Returning a string representation of the number of albums and songs available
Text manipulation like that is always a pain. I like to extract functions for things like this, though.

private static final String simplePlural (int count, String noun) {
    if (count == 1) {
        return "1 " + noun;
    }
    return count + " " + noun + "s";
}


With that function, your code becomes:

public String toAlbumSongCount() {
    return simplePlural(albumCount(), "album") 
       + ", " + simplePlural(songCount(), "song");
}


I know there's no StringBuilder in there, but the performance benefit for something that's seldom used, will be negligible, and this is more readable.

Note that the code above adds a space after the comma, which your code is missing.