Polymorphism (1A) Young Won Lim 8/22/13

Transcription

1 Polymorhism (1A)

2 Coyright (c) Young W. Lim. Permission is granted to coy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version ublished by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A coy of the license is included in the section entitled "GNU Free Documentation License". Please send corrections (or suggestions) to youngwlim@hotmail.com. This document was roduced by using OenOffice.

3 Base & Derived Class Objects #include <stdio.h> class Poly { virtual void { rintf("poly:: is called... \n"); class Rect : ublic Poly { (virtual) void { rintf("rect:: is called... \n"); class Circle : ublic Poly { (virtual) void { rintf("circle:: is called... \n"); Poly ; Rect ; Circle ; Polymorhism 3

4 Base & Derived Class Pointers (1) Poly *; Rect *r; Circle *c; Polymorhism 4

5 Base & Derived Class Pointers (2) 1 r c 2 3 = &; r = &; c = &; 1 = &; 2 = &; 3 = &; Polymorhism 5

6 Base & Derived Class Pointers (3) c1 1 c2 incomlete object 2 3 c3 incomlete object c1 = (Circle *) &; c2 = (Circle *) &; c3 = (Circle *) &; 1 = &; 2 = &; 3 = &; Danger of Run Time Error!! No roblem!! Polymorhism 6

7 Non Virtual Member Functions (1) #include <stdio.h> class Poly { void { rintf("poly:: is called... \n"); class Rect : ublic Poly { void { rintf("rect:: is called... \n"); class Circle : ublic Poly { void { rintf("circle:: is called... \n"); Hiding base class member functions.;.;.; Polymorhism 7

8 Non Virtual Member Functions (2) #include <stdio.h> class Poly { void { rintf("poly:: is called... \n"); 1 class Rect : ublic Poly { void { rintf("rect:: is called... \n"); 2 3 class Circle : ublic Poly { void { rintf("circle:: is called... \n"); Poly:: is called three times 1 = &; 2 = &; 3 = &; 1->; 2->; 3->; Polymorhism 8

9 Virtual Member Functions (1) #include <stdio.h> 1 class Poly { virtual void { rintf("poly:: is called... \n"); class Rect : ublic Poly { (virtual) void { rintf("rect:: is called... \n"); 2 3 class Circle : ublic Poly { (virtual) void { rintf("circle:: is called... \n"); Virtual functions mechanism: tye deendent function calls at run time (secial run time handling of invocations) when invoked through a ublic base ointer 1 = &; 2 = &; 3 = &; 1->; 2->; 3->; Polymorhism 9

10 Virtual Member Functions (2) #include <stdio.h> class Poly { virtual void { rintf("poly:: is called... \n"); class Rect : ublic Poly { (virtual) void { rintf("rect:: is called... \n"); class Circle : ublic Poly { (virtual) void { rintf("circle:: is called... \n"); int main(void) { Poly, *; Rect, *r; Circle, *c; = &; ->; = &; ->; = &; ->; Without the virtual keyword, Poly::func is called 3 times. Poly:: Rect:: Circle:: Polymorhism 10

11 Pure Virtual Member Functions #include <stdio.h> class Poly { virtual void = 0; class Rect : ublic Poly { (virtual) void { rintf("rect:: is called... \n"); class Circle : ublic Poly { (virtual) void { rintf("circle:: is called... \n"); int main(void) { Poly, *; Rect, *r; Circle, *c; = &; ->; = &; ->; = &; ->; Rect:: Circle:: Classes containing ure virtual functions are termed "abstract"; they cannot be instantiated directly. Polymorhism 11

12 Virtual Function Mechanism If a virtual function is called through a ublic base ointer then actual tye of the object is used to choose the roer one among a grou of comatible virtual functions A call to a virtual function is done through a base reference or ointer treated secially at run time Unlike regular functions a virtual function call involves choosing one in a grou of comatible virtual functions according to the actual object tye at run time void foo(poly * ) { can be determined at run time ublic base ointer ->; ->; ->; a grou of comatible virtual functions Poly:: Rect:: Circle:: Polymorhism 12

13 Virtual Function Table comile time vtab f1() fx() Poly:: void foo(poly * ) { can be determined at run time vtab f1() fx() Rect:: vtab f1() fx() Circle:: At run time, the stored address of the vtab ointed by the object to which the base ointer oints, determines the actual address of the function run time The comiler translates the virtual function call into the index to the vtab Polymorhism 13

14 Run Time Tye Identification comile time RTTI Run-Time Tye Information Run-Time Tye Identification a C++ mechanism that exoses information about an object's data tye at runtime. dynamic_cast tyeid Polymorhism 14

15 Dynamic Cast comile time void foo(poly * ) { can be determined at run time Rect *RectPointer; Circle *CirclePointer; RectPointer = dynamic_cast <Rect> (); if (RectPointer!= NULL) { CirclePointer = dynamic_cast <Circle> (); if (CirclePointer!= NULL) { do secific things ertain to Rect do secific things ertain to Circle Polymorhism 15

16 Class Structure A data1a func1a() Class A data1a func1a() AA data2a func2a() AB data2b func2b() Class AA data1a func1a() data2a func2a() AAA data3a func3a() AAB data3b func3b() Class AA data1a func1a() data2a func2a() data3a func3a() Polymorhism 16

17 Abstract Class (1) A data1a Class A data1a AA data2a AB data2b Class AA data1a data2a AAA data3a AAB data3b Class AAA data1a data2a data3a Polymorhism 17

18 Abstract Class (2) A data1a class A { virtual void const = 0; AA data2a AB data2b class AA ublic A { virtual void const = 0; AAA data3a AAB data3b class AAA ublic AA { void { can be defined here. Polymorhism 18

19 References [1] Java in a nutshell, 4 th ed, David Flanagan [2] An Introduction to Object-Oriented Programming with Java, C. Thomas, Wu [3] Power Java, I. K. Chun (in Korean)