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Editor to share with you how to use the UML sequence diagram, I believe that most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's go to understand it!

UML sequence diagram

The UML sequence diagram shows the detailed flow of a specific use case (or part of a use case). It is almost self-describing and shows the call relationships between different objects in the process, as well as different calls to different objects in great detail.

The UML sequence diagram has two dimensions: the vertical dimension shows the sequence of messages / calls in the chronological order in which they occur, and the horizontal dimension shows the object instance to which the message is sent.

The drawing of UML sequence diagram is very simple. Across the top of the diagram, each box (see figure 4) represents an instance (object) of each class. In the box, the class instance name and the class name are separated by spaces / colons / spaces, for example, myReportGenerator:ReportGenerator. If a class instance sends a message to another class instance, draw a connection with an open arrow pointing to the receiving class instance, and place the name of the message / method on the connection. For some particularly important messages, you can draw a dashed line with an open arrow pointing to the instance of the originating class, marking the return value on the dotted line. As far as I'm concerned, I always like to draw dotted lines that include return values, and this extra information makes UML sequence diagrams easier to read.

Reading UML sequence diagrams is also very easy. Start with the "driver" class instance of the startup sequence in the upper-left corner, and then read down each message. Remember: although the example UML sequence diagram shown in figure 4 shows the return message for each message sent, this is only optional.

Figure 4: an example UML sequence diagram

By reading the sample UML sequence diagram in figure 4, you can see how to create an CD sales report (CDSalesReport). The aServlet object represents an instance of the driver class. AServlet sends a message to an instance of the ReportGenerator class named gen. The message is marked generateCDSalesReport, indicating that the ReportGenerator object implements the message handler. Further understanding shows that the generateCDSalesReport message tag includes a cdId in parentheses, indicating that aServlet passes a parameter named cdId with the message. When the gen instance receives a generateCDSalesReport message, it then calls the CDSalesReport class and returns an instance of aCDReport. The gen instance then calls the returned aCDReport instance, passing parameters to it each time a message is called. At the end of the sequence, the gen instance returns an aCDReport to its caller, aServlet.

Please note that the UML sequence diagram in figure 4 is too detailed compared to a typical UML sequence diagram. However, I think it's easy enough to understand, and it shows how to represent nested calls. It is sometimes necessary for junior developers to break down a sequence to this level of detail, which helps them understand the relevant content.

The above is all the contents of the article "how to use UML sequence diagrams". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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