[JNI]Accessing Arrays

分兩種情況:

(1)基本元素數組

(2)對象數組

 

(1)基本元素數組

(i)拷貝基本元素數組:

JNIEXPORT jint JNICALL Java_IntArray_sumArray(JNIEnv *env, jobject obj, jintArray arr)
{
    jint buf[10];
    jint i, sum = 0;
    (*env)->GetIntArrayRegion(env, arr, 0, 10, buf);            //arr-->buf
    for (i = 0; i < 10; i++) {
        sum += buf[i];
    }
    return sum;
}

GetIntArrayRegion的第三個參數0表示arr的起始索引,第四個參數10表示要拷貝的元素個數.

(ii)獲取基本元素數組的指針:

GetIntArrayElements/ReleaseIntArrayElements

JNIEXPORT jint JNICALL Java_IntArray_sumArray(JNIEnv *env, jobject obj, jintArray arr)
{
    jint *carr;
    jint i, sum = 0;
    carr = (*env)->GetIntArrayElements(env, arr, NULL);
    if (carr == NULL) {
        return 0; /* exception occurred */
    }
    for (i=0; i<10; i++) {
        sum += carr[i];
    }
    (*env)->ReleaseIntArrayElements(env, arr, carr, 0);
    return sum;
}

 

(2)對象數組

獲取/設置對象數組:

GetObjectArrayElement/SetObjectArrayElement

JNIEXPORT jobjectArray JNICALL Java_ObjectArrayTest_initInt2DArray(JNIEnv *env,jclass cls,int size)
{
    jobjectArray result;
    int i;
    jclass intArrCls = (*env)->FindClass(env, "[I");        //int[]!!!
    if (intArrCls == NULL) {
        return NULL;         /* exception thrown */
    }
    result = (*env)->NewObjectArray(env, size, intArrCls,NULL);
    if (result == NULL) {
        return NULL;         /* out of memory error thrown */
    }
    for (i = 0; i < size; i++) {
        jint tmp[256];       /* make sure it is large enough! */
        int j;
        jintArray iarr = (*env)->NewIntArray(env, size);
        if (iarr == NULL) {
            return NULL;     /* out of memory error thrown */
        }
        for (j = 0; j < size; j++) {
            tmp[j] = i + j;
        }
        (*env)->SetIntArrayRegion(env, iarr, 0, size, tmp);
        (*env)->SetObjectArrayElement(env, result, i, iarr);
        (*env)->DeleteLocalRef(env, iarr);
}
    return result;
}

如上代碼創建一個二維數組，如果size設置爲3，二維數組如下:

0 1 2

1 2 3

2 3 4

 

參考資料:

[1]The Java™ Native Interface Programmer’s Guide and Specification.pdf