Re: [Jython-users] subclassing problems

[<bc...@wo...>]

[Erlend V Bøe]

>I'm having some problems with the following situation:
>
>I have a Java class that I extend in Jython.
>When I try to use this Jython class from Java, I get an exception similar to 
>the following: "TypeError: instance already instantiated for 
>problem.JavaClass"
>
>What am I doing wrong?

You need a python constructor in your PyClass, and when using jythonc,
the constructor must *not* call the superclass ctor. Something along the
lines of:

import problem

_jythonc = 1

class PyClass(problem.JavaClass):
    def __init__(self, s=None):
        if not _jythonc:
            problem.JavaClass.__init__(self, s)

    def myMethod(self):
        "@sig void myMethod()"
        print "python method myMethod called"

if __name__ == "__main__":
    _jythonc = 0
    x = PyClass("hi from python")
    x.myMethod()




In the generated PyClass.java, we have code like:

public class PyClass extends problem.JavaClass 
    implements org.python.core.PyProxy
{
    public PyClass(java.lang.String arg0) {
        super(arg0);
        Py.initProxy(this, ... new Object[] {arg0}, ...);
    }
}

i.e, the JavaClass ctor is called before any python code gets to
execute. Without the __init__() method, jython will automaticly call the
JavaClass ctor (again) and the exception "instance already instantiated"
is thrown.

regards,
finn