Qt. Why is a derived class created by default?

Question

Qt

I just started learning Qt Framework. Created "Application Qt Widgets"

And by default a derived class from QWidget was added.

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

namespace Ui {
    class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

    private:
        Ui::Widget *ui;

    public:
        explicit Widget(QWidget *parent = 0);
        ~Widget();
};

#endif // WIDGET_H

Is it required or what?
I commented out the header file and method definitions, created an object from QWidget, instead of a derived Widget. Everything started exactly the same way.
I'm reading "Qt 5.3. Professional C++ Programming. Max Schlee"
There are few and not very good examples. Can you advise, if there is, something else, plus to this.

Answer 1

It will work, why not. But when you want to modify it somehow, you can’t do without inheritance.