How to create the instance of a concrete implementation of a class in C++ as in Java?

Maybe it’s a little weird question, but: I’m not so much familiar with C++.

Let’s say we have an abstract class A and a class B that extends it:

abstract class A {
    abstract void foo();
}

class B extends A {
    @Override
    void foo() {
        // . . .
    }
}

Then, in the Test class, we can create an instance of B this way:

class Test {
    A a = new B();
}

Can I do something like this in C++?

Because, when I do the same in C++, I receive something like this:

(I have an abstract class Customer that’s being extended by other class. There’s being performed smth like this Customer* customer = new OnlineCustomer();)

>Solution :

In C++ you can’t construct an abstract class, but you can make a pointer to an abstract class. Here’s a direct translation of your code to C++:

#include <iostream>

struct A // structs are classes that are default public
{
    // having at least one method be
    // "= 0" flags the class as abstract:
    virtual void foo() = 0;
    virtual ~A() = default;
};

struct B : A
{
    void foo() override
    {
        std::cout << "Hello World" << std::endl;
    }
};

int main()
{
    // Test:
    // (in C++ not everything is about classes!)

    // Where 'a' OWNS the data:
    A* a1 = new B;
    a1->foo();
    delete a1;

    // Where 'a' REFERS to the data:
    B b;
    A* a2 = &b;
    a2->foo();
}

demo

Note that where Java is all about OOP and inheritance, in C++ OOP is just one of the tools in the tool box, and inheritance – although it has its place – is often seen as causing more problems than it solves (often templates or functional programming or composition would do better).