— Scott McNealy, Sun Microsystems Chairman, President and ceo

}
}
class Test {
public void go() {
Book b1 = new Book(“How Cats Work”);
Book b2 = new Book(“Remix your Body”);
Book b3 = new Book(“Finding Emo”);
BookCompare bCompare = new BookCompare();
TreeSet tree = new TreeSet(bCompare);
tree.add(new Book(“How Cats Work”);
tree.add(new Book(“Finding Emo”);
tree.add(new Book(“Remix your Body”);
System.out.println(tree);
}
}
how TreeSets 
sort

---

collections 
with 
generics
you are here
4
567
We’ve seen Lists and Sets, now we’ll use a Map
Lists and Sets are great, but sometimes a Map is the best collection (not Collection 
with a capital “C”—remember that Maps are part of Java collections but they don’t 
implement the Collection interface).
Imagine you want a collection that acts like a property list, where you give it a name 
and it gives you back the value associated with that name. Although keys will often be 
Strings, they can be any Java object (or, through autoboxing, a primitive).
import java.util.*;
public class TestMap {
public static void main(String[] args) {
HashMap

 scores = new HashMap

();
scores.
put(“Kathy”, 42);
scores.
put(“Bert”, 343);
scores.
put(“Skyler”, 420);
System.out.println(scores);
System.out.println(
scores.
get(“Bert”)
);
}
}
Map
“Ball” “Fish” “Car”
“Ball1” “Ball2” “Ball3” “Ball4”
Each element in a Map is actually 
TWO objects—a 
key and a value.
You can have duplicate 
values, but 
NOT duplicate 
keys.
Map example
HashMap needs TWO type parameters—
one for the key and one for the value.
Use put() instead of add(), and now of course 
it takes two arguments (key, value).