Package org.apache.commons.collections4

Class IteratorUtils

  • public class IteratorUtils
extends java.lang.Object
    Provides static utility methods and decorators for Iterator instances. The implementations are provided in the iterators subpackage.
    Since:
    2.1

    • Method Summary

      All Methods Static Methods Concrete Methods 
      Modifier and Type Method 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​(java.lang.Object array)
      Gets an iterator over an object or primitive array.
      static <E> ResettableIterator<E> arrayIterator​(java.lang.Object array, int start)
      Gets an iterator over the end part of an object or primitive array.
      static <E> ResettableIterator<E> arrayIterator​(java.lang.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​(java.lang.Object array)
      Gets a list iterator over an object or primitive array.
      static <E> ResettableListIterator<E> arrayListIterator​(java.lang.Object array, int start)
      Gets a list iterator over the end part of an object or primitive array.
      static <E> ResettableListIterator<E> arrayListIterator​(java.lang.Object array, int start, int end)
      Gets a list iterator over part of an object or primitive array.
      static <E> java.util.Enumeration<E> asEnumeration​(java.util.Iterator<? extends E> iterator)
      Gets an enumeration that wraps an iterator.
      static <E> java.lang.Iterable<E> asIterable​(java.util.Iterator<? extends E> iterator)
      Gets an Iterable that wraps an iterator.
      static <E> java.util.Iterator<E> asIterator​(java.util.Enumeration<? extends E> enumeration)
      Gets an iterator that provides an iterator view of the given enumeration.
      static <E> java.util.Iterator<E> asIterator​(java.util.Enumeration<? extends E> enumeration, java.util.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> java.lang.Iterable<E> asMultipleUseIterable​(java.util.Iterator<? extends E> iterator)
      Gets an iterable that wraps an iterator.
      static <E> BoundedIterator<E> boundedIterator​(java.util.Iterator<? extends E> iterator, long max)
      Decorates the specified iterator to return at most the given number of elements.
      static <E> BoundedIterator<E> boundedIterator​(java.util.Iterator<? extends E> iterator, long offset, long max)
      Decorates the specified iterator to return at most the given number of elements, skipping all elements until the iterator reaches the position at offset.
      static <E> java.util.Iterator<E> chainedIterator​(java.util.Collection<java.util.Iterator<? extends E>> iterators)
      Gets an iterator that iterates through a collections of Iterators one after another.
      static <E> java.util.Iterator<E> chainedIterator​(java.util.Iterator<? extends E>... iterators)
      Gets an iterator that iterates through an array of Iterators one after another.
      static <E> java.util.Iterator<E> chainedIterator​(java.util.Iterator<? extends E> iterator1, java.util.Iterator<? extends E> iterator2)
      Gets an iterator that iterates through two Iterators one after another.
      static <E> java.util.Iterator<E> collatedIterator​(java.util.Comparator<? super E> comparator, java.util.Collection<java.util.Iterator<? extends E>> iterators)
      Gets an iterator that provides an ordered iteration over the elements contained in a collection of Iterators.
      static <E> java.util.Iterator<E> collatedIterator​(java.util.Comparator<? super E> comparator, java.util.Iterator<? extends E>... iterators)
      Gets an iterator that provides an ordered iteration over the elements contained in an array of Iterators.
      static <E> java.util.Iterator<E> collatedIterator​(java.util.Comparator<? super E> comparator, java.util.Iterator<? extends E> iterator1, java.util.Iterator<? extends E> iterator2)
      Gets an iterator that provides an ordered iteration over the elements contained in a collection of ordered Iterators.
      static <E> boolean contains​(java.util.Iterator<E> iterator, java.lang.Object object)
      Checks if the object is contained in the given iterator.
      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> java.util.Iterator<E> filteredIterator​(java.util.Iterator<? extends E> iterator, Predicate<? super E> predicate)
      Gets an iterator that filters another iterator.
      static <E> java.util.ListIterator<E> filteredListIterator​(java.util.ListIterator<? extends E> listIterator, Predicate<? super E> predicate)
      Gets a list iterator that filters another list iterator.
      static <E> E find​(java.util.Iterator<E> iterator, Predicate<? super E> predicate)
      Finds the first element in the given iterator which matches the given predicate.
      static <E> E first​(java.util.Iterator<E> iterator)
      Shortcut for get(iterator, 0).
      static <E> void forEach​(java.util.Iterator<E> iterator, Closure<? super E> closure)
      Applies the closure to each element of the provided iterator.
      static <E> E forEachButLast​(java.util.Iterator<E> iterator, Closure<? super E> closure)
