I want to know whats the Relationship between a common wall (that are located In an adjoining room ) and the rooms.
As i know the relationship between a room and its walls is Composition not Aggregation (am i right ?)

And according to the definition of Composition the contained object can't be shared between two containers, whereas in aggregation it is possible.

now i am confused that whats the best modeling approach to represent the relationship between a common wall and the rooms located next to it ?

It would be highly Appreciated if you could provide your advices with some code.

|--------|--------|

Approch1:

(wall class ---- room class) /Composition

Approach2:

wall class ----- room class /Aggregation

Approch3:

we have a wall class and a Common wall class , Common wall class inherits from wall class

adjoining room class ---- (1) Common wall class /Aggregation
adjoining room class ---- (6) wall class / composition

Approach4: I am a developer not a designer :) so this is my idea :

class Room 
{
  private wall _firstwall  ;
  private wall _secondtwall;
  private wall _thirdwall  ; 
  private wall _commonwall ;

public Room( CommonWall commonwall)
 {
 _firstwall=new Wall();
 _secondtwall=new Wall();
 _thirdwall=new Wall();
 _commonwall=commonwall;
 }

}

Class CommonWall:Wall
{
 //...
}

// in somewher :

 static void main()
{
  Wall _commonWall=new Wall();
  Room room1=new Room(_commonWall);
  Room room2=new Room(_commonWall);
  Room [] adjacentRoom =new Room[2]{room1,room2};
}

Edit 1: I think this is a clear question but just for more clarification :

The point of the question is to find out whats the best pattern or approach to model a relationship for an object that is a component of two other objects in the same time.

and about my example : waht i mean by a "room" ?,surely i mean an enclosed square room with 4 walls and one door.but in this case one of these walls is a common wall and is shared between two adjacent rooms.