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假设一个人有一个超类的形状，两个子类是正方形和三角形。然后可以制作一个包含正方形和三角形对象的类型形状数组吗？如果是这样，这样做的最佳做法是什么？

下面我想知道的例子是可能的：

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);
}

编辑

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);
        }
    }

}

像这样的东西不起作用，为什么？

4

1 回答 1

0

您有两个类是 Shape 类的子类。这两个类覆盖了scaled_area字段。这意味着通过shape_arr对 scaled_area 的任何引用正在调用尚未分配任何值的超类字段。此外，当存储在字段区域中的值是默认值（0 表示 int）时，您在声明期间计算scale_area的值。这是一个可行的重新排列：

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);
        }
    }

}
于 2020-06-29T02:34:17.377 回答