      Executes the given closure on each but the last element in the iterator.
      static <E> E get​(java.util.Iterator<E> iterator, int index)
      Returns the index-th value in Iterator, throwing IndexOutOfBoundsException if there is no such element.
      static java.util.Iterator<?> getIterator​(java.lang.Object obj)
      Gets a suitable Iterator for the given object.
      static <E> int indexOf​(java.util.Iterator<E> iterator, Predicate<? super E> predicate)
      Returns the index of the first element in the specified iterator that matches the given predicate.
      static boolean isEmpty​(java.util.Iterator<?> iterator)
      Checks if the given iterator is empty.
      static <E> ResettableIterator<E> loopingIterator​(java.util.Collection<? extends E> coll)
      Gets an iterator that loops continuously over the supplied collection.
      static <E> ResettableListIterator<E> loopingListIterator​(java.util.List<E> list)
      Gets an iterator that loops continuously over the supplied list.
      static <E> boolean matchesAll​(java.util.Iterator<E> iterator, Predicate<? super E> predicate)
      Answers true if a predicate is true for every element of an iterator.
      static <E> boolean matchesAny​(java.util.Iterator<E> iterator, Predicate<? super E> predicate)
      Answers true if a predicate is true for any element of the iterator.
      static NodeListIterator nodeListIterator​(org.w3c.dom.Node node)
      Gets an Iterator that wraps the specified node's childNodes.
      static NodeListIterator nodeListIterator​(org.w3c.dom.NodeList nodeList)
      Gets an Iterator that wraps the specified NodeList.
      static <E> java.util.Iterator<E> objectGraphIterator​(E root, Transformer<? super E,​? extends E> transformer)
      Gets an iterator that operates over an object graph.
      static <E> java.util.Iterator<E> peekingIterator​(java.util.Iterator<? extends E> iterator)
      Gets an iterator that supports one-element lookahead.
      static <E> java.util.Iterator<E> pushbackIterator​(java.util.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> java.util.ListIterator<E> singletonListIterator​(E object)
      Gets a singleton list iterator.
      static int size​(java.util.Iterator<?> iterator)
      Returns the number of elements contained in the given iterator.
      static <E> SkippingIterator<E> skippingIterator​(java.util.Iterator<E> iterator, long offset)
      Decorates the specified iterator to skip the first N elements.
      static java.lang.Object[] toArray​(java.util.Iterator<?> iterator)
      Gets an array based on an iterator.
      static <E> E[] toArray​(java.util.Iterator<? extends E> iterator, java.lang.Class<E> arrayClass)
      Gets an array based on an iterator.
      static <E> java.util.List<E> toList​(java.util.Iterator<? extends E> iterator)
      Gets a list based on an iterator.
      static <E> java.util.List<E> toList​(java.util.Iterator<? extends E> iterator, int estimatedSize)
      Gets a list based on an iterator.
      static <E> java.util.ListIterator<E> toListIterator​(java.util.Iterator<? extends E> iterator)
      Gets a list iterator based on a simple iterator.
      static <E> java.lang.String toString​(java.util.Iterator<E> iterator)
      Returns a string representation of the elements of the specified iterator.
      static <E> java.lang.String toString​(java.util.Iterator<E> iterator, Transformer<? super E,​java.lang.String> transformer)
      Returns a string representation of the elements of the specified iterator.
      static <E> java.lang.String toString​(java.util.Iterator<E> iterator, Transformer<? super E,​java.lang.String> transformer, java.lang.String delimiter, java.lang.String prefix, java.lang.String suffix)
      Returns a string representation of the elements of the specified iterator.
      static <I,​O>
      java.util.Iterator<O>      		 transformedIterator​(java.util.Iterator<? extends I> iterator, Transformer<? super I,​? extends O> transform)
      Gets an iterator that transforms the elements of another iterator.
      static <E> java.util.Iterator<E> unmodifiableIterator​(java.util.Iterator<E> iterator)
      Gets an immutable version of an Iterator.
      static <E> java.util.ListIterator<E> unmodifiableListIterator​(java.util.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.
      static <E> ZippingIterator<E> zippingIterator​(java.util.Iterator<? extends E>... iterators)
      Returns an iterator that interleaves elements from the decorated iterators.
      static <E> ZippingIterator<E> zippingIterator​(java.util.Iterator<? extends E> a, java.util.Iterator<? extends E> b)
      Returns an iterator that interleaves elements from the decorated iterators.
      static <E> ZippingIterator<E> zippingIterator​(java.util.Iterator<? extends E> a, java.util.Iterator<? extends E> b, java.util.Iterator<? extends E> c)
      Returns an iterator that interleaves elements from the decorated iterators.

