JNI doesn't initialize Class Obj with String - string

Question

Below is my C and Java code. Java called function1 to collect a String and an integer and return them using ResultCollector object. The ResultCollector is an outer class, in other words, it is not nested inside the ResultCollecter class. Also, it has three constructors. I have other functions that are fine with a constructor with (IF)V signature. Also, the third constructor is not working as well (i.e. (II)V).
Java code is:
package user.directory;
public class ResultCollector {
private int err;
private float resVal;
private String resID;
/**
* Signature (IF)V
*/
public ResultCollector(int err, float value) {
this.err = err;
this.resVal = value;
}
/**
* Signature (II)V
*/
public ResultCollector(int err, int value) {
this.err = err;
this.resVal = (float) value;
}
/**
* Signature (ILjava/lang/;)V
*/
public ResultCollector(int err, char[] id) {
this.err = err;
this.resID = String.copyValueOf(id);
}
public String id() {
return resID;
}
public int err() {
return err;
}
public float value() {
return resVal;
}
public void setParam(int err, String id, float value) {
this.err = err;
this.resID = id;
this.resVal = value;
}
}
And C code is:
JNIEXPORT jobject JNICALL Java_project_function1(
JNIEnv *env, jobject obj, jint index) {
jint t;
char *id = C function to return string;
t = an error that is needed;
if (c == NULL)
// throw exception
return NULL;
jstring name = (*env)->NewStringUTF(env, id);
if (name == NULL)
// throw exception
return NULL;
jclass c = (*env)->FindClass(env,
"user/directory/ResultCollector");
jmethodID constr = (*env)->GetMethodID(env, c, "<init>", "(ILjava/lang/String;)V");
if (constr == NULL)
//cannot get the constructor correctly
return NULL;
jobject result = (*env)->NewObject(env, c, constr, t, name);
return result;
}
My question is: How I can initialize an outer class? Where does it go wrong in this code?

Answer 1

char[] is not the same as String. The signature for your constructor function should be (I[C)V ([ indicates an array, C is for char):
jmethodID constr = (*env)->GetMethodID(env, c, "<init>", "(I[C)V");
You will also need to pass a jcharArray instead of a jstring. You can create the jcharArray like this:
int len = strlen(id);
jcharArray charArray = (*env)->NewCharArray(env, len);
(*env)->SetCharArrayRegion(env, charArray, 0, len, id);
Alternatively, you can change your Java code to accept a String instead of a char[]:
public ResultCollector(int err, String id) {
this.err = err;
this.resID = id;
}