public class

LoopingListIterator

extends Object
implements ResettableListIterator
java.lang.Object
   ↳ org.apache.commons.collections.iterators.LoopingListIterator

Class Overview

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.

Summary

Public Constructors
LoopingListIterator(List list)
Constructor that wraps a list.
Public Methods
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.
[Expand]
Inherited Methods
From class java.lang.Object
From interface java.util.Iterator
From interface java.util.ListIterator
From interface org.apache.commons.collections.ResettableIterator
From interface org.apache.commons.collections.ResettableListIterator

Public Constructors

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

Public Methods

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 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

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

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

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

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.

Returns
  • the index of the element that would be returned if next() were called
Throws
NoSuchElementException if there are no elements in the list

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

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.

Returns
  • the index of the element that would be returned if previous() were called
Throws
NoSuchElementException if there are no elements in the list

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.

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

public void reset ()

Resets the iterator back to the start of the list.

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 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

public int size ()

Gets the size of the list underlying the iterator.

Returns
  • the current list size