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 1686855 2015-06-22 13:00:27Z tn $

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `ReverseListIterator(List<E> list)` Constructor that wraps a list.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `add(E obj)` Adds a new element to the list between the next and previous elements.
    `boolean` | `hasNext()` Checks whether there is another element.
    `boolean` | `hasPrevious()` Checks whether there is a previous element.
    `E` | `next()` Gets the next element.
    `int` | `nextIndex()` Gets the index of the next element.
    `E` | `previous()` Gets the previous element.
    `int` | `previousIndex()` Gets the index of the previous element.
    `void` | `remove()` Removes the last returned element.
    `void` | `reset()` Resets the iterator back to the start (which is the end of the list as this is a reversed iterator)
    `void` | `set(E obj)` Replaces the last returned element.

    - ### Methods inherited from class java.lang.Object

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

- - ### Constructor Detail

    - #### 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

  - ### Method Detail

    - #### 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>`

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