Class IteratorUtils

Method Details

• 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

• unmodifiableIterator

  public static Iterator unmodifiableIterator(Iterator iterator)

  Gets an immutable version of an Iterator. The returned object will always throw an UnsupportedOperationException for the Iterator.remove() method.

  Parameters:

  iterator - the iterator to make immutable

  Returns:

  an immutable version of the iterator

• unmodifiableListIterator

  public static ListIterator unmodifiableListIterator(ListIterator 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.

  Parameters:

  listIterator - the iterator to make immutable

  Returns:

  an immutable version of the iterator

• unmodifiableMapIterator

  public static MapIterator unmodifiableMapIterator(MapIterator mapIterator)

  Gets an immutable version of a MapIterator. The returned object will always throw an UnsupportedOperationException for the Iterator.remove(), MapIterator.setValue(Object) methods.

  Parameters:

  mapIterator - the iterator to make immutable

  Returns:

  an immutable version of the iterator

• 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