how to define an inner class outside of the outer class

Question

I have a question similar to "Defining inner class outside java file". But the questioner, there, just wanted to do something which is possible by letting the classes to be all in a package.

Similar to him I would like to define some classes as the inner objects of an outer object; but I would like to have access to the dynamic fields of that object. To avoid having a crowded classes, I would like to define them in some other "innerClasses.java". Using "extend" only makes me able to use its static fields. But, I would like to access the dynamic fields like an inner object.

As a short example (but in fact a big example would be problematical) I would like this class in the class "OuterClass.java"

public class OuterClass{
    double nonStaticField
}

And each of these classes in other classes

public class InnerClass1OfOuterClass{
    ...
}

public class InnerClass2OfOuterClass{
    ...
}

public class InnerClass3OfOuterClass{
    ...
}

public class InnerClass4OfOuterClass{
    ...
}

....

Answer 1

The "natural" way would be the other way around: to let an inner class extend some abstract class containing the major code:

class Outer {
    class Inner extends InnerBase<Outer> {
        ... little code
    }
}

class InnerBase<T> {
    protected int eger;
    ... most code
}

Then there is delegating to a different class too.

Now if you still want to extend Inner:

class InnerBase<T> {
    protected int eger;
    ... most code
}

class Sinner extends Outer.Inner {
}

Outer outer = new Outer();
Inner sinner = outer.new Sinner();

For practical purposes you might create in Outer

protected Inner createInner() { return new Inner(); }

and extend Outer, overriding the factory method createInner.

This code design might be a bit circumstantial, hence my "natural" in the beginning.