blocks|key|1425288|text|如果您已经查看了文档，并且仍然有问题，那么这些问题应该是您的初始问题的一部分。在本例中，示例中的JNI函数创建了许多数组。外部数组由一个用JNI函数NewObjectArray()创建的“Object”数组组成。从JNI的角度来看，这就是一个二维数组，一个包含许多其他内部数组的对象数组。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1425289|下面的for循环使用JNI函数NewIntArray()创建int[]类型的内部数组。如果您只想返回一个一维数组的int，那么可以使用NewIntArray()函数来创建返回值。如果您想创建一个一维数组的字符串数组，那么您可以使用NewObjectArray()函数，但要为该类使用不同的参数。|1425290|由于您希望返回一个整型数组，因此您的代码将如下所示：|1425291|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%2B%2B)+{
+++++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;
}|code-block|syntax|javascript|1425292|entityMap^0|22|G|0|F|D|1V|D|37|G|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|C]|$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|10|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|11|8|@]|D|@]|E|$M|N]]|$1|O|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|P|$]]

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 <code>NewObjectArray()</code>. 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 <code>NewIntArray()</code>. If you just wanted to return a single dimensional array of ints, then the <code>NewIntArray()</code> 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 <code>NewObjectArray()</code> 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:

<pre><code>JNIEXPORT jintArray JNICALL Java_ArrayTest_initIntArray(JNIEnv *env, jclass cls, int size)
{
 jintArray result;
 result = (*env)-&gt;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 &lt; 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)-&gt;SetIntArrayRegion(env, result, 0, size, fill);
 return result;
}
</code></pre>

blocks|key|1210418|text|如果有人想知道如何返回String[]数组：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1210419|java代码|1210420|private+native+String[]+data();|code-block|syntax|javascript|1210421|原生导出|1210422|JNIEXPORT+jobjectArray+JNICALL+Java_example_data()+(JNIEnv+*,+jobject);|1210423|本机代码|1210424|++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%2B%2B)+{++
++++++++env->SetObjectArrayElement(++
++++++++ret,i,env->NewStringUTF(message[i]));++
++++}++
++++return(ret);++
++}++|1210425|来自链接：http://www.coderanch.com/t/326467/java/java/Returning-String-array-program-Java|offset|length|1210426|entityMap|0|LINK|mutability|MUTABLE|url|http://www.coderanch.com/t/326467/java/java/Returning-String-array-program-Java^0|0|0|0|0|0|0|0|5|27|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|13|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|14|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|15|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|16|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|17|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|18|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|19|8|@]|9|@$S|1A|T|1B|1|1C]]|A|$]]|$1|U|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]]]

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

java code

<pre><code>private native String[] data();
</code></pre>

native export

<pre><code>JNIEXPORT jobjectArray JNICALL Java_example_data() (JNIEnv *, jobject);
</code></pre>

native code

<pre><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-&gt;NewObjectArray(5, 
 env-&gt;FindClass("java/lang/String"), 
 env-&gt;NewStringUTF("")); 

 for(i=0;i&lt;5;i++) { 
 env-&gt;SetObjectArrayElement( 
 ret,i,env-&gt;NewStringUTF(message[i])); 
 } 
 return(ret); 
 } 
</code></pre>

from link:
<a href="http://www.coderanch.com/t/326467/java/java/Returning-String-array-program-Java">http://www.coderanch.com/t/326467/java/java/Returning-String-array-program-Java</a>

blocks|key|1210472|text|简单的解决方案是将数组数据从C写到一个文件中，然后从Java访问该文件|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1210473|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Simple solution is that write the array data in a file from C,and then access the file from Java

blocks|key|1425454|text|根据提出的问题，这在第一个答案中已经解释过了，我们如何通过jobjectArray传递int[]。但这里是一个示例，我们如何返回一个包含数据列表的jobjectArray。例如，当有人需要返回2D格式的数据来绘制带有x和y点的线条时，这可能会很有帮助。以下示例展示了jobjectArray如何以以下格式返回数据：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1425455|JNI的Java输入：|1425456|X个浮点的数组Arraylist|offset|length|style|CODE|1425457|JNI输出到java：|1425458|X个浮点的jobjectArrayArraylist|1425459|++++extern+"C"+JNIEXPORT+jobjectArray+JNICALL
++++++++_MainActivity_callOpenCVFn(
++++++++++++++++JNIEnv+*env,+jobject+/*+this+*/,
++++++++++++++++jobjectArray+list)+{

