SETS AND MAPS - Introduction to Java Programming: Comprehensive Version - page 815

21.20

Show the output of the following code:

public class Test {
public static void main(String[] args) {
Map<String, String> map = new LinkedHashMap<>();
map.put( "123" , "John Smith" );
map.put( "111" , "George Smith" );
map.put( "123" , "Steve Yao" );
map.put( "222" , "Steve Yao" );
System.out.println( "(1) " + map);
System.out.println( "(2) " + new TreeMap<String, String>(map));
}
}

21.6 Case Study: Occurrences of Words
This case study writes a program that counts the occurrences of words in a text and
displays the words and their occurrences in alphabetical order of the words.

Key
Point

The program uses a TreeMap to store an entry consisting of a word and its count. For
each word, check whether it is already a key in the map. If not, add an entry to the map
with the word as the key and value 1 . Otherwise, increase the value for the word (key)
by 1 in the map. Assume the words are case insensitive; e.g., Good is treated the same
as good .
Listing 21.9 gives the solution to the problem.

L ISTING 21.9

CountOccurrenceOfWords.java
1 import java.util.*;
2
3 public class CountOccurrenceOfWords {
4 public static void main(String[] args) {
5 // Set text in a string
6 String text = "Good morning. Have a good class. " +
7 "Have a good visit. Have fun!" ;

8
9 // Create a TreeMap to hold words as key and count as value

10 Map<String, Integer> map = new TreeMap<>(); tree map

11
12 String[] words = text.split( "[ \n\t\r.,;:!?(){" );
13

split string

for ( int i = 0 ; i < words.length; i++) {

14 String key = words[i].toLowerCase();

15
16 if (key.length() > 0 ) {

17 if (!map.containsKey(key)) {

18 map.put(key, 1 );

add entry

19 }
20 else {
21 int value = map.get(key);
22 value++;
23 map.put(key, value); update entry

24 }
25 }
26 }
27
28 // Get all entries into a set

29 Set<Map.Entry<String, Integer>> entrySet = map.entrySet();

entry set

30