UML Class Diagram for Class GradeBook

Recall from Section 1.3 that the UML is a standardized graphical language used by software developers to represent their object-oriented systems. In the UML, each class is modeled in a UML class diagram as a rectangle with three compartments. Figure 3.2 presents a class diagram for class GradeBook (Fig. 3.1). The top compartment contains the class’s name centered horizontally and in boldface type. The middle compartment contains the class’s attributes, which correspond to data members in C++. This compartment is currently empty, because class GradeBook does not yet have any attributes. (Section 3.4 presents a version of class GradeBook with an attribute.) The bottom compartment contains the class’s operations, which correspond to member functions in C++. The UML models operations by listing the operation name followed by a set of parentheses. Class GradeBook has only one member function, displayMessage, so the bottom compartment of Fig. 3.2 lists one operation with this name. Member function displayMessage does not require additional information to perform its tasks, so the parentheses following displayMessage in the class diagram are empty, just as they are in the member function’s header in line 12 of Fig. 3.1. The plus sign (+) in front of the operation name indicates that displayMessage is a public operation in the UML (i.e., a public member function in C++).

Fig. 3.2. UML class diagram indicating that class GradeBook has a public displayMessage operation.