Java Reference
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they were inserted. TreeSet stores elements sorted. All the methods in HashSet ,
LinkedHashSet , and TreeSet are inherited from the Collection interface.
4. The Map interface maps keys to the elements. The keys are like indexes. In List ,
the indexes are integers. In Map , the keys can be any objects. A map cannot contain
duplicate keys. Each key can map to at most one value. The Map interface provides
the methods for querying, updating, and obtaining a collection of values and a set
of keys.
5.
Three types of maps are supported: HashMap , LinkedHashMap , and TreeMap .
HashMap is efficient for locating a value, inserting an entry, and deleting an entry.
LinkedHashMap supports ordering of the entries in the map. The entries in a Hash-
Map are not ordered, but the entries in a LinkedHashMap can be retrieved either in
the order in which they were inserted into the map (known as the insertion order )
or in the order in which they were last accessed, from least recently accessed to
most recently ( access order ). TreeMap is efficient for traversing the keys in a sorted
order. The keys can be sorted using the Comparable interface or the Comparator
interface.
Q UIZ
Answer the quiz for this chapter online at www.cs.armstrong.edu/liang/intro10e/quiz.html .
P ROGRAMMING E XERCISES
Sections 21.2-21.4
21.1
( Perform set operations on hash sets ) Create two linked hash sets { "George" ,
"Jim" , "John" , "Blake" , "Kevin" , "Michael" } and { "George" , "Katie" ,
"Kevin" , "Michelle" , "Ryan" } and find their union, difference, and intersec-
tion. (You can clone the sets to preserve the original sets from being changed by
these set methods.)
21.2
( Display nonduplicate words in ascending order ) Write a program that reads
words from a text file and displays all the nonduplicate words in ascending order.
The text file is passed as a command-line argument.
**21.3
( Count the keywords in Java source code ) Revise the program in Listing 21.7. If
a keyword is in a comment or in a string, don't count it. Pass the Java file name
from the command line. Assume that the Java source code is correct and line
comments and paragraph comments do not overlap.
*21.4
( Count consonants and vowels ) Write a program that prompts the user to enter a
text file name and displays the number of vowels and consonants in the file. Use
a set to store the vowels A , E , I , O , and U .
***21.5
( Syntax highlighting ) Write a program that converts a Java file into an HTML
file. In the HTML file, the keywords, comments, and literals are displayed in
bold navy, green, and blue, respectively. Use the command line to pass a Java file
and an HTML file. For example, the following command
java Exercise21_05 Welcome.java Welcome.html
converts Welcome.java into Welcome.html . Figure 21.8a shows a Java file. The
corresponding HTML file is shown in Figure 21.8b.
 
 
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