org.apache.commons.collections4.iterators
Class ReverseListIterator<E>

java.lang.Object
  org.apache.commons.collections4.iterators.ReverseListIterator<E>

All Implemented Interfaces:

Iterator<E>, ListIterator<E>, OrderedIterator<E>, ResettableIterator<E>, ResettableListIterator<E>

public class ReverseListIterator<E>
extends Object
implements ResettableListIterator<E>

Iterates backwards through a List, starting with the last element and continuing to the first. This is useful for looping around a list in reverse order without needing to actually reverse the list.

The first call to next() will return the last element from the list, and so on. The hasNext() method works in concert with the next() method as expected. However, the nextIndex() method returns the correct index in the list, thus it starts high and reduces as the iteration continues. The previous methods work similarly.

Since:

3.2

Version:

$Id: ReverseListIterator.java 1469004 2013-04-17 17:37:03Z tn $

ReverseListIterator

public ReverseListIterator(List<E> list)

Constructor that wraps a list.

Parameters:

list - the list to create a reversed iterator for

Throws:

NullPointerException - if the list is null

hasNext

public boolean hasNext()

Checks whether there is another element.

Specified by:

hasNext in interface Iterator<E>

Specified by:

hasNext in interface ListIterator<E>

Returns:

true if there is another element

next

public E next()

Gets the next element. The next element is the previous in the list.

Specified by:

next in interface Iterator<E>

Specified by:

next in interface ListIterator<E>

Returns:

the next element in the iterator

nextIndex

public int nextIndex()

Gets the index of the next element.

Specified by:

nextIndex in interface ListIterator<E>

Returns:

the index of the next element in the iterator

hasPrevious

public boolean hasPrevious()

Checks whether there is a previous element.

Specified by:

hasPrevious in interface ListIterator<E>

Specified by:

hasPrevious in interface OrderedIterator<E>

Returns:

true if there is a previous element

previous

public E previous()

Gets the previous element. The next element is the previous in the list.

Specified by:

previous in interface ListIterator<E>

Specified by:

previous in interface OrderedIterator<E>

Returns:

the previous element in the iterator

previousIndex

public int previousIndex()

Gets the index of the previous element.

Specified by:

previousIndex in interface ListIterator<E>

Returns:

the index of the previous element in the iterator

remove

public void remove()

Removes the last returned element.

Specified by:

remove in interface Iterator<E>

Specified by:

remove in interface ListIterator<E>

Throws:

UnsupportedOperationException - if the list is unmodifiable

IllegalStateException - if there is no element to remove

set

public void set(E obj)

Replaces the last returned element.

Specified by:

set in interface ListIterator<E>

Parameters:

obj - the object to set

Throws:

UnsupportedOperationException - if the list is unmodifiable

IllegalStateException - if the iterator is not in a valid state for set

add

public void add(E obj)

Adds a new element to the list between the next and previous elements.

Specified by:

add in interface ListIterator<E>

Parameters:

obj - the object to add

Throws:

UnsupportedOperationException - if the list is unmodifiable

IllegalStateException - if the iterator is not in a valid state for set

reset

public void reset()

Resets the iterator back to the start (which is the end of the list as this is a reversed iterator)

Specified by:

reset in interface ResettableIterator<E>