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java.lang.Object
org.apache.commons.collections.IteratorUtils
public class IteratorUtils
extends java.lang.Object
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.
Field Summary | |
static ResettableIterator |
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static ResettableListIterator |
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static MapIterator |
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static OrderedIterator |
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static OrderedMapIterator |
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Constructor Summary | |
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Method Summary | |
static ResettableIterator |
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static ResettableIterator |
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static ResettableIterator |
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static ResettableIterator |
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static ResettableIterator |
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static ResettableIterator |
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static ResettableListIterator |
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static ResettableListIterator |
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static ResettableListIterator |
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static ResettableListIterator |
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static ResettableListIterator |
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static ResettableListIterator |
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static Enumeration |
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static Iterator |
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static Iterator |
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static Iterator |
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static Iterator |
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static Iterator |
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static Iterator |
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static Iterator |
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static Iterator |
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static ResettableIterator |
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static ResettableListIterator |
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static MapIterator |
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static OrderedIterator |
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static OrderedMapIterator |
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static Iterator |
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static ListIterator |
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static Iterator |
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static ResettableIterator |
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static Iterator |
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static ResettableIterator |
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static ListIterator |
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static Object[] |
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static Object[] |
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static List |
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static List |
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static ListIterator |
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static Iterator |
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static Iterator |
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static ListIterator |
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static MapIterator |
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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. UseEmptyIterator.INSTANCE
for compatability with Commons Collections 2.1.1.
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. UseEmptyListIterator.INSTANCE
for compatability with Commons Collections 2.1.1.
public static final MapIterator EMPTY_MAP_ITERATOR
A map iterator over no elements.
public static final OrderedIterator EMPTY_ORDERED_ITERATOR
An ordered iterator over no elements.
public static final OrderedMapIterator EMPTY_ORDERED_MAP_ITERATOR
An ordered map iterator over no elements.
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
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 iteratestart
- the index to start iterating at
- Returns:
- an iterator over part of the array
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 iteratestart
- the index to start iterating atend
- the index to finish iterating at
- Returns:
- an iterator over part of the array
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. Usenew ArrayIterator(array)
for compatability.
- Parameters:
array
- the array over which to iterate
- Returns:
- an iterator over the array
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. Usenew ArrayIterator(array,start)
for compatability.
- Parameters:
array
- the array over which to iteratestart
- the index to start iterating at
- Returns:
- an iterator over part of the array
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. Usenew ArrayIterator(array,start,end)
for compatability.
- Parameters:
array
- the array over which to iteratestart
- the index to start iterating atend
- the index to finish iterating at
- Returns:
- an iterator over part of the array
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
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 iteratestart
- the index to start iterating at
- Returns:
- a list iterator over part of the array
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 iteratestart
- the index to start iterating atend
- the index to finish iterating at
- Returns:
- a list iterator over part of the array
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
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 iteratestart
- the index to start iterating at
- Returns:
- a list iterator over part of the array
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 iteratestart
- the index to start iterating atend
- the index to finish iterating at
- Returns:
- a list iterator over part of the array
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
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
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 useremoveCollection
- the collection to remove elements from
- Returns:
- a new iterator
public static Iterator chainedIterator(Collection iterators)
Gets an iterator that iterates through a collections ofIterator
s one after another.
- Parameters:
iterators
- the iterators to use, not null or empty or contain nulls
- Returns:
- a combination iterator over the iterators
public static Iterator chainedIterator(Iterator iterator1, Iterator iterator2)
Gets an iterator that iterates through twoIterator
s one after another.
- Parameters:
iterator1
- the first iterators to use, not nulliterator2
- the first iterators to use, not null
- Returns:
- a combination iterator over the iterators
public static Iterator chainedIterator(Iterator[] iterators)
Gets an iterator that iterates through an array ofIterator
s one after another.
- Parameters:
iterators
- the iterators to use, not null or empty or contain nulls
- Returns:
- a combination iterator over the iterators
public static Iterator collatedIterator(Comparator comparator, Collection iterators)
Gets an iterator that provides an ordered iteration over the elements contained in a collection ofIterator
s. Given two orderedIterator
sA
andB
, theIterator.next()
method will return the lesser ofA.next()
andB.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 orderiterators
- the iterators to use, not null or empty or contain nulls
- Returns:
- a combination iterator over the iterators
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 orderedIterator
s. Given two orderedIterator
sA
andB
, theIterator.next()
method will return the lesser ofA.next()
andB.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 orderiterator1
- the first iterators to use, not nulliterator2
- the first iterators to use, not null
- Returns:
- a combination iterator over the iterators
public static Iterator collatedIterator(Comparator comparator, Iterator[] iterators)
Gets an iterator that provides an ordered iteration over the elements contained in an array ofIterator
s. Given two orderedIterator
sA
andB
, theIterator.next()
method will return the lesser ofA.next()
andB.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 orderiterators
- the iterators to use, not null or empty or contain nulls
- Returns:
- a combination iterator over the iterators
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. UseEmptyIterator.INSTANCE
for compatability with Commons Collections 2.1.1.
- Returns:
- an iterator over nothing
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. UseEmptyListIterator.INSTANCE
for compatability with Commons Collections 2.1.1.
- Returns:
- a list iterator over nothing
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
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
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
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 nullpredicate
- the predicate to use as a filter, not null
- Returns:
- a new filtered iterator
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 nullpredicate
- the predicate to use as a filter, not null
- Returns:
- a new filtered iterator
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
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
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 aTransformer
to extract the iterators and elements. Its main benefit is that no intermediateList
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 -- LeafThe followingTransformer
, 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 iteratortransformer
- the transformer to use, see above, null uses no effect transformer
- Returns:
- a new object graph iterator
- Since:
- Commons Collections 3.1
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. Usenew SingletonIterator(object)
for compatability.
- Parameters:
object
- the single object over which to iterate
- Returns:
- a singleton iterator over the object
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
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
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 nullarrayClass
- the class of array to create
- Returns:
- an array of the iterator contents
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
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 nullestimatedSize
- the initial size of the ArrayList
- Returns:
- a list of the iterator contents
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
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 nulltransform
- the transform to use, not null
- Returns:
- a new transforming iterator
public static Iterator unmodifiableIterator(Iterator iterator)
Gets an immutable version of anIterator
. The returned object will always throw anUnsupportedOperationException
for theIterator.remove
method.
- Parameters:
iterator
- the iterator to make immutable
- Returns:
- an immutable version of the iterator
public static ListIterator unmodifiableListIterator(ListIterator listIterator)
Gets an immutable version of aListIterator
. The returned object will always throw anUnsupportedOperationException
for theIterator.remove
,ListIterator.add
andListIterator.set
methods.
- Parameters:
listIterator
- the iterator to make immutable
- Returns:
- an immutable version of the iterator
public static MapIterator unmodifiableMapIterator(MapIterator mapIterator)
Gets an immutable version of aMapIterator
. The returned object will always throw anUnsupportedOperationException
for theIterator.remove
,MapIterator.setValue(Object)
methods.
- Parameters:
mapIterator
- the iterator to make immutable
- Returns:
- an immutable version of the iterator