Array of Object Array (2d arrays) JNI

Question

I'm struggling with creating a 2d array of my custom object type ShareStruct:

jobjectArray ret ;
jobjectArray ins ;
jobjectArray outs;

jclass myClass = (*env)->FindClass(env,"org/apache/s4/core/ShareStruct");
if (myClass==NULL) fprintf(stderr, "Class ShareStruct not found");

jclass myClassArray = (*env)->FindClass(env, "[Lorg/apache/s4/core/ShareStruct");
if (myClassArray==NULL) fprintf(stderr, "Class ShareStruct[] not found");

ins = (*env)->NewObjectArray(env, in, myClass, NULL);
outs = (*env)->NewObjectArray(env, out, myClass, NULL);
ret = (*env)->NewObjectArray(env, 2, myClassArray, NULL);

The first class loading works (the ShareStruct is fine), but the other one (trying to load a ShareStruct[] class) doesn't. I've tried both with and without the L but no luck. Any ideas? I'm new with JNI.

Thanks!

have updated my answer, did it help? – bobby Aug 03 '12 at 09:47 — bobby, Aug 03 '12 at 09:47

score 5 · Accepted Answer · edited May 23 '17 at 12:16

5

This jclass myClassArray = (*env)->FindClass(env, "[Lorg/apache/s4/core/ShareStruct"); is wrong. To create the array do something like

 ret = (*env)->NewObjectArray(env,sizeOfArray,myClass,NULL);  
(*env)->SetObjectArrayElement( env, ret,index, sharedStructObj);

Here sharedStructObj will have to be created by newObject.
Section 3.3.5 of JNI programmer's guide has a good related example

This is also nice Create, populate and return 2D String array from native code (JNI/NDK)

EDIT based on comment

in = (*env)->NewObjectArray(env,sizeOfArray,myClass,NULL);
out = (*env)->NewObjectArray(env,sizeOfArray,myClass,NULL);
ret= (*env)->NewObjectArray(env,sizeOfArray,myClass,NULL);
(*env)->SetObjectArrayElement( env, ret,0, in); 
(*env)->SetObjectArrayElement( env, ret,1, out);

edited May 23 '17 at 12:16

Community

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answered Jul 27 '12 at 07:07

bobby

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But I want to create an array of ShareStruct[], so the java equivalent would be ShareStruct[][]. I don't see how this code does that :( Effectively, I want to do : ShareStruct[] in; ShareStruct[] out; ShareStruct[][] ret ; ret[0] = in ; ret[1] = out ; – user1018513 Jul 27 '12 at 10:56
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This is a good answer, but "Section 3.3.5 of JNI programmer's guide has a good related example", link is dead as of 2016-05-18. – CloudyTrees May 18 '16 at 21:34
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link to JNI Programmer's guide (Section 3.3.5 has the example mentioned by @CloudyTrees): http://barbie.uta.edu/~jli/Resources/Resource%20Provisoning&Performance%20Evaluation/85.pdf – I L Aug 15 '19 at 16:08

score 1 · Answer 2 · answered Aug 21 '13 at 14:28

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You have to use an object array for the outer array:

jclass myClassArray = (*env)->FindClass(env, "[Ljava/lang/Object;");

in a similar case with a 2D String array worked for me. Please also recognize the trailing semicolon in the string.

answered Aug 21 '13 at 14:28

miro

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score 1 · Answer 3 · edited Mar 21 '18 at 17:17

1

I do not know if this question is still relevant, but I think you simply forgot the semicolon at the end of your array class specification:

jclass myClassArray = (*env)->FindClass(env, "[Lorg/apache/s4/core/ShareStruct;");

edited Mar 21 '18 at 17:17

Albert Lazaro de Lara

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answered Mar 21 '18 at 15:17

Eric

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Array of Object Array (2d arrays) JNI

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