Question

I understand the basics of inheritance but this one is confusing me. How would you go about saying:

• An album object has one or more artist objects
• An album object has one or more song objects

My current code only will only allow one song per object:

class Song extends Album{}
class Album extends Artist{}

I’m sure i’m overlooking something important. Any thoughts?

I’m doing this in PHP

Answer 1

An album has one or more artist objects. Inheritance would mean an album is an artist. What you need is (EDIT) aggregation:

class Album
{
  public $artists = array(); // Array of Artist instances
  public $songs   = array(); // Array of Song instances
}

Aggregation means every Artist and Song instance may belong to other Albums. With composition, an artist or song may belong to a single Album.