是否可以在超类类型的数组中包含子类数组

Question

suppose one has a super-class of shapes two sub-classes of square and triangle. could one then make an array of type shapes containing square and triangle objects? if so what would be the best practice for doing so?

example below of what i want to know is possible:

class shapes{
    protected int linear_scale_factor = 4;
}

class square extends shapes {
    int area;
    int scaled_area = area * linear_scale_factor**2;
}

class triangle extends shapes {
   int area;
   int scaled_area = area * linear_scale_factor**2;

}

class main{
   shapes[] shapes_arr = new shapes[8];
   shapes_arr[0] = new square(34);
}

edit

class shapes{
    protected int linear_scale_factor = 4;
    protected int scaled_area ;
}

class square extends shapes {
    int area;
    int scaled_area = area * linear_scale_factor*linear_scale_factor;
    
    public square(int i){
        area = i;
    }
}

class triangle extends shapes {
   int area;
   int scaled_area = area * linear_scale_factor*linear_scale_factor;

   public triangle(int i){
       area = i;
   }

}

class main{
    public static void main(String[] args) {
        shapes[] shapes_arr = new shapes[8];
        shapes_arr[0] = new square(34);
        shapes_arr[1] = new triangle(12);
        shapes_arr[2] = new square(453);


        for(shapes shape : shapes_arr){
            System.out.println(shape.scaled_area);
        }
    }

}

something like this doesn't work, why?

Answer 1

You have two classes that are subclasses of the Shape class. The two classes override the field scaled_area . This means the any reference to scaled_area via shapes_arr is calling the superclass field, which has not been assigned any value. Furthermore, you are computing the value for scale_area during declaration when the values stored in the field area are defaults (0 for int). Here is a possible rearrangement that can work:

class shapes{
    protected int linear_scale_factor = 4;
    protected int scaled_area ;
}

class square extends shapes {
    int area;
    public square(int i){
        area = i;
        scaled_area = area * linear_scale_factor*linear_scale_factor;
    }
}

class triangle extends shapes {
   int area;
   

   public triangle(int i){
       area = i;
       scaled_area = area * linear_scale_factor*linear_scale_factor;
   }

}

class main{
    public static void main(String[] args) {
        shapes[] shapes_arr = new shapes[8];
        shapes_arr[0] = new square(34);
        shapes_arr[1] = new triangle(12);
        shapes_arr[2] = new square(453);


        for(shapes shape : shapes_arr){
            System.out.println(shape.scaled_area);
        }
    }

}