— Scott McNealy, Sun Microsystems Chairman, President and ceo

TreeSets and 
sorting

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collections 
with 
generics
you are here
4
565
What you MUST know about TreeSet...
import java.util.*;
public class TestTree {
public static void main (String[] args) {
new TestTree().go();
}
public void go() {
Book b1 = new Book(“How Cats Work”);
Book b2 = new Book(“Remix your Body”);
Book b3 = new Book(“Finding Emo”);

TreeSet tree = new TreeSet();
tree.add(b1);
tree.add(b2);
tree.add(b3);
System.out.println(tree);
}
}
class Book {
String title;
public Book(String t) {
title = t;
}
}
Sharpen your pencil
Look at this code. 
Read it carefully, then 
answer the questions 
below. (Note: there 
are no syntax errors 
in this code.)
1). What is the result when you compile this code?
2). If it compiles, what is the result when you run the TestTree class?
3). If there is a problem (either compile-time or runtime) with this code, how would you fix it?
TreeSet looks easy, but make sure you really understand what you need to 
do to use it. We thought it was so important that we made it an exercise so 
you’d have to think about it. Do NOT turn the page until you’ve done this. 
We mean it.

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566
 
chapter 16
TreeSet elements MUST be comparable
TreeSet can’t read the programmer’s mind to figure out how the 
object’s should be sorted. You have to tell the TreeSet how.
class Book