      • Methods inherited from class java.lang.Object

        equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Field Detail

      • EMPTY_ITERATOR

        public static final ResettableIterator EMPTY_ITERATOR
        An iterator over no elements.

      • EMPTY_LIST_ITERATOR

        public static final ResettableListIterator EMPTY_LIST_ITERATOR
        A list iterator over no elements.

      • 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.

        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.

        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.

        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> java.util.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.
        Type Parameters:
        E - the element type
        Parameters:
        array - the array over which to iterate
        Returns:
        an iterator over the array
        Throws:
        java.lang.NullPointerException - if array is null

      • arrayIterator

        public static <E> ResettableIterator<E> arrayIterator​(java.lang.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:
        java.lang.IllegalArgumentException - if the array is not an array
        java.lang.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.
        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:
        java.lang.IndexOutOfBoundsException - if start is less than zero or greater than the length of the array
        java.lang.NullPointerException - if array is null

      • arrayIterator

        public static <E> ResettableIterator<E> arrayIterator​(java.lang.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:
        java.lang.IllegalArgumentException - if the array is not an array
        java.lang.IndexOutOfBoundsException - if start is less than zero or greater than the length of the array
        java.lang.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.
        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:
        java.lang.IndexOutOfBoundsException - if array bounds are invalid
        java.lang.IllegalArgumentException - if end is before start
        java.lang.NullPointerException - if array is null

      • arrayIterator

        public static <E> ResettableIterator<E> arrayIterator​(java.lang.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:
        java.lang.IllegalArgumentException - if the array is not an array or end is before start
        java.lang.IndexOutOfBoundsException - if array bounds are invalid
        java.lang.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:
        java.lang.NullPointerException - if array is null

      • arrayListIterator

        public static <E> ResettableListIterator<E> arrayListIterator​(java.lang.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:
        java.lang.IllegalArgumentException - if the array is not an array
        java.lang.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:
        java.lang.IndexOutOfBoundsException - if start is less than zero
        java.lang.NullPointerException - if array is null

      • arrayListIterator

        public static <E> ResettableListIterator<E> arrayListIterator​(java.lang.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:
        java.lang.IllegalArgumentException - if the array is not an array
        java.lang.IndexOutOfBoundsException - if start is less than zero
        java.lang.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:
        java.lang.IndexOutOfBoundsException - if array bounds are invalid
        java.lang.IllegalArgumentException - if end is before start
        java.lang.NullPointerException - if array is null

      • arrayListIterator

        public static <E> ResettableListIterator<E> arrayListIterator​(java.lang.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:
        java.lang.IllegalArgumentException - if the array is not an array or end is before start
        java.lang.IndexOutOfBoundsException - if array bounds are invalid
        java.lang.NullPointerException - if array is null

