Package org.apache.commons.collections4.iterators

Class 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

    • 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

      • 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

      • 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>