Dictionaries

1
Dictionaries

• Chapter 17

2
Chapter Contents

• Specifications for the ADT Dictionary
• Java Interface
• Iterators
• Applications
• Phone Book
• Frequency of Words
• Concordance of Words
• Java Class Library Map Interface

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
• getValueIterator

• 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 beginnings of TelephoneDirectory

import java.io.import java.util.public
class TelephoneDirectory private DictionaryInt
erface phoneBook private static final String
DELIMITERS " \n\r\t" public
TelephoneDirectory() phoneBook new
SortedDictionary() . . .
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 getPhoneN
umber(String first, String last)
public String getPhoneNumber(Name personName)
/ Task Interacts with user /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
  FrequencyCounter
  
• 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 gives line (or page) number
• A word may appear multiple times
• Appears once in index/concordance
• Associated data is a list of line (page) numbers

12
Concordance...Example

• Learning without thought is labor lost
• thought without learning is perilous.
• is 1 2
• labor 1
• learning 1 2
• lost 1
• perilous 2
• thought 1 2
• without 1 2

13
Java Class Library The Interface Map

• A list of method signatures in Map
• Note similarity to ADT Dictionary
• Not String-specific!

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()