[Py4j-users] How do I cast Java objects between types on the Python side?

[Chris A. <chr...@gm...>]

Hi all.

I'm trying to implement this code in Python: (from
http://www.hypergraphdb.org/learn?page=IntroStoreData&project=hypergraphdbat
the bottom, modified so I don't have to implement a class on the Java
side)

bookHandle = graph.add("asdf")
priceHandle = graph.add(9.95)
link = new gateway.jvm.org.hypergraphdb.HGValueLink("price", bookHandle,
priceHandle)


The problem is that in the Python code, the call to graph.add() from
the Python side is yielding an object of type
WeakHandle that implements HGLiveHandle, and HGValueLink only accepts
HGHandle[] in its arguments. The end result is

that the java side throws an exception saying that a HGValueLink
constructor doesn't exist that takes
[String, handle.WeakHandle, handle.WeakHandle].

(Relevant javadocs at
http://www.kobrix.com/javadocs/hgcore/org/hypergraphdb/HGValueLink.html,
http://www.kobrix.com/javadocs/hgcore/org/hypergraphdb/HyperGraph.html,
http://www.kobrix.com/javadocs/hgcore/org/hypergraphdb/handle/HGLiveHandle.html
)

In the linked example the two handles are declared as HGHandle when
they're instantiated, so there's no problem when the method call does
typechecking.

It seems to me, then, that the easiest way to rectify this is to use
some facility of the Gateway to re-cast the object returned from
graph.add() as HGHandle, and then just pass that the the HGValueLink
constructor as it wants.

Can I do that from the gateway as it exists, or do I have to add a
method to my server code to cast it? Am I missing an easier and more
obvious solution in my Java inexperience?

Thanks,
Chris