JNI and multidimentional arrays

Question

Hi
I'm dealing with C functions that used multidimentional arrays like tab[10][200]
I don't know how to get them from my JAVA code using
GetObjectArrayElement(JNIEnv *env, jobjectArray array, jsize index)
or
GetIntArrayRegion(JNIEnv *env, jobjectArray array, start, lenght ...)
I seems that it is working only with one dimentional arrays ?
Am I right ?
Does anybody knows how to do with multidimentional ?
Thank you !

Answer 1

I'm dealing with C functions that used
multidimentional arrays like tab[10][200]Multidimensional arrays are awkward to deal with.
A multidimensional array in Java is an array of arrays. In effect they are like 'ragged' arrays in C, not like 'rectangular' ones. There is no way to get a 2-dimensional primitive array that contains the contents of a 2-dimensional Java array. In fact there is no way to directly access elements of a 2-dimensional Java array at all.
In order to navigate around in a multidimensional Java array from native code, let's say you have int[10][15] and you want to get the element at [5][8]. You must use GetObjectArrayElement(env, arrayObject, 5) and this will give you the 15-element int array. Now you can use GetIntArrayRegion() or whatever to retrieve those ints. If it had been an array of objects instead of primitives then you would have to use GetObjectArrayElement on the "inner" array as well, of course.
So your only real choice is to use a for loop. The outer for loop gets the array of primitives and then you can use GetIntArrayRegion and memcpy() etc. to copy that array into the appropriate row of your C array.
If you had a 3-dimensional array you'd have to repeat this process because the first time through it would return a 2-dimensional array.