Iterators - Data Structures and Abstractions with Java - page 373

String nextName = countingIterator.next();
if (currentName.equals(nextName))
nameCount++;
} // end while
System.out.println(currentName + " occurs " + nameCount + " times.");
} // end while

To reset countingIterator to the list's beginning, we call the constructor again, since Iterator
does not have a method for this purpose.
With the names given in Figure 15-4, these statements produce the following output:

Brad occurs 2 times.
Jane occurs 3 times.
Bob occurs 1 times.
Jane occurs 3 times.
Bette occurs 1 times.
Brad occurs 2 times.
Jane occurs 3 times.
Brenda occurs 1 times.

As you can see, since nameIterator (your left hand) encounters Brad twice and Jane three times,
the computation in the inner loop is repeated needlessly. For example, we compute that Brad occurs
twice each time nameIterator encounters Brad .
If SeparateIterator supports a remove operation, and if we are allowed to destroy the list, we
can remove the duplicate entries—and thereby prevent the repeated computations—by modifying
the if statement as follows:

if (currentName.equals(nextName))
{

nameCount++;
if (nameCount > 1)
countingIterator.remove();
} // end if

When nameCount exceeds 1, nextName must be a name that the iterator countingIterator has
retrieved from the list more than once. Thus, we remove that entry so that nameIterator will not
encounter it. We do so by invoking countingIterator.remove(). The iterator countingIterator
then continues with the next entry. Exercise 8 at the end of this chapter considers the case when we
cannot destroy the list.

A Separate Class Iterator

We will now examine an implementation of the public class SeparateIterator used in the previ-
ous examples. This class implements the interface java.util.Iterator .

15.12

An outline of the class SeparateIterator . In the previous examples, we connect an iterator—
which is an instance of the class SeparateIterator —with a list by invoking the class's construc-
tor. To accomplish this connection, the class needs a data field that references the list. As you can
see in Listing 15-2, the constructor assigns this reference to the field. Also, notice that we make the
definition of SeparateIterator independent of a particular implementation of the list, such as
AList or LList , by defining the field list as an instance of ListInterface .
In addition to connecting the iterator to the list in question, the constructor initializes it so the itera-
tion will begin at the first entry in the list. To enable this, the class has another data field nextPosition