《面向对象软件工程》课程PPT教学课件（英文版）Chapter 3：Basing Software Development on Reusable Technology

object-Oriented Software Engineering Practical Software development using uml and Java Chapter 3 Basing software development on Reusable Technology www.oseng.com

Object-Oriented Software Engineering Practical Software Development using UML and Java Chapter 3: Basing Software Development on Reusable Technology

3.1 Building on the Experience of others Software engineers should avoid re-developing software already developed Types of reuse Reuse of expertise Reuse of standard designs and algorithms Reuse of libraries of classes or procedures Reuse of powerful commands built into languages and operating systems Reuse of frameworks Reuse of complete applications www.oseng.com O Lethbridge/Laganiere 2001 Chap 3: Basing Development on Reusable

© Lethbridge/Laganière 2001 Chap. 3: Basing Development on Reusable Technology 2 3.1 Building on the Experience of Others Software engineers should avoid re-developing software already developed Types of reuse: • Reuse of expertise • Reuse of standard designs and algorithms • Reuse of libraries of classes or procedures • Reuse of powerful commands built into languages and operating systems • Reuse of frameworks • Reuse of complete applications

3.2 Reusability and Reuse in SE R euse an nd design for reusability should be part of the culture of software development organizations But there are problems to overcome Why take the extra time needed to develop something that will benefit other projects/customers? Management may only reward the efforts of people who create the visible final products Reusable software are often created in a hurry and without enough attention to quality www.oseng.com O Lethbridge/Laganiere 2001 Chap 3: Basing Development on Reusable

© Lethbridge/Laganière 2001 Chap. 3: Basing Development on Reusable Technology 3 3.2 Reusability and Reuse in SE Reuse and design for reusability should be part of the culture of software development organizations But there are problems to overcome: • Why take the extra time needed to develop something that will benefit other projects/customers? • Management may only reward the efforts of people who create the visible ‘final products’. • Reusable software are often created in a hurry and without enough attention to quality

A vicious cycle Developers tend not develop high quality reusable components, so there is often little to reuse To solve the problem, recognize that: This vicious cycle costs money Investment in reusable code is important Attention to quality of reusable components is essential -So that potential reusers have confidence in them The quality of a software product is only as good as its lowest-quality reusable component Developing reusable components can often simplify de lesign www.oseng.com O Lethbridge/Laganiere 2001 Chap 3: Basing Development on Reusable 4

© Lethbridge/Laganière 2001 Chap. 3: Basing Development on Reusable Technology 4 A vicious cycle Developers tend not develop high quality reusable components, so there is often little to reuse To solve the problem, recognize that: • This vicious cycle costs money • Investment in reusable code is important • Attention to quality of reusable components is essential —So that potential reusers have confidence in them —The quality of a software product is only as good as its lowest-quality reusable component • Developing reusable components can often simplify design

3.3 Frameworks: Reusable Subsystems A framework is reusable software that implements a generic solution to a generalized problem It provides common facilities applicable to different application programs Principle: Applications that do different, but related, things tend to have quite similar designs www.oseng.com O Lethbridge/Laganiere 2001 Chap 3: Basing Development on Reusable

© Lethbridge/Laganière 2001 Chap. 3: Basing Development on Reusable Technology 5 3.3 Frameworks: Reusable Subsystems A framework is reusable software that implements a generic solution to a generalized problem. • It provides common facilities applicable to different application programs. Principle: Applications that do different, but related, things tend to have quite similar designs

Frameworks to promote reuse A framework is intrinsically incomplete Certain classes or methods are used by the framework but are missing(slots) Some functionality is optional Allowance is made for developer to provide it (hooks) Developers use the services that the framework provides Taken together the services are called the Application Program Interface(APD) www.oseng.com O Lethbridge/Laganiere 2001 Chap 3: Basing Development on Reusable 6

© Lethbridge/Laganière 2001 Chap. 3: Basing Development on Reusable Technology 6 Frameworks to promote reuse A framework is intrinsically incomplete • Certain classes or methods are used by the framework, but are missing (slots) • Some functionality is optional — Allowance is made for developer to provide it (hooks) • Developers use the services that the framework provides —Taken together the services are called the Application Program Interface (API)

Object-oriented frameworks In the object oriented paradigm, a framework is composed of a library of classes The API is defined by the set of all public methods of these classes Some of the classes will normally be abstract www.oseng.com O Lethbridge/Laganiere 2001 Chap 3: Basing Development on Reusable

© Lethbridge/Laganière 2001 Chap. 3: Basing Development on Reusable Technology 7 Object-oriented frameworks In the object oriented paradigm, a framework is composed of a library of classes. • The API is defined by the set of all public methods of these classes. • Some of the classes will normally be abstract

Examples of frameworks a framework for payroll management a framework for frequent buyer clubs a framework for university registration a framework for e-commerce web sites A framework for controlling microwave ovens www.oseng.com O Lethbridge/Laganiere 2001 Chap 3: Basing Development on Reusable 8

© Lethbridge/Laganière 2001 Chap. 3: Basing Development on Reusable Technology 8 Examples of frameworks • A framework for payroll management • A framework for frequent buyer clubs • A framework for university registration • A framework for e-commerce web sites • A framework for controlling microwave ovens

Types of frameworks a horizontal framework provides general application facilities that a large number of applications can use .A vertical framework(application framework is more complete but still needs some slots to be filled to adapt it to specifIc application needs Application Services offere Application by the framework Horizontal framew ork Vertical framew ork Code to be provided to adapt the framew ork to the needs of the application www.oseng.com O Lethbridge/Laganiere 2001 Chap 3: Basing Development on Reusable

© Lethbridge/Laganière 2001 Chap. 3: Basing Development on Reusable Technology 9 Types of frameworks •A horizontal framework provides general application facilities that a large number of applications can use •A vertical framework (application framework) is more ‘complete’ but still needs some slots to be filled to adapt it to specific application needs Application Application Horizontal framew ork Vertical framew ork Code to be provided to adapt the framew ork to the needs of the application Services offered by the framew ork

3.4 The client-Server Architecture a distributed system is a system in which: computations are performed by separate programs normally running on separate pieces of hardware that co-operate to perform the task of the system server a program that provides a service for other programs that connect to it using a communication channe Client a program that accesses a server (or several servers )to obtain services a server may be accessed by many clients simultaneously www.oseng.com O Lethbridge/Laganiere 2001 Chap 3: Basing Development on Reusable

© Lethbridge/Laganière 2001 Chap. 3: Basing Development on Reusable Technology 10 3.4 The Client-Server Architecture A distributed system is a system in which: • computations are performed by separate programs • … normally running on separate pieces of hardware • … that co-operate to perform the task of the system. Server: • A program that provides a service for other programs that connect to it using a communication channel Client • A program that accesses a server (or several servers) to obtain services • A server may be accessed by many clients simultaneously