+++++++++//Finding+arrayList+class+and+float+class(2+lists+,+one+x+and+another+is+y)
++++++++++++static+jclass+arrayListCls+=+static_cast<jclass>(env->NewGlobalRef(env->FindClass("java/util/ArrayList")));
++++++++++++jclass+floatCls+=+env->FindClass("java/lang/Float");
+++++++++//env+initialization+of+list+object+and+float
++++++++++++static+jmethodID+listConstructor+=+env->GetMethodID(arrayListCls,+"<init>",+"(I)V");
++++++++++++jmethodID+alGetId++=+env->GetMethodID(arrayListCls,+"get",+"(I)Ljava/lang/Object;");
++++++++++++jmethodID+alSizeId+=+env->GetMethodID(arrayListCls,+"size",+"()I");
++++++++++++static+jmethodID+addElementToList+=+env->GetMethodID(arrayListCls,+"add",+"(Ljava/lang/Object;)Z");

++++++++++++jmethodID+floatConstructor+=+env->GetMethodID(+floatCls,+"<init>",+"(F)V");
++++++++++++jmethodID+floatId+=+env->GetMethodID(floatCls,"floatValue",+"()F");


++++++++//null+check(if+null+then+return)
++++++++if+(arrayListCls+==+nullptr+%7C%7C+floatCls+==+nullptr)+{
++++++++++++return+0;
++++++++}

++++//+++++Get+the+value+of+each+Float+list+object+in+the+array
++++++++jsize+length+=+env->GetArrayLength(list);

++++++++//If+empty
++++++++if+(length+<+1)+{
++++++++++++env->DeleteLocalRef(arrayListCls);
++++++++++++env->DeleteLocalRef(floatCls);
++++++++++++return+0;
++++++++}

//+Creating+an+output+jObjectArray
++++jobjectArray+outJNIArray+=+env->NewObjectArray(length,+arrayListCls,+0);

++++++++//taking+list+of+X+and+Y+points+object+at+the+time+of+return
++++++++jobject++xPoint,yPoint,xReturnObject,yReturnObject;

++++++++++++//getting+the+xList,yList+object+from+the+array
++++++++++++jobject+xObjFloatList+=+env->GetObjectArrayElement(list,+0);
++++++++++++jobject+yObjFloatList+=+env->GetObjectArrayElement(list,+1);


+++++//+number+of+elements+present+in+the+array+object
++++++++int+xPointCounts+=+static_cast<int>(env->CallIntMethod(xObjFloatList,+alSizeId));

++++++++static+jfloat+xReturn,+yReturn;
++++++++++++++++jobject+xReturnArrayList+=+env->NewObject(arrayListCls,listConstructor,0);
++++++++jobject+yReturnArrayList+=+env->NewObject(arrayListCls,listConstructor,0);

++++for+(int+j+=+0;+j+<+xPointCounts;+j%2B%2B)+{
++++++++++++//Getting+the+x+points+from+the+x+object+list+in+the+array
++++++++++++xPoint+=+env->CallObjectMethod(xObjFloatList,+alGetId,+j);
++++++++++++//Getting+the+y+points+from+the+y+object+list+in+the+array
++++++++++++yPoint+=+env->CallObjectMethod(yObjFloatList,+alGetId,+j);

//Returning+jobjectArray(Here+I+am+returning+the+same+x+and+points+I+am+receiving+from+java+side,+just+to+show+how+to+make+the+returning+`jobjectArray`)++

++++++++++++//float+x+and+y+values
++++++++++++xReturn+=static_cast<jfloat+>(env->CallFloatMethod(xPoint,+floatId,j));
++++++++++++yReturn+=static_cast<jfloat+>(env->CallFloatMethod(yPoint,+floatId,j));


++++++++++++xReturnObject+=+env->NewObject(floatCls,floatConstructor,xReturn);
+++++++++++++yReturnObject+=+env->NewObject(floatCls,floatConstructor,yReturn);

++++++++++++env->CallBooleanMethod(xReturnArrayList,addElementToList,xReturnObject);


++++++++++++env->CallBooleanMethod(yReturnArrayList,addElementToList,yReturnObject);
++++++++++++env->SetObjectArrayElement(outJNIArray,0,xReturnArrayList);
++++++++++++env->SetObjectArrayElement(outJNIArray,1,yReturnArrayList);
++++++++__android_log_print(ANDROID_LOG_ERROR,+"List+of+X+and+Y+are+saved+in+the+array","%25d",+3);

++++}

++++return+outJNIArray;|code-block|syntax|javascript|1425460|entityMap^0|0|0|7|9|0|0|5|L|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|W|8|@$F|X|G|Y|H|I]]|9|@]|A|$]]|$1|J|3|K|5|6|7|Z|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|10|8|@$F|11|G|12|H|I]]|9|@]|A|$]]|$1|N|3|O|5|P|7|13|8|@]|9|@]|A|$Q|R]]|$1|S|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|T|$]]

Based on the asked question, this is already explained in the first answer that how can we pass int[] via jobjectArray. But Here is an example how we can return a jobjectArray which contains lists of data. This can be helpful for situations for example: when someone needs to return data in 2D format to draw some line with x and y points. The below example shows how a jobjectArray can return data in the form of following format:

