Java and Jython integration issue with method names

Question

I'm following the instruction in Jython and Java Integration.

The idea is simple; make Java interface, and matching python class. The issue is that with a interface function setX(), and setY(), I always get an error when I execute the file. I had to modify the name to such as setXvalue() or setYvalue() to avoid the error.

Exception in thread "main" java.lang.NoClassDefFoundError: Could not initialize class    
org.python.core.PyTraceback
at org.python.core.PyException.tracebackHere(PyException.java:158)

at org.python.core.PyObject._jcall(PyObject.java:3587)
at org.python.proxies.Arith$Arith$0.setX(Unknown Source) <-- ERROR???
at Main.main(Main.java:14)

package org.jython.book.interfaces;

This is a Java interface.

public interface ArithType {

    public void setX(int x); // <-- Error
    public void setYa(int x);
    public int getXa();
    public int getYa();
    public int add();
}

This is partial python class.

class Arith(ArithType):
    ''' Class to hold building objects '''

    def setX(self, x): # << Error
        self.x = x

You can find the source to test at this site - https://dl.dropboxusercontent.com/u/10773282/2013/Archive.zip

What's wrong with this? Why the method name setX() or setY() causes an error in execution?

volferine · Accepted Answer · 2013-10-08 09:21:54Z

1

Be careful with accessing attributes of an object in Jython; Jython uses implicit getters/setters, so reading from self.x invokes self.getX() and so on. Changing all occurrences of self.x to self._x (ditto for y) in your jython code made it work (for me). It is actually a convention in Python to name non-public members as _....

answered Oct 8, 2013 at 9:21

volferine

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