Lesson 52nd abstract classes and interfaces in C + +

What is an abstract class?

Problem:

Does the shape class need to exist?

Abstract classes are required to be supported in object-oriented.

An exploration of abstract classes:

The compilation results are as follows:

Refine the example:

1#include <iostream>2#include <string>3 4 using namespacestd;5 6 classShape7 {8  Public:9     Virtual DoubleArea () =0;Ten }; One  A classRect: PublicShape - { -     intMa; the     intMB; -  Public: -Rect (intAintb) -     { +Ma =A; -MB =b; +     } A     DoubleArea () at     { -         returnMA *MB; -     } - }; -  - classCircle: PublicShape in { -     intMr; to  Public: +Circle (intR) -     { theMr =R; *     } $     DoubleArea ()Panax Notoginseng     { -         return 3.14* Mr *Mr; the     } + }; A  the voidArea (shape*p) + { -     Doubler = p->Area (); $      $cout <<"r ="<< R <<Endl; - } -  the intMain () - {WuyiRect rect (1,2); theCircle Circle (Ten); -      WuArea (&rect); -Area (&circle); About      $     return 0; -}

The pure virtual function is to be overridden in a subclass.

Operation Result:

Abstract classes cannot define objects, but abstract classes can define pointers.

Abstract classes and pure virtual functions:

Interface:

C + + does not have a real interface, no specific syntax support, the following language C #, Java has interfaces.

Interface Example:

1#include <iostream>2#include <string>3 4 using namespacestd;5 6 classChannel7 {8  Public:9     Virtual BOOLOpen () =0;Ten     Virtual voidClose () =0; One     Virtual BOOLSendChar* BUF,intLen) =0; A     Virtual intReceiveChar* BUF,intLen) =0; - }; -  the intMain () - { -     return 0; -}

We only define the function, which is an interface.

Summary:

Lesson 52nd abstract classes and interfaces in C + +