Iterators - Data Structures and Abstractions with Java - page 389

FIGURE 15-9

The effect of a call to previous on a list

(a) Before previous()

(b) After previous() returns Joey

Jamie
Joey
Rachel
Monica
Ross

Jamie
Joey
Rachel
Monica
Ross

Iterator cursor

Iterator cursor

15.36

The indices of the current and previous entries. As Figure 15-10 shows, the methods nextIndex
and previousIndex each return the index of the entry that a subsequent call to next or previous ,
respectively, would return. Note that the iterator numbers the list's entries beginning with 0, instead
of 1 as the ADT list operations do. If a call to next would throw an exception because the iterator is
at the end of the list, nextIndex returns the size of the list. Similarly, if a call to previous would
throw an exception because the iterator is at the beginning of the list, previousIndex returns - 1.

FIGURE 15-10

The indices returned by the methods nextIndex and previousIndex

Jamie
Joey
Rachel
Monica
Ross

previousIndex() returns the index of Joey
nextIndex() returns the index of Rachel

Iterator cursor

Note: The interface ListIterator specifies nine methods, including the three methods
that Iterator specifies. They are hasNext , hasPrevious , next , previous , nextIndex ,
previousIndex , add , remove , and set .

Using the Interface ListIterator

15.37

Example: Traversals. Let's look at an example of the methods that work with the current and
previous entries and then use it to describe the remaining methods in the interface. We make the
following assumptions:

The interface ListIterator is implemented as an inner class of the class that implements
the ADT list.

●

The iterator includes the operations add , remove , and set .

●

The method getIterator is added to the ADT list.

●

The list nameList contains the following names:
Jess
Jim
Josh

●

The iterator traverse is defined as follows:

●

ListIterator<String> traverse = nameList.getIterator();