//All instances of books/other media are instantiated within the Catalog constructor public Catalog() { Books = CatalogToDisk.GenerateBookListFromDisk(); CDs = CatalogToDisk.GenerateMusicCdListFromDisk(); Magazines = CatalogToDisk.GenerateMagazineListFromDisk(); Medias = new List <Media>(); Medias.AddRange(Books); Medias.AddRange(Magazines); Medias.AddRange(CDs); }