class _jstring : public _jobject {};
class _jarray : public _jobject {};

И что это тебе даёт?
Вот для примера, как будет выглядеть вызов функции через JNI (то, что у меня просто генерировалось):

bool Collection::add( const Object& p0 )
{
	JNIEnv* env = Jvm::get().getEnv();
	static jmethodID this_method = 0;
	if ( !this_method )
	{
		this_method = env->GetMethodID( this_class_.getClass(CLASS_NAME), "add", "(Ljava/lang/Object;)Z" );
		if ( !this_method )
			check_throw( env, "Method add in class Collection not found" );
	}
	bool result = env->CallBooleanMethod( jref_, this_method, p0.getJObjectValue() ) != 0;
	check( env, "Method add in class Collection failed" );
	return result;
}

void JVM::create()
{
	library_handle_ = LoadLibrary( jvm_path_.c_str() );
	if ( !library_handle_ )
		throw ccm_error( std::string( "Can't load JVM from " + jvm_path_ ).c_str() );
	createJavaVMPtr = (CreateJavaVM_t) GetProcAddress( library_handle_, "JNI_CreateJavaVM" );
	if ( ! createJavaVMPtr )
		throw ccm_error( std::string("Can't find JNI_CreateJavaVM in " + jvm_path_).c_str() );
	env_ = 0;
	JavaVMInitArgs vm_args;
	JavaVMOption options[1];
	std::string cl_path = "-Djava.class.path=" + class_path_;
	options[0].optionString = const_cast<char*>( cl_path.c_str() );
	vm_args.version = 0x00010002;
	vm_args.options = options;
	vm_args.nOptions = 1;
	vm_args.ignoreUnrecognized = JNI_TRUE;
	if ( createJavaVMPtr( &jvm_, reinterpret_cast<void**>(&env_), &vm_args ) < 0 )
		throw ccm_error( "Cannot create JVM" );
	if ( !env_ || !jvm_ )
		throw ccm_error( "Cannot initialize JVM" );
}