title: Fast and proper accessing
body: <p>I am creating a game, where each player controls a class Country. The Country has 
  a <code>list of MilitaryUnits</code>. The <code>MilitaryUnits</code> have locations on a 2 dimensional map. If I want to get the <code>MilitaryUnit</code> on location(2,3), and then see to which country he belongs, I need to have a field in class <code>MilitaryUnit</code> with his owner country, but in this way two classes are going to point to each other. Is there a better way of doing this?</p>