12.6. Identifying Class Operations

[Note: This section can be taught after Chapter 6.]

In this section, we determine some of the class operations (or behaviors) needed to implement the ATM system. An operation is a service that objects of a class provide to clients (users) of the class. Consider the operations of some real-world objects. A radio’s operations include setting its station and volume (typically invoked by a person’s adjusting the radio’s controls). A car’s operations include accelerating (invoked by the driver’s pressing the accelerator pedal), decelerating (invoked by the driver’s pressing the brake pedal or releasing the gas pedal), turning and shifting gears. Software objects can offer operations as well—for example, a software graphics object might offer operations for drawing a circle, drawing a line, drawing a square and the like. A spreadsheet software object might offer operations like printing the spreadsheet, totaling the elements in a row or column and graphing information in the spreadsheet as a bar chart or pie chart.