    
    NullPointerException - if array is null
  - arrayIterator
```
public static <E> ResettableIterator<E> arrayIterator(Object array,
                                      int start,
                                      int end)
```
    Gets an iterator over part of an object or primitive array.
    This method will handle primitive arrays as well as object arrays. The primitives will be wrapped in the appropriate wrapper class.
    
    Type Parameters:
    E - the element type
    Parameters:
    array - the array over which to iterate
    start - the index to start iterating at
    end - the index to finish iterating at
    
    Returns:
    an iterator over part of the array
    
    Throws:
    
    IllegalArgumentException - if the array is not an array or end is before start
    
    IndexOutOfBoundsException - if array bounds are invalid
    
    NullPointerException - if array is null
  - arrayListIterator
```
public static <E> ResettableListIterator<E> arrayListIterator(E... array)
```
    Gets a list iterator over an object array.
    
    Type Parameters:
    E - the element type
    Parameters:
    array - the array over which to iterate
    
    Returns:
    a list iterator over the array
    
    Throws:
    
    NullPointerException - if array is null
  - arrayListIterator
```
public static <E> ResettableListIterator<E> arrayListIterator(Object array)
```
    Gets a list iterator over an object or primitive array.
    This method will handle primitive arrays as well as object arrays. The primitives will be wrapped in the appropriate wrapper class.
    
    Type Parameters:
    E - the element type
    Parameters:
    array - the array over which to iterate
    
    Returns:
    a list iterator over the array
    
    Throws:
    
    IllegalArgumentException - if the array is not an array
    
    NullPointerException - if array is null
  - arrayListIterator
```
public static <E> ResettableListIterator<E> arrayListIterator(E[] array,
                                              int start)
```
    Gets a list iterator over the end part of an object array.
    
    Type Parameters:
    E - the element type
    Parameters:
    array - the array over which to iterate
    start - the index to start iterating at
    
    Returns:
    a list iterator over part of the array
    
    Throws:
    
    IndexOutOfBoundsException - if start is less than zero
    
    NullPointerException - if array is null
  - arrayListIterator
```
public static <E> ResettableListIterator<E> arrayListIterator(Object array,
                                              int start)
```
    Gets a list iterator over the end part of an object or primitive array.
    This method will handle primitive arrays as well as object arrays. The primitives will be wrapped in the appropriate wrapper class.
    
    Type Parameters:
    E - the element type
    Parameters:
    array - the array over which to iterate
    start - the index to start iterating at
    
    Returns:
    a list iterator over part of the array
    
    Throws:
    
    IllegalArgumentException - if the array is not an array
    
    IndexOutOfBoundsException - if start is less than zero
    
    NullPointerException - if array is null
  - arrayListIterator
```
public static <E> ResettableListIterator<E> arrayListIterator(E[] array,
                                              int start,
                                              int end)
```
    Gets a list iterator over part of an object array.
    
    Type Parameters:
    E - the element type
    Parameters:
    array - the array over which to iterate
    start - the index to start iterating at
    end - the index to finish iterating at
    
    Returns:
    a list iterator over part of the array
    
    Throws:
    
    IndexOutOfBoundsException - if array bounds are invalid
    
    IllegalArgumentException - if end is before start
    
    NullPointerException - if array is null
  - arrayListIterator
```
public static <E> ResettableListIterator<E> arrayListIterator(Object array,
                                              int start,
                                              int end)
```
    Gets a list iterator over part of an object or primitive array.
    This method will handle primitive arrays as well as object arrays. The primitives will be wrapped in the appropriate wrapper class.
    
    Type Parameters:
    E - the element type
    Parameters:
    array - the array over which to iterate
    start - the index to start iterating at
    end - the index to finish iterating at
    
    Returns:
    a list iterator over part of the array
    
    Throws:
    
    IllegalArgumentException - if the array is not an array or end is before start
    
    IndexOutOfBoundsException - if array bounds are invalid
    
    NullPointerException - if array is null
  - unmodifiableIterator
```
public static <E> Iterator<E> unmodifiableIterator(Iterator<E> iterator)
```
    Gets an immutable version of an Iterator. The returned object will always throw an UnsupportedOperationException for the Iterator.remove() method.
    
