From: Charles Oliver Nutter <headius@...>
Date: 2009-06-11T02:35:28+09:00
Subject: Re: JRuby: Instance/Object method ovveride on a JPanel fails?

On Wed, Jun 10, 2009 at 12:20 PM, Curator1<rsilvetz@gmail.com> wrote:
> I like when learning a new language to play around with how to do
> things.  So in one case I did the two standard java idioms in JRuby to
> display an image [methods dispaly and display2], and then decided to
> try the Ruby idiom of modifying an object on the fly and over-ride
> it's paintComponent(g) method as shown below [method display3].  I am
> pretty sure I got the idiom right, so am I bumping up against a
> limitation of JRuby or have I botched the invocation or is it a
> bug....
...
>   def display3(image) #using anonymous instance
>     x=image.getWidth
>     y=image.getHeight
>     frame=JFrame.new("Quick Display 3")
>     frame.setSize(x,y)
>     panel=javax.swing.JPanel.new
> #let's do an instance over-ride.
>     class << panel
...
> import javax.imageio.ImageIO
> #debugger will need to insert their own jpg file below
> img = ImageIO.read(java.io.File.new("G:\\wildpics\
> \crystal_face.jpg"));
> u=TinoGraphics::Utility.new
> u.display2(img) #works as expected!
> u.display3(img) #does not work :(

Yes, this is expected. In the display2 case you're actually extending
a Java class, so you gain the ability to override whatever methods you
like. In the display3 case, the Java inheritance/dispatch semantics
are already set in stone, and we can't force Java to dispatch to Ruby
from already-bound Java code. Your best options would be to just
create another subclass or create a single subclass for which you can
provide different logic on a per-object basis (like a version that
delegates to an object of your choice, and then you just provide it on
construct or set it into an attribute.

- Charlie