Java input to the JNI: 
Array[<code>Arraylist</code> of x float points][<code>Arraylist</code> of y float points]

JNI output to java: 
<code>jobjectArray</code>[<code>Arraylist</code> of x float points] [<code>Arraylist</code> of y float points]

<pre><code> extern "C" JNIEXPORT jobjectArray JNICALL
 _MainActivity_callOpenCVFn(
 JNIEnv *env, jobject /* this */,
 jobjectArray list) {

 //Finding arrayList class and float class(2 lists , one x and another is y)
 static jclass arrayListCls = static_cast&lt;jclass&gt;(env-&gt;NewGlobalRef(env-&gt;FindClass("java/util/ArrayList")));
 jclass floatCls = env-&gt;FindClass("java/lang/Float");
 //env initialization of list object and float
 static jmethodID listConstructor = env-&gt;GetMethodID(arrayListCls, "&lt;init&gt;", "(I)V");
 jmethodID alGetId = env-&gt;GetMethodID(arrayListCls, "get", "(I)Ljava/lang/Object;");
 jmethodID alSizeId = env-&gt;GetMethodID(arrayListCls, "size", "()I");
 static jmethodID addElementToList = env-&gt;GetMethodID(arrayListCls, "add", "(Ljava/lang/Object;)Z");

 jmethodID floatConstructor = env-&gt;GetMethodID( floatCls, "&lt;init&gt;", "(F)V");
 jmethodID floatId = env-&gt;GetMethodID(floatCls,"floatValue", "()F");


 //null check(if null then return)
 if (arrayListCls == nullptr || floatCls == nullptr) {
 return 0;
 }

 // Get the value of each Float list object in the array
 jsize length = env-&gt;GetArrayLength(list);

 //If empty
 if (length &lt; 1) {
 env-&gt;DeleteLocalRef(arrayListCls);
 env-&gt;DeleteLocalRef(floatCls);
 return 0;
 }

// Creating an output jObjectArray
 jobjectArray outJNIArray = env-&gt;NewObjectArray(length, arrayListCls, 0);

 //taking list of X and Y points object at the time of return
 jobject xPoint,yPoint,xReturnObject,yReturnObject;

 //getting the xList,yList object from the array
 jobject xObjFloatList = env-&gt;GetObjectArrayElement(list, 0);
 jobject yObjFloatList = env-&gt;GetObjectArrayElement(list, 1);


 // number of elements present in the array object
 int xPointCounts = static_cast&lt;int&gt;(env-&gt;CallIntMethod(xObjFloatList, alSizeId));

 static jfloat xReturn, yReturn;
 jobject xReturnArrayList = env-&gt;NewObject(arrayListCls,listConstructor,0);
 jobject yReturnArrayList = env-&gt;NewObject(arrayListCls,listConstructor,0);

 for (int j = 0; j &lt; xPointCounts; j++) {
 //Getting the x points from the x object list in the array
 xPoint = env-&gt;CallObjectMethod(xObjFloatList, alGetId, j);
 //Getting the y points from the y object list in the array
 yPoint = env-&gt;CallObjectMethod(yObjFloatList, alGetId, j);

//Returning jobjectArray(Here I am returning the same x and points I am receiving from java side, just to show how to make the returning `jobjectArray`) 

 //float x and y values
 xReturn =static_cast&lt;jfloat &gt;(env-&gt;CallFloatMethod(xPoint, floatId,j));
 yReturn =static_cast&lt;jfloat &gt;(env-&gt;CallFloatMethod(yPoint, floatId,j));


 xReturnObject = env-&gt;NewObject(floatCls,floatConstructor,xReturn);
 yReturnObject = env-&gt;NewObject(floatCls,floatConstructor,yReturn);

 env-&gt;CallBooleanMethod(xReturnArrayList,addElementToList,xReturnObject);


 env-&gt;CallBooleanMethod(yReturnArrayList,addElementToList,yReturnObject);
 env-&gt;SetObjectArrayElement(outJNIArray,0,xReturnArrayList);
 env-&gt;SetObjectArrayElement(outJNIArray,1,yReturnArrayList);
 __android_log_print(ANDROID_LOG_ERROR, "List of X and Y are saved in the array","%d", 3);

 }

 return outJNIArray;
</code></pre>

I am attempting to use the android NDK.

Is there a way to return an array (in my case an <code>int[]</code>) created in JNI to Java? If so, please provide a quick example of the JNI function that would do this.

-Thanks

How to return an array from JNI to Java?

Java

我正在尝试使用android NDK。有没有办法将在JNI中创建的数组(在我的例子中是一个int[])返回给Java？如果是这样，请提供一个执行此操作的JNI函数的快速示例。-Thanks

问如何将数组从JNI返回到Java？
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