    Type Parameters:
    E - the element type
    Parameters:
    iterator - the iterator to make immutable
    
    Returns:
    an immutable version of the iterator
  - unmodifiableListIterator
```
public static <E> ListIterator<E> unmodifiableListIterator(ListIterator<E> listIterator)
```
    Gets an immutable version of a ListIterator. The returned object will always throw an UnsupportedOperationException for the Iterator.remove(), ListIterator.add(E) and ListIterator.set(E) methods.
    
    Type Parameters:
    E - the element type
    Parameters:
    listIterator - the iterator to make immutable
    
    Returns:
    an immutable version of the iterator
  - unmodifiableMapIterator
```
public static <K,V> MapIterator<K,V> unmodifiableMapIterator(MapIterator<K,V> mapIterator)
```
    Gets an immutable version of a MapIterator. The returned object will always throw an UnsupportedOperationException for the Iterator.remove(), MapIterator.setValue(Object) methods.
    
    Type Parameters:
    K - the key type
    V - the value type
    Parameters:
    mapIterator - the iterator to make immutable
    
    Returns:
    an immutable version of the iterator
  - chainedIterator
```
public static <E> Iterator<E> chainedIterator(Iterator<? extends E> iterator1,
                              Iterator<? extends E> iterator2)
```
    Gets an iterator that iterates through two Iterators one after another.
    
    Type Parameters:
    E - the element type
    Parameters:
    iterator1 - the first iterator to use, not null
    iterator2 - the second iterator to use, not null
    
    Returns:
    a combination iterator over the iterators
    
    Throws:
    
    NullPointerException - if either iterator is null
  - chainedIterator
```
public static <E> Iterator<E> chainedIterator(Iterator<? extends E>... iterators)
```
    Gets an iterator that iterates through an array of Iterators one after another.
    
    Type Parameters:
    E - the element type
    Parameters:
    iterators - the iterators to use, not null or empty or contain nulls
    
    Returns:
    a combination iterator over the iterators
    
    Throws:
    
    NullPointerException - if iterators array is null or contains a null
  - chainedIterator
```
public static <E> Iterator<E> chainedIterator(Collection<Iterator<? extends E>> iterators)
```
    Gets an iterator that iterates through a collections of Iterators one after another.
    
    Type Parameters:
    E - the element type
    Parameters:
    iterators - the iterators to use, not null or empty or contain nulls
    
    Returns:
    a combination iterator over the iterators
    
    Throws:
    
    NullPointerException - if iterators collection is null or contains a null
    
    ClassCastException - if the iterators collection contains the wrong object type
  - collatedIterator
```
public static <E> Iterator<E> collatedIterator(Comparator<? super E> comparator,
                               Iterator<? extends E> iterator1,
                               Iterator<? extends E> iterator2)
```
    Gets an iterator that provides an ordered iteration over the elements contained in a collection of ordered Iterators.
    Given two ordered Iterators A and B, the Iterator.next() method will return the lesser of A.next() and B.next().
    The comparator is optional. If null is specified then natural order is used.
    
    Type Parameters:
    E - the element type
    Parameters:
    comparator - the comparator to use, may be null for natural order
    iterator1 - the first iterators to use, not null
    iterator2 - the first iterators to use, not null
    
    Returns:
    a combination iterator over the iterators
    
    Throws:
    
    NullPointerException - if either iterator is null
  - collatedIterator
```
public static <E> Iterator<E> collatedIterator(Comparator<? super E> comparator,
                               Iterator<? extends E>... iterators)
```
    Gets an iterator that provides an ordered iteration over the elements contained in an array of Iterators.
    Given two ordered Iterators A and B, the Iterator.next() method will return the lesser of A.next() and B.next() and so on.
    The comparator is optional. If null is specified then natural order is used.
    
    Type Parameters:
    E - the element type
    Parameters:
    comparator - the comparator to use, may be null for natural order
    iterators - the iterators to use, not null or empty or contain nulls
    
    Returns:
    a combination iterator over the iterators
    
    Throws:
    
    NullPointerException - if iterators array is null or contains a null value
  - collatedIterator
```
public static <E> Iterator<E> collatedIterator(Comparator<? super E> comparator,
                               Collection<Iterator<? extends E>> iterators)
```
    Gets an iterator that provides an ordered iteration over the elements contained in a collection of Iterators.
    Given two ordered Iterators A and B, the Iterator.next() method will return the lesser of A.next() and B.next() and so on.
    The comparator is optional. If null is specified then natural order is used.
    
