Assigning Superclass to Subclass

public class Main {
    public static void main(String[] args) {
        GObj[] gobj = { new Rect(), new Circle() };
        Circle circle = gobj[0];
    }
}

public class Main {
    public static void main(String[] args) {
        GObj[] gobj = { new Rect(), new Circle() };
        Circle circle = (Circle)gobj[0];
    }
}

What happened when the progam ran?