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| JNIExport jint JNICALL Java_IntArray_sumArray(JNIEnv *env, jobject obj,
jintArray arr){
jsize len = *env->GetArrayLength(env,arr);
jint *body = *env->GetIntArrayElements(env,arr,0);
for (jint i = 0; i < len; ++i){
sum += body[i];
}
*env->ReleastIntArrayElements(env, arr, body, 0);
} |
| JNI Function | Description |
Get<Type>ArrayRegion
Set<Type>ArrayRegion | Copies the contents of primitive arrays to or from a pre-allocated C buffer. |
Get<Type>ArrayElements
Release<Type>ArrayElements | Obtains a pointer to the contents of a primitive array. May return a copy of the array. |
| GetArrayLength | Returns the number of elements in the array. |
| New<Type>Array | Creates an array with the given length. |
GetPrimitiveArrayCritical
ReleasePrimitiveArrayCritical | Obtains or releases a pointer to the contents of a primitive array. These functions allow virtual machines to disable garbage collection while the native code accesses the contents of primitive arrays. |
JNI Array Example program
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| class SortArray {
private native int[] sort(int[] arr); //native method
static //static initializer code
{
System.loadLibrary("SortArray");
}
public static void main(String[] args)
{
int iArr[] = {4,5,2,7,1,9}; // Input array
int oArr[]; //Output array
SortArray arr = new SortArray();
System.out.println("Unsorted array: ");
for(int i = 0; i < iArr.length; i++){
System.out.println(iArr[i] + " ");
}
oArr = arr.sort(iArr);
System.out.println("Sorted array: ");
for(int i = 0; i < oArr.length; i++){
System.out.println(oArr[i] + " ");
}
}
} |
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| /* DO NOT EDIT THIS FILE - it is machine generated */
#include
/* Header for class SortArray */
#ifndef _Included_SortArray
#define _Included_SortArray
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: SortArray
* Method: sort
* Signature: ([I)[I
*/
JNIEXPORT jintArray JNICALL Java_SortArray_sort
(JNIEnv *, jobject, jintArray);
#ifdef __cplusplus
}
#endif
#endif |
The C++ implementation file SortArray.cpp will be:
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| #include "SortArray.h"
#include "jni.h"
/*
* Class: SortArray
* Method: sort
* Signature: ([I)[I
*/
JNIEXPORT jintArray JNICALL Java_SortArray_sort
(JNIEnv *env, jobject obj, jintArray arr){
jsize arrLength = env->GetArrayLength(arr);
jintArray arrSorted = env->NewIntArray(arrLength);
jint *arrOut = NULL;
arrOut = env->GetIntArrayElements(arr, 0);
for(jsize x = 0; x < arrLength; x++){
for(jsize y = 0; y < arrLength - 1; y++){
if(arrOut[y] > arrOut[y+1]){
jsize temp = arrOut[y+1];
arrOut[y+1] = arrOut[y];
arrOut[y] = temp;
}
}
}
env->SetIntArrayRegion(arrSorted, 0, arrLength, arrOut);
env->ReleaseIntArrayElements(arr, arrOut, 0);
return arrSorted;
} |
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