I was trying to sharp my OOD thinking. Here is my question.

Suppose you want to design a music mp3 player. And I got a class with a collection of playlists.

```
class Player {
    Map<String, List<Song>> playlists;    // <Name, PlayList>
    public void play (Song song) {
        // decode song
        // play song
    }
    public void play (String playlistName) {
        // play a playlist
        for (Song song : playlists.get(playlistName)) {
            play (song);
        }
    }
    public void stop () {
        // stop playing
    }
    public void pause () {
        // pause, resume playing the last song when hit play again
    }
}

```

Let's assume "Song" already contains all the metadata of a song. All the functionalities of methods have been described. I got stucked when I was trying to realize the "pause" method. What would you do to realize this?

Thanks!