Package org.apache.commons.collections.iterators

Class LoopingListIterator

java.lang.Object
org.apache.commons.collections.iterators.LoopingListIterator
All Implemented Interfaces:
Iterator, ListIterator, ResettableIterator, ResettableListIterator
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: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
Author:
Eric Crampton <ccesc@eonomine.com>

  • Constructor Summary

    Constructors
    Constructor
    Description
    LoopingListIterator(List list)
    Constructor that wraps a list.

  • Method Summary

    Modifier and Type
    Method
    Description
    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.

    Methods inherited from class java.lang.Object

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

    Methods inherited from interface java.util.Iterator

    forEachRemaining

  • 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
      Throws:
      NullPointerException - if the list it null

  • Method Details

    • 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 Iterator
      Specified by:
      hasNext in interface ListIterator
      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.

      Specified by:
      next in interface Iterator
      Specified by:
      next in interface ListIterator
      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 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 ListIterator
      Returns:
      the index of the element that would be returned if next() were called
      Throws:
      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 ListIterator
      Returns:
      true if there are more elements

    • 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.

      Specified by:
      previous in interface ListIterator
      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 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 ListIterator
      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 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 Iterator
      Specified by:
      remove in interface ListIterator
      Throws:
      UnsupportedOperationException - if the remove method is not supported by the iterator implementation of the underlying list

    • 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.

      Specified by:
      add in interface ListIterator
      Parameters:
      obj - the element to insert
      Throws:
      UnsupportedOperationException - if the add method is not supported by the iterator implementation of the underlying list

    • 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.

      Specified by:
      set in interface ListIterator
      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

    • 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