Dictionaries

1
Dictionaries

• Chapter 17

2
Chapter Contents

• Specifications for the ADT Dictionary
• A Java Interface
• Iterators
• Using the ADT Dictionary
• A Directory of Telephone Numbers
• The Frequency of Words
• A Concordance of Words
• Java Class Library the Interface Map

3
Specifications for the ADT Dictionary

• Contains entries that each have two parts
• A key word or search key
• A value associated with the key

Fig. 17-1 An English dictionary.
4
Specifications for the ADT Dictionary

• Data
• Pairs of objects (key, value)
• Number of pairs in the collection
• Operations

• add
• remove
• getValue
• contains
• getKeyIterator

• isEmpty
• isFull
• getSize
• clear

5
Iterators

• Note that getKeyIterator and getValueIterator
  return iterators
• Create iterators for a dictionary myTable
  withIterator keyIterator myTable.getKeyIterator
  ()Iterator valueIterator myTable.getValueItera
  tor()
• An iteration of a dictionary's values
• Corresponds to an iteration of the search keys

6
Iterators
Fig. 17-2 Two iterators that traverse a
dictionary's keys and values in parallel.
7
Using the ADT Dictionary

• A directory of telephone numbers

Fig 17-3 A class diagram for a telephone
directory.
8
A Directory of Telephone Numbers

• The beginning of the implementation of the class
  TelephoneDirectory

import java.io.import java.util.public
class TelephoneDirectory private
DictionaryInterface phoneBook private static
final String DELIMITERS " \n\r\t" public
TelephoneDirectory() phoneBook new
SortedDictionary() // end default
constructor . . .
9
A Directory of Telephone Numbers

• Other methods may include

/ Task Reads a text file of names and
telephone numbers. _at_param dataFile a text file
that is open for input /public void
readFile(BufferedReader dataFile) throws
IOException public String getPhoneNumber(String
firstName, String lastName) public String
getPhoneNumber(Name personName) / Task Finds
the telephone number of the person whose name
is given by the user. _at_return the desired
phone number as a string, or null if no phone
number is found, or the string "quit" if the
user enters quit instead of a name /public
String getPhoneNumber()
10
The Frequency of Words

• We seek an ADT that will enable us to count each
  occurrence of a word as it is read from a text
  file
• To determine the frequency of a word
• The word must be the search key
• The data field will be of the class
  FrequenceyCounter
• Read a word from the file
• If not in dictionary, add it, initialize word
  count 1
• If it is in the dictionary, increment the word
  count

11
A Concordance of Words

• Provide an index for finding a word in a file
• Index would give the page number
• A concordance would give the line number of a
  word (in a smaller file of words)
• A word may appear multiple times in the file
• Appears once in index/concordance
• The associated data is a list of page/line numbers

12
Java Class Library The Interface Map

• A list of method signatures in Map
• Note similarity to methods developed in this
  chapter

public Object put(Object key, Object
value)public Object remove(Object key)public
Object get(Object key)public boolean
containsKey(Object key)public boolean
containsValue(Object value)public Set
keySet()public Collection values()public
boolean isEmpty()public int size()public void
clear()