Question

I’m using SWIG to export a c++ class to Java, but ran into a problem trying to force the proxy object to implement an interface.

I scoured the SWIG documentation and found you could use “%pragma(java) jniclassinterfaces=x” to have the JNI class implement a given interface, and use “%pragma(java) moduleinterfaces=x” to have the module implement any given interface, but no corresponding pragma for the actual proxy object.

I would prefer having SWIG generate the ‘implements X’ code, as trying to add that implementation later on is proving difficult. For example, if I try to subclass the SWIG proxy and then implement the interface, I run into issues because I’m also using generics:

interface IVector<VectorType> {
   VectorType add(VectorType other);
   ...
}

So something like this fails:

class MyVector extends MyProxyVector implements IVector<MyVector> {
    MyVector add(MyVector other) {
        return (MyVector) super.add(other);
    }
}

because it would require casting a parent to a child class.

The only other ways I can come up with getting around this problem is to either create a wrapper class or use a copy constructor. Both seem somewhat inefficient as their entire purpose to to implement the one interface.

Answer 1

This should be handled via the typemaps mechanism.
The following code:

%module test

%typemap(javainterfaces) Foo "SomeInterface"
%typemap(javabase) Foo "SomeBase"

struct Foo {
};

Sets the bases and interfaces for Foo, like so:

public class Foo extends SomeBase implements SomeInterface {

//...

in the generated Java proxy class.