why does jni formula successfully jthrowable's getmessage method?

i'm perplexing opening summary jthrowable while handing an difference generated i destroy class. however, i am amateurish opening summary id getmessage() jthrowable object, i don't know why. i've attempted changing signature getmessage "()ljava/lang/string" (without semicolon during end, nonetheless that's necessary, right?) joy. i'm confused harm this. i even attempted replacing getmessage tostring, that didn't work. apparently i'm doing something trivially wrong here.

here's formula i'm using:

jthrowable java_exception;
jclass java_class;
jmethodid method;

java_exception = (*jenv)->exceptionoccurred(jenv);
assert (java_exception != null);
java_class = (*jenv)->getobjectclass (jenv, java_exception);
assert (java_class != null);
method = (*jenv)->getmethodid (jenv, java_class, "getmessage", "()ljava/lang/string;");
if (method == null) {
printf ("seriously, i here?!\n");
(*jenv)->exceptiondescribe (jenv);
return;
}

the cost formula (amongst things) looks this:

seriously, i here?!

difference thread "main" java.lang.noclassdeffounderror: com/planet/core360/docgen/processor

javap -p -s java.lang.throwable gives me this:

compiled "throwable.java"

open category java.lang.throwable extends java.lang.object implements java.io.serializable{

...

open java.lang.string getmessage();

signature: ()ljava/lang/string;

...