////   This file contains the C++ code from Program 5.1 of//   "Data Structures and Algorithms//    with Object-Oriented Design Patterns in C++"//   by Bruno R. Preiss.////   Copyright (c) 1998 by Bruno R. Preiss, P.Eng.  All rights reserved.////   http://www.pads.uwaterloo.ca/Bruno.Preiss/books/opus4/programs/pgm05_01.cpp//class Object{protected:    virtual int CompareTo (Object const&) const = 0;public:    virtual ~Object ();    virtual bool IsNull () const;    virtual int Compare (Object const&) const;    virtual HashValue Hash () const = 0;    virtual void Put (ostream&) const = 0;};