AudioMan's immutable TrackFilter object is used to filter tracks for the models. The models receive notification any time a mutator changes the repository. Some of these notifications don't apply to what the model is currently holding, like albums for a specific artist for example.

The TrackFilter object's constructor takes three parameters: playlist, artist and album; and has two methods: acceptAdd() and acceptRemove() that both return boolean.

If acceptAdd(track) is true, then the track should be added to the model. If acceptRemove(track) is true, then the track should be removed from the model. I used to have one method called accept() but then during unit testing I noticed a slight difference in filtering when a track was added and when it was removed, so I needed a method for each situation. If you are curious, check out the code for the exact situation. :)

The accept...(track) methods determine their boolean output by comparing the track parameter against the parameters given in the constructor. If the playlist, artist and album names all match, then the method returns true. If any of the parameters are null then that means "all".

So when each model is made it is given a TrackFilter to use. Each new model has a new TrackFilter to determine what notify messages reach it and actually change the model. The rest of the notifications are ignored.

The TrackFilter class was inspired by Java's FileFilter interface.