Design Patterns Explained: A New Perspective on Object-Oriented Design

Initial Requirements of the Case Study

Suppose I am writing an e-tail system that supports sales in the United States. The general architecture has a controller object that handles sales requests. It identifies when a sales order is being requested and hands the request off to a SalesOrder object to process the order.

The system looks something like Figure 14-1.

Figure 14-1. Sales order architecture for an e-tail system.

The functions of SalesOrder include

• Allow for filling out the order with a GUI.

• Handle tax calculations.

• Process the order. Print a sales receipt.

Some of these functions are likely to be implemented with the help of other objects. ...