Get an object from an object with JNI in C

Question

public class Student { private People people; private Result result; private int amount; } 

Here is a sample class in Java; in C, I tried to get “people” in “Student,” but I failed. However, I can get int type "amount" from "Student".

 jobject getObjectFromObject(JNIEnv *env, jobject obj, const char * fieldName) { jfieldID fid; /* store the field ID */ jobject i; /* Get a reference to obj class */ jclass cls = (*env)->GetObjectClass(env, obj); /* Look for the instance field s in cls */ fid = (*env)->GetFieldID(env, cls, fieldName, "L"); if (fid == NULL) { return 0; /* failed to find the field */ } /* Read the instance field s */ i = (*env)->GetObjectField(env, obj, fid); return i; } 

I am trying to pass "people" as fieldName to a method, but it still gives the following error: "java.lang.NoSuchFieldError: people"

Answer 1

As described here , in the GetFieldID method you cannot use only “L” as the type signature, you must specify the class name after that.

For example, if you want to indicate that the argument is String , you will need to use Ljava/lang/String; (the end semicolon is part of the signature!).

For your custom class called People , assuming it in the package your.package.name , you will need to use Lyour/package/name/People; like a signature type.