9.1. Summary of Steps in Building Classes and Routines

Class construction can be approached from numerous directions, but usually it's an iterative process of creating a general design for the class, enumerating specific routines within the class, constructing specific routines, and checking class construction as a whole. As Figure 9-1 suggests, class creation can be a messy process for all the reasons that design is a messy process (reasons that are described in Section 5.1, "Design Challenges").

Figure 9-1. Details of class construction vary, but the activities generally occur in the order shown here

Steps in Creating a Class

The key steps in constructing a class are:

Create a general design for the class Class design includes numerous specific issues. Define the class's specific responsibilities, define what "secrets" the class will hide, and define exactly what abstraction the class interface will capture. Determine whether the class will be derived from another class and whether other classes will be allowed to derive from it. Identify the class's key public methods, and identify and design any nontrivial data members used by the class. Iterate through these topics as many times as needed to create a straightforward design for the routine. These considerations and many others are discussed in more detail in Chapter 6, "Working Classes."

Construct each routine within the class Once you've identified the class's major routines in the first step, you must construct each specific routine. Construction of each routine typically unearths the need for additional routines, both minor and major, and issues arising from creating those additional routines often ripple back to the overall class design.

Review and test the class as a whole Normally, each routine is tested as it's created. After the class as a whole becomes operational, the class as a whole should be reviewed and tested for any issues that can't be tested at the individual-routine level.

Steps in Building a Routine

Many of a class's routines will be simple and straightforward to implement: accessor routines, pass-throughs to other objects' routines, and the like. Implementation of other routines will be more complicated, and creation of those routines benefits from a systematic approach. The major activities involved in creating a routine designing the routine, checking the design, coding the routine, and checking the code are typically performed in the order shown in Figure 9-2.

Figure 9-2. These are the major activities that go into constructing a routine. They're usually performed in the order shown

Experts have developed numerous approaches to creating routines, and my favorite approach is the Pseudocode Programming Process, described in the next section.