org.apache.commons.collections.iterators

Class LoopingListIterator

Implemented Interfaces:
Iterator, 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.

Version:
$Revision: 405920 $ $Date: 2006-05-12 23:48:04 +0100 (Fri, 12 May 2006) $
Author:
Eric Crampton
Since:
Commons Collections 3.2

Constructor Summary

LoopingListIterator(List list)
Constructor that wraps a list.

Method Summary

void
add(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.
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().
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(Object obj)
Replaces the last element that was returned by next() or previous().
int
size()
Gets the size of the list underlying the iterator.

Constructor Details

LoopingListIterator

public LoopingListIterator(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

Method Details

add

public void add(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.

Parameters:
obj - the element to insert

hasNext

public boolean hasNext()
Returns:
true if there are more elements

hasPrevious

public boolean hasPrevious()
Returns:
true if there are more elements

next

public Object next()
Returns the next object in the list.

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

Returns:
the object after the last element returned

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.

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

previous

public 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.

Returns:
the object before the last element returned

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.

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

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.


reset

public void reset()
Resets the iterator back to the start of the list.
Specified by:
reset in interface ResettableListIterator
reset in interface ResettableIterator

set

public void set(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.

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

size

public int size()
Gets the size of the list underlying the iterator.
Returns:
the current list size

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