Can I initialize virtual functions outside a class?

[Ch1156]

I want to know if i can initialize a virtual function outside a class, the function will have a lot of code and I don't want to clutter up my class.

#include <SFGUI/SFGUI.hpp>
#include <SFML/Graphics.hpp>

#include <iostream>
#include <string>
#include <vector>

using namespace std;

class App
{
    public:
        void Program();
        virtual void Window();

    private:
        sfg::SFGUI sfgui;
        sfg::Desktop dtop;
        sfg::Window::Ptr main_window;
};

class SFGUIWindow
{
    public:
        virtual void Window();

    private:

};

void SFGUIWindow::Window()
{

}

int main()
{

    return 0;
}

[Ch1156]

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