    Type Parameters:
    E - the element type
    Parameters:
    comparator - the comparator to use, may be null for natural order
    iterators - the iterators to use, not null or empty or contain nulls
    
    Returns:
    a combination iterator over the iterators
    
    Throws:
    
    NullPointerException - if iterators collection is null or contains a null
    
    ClassCastException - if the iterators collection contains the wrong object type
  - objectGraphIterator
```
public static <E> Iterator<E> objectGraphIterator(E root,
                                  Transformer<? super E,? extends E> transformer)
```
    Gets an iterator that operates over an object graph.
    This iterator can extract multiple objects from a complex tree-like object graph. The iteration starts from a single root object. It uses a Transformer to extract the iterators and elements. Its main benefit is that no intermediate List is created.
    For example, consider an object graph:
```
                 |- Branch -- Leaf
                 |         \- Leaf
         |- Tree |         /- Leaf
         |       |- Branch -- Leaf
  Forest |                 \- Leaf
         |       |- Branch -- Leaf
         |       |         \- Leaf
         |- Tree |         /- Leaf
                 |- Branch -- Leaf
                 |- Branch -- Leaf
```
    The following Transformer, used in this class, will extract all the Leaf objects without creating a combined intermediate list:
```
 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();
 }
```
    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.
    Under many circumstances, linking Iterators together in this manner is more efficient (and convenient) than using nested for loops to extract a list.
    Type Parameters:
    E - the element type
    Parameters:
    root - the root object to start iterating from, null results in an empty iterator
    transformer - the transformer to use, see above, null uses no effect transformer
    
    Returns:
    a new object graph iterator
    Since:
    
    3.1
  - transformedIterator
```
public static <I,O> Iterator<O> transformedIterator(Iterator<? extends I> iterator,
                                    Transformer<? super I,? extends O> transform)
```
    Gets an iterator that transforms the elements of another iterator.
    The transformation occurs during the next() method and the underlying iterator is unaffected by the transformation.
    
    Type Parameters:
    I - the input type
    O - the output type
    Parameters:
    iterator - the iterator to use, not null
    transform - the transform to use, not null
    
    Returns:
    a new transforming iterator
    
    Throws:
    
    NullPointerException - if either parameter is null
  - filteredIterator
```
public static <E> Iterator<E> filteredIterator(Iterator<? extends E> iterator,
                               Predicate<? super E> predicate)
```
    Gets an iterator that filters another iterator.
    The returned iterator will only return objects that match the specified filtering predicate.
    
    Type Parameters:
    E - the element type
    Parameters:
    iterator - the iterator to use, not null
    predicate - the predicate to use as a filter, not null
    
    Returns:
    a new filtered iterator
    
    Throws:
    
    NullPointerException - if either parameter is null
  - filteredListIterator
```
public static <E> ListIterator<E> filteredListIterator(ListIterator<? extends E> listIterator,
                                       Predicate<? super E> predicate)
```
    Gets a list iterator that filters another list iterator.
    The returned iterator will only return objects that match the specified filtering predicate.
    
    Type Parameters:
    E - the element type
    Parameters:
    listIterator - the list iterator to use, not null
    predicate - the predicate to use as a filter, not null
    
    Returns:
    a new filtered iterator
    
    Throws:
    
    NullPointerException - if either parameter is null
  - loopingIterator
```
public static <E> ResettableIterator<E> loopingIterator(Collection<? extends E> coll)
```
    Gets an iterator that loops continuously over the supplied collection.
    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.
    
    Type Parameters:
    E - the element type
    Parameters:
    coll - the collection to iterate over, not null
    
    Returns:
    a new looping iterator
    
    Throws:
    
    NullPointerException - if the collection is null
  - loopingListIterator
```
public static <E> ResettableListIterator<E> loopingListIterator(List<E> list)
```
    Gets an iterator that loops continuously over the supplied list.
    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.
    
