— Scott McNealy, Sun Microsystems Chairman, President and ceo

hashCode()
742
hashCode()
742
title: Circles
hashCode: 742
title: Circles
hashCode: 742
HashSet
Your hashcodes 
are the same, but are 
you REALLY equal?
Object you’re trying 
to add runs its equals() 
method, comparing itself 
to bar, and returns true.
Object already IN 
the HashSet.
Song
foo
Song
bar
equals( bar )
true

---

562
 
chapter 16
The Song class with overridden 
hashCode() and equals()
class Song implements Comparable{
String title;
String artist;
String rating;
String bpm;
public boolean 
equals(Object aSong)
 {
Song s = (Song) aSong;
return getTitle().equals(s.getTitle());
}
public int 
hashCode()
 {
return title.hashCode();
}
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; 
}
}
The HashSet (or anyone else calling this 
method) sends it another Song.
The GREAT news is that title is a String, 
and Strings have an overridden equals() 
method. So all we have to do is ask one 
title if it’s equal to the other song’s title.
Same deal here... the String class has an overridden 
hashCode() method, so you can just return the result of 
calling hashCode() on the title. Notice how hashCode() 
and equals() are using the SAME instance variable.