JNI如何将Java对象数组传递给相同对象类型的C ++数组

Question

I have an array of type Foo in my java code which I want to pass to c++. In the c++ code, I also have the same class named Foo . all I want is to transfer this array via JNI.

I have a call like this:

#include "headers/Foo.h"

extern "C"
    JNIEXPORT void
    JNICALL Java_main_Main_Interface(JNIEnv *env, jobject obj, jobjectArray foo){
        jint size = env->GetArrayLength(foo);
        Foo cfoo[size];
        for(int i = 0; i < size; i++){
            cfoo[i] = env->GetObjectArrayElement(foo, i);
        }
}

This is, however, giving me an error: Type 'Foo' and 'jobject' are not compatible

I understand this error but what should I do to eliminate it? should I cast the jobject to type Foo? will c++ understand the object that way? or am I missing some JNI calls?

Answer 1

I understand this error

No, I don't think you do.

The type named Foo in your C++ code is not related to your Java Foo . Having the same name does not produce this effect across the JNI boundary, regardless of the similarity or dissimilarity of the types' members. Thus, yours is not merely a syntactic issue, but rather a much more fundamental one.

but what should I do to eliminate it? should I cast the jobject to type Foo? will c++ understand the object that way? or am I missing some JNI calls?

That depends to some extent on the nature of the C++ Foo , and of how you want it to work.

One option would be to initialize each C++ Foo by copying the needed members of the corresponding Java Foo . That would involve JNI calls to read object fields or to invoke methods on the jobject , or both. Details depend on the two Foo s.

Alternatively, you could rewrite or subclass the C++ Foo to be a wrapper for a jobject representing the corresponding Java Foo , with C++ methods delegating to the jobject via JNI calls. That's pretty much the same thing as the other, really, but with finer granularity and, accordingly, different performance tradeoffs.