Interfaces in C++ (Abstract Classes)
Previous Page
Next Page
An interface describes the behavior or capabilities of a C++ class without
committing to a particular implementation of that class.
The C++ interfaces are implemented usingabstract classesand these
abstract classes should not be confused with data abstraction which is a
concept of keeping implementation details separate from associated data.
A class is made abstract by declaring at least one of its functions aspure
virtualfunction. A pure virtual function is specified by placing "= 0" in its
declaration as follows −
class Box {
public:
// pure virtual function
virtual double getVolume() = 0;
private:
double length; // Length of a box
double breadth; // Breadth of a box
double height; // Height of a box
};
The purpose of anabstract class(often referred to as an ABC) is to provide
an appropriate base class from which other classes can inherit. Abstract
classes cannot be used to instantiate objects and serves only as aninterface.
Attempting to instantiate an object of an abstract class causes a compilation
error.
Thus, if a subclass of an ABC needs to be instantiated, it has to implement
each of the virtual functions, which means that it supports the interface
declared by the ABC. Failure to override a pure virtual function in a derived
class, then attempting to instantiate objects of that class, is a compilation
error.
Classes that can be used to instantiate objects are calledconcrete classes.
Abstract Class Example
