Containers, Blocks, and Iterators
A jukebox with one song is unlikely to be popular (except perhaps in
some very, very scary bars), so pretty soon we'll have to start thinking about
producing a catalog of available songs and a playlist of songs waiting
to be played. Both of these are containers: objects that hold
references to one or more other objects.
Both the catalog and the playlist need a similar set of methods: add a
song, remove a song, return a list of songs, and so on. The playlist
may perform additional tasks, such as inserting advertising every so
often or keeping track of cumulative play time, but we'll worry
about these things later. In the meantime, it seems like a good idea
to develop some kind of generic
class, which we can
specialize into catalogs and playlists.