jython-users

[Jython-users] Constructing an instance from a reference to a java method

[Updike, C. <Cla...@jh...>]

I'm trying to construct an instance of a java object given a reference
to a=20
method of a java class.  It is simple to do it for a jython class:

>>> from org.python.core import PyMethod, PyReflectedFunction
>>> def instanceFromMethod(method):
...    if type(method) =3D=3D PyMethod:
...       return method.im_class()
...    elif type(method) =3D=3D PyReflectedFunction:
...       print "Sorry..."
...    else:
...       raise Exception("Must be a function or a reflected function")
...
>>> class X:
...    def f(self):
...       pass
...
>>> instanceFromMethod(X.f)
<__main__.X instance at 6814979>
>>>

But I don't know how to do anything similar when it is a java-based
method:

>>> from java.lang import Object
>>> instanceFromMethod(Object.toString)
Sorry...

PyReflectedFunction doesn't seem to expose anything traceable back to
the original
class (or proxy thereof).  Does anyone have any ideas?

TIA,
Clark

Re: [Jython-users] Constructing an instance from a reference to a java method

[Oti <oh...@ya...>]

[ Updike, Clark ]

> I'm trying to construct an instance of a java object given a
> reference
> to a 
> method of a java class.  It is simple to do it for a jython class:
> 
> >>> from org.python.core import PyMethod, PyReflectedFunction
> >>> def instanceFromMethod(method):
> ...    if type(method) == PyMethod:
> ...       return method.im_class()
> ...    elif type(method) == PyReflectedFunction:
> ...       print "Sorry..."
> ...    else:
> ...       raise Exception("Must be a function or a reflected
> function")
> ...
> >>> class X:
> ...    def f(self):
> ...       pass
> ...
> >>> instanceFromMethod(X.f)
> <__main__.X instance at 6814979>
> >>>
> 
> But I don't know how to do anything similar when it is a java-based
> method:
> 
> >>> from java.lang import Object
> >>> instanceFromMethod(Object.toString)
> Sorry...
> 
> PyReflectedFunction doesn't seem to expose anything traceable back to
> the original
> class (or proxy thereof).  Does anyone have any ideas?
¨

Hi Clark,

only some thoughts, not a real solution.
Your code only works if you have no inheritance:

>>> class X:
...  def f(self):
...   pass
... 
>>> class Y(X):
...  def g(self):
...   pass
... 
>>> Y.f.im_class()
<__main__.X instance at 31248093>
>>> 

i suppose you expected an instance of Y here, didn't you ?

If not, you can do the same with PyReflectedFunctions. I have 3
examples below.

1. Method really defined on class itself:

>>> from java.lang import Throwable
>>> Throwable.printStackTrace.argslist[0].declaringClass
<jclass java.lang.Throwable at 27988400>
>>> 

2. Method defined by an interface:

>>> from java.lang import Short
>>> Short.byteValue.argslist[0].declaringClass
<jclass java.lang.Number at 32519825>
>>> 

3. Method defined by a superclass:

>>> from java.lang import Short
>>> Short.toString.argslist[0].declaringClass
<jclass java.lang.Object at 21573890>
>>> 


Best wishes,
Oti.