1. Dictionaries Chapter 17

2. 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. 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. 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. 5 Iterators Note that getKeyIterator and getValueIterator return iterators Create iterators for a dictionary myTable with Iterator keyIterator = myTable.getKeyIterator(); Iterator valueIterator = myTable.getValueIterator(); An iteration of a dictionary's values Corresponds to an iteration of the search keys

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

7. 7 Using the ADT Dictionary A directory of telephone numbers Fig 17-3 A class diagram for a telephone directory.

8. 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. 9 A Directory of Telephone Numbers Other methods may include: /** Task: Reads a text file of names and telephone numbers. * @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. * @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. 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. 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. 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();