how to interact with java object in cpp

how to interact with java object in cpp
http://www.blogjava.net/vagasnail/articles/301124.html
also frameworks\base\core\jni\android_app_NativeActivity.cpp
static const char* const kNativeActivityPathName = "android/app/NativeActivity";

#define FIND_CLASS(var, className) \
        var = env->FindClass(className); \
        LOG_FATAL_IF(! var, "Unable to find class " className); \
        var = jclass(env->NewGlobalRef(var));

#define GET_METHOD_ID(var, clazz, methodName, fieldDescriptor) \
        var = env->GetMethodID(clazz, methodName, fieldDescriptor); \
        LOG_FATAL_IF(! var, "Unable to find method" methodName);
       
int register_android_app_NativeActivity(JNIEnv* env)
{
    //LOGD("register_android_app_NativeActivity");

    FIND_CLASS(gNativeActivityClassInfo.clazz, kNativeActivityPathName);
   
    GET_METHOD_ID(gNativeActivityClassInfo.dispatchUnhandledKeyEvent,
            gNativeActivityClassInfo.clazz,
            "dispatchUnhandledKeyEvent", "(Landroid/view/KeyEvent;)V");
    GET_METHOD_ID(gNativeActivityClassInfo.preDispatchKeyEvent,
            gNativeActivityClassInfo.clazz,
            "preDispatchKeyEvent", "(Landroid/view/KeyEvent;I)V");

    GET_METHOD_ID(gNativeActivityClassInfo.finish,
            gNativeActivityClassInfo.clazz,
            "finish", "()V");
    GET_METHOD_ID(gNativeActivityClassInfo.setWindowFlags,
            gNativeActivityClassInfo.clazz,
            "setWindowFlags", "(II)V");
    GET_METHOD_ID(gNativeActivityClassInfo.setWindowFormat,
            gNativeActivityClassInfo.clazz,
            "setWindowFormat", "(I)V");
    GET_METHOD_ID(gNativeActivityClassInfo.showIme,
            gNativeActivityClassInfo.clazz,
            "showIme", "(I)V");
    GET_METHOD_ID(gNativeActivityClassInfo.hideIme,
            gNativeActivityClassInfo.clazz,
            "hideIme", "(I)V");

    return AndroidRuntime::registerNativeMethods(
        env, kNativeActivityPathName,
        g_methods, NELEM(g_methods));
}