How to return an array from JNI to Java?

Question

If you've examined the documentation and still have questions that should be part of your initial question. In this case, the JNI function in the example creates a number of arrays. The outer array is comprised of an 'Object' array creating with the JNI function NewObjectArray(). From the perspective of JNI, that's all a two dimensional array is, an object array containing a number of other inner arrays.

The following for loop creates the inner arrays which are of type int[] using the JNI function NewIntArray(). If you just wanted to return a single dimensional array of ints, then the NewIntArray() function is what you'd use to create the return value. If you wanted to create a single dimensional array of Strings then you'd use the NewObjectArray() function but with a different parameter for the class.

Since you want to return an int array, then your code is going to look something like this:

JNIEXPORT jintArray JNICALL Java_ArrayTest_initIntArray(JNIEnv *env, jclass cls, int size)
{
 jintArray result;
 result = (*env)->NewIntArray(env, size);
 if (result == NULL) {
     return NULL; /* out of memory error thrown */
 }
 int i;
 // fill a temp structure to use to populate the java int array
 jint fill[size];
 for (i = 0; i < size; i++) {
     fill[i] = 0; // put whatever logic you want to populate the values here.
 }
 // move from the temp structure to the java structure
 (*env)->SetIntArrayRegion(env, result, 0, size, fill);
 return result;
}

if someone would like to know how to return String[] array:

java code

private native String[] data();

native export

JNIEXPORT jobjectArray JNICALL Java_example_data() (JNIEnv *, jobject);

native code

  JNIEXPORT jobjectArray JNICALL   
               Java_example_data  
  (JNIEnv *env, jobject jobj){  

    jobjectArray ret;  
    int i;  

    char *message[5]= {"first",   
                       "second",   
                       "third",   
                       "fourth",   
                       "fifth"};  

    ret= (jobjectArray)env->NewObjectArray(5,  
         env->FindClass("java/lang/String"),  
         env->NewStringUTF(""));  

    for(i=0;i<5;i++) {  
        env->SetObjectArrayElement(  
        ret,i,env->NewStringUTF(message[i]));  
    }  
    return(ret);  
  }  

from link: http://www.coderanch.com/t/326467/java/java/Returning-String-array-program-Java