Can an Object have multiple Compare methods for ordering based on different values?

Question

Say I have a Song object like

public Song(){
  String artist, title;
  StringBuilder lyrics;
  int rank;
}

Is it possible to have multiple compare methods that, depending on the collection used, sort by a particular field? This object already has a compare method for ordering based on the artist and title values, and I would like to be able to order based on the rank.

My current project requires us to run a search on the lyrics of the Song and return a high to low match list. I want to use a PriorityQueue to hold the matches based on rank value.

Normally I would simply create another object to hold the Song and the rank, but this project not only plugs into a GUI interface provided by the professor, which requires any results be passed in an Song[] array, but prints out the first ten values as Rank, Artist, Title.

I can use toArray() to convert the queue, but if I use it to store anything other than Song objects, it will throw an ArrayStoreException.

So is this possible, or do I have to modify the existing compare method to sort by integer value?

Answer 1

Use a Comparator.

Comparator<Song> rankOrder =  new Comparator<Song>() {
        public int compare(Song s1, Song e2) {
            return s1.rank - s2.rank;
        }
    };
Collections.sort(songs, rankOrder);

See http://download.oracle.com/javase/tutorial/collections/interfaces/order.html

Answer 2

Most ordered collections have a constructor that takes a Comparator as an argument. Define a few static comparators in your Song class and then define things as follows:

Set<Song> allSongs = new TreeSet<Song>(Song.BY_TITLE);
PriorityQueue<Song> rankedSongs = new PriorityQueue<Song>(10, Song.BY_RANK);

There are utility classes (e.g., Guava Ordering) that can help you build up other comparators from the basics.