Inheritance for beginners

Question

I just started to learn java, so now i read about such possibility as inheritance, so try to create class that must create object - box. And using inheritance implement new properties to created object. I try to put each class in separate file, so after creating class, try to use it in ``` public static void main(String[] args) ``` So class Inheritance: ``` public class Inheritance { double width; double height; double depth; Inheritance (Inheritance object){ width = object.width; height = object.height; depth = object.depth; } Inheritance ( double w, double h, double d){ width = w; height = h; depth = d; } Inheritance (){ width = -1; height = -1; depth = -1; } Inheritance (double len){ width=height=depth=len; } double volumeBox (){ return width*height*depth; } class BoxWeight extends Inheritance { double weight; BoxWeight (double w, double h, double d, double m){ super(w,h,d); weight = m; } } ``` But, when i try to use BoxWeight in main class, during using i got an error ``` public c…

Accepted Answer

As it stands, `BoxWeight` requires an instance of `Inheritance` to work (just like accessing a non-static variable or function requires an instance, so accessing a non-static inner class also does). If you change it to `static` it would work, but this isn't required.

`BoxWeight` doesn't need to be inside the `Inheritance` class.

Instead, remove `BoxWeight` out of the `Inheritance` class.

And change `Inheritance.BoxWeight` to `BoxWeight`.

EDIT: Just for completeness, you could also make it:

```
Inheritance.BoxWeight mybox1 = new Inheritance().new BoxWeight(...);
```

`Inheritance.BoxWeight` is just the type, so the above does not apply. But to create an instance of `BoxWeight`, you need an `Inheritance` object, which you create with `new Inheritance()`.

Inheritance for beginners

Solution

Problem