精通C#面向对象编程基础与实践

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" Beginning C# Object-Oriented Programming, 2nd Edition" 是一本专注于C#编程和面向对象设计的入门书籍，旨在帮助读者理解和掌握面向对象编程的基本概念和高级原则。作者希望通过本书填补大多数初学者在理解编程方法论和设计方面的空白。这本书有两个主要目标：一是教导读者C#编程的基础知识，包括语法和基本编程技巧；二是深入讲解面向对象编程的高级理念，如类结构设计、对象交互建模和实际案例研究。书中内容涵盖了从面向对象编程的概述到具体实践的各种主题。在面向对象编程（OOP）的概述中，读者将学习到封装、继承、多态等核心概念，这些都是理解和应用C#的关键。在设计OOP解决方案时，作者会引导读者如何识别类结构，如何模拟对象间的交互，以及通过一个案例研究来实践这些理论。随着书的深入，读者将接触到.NET框架和Visual Studio的介绍，这两个工具对于C#开发至关重要。之后，书中详细介绍了如何创建类、构建类层次结构，以及实现对象间的协作。在处理集合和数据访问层时，作者将展示如何有效地管理和操作数据。为了满足不同类型的项目需求，书中的后续章节分别探讨了开发Windows Presentation Foundation (WPF) 应用、Web应用程序、Windows Store应用程序以及如何开发和消费Web服务。最后，通过一个具体的办公室用品订购应用的开发案例，读者可以将所学知识综合运用到实际项目中。这本书为C#初学者提供了一个全面的学习路径，不仅教授了语言基础，更注重培养面向对象的设计思维和实践能力。通过阅读此书，读者不仅可以掌握C#编程，还能深入了解并运用面向对象编程的高级技巧，从而提升自己的软件开发水平。

CHAPTER 2 ■ DESIGNING OOP SOLUTIONS: IDENTIFYING THE CLASS STRUCTURE

Introducing Use Cases

Use cases describe how external entities will use a system. These external entities can be human or other systems

(called actors in UML terminology). The description emphasizes the users’ view of the system and the interaction

between the users and the system. Use cases help to further define system scope and boundaries. They are usually

in the form of a diagram, along with a textual description of the interaction taking place. Figure 2-1 shows a generic

diagram that consists of two actors represented by stick figures, the system represented by a rectangle, and use cases

depicted by ovals inside the system boundaries.

Actor 1

System

Use case 1

Use case 2

Use case 3

Actor 2

Figure 2-1. Generic use case diagram with two actors and three use cases

Use cases are developed from the SRS document. The actor is any outside entity that interacts with the system.

An actor could be a human user (for instance, a rental agent), another software system (for instance, a software billing

system), or an interface device (for instance, a temperature probe). Each interaction that occurs between an actor and

the system is modeled as a use case.

The sample use case shown in Figure

2-2 was developed for the flight-booking application introduced in the

previous section. It shows the use case diagram for the requirement “Customers can search for flights based on

destination and departure times.”

Customer

View Flight Info

Figure 2-2. View Flight Info use case

CHAPTER 2 ■ DESIGNING OOP SOLUTIONS: IDENTIFYING THE CLASS STRUCTURE

Along with the graphical depiction of the use case, many designers and software developers find it helpful to

provide a textual description of the use case. The textual description should be succinct and focused on what is

happening, not on how it is occurring. Sometimes any preconditions or postconditions associated with the use case

are also identified. The following text further describes the use case diagram shown in Figure 2-2.

•฀Description: A customer views the flight information page. The customer enters flight search

information. After submitting the search request, the customer views a list of flights matching

the search criteria.

•฀Preconditions: None.

•฀Postconditions: The customer has the opportunity to log in and proceed to the flight-booking page.

As another example, take a look at the Reserve Seat use case shown in Figure 2-3.

Customer

Reserve Seat

View Flight Info

«include»

Figure 2-3. Reserve Seat use case diagram

The following text further describes the use case diagram shown in Figure

2-3.

•฀Description: The customer enters the flight number and indicates the seats being requested.

After the customer submits the request, some confirmation information is displayed.

•฀Preconditions: The customer has looked up the flight information. The customer has logged in

and is viewing the flight-booking screen.

•฀Postconditions: The customer is sent a confirmation e-mail outlining the flight details and the

cancellation policy.

As you can see from Figure 2-3, certain relationships can exist between use cases. The Reserve Seat use case

includes the View Flight Info use case. This relationship is useful because you can use the View Flight Info use

case independently of the Reserve Flight use case. This is called inclusion. You cannot use the Reserve Seat use case

independently of the View Flight Info use case, however. This is important information that will affect how you

model the solution.

Another way that use cases relate to each other is through extension. You might have a general use case that

is the base for other use cases. The base use case is extended by other use cases. For example, you might have a

Corporate Customer and Register Retail Customer use cases that extend the base use case. The difference between

extension and inclusion is that, in extension, the base use case being extended is not used on its own. Figure

2-4

demonstrates how you model this in a use case diagram.

CHAPTER 2 ■ DESIGNING OOP SOLUTIONS: IDENTIFYING THE CLASS STRUCTURE

A common mistake when developing use cases is to include actions initiated by the system itself. The emphasis

of the use case is on the interaction between external entities and the system. Another common mistake is to include a

description of the technical requirements of the system. Remember that use cases do not focus on how the system will

perform the functions, but rather on what functions need to be incorporated in the system from the user’s standpoint.

After you have developed the use cases of the system, you can begin to identify the internal system objects that

will carry out the system’s functional requirements. You do this using a class diagram.

Customer

«extends»

Figure 2-4. Extending use cases

ACTIVITY 2-1. CREATING A USE CASE DIAGRAM

After completing this activity, you should be familiar with the following:

how to produce a use case diagram to define a system’s scope•฀

how to use a UML modeling tool to create and document a use case diagram•฀

Examining the SRS

The software user group you belong to has decided to pool its resources and create a lending library. Lending

items include books, movies, and video games. Your task is to develop the application that will keep track of the

loan item inventory and the lending of items to the group members. After interviewing the group’s members and

officers, you have developed a SRS document that includes the following functional requirements:

Only members of the user group can borrow items.•฀

Books can be borrowed for four weeks.•฀

Movies and games can be borrowed for one week.•฀

Items can be renewed if no one is waiting to borrow them.•฀

Members can only borrow up to four items at the same time.•฀

A reminder is e-mailed to members when an item becomes overdue.•฀

A fine is charged for overdue items.•฀

Members with outstanding overdue items or fines can’t borrow new items.•฀

A secretary is in charge of maintaining item inventory and purchasing items to add to the inventory.•฀

A librarian has been appointed to track lending and send overdue notices.•฀

The librarian is also responsible for collecting fines and updating fine information.•฀

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