Calling more than a Java method from C++

Question

Hi everyone,
I haven't found any example with infomation about calling a second Java method from C++,after creating a VM from C++ also.
Here is the code I'm testing:
JNIEnv *env;
JavaVM *jvm;
JDK1_1InitArgs vm_args;
jint res;
jclass cls;
jmethodID mid;
jobject jobj;
char classpath[1024];
vm_args.version = 0x00010001;
JNI_GetDefaultJavaVMInitArgs(&vm_args);
sprintf(classpath, "%s%c%s",
vm_args.classpath, PATH_SEPARATOR, USER_CLASSPATH);
vm_args.classpath = classpath;
res = JNI_CreateJavaVM(&jvm,(void **)&env,&vm_args);
if (res < 0) {
fprintf(stderr, "Can't create Java VM\n");
exit(1);
cls = env->FindClass("Consola");
if (cls == 0) {
fprintf(stderr, "Can't find Prog class\n");
exit(2);
mid = env->GetMethodID(cls, "<init>", "()V");
if (mid == 0) {
fprintf(stderr, "Can't find Prog.main\n");
exit(3);
jobj = env->NewObject(cls, mid);
if (jobj == 0) {
fprintf(stderr, "Can't find Prog.main\n");
exit(4);
jmethodID mid2 = env->GetMethodID(cls, "isVisible", "()Z");
if (mid2 == 0) {
fprintf(stderr, "Can't find Prog.main\n");
exit(5);
jboolean b = env->CallBooleanMethod(cls, mid);
All works fine till the last line.
Folowing message appears in screen running the last code line:
Runtime error!
Program: s:\client\mcc_cyg\debg\debug\debgnt.exe
abnormal program termination
What to do ?
Thanks in advance.
Ignasi Villagrasa.

Answer 1

There should be examples of this in the JNI tutorial.
Also suggest a book: essential JNI by Rob Gordon
Briefly, what you need is a reference to the JVM. (I assume you have this - either because it was given to you when your C code started the JVM, or because it was passed as an argument to your native method.)
With the reference, you can look up a class, and look up a method, and call the method.
What about an object reference?
o You can call a method on an object which was passed to your native method.
o You can ask one object for a reference to another object.
o You can call a java constructor, which will return a reference.