![]() Again, notice that the implementation is indistinguishable from association. Therefore I find this relationship useless in the kinds of diagrams I draw.Ĭomposition is a special form of aggregation, as shown in Figure 3-16. How often am I concerned about making sure that instances form aĭirected acyclic graph? Not very often. I don't find this to be a particularly useful definition. See Figure 3-15ģ.15 Illegal cycles of aggregation between instances. A single object cannot be an aggregate of itself, two objects cannot be aggregates ofĮach other, three objects cannot form a ring of aggregation, and so on. Therefore instances cannot form cycles of aggregations. The one hard rule that UML gives us regarding aggregations is simply this: A whole cannot be its own part. In fact, this relationship has been dropped from UML 2.0. For that reason I don't use the relationship at all, and This leads to confusion because various programmersĪnd analysts adopt their own pet definitions for the relationship. Unfortunately, UML does not provide a strong definition for this relationship. Notice that the implementation shown in Figure 3-14 is indistinguishable from association. Figure 3-14 shows how it is drawn and implemented. UML diagrams, I've never had occasion to use class properties for anything.Īggregation is a special form of association that connotes a "whole/part" relationship. Personally, in the many years that I've been writing The property, I don't know when you'd this useful. You can write the name in italics, or you can use In UML there are two ways to denote that a class or a method is abstract. You just have to make sure that the people who are reading your diagrams know what your stereotype means. I often use stereotypes like «persistent», «C-API», «struct», or «function». You can make your own stereotypes if you like. Booch 4 used to call these class utilities. It's not standard UML, but it's much more convenient.Īll the methods and variables of a «utility» class are static. Use the shorthand in the lower part of Figure 3-9 to make the drawing easier. I draw interfaces so often that spelling the whole stereotype out at the white board can be pretty inconvenient. The only variables they can have are static variables. Moreover, «interface»Ĭlasses can have no instance variables. The other isĪll the methods of classes marked with this stereotype are abstract. «interface» is one of two standard stereotypes that can be used by Java programmers. The «interface» denotation in Figure 3-8 is a class stereotype. But there are times when they can be helpful.Ĭlass stereotypes appear between guillemet 3 characters, usually above the name of the class. Most of the time these detailsĪnd adornments should not be added. There are a vast number of details and adornments that can be added to UML class diagrams.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |