Iterators - Data Structures and Abstractions with Java - page 383

nextIndex++; // advance iterator
return nextEntry;

}
else
throw new NoSuchElementException("Illegal call to next(); " +
"iterator is after end of list.");

} // end next

15.28

The remove method . Removing an entry from the list involves shifting entries within the array
list . Since we have already developed that code for the list's remove method, we will call it
instead of accessing the array list directly. To do that, we need the position number of the list
entry to be removed, rather than its array index. Recall from Segment 12.1 that the position number
of an entry in a list begins at 1, so it is 1 larger than the corresponding array index.
Figure 15-8 illustrates how to use nextIndex in this implementation. The figure shows the
array of list entries and the index nextIndex just before the call to next , just after the call to next
but before the call to remove , and just after the call to remove . Part b shows that next returns a ref-
erence to the next entry, Chris , in the iteration and then increments nextIndex . The method
remove must remove this entry from the list. Since nextIndex is now 1 larger than the index of
Chris , it is the position number of the list entry that must be removed. After Chris is removed in
Part c , the next entry— Deb —moves to the next lower-numbered position in the array. Thus,
remove decrements nextIndex so that it remains the index of the next entry in the iteration.

FIGURE 15-8

The array of list entries and nextIndex (a) just before the call to
next ; (b) just after the call to next but before the call to remove ;
(c) after the call to remove

(c) After remove() removes Chris

(a) Before next() (b) After next() returns Chris

Art Art Art

Bart Bart Bart

Iterator cursor
nextIndex = 2

Iterator cursor

nextIndex = 2

Chris Chris Deb

Iterator cursor
nextIndex = 3

Deb Deb Elly

Elly Elly

The method remove has the following implementation within the inner class IteratorForArrayList :

public void remove()
{

if (wasNextCalled)
{

// nextIndex was incremented by the call to next, so it
// is the position number of the entry to be removed
ArrayListWithIterator. this .remove(nextIndex);
nextIndex--; // index of next entry in iteration