JNI学习-- C调用java方法

 步骤：

1.通过类名获取jclass对象

2.通过jclass对象拿到jmethodId

3.通过JNIEnv*对象调用jmethodId对象

JNIEXPORT void JNICALL Java_com_vincent_jni_callback_JNI_1dataprovider_sayHello
  (JNIEnv *env, jobject obj, jstring str){

    //1.通过反射拿到 class
    //     jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);

    //env ：jni指针对象  ，"com/vincent/jni/callback/JNI_dataprovider" 类全名
    jclass clazz =(*env)->FindClass(env,"com/vincent/jni/callback/JNI_dataprovider");

    if(clazz==0){

        LOGI("find class error");

return;
    }
    //2.拿到相应方法的methodID
    //    jmethodID GetMethodID(jclass clazz, const char* name, const char* sig)

        LOGI("find class success");

        // env,clazz（java对象）,方法名，方法签名（javap获取）
jmethodID methoID = (*env)->GetMethodID(env,clazz,"javaSayHello","(Ljava/lang/String;)V");
//3.调用方法
//    void        (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);

(*env)->CallVoidMethod(env,obj,methoID,str);

}

JNIEXPORT jint JNICALL Java_com_vincent_jni_callback_JNI_1dataprovider_subXAndY(
    JNIEnv * env, jobject obj, jint x, jint y) {

//1.通过反射拿到 class
//    jclass      (*FindClass)(JNIEnv*, const char*);

jclass clazz2 = (*env)->FindClass(env,
        "com/vincent/jni/callback/JNI_dataprovider");

if (clazz2 == 0) {

    LOGI("find class error");

    return 0;
}
//2.拿到相应方法的methodID
//       jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);

LOGI("find class success");

jmethodID methoID2 = (*env)->GetMethodID(env, clazz2, "javaSubXAndY", "(II)I");
//3.调用方法
//   jint        (*CallIntMethod)(JNIEnv*, jobject, jmethodID, ...);;

return (*env)->CallIntMethod(env, obj, methoID2, x, y);

}