How do I define the JNI method signature of a generic class?

Question

I have a base class defined in java. I would like to call a native method like so:

public class Base<T>
{
    public void doSomething()
    {
        nativeDoSomething();
    }

    private native void nativeDoSomething();
}

My question is, how do I specify the jni method signature of a generic class?

score 4 · Answer 1 · answered Dec 15 '15 at 04:37

I'm late here, but I'll add it for future references.

Generics in Java are implemented using Type Erasure, which basically is: generics exists only in compile-time: they are gone after that, not existing in run-time.

This means that, even though you can have a method like public native void blah(E genericOne, F genericTwo), when compiled, it is actually converted to public native void blah(Object genericOne, Object genericTwo).

This way, you don't need to even care about generics when using the Java Native Interface: everything is converted down to Object, so you can simply reference them as a jobject.

The same goes for the Java classes: you can simply reference them as a jclass.

score 3 · Accepted Answer · answered Sep 05 '13 at 23:49

3

javah seems to ignore generics:

JNIEXPORT void JNICALL Java_Base_nativeDoSomething
   (JNIEnv *, jobject);

answered Sep 05 '13 at 23:49

Eugene

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score 0 · Answer 3 · answered Sep 06 '13 at 00:17

0

With javah. Don't try to figure it out yourself when there's a tool that does it for youl.

answered Sep 06 '13 at 00:17

user207421

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As mentioned above, javah appears to ignore generics. – MM. Sep 06 '13 at 17:52
@MM So the implication is therefore that generics do not form part of native method signatures, which is what the other answers here also say. – user207421 Jul 18 '16 at 21:06

How do I define the JNI method signature of a generic class?

3 Answers3