Class 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 incompatabilities 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:
    Commons Collections 2.1
    Version:
    $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
    Author:
    Stephen Colebourne, Phil Steitz
    • 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 compatability 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 compatability 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.
    • Constructor Detail

      • IteratorUtils

        public IteratorUtils()
        IteratorUtils is not normally instantiated.
    • Method Detail

      • emptyIterator

        public static ResettableIterator 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 compatability with Commons Collections 2.1.1.

        Returns:
        an iterator over nothing
      • emptyListIterator

        public static ResettableListIterator 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 compatability with Commons Collections 2.1.1.

        Returns:
        a list iterator over nothing
      • emptyOrderedIterator

        public static OrderedIterator emptyOrderedIterator()
        Gets an empty ordered iterator.

        This iterator is a valid iterator object that will iterate over nothing.

        Returns:
        an ordered iterator over nothing
      • emptyMapIterator

        public static MapIterator emptyMapIterator()
        Gets an empty map iterator.

        This iterator is a valid map iterator object that will iterate over nothing.

        Returns:
        a map iterator over nothing
      • emptyOrderedMapIterator

        public static OrderedMapIterator emptyOrderedMapIterator()
        Gets an empty ordered map iterator.

        This iterator is a valid map iterator object that will iterate over nothing.

        Returns:
        a map iterator over nothing
      • singletonIterator

        public static ResettableIterator singletonIterator​(Object 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 compatability.

        Parameters:
        object - the single object over which to iterate
        Returns:
        a singleton iterator over the object
      • singletonListIterator

        public static ListIterator singletonListIterator​(Object object)
        Gets a singleton list iterator.

        This iterator is a valid list iterator object that will iterate over the specified object.

        Parameters:
        object - the single object over which to iterate
        Returns:
        a singleton list iterator over the object
      • arrayIterator

        public static ResettableIterator arrayIterator​(Object[] 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 compatability.

        Parameters:
        array - the array over which to iterate
        Returns:
        an iterator over the array
        Throws:
        NullPointerException - if array is null
      • arrayIterator

        public static ResettableIterator 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.

        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 ResettableIterator arrayIterator​(Object[] 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 compatability.

        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 ResettableIterator 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.

        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 ResettableIterator arrayIterator​(Object[] 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 compatability.

        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 ResettableIterator 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.

        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
        IndexOutOfBoundsException - if array bounds are invalid
        IllegalArgumentException - if end is before start
        NullPointerException - if array is null
      • arrayListIterator

        public static ResettableListIterator arrayListIterator​(Object[] array)
        Gets a list iterator over an object array.
        Parameters:
        array - the array over which to iterate
        Returns:
        a list iterator over the array
        Throws:
        NullPointerException - if array is null
      • arrayListIterator

        public static ResettableListIterator 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.

        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 ResettableListIterator arrayListIterator​(Object[] array,
                                                               int start)
        Gets a list iterator over the end part of an object array.
        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 ResettableListIterator 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.

        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 ResettableListIterator arrayListIterator​(Object[] array,
                                                               int start,
                                                               int end)
        Gets a list iterator over part of an object array.
        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 ResettableListIterator 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.

        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
        IndexOutOfBoundsException - if array bounds are invalid
        IllegalArgumentException - if end is before start
        NullPointerException - if array is null
      • chainedIterator

        public static Iterator chainedIterator​(Iterator iterator1,
                                               Iterator iterator2)
        Gets an iterator that iterates through two Iterators one after another.
        Parameters:
        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
      • chainedIterator

        public static Iterator chainedIterator​(Iterator[] iterators)
        Gets an iterator that iterates through an array of Iterators one after another.
        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 Iterator chainedIterator​(Collection iterators)
        Gets an iterator that iterates through a collections of Iterators one after another.
        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 Iterator collatedIterator​(Comparator comparator,
                                                Iterator iterator1,
                                                Iterator 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.

        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 Iterator collatedIterator​(Comparator comparator,
                                                Iterator[] 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.

        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
      • collatedIterator

        public static Iterator collatedIterator​(Comparator comparator,
                                                Collection 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.

        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 Iterator objectGraphIterator​(Object root,
                                                   Transformer 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.

        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:
        Commons Collections 3.1
      • transformedIterator

        public static Iterator transformedIterator​(Iterator iterator,
                                                   Transformer 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.

        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 Iterator filteredIterator​(Iterator iterator,
                                                Predicate predicate)
        Gets an iterator that filters another iterator.

        The returned iterator will only return objects that match the specified filtering predicate.

        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 ListIterator filteredListIterator​(ListIterator listIterator,
                                                        Predicate predicate)
        Gets a list iterator that filters another list iterator.

        The returned iterator will only return objects that match the specified filtering predicate.

        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 ResettableIterator loopingIterator​(Collection 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.

        Parameters:
        coll - the collection to iterate over, not null
        Returns:
        a new looping iterator
        Throws:
        NullPointerException - if the collection is null
      • loopingListIterator

        public static ResettableListIterator loopingListIterator​(List 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.

        Parameters:
        list - the list to iterate over, not null
        Returns:
        a new looping iterator
        Throws:
        NullPointerException - if the list is null
        Since:
        Commons Collections 3.2
      • asIterator

        public static Iterator asIterator​(Enumeration enumeration)
        Gets an iterator that provides an iterator view of the given enumeration.
        Parameters:
        enumeration - the enumeration to use
        Returns:
        a new iterator
      • asIterator

        public static Iterator asIterator​(Enumeration enumeration,
                                          Collection removeCollection)
        Gets an iterator that provides an iterator view of the given enumeration that will remove elements from the specified collection.
        Parameters:
        enumeration - the enumeration to use
        removeCollection - the collection to remove elements from
        Returns:
        a new iterator
      • asEnumeration

        public static Enumeration asEnumeration​(Iterator iterator)
        Gets an enumeration that wraps an iterator.
        Parameters:
        iterator - the iterator to use, not null
        Returns:
        a new enumeration
        Throws:
        NullPointerException - if iterator is null
      • toListIterator

        public static ListIterator toListIterator​(Iterator 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.

        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 Object[] toArray​(Iterator iterator,
                                       Class 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.

        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 is null
        NullPointerException - if arrayClass is null
        ClassCastException - if the arrayClass is invalid
      • toList

        public static List toList​(Iterator 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.

        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 List toList​(Iterator 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.

        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 handles 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
        Parameters:
        obj - the object to convert to an iterator
        Returns:
        a suitable iterator, never null