Abstract Classes in C++

Abstract classes are a powerful feature of C++ that allow you to define interfaces for your classes without providing an implementation. They are commonly used in design patterns to define a common interface for a group of related classes. In this article, we will explore what abstract classes are, how they work, and how you can use them in your own code.

What are Abstract Classes?

In C++, an abstract class is a class that contains one or more pure virtual functions. A pure virtual function is a function that is declared in the class but has no implementation. Abstract classes cannot be instantiated directly, but they can be used as base classes for other classes.

Abstract classes are used to define interfaces for a group of related classes. By defining a common interface, you can write code that works with any class that implements that interface, without having to know the specific details of each class. This is a powerful feature that allows you to write flexible and reusable code.

How do Abstract Classes Work?

#include <iostream>



class AbstractClass {

public:
    virtual void doSomething() = 0;
    virtual void doSomethingElse() = 0;
};

class ConcreteClass : public AbstractClass {

public:
    void doSomething() override {
        std::cout << "Doing something" << std::endl;
    }

    void doSomethingElse() override {
        std::cout << "Doing something else" << std::endl;
    }
};

int main() {
    ConcreteClass concrete;
    concrete.doSomething();
    concrete.doSomethingElse();
    return 0;
}

In this example, we have defined an abstract class AbstractClass with two pure virtual functions doSomething and doSomethingElse. We then define a concrete class ConcreteClass that inherits from AbstractClass and provides implementations for the pure virtual functions. We can then create an instance of ConcreteClass and call the doSomething and doSomethingElse functions.

The Factory Method design pattern is a creational pattern that uses abstract classes to define an interface for creating objects. The Factory Method pattern allows you to create objects without specifying the exact class of object that will be created. Instead, you define an abstract class that contains a method for creating objects, and then provide concrete implementations of that method in subclasses. This allows you to write code that works with any class that implements the factory method interface, without having to know the specific details of each class.

A real-world example of the Factory Method pattern is a GUI toolkit that provides a common interface for creating windows, buttons, and other GUI components. The GUI toolkit defines an abstract class ComponentFactory that contains a method createComponent for creating components. Subclasses of ComponentFactory provide concrete implementations of createComponent for creating specific types of components, such as WindowsComponentFactory for creating windows components and LinuxComponentFactory for creating Linux components. This allows you to write code that works with any class that implements the ComponentFactory interface, without having to know the specific details of each class.