— Scott McNealy, Sun Microsystems Chairman, President and ceo

HashSet songSet = new HashSet();
songSet.addAll(songList); 
System.out.println(songSet);
}
// getSongs() and addSong() methods
}
File Edit Window Help GetBetterMusic
%java Jukebox6
[Pink Moon, Somersault, Shiva Moon, Circles, Deep Channel, 
Passenger, Listen, Listen, Listen, Circles]
[Circles, Circles, Deep Channel, Listen, Listen, Listen, 
Passenger, Pink Moon, Shiva Moon, Somersault]
[Pink Moon, Listen, Shiva Moon, Circles, Listen, Deep Channel, 
Passenger, Circles, Listen, Somersault]
Here we create a new HashSet 
parameterized to hold Songs.
We didn’t change getSongs(), so it still puts the songs in an ArrayList
HashSet has a simple addAll() method that can 
take another collection and use it to populate 
the HashSet. It’s the same as if we added each 
song one at a time (except much simpler).
The Set didn’t help!!
We still have all the duplicates!
Before sorting 
the ArrayList.
After sorting 
the ArrayList 
(by title).
After putting it 
into a HashSet, 
and printing the 
HashSet (we didn’t 
call sort() again).
(And it lost its sort order 
when we put the list into a 
HashSet, but we’ll worry about 
that one later...)

---

560
 
chapter 16
What makes t wo objects equal?
First, we have to ask—what makes two Song references 
duplicates? They must be considered equal. Is it simply two 
references to the very same object, or is it two separate objects 
that both have the same title?
This brings up a key issue: reference equality vs. object equality.
$
Reference
equality