      • boundedIterator

        public static <E> BoundedIterator<E> boundedIterator​(java.util.Iterator<? extends E> iterator,
                                                     long max)
        Decorates the specified iterator to return at most the given number of elements.
        Type Parameters:
        E - the element type
        Parameters:
        iterator - the iterator to decorate
        max - the maximum number of elements returned by this iterator
        Returns:
        a new bounded iterator
        Throws:
        java.lang.NullPointerException - if the iterator is null
        java.lang.IllegalArgumentException - if max is negative
        Since:
        4.1

      • boundedIterator

        public static <E> BoundedIterator<E> boundedIterator​(java.util.Iterator<? extends E> iterator,
                                                     long offset,
                                                     long max)
        Decorates the specified iterator to return at most the given number of elements, skipping all elements until the iterator reaches the position at offset.

        The iterator is immediately advanced until it reaches the position at offset, incurring O(n) time.

        Type Parameters:
        E - the element type
        Parameters:
        iterator - the iterator to decorate
        offset - the index of the first element of the decorated iterator to return
        max - the maximum number of elements returned by this iterator
        Returns:
        a new bounded iterator
        Throws:
        java.lang.NullPointerException - if the iterator is null
        java.lang.IllegalArgumentException - if either offset or max is negative
        Since:
        4.1

      • unmodifiableIterator

        public static <E> java.util.Iterator<E> unmodifiableIterator​(java.util.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> java.util.ListIterator<E> unmodifiableListIterator​(java.util.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> java.util.Iterator<E> chainedIterator​(java.util.Iterator<? extends E> iterator1,
                                                        java.util.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:
        java.lang.NullPointerException - if either iterator is null

      • chainedIterator

        public static <E> java.util.Iterator<E> chainedIterator​(java.util.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:
        java.lang.NullPointerException - if iterators array is null or contains a null

      • chainedIterator

        public static <E> java.util.Iterator<E> chainedIterator​(java.util.Collection<java.util.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:
        java.lang.NullPointerException - if iterators collection is null or contains a null
        java.lang.ClassCastException - if the iterators collection contains the wrong object type

      • collatedIterator

        public static <E> java.util.Iterator<E> collatedIterator​(java.util.Comparator<? super E> comparator,
                                                         java.util.Iterator<? extends E> iterator1,
                                                         java.util.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:
        java.lang.NullPointerException - if either iterator is null

      • collatedIterator

        public static <E> java.util.Iterator<E> collatedIterator​(java.util.Comparator<? super E> comparator,
                                                         java.util.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:
        java.lang.NullPointerException - if iterators array is null or contains a null value

      • collatedIterator

        public static <E> java.util.Iterator<E> collatedIterator​(java.util.Comparator<? super E> comparator,
                                                         java.util.Collection<java.util.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:
        java.lang.NullPointerException - if iterators collection is null or contains a null
        java.lang.ClassCastException - if the iterators collection contains the wrong object type

      • objectGraphIterator

        public static <E> java.util.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> java.util.Iterator<O> transformedIterator​(java.util.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:
        java.lang.NullPointerException - if either parameter is null

      • filteredIterator

        public static <E> java.util.Iterator<E> filteredIterator​(java.util.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:
        java.lang.NullPointerException - if either parameter is null

      • filteredListIterator

        public static <E> java.util.ListIterator<E> filteredListIterator​(java.util.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:
        java.lang.NullPointerException - if either parameter is null

      • loopingIterator

        public static <E> ResettableIterator<E> loopingIterator​(java.util.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:
        java.lang.NullPointerException - if the collection is null

      • loopingListIterator

        public static <E> ResettableListIterator<E> loopingListIterator​(java.util.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:
        java.lang.NullPointerException - if the list is null
        Since:
        3.2

      • nodeListIterator

        public static NodeListIterator nodeListIterator​(org.w3c.dom.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, may not be null
        Returns:
        a new, single use Iterator
        Throws:
        java.lang.NullPointerException - if nodeList is null
        Since:
        4.0

      • nodeListIterator

        public static NodeListIterator nodeListIterator​(org.w3c.dom.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, may not be null
        Returns:
        a new, single use Iterator
        Throws:
        java.lang.NullPointerException - if node is null
        Since:
        4.0

