Issue1561

# file: UnimplementedMethodOnInterfaceBug.py

def test_unimplemented_interface():
    from java.lang import Runnable

    class RunMethodNotImplemented(Runnable):
        pass

    test_failure = "failure: should have thrown an un-implemented method exception"

    try:
        run = RunMethodNotImplemented()
        result = run.run()
        # result will be 0, should throw exception
        raise Exception(test_failure)
    except Exception, e:
        if e.message == test_failure:
            raise e
        else:
            pass

if __name__ == "__main__":
    test_unimplemented_interface()

this is related to #1432 and #1437

Deferred to 2.6 - this needs the custom proxy support

Time to revisit for 2.7

Let's look at the output of the proxy maker for a class implementing Callable:

    public Object call() throws Exception {
        final PyObject findPython = ProxyMaker.findPython((PyProxy)this, "call");
        if (findPython != null) {
            final PyObject pyObject = findPython;
            try {
                return Py.tojava(pyObject._jcallexc((Object[])Py.EmptyObjects), (Class)Class.forName("java.lang.Object"));
            }
            catch (Exception ex) {
                throw ex;
            }
            catch (Throwable t) {
                pyObject._jthrow(t);
                return null;
            }
        }
        return null;
    }

(See the decompilation example in https://github.com/jimbaker/clamped#writing-a-python-class-to-use-clamp)

That last `return null` is where the problem occurs. Although this is a somewhat big change for existing code, it's an appropriate one and is likely hiding bugs. In particular:

exception NotImplementedError
This exception is derived from RuntimeError. In user defined base classes, abstract methods should raise this exception when they require derived classes to override the method.

This Python-specific exception is likely a better exception than UnsupportedOperationException; in either case, it's derived from RuntimeException

This is a breaking change for users, so if it's going in, it has to be in for beta 4 of 2.7.0. Or wait to Jython 3.

Related/near duplicate of #1785

Fix for beta 4

Must fix before beta 4

Fixed as of https://hg.python.org/jython/rev/3235ec531b41