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Inheritance - eclipse plugins vs. java [message #755869]

Wed, 09 November 2011 21:57

Jiri Janecek

Messages: 12
Registered: February 2011

Junior Member

Hello,

I discovered an interesting situation shown on the figure. Please can smb. explain me why it is not possible to access method M1() when instantiating B in C? When I add generic covering of M1 to B (only calling super) everything seems to be ok but without this M1 is not visible in B when I create an instance of B in C and try to call b.M1().

Or if it is possible what could be wrong?

Normally there is no need to cover every method from super object in subobject ...

http://www.image-share.com/upload/1046/15.png

Sorry for improvised diagram I have no tool at the moment.

Example is attached.

Thanks

Jiri

Attachment: dependencies_test.zip
(Size: 13.66KB, Downloaded 197 times)

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Re: Inheritance - eclipse plugins vs. java [message #756011 is a reply to message #755869]

Thu, 10 November 2011 13:16

Paul Webster

Messages: 6859
Registered: July 2009
Location: Ottawa

Senior Member

Plugin C can't see A.M1 unless it imports the package that contains A or requires plugin A (or plugin B re-exports stuff from plugin A, which is generally frowned upon).

It's not about inheritance, but about classloaders and runtime. In your plain java example, everything is in one classloader so there's no problem.

PW

Paul Webster
http://wiki.eclipse.org/Platform_Command_Framework
http://wiki.eclipse.org/Command_Core_Expressions
http://wiki.eclipse.org/Menu_Contributions

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Re: Inheritance - eclipse plugins vs. java [message #756080 is a reply to message #756011]

Thu, 10 November 2011 19:36

Jiri Janecek

Messages: 12
Registered: February 2011

Junior Member

I tried to re-export A in B and in my example it is working but I am not sure if I understand
good, so is re-export correct solution for my problem or am I misusing re-export?

Thanks Paul for your help.

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Re: Inheritance - eclipse plugins vs. java [message #756209 is a reply to message #756080]

Fri, 11 November 2011 13:47

Paul Webster

Messages: 6859
Registered: July 2009
Location: Ottawa

Senior Member

You've tightly coupled A and B, and re-exporting is the sledge hammer. In effect you're saying that consumers should use B and that A is a meaningless module ... which begs the question, why not just suck A into B and get rid of the extraneous plugin?

C should simply import the A package or require the A bundle. It obviously has a dependency on A, especially at the superclass level since it needs A.M1.

PW

Paul Webster
http://wiki.eclipse.org/Platform_Command_Framework
http://wiki.eclipse.org/Command_Core_Expressions
http://wiki.eclipse.org/Menu_Contributions

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Re: Inheritance - eclipse plugins vs. java [message #756210 is a reply to message #756080]

Fri, 11 November 2011 13:48

Thomas Schindl

Messages: 6651
Registered: July 2009

Senior Member

Are you talking about compile time or runtime. If you are talking about
compile time there's a mismatch between:
* javac (only has a flat class hierarchy)
* java (has a hierarchical class model)

See http://mcaffer.com/2011/01/managing-development-time-dependencies/

Tom

Am 10.11.11 20:36, schrieb Jiri Janecek:
> I tried to re-export A in B and in my example it is working but I am not
> sure if I understand
> good, so is re-export correct solution for my problem or am I misusing
> re-export?
>
> Thanks Paul for your help.

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Re: Inheritance - eclipse plugins vs. java [message #756213 is a reply to message #756209]

Fri, 11 November 2011 14:04

Thomas Schindl

Messages: 6651
Registered: July 2009

Senior Member

Hi,

If I get the problem right the problem is something that is a mismatch
between PDE&javac und JVM.

Bundle A:
---------
class A {
public void m() {
}
}

Bundle B requires A:
--------------------
class B extends A {
public void m2() {
}
}

Bundle C requires B:
--------------------
class C {
void main() {
new B().m(); // javac will cry
}
}

The problem here really is the compile time as Jeff described in his
blog because at runtime this would work perfectly.

Tom

Am 11.11.11 14:47, schrieb Paul Webster:
> You've tightly coupled A and B, and re-exporting is the sledge hammer.
> In effect you're saying that consumers should use B and that A is a
> meaningless module ... which begs the question, why not just suck A into
> B and get rid of the extraneous plugin?
>
> C should simply import the A package or require the A bundle. It
> obviously has a dependency on A, especially at the superclass level
> since it needs A.M1.
>
> PW
>

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