      • peekingIterator

        public static <E> java.util.Iterator<E> peekingIterator​(java.util.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:
        java.lang.NullPointerException - if the iterator is null
        Since:
        4.0

      • pushbackIterator

        public static <E> java.util.Iterator<E> pushbackIterator​(java.util.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:
        java.lang.NullPointerException - if the iterator is null
        Since:
        4.0

      • skippingIterator

        public static <E> SkippingIterator<E> skippingIterator​(java.util.Iterator<E> iterator,
                                                       long offset)
        Decorates the specified iterator to skip the first N elements.
        Type Parameters:
        E - the element type
        Parameters:
        iterator - the iterator to decorate
        offset - the first number of elements to skip
        Returns:
        a new skipping iterator
        Throws:
        java.lang.NullPointerException - if the iterator is null
        java.lang.IllegalArgumentException - if offset is negative
        Since:
        4.1

      • zippingIterator

        public static <E> ZippingIterator<E> zippingIterator​(java.util.Iterator<? extends E> a,
                                                     java.util.Iterator<? extends E> b)
        Returns an iterator that interleaves elements from the decorated iterators.
        Type Parameters:
        E - the element type
        Parameters:
        a - the first iterator to interleave
        b - the second iterator to interleave
        Returns:
        an iterator, interleaving the decorated iterators
        Throws:
        java.lang.NullPointerException - if any iterator is null
        Since:
        4.1

      • zippingIterator

        public static <E> ZippingIterator<E> zippingIterator​(java.util.Iterator<? extends E> a,
                                                     java.util.Iterator<? extends E> b,
                                                     java.util.Iterator<? extends E> c)
        Returns an iterator that interleaves elements from the decorated iterators.
        Type Parameters:
        E - the element type
        Parameters:
        a - the first iterator to interleave
        b - the second iterator to interleave
        c - the third iterator to interleave
        Returns:
        an iterator, interleaving the decorated iterators
        Throws:
        java.lang.NullPointerException - if any iterator is null
        Since:
        4.1

      • zippingIterator

        public static <E> ZippingIterator<E> zippingIterator​(java.util.Iterator<? extends E>... iterators)
        Returns an iterator that interleaves elements from the decorated iterators.
        Type Parameters:
        E - the element type
        Parameters:
        iterators - the array of iterators to interleave
        Returns:
        an iterator, interleaving the decorated iterators
        Throws:
        java.lang.NullPointerException - if any iterator is null
        Since:
        4.1

      • asIterator

        public static <E> java.util.Iterator<E> asIterator​(java.util.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, may not be null
        Returns:
        a new iterator
        Throws:
        java.lang.NullPointerException - if enumeration is null

      • asIterator

        public static <E> java.util.Iterator<E> asIterator​(java.util.Enumeration<? extends E> enumeration,
                                                   java.util.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, may not be null
        removeCollection - the collection to remove elements from, may not be null
        Returns:
        a new iterator
        Throws:
        java.lang.NullPointerException - if enumeration or removeCollection is null

      • asEnumeration

        public static <E> java.util.Enumeration<E> asEnumeration​(java.util.Iterator<? extends E> iterator)
        Gets an enumeration that wraps an iterator.
        Type Parameters:
        E - the element type
        Parameters:
        iterator - the iterator to use, may not be null
        Returns:
        a new enumeration
        Throws:
        java.lang.NullPointerException - if iterator is null

      • asIterable

        public static <E> java.lang.Iterable<E> asIterable​(java.util.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, may not be null
        Returns:
        a new, single use Iterable
        Throws:
        java.lang.NullPointerException - if iterator is null

      • asMultipleUseIterable

        public static <E> java.lang.Iterable<E> asMultipleUseIterable​(java.util.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, may not be null
        Returns:
        a new, multiple use iterable
        Throws:
        java.lang.NullPointerException - if iterator is null

      • toListIterator

        public static <E> java.util.ListIterator<E> toListIterator​(java.util.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, may not be null
        Returns:
        a new iterator
        Throws:
        java.lang.NullPointerException - if iterator parameter is null

