android ndk - Subclass a C++ abstract class in Java using JNI -

i have c++ library have use in existing android implementation. i'm using android ndk , using c++ classes via jni.

however, not able find how subclass c++ abstract class in java using jni.

problems face: aim provide java implementation virtual methods in c++ subclassing abstract c++ class. have loaded native library , i'm trying declare native methods. c++ methods have keyword 'virtual'. when declare native functions in java after loading c++ library, 'virtual' not recognized. wrong here?

any appreciated. i'm newbie jni. in advance.

let's consider have c++ class:

class ivehicle { public:    virtual void run() {}; // not-pure virtual here simplicity of wrapper, pure (see end of post)    virtual int  getsize() const; // want reuse in java }; 

we want create class bot in java extends class ivehicle in sense calls super invoke c++ code ivehicle::getsize() and, c++ point of view, can use instances of bot ivehicle* variables. that's tough since c++ provides no built-in functionality reflection.

here 1 possible solution.

to use c++ class in java need generate java wrapper, i.e:

class ivehicle {    public void run() { native_run(); }    public int  getsize() { return native_getsize(); }     private native void native_run();    private native int  native_getsize();     // typecasted pointer in c++    private int nativeobjectholder;     // create c++ object    native static private int createnativeobject(); } 

the usage in java simple:

class bot extends ivehicle {    public int getsize()    {       if ( condition ) return 0;        // call c++ code       return super.getsize();    } } 

however, there c++ part code:

static jfieldid gnativeobjectholderfieldid;  jniexport void jnicall java_com_test_ivehicle_run( jnienv* env, jobject thiz ) {    int value = env->getintfield(thiz, gnativeobjectholderfieldid);    ivehicle* obj = (ivehicle*)obj;     // todo: add checks here, null , dynamic casting     obj->run(); } 

the similar code getsize().

then creating instance of java's bot have call createnativeobject() , assign returned value nativeobjectholder field.

jniexport int jnicall java_com_test_ivehicle_createnativeobject( jnienv* env, jobject thiz ) {    ivehicle* obj = new ivehicle;    return (int)obj;     } 

so, scheme. make work need add destruction code , parse c++ classes generate glue code.

added:

in case ivehicle abstract have generate non-abstract wrapper able instantiate:

class ivehicle {    virtual void run() = 0; }  class ivehicle_wrapper: public ivehicle {    virtual void run() { error("abstract method called"); }; } 

and instantiate ivehicle_wrapper in createnativeobject(). vuala! have inherited abstract c++ class in java.