Re: [Jython-users] java->python problems

[dman <ds...@ri...>]

On Fri, Nov 02, 2001 at 03:50:12PM +0000, Finn Bock wrote:
| [dman]
| 
| >I'm trying to use Jython(c) to allow using Moshe Zadka's PMS framework
| >along with a Java/Swing GUI for a school project.  (The other group
| >members are writing the gui and they don't know python)  I've run into
| >a couple of problems, though, all related to java's type system.
| >
| >There are several modules in the PMS package.  I have taken the base
| >classes of the inheritance tree and made them inherit from
| >java.lang.Object and added the @sig lines.  A simplified example :
| >
| >----- PMS/AbstractFolder.py
| >class AbstractFolder( java.lang.Object ) : pass
| >
| >----- PMS/Folder.py
| >import AbstractFolder
| >class Folder( AbstractFolder.AbstractFolder ) : pass
| >
| >
| >I also have the following class as a factory for the GUI to create a
| >hardcoded folder for the prototype demo.
| >
| >----- DemoFolder1.py
| >class DemoFolder1( java.lang.Object ) :
| >    def make( self , name ) :
| >        """
| >        @sig public Object make( String name )
| >        """
| >
| >        server = PMS.MaildirServer.MaildirServer( "server_name" , "." )
| >        PMS.Configuration.Configuration().servers[ server ] = lambda x : x
| >        folder = PMS.Folder.Folder( server , name )
| >        folder.create()
| >
| >        print folder.__class__ # correctly prints "PMS.Folder.Folder"
| >        return folder
| >
| >
| >
| >I used jythonc to compile the stuff, and everything compiles fine.
| >The Java code that uses this looks like :
| >
| >
| >            Object folder = (new DemoFolder1()).make( "Demo1" );
| >            MailMessage.Message message = new MailMessage.Message();
| >
| >            // This line prints out
| >            // org.python.proxies.PMS.Folder$Folder$2
| >            System.out.println( folder.getClass() ) ;
| 
| The strange classname comes from the dynamic proxy generation.

Yeah, the name is nicely self-documenting :-).

| Verify if jythonc created a java class for the Folder class. You
| check that in the stdout from jythonc where there should be a line
| like:
| 
|  Folder extends java.lang.Object
| 
| If no such line is written, it is because jythonc failed to detect
| that Folder is a java subclass.

What I see is :

  AbstractFolder module
      AbstractFolder extends java.lang.Object
      NoSuchMessageError extends java.lang.Exception
  Folder module
      Folder extends AbstractFolder


So Folder is indirectly a java subclass.


I had originally tried

    class Folder( java.lang.Object , AbstractFolder.AbstractFolder ) : pass

but jythonc raises :

    TypeError: no multiple inheritance for Java classes: org.python.proxies.AbstractFolder$AbstractFolder$6 and java.lang.Object



Kevin Butler wrote to me off-list and mentioned trying the __tojava__
stuff.  This fails because I can't cast the above class to PyObject.
If I change the @sig to return PyObject, then the __tojava__ call
succeeds, but gives me a PySingleton instance, not a Folder instance.


Is there a solution other than creating a python class to provide
pseudo-reflection to java?  (it takes a java.lang.Object and a name
and invokes it in python ; this works but isn't natural from the java
side)

Thanks for your response!

-D