    Type Parameters:
    E - the element type
    Parameters:
    list - the list to iterate over, not null
    
    Returns:
    a new looping iterator
    
    Throws:
    
    NullPointerException - if the list is null
    Since:
    
    3.2
  - nodeListIterator
```
public static NodeListIterator nodeListIterator(NodeList nodeList)
```
    Gets an Iterator that wraps the specified NodeList. The returned Iterator can be used for a single iteration.
    
    Parameters:
    nodeList - the node list to use, not null
    
    Returns:
    a new, single use Iterator
    
    Throws:
    
    NullPointerException - if nodeList is null
    Since:
    
    4.0
  - nodeListIterator
```
public static NodeListIterator nodeListIterator(Node node)
```
    Gets an Iterator that wraps the specified node's childNodes. The returned Iterator can be used for a single iteration.
    Convenience method, allows easy iteration over NodeLists:
```
   Iterator<Node> iterator = IteratorUtils.nodeListIterator(node);
   for(Node childNode : IteratorUtils.asIterable(iterator)) {
     ...
   }
 
```
    Parameters:
    node - the node to use, not null
    
    Returns:
    a new, single use Iterator
    
    Throws:
    
    NullPointerException - if node is null
    Since:
    
    4.0
  - peekingIterator
```
public static <E> Iterator<E> peekingIterator(Iterator<? extends E> iterator)
```
    Gets an iterator that supports one-element lookahead.
    
    Type Parameters:
    E - the element type
    Parameters:
    iterator - the iterator to decorate, not null
    
    Returns:
    a peeking iterator
    
    Throws:
    
    NullPointerException - if the iterator is null
    Since:
    
    4.0
  - pushbackIterator
```
public static <E> Iterator<E> pushbackIterator(Iterator<? extends E> iterator)
```
    Gets an iterator that supports pushback of elements.
    
    Type Parameters:
    E - the element type
    Parameters:
    iterator - the iterator to decorate, not null
    
    Returns:
    a pushback iterator
    
    Throws:
    
    NullPointerException - if the iterator is null
    Since:
    
    4.0
  - asIterator
```
public static <E> Iterator<E> asIterator(Enumeration<? extends E> enumeration)
```
    Gets an iterator that provides an iterator view of the given enumeration.
    
    Type Parameters:
    E - the element type
    Parameters:
    enumeration - the enumeration to use
    
    Returns:
    a new iterator
  - asIterator
```
public static <E> Iterator<E> asIterator(Enumeration<? extends E> enumeration,
                         Collection<? super E> removeCollection)
```
    Gets an iterator that provides an iterator view of the given enumeration that will remove elements from the specified collection.
    
    Type Parameters:
    E - the element type
    Parameters:
    enumeration - the enumeration to use
    removeCollection - the collection to remove elements from
    
    Returns:
    a new iterator
  - asEnumeration
```
public static <E> Enumeration<E> asEnumeration(Iterator<? extends E> iterator)
```
    Gets an enumeration that wraps an iterator.
    
    Type Parameters:
    E - the element type
    Parameters:
    iterator - the iterator to use, not null
    
    Returns:
    a new enumeration
    
    Throws:
    
    NullPointerException - if iterator is null
  - asIterable
```
public static <E> Iterable<E> asIterable(Iterator<? extends E> iterator)
```
    Gets an Iterable that wraps an iterator. The returned Iterable can be used for a single iteration.
    
    Type Parameters:
    E - the element type
    Parameters:
    iterator - the iterator to use, not null
    
    Returns:
    a new, single use Iterable
    
    Throws:
    
    NullPointerException - if iterator is null
  - asMultipleUseIterable
```
public static <E> Iterable<E> asMultipleUseIterable(Iterator<? extends E> iterator)
```
    Gets an iterable that wraps an iterator. The returned iterable can be used for multiple iterations.
    
    Type Parameters:
    E - the element type
    Parameters:
    iterator - the iterator to use, not null
    
    Returns:
    a new, multiple use iterable
    
    Throws:
    
    NullPointerException - if iterator is null
  - toListIterator
```
public static <E> ListIterator<E> toListIterator(Iterator<? extends E> iterator)
```
    Gets a list iterator based on a simple iterator.
    As the wrapped Iterator is traversed, a LinkedList of its values is cached, permitting all required operations of ListIterator.
    