      • toArray

        public static java.lang.Object[] toArray​(java.util.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:
        java.lang.NullPointerException - if iterator parameter is null

      • toArray

        public static <E> E[] toArray​(java.util.Iterator<? extends E> iterator,
                              java.lang.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:
        java.lang.NullPointerException - if iterator parameter or arrayClass is null
        java.lang.ArrayStoreException - if the arrayClass is invalid

      • toList

        public static <E> java.util.List<E> toList​(java.util.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:
        java.lang.NullPointerException - if iterator parameter is null

      • toList

        public static <E> java.util.List<E> toList​(java.util.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:
        java.lang.NullPointerException - if iterator parameter is null
        java.lang.IllegalArgumentException - if the size is less than 1

      • getIterator

        public static java.util.Iterator<?> getIterator​(java.lang.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

      • forEach

        public static <E> void forEach​(java.util.Iterator<E> iterator,
                               Closure<? super E> closure)
        Applies the closure to each element of the provided iterator.
        Type Parameters:
        E - the element type
        Parameters:
        iterator - the iterator to use, may be null
        closure - the closure to apply to each element, may not be null
        Throws:
        java.lang.NullPointerException - if closure is null
        Since:
        4.1

      • forEachButLast

        public static <E> E forEachButLast​(java.util.Iterator<E> iterator,
                                   Closure<? super E> closure)
        Executes the given closure on each but the last element in the iterator.

        If the input iterator is null no change is made.

        Type Parameters:
        E - the type of object the Iterator contains
        Parameters:
        iterator - the iterator to get the input from, may be null
        closure - the closure to perform, may not be null
        Returns:
        the last element in the iterator, or null if iterator is null or empty
        Throws:
        java.lang.NullPointerException - if closure is null
        Since:
        4.1

      • find

        public static <E> E find​(java.util.Iterator<E> iterator,
                         Predicate<? super E> predicate)
        Finds the first element in the given iterator which matches the given predicate.

        A null or empty iterator returns null.

        Type Parameters:
        E - the element type
        Parameters:
        iterator - the iterator to search, may be null
        predicate - the predicate to use, may not be null
        Returns:
        the first element of the iterator which matches the predicate or null if none could be found
        Throws:
        java.lang.NullPointerException - if predicate is null
        Since:
        4.1

      • indexOf

        public static <E> int indexOf​(java.util.Iterator<E> iterator,
                              Predicate<? super E> predicate)
        Returns the index of the first element in the specified iterator that matches the given predicate.

        A null or empty iterator returns -1.

        Type Parameters:
        E - the element type
        Parameters:
        iterator - the iterator to search, may be null
        predicate - the predicate to use, may not be null
        Returns:
        the index of the first element which matches the predicate or -1 if none matches
        Throws:
        java.lang.NullPointerException - if predicate is null
        Since:
        4.1

      • matchesAny

        public static <E> boolean matchesAny​(java.util.Iterator<E> iterator,
                                     Predicate<? super E> predicate)
        Answers true if a predicate is true for any element of the iterator.

        A null or empty iterator returns false.

        Type Parameters:
        E - the type of object the Iterator contains
        Parameters:
        iterator - the Iterator to use, may be null
        predicate - the predicate to use, may not be null
        Returns:
        true if any element of the collection matches the predicate, false otherwise
        Throws:
        java.lang.NullPointerException - if predicate is null
        Since:
        4.1

      • matchesAll

        public static <E> boolean matchesAll​(java.util.Iterator<E> iterator,
                                     Predicate<? super E> predicate)
        Answers true if a predicate is true for every element of an iterator.

        A null or empty iterator returns true.

        Type Parameters:
        E - the type of object the Iterator contains
        Parameters:
        iterator - the Iterator to use, may be null
        predicate - the predicate to use, may not be null
        Returns:
        true if every element of the collection matches the predicate or if the collection is empty, false otherwise
        Throws:
        java.lang.NullPointerException - if predicate is null
        Since:
        4.1

      • isEmpty

        public static boolean isEmpty​(java.util.Iterator<?> iterator)
        Checks if the given iterator is empty.

