— Scott McNealy, Sun Microsystems Chairman, President and ceo

550
 
chapter 16
The new, improved, comparable Song class
We decided we want to sort by title, so we implement the compareTo() 
method to compare the title of the Song passed to the method against 
the title of the song on which the compareTo() method was invoked. 
In other words, the song running the method has to decide how its 
title compares to the title of the method parameter.
Hmmm... we know that the String class must know about alphabetical 
order, because the sort() method worked on a list of Strings. We know 
String has a compareTo() method, so why not just call it? That way, we 
can simply let one title String compare itself to another, and we don’t 
have to write the comparing/alphabetizing algorithm!
class 
Song
 
implements Comparable 
{
String title;
String artist;
String rating;
String bpm;


 
public int compareTo(Song s) {
return title.compareTo(s.getTitle());
}
Song(String t, String a, String r, String b) {
title = t;
artist = a;
rating = r;
bpm = b;
}
public String getTitle() {
return title;
}
public String getArtist() { 
return artist;
}
public String getRating() {
return rating;
}
public String getBpm() {
return bpm;
}

public String toString() {
return title; 
} 
}
Usually these match...we’re specifying the type that 
the implementing class can be compared against. 
This means that Song objects can be compared to 
other Song objects, for the purpose of sorting.
Simple! We just pass the work 
on to the title String objects, 
since we know Strings have a 
compareTo() method.
The sort() method sends a Song to compareTo() 
to see how that Song compares to the Song on 
which the method was invoked.
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