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Hannes.Heckner@munich.ixos.de wrote:

> How can I make foo final in the derivation by OVERLOADING
> foo from the Base class?

You can't. Variables aren't overridden, they are merely shadowed. 
(Overloading is something different, by the way.) The Java Language 
Specification explains this in more detail.

> If you know a solution to this problem, please submit 
> it to http://www.the-codebook.com/show_code.asp?ProblemId=1356

Post in news, expect answers in news...

-- 
Jon Skeet - skeet@pobox.com
http://www.pobox.com/~skeet/

First of all, you don't overload nor override instance variables, but
you *shadow* them instead. Variables are not treated as methods, which
take part in polymorphism AKA dynamic binding. The way you have it, only
the 'foo' at the base class will be seen by the doFoo() in said class.
You need to override the doFoo() in class Derivation to print its own
'foo'.

Tony Alicea


-------------------------
Hannes Heckner wrote:
> 
> Hi,
> 
> I tried to following example to have my member variable foo
> read-only in the derivation:
> 
> public class Class1
> {
>         /**
>          * The main entry point for the application.
>          *
>          * @param args Array of parameters passed to the application
>          * via the command line.
>          */
>         public static void main (String[] args)
>         {
>                 // TODO: Add initialization code here
>                 Base b = new Base();
>                 Derivation d = new Derivation();
>                 b.doFoo();
>                 d.doFoo();
>         }
> }
> 
> class Base
> {
>         protected int foo = 0;
> 
>         public void doFoo()
>         {
>                 System.out.println(""+foo);
>         }
> }
> 
> class Derivation extends Base
> {
>         final int foo = 1;
> }
> 
> Unfortunately it seems that the Derivation class DOES NOT
> overload foo! Therefore you will get the following output:
> 0
> 0
> 
> How can I make foo final in the derivation by OVERLOADING
> foo from the Base class?
> 
> If you know a solution to this problem, please submit it to http://www.the-codebook.com/show_code.asp?ProblemId=1356
> 
> +++++++++++ Posted via The-Codebook.Com, The Source for Developers +++++++++++
> http://www.The-Codebook.com/                      Java, VisualBasic, VisualC++

Hehe you can't and you shouldn't be able to.

Derivation inherits from Base and must, must, must fulfill the same
interface contract as Base, because by definition I must be able to
substitute an instance of Derivation for an instance of Base, anywhere I
wanted to and it must make sense and work. Making a member variable
read-only in Derivation that was writable in Base would break this.

To do what you "actually" want (isn't intuition wonderful) I expect you need
to reconsider your class hierarchy.

Perhaps something like:

public abstract class Parent
{
    private int foo;
    public int getFoo() {return foo;}
    protected void setFoo(int argFoo) {this.foo = argFoo;}
}

public class ChildWithWritableFoo
{
    public void setFoo(int argFoo) {super.setFoo(argFoo))
}

public class ChildWithReadOnlyFoo
{
}


Hannes Heckner <Hannes.Heckner@munich.ixos.de> wrote in message
news:951828737327@munich.ixos.de...
> Hi,
>
> I tried to following example to have my member variable foo
> read-only in the derivation:
>
> public class Class1
> {
> /**
> * The main entry point for the application.
> *
> * @param args Array of parameters passed to the application
> * via the command line.
> */
> public static void main (String[] args)
> {
> // TODO: Add initialization code here
> Base b = new Base();
> Derivation d = new Derivation();
> b.doFoo();
> d.doFoo();
> }
> }
>
> class Base
> {
> protected int foo = 0;
>
> public void doFoo()
> {
> System.out.println(""+foo);
> }
> }
>
> class Derivation extends Base
> {
> final int foo = 1;
> }
>
>
>
> Unfortunately it seems that the Derivation class DOES NOT
> overload foo! Therefore you will get the following output:
> 0
> 0
>
> How can I make foo final in the derivation by OVERLOADING
> foo from the Base class?
>
> If you know a solution to this problem, please submit it to
http://www.the-codebook.com/show_code.asp?ProblemId=1356
>
> +++++++++++ Posted via The-Codebook.Com, The Source for Developers
+++++++++++
> http://www.The-Codebook.com/                      Java, VisualBasic,
VisualC++

Jon Skeet wrote:

> Hannes.Heckner@munich.ixos.de wrote:
>
> > How can I make foo final in the derivation by OVERLOADING
> > foo from the Base class?
>
> You can't. Variables aren't overridden, they are merely shadowed.
> (Overloading is something different, by the way.) The Java Language
> Specification explains this in more detail.
>

Yes, what you can do is create an accessor method for a private variable
and override it in the  descendant class.

>
> > If you know a solution to this problem, please submit
> > it to http://www.the-codebook.com/show_code.asp?ProblemId=1356
>
> Post in news, expect answers in news...
>
> --
> Jon Skeet - skeet@pobox.com
> http://www.pobox.com/~skeet/

--
IRISA-INRIA, Campus de Beaulieu, 35042 Rennes cedex, France
T�l: +33 (0) 2 99 84 71 00, Fax: +33 (0) 2 99 84 71 71

Noelle.Adam@irisa.fr wrote:

> > Hannes.Heckner@munich.ixos.de wrote:
> >
> > > How can I make foo final in the derivation by OVERLOADING
> > > foo from the Base class?
> >
> > You can't. Variables aren't overridden, they are merely shadowed.
> > (Overloading is something different, by the way.) The Java Language
> > Specification explains this in more detail.
> 
> Yes, what you can do is create an accessor method for a private variable
> and override it in the  descendant class.

That's still not overloading foo. I may be a way round the problem, but 
the specific qusetion "How can I make foo final [...] by overloading foo 
[...]" still has the answer "You can't."

-- 
Jon Skeet - skeet@pobox.com
http://www.pobox.com/~skeet/