        A null or empty iterator returns true.

        Parameters:
        iterator - the Iterator to use, may be null
        Returns:
        true if the iterator is exhausted or null, false otherwise
        Since:
        4.1

      • contains

        public static <E> boolean contains​(java.util.Iterator<E> iterator,
                                   java.lang.Object object)
        Checks if the object is contained in the given iterator.

        A null or empty iterator returns false.

        Type Parameters:
        E - the type of object the Iterator contains
        Parameters:
        iterator - the iterator to check, may be null
        object - the object to check
        Returns:
        true if the object is contained in the iterator, false otherwise
        Since:
        4.1

      • get

        public static <E> E get​(java.util.Iterator<E> iterator,
                        int index)
        Returns the index-th value in Iterator, throwing IndexOutOfBoundsException if there is no such element.

        The Iterator is advanced to index (or to the end, if index exceeds the number of entries) as a side effect of this method.

        Type Parameters:
        E - the type of object in the Iterator
        Parameters:
        iterator - the iterator to get a value from
        index - the index to get
        Returns:
        the object at the specified index
        Throws:
        java.lang.IndexOutOfBoundsException - if the index is invalid
        Since:
        4.1

      • first

        public static <E> E first​(java.util.Iterator<E> iterator)
        Shortcut for get(iterator, 0).

        Returns the first value in Iterator, throwing IndexOutOfBoundsException if there is no such element.

        The Iterator is advanced to 0 (or to the end, if 0 exceeds the number of entries) as a side effect of this method.

        Type Parameters:
        E - the type of object in the Iterator
        Parameters:
        iterator - the iterator to get a value from
        Returns:
        the first object
        Throws:
        java.lang.IndexOutOfBoundsException - if the request is invalid
        Since:
        4.2

      • size

        public static int size​(java.util.Iterator<?> iterator)
        Returns the number of elements contained in the given iterator.

        A null or empty iterator returns 0.

        Parameters:
        iterator - the iterator to check, may be null
        Returns:
        the number of elements contained in the iterator
        Since:
        4.1

      • toString

        public static <E> java.lang.String toString​(java.util.Iterator<E> iterator)
        Returns a string representation of the elements of the specified iterator.

        The string representation consists of a list of the iterator's elements, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (a comma followed by a space). Elements are converted to strings as by String.valueOf(Object).

        Type Parameters:
        E - the element type
        Parameters:
        iterator - the iterator to convert to a string, may be null
        Returns:
        a string representation of iterator
        Since:
        4.1

      • toString

        public static <E> java.lang.String toString​(java.util.Iterator<E> iterator,
                                            Transformer<? super E,​java.lang.String> transformer)
        Returns a string representation of the elements of the specified iterator.

        The string representation consists of a list of the iterable's elements, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (a comma followed by a space). Elements are converted to strings as by using the provided transformer.

        Type Parameters:
        E - the element type
        Parameters:
        iterator - the iterator to convert to a string, may be null
        transformer - the transformer used to get a string representation of an element
        Returns:
        a string representation of iterator
        Throws:
        java.lang.NullPointerException - if transformer is null
        Since:
        4.1

      • toString

        public static <E> java.lang.String toString​(java.util.Iterator<E> iterator,
                                            Transformer<? super E,​java.lang.String> transformer,
                                            java.lang.String delimiter,
                                            java.lang.String prefix,
                                            java.lang.String suffix)
        Returns a string representation of the elements of the specified iterator.

        The string representation consists of a list of the iterator's elements, enclosed by the provided prefix and suffix. Adjacent elements are separated by the provided delimiter. Elements are converted to strings as by using the provided transformer.

        Type Parameters:
        E - the element type
        Parameters:
        iterator - the iterator to convert to a string, may be null
        transformer - the transformer used to get a string representation of an element
        delimiter - the string to delimit elements
        prefix - the prefix, prepended to the string representation
        suffix - the suffix, appended to the string representation
        Returns:
        a string representation of iterator
        Throws:
        java.lang.NullPointerException - if either transformer, delimiter, prefix or suffix is null
        Since:
        4.1