CODEWITHSUNDEEP
javainheritance
hbk
hbk

Reputation: 11184

Inheritance for beginners

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 class MainModule {
    public static void main(String[] args) {
    Inheritance.BoxWeight mybox1 = new Inheritance.BoxWeight(9, 9, 9, 9);
....

Error - No enclosing instance of type Inheritance is accessible. Where i'm wrong?

Upvotes: 5

Views: 224

Answers (6)

Scarecrow
Scarecrow

Reputation: 4137

Problem is in this line 

Inheritance.BoxWeight mybox1 = new Inheritance.BoxWeight(9, 9, 9, 9);

use 

BoxWeight mybox1 = new BoxWeight(9.0, 9.0, 9.0, 9.0);

Upvotes: -1

Arsen Alexanyan
Arsen Alexanyan

Reputation: 3141

Inheritance.BoxWeight mybox1 = new Inheritance().new BoxWeight(9, 9, 9, 9);

You are here using both principles inheritance and inner class. Suppose that your class BoxWeight doesn't extend Inheritance class. Your inner class has access of the outer class some properties and methods which are object instance level attributes. So You should create new Inheritance() then by using this instance create an instance of BoxWeight.

Upvotes: 1

Bernhard Barker
Bernhard Barker

Reputation: 55589

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().

Upvotes: 4

jlordo
jlordo

Reputation: 37813

If you want to keep your classes nested and not static (I don't see a good reason for it), you can also use:

Inheritance.BoxWeight mybox1 = new Inheritance().new BoxWeight(9, 9, 9, 9);

Upvotes: 1

Philip Whitehouse
Philip Whitehouse

Reputation: 4157

Ignoring the fact that this is an entirely arbitrary homework problem with crazy names, that extending a class inside the abstract class is an odd situation and that it makes no sense for a BoxWeight to be inside an Inheritance:

   ...
   Inheritance i = new Inheritance(0, 0, 0, 0);
   Inheritance.BoxWeight mybox1 = i.new BoxWeight(9, 9, 9, 9);
   ...

i is the 'enclosing object'.

Upvotes: 0

Asaph
Asaph

Reputation: 162771

Change

class BoxWeight extends Inheritance

to

static class BoxWeight extends Inheritance

This should allow your code to compile. However, in addition to using the inheritance feature of java, you're also using an inner class, which isn't really necessary in this case and is likely confusing things for you. If you pull BoxWeight out into its own file, and reference it without the Inheritance. prefix, I think you'll find things to be easier to understand.

Upvotes: 3

Related Questions