org.apache.commons.collections.iterators
Class LoopingListIterator

java.lang.Object
  org.apache.commons.collections.iterators.LoopingListIterator

All Implemented Interfaces:

java.util.Iterator, java.util.ListIterator, ResettableIterator, ResettableListIterator

public class LoopingListIterator
extends java.lang.Object
implements ResettableListIterator

A ListIterator that restarts when it reaches the end or when it reaches the beginning.

The iterator will loop continuously around the provided list, unless there are no elements in the collection to begin with, or all of the elements have been removed.

Concurrent modifications are not directly supported, and for most collection implementations will throw a ConcurrentModificationException.

Since:

Commons Collections 3.2

Version:

$Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $

Author:

Eric Crampton

Constructor Summary

LoopingListIterator(java.util.List list)
Constructor that wraps a list.

Method Summary

void	add(java.lang.Object obj) Inserts the specified element into the underlying list.
boolean	hasNext() Returns whether this iterator has any more elements.
boolean	hasPrevious() Returns whether this iterator has any more previous elements.
java.lang.Object	next() Returns the next object in the list.
int	nextIndex() Returns the index of the element that would be returned by a subsequent call to next().
java.lang.Object	previous() Returns the previous object in the list.
int	previousIndex() Returns the index of the element that would be returned by a subsequent call to previous().
void	remove() Removes the previously retrieved item from the underlying list.
void	reset() Resets the iterator back to the start of the list.
void	set(java.lang.Object obj) Replaces the last element that was returned by next() or previous().
int	size() Gets the size of the list underlying the iterator.

Methods inherited from class java.lang.Object

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

Constructor Detail

LoopingListIterator

public LoopingListIterator(java.util.List list)

Constructor that wraps a list.

There is no way to reset a ListIterator instance without recreating it from the original source, so the List must be passed in and a reference to it held.

Parameters:

list - the list to wrap

Throws:

java.lang.NullPointerException - if the list it null

Method Detail

hasNext

public boolean hasNext()

Returns whether this iterator has any more elements.

Returns false only if the list originally had zero elements, or all elements have been removed.

Specified by:

hasNext in interface java.util.Iterator

Specified by:

hasNext in interface java.util.ListIterator

Returns:

true if there are more elements

next

public java.lang.Object next()

Returns the next object in the list.

If at the end of the list, returns the first element.

Specified by:

next in interface java.util.Iterator

Specified by:

next in interface java.util.ListIterator

Returns:

the object after the last element returned

Throws:

java.util.NoSuchElementException - if there are no elements in the list

nextIndex

public int nextIndex()

Returns the index of the element that would be returned by a subsequent call to next().

As would be expected, if the iterator is at the physical end of the underlying list, 0 is returned, signifying the beginning of the list.

Specified by:

nextIndex in interface java.util.ListIterator

Returns:

the index of the element that would be returned if next() were called

Throws:

java.util.NoSuchElementException - if there are no elements in the list

hasPrevious

public boolean hasPrevious()

Returns whether this iterator has any more previous elements.

Returns false only if the list originally had zero elements, or all elements have been removed.

Specified by:

hasPrevious in interface java.util.ListIterator

Returns:

true if there are more elements

previous

public java.lang.Object previous()

Returns the previous object in the list.

If at the beginning of the list, return the last element. Note that in this case, traversal to find that element takes linear time.

Specified by:

previous in interface java.util.ListIterator

Returns:

the object before the last element returned

Throws:

java.util.NoSuchElementException - if there are no elements in the list

previousIndex

public int previousIndex()

Returns the index of the element that would be returned by a subsequent call to previous().

As would be expected, if at the iterator is at the physical beginning of the underlying list, the list's size minus one is returned, signifying the end of the list.

Specified by:

previousIndex in interface java.util.ListIterator

Returns:

the index of the element that would be returned if previous() were called

Throws:

java.util.NoSuchElementException - if there are no elements in the list

remove

public void remove()

Removes the previously retrieved item from the underlying list.

This feature is only supported if the underlying list's iterator method returns an implementation that supports it.

This method can only be called after at least one next() or previous() method call. After a removal, the remove method may not be called again until another next() or previous() has been performed. If the reset() is called, then remove may not be called until next() or previous() is called again.

Specified by:

remove in interface java.util.Iterator

Specified by:

remove in interface java.util.ListIterator

Throws:

java.lang.UnsupportedOperationException - if the remove method is not supported by the iterator implementation of the underlying list

add

public void add(java.lang.Object obj)

Inserts the specified element into the underlying list.

The element is inserted before the next element that would be returned by next(), if any, and after the next element that would be returned by previous(), if any.

This feature is only supported if the underlying list's List.listIterator() method returns an implementation that supports it.

Specified by:

add in interface java.util.ListIterator

Parameters:

obj - the element to insert

Throws:

java.lang.UnsupportedOperationException - if the add method is not supported by the iterator implementation of the underlying list

set

public void set(java.lang.Object obj)

Replaces the last element that was returned by next() or previous().

This feature is only supported if the underlying list's List.listIterator() method returns an implementation that supports it.

Specified by:

set in interface java.util.ListIterator

Parameters:

obj - the element with which to replace the last element returned

Throws:

java.lang.UnsupportedOperationException - if the set method is not supported by the iterator implementation of the underlying list

reset

public void reset()

Resets the iterator back to the start of the list.

Specified by:

reset in interface ResettableIterator

Specified by:

reset in interface ResettableListIterator

size

public int size()

Gets the size of the list underlying the iterator.

Returns:

the current list size