— Scott McNealy, Sun Microsystems Chairman, President and ceo

564
 
chapter 16
And if we want the set to stay 
sorted, we’ve got TreeSet
import java.util.*;
import java.io.*;
public class Jukebox8 { 
ArrayList songList = new ArrayList();
int val;
public static void main(String[] args) {
new Jukebox8().go();
}
public void go() { 
getSongs(); 
System.out.println(songList);
Collections.sort(songList);
System.out.println(songList);
TreeSet songSet = new TreeSet();
songSet.addAll(songList);
System.out.println(songSet); 
}
void getSongs() {
try {
File file = new File(“SongListMore.txt”);
BufferedReader reader = new BufferedReader(new FileReader(file));
String line = null;
while ((line= reader.readLine()) != null) {
addSong(line);
}
} catch(Exception ex) {
ex.printStackTrace();
}
}
void addSong(String lineToParse) {
String[] tokens = lineToParse.split(“/”);
Song nextSong = new Song(tokens[0], tokens[1], tokens[2], tokens[3]);
songList.add(nextSong); 
}
}
TreeSet is similar to HashSet in that it prevents duplicates. But it also keeps the list sorted. It works 
just like the sort() method in that if you make a TreeSet using the set’s no-arg constructor, the 
TreeSet uses each object’s compareTo() method for the sort. But you have the option of passing 
a Comparator to the TreeSet constructor, to have the TreeSet use that instead. The downside to 
TreeSet is that if you don’t need sorting, you’re still paying for it with a small performance hit. But 
you’ll probably find that the hit is almost impossible to notice for most apps.
Instantiate a TreeSet instead of HashSet. 
Calling the no-arg TreeSet constructor 
means the set will use the Song object’s 
compareTo() method for the sort.
(We could have passed in a Comparator.)
We can add all the songs from the HashSet 
using addAll(). (Or we could have added the 
songs individually using songSet.add() just 
the way we added songs to the ArrayList.)