# JRuby: Instance/Object method ovveride on a JPanel fails?

**URL:** <https://www.ruby-forum.com/t/jruby-instance-object-method-ovveride-on-a-jpanel-fails/169966>\
**Category:** Ruby\
**Created:** [June 10, 2009, 7:20pm UTC](https://www.ruby-forum.com/t/jruby-instance-object-method-ovveride-on-a-jpanel-fails/169966 "2009-06-10T19:20:55Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Curator1](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/eada6e/32.png) [@Curator1](https://www.ruby-forum.com/u/Curator1)\
**Post date:** [June 10, 2009, 7:20pm UTC](https://www.ruby-forum.com/t/jruby-instance-object-method-ovveride-on-a-jpanel-fails/169966/1 "2009-06-10T19:20:55Z")

</div>

With the caveat I’m new to JRuby but have 20 years of software  
experience:

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…

module TinoGraphics  
require ‘java’  
import java.awt.image.BufferedImage  
import javax.swing.JButton  
import javax.swing.JFrame  
class TGPanel \< javax.swing.JPanel  
def initialize(image)  
@image=image  
super()  
end  
def paintComponent(g)  
g.drawImage(@image,0,0,@image.getWidth,@image.getHeight,self)  
puts “paintComponent of TGPanel”  
end  
end

class Utility  
def initialize  
#for future use  
end  
def resize(original,xscale,yscale)  
x=original.getWidth/xscale  
y=original.getHeight/yscale  
b2=original.getScaledInstance(x,y,BufferedImage::SCALE\_SMOOTH)  
bi2=BufferedImage.new(x,y,BufferedImage::TYPE\_INT\_RGB)  
graphics = bi2.createGraphics  
graphics.drawImage(b2,0,0,nil)  
graphics.dispose  
return bi2  
end  
def resize(original,x,y)  
b2=original.getScaledInstance(x,y,BufferedImage::SCALE\_SMOOTH)  
bi2=BufferedImage.new(x,y,BufferedImage::TYPE\_INT\_RGB)  
graphics = bi2.createGraphics  
graphics.drawImage(b2,0,0,nil)  
graphics.dispose  
return bi2  
end  
def display(image) #plain old JButton/Icon hack  
x=image.getWidth  
y=image.getHeight  
frame=JFrame.new(“Quick Display”)  
frame.setSize(x,y)  
panel=JButton.new(javax.swing.ImageIcon.new(image))  
frame.setContentPane(panel)  
frame.setVisible(true)  
end  
def display2(image) #using inheritance  
x=image.getWidth  
y=image.getHeight  
frame=JFrame.new(“Quick Display 2”)  
frame.setSize(x,y)  
panel=TGPanel.new(image)

```
 frame.setContentPane(panel)
 frame.setVisible(true)

```

end  
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  
def setImage(image)  
@image=image  
end  
def getImage  
@image  
end  
def paintComponent(g)  
g.drawImage(@image,  
0,0,@image.getWidth,@image.getHeight,self)  
puts “paintComponent of panel instance”  
end  
end  
panel.setImage(image)  
frame.setContentPane(panel)  
frame.setVisible(true)  
frame.repaint  
end  
end  
end

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 ☹

---

<div class="post-metadata">

**Author:** ![Curator1](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/eada6e/32.png) [@Curator1](https://www.ruby-forum.com/u/Curator1)\
**Post date:** [June 10, 2009, 7:36pm UTC](https://www.ruby-forum.com/t/jruby-instance-object-method-ovveride-on-a-jpanel-fails/169966/2 "2009-06-10T19:36:48Z")

</div>

On Wed, Jun 10, 2009 at 12:20 PM, Curator1[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> I like when learning a new language to play around with how to do  
> things. Â 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]. Â 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…  
> …  
> Â def display3(image) #using anonymous instance  
> Â Â x=image.getWidth  
> Â Â y=image.getHeight  
> Â Â frame=JFrame.new(“Quick Display 3”)  
> Â Â frame.setSize(x,y)  
> Â Â panel=javax.swing.JPanel.new  
> #let’s do an instance over-ride.  
> Â Â 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