Why does using a static jclass variable within a method crash the JVM?

Question

I have some native code, that in a single thread, loops over a Java method. To improve performance, I tried this:
    static jclass clazz = env->FindClass("foo");
    /*FIXME: GetStaticMethodID crashes with "Bad global or local reference"*/
    jmethodID mid = env->GetStaticMethodID(clazz, "makeEvent", sig);But with the static declaration of clazz, the JVM crashes on the second iteration. Why? Is this really any different then using a C++ member field ?
My loop is really a bit more complicated then this, in that it starts several calls up. I hate the idea of
A) actually calling FindClass every iteration.
B) passing the clazz pointer through 3 layers of calls, just to avoid calling FindClass
Is there a better way?
Thanks!

Answer 1

Well I tried this, and it does not compile, becuase NewGlobalRef returns jobject not jclass.
Yes "jclass" is a pointer to a c++ object jclass, and jclass extends _object. However,
static jclass myGlobalRef dynamic_cast<jclass>( NewGlobalRef (myJClass));Does not compile either. The error is
error C2683: 'dynamic_cast' : '_jobject' is not a polymorphic type
static jclass myGlobalRef static_cast<jclass>( NewGlobalRef (myJClass));
DOES compile, but it is very dangerous. And using static_cast when dynamic_cast fails is a super-bad idea.
Just for laughs, I tried it anyway, and when I use -Xcheck:jni, the JVM dies with a fatal error.
Edited by: charlweed on Sep 19, 2009 3:56 PM
Typo