Operations of Class Keypad

From the phrase “receives numeric input from the user” listed by class Keypad in Fig. 22.16, we conclude that class Keypad should perform a getInput operation. Because the ATM’s keypad, unlike a computer keyboard, contains only the numbers 0–9, we specify that this operation returns an integer value. Recall from the requirements document that in different situations the user may be required to enter a different type of number (e.g., an account number, a PIN, the number of a menu option, a deposit amount as a number of cents). Class Keypad simply obtains a numeric value for a client of the class—it does not determine whether the value meets any specific criteria. Any class that uses this operation must verify that the user enters appropriate numbers, and if not, display error messages via class Screen). [Note: When we implement the system, we simulate the ATM’s keypad with a computer keyboard, and for simplicity we assume that the user does not enter nonnumeric input using keys on the computer keyboard that do not appear on the ATM’s keypad.]