«

Hi,

I am a naive JAVA user. Can you please tell me, oh how to implement
the following scenario

A
^ ^
/ \
B C
^ ^
\ /
D

Classes B and C extends class A, but how to define class D, such that
members of both B and C are available to D.

Thanks
>> manjunath

wrote in comp.lang.java.programmer:
> Classes B and C extends class A, but how to define class D, such that
> members of both B and C are available to D.

Java does not support multiple inheritance, so class D can not
provide the methods through Java's inheritance mechanism.

Internet contains a lot of information about this. Search Google
for "java multiple inheritance".

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wrote:
> Hi,
>
> I am a naive JAVA user. Can you please tell me, oh how to implement
> the following scenario
>
> A
> ^ ^
> / \
> B C
> ^ ^
> \ /
> D
>
> Classes B and C extends class A, but how to define class D, such that
> members of both B and C are available to D.
>
> Thanks
>
>>>manjunath
>
>

You can't. Make D a subclass of A, just like B and C. If you want to
specify some additional behaviour for D then define interface(s) that it
must implement, along with (optionally) either B, C, or both B and C.

John

You cannot do that. Java does not support multiply inheritence of
*implementation*.

However, if you were to make A, B and C _interfaces_, then D could
implement both B and C. Then, using patterns (such as
Wrapper/Decorator), you could do the following:

A--extended by-->B--implemented by-->Bimpl
A--extended by-->C--implemented by-->Cimpl

D--extends both-->[B,C]--contains instances of-->[Bimpl,Cimpl]

Then your D could pass calls to those methods defined in the A, B and C
interfaces to the specific instance variables of tyep Bimpl and Cimpl
as necessary.

Darryl L. Pierce wrote:
> You cannot do that. Java does not support multiply inheritence of
> *implementation*.
>
> However, if you were to make A, B and C _interfaces_, then D could
> implement both B and C. Then, using patterns (such as
> Wrapper/Decorator), you could do the following:
>
> A--extended by-->B--implemented by-->Bimpl
> A--extended by-->C--implemented by-->Cimpl
>
> D--extends both-->[B,C]--contains instances of-->[Bimpl,Cimpl]
>
> Then your D could pass calls to those methods defined in the A, B and C
> interfaces to the specific instance variables of tyep Bimpl and Cimpl
> as necessary.
>

In our paper

On Multiple Inheritance in Java
L. Bettini, M. Loreti, B. Venneri. Technology of Object-Oriented
Languages, Systems and Architectures, Proc. of TOOLS Eastern Europe
2002, (Theo D'Hondt, Ed.), pages 1-15, Kluwer Academic Publishers, 2003.
http://music.dsi.unifi.it/abstracts/multipinh-abs.html
http://music.dsi.unifi.it/papers/multipinh.ps.gz

we provide a general algorithm to automatically implement multiple
inheritance in Java; this also shows that it is not straighforward to
simulate the exact semantics of multiple inheritance through interfaces
and object composition.

Lorenzo

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| Lorenzo Bettini ICQ# lbetto, 16080134 |
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