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Madhur Ahuja
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 Posted: Mon Sep 20, 2004 12:41 pm Post subject: attempting to assign weaker access privileges |
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Hello
This error normally occurs when a subclass overrides a method
but doesnt preserves the original access type like public.
However I am not able to understand what is the meaning of this
error especially what it means when it says *weaker*.
--
Madhur Ahuja [madhur<underscore>ahuja<at>yahoo<dot>com]
Homepage & other stuff
http://madhur.netfirms.com
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Paul Lutus
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| Posted: Mon Sep 20, 2004 6:16 pm Post subject: Re: attempting to assign weaker access privileges |
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Madhur Ahuja wrote:
| Quote: | Hello
This error normally occurs when a subclass overrides a method
but doesnt preserves the original access type like public.
However I am not able to understand what is the meaning of this
error especially what it means when it says *weaker*.
|
If you have a method in a parent class with a given access, and if you
override it while also giving it less general (example: private) access,
this error will result. This restriction exists because if access were
freely modifiable in subclasses, the entire idea of access control would
have no meaning - one could override the intent of the class designer along
with the methods.
http://www.janeg.ca/scjp/overload/overridingMethods.html
--
Paul Lutus
http://www.arachnoid.com
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Stefan Schulz
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| Posted: Mon Sep 20, 2004 9:16 pm Post subject: Re: attempting to assign weaker access privileges |
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On Mon, 20 Sep 2004 11:16:59 -0700, Paul Lutus <nospam (AT) nosite (DOT) zzz> wrote:
| Quote: | Madhur Ahuja wrote:
Hello
This error normally occurs when a subclass overrides a method
but doesnt preserves the original access type like public.
However I am not able to understand what is the meaning of this
error especially what it means when it says *weaker*.
If you have a method in a parent class with a given access, and if you
override it while also giving it less general (example: private) access,
this error will result. This restriction exists because if access were
freely modifiable in subclasses, the entire idea of access control would
have no meaning - one could override the intent of the class designer
along with the methods.
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This is not actually a problem as long as you "widen" access. (e.g. make a
protected method public in a subclass). There are a few things you can not
do, however:
* publish private methods. Easy, since you can not access them from your
subclass. You _can_ however create a public method with the same signature.
* Narrow access. You can not make a public method protected in the
subclass.
Otherwise, the concept of Object Polymorphism would plainly not work. (An
instance of a subclass could not be assumed to have all the public methods
of the superclass)
* (For some strange reason) Modify return values. Yes, even if the new
Return value is a subclass of the old one, you must keep return types
equal. The rationale for this is not really apparent to me, but that's the
way it is
See you
Stefan
--
Using Opera's revolutionary e-mail client: http://www.opera.com/m2/
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