Re: JNI return jobjectArray

Lew <>
Sun, 30 Sep 2012 21:14:12 -0700 (PDT)
markspace wrote:

Philipp Kraus wrote:

You are not right,

I'm not right? And yet...

heap, but how can I push back the reference

...the problem still exists.

In detail I have got a native (C) methode, that shows in Java:

Truthfully, there is not enough detail here for me to guess what the
problem really is. You're showing method signatures but no code.

What he did show was a parameter passed from Java as a C++ reference.

Does that even work? Java doesn't have anything like C++ references to pass.

That being the advice the OP blew off immediately.

If I call in Java this code:

Double[] x = null;

'x' is equivalent to a pointer, not a reference.

Pardon my ignorance, but what if you used a pointer in the native code
instead of a reference?

Double[][] y = null;

myclass.mymethod(x, y);

Java convention calls for type names to start with an upper-case letter
and use camel case.

No this will not work. I guess I was not specific enough: *you* have to
create a reference to the array reference you want to modify. That

Well, in C++ terms, wouldn't that be a pointer?

doesn't happen if the parameter is null.

   Double x = { {1.2} };

Now you have something to modify. Java does NOT have pass by reference,
you must do it yourself. I did a Google search, and I didn't see the
solution, so here I guess is some lost knowledge. This is Java, you'll
have to translate to C++ on your own:

class Example {

   // manual "pass by reference"

   void makeNewDoubleArray( Double [][] x ) {
     x[0] = new Double[] { 1.1, 2.2, 3.3 };

   public static void main( String... args ) {
     Double[] y = {0.0};
     Double[][] wrapper = { {} };
     wrapper[0] = y; // pack
     makeNewDoubleArray( wrapper );
     y = wrapper[0] // unpack
     System.out.println( java.util.Arrays.deepToString( y ) );

Code is untested; watch out for silly errors.

I am ignorant of the ways of JNI, so my question might be extraordinarily
off base.


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