    Type Parameters:
    E - the element type
    Parameters:
    iterator - the iterator to use, not null
    
    Returns:
    a new iterator
    
    Throws:
    
    NullPointerException - if iterator parameter is null
  - toArray
```
public static Object[] toArray(Iterator<?> iterator)
```
    Gets an array based on an iterator.
    As the wrapped Iterator is traversed, an ArrayList of its values is created. At the end, this is converted to an array.
    
    Parameters:
    iterator - the iterator to use, not null
    
    Returns:
    an array of the iterator contents
    
    Throws:
    
    NullPointerException - if iterator parameter is null
  - toArray
```
public static <E> E[] toArray(Iterator<? extends E> iterator,
              Class<E> arrayClass)
```
    Gets an array based on an iterator.
    As the wrapped Iterator is traversed, an ArrayList of its values is created. At the end, this is converted to an array.
    
    Type Parameters:
    E - the element type
    Parameters:
    iterator - the iterator to use, not null
    arrayClass - the class of array to create
    
    Returns:
    an array of the iterator contents
    
    Throws:
    
    NullPointerException - if iterator parameter or arrayClass is null
    
    ClassCastException - if the arrayClass is invalid
  - toList
```
public static <E> List<E> toList(Iterator<? extends E> iterator)
```
    Gets a list based on an iterator.
    As the wrapped Iterator is traversed, an ArrayList of its values is created. At the end, the list is returned.
    
    Type Parameters:
    E - the element type
    Parameters:
    iterator - the iterator to use, not null
    
    Returns:
    a list of the iterator contents
    
    Throws:
    
    NullPointerException - if iterator parameter is null
  - toList
```
public static <E> List<E> toList(Iterator<? extends E> iterator,
                 int estimatedSize)
```
    Gets a list based on an iterator.
    As the wrapped Iterator is traversed, an ArrayList of its values is created. At the end, the list is returned.
    
    Type Parameters:
    E - the element type
    Parameters:
    iterator - the iterator to use, not null
    estimatedSize - the initial size of the ArrayList
    
    Returns:
    a list of the iterator contents
    
    Throws:
    
    NullPointerException - if iterator parameter is null
    
    IllegalArgumentException - if the size is less than 1
  - getIterator
```
public static Iterator<?> getIterator(Object obj)
```
    Gets a suitable Iterator for the given object.
    This method can handle objects as follows
    - null - empty iterator
    - Iterator - returned directly
    - Enumeration - wrapped
    - Collection - iterator from collection returned
    - Map - values iterator returned
    - Dictionary - values (elements) enumeration returned as iterator
    - array - iterator over array returned
    - object with iterator() public method accessed by reflection
    - object - singleton iterator
    - NodeList - iterator over the list
    - Node - iterator over the child nodes
    Parameters:
    obj - the object to convert to an iterator
    
    Returns:
    a suitable iterator, never null

Class IteratorUtils

Field Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

EMPTY_ITERATOR

EMPTY_LIST_ITERATOR

EMPTY_ORDERED_ITERATOR

EMPTY_MAP_ITERATOR

EMPTY_ORDERED_MAP_ITERATOR

Method Detail

emptyIterator

emptyListIterator

emptyOrderedIterator

emptyMapIterator

emptyOrderedMapIterator

singletonIterator

singletonListIterator

arrayIterator

arrayIterator

arrayIterator

arrayIterator

arrayIterator

arrayIterator

arrayListIterator

arrayListIterator

arrayListIterator

arrayListIterator

arrayListIterator

arrayListIterator

unmodifiableIterator

unmodifiableListIterator

unmodifiableMapIterator

chainedIterator

chainedIterator

chainedIterator

collatedIterator

collatedIterator

collatedIterator

objectGraphIterator

transformedIterator

filteredIterator

filteredListIterator

loopingIterator

loopingListIterator

nodeListIterator

nodeListIterator

peekingIterator

pushbackIterator

asIterator

asIterator

asEnumeration

asIterable

asMultipleUseIterable

toListIterator

toArray

toArray

toList

toList

getIterator