Clean up of objects created using NewObject()

Question

Hello
I've just started playing around with JNI in order to create a Java API layer on top of an existing C++ library. I figured out how to create an instance of a Java class in native code using env->NewObject() method. My question is who takes care of cleaning up this object? Is it my responsibility ?
jclass cl = env->FindClass("MyJavaClass");
jmethodID ctorId = env->GetMethodID(cl, "<init>", "()V");
jobject obj = env->NewObject(cl, ctorId);
// set member field (int)
jfieldID fid = env->GetFieldID(cl, "i", "I");
env->SetIntField(obj, fid, 5);
// set member field (string)
fid = env->GetFieldID(cl, "buffer", "Ljava/lang/String;");
jstring jstr = env->NewStringUTF("hello from cpp");
env->SetObjectField(obj, fid, jstr);
// return object back to Java
return obj;Thanks
Amit

Answer 1

See the [JNI Reference|http://java.sun.com/j2se/1.5.0/docs/guide/jni/spec/design.html#wp529], section 'Implementing local references'.
Notes:
(a) If you are constructing an object to return to the Java code obviously you don't want to free it yourself.
(b) Anything you construct inside a JNI method apart from the return value and anything reachable from it can be released by the JVM when the JNI method returns.
(c) You can use DeleteLocalRef() or Push/PopLocalFrame() to manage objects you create yourself if you like, but unless you do large amounts of object creation, or you have callbacks into Java code, it's not really necessary.
(d) All this also applies to references that you acquire via JNI calls (e.g. jclass references).
(e) Another thing often overlooked is that the result of GetStringChars() or GetStringUTFChars() also needs to be released, with ReleaseStringChars() or ReleaseStringUTFChars().