Under rare circumstances, an attribute is public, meaning that it is visible to other objects outside its class. These attributes are hidden from all classes except immediate subclasses. Attributes may also be protected, indicated with a pound symbol (#). This is represented on a class diagram by a minus sign in front of the attribute name. The attributes (or properties) are usually designated as private, or only available in the object. The filled-in diamonds show aggregation and the empty diamond shows a whole-part relationship. Later in the chapter we will discuss the meaning of the diamond symbols shown in this figure. The class diagram shows data storage requirements as well as processing requirements. The area directly below the name shows the attributes, and the bottom portion lists the methods. Notice that the name is centered at the top of the class, usually in boldface type. Methods are small sections of code that work with the attributes.įigure below illustrates a class diagram for course offerings. Attributes are what the class knows about characteristics of the objects, and methods (also called operations) are what the class knows about how to do things. In the simplest format, the rectangle may include only the class name, but may also include the attributes and methods. A class diagram also shows the nature of the relationships between classes.Ĭlasses are represented by a rectangle on a class diagram. Class diagrams show the static features of the system and do not represent any particular processing. Because programming occurs at the class level, defining classes is one of the most important object-oriented analysis tasks. Object-oriented methodologies work to discover classes, attributes, methods, and relationships between classes.
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