Parameterizing superclass with static member class from subclass

xgord :

Is there a way to parameterize a superclass with a static member class of the subclass?

Contrived Example

ExampleSuperClass.java:

package foo;

public class ExampleSuperClass<T> {
    protected T field;

    public ExampleSuperClass(T field) {
        this.field = field;
    }

    public T getField() {
        return field;
    }
}

ExampleSubClass.java:

package foo;

public class ExampleSubClass extends ExampleSuperClass<Member> {

    static class Member {

    }

    public ExampleSubClass() {
        super(new Member());
    }
}

Compilation fails on ExampleSubClass.java with error:

[javac] ExampleSubClass.java:3: error: cannot find symbol
[javac] public class ExampleSubClass extends ExampleSuperClass<Member> {
[javac]                                                        ^
[javac]   symbol: class Member
[javac] 1 error

or in Eclipse with:

Member cannot be resolved to a type

in Eclipse the super invocation also has the error:

The constructor ExampleSuperClass(Member) refers to missing type Member

It works fine (aka no errors) if ExampleSubClass is instead parameterized with another package-protected top-level class.

Summary

The driving force behind this is that I have a generic super class and many different ${SubClass-extends-GenericSuperClass}.java and ${ClassUsedBySubClass}.java pairs. But since ClassUsedBySubClass is only ever referenced by SubClass, it would be nice to:

1. restrict ClassUsedBySubClass's access by making it a static member class and
2. cut down on the number of files by not giving ClassUsedBySubClass its own file.

So, is there a way to use a subclass's member class in parameterizing the superclass?

If there isn't -- is there an alternative approach?

dasblinkenlight :

Yes, you can do it. However, since Java uses the scope outside the declaration for name resolution, you must qualify Member with the name of ExampleSubClass:

public class ExampleSubClass extends ExampleSuperClass<ExampleSubClass.Member> {
    ...
}