An Introduction to Data Structures - Java Concepts - page 920

private Node position;
private Node previous;
}
. . .
}

Each iterator object has a reference position to the last visited node. We also store
a reference to the last node before that. We will need that reference to adjust the links
properly in the remove method.

The next method is simple. The position reference is advanced to
position.next , and the old position is remembered in previous . There is a
special case, howeverȌif the iterator points before the first element of the list, then
the old position is null , and position must be set to first .

private class LinkedListIterator
implements ListIterator
{
. . .
public Object next()
{
if (!hasNext())
throw new NoSuchElementException();
previous = position; // Remember for remove
if (position == null)
position = first;
else
position = position.next;
return position.data;
}
. . .
}

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675

The next method is supposed to be called only when the iterator is not yet at the end
of the list. The iterator is at the end if the list is empty (that is, first == null ) or
if there is no element after the current position ( position.next == null ).

private class LinkedListIterator
implements ListIterator
{
. . .
public boolean hasNext()
{