CODEWITHSUNDEEP
javajava-native-interface
keerthana
keerthana

Reputation: 85

how to access elements from jobjectarray in jni

I have a java method which is called from my native method and returns an object array to the native code.

The elements of the object array are set as,

  Object[] arr = new Object[10];
    arr[0] = new Integer(12);
    arr[1] = new Float(25.5f);

I receive this array in my native code as follows,

  jobjectArray a = (jobjectArray)(*env)->CallStaticObjectMethodA(env, <class_id>, <method_id>, <parameter_list>);

I have the datatype of each of the element stored in object array. So based on the datatype how can I access the corresponding integer and float value in my native method.

I tried the following,

 jobject obj = (*env)->GetObjectArrayElement(env, a, 0);
    int num = (jint)obj;

But the value, that is set to num is incorrect.

Upvotes: 2

Views: 4045

Answers (1)

Jorn Vernee
Jorn Vernee

Reputation: 33865

Java does auto-unboxing when you convert an Integer to an int. But that mechanic doesn't exist in C. What you're doing is taking the memory address of the element and interpreting it as an int.

If you want to get an int from an Integer on the C side, you will have to call intValue:

jobject objInteger = (*env)->GetObjectArrayElement(env, a, 0);    

jclass cInteger = (*env)->FindClass(env, "java/lang/Integer");
jmethodID intValue = (*env)->GetMethodID(env, cInteger, "intValue", "()I");
int i = (*env)->CallIntMethod(env, objInteger, intValue);

Upvotes: 2

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