org.apache.commons.collections.iterators

Class LoopingListIterator

public class LoopingListIterator extends 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: 405920 $ $Date: 2006-05-12 23:48:04 +0100 (Fri, 12 May 2006) $

Author: Eric Crampton

Constructor Summary
LoopingListIterator(List list)
Constructor that wraps a list.
Method Summary
voidadd(Object obj)
Inserts the specified element into the underlying list.
booleanhasNext()
Returns whether this iterator has any more elements.
booleanhasPrevious()
Returns whether this iterator has any more previous elements.
Objectnext()
Returns the next object in the list.
intnextIndex()
Returns the index of the element that would be returned by a subsequent call to LoopingListIterator.
Objectprevious()
Returns the previous object in the list.
intpreviousIndex()
Returns the index of the element that would be returned by a subsequent call to LoopingListIterator.
voidremove()
Removes the previously retrieved item from the underlying list.
voidreset()
Resets the iterator back to the start of the list.
voidset(Object obj)
Replaces the last element that was returned by LoopingListIterator or LoopingListIterator.
intsize()
Gets the size of the list underlying the iterator.

Constructor Detail

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

Throws: NullPointerException if the list it null

Method Detail

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 LoopingListIterator, if any, and after the next element that would be returned by LoopingListIterator, 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

Throws: UnsupportedOperationException if the add method is not supported by the iterator implementation of the underlying list

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.

Returns: true if there are more elements

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.

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

Throws: 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 LoopingListIterator.

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

Throws: NoSuchElementException if there are no elements in the list

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

Throws: 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 LoopingListIterator.

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

Throws: 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 List#iterator iterator method returns an implementation that supports it.

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

Throws: UnsupportedOperationException if the remove 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.

set

public void set(Object obj)
Replaces the last element that was returned by LoopingListIterator or LoopingListIterator.

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

Throws: UnsupportedOperationException if the set method is not supported by the iterator implementation of the underlying list

size

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

Returns: the current list size

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