Package org.apache.commons.collections4.iterators

Class LoopingListIterator<E>

java.lang.Object
org.apache.commons.collections4.iterators.LoopingListIterator<E>
Type Parameters:
E - the type of elements returned by this iterator.
All Implemented Interfaces:
Iterator<E>, ListIterator<E>, OrderedIterator<E>, ResettableIterator<E>, ResettableListIterator<E>
public class LoopingListIterator<E> extends Object implements ResettableListIterator<E>
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:
3.2

  • Constructor Summary

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

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    add(E 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.
    E
    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().
    E
    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(E 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<E> 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 is null

  • Method Details

    • add

      public void add(E 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<E>
      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.

      Specified by:
      hasNext in interface Iterator<E>
      Specified by:
      hasNext in interface ListIterator<E>
      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.

      Specified by:
      hasPrevious in interface ListIterator<E>
      Specified by:
      hasPrevious in interface OrderedIterator<E>
      Returns:
      true if there are more elements

    • next

      public E 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<E>
      Specified by:
      next in interface ListIterator<E>
      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<E>
      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 E 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<E>
      Specified by:
      previous in interface OrderedIterator<E>
      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<E>
      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<E>
      Specified by:
      remove in interface ListIterator<E>
      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.
      Specified by:
      reset in interface ResettableIterator<E>

    • set

      public void set(E 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<E>
      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