Java Reference
In-Depth Information
Programming Tip:
When using a
Scanner
object to process text, any character can be a
delimiter if it does not occur in any desired token. You create a string of these delimiters using a
special notation and give it to the
Scanner
method
useDelimiter
. Consult Segment A.82 of
Appendix A for more details.
19.16
The following implementation of the method
readFile
reflects the previous discussion:
/** Reads a text file of words and counts their frequencies
of occurrence.
@param data a text scanner for the text file of data */
public void
readFile(Scanner data)
{
data.useDelimiter("\\W+");
while
(data.hasNext())
{
String nextWord = data.next();
nextWord = nextWord.toLowerCase();
Integer frequency = wordTable.getValue(nextWord);
if
(frequency ==
null
)
{
// add new word to table
wordTable.add(nextWord,
new
Integer(1));
}
else
{
// increment count of existing word; replace wordTable entry
frequency++;
wordTable.add(nextWord, frequency);
}
// end if
}
// end while
data.close();
}
// end readFile
Question 7
The previous method
readFile
does not call
contains
to see whether a word
is already in the dictionary, but instead calls
getValue
. Why did we do this?
19.17
Displaying the dictionary.
Now that we have created the dictionary, we need to display the results.
An iteration of the search keys will produce the words in alphabetical order. A parallel iteration of
the values provides the corresponding frequencies. The following method is a possible solution for
this task:
public void
display()
{
Iterator<String> keyIterator = wordTable.getKeyIterator();
Iterator<Integer> valueIterator = wordTable.getValueIterator();
while
(keyIterator.hasNext())
{
System.out.println(keyIterator.next() + " " +
valueIterator.next());
}
// end while
}
// end display
Question 8
Implement a second method
display
for the class
FrequencyCounter
that dis-
plays only words that occur with a frequency given as the method's sole parameter.
