Prev: Java reg exp question
Next: Example of building a list of file names?
From: MRe on 4 Feb 2010 13:10
Hi,

Two example programs below, I'm wondering if someone could tell me
why example 1 doesn't work, given that example 2 does? The error says
that a nested class has protected access, but I am accessing it from
an inheriting class

Thank you,
Kind regards,
Eliott

/////////////////////////////////////////////////////////////////////
// Example 1
/////////////////////////////////////////////////////////////////////

// test/A.java

package test;

import test.A.NA;

public class A<T extends NA>
{

protected static class NA
{
}

}

// test/extend/B.java

package test.extend;

import test.A;
import test.extend.B.NB;

public class B
extends A<NB>
{

// ERROR : test.A.NA has protected access in nestedtest.A
protected static class NB
extends A.NA
{
}

}

/////////////////////////////////////////////////////////////////////
// Example 2
/////////////////////////////////////////////////////////////////////

// test/A.java

package test;

public class A<T>
{

protected static class NA
{
}

}

// test/extend/B.java

package test.extend;

import test.A;

public class B
extends A<Void>
{

// No error
protected static class NB
extends A.NA
{
}

}
From: Lew on 4 Feb 2010 14:47
MRe wrote:
> Two example programs below, I'm wondering if someone could tell me
> why example 1 doesn't work, given that example 2 does? The error says
> that a nested class has protected access, but I am accessing it from
> an inheriting class
>
> /////////////////////////////////////////////////////////////////////
> // Example 1
> /////////////////////////////////////////////////////////////////////
>
> // test/A.java
>
> package test;
>
> import test.A.NA;
^^
This import accomplishes nothing.

> public class A<T extends NA>

The use of type 'NA' here requires that 'NA' be public. You've exposed 'NA'
to view beyond same-package or inheriting types.

> {
>
> protected static class NA
> {
> }
>
> }
>
> // test/extend/B.java
>
> package test.extend;
>
> import test.A;
> import test.extend.B.NB;
^^
This import accomplishes nothing.

> public class B
> extends A<NB>

'NB' has to extend 'NA', but you are declaring it "above" the inheriting
scope, so 'NA' is not visible.

> {
>
> // ERROR : test.A.NA has protected access in nestedtest.A

What *exactly* does the error message state, in its entirety? Copy and paste;
do not paraphrase or redact.

> protected static class NB
> extends A.NA
> {
> }
>
> }
>
> /////////////////////////////////////////////////////////////////////
> // Example 2
> /////////////////////////////////////////////////////////////////////
>
> // test/A.java
>
> package test;
>
> public class A<T>

This declaration does not elevate any protected member to public view.

> {
>
> protected static class NA
> {
> }
>
> }
>
> // test/extend/B.java
>
> package test.extend;
>
> import test.A;
>
> public class B
> extends A<Void>

This declaration does not require a public view of any protected member.

> {
>
> // No error
> protected static class NB
> extends A.NA

This declaration is contained within the declaration scope of an inheriting
class and is therefore legal.

> {
> }
>
> }

--
Lew
From: markspace on 4 Feb 2010 17:13
MRe wrote:
> The error says
> that a nested class has protected access, but I am accessing it from
^^^^^^^^^
> an inheriting class
^^^^^^^^^^


Now go read up on what protected actually does (hint: I used Google to
find this, it was the first link):

<http://java.sun.com/docs/books/tutorial/java/javaOO/accesscontrol.html>

From: MRe on 4 Feb 2010 19:27
Hi Lew,

Thank you for the response..

> > import test.A.NA;
>
>                  ^^
> This import accomplishes nothing.

That's what I thought, but NetBeans6.8 seems to insist

> > public class A<T extends NA>
>
> The use of type 'NA' here requires that 'NA' be public.  You've exposed 'NA'
> to view beyond same-package or inheriting types.

Oh, well that makes sense. I guess I missed it because Java didn't
complain. I see now that it will compile in the absence of B so long
as I keep every thing in the test package. I was mixing up several
different things; sorry. Thank you :)

> >    // ERROR : test.A.NA has protected access in nestedtest.A
>
> What *exactly* does the error message state, in its entirety?  Copy and paste;
> do not paraphrase or redact.

That was the whole error.

> > public class A<T>
>
> This declaration does not elevate any protected member to public view.
>
> > public class B
> > extends      A<Void>
>
> This declaration does not require a public view of any protected member.
>
> >    // No error
> >    protected static class NB
> >    extends                A.NA
>
> This declaration is contained within the declaration scope of an inheriting
> class and is therefore legal.

Understood. Thank you

> Lew

Thanks again,
Kind regards,
Eliott
From: MRe on 4 Feb 2010 19:42
On Feb 4, 10:13 pm, markspace <nos...(a)nowhere.com> wrote:
> MRe wrote:
> > The error says
> > that a nested class has protected access, but I am accessing it from
>                           ^^^^^^^^^
> an inheriting class
>    ^^^^^^^^^^
>
> Now go read up on what protected actually does (hint: I used Google to
> find this, it was the first link):
>
> <http://java.sun.com/docs/books/tutorial/java/javaOO/accesscontrol.html>

Hi markspace,

Thank you for the response and interesting link.

I'm not sure I understand the mistake I've made in the quote you've
highlighted (given the context in which you've quoted it) - as far as
I can tell, the linked document affirms what I've said?

Thank you again for the link; a concise and very useful find.
Kind regards,
Eliott
 |  Next  |  Last
Pages: 1 2 3
Prev: Java reg exp question
Next: Example of building a list of file names?