运行期类型鉴定

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Detecting types
 The idea of run-time type identification (RTTI) seems fairly simple at first: it lets you find the exact type of an object when you only have a reference to the base type.
 However, the need for RTTI uncovers a whole plethora of interesting (and often perplexing) OO design issues, and raises fundamental questions of how you should structure your programs.
 This chapter looks at the ways that Java allows you to discover information about objects and classes at run-time. This takes two forms: “traditional” RTTI, which assumes that you have all the types available at compile-time and run-time, and the “reflection” mechanism, which allows you to discover class information solely at run-time. The “traditional” RTTI will be covered first, followed by a discussion of reflection.
The need for RTTI

运行期类型鉴定
    运行期类型鉴定的概念初看非常简单——手上只有基础类型的一个句柄时，利用它判断一个对象的正确类型。
 然而，对RTTI的需要暴露出了面向对象设计许多有趣的问题，并把程序的构造问题正式摆上了桌面。
 本章将讨论如何利用Java在运行期间查找对象和类信息。这主要采取两种形式：一种是“传统”RTTI，它假定我们已在编译和运行期拥有所有类型；另一种是Java1.1特有的“反射”机制，利用它可在运行期独立查找类信息。首先讨论“传统”的RTTI，再讨论反射问题。
对RTTI的需要

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