Package org.apache.commons.collections4.iterators

Class LoopingListIterator<E>

  • All Implemented Interfaces:
    java.util.Iterator<E>, java.util.ListIterator<E>, OrderedIterator<E>, ResettableIterator<E>, ResettableListIterator<E>
    public class LoopingListIterator<E>
extends java.lang.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​(java.util.List<E> list)
      Constructor that wraps a list.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      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

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

      • Methods inherited from interface java.util.Iterator

        forEachRemaining

    • Constructor Detail

      • LoopingListIterator

        public LoopingListIterator​(java.util.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:
        java.lang.NullPointerException - if the list it null

    • Method Detail

      • 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 java.util.Iterator<E>
        Specified by:
        hasNext in interface java.util.ListIterator<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 java.util.Iterator<E>
        Specified by:
        next in interface java.util.ListIterator<E>
        Returns:
        the object after the last element returned
        Throws:
        java.util.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 java.util.ListIterator<E>
        Returns:
        the index of the element that would be returned if next() were called
        Throws:
        java.util.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 java.util.ListIterator<E>
        Specified by:
        hasPrevious in interface OrderedIterator<E>
        Returns:
        true if there are more elements

      • 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 java.util.ListIterator<E>
        Specified by:
        previous in interface OrderedIterator<E>
        Returns:
        the object before the last element returned
        Throws:
        java.util.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 java.util.ListIterator<E>
        Returns:
        the index of the element that would be returned if previous() were called
        Throws:
        java.util.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 java.util.Iterator<E>
        Specified by:
        remove in interface java.util.ListIterator<E>
        Throws:
        java.lang.UnsupportedOperationException - if the remove method is not supported by the iterator implementation of the underlying list

      • 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 java.util.ListIterator<E>
        Parameters:
        obj - the element to insert
        Throws:
        java.lang.UnsupportedOperationException - if the add method is not supported by the iterator implementation of the underlying list

      • 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 java.util.ListIterator<E>
        Parameters:
        obj - the element with which to replace the last element returned
        Throws:
        java.lang.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<E>

      • size

        public int size()
        Gets the size of the list underlying the iterator.
        Returns:
        the current list size