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POOOP: How do I deal with objects that have mutual relations?
 

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    <p>Let's say there are two classes related to each other via some relations. For example, a <code>Student</code> maintains a list of the <code>Class</code>es he takes, and each <code>Class</code> has a list of <code>Student</code>s taking it. Then I am afraid of letting the <code>Student</code> directly being able to modify its set of <code>Class</code>es, because each modification would have to be followed by a similar modification of a <code>Class</code>'s list of <code>Student</code>s, and vice versa.</p> <p>One solution is to have a class whose sole purpose is to keep track of <code>Class</code>-<code>Student</code> relations, say <code>Registrar</code>. But then if some method in <code>Student</code> requires knowledge of its <code>Class</code> list, the <code>Student</code> needs to be passed the <code>Registrar</code>. This seems bad. It seems <code>Student</code> shouldn't have access to the <code>Registrar</code>, where it can also access other <code>Student</code>s. I can think of a solution, creating a class that acts as a mediator between <code>Student</code> and <code>Registrar</code>, showing the <code>Student</code> only what it needs to know, but this seems possibly like overkill. Another solution is to remove from <code>Student</code> any method that needs to access its classes and put it instead in <code>Registrar</code> or some other class that has access to <code>Registrar</code>.</p> <p>The reason I'm asking is that I'm working on a chess game in Java. I'm thinking about the Piece-Cell relations and the Piece-Player relations. If in the above example it wasn't OK for a <code>Student</code> to have access to the <code>Registrar</code>, is it OK here for a <code>Piece</code> to have access to the <code>Board</code>, since a <code>Piece</code> needs to look around anyway to decide if a move is valid?</p> <p>What's the standard practice in such cases?</p>
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