介绍

Object Hierarchies and Design Patterns

There is more to object-oriented programming than simply encapsulating in an object some data and the procedures for manipulating those data. Object-oriented methods deal also with the classification of objects and they address the relationships between different classes of objects.

The primary facility for expressing relationships between classes of objects is derivation--new classes can be derived from existing classes. What makes derivation so useful is the notion of inheritance. Derived classes inherit the characteristics of the classes from which they are derived. In addition, inherited functionality can be overridden and additional functionality can be defined in a derived class.

A feature of this book is that virtually all the data structures are presented in the context of a single class hierarchy. In effect, the class hierarchy is a taxonomy of data structures. Different implementations of a given abstract data structure are all derived from the same abstract base class. Related base classes are in turn derived from classes that abstract and encapsulate the common features of those classes.

In addition to dealing with hierarchically related classes, experienced object-oriented designers also consider very carefully the interactions between unrelated classes. With experience, a good designer discovers the recurring patterns of interactions between objects. By learning to use these patterns, your object-oriented designs will become more flexible and reusable.

Recently, programmers have to started name the common design patterns. In addition, catalogs of the common patterns are now being compiled and published[15].

The following object-oriented design patterns are used throughout this text:

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• Containers
• Enumerators
• Visitors
• Cursors
• Adapters
• Singletons