Invoking a method that modifies an input parameter #83

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1. dfdx commented on Aug 18, 2018

   

   dfdx

   on Aug 18, 2018

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   JavaCall automatically converts Julia arrays to Java arrays and vice versa, but they don't share memory. What you pass to the Java method is actually a copy, that's why the argument isn't modified.

   If you can add custom class to JVM, then the easiest way to overcome it would be to change signature to take ArrayList or return modified array (although this will lead to double conversion - between Julia and Java arrays).

   Another approach would be to wrap Java arrays into a special type (say, JavaArrray) that you can pass and extract explicitly. But it's quite a big piece of work since Java treats all the primitive and object arrays differently (e.g. you construct byte[] using NewByteArray, int[] using NewIntArray, Object[] using NewObjectArray, etc.; access to elements is also specific for each array type).
2. sorokod commented on Aug 19, 2018

   

   sorokod

   on Aug 19, 2018

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   Yes, an adapter can work, but an extra copy is a concern.
3. dfdx commented on Aug 19, 2018

   

   dfdx

   on Aug 19, 2018

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   If you have a lot of code already working with byte[], you can create a no-copy wrapper for it instead of ArrayList. Something like:

   class ArrayWrapper {
       private byte[];
      // constructor and accessors
   }