Read again the last paragraph of Section 9.3.2. Try to draw a communication diagram that illustrates that situation. Why is it a worse design than the diagram presented in Figure 9.29?

Section 9.3.2.

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9.3.2 Visibility by parameter Visibility by parameter is obtained when an object A, performing a method, receives an object B as a parameter. In that case, the object A can communicate to B even if their classes are not associated. Consider the example of Figure 9.24, where the Book class has no association to the Delivery class. Therefore, no instance of Book may send a message directly to an instance of Delivery or vice versa. Consider an instance of Order that is linked to an instance of Book and to an instance of Delivery as shown in Figure 9.25. Now, consider that the instance of Order sends a message registerWeight to the instance of Delivery, passing a reference to the instance of Book as an argument, as shown in Figure 9.26. Then, the instance of Delivery acquires visibility by parameter to the instance of Book. In the case of visibility by parameter, it should be assumed that the object that sends the argu- ment originally has some kind of visibility to the object that was sent.