Title: Possible problem with subclasses of Java classes, constructors, and reflection
Type: behaviour Severity: normal
Components: Core Versions: 2.5b1
Status: closed Resolution: wont fix
Dependencies: Superseder:
Assigned To: fwierzbicki Nosy List: aviflax, cgroves, fwierzbicki
Priority: high Keywords:

Created on 2009-02-22.04:37:53 by aviflax, last changed 2009-03-30.20:43:54 by aviflax.

File name Uploaded Description Edit Remove aviflax, 2009-02-24.17:25:02 java class and jython script which illustrate the problem
msg4155 (view) Author: Avi Flax (aviflax) Date: 2009-02-22.04:37:52
I'm working on using the Java library Restlet with Jython (going well,
plan to write an article about it soon) and I'm encountering this problem:

from org.restlet.resource import Resource

class my_resource(Resource):
    def __init__(self):
        # By default, modifiable is False. Let's set it to True.

# Prints True as one would expect
print my_resource().isModifiable()

# Create an instance using Java reflection
obj = my_resource.getClass(my_resource).getConstructor(my_resource,

# Prints False, which means that when one uses Java reflection, the
Jython subclass' constructor isn't properly called, or something
print obj.isModifiable()


This is a showstopper for me, because Restlet internally uses reflection
all over the place.

Other than this issue, the project is going well. I look forward to
verification that my observation about this behaviour is correct!
msg4160 (view) Author: Avi Flax (aviflax) Date: 2009-02-24.14:31:51
One more thought: the constructor *is* being run, because if I set a
Python attribute on self, such as = bar, then _that_ *is*
accessible from the method. It's only modifying fields of the Java class
(via a setter) that seems to not function.

I wonder if this might have something to do with the constructor and the
method seeming to have references to different object instances? What I
mean is, if I add 'print str(self)' to the constructor and the method,
they print the Java object ID -- which is different!
msg4161 (view) Author: Frank Wierzbicki (fwierzbicki) Date: 2009-02-24.16:52:14
Are you able to reduce this to a simple Java class that shows the bug? 
That would help us narrow down the cause.
msg4162 (view) Author: Avi Flax (aviflax) Date: 2009-02-24.17:04:33
Sure, I can do that!
msg4163 (view) Author: Avi Flax (aviflax) Date: 2009-02-24.17:25:02
attaching zipfile containing a java class and a jython script which
illustrate the problem
msg4164 (view) Author: Frank Wierzbicki (fwierzbicki) Date: 2009-02-25.19:09:00
Thanks for the test files, that should help.
msg4393 (view) Author: Frank Wierzbicki (fwierzbicki) Date: 2009-03-30.18:08:04
So I don't think this can really be fixed.  Semantically I think you are
going around Jython by calling getClass() followed by getConstructor().
 I don't see how we could intercept this sort of behavior in a general
way.  Two workarounds:

you could call __init__ manually after calling the constructor, or you
can just call my_reticulator()
msg4396 (view) Author: Avi Flax (aviflax) Date: 2009-03-30.20:43:54
OK, I understand. I can work around it in my specific case fairly easily.
Date User Action Args
2009-03-30 20:43:54aviflaxsetmessages: + msg4396
2009-03-30 18:08:05fwierzbickisetstatus: open -> closed
resolution: wont fix
messages: + msg4393
2009-03-14 15:11:01fwierzbickisetpriority: high
2009-03-02 20:37:23fwierzbickisetassignee: fwierzbicki
2009-02-25 19:09:00fwierzbickisetmessages: + msg4164
2009-02-24 17:25:02aviflaxsetfiles: +
messages: + msg4163
2009-02-24 17:04:33aviflaxsetmessages: + msg4162
2009-02-24 16:52:14fwierzbickisetmessages: + msg4161
2009-02-24 16:51:28fwierzbickisetnosy: + fwierzbicki
2009-02-24 14:31:52aviflaxsetmessages: + msg4160
2009-02-23 12:12:49cgrovessetnosy: + cgroves
2009-02-22 04:37:53aviflaxcreate