Re: JNI working with jvalue (union)

From: Thomas Fritsch <i.dont.like.spam@xxxxxxxxxxx>
Date: Mon, 19 Sep 2005 15:51:57 GMT

Thomas Gärtner schrieb:

we are using Java JNI to call C++ methods from a java application. Java is calling a get method to get data, the type of this data is variable (int, double, string)

Is the JNI jvalue (union) datatype the right usage for this? For example:

No, you have to use the exact prototypes as generated by the javah-tool from your class file (more precisely: from its methods declared as native). Using slightly different prototypes won't work.

JNIEXPORT void JNICALL getFromCppToJava(JNIEnv *env, jvalue var)
{
   // i keep it very simple
   var.jint = 5,
}
How is this resolved in java? How is the access to this union?

Declare several native methods (one for int, double, String) in your Java code. Implement the same number of C/C++ methods (with the javah-generated prototypes). However, you may decide that all these methods call the same C/C++ utility function, which will then do the actual work.

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References:
- JNI working with jvalue (union)
  - From: Thomas Gärtner

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