#ifndef LINK_H
#define LINK_H


/* Link.h -- declarations for singly-linked list element

        THIS SOFTWARE FITS THE DESCRIPTION IN THE U.S. COPYRIGHT ACT OF A
        "UNITED STATES GOVERNMENT WORK".  IT WAS WRITTEN AS A PART OF THE
        AUTHOR'S OFFICIAL DUTIES AS A GOVERNMENT EMPLOYEE.  THIS MEANS IT
        CANNOT BE COPYRIGHTED.  THIS SOFTWARE IS FREELY AVAILABLE TO THE
        PUBLIC FOR USE WITHOUT A COPYRIGHT NOTICE, AND THERE ARE NO
        RESTRICTIONS ON ITS USE, NOW OR SUBSEQUENTLY.

Author:
        K. E. Gorlen
        Computer Systems Laboratory, DCRT
        National Institutes of Health
        Bethesda, MD 20892

log:    LINK.H $
Revision 1.2  95/01/29  13:27:18  NT_Test_Machine
*** empty log message ***

Revision 1.1  92/11/10  12:43:02  Anthony_Scian
.

 * Revision 3.0  90/05/20  00:20:02  kgorlen
 * Release for 1st edition.
 * 
*/

#include "Object.h"

class LinkedList;

class Link: public VIRTUAL Object {     // abstract class
        DECLARE_MEMBERS(Link);
        Link* next;                     // pointer to next Link or nil 
        static Link *const nilLink;     // end of list marker
        friend class LinkedList;
protected:
        Link()                          { next = NULL; }
        Link(Link* nextlink)            { next = nextlink; }
        Link(const Link&)               { next = NULL; }
public:
        ~Link();
        Link* nextLink() const          { return next; }
        Link* nextLink(Link* nextlink)  { next = nextlink; return next; }
        bool isListEnd() const          { return this == nilLink; }
        virtual int compare(const Object&) const = 0;
        virtual Object* copy() const;   // deepCopy()
        virtual void deepenShallowCopy();
        virtual unsigned hash() const = 0;
        virtual bool isEqual(const Object&) const = 0;
        virtual void printOn(ostream& strm =cout) const = 0;
};

#endif