csdn_文档中心_oo三步曲之浅析oo的基石.htm

csdn10年中间经典帖子

            </SPAN></SPAN></B><SPAN lang=EN-US>Booch</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">曾经在他自己的</SPAN><SPAN 
            lang=EN-US>OO</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">领域内的名著</SPAN><SPAN 
            lang=EN-US>[Booch 94]</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中开篇就论叙到了复杂性是软件开发过程中所故有的特质。而人们处理复杂性的最根本武器就是抽象。广义的抽象代表的是对复杂系统的简化描叙或规格说明，为了突出系统的本质属性而故意忽略其中的非实质性细节。“一个概念只有当能被最终用来实现的机制独立的描叙，理解，分析时，才将这个概念限定为抽象的概念”。而</SPAN><SPAN 
            lang=EN-US>Booch</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">也给出了他心目中关于</SPAN><SPAN 
            lang=EN-US>OO</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">领域内的狭义抽象定义：“抽象表示一个对象与其他所有对象相区别的基本特征，因此提供了同观察者角度有关的清晰定义的概念界限。”因此，根据不同观察角度，我们可以针对</SPAN><SPAN 
            lang=EN-US>OOP</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">给出不同级别的抽象层次。通常，面对一个典型的面向对象程序，<SPAN 
            lang=EN-US>[Budd 2002]</SPAN>将其分成五个抽象层，分别覆盖了</SPAN><SPAN 
            lang=EN-US>OOP</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中的分析，设计与编程的各个阶段：</SPAN></P>
            <P class=MsoNormal 
            style="MARGIN-LEFT: 39pt; TEXT-INDENT: -18pt; mso-list: l1 level1 lfo1; tab-stops: list 39.0pt"><SPAN 
            lang=EN-US>1，<SPAN style="FONT: 7pt 'Times New Roman'">&nbsp; 
            </SPAN></SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">最高级别的抽象层上，程序被看成是由很多相互作用并且遵守契约的对象所组成的对象集合。对象之间相互合作完成程序的计算任务。这个抽象级别上的典型代表就是设计模式思想（</SPAN><SPAN 
            lang=EN-US>Design Pattern</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）。</SPAN></P>
            <P class=MsoNormal 
            style="MARGIN-LEFT: 39pt; TEXT-INDENT: -18pt; mso-list: l1 level1 lfo1; tab-stops: list 39.0pt"><SPAN 
            lang=EN-US>2，<SPAN style="FONT: 7pt 'Times New Roman'">&nbsp; 
            </SPAN></SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">第二个抽象层就是一个对象集单元，也就是一群定义之间有相互联系的对象，在程序设计语言级别来看</SPAN><SPAN 
            lang=EN-US>Java</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中是</SPAN><SPAN 
            lang=EN-US>packages,C++</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中是</SPAN><SPAN 
            lang=EN-US>name space</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。这个抽象级别上的典型代表就是模块化思想</SPAN><SPAN 
            lang=EN-US>(Modularity)</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。</SPAN></P>
            <P class=MsoNormal 
            style="MARGIN-LEFT: 39pt; TEXT-INDENT: -18pt; mso-list: l1 level1 lfo1; tab-stops: list 39.0pt"><SPAN 
            lang=EN-US>3，<SPAN style="FONT: 7pt 'Times New Roman'">&nbsp; 
            </SPAN></SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">第三个抽象层所代表的是典型的</SPAN><SPAN 
            lang=EN-US>OOP</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">模式：客户</SPAN><SPAN 
            lang=EN-US>/</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">服务器模型，这主要是用来抽象两个对象之间的互交过程。在这个抽象级别上的典型代表就是对象之间的消息机制</SPAN><SPAN 
            lang=EN-US>(Message Passing)</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。</SPAN></P>
            <P class=MsoNormal 
            style="MARGIN-LEFT: 39pt; TEXT-INDENT: -18pt; mso-list: l1 level1 lfo1; tab-stops: list 39.0pt"><SPAN 
            lang=EN-US>4，<SPAN style="FONT: 7pt 'Times New Roman'">&nbsp; 
            </SPAN></SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">第四个抽象层就是针对一组相似对象定义一个类作为生成对象的模板，类定义了对象的对外使用接口以及继承对象所需的内部继承接口，而这个抽象层次的典型代表就是接口编程</SPAN><SPAN 
            lang=EN-US>(Interface Programming)</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。</SPAN></P>
            <P class=MsoNormal 
            style="MARGIN-LEFT: 39pt; TEXT-INDENT: -18pt; mso-list: l1 level1 lfo1; tab-stops: list 39.0pt"><SPAN 
            lang=EN-US>5，<SPAN style="FONT: 7pt 'Times New Roman'">&nbsp; 
            </SPAN></SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">第五个抽象层就是实现一个类所需要的方法和成员变量的实现</SPAN><SPAN 
            lang=EN-US>(Implementation)</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。在这里</SPAN><SPAN 
            lang=EN-US>OOP</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">最终和</SPAN><SPAN 
            lang=EN-US>POP</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">（</SPAN><SPAN 
            lang=EN-US>Procedure-Oriented Programming</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）相融合。</SPAN></P>
            <P class=MsoNormal><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">当然，我们可以根据各自的观察角度划分成更细的抽象层次比如说针对第五层抽象用到的</SPAN><SPAN 
            lang=EN-US>POP</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">理论，我们还可以进一步的划分出控制抽象（三种完全描叙图灵机计算模型所需要的控制结构）以及数据抽象（</SPAN><SPAN 
            lang=EN-US>ADTs</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）等等，并由此继续下去（如果你的想象力足够丰富的话：）。</SPAN></P>
            <P class=MsoNormal><SPAN lang=EN-US>&nbsp;<o:p></o:p></SPAN></P>
            <P class=MsoNormal><SPAN lang=EN-US>&nbsp;<o:p></o:p></SPAN></P>
            <P class=MsoNormal><B><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">什么是</SPAN><SPAN 
            lang=EN-US>OOP</SPAN></B><B><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">？</SPAN></B></P>
            <P class=MsoNormal><SPAN lang=EN-US>&nbsp;<o:p></o:p></SPAN></P>
            <P class=MsoNormal><SPAN lang=EN-US><SPAN 
            style="mso-tab-count: 1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
            </SPAN>OOP</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的许多原始思想都来之于</SPAN><SPAN 
            lang=EN-US>Simula</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">语言，并在</SPAN><SPAN 
            lang=EN-US>Smalltalk</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">语言的完善和标准化过程中得到更多的扩展和对以前的思想的重新注解。可以说</SPAN><SPAN 
            lang=EN-US>OO</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">思想和</SPAN><SPAN 
            lang=EN-US>OOPL</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">几乎是同步发展相互促进的。与函数式程序设计（</SPAN><SPAN 
            lang=EN-US>functional-programming</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）和逻辑式程序设计（</SPAN><SPAN 
            lang=EN-US>logic-programming</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）所代表的接近于机器的实际计算模型所不同的是，</SPAN><SPAN 
            lang=EN-US>OOP</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">几乎没有引入精确的数学描叙，而是倾向于建立一个对象模型，它能够近似的反映应用领域内的实体之间的关系，其本质是更接近于一种人类认知事物所采用的哲学观的计算模型。由此，导致了一个自然的话题，那就是</SPAN><SPAN 
            lang=EN-US>OOP</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">到底是什么？</SPAN><SPAN 
            lang=EN-US>[D&amp;T 1988][B.S 1991] .</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。在</SPAN><SPAN 
            lang=EN-US>OOP</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中，对象作为计算主体，拥有自己的名称，状态以及接受外界消息的接口。在对象模型中，产生新对象，旧对象销毁，发送消息，响应消息就构成</SPAN><SPAN 
            lang=EN-US>OOP</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">计算模型的根本。</SPAN></P>
            <P class=MsoNormal><SPAN lang=EN-US>&nbsp;<o:p></o:p></SPAN></P>
            <P class=MsoNormal><SPAN lang=EN-US><SPAN 
            style="mso-tab-count: 1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
            </SPAN></SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">对象的产生有两种基本方式。一种是以原型（</SPAN><SPAN 
            lang=EN-US>prototype</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）对象为基础产生新的对象。一种是以类（</SPAN><SPAN 
            lang=EN-US>class</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）为基础产生新对象。原型的概念已经在认知心理学中被用来解释概念学习的递增特性，原型模型本身就是企图通过提供一个有代表性的对象为基础来产生各种新的对象，并由此继续产生更符合实际应用的对象。而原型</SPAN><SPAN 
            lang=EN-US>-</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">委托也是</SPAN><SPAN 
            lang=EN-US>OOP</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中的对象抽象，代码共享机制中的一种。一个类提供了一个或者多个对象的通用性描叙。从形式化的观点看，类与类型有关，因此一个类相当于是从该类中产生的实例的集合。而这样的观点也会带来一些矛盾，比较典型的就是在继承体系下，子集（子类）对象和父集（父类）对象之间的行为相融性可能很难达到，这也就是</SPAN><SPAN 
            lang=EN-US>OOP</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中常被引用的</SPAN><SPAN 
            lang=EN-US>---</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">子类型（</SPAN><SPAN 
            lang=EN-US>subtype</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）不等于子类（</SPAN><SPAN 
            lang=EN-US>subclass</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）</SPAN><SPAN 
            lang=EN-US>[Budd 2002]</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。而在一种所有皆对象的世界观背景下，在类模型基础上还诞生出了一种拥有元类（</SPAN><SPAN 
            lang=EN-US>metaclass</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）的新对象模型。即类本身也是一种其他类的对象。以上三种根本不同的观点各自定义了三种基于类（</SPAN><SPAN 
            lang=EN-US>class-based</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）</SPAN><SPAN 
            lang=EN-US>,</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">基于原型（</SPAN><SPAN 
            lang=EN-US>prototype-based</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）和基于元类（</SPAN><SPAN 
            lang=EN-US>metaclass-based</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）的对象模型。而这三种对象模型也就导致了许多不同的程序设计语言（如果我们暂时把静态与动态的差别放在一边）。是的，我们经常接触的</SPAN><SPAN 
            lang=EN-US>C++,Java</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">都是使用基于类的对象模型，但除此之外还有很多我们所没有接触的</SPAN><SPAN 
            lang=EN-US>OOPL</SPAN><SPAN 
            style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">采用了完全不一样的对象模型，他们是在用另外一种观点诠